Vet-Diag-FINALS-REVIEWER PDF - Veterinary Radiology

Module 2: Application of Radiology Discussion Directional Terminology The directional terms can be combined for oblique views. The following directional terms are quoted from Sirois et al., (2010). 1. Dorsoventral (DV): This term describes a radiograph produced when the primary x-ray beam enters t...

Module 2: Application of Radiology Discussion Directional Terminology The directional terms can be combined for oblique views. The following directional terms are quoted from Sirois et al., (2010). 1. Dorsoventral (DV): This term describes a radiograph produced when the primary x-ray beam enters the dorsal (topline or spinal) surface and exits the ventral (sternal or thorax and abdomen) surface of the patient. 2. Ventrodorsal (VD): This term describes a radiograph produced when the primary x-ray beam enters the ventral surface and exits the dorsal surface of the patient. 3. Medial (M): This term refers to the direction toward an animal’s midline. The term is usually used in combination with other directional terms to describe oblique projections. 4. Lateral: The term describes a radiograph produced when the primary x-ray beam enters from the side, away from the median plane or midline of the patient’s body. 5. Proximal (Pr): This is a relative directional term that indicates a structure located closer to the point of attachment or origin from another structure or closer to the midline of the animal. 6. Distal (Di): This is a relative directional term that indicates a structure located farther from the point of attachment or origin of another structure or away from the midline of the animal. 7. Rostral: This relative directional term indicates a structure located closer to the nares from any point on the head. 8. Cranial (Cr): This relative directional term indicates a structure located closer to the animal’s head from any part of the body. 9. Caudal (Cd): This relative directional term indicates a structure located closer to the animal’s tail from any part of the body. 10. Plantar: This term is used to describe the caudal (posterior) surface of the hindlimb distal to the tarsus; the correct term for the surface proximal to the tarsus is caudal. 11. Palmar: This term is used to describe the caudal (posterior) surface of the forelimb distal to the carpus; the correct term for the surface proximal to the carpus is caudal. 12. Craniocaudal (CrCd): This term describes a radiographic projection obtained by- passing the primary X-ray beam from the cranial surface to the caudal surface of a structure. It is most commonly used for radiographs involving the extremities proximal to the carpus or tarsus. Older veterinary literature may refer to this radiographic projection as anterior-posterior (AP). 13. Caudocranial (CdCr): This term describes a radiographic projection obtained by- passing the primary X-ray beam from the caudal surface to the cranial surface of a structure. It is most commonly used for radiographs involving the extremities proximal to the carpus or tarsus. Older veterinary literature may refer to this radiographic projection as posterior-anterior (PA). 14. Dorsopalmar (Dpa): This term is used to describe radiographic views distal to the carpus obtained by-passing the primary X-ray beam from the dorsal direction to the palmar surface of the forelimb. Older veterinary literature may refer to this radiographic projection as anterior-posterior (AP). 15. Palmar dorsal (PaD): This term is used to describe radiographic views distal to the carpus obtained by-passing the primary X-ray beam from the palmar surface of the forelimb toward the dorsal surface of the body. Older veterinary literature may refer to this radiographic projection as posterior-anterior (PA). 16. Dorsoplantar (Dpl): This term is used to describe radiographic views distal to the tarsus obtained by-passing the primary X-ray beam from the dorsal direction to the plantar surface of the hindlimb. Older veterinary literature may refer to this radiographic projection as anterior-posterior (AP). 17. Plantardorsal (PlD): This term is used to describe radiographic views distal to the tarsus obtained by-passing the primary X-ray beam from the plantar surface of the forelimb toward the dorsal surface of the body. Older veterinary literature may refer to this radiographic projection as posterior-anterior (PA). 18. Oblique (O): This term refers to radiographic projections taken with the primary beam entering at an angle other than 90 degrees to the anatomical area of interest. Oblique projections are sometimes used to obtain images of structures that might be superimposed over other structures with standard 90-degree views. Nearly all dental radiographs are obtained using oblique angles. The positioning of small animal patients requires sedation or general anesthesia, positional devices, and minimized manual restraint as much as possible. The primary goal is to find the most suitable posture to produce an accurate reproduction of x-ray images of the anatomical area. There are essential factors to be considered for accurate reproduction of radiographs; these are: 1. The welfare of the patient 2. Restraint and immobilization of the patient 3. Minimal trauma to the area of interest 4. The least risk of exposing those assisting with the examination to radiation Principle of Radiographic Positioning The comfort and welfare of the patient should be considered at all times. To minimize the animal's anxiety, they should be handled in a slow, quiet manner with a calm, soft voice and gentle stroking. Quick, loud movements and severe restraint usually result in a frightened, tense, and even aggressive patient (Burk & Feeney, 2003; Thrall, 2017). Technical preparation that should be done before positioning the animal on the table are: 1. The patient’s body or part of its anatomical interest should be measured. 2. The exposure technique should be determined. 3. The cassette must be placed already on the table or the Bucky tray. 4. Labels in the X-ray film should be made.  Measurement: A caliper is used to measure the anatomic area of interest prior to radiography. It measures the part's thickness in centimeter increment. If the technician or radiographer is uncertain about where to measure a particular part, the measurement should be made over the part's thickest area if there is a large difference in thickness in a particular area and advice to make two separate radiographs with different exposures.  A radiograph is a 2D picture of a 3D structure. The minimum recommended angles are two, these two are the two views of each anatomic area taken at right angles to each other. The importance of two views is demonstrated when taking a radiograph of a fractured bone. Another recommendation is to position the area of interest closest to the film. If a limb is being radiographed, it may be helpful to include a radiograph of the opposite corresponding limb. This will allow the pathologic structure of one leg to be compared with the other's normal anatomy. It is possible to radiograph more than one view on the same piece of film, the technician may add a lead sheet, this may split the cassettes. Splitting a cassette is only possible when the cassette is used on the tabletop.  The shaft of the long bones (humerus and femur) and its joints in the proximal and distal parts should be included in the radiographs.  Positioning: the patient should be clean and free of any debris, free of collars, harness, and leashes, free of bandages, splints, and casts. Pedal radiography in horses may require removing the shoe and cleaning the frog to alleviate any artifacts. For radiography of small animal abdomen, the GIT must be free of ingesta and fecal material.  Chemical restraint is preferred during radiography. If manual restraint is necessary, all personnel should wear a radiographic suite during exposure and must be  adequately shielded. Note that handling the canine patient usually responds to a calm, authoritative approach, whereas a feline patient will resist restraint.  Film identification: proper labeling of a radiograph is compulsory for legal and practical reasons. It should include appropriate patient information. Also, a marker must be used to identify the right and left (R or L) side of the patient, the limb being radiographed (cranial or caudal), and the view. Place the marker on the lateral aspect of the extremity of the cassette for craniocaudal or caudocranial views. For dorsoventral or ventrodorsal views, the marker (lead) should indicate "R" or "L" on the appropriate side of the animal. It is usually placed cranially to (in front) of the leg when taking lateral projection. Use a sequential marking with appropriate numbers that identify time elapsed or order taken if necessary. Veterinary Diagnostic Imaging Special Consideration for Avian Radiography Physical restraints are sometimes unacceptable, especially in powerful, large birds, fractious and highly stressed birds, and birds experiencing a serious injury that can be exacerbated due to struggling. In cases like these, chemical restraint through inhalation anesthesia using isoflurane or sevoflurane is needed. A bird board is a plexiglass positioning aid useful for both avian and some reptile patients (Figure 12A-B). If imaging a parrot or raptor, leather gloves should be worn when placing the patient on the bird board. Masking tape is the best tape to use when taping the wings down on a bird. When the tape is removed, always remove it in the direction the feathers are pointed. If imaging a raptor or parrot, placing a gauze roll for each foot so the bird can grasp it will help prevent having fingers or clothes grasped by the bird (Nugent-Deal, n.d.; Sirois et al., 2010). Projections The following directional projections are adapted from Sirois et al. (2010). 1. Lateral View of the Avian Patient o Positioning: The bird should be placed in lateral recumbency. The neck should be extended, and a sponge can be used to support the head. To avoid obstruction of the primary beam passing to the bird's body, the wings are extended dorsally and secured with a tape at the carpal joint. The sternum should be placed parallel to the cassette with the legs pulled caudally and secured with tape. o Centering: Midsternum o Collimation: Whole-body but larger bird species require two radiographic capture; one view for the wings and the other is the main body. o Measurement: Measure the thickest point of the chest Note: In this projection, the following organs are examined: heart, proventriculus, spleen, kidneys, and lungs. 2. Ventrodorsal View of the Avian Patient o Positioning: The bird is placed in dorsal recumbency. The neck should be extended, and a sponge can be used to support the head. To avoid obstruction of the primary beam to the bird's body, the wings are extended laterally and secured with a tape at the carpal joint. The sternum should be placed directly over the spinal column with the legs are pulled caudally and secured individually with a tape. o Centering: Midsternum o Collimation: Whole body o Measurement: Measure the thickest point of the chest Note: In this projection, the following organs are examined: liver, gizzard, lungs, and heart. 3. Lateral Projection of the Head o Positioning: Lateral with head restraint used to position the head of the bird. The tape is used to open the beak. o Centering: Along with the eyes of the bird o Collimation: Whole head o Remarks: Perform only this procedure, especially in raptors, if they are under the influence of anesthesia. 4. Ventrodorsal Projection of the Head  o Positioning: Spinal recumbency with the beak taped in the cassette to partially lift the head. The additional tape is used in the neck to support the upper tape in lifting the head. o Centering: Neck o Collimation: Whole head o Remarks: Care must be observed, especially in putting the tape in partially sedated birds especially, raptors. 5. Lateral view of the Foot o Positioning: Lateral recumbency, especially the affected side. The tape is used to position the affected feet partially, and the other one is tied to a string to avoid the superimposition of the two. o Centering: Below the hypotarsus o Collimation: Whole area o Remarks: Care must be observed, especially in putting the tape in partially sedated birds especially, raptors. 6. Caudocranial View of the Wings (For manual positioning) o Positioning: Partially sedated birds can be held by the person by their talons using leather gloves, with the other hand positioning the fractious wings. o Centering: Midshaft of the radius and ulna o Collimation: Whole area Indications for Avian Radiography The following are the indications of radiography in birds (Ayers, 2012): Examination of the musculoskeletal system o Change in bone density (osteopenia or osteosclerosis) o Evaluation of the lesion distribution especially in cancer cell metastasis o Assessment of the bone structure and fractures (e.g., fracture of the wings, disruption of bone continuity, and bone imagination) o Assessment of metabolic bone diseases o Assessment of bone infection and inflammations, especially in the synovial joints (e.g., arthritis, synovitis, and fungal osteomyelitis) Examination of the cardiovascular and respiratory system o Evaluation of pneumonia, pulmonary edema, and tracheal diseases o Detection of foreign body and tumor growth o Assessment of respiratory infection and disorders (e.g., fungal infection of the air sac and hypovitaminosis A) o Detection of congenital disorders seen usually in juvenile birds  o Cardiomegaly Examination of the coelomic organ/cavity o Assessment of the gastrointestinal motility especially in contrast media study o Assessment of egg bound or dystocia o Evaluation of tumor growth, formation, and metastasis o Assessment of metabolic diseases and poisoning (e.g., lead poisoning) o Detection of foreign body and fractures o Organ abnormalities (e.g., hepatitis, splenomegaly, and stomach rupture) Special Consideration for Lizard Radiography Most lizards do not need to be sedated for radiography, but chemical restraint can be used if necessary. In most cases, the patient will just sit there while the radiographs are being taken. Radiolucent sponges can be used to position the patient. You can also use vagal stimulation or the "vagal response" to calm the patient if needed (Figure 13). The vagal response in iguanas and large lizard species can be induced by gently applying digital pressure to both eyes for a few seconds to a few minutes. The patient will usually respond with a decrease in heart rate and blood pressure. The vagal response induces a short-term trance-like state allowing time to take radiographs and, in some cases, even draw blood (Nugent-Deal, n.d.; Sirois et al., 2010). Projections The following directional projections are adapted from Sirois et al. (2010). 1. Ventrodorsal View of the Lizard o Positioning: The lizard should be placed in ventral recumbency. The forelimbs and hindlimbs are gently placed lateral to the body. The tape can be used to secure the animal in position. o Centering: Midbody region o Collimation: Whole body, including the head, legs, and cranial aspect of the tail o Measurement: Measure the thickest point of the body 2. Lateral View of the Lizard o Positioning: The lizard should be placed in right lateral recumbency. The forelimbs are pulled ventrally to the body's cranial direction, while the hindlimbs are pulled ventrally to the body's caudal direction. The tape can be used to secure the animal in position. o Centering: Midbody region o Collimation: Whole body, including the head, legs, and cranial aspect of the tail o Measurement: Measure the thickest point of the body 3. Lateral View of the Lizard using Horizontal Beam o Positioning: The lizard should be placed in ventrodorsal recumbency. The cassette is placed in the lateral part of the body in a standing position. Ensure that the body is as close to the cassette as possible. The X-ray source is placed in a horizontal position. o Centering: Midbody region o Collimation: Whole body, including the head, legs, and cranial aspect of the tail o Measurement: Measure the thickest point of the body Special Consideration for Snake Radiography Restraint of a snake can be challenging. Anatomically, all snakes are characterized by an elongated body without the presence of limbs. Tape and sandbag restraints prove to be ineffective. Generally, manual restraint is the best. Manual restraint or the use of acrylic tubes is the most common form of restraint for snakes. In large snakes, the radiographs are taken in sections from head to tail and labeled with numbered lead markers to delineate each section. In some cases, sedation is needed to take a good radiograph, especially in highly venomous or aggressive snakes (Nugent-Deal, n.d.; Lavin, 2003; Sirois et al., 2010). Projections The following directional projections are adapted from Lavin (2003). 1. Ventrodorsal View of the Snake Small non-venomous snakes can be placed directly on the cassette. If the patient is active, it can be placed in double-open-ended cardboard or radiolucent plastic box. The box is then placed on the top of the cassette, and the exposure is taken. o Positioning: A plastic tube can be used to position the snake o Centering: It depends on your area of interest or the fractious area o Collimation: Area of interest o Comment: When radiographing a snake in segments, it is important to number or label each projection to be viewed in the proper sequence. 2. Lateral View using Horizontal beam o Positioning: The snake should be placed in ventrodorsal recumbency. Radiolucent plastic tubing can be used to manipulate the body of the animal. The cassette is placed in the lateral part of the body in a standing position.  Ensure that the body is as close to the cassette as possible. The X-ray source is placed in a horizontal position. o Centering: It depends on your area of interest or the fractious area o Collimation: Area of interest o Comment: When radiographing a snake in segments, it is important to number or label each projection to be viewed in the proper sequence. Indications for Reptile Radiography Radiography in reptiles is becoming more available today. However, despite the availability of references in conducting a radiograph in these animals, the radiographic contrast and quality are often weak due to a number of factors (e.g., intracoelomic fat bodies and superimposition of organs and structures). As such, when presented with an unfamiliar species for imaging, it is best to radiograph at the same time a healthy representative animal of similar species. It is also worth mentioning that the position and size of the internal organs of the reptiles are dependent on the size of the surrounding organs and the nutritional status of the patient. Such instances can be seen in gravid patients. Some of the species make it difficult to get a diagnostic image, they use air as a defense mechanism (e.g., dive reflex and rapid inflation), distorting the normal respiratory radiographic appearance. The following are the indications of radiography in reptiles (Cassel, 2014):  Assessment of respiratory and cardiac diseases (e.g., pneumonia, tracheal collapse, foreign body, neoplastic cell metastasis, cardiomegaly, and other congenital diseases).  Evaluation of the musculoskeletal system in cases of injury, fracture, nutritional bone diseases, spinal osteopathy, osteitis deformans, and tumor occurrence.  Assessment of the coelomic cavity, especially the gastro-intestinal organs in cases of obstruction, foreign body, and rupture.  Evaluation of the reproductive organs in cases of dystocia or egg bound. Projections and Special Consideration The following directional projections are adapted from Sirois et al. (2010) and Nugent- Deal (n.d.). 1. Dorsoventral View of the Turtle The dorsoventral view is used primarily to look at the gastrointestinal (GI) tract, shell, and to some extent, the limbs, head, and neck.  o Positioning: The turtle should be placed in ventral recumbency. The forelimbs and hindlimbs are gently placed lateral to the body. The tape can be used to secure the animal in position. o Centering: Midbody region o Collimation: Whole body, including the head, legs, and cranial aspect of the tail. o Measurement: Measure the thickest point of the body. Due to the thickened shell and retraction of the head and appendages, capturing them in a radiograph can be difficult. The limbs or the head should be extended away from the body, but care must be practiced during the manipulation of these body parts, especially when it is injured. The x-ray beam is collimated and coned-down as much as possible to the area of interest. 2. Lateral View of the Turtle using Horizontal Beam The lateral view primarily looks at the lungs (although there is a great deal of summation) and the GI tract. o Positioning: The lizard should be placed in ventrodorsal recumbency. The cassette is placed in the lateral part of the body in a standing position. Ensure that the body is as close to the cassette as possible. The X-ray source is placed in a horizontal position. o Centering: Midbody region o Collimation: Whole body, including the head, legs, and cranial aspect of the tail o Measurement: Measure the thickest point of the body 3. Craniocaudal View of the Turtle The craniocaudal view is used to observe both the left and right lung fields, which are now separated. Evidence of lung pathology (pneumonia) can often be observed with the craniocaudal view. It is important to note that proper technique is essential. Radiographic techniques that are too “light” can cause the lungs to look as though pneumonia is present when it is not. Conversely, radiographic techniques that are too “dark” can overexpose the lung tissue and cause the lungs to look normal even if pneumonia is present. o Positioning: Horizontal and vertical beams can be used. A plastic container can be used for a horizontal beam to raise the turtle with tape to hold it. A vertical beam can be achieved with the aid of a v-trough and a foam wedge. o Centering: Between the carapace and the plastron o Collimation: Whole bod o Comments: Care must be applied to those turtles that have broken carapace for the lungs might be affected. Indications for Chelonian Radiography Due to the anatomical structure of turtles, with half of its body occupied by the lungs and the other for the coelomic organs, “most” of the radiographic processes are indicated in the assessment of these two cavities. Pneumonia and peritonitis are the common diseases seen in turtles, especially those seen in the wild. For turtles raised in captivity, the most common disease is the nutritional bone diseases and reproductive related diseases (dystocia/egg bound). For the other indications of radiography in turtles, it is included in the indication for radiography in reptiles seen in our previous topics (Cassel, 2014). Special Consideration for Rabbit Radiography Rabbits are docile and shy animals. They do not vocalize when experiencing pain, and they tend to stay still in a corner. They are easily frightened, and thus proper approach in handling must be observed. Proper restraint techniques must be applied in these delicate animals to avoid further injury. Before picking up the animal, the personnel must observe first the behavior of the animal and its surrounding. The following are the basic guidelines in handling and restraining rabbits (e.g., cage or nest) (Nugent-Deal, n.d.; VMCLI, n.d.):  In picking up the rabbit, grab the scruff of the neck with one hand and lift it while placing the other hand under the rump for support. To lessen the stress experienced by the animal, a towel can be placed securely around it.  Do not pick the rabbit by grabbing its ears! It is painful for the animal, and it might exacerbate the current condition/ailments it is experiencing.  In holding the rabbit, apply the same technique in picking up the animal, but the other hand in the rump is moved to the abdomen area for support. This is usually done in cases of thoracic, abdominal, or hindlimb injuries.  Rabbits seldom bite, the common injury caused by this animal is through their sharp nails in the hindlimb. Rabbit’s foot is covered in fur, be careful in putting down a rabbit on smooth surfaces since it might cause injury or dislocation of the hip when it tries to hop. Projections The following directional projections are for rabbit and hare, and it is adapted from Lavin (2003), Nugent-Deal (n.d.), and Sirois et al., (2010). 1. Lateral View of the Abdomen o Positioning: The animal should be placed in right lateral recumbency. The forelimbs should be extended cranially, and the hindlimb caudally, it can be secured with tape. The sternum should be placed parallel to the cassette; this can be accomplished using a sponge. o Centering: Center slightly cranial of the last rib o Collimation: Slightly cranial of the xiphoid and slightly caudal of the pubis o Measurement: Measure at the last rib 2. Ventrodorsal View of the Abdomen  o Positioning: The animal should be placed in dorsal recumbency. The front portion is secured with sandbags to keep the trunk bilaterally symmetrical, with the hindlimbs are extended caudally and secured with sandbags or tape. o Centering: Slightly caudal to the last rib o Collimation: Slightly cranial of the xiphoid and slightly caudal of the pubis o Measurement: Measure at the last rib 3. Lateral View of the Thorax o Positioning: The animal should be placed in right lateral recumbency. The forelimbs should be extended cranially, and the hindlimb caudally, it can be secured with tape. The sternum should be placed parallel to the cassette; this can be accomplished using a sponge. o Centering: Center on sternum o Collimation: Slightly cranial of the thoracic inlet and slightly caudal of the last rib o Measurement: Measure at the last rib 4. Ventrodorsal View of the Thorax o Positioning: The animal should be placed in dorsal recumbency. The forelimbs should be extended cranially, and the hindlimb caudally, it can be secured with tape. The sternum should be placed directly over the spinal column. o Centering: Center on fourth intercostal space o Collimation: Slightly cranial of the thoracic inlet and slightly caudal of the last rib o Measurement: Measure at the last rib Indications for Lagomorph Radiography Rabbits and other lagomorphs (e.g., hare) possess a relatively small thoracic cavity and a large abdominal region. Below are the indications of radiography per body cavity (Table 5). Table 5. Indications of lagomorph radiography per body part. Body Part Indications Thorax Heart disease is becoming popular in geriatric patients. -The radiographic signs of heart problem (e.g., cardiomegaly) include an enlarged heart shadow, an elevated trachea, and occurrence of pleural effusion. Lower respiratory disease is common in rabbits, and upon radiography, infiltrations are seen. Tumors are also identified during radiography. Abdomen In abdominal radiography, the following organs are identified: stomach, intestines, bladder, kidneys, and liver. The kidneys may appear displaced ventrally by fat in the retroperitoneal space. Gastrointestinal disease is common in rabbits. The most common disorder is gastrointestinal ileus. -Under radiography, it appears as a gas filled stomach and/or gas filled intestines, especially the cecum. The radiopaque substance in the stomach seen in ileus are made of a combination of ingesta, hair, and fluid. If the stomach is greatly distended, this may represent a true obstruction. -Pyloric obstruction is characterized by a large, fluidfilled stomach and the intestines may look normal. If an obstruction is present and not treated, the stomach may rupture.  -The presence of a ruptured stomach in a rabbit is seen in the radiograph as free gas in the abdomen. Ileus is characterized by a diffuse gastrointestinal gas pattern. -Contrast radiographs can be used to differentiate between ileus and obstruction. Urinary and Urolithiasis is the most common urinary tract problem in rabbits. reproductive system -Renal and ureteral calculi are less commonly observed but can be present at the same time. It may be difficult radiographically to discriminate between renal calculi and renal mineralization and dystrophic calcification. In intact females, check abdominal radiographs for evidence of an abnormal uterus. -This is viewed radiographically as an increased uterine size, increase in radio-opacity, and displacement of other organs. Pregnancy assessment in rabbits is also done using radiography. Head Jaw abscesses, dental diseases, middle and inner ear disease (e.g., chronic disease) are the common indication of head radiography in rabbits. Other indication for radiology of the head includes exophthalmos, dacrocystitis, and tumor assessment. Skeletal system Osteoarthritis is common in rabbits. The other indications are in the evaluation of luxation, assessment of fibrosarcoma and osteosarcoma. Special Consideration for Rodent Radiography Small mammals such as rats, mice, gerbils, and even ferrets are hyperactive in nature. It requires the full attention of the handler to avoid escape and being bitten by these animals. In order to conduct a successful x-ray, most of these animals are induced in general anesthesia. The common practice for sedation is through gas anesthetics since they are difficult to be given intravenously. In taking a radiograph of these animals, they are usually positioned and taped on plexiglass or directly in the cassette. The use of non- screen film may help in examining fine structures. In many cases, short exposure times are required due to the rapid rates of respiration. The usual radiograph series of small exotic mammals include a whole body capture, ventrodorsal, and right lateral. Usually, the dorsoventral view is less used since the vertebral column and the pelvic bones covers the most important abdominal organs of these animals which are the stomach and the intestines. Similar to rabbits, the most common problem in small mammals are ileus and intestinal obstruction (Nugent- Deal, n.d.; Sirois et al., 2010). In terms of restraint, in a strange surroundings, mice will frequently bite an unfamiliar handler. First, grasp the tail near to the base and then position the mouse on a non-slip surface. While still grasping the tail, the scruff may now be grasped firmly between the thumb and forefinger of the hand. For rats, they are best picked up by encircling the pectoral girdle immediately behind the front limbs with the thumb and finger of one hand while bringing the other hand underneath the rear limbs to support the rat’s weight. Fractious patients should not be restrained directly since they are delicate, and the handler might exacerbate further the fracture (Nugent-Deal, n.d.; Sirois et al., 2010). Indications for Rodent Radiography In general, the indication of performing radiography in rodents is similar to the rabbits Ultrasonography Discussion Technical Aspects The sound is capable of carrying information, and it travels in waves from one location to another. It transmits energy by alternating regions of low pressure (rarefaction) and high pressure (compression). Unlike light and radio waves, sound waves require a medium through which to travel. Frequency, wavelength, and velocity are parameters used to describe sound waves; these terms are also used about electromagnetic radiation (Figure 14) (Thrall, 2017). The principle of echo formation is important because echoes contain diagnostic information about the structures being imaged. The interface that causes the echo reflection and the angle at which the sound wave strikes the reflector, or the angle of incidence, should be considered. The acoustic impedance of a tissue is the product of the tissue's physical density and sound velocity within the tissue. Changes in acoustic impedance from one tissue to another determine how much of the sound wave is reflected and transmitted into the second tissue. The amplitude of the returning echo, which is used to make the image, is proportional to the difference in acoustic impedance in two adjacent tissues or substances. If two tissues have no difference in acoustic impedance, then no echo is created. Suppose a large difference in acoustic impedance exists between two tissues. Almost all the sound is reflected in an echo (Lavin, 2003; Thrall, 2017). Simply, the tissue's elasticity determines the way sound interacts with the tissue: reflection, transmission, or refraction. Air scatters sound, and water transmits sound with little attenuation or reflection (Table 6). This lack of attenuation creates distant enhancement, an ultrasound artifact that indicates the presence of fluid. Minerals and metals are very reflective. The bone is not penetrated by sound, causing an acoustic shadowing that lacks echoes beyond the reflecting object. The echogenicity of tissues is an indication of the liquid or solid composition of the tissue. Tissues that reflect very few echoes to none are known as anechoic, they appear black, and an example of this is the full urinary bladder. Tissues reflecting few echoes are known as hypoechoic, they appear grayish, and an example of this is the medullary papillae. On the other hand, tissues reflecting higher echoes and appear as bright or white are hyperechoic. An example of this is the bladder stone and bones (Table 7) (Lavin, 2003). Table 6. Types of echogenicity and their appearance in the ultrasound monitor. Echogenicity Appearance Hyperechoic Brighter than surrounding structures/bright white Hypoechoic Darker than the surrounding Anechoic Black in color Echogenic The bright white appearance against a black background. Homogenous A Uniform shade of gray throughout the organ denotes the normal appearance of the organ. Heterogenous Nonuniform shades of gray throughout the organ denote the abnormal appearance of the organ. Note. Adapted from RadiologyKey (n.d.), Types of echogenicity and their appearance https://radiologykey.com/abdominal-ultrasound/ Table 7. Echogenicity based on tissue type. Tissue Type Echogenicity Bone Hyperechoic Tendon Hyperechoic Ligament Hyperechoic Nerve Hyperechoic/Hypoechoic Muscle Hyperechoic lines/hypoechoic background Fat Hypoechoic Vascular structure (i.e., arteries,Anechoic veins) Cyst Anechoic A hyperechoic image is bright (i.e., white), a hypoechoic image is darker (i.e., gray), and an anechoic image is completely dark (i.e., black). Note. Adapted from “Ultrasonography as a diagnostic, therapeutic, and research tool in orthopedic surgery” by X. Li, et al., 2018, Journal of the American Academy of Orthopedic Surgeons, 26(6), 187-196. Transducers In ultrasonography, the transducers are the ones that convert the electrical current into sound waves, and accept the sound waves from the object and convert it back to an electric current. The conversion process is accomplished by the piezoelectric crystals placed inside the transducer. As an electric charge is applied to a piezoelectric crystal, the material deforms and creates sound waves. Conversely, when the sound waves are applied to piezoelectric crystals, they produce an electric signal (Figure 15). To put it simply, the same crystals are used to send and receive sound waves, but the two processes cannot occur simultaneously. Typically in ultrasonographic imaging, the sound waves emitted by the transducer is less than 1% of the time compared to the sound waves it receives (99% of the time) (Thrall, 2017). The transducers come in many sizes and shapes. The selection of a transducer will depend on the anatomical region of interest and its physical properties. The array transducers (commonly known as electronic transducers) are composed of small elements arranged differently. The elements may be arranged in a curved line (known as a convex array), rectangle line (known as a linear array), or in a concentric ring-like fashion (known as an annular array). The elements that compose these transducers are electronically fired in various sequences to create different-shaped fields of view (e.g., rectangular, wedge) or focus the sound beam at specific depths (Figure 16) (Thrall, 2017). Two basic shapes of ultrasound fields of view are commonly encountered. Images made using a sector transducer are pie-shaped, and images made using a linear transducer are rectangular. The amount or ratio of the transducer head that contacts the patient is known as a footprint. Sector images are often produced from transducers with a small footprint, whereas linear transducers usually have larger footprints. For thoracic imaging, sector-shaped transducers are preferable because images must be acquired intercostally. For abdominal imaging, the use of sector or linear transducers is often dictated by the sonographer's personal preference and the anatomic structure being imaged. In most instances, more than one transducer is used during a single examination (Thrall, 2017). Principles of Ultrasonography Ultrasound machines operate in a pulse mode setting, meaning the sounds emits only a few sound cycles into the target tissue and then spend the rest of the time listening and converting the sounds into an image. The "pulse repetition frequency (PRF)" is when this pattern of sending waves and listening to the echo is repeated within the 1-second cycle. On the other hand, the "spatial pulse length (SPL)" is the length of space in one pulse of ultrasound; this is important, especially in axial resolution (Thrall, 2017). Resolution is an ultrasound machine's ability to distinguish echoes based on space, time, and strength. The better the resolution, the more likely an abnormality can be identified. As the frequency of an ultrasound wave increases, the resolution increases. A transducer of the highest possible frequency should be used to get the best possible resolution. Axial resolution is the ability to distinguish two separate reflectors along the direction in which the sound wave travels (Figure 17). It is equal to half the SPL. As previously mentioned, SPL is the length of space over which the pulse of a sound wave travels. When two reflectors are separated by a greater distance than half the SPL, these two reflectors' echoes do not overlap as they return to the transducer and are displayed as distinct echoes. If the distance between the reflectors is less than half the SPL, the returning echoes overlap and are displayed as a single echo. Because transducers with higher frequency have a shorter SPL, axial resolution is improved (Thrall, 2017). Lateral resolution is the ability to distinguish two separate reflectors perpendicular to the direction in which the sound wave travels (Figure 17). The width of the ultrasound beam determines this. To recognize the objects discretely, the ultrasound beam must be narrower than the distance between the objects. The width of an ultrasound beam decreases with increasing frequency. In a focused ultrasound beam, where the beam's width is restricted, the lateral resolution is best at the focal point of the ultrasound beam because this is the narrowest part of the beam (Thrall, 2017). Display Appearance We have discussed the principle of conversion electric current to waves and vice versa in the transducer in our previous topics. In this part, we will discuss the modes of display in the monitor of the ultrasound. Two modes of echo display are commonly used in ultrasonography: brightness mode (B- mode, B scan, or grayscale) and motion mode (M-mode). B-mode is commonly used in both abdominal and cardiac imaging. M-mode is used only for echocardiography. B-mode images are composed of a collection of dots that correspond to the returning echo's amplitude or strength. These dots are displayed on a black background, and the brightness or grayscale of the dot is highest (whitest) for the strongest returning echoes. The depth of the structure returning the echoes determines the position of the dots relative to the position of the transducer. Multiple thin scan lines make up a complete image so that B-mode images look like a slice of tissue (Thrall, 2017). M-mode records a thin section of an ultrasound image over time. The region for M-mode imaging is chosen using a B-mode image; the selected M-mode region is usually represented on the screen as a line. Once the M-mode cursor is in the desired location, M-mode is activated. On an M-mode image, the image's depth is displayed on the vertical axis, and time is displayed on the horizontal axis. The brightness of the dots is proportional to the strength of the returning echoes, as in B-mode. When holding the transducer stationary, the examiner can evaluate how structures move over time. M-mode imaging is used most commonly in echocardiography to evaluate the function of the ventricles and heart valves. The orientation of the B-mode image varies with the structure being imaged. The screen's left side is cranial, and the top of the screen is dorsal (toward the patient’s spine) for longitudinal images. For transverse images, the left side of the screen is dorsal. For cardiac imaging, the screen's right side is cranial (toward the patient's head) with long-axis images (Thrall, 2017). The portion of the image closest to the transducer, usually the top of the screen, is called the near field, and the opposite side is called the far-field (Thrall, 2017). Artifacts Any part of an image that does not accurately represent the anatomy of a patient's physiology is an imaging artifact (Table 8). In diagnostic radiology, artifacts hinder the evaluation of the image and are undesirable. In ultrasound imaging, artifacts are not always undesirable and may enhance the evaluation of structures by providing insight regarding the composition of structures. For example, sonographic imaging of a fluid-filled structure is characterized by enhancing soft tissues distal to the fluid-filled structure. In contrast, with a hypoechoic tissue mass, which may appear like a fluid-filled structure, there is no distal enhancement. Before discussing specific artifacts, it is important to remember assumptions made when using ultrasound (Thrall, 2017). Below are the assumptions followed under ultrasonography: The sonic waves (sound) travels in a straight line. Objects located on the beam axis are the only source of echoes. In a single reflection, the echoes return to the transducer. The sound speed in the tissue is constant. The amplitude of returning echoes is related directly to the reflecting or scattering properties of distant objects. The distance and/or depth to the reflecting or scattering object is proportional to the round- trip travel time of the sound wave, The sound wave energy is uniformly attenuated. Table 8. Common artifacts seen in ultrasonography. Artifact Remarks Acoustic shadow It is a region of decreased echogenicity distal to structures with high reflectivity. -Naturally occurring acoustic shadows are found at soft-tissue/bone and soft tissue/gas, such as in bowel and lung interfaces. -Pathologic acoustic shadows occur most commonly with cystic, renal, or cholecystic calculi. Acoustic Region of increased echogenicity behind structures enhancement of low attenuation. This results in areas of increased echogenicity distal to areas of low attenuation. -The two most common sites for acoustic enhancement are distal to the gallbladder and distal to the urinary bladder. Reverberation This occurs when the sound waves reflect multiple artifacts times between two strong reflectors. Reverberation artifacts appear as multiple hyperechoic foci that occur at regular intervals. -Reverberation occurs when the sound wave encounters an area of high reflectivities, such as  bowel gas, and the sound wave is reflected toward the transducer. Comet tail andBoth are a variation of a reverberation artifact. ring-down artifacts -The reverberation is caused by two closely spaced, discrete, highly reflective surfaces for comet tail artifacts. Comet tail can be created by the front and back of a gas bubble or a small metallic object such as a pellet. On display, these artifacts appear as thin, hyperechoic bands with a triangular, tapered shape in which the sequential echoes are so close together that they are not seen as distinct echoes. -Ring-down is created when ultrasound reverberates within fluid trapped between a tetrahedron of air bubbles. Mirror-image Appear as a duplication of a normal structure on the artifacts opposite side of a strong reflector. -This is most commonly encountered when the liver is imaged with the diaphragm/lung interface, acting as a highly reflective structure. Apparent duplication of the gallbladder can be used to explain the artifact. Side lobes andSecondary sound waves that emanate in a different grating lobes direction than the primary sound beams. -Side lobes are associated with al transducers and originate from additional mode vibrations of the piezoelectric crystal. -Grating lobes emanate from array transducers. In each instance, these lobes result in an error in positioning of the returning echo. Slice thicknessThese are noticed most commonly in association with artifacts the urinary bladder and gallbladder. In these structures, slice thickness artifacts mimic the presence of sludge or sediment.  -When the periphery of the urinary bladder is imaged, part of the primary sound beam's thickness strikes the bladder wall while the other part strikes anechoic urine. -The computer averages these two parts to create the pseudo-sludge artifact. The surface of the pseudo- sludge is usually curved, but the surface of the real sludge is flat. Refraction This occurs as the sound wave traverses tissues of different acoustic impedance. As the sound wave moves to the new medium, it is bent. -The sound wave's bending may result in the display of organs in incorrect locations, usually to the side of their actual location. -Refraction artifacts may lead to measurement errors because organs may appear wider than normal. Edge-shadowing These are refraction artifacts created when sound artifacts waves are bent as they encounter a curved surface tangentially. -These occur commonly when the kidneys, urinary bladder, or gallbladder is imaged Note. Adapted from Textbook of veterinary diagnostic radiology (p. 23- 27), by D.E. Thrall, 2017. Elsevier Health Sciences. Doppler Modes The Doppler ultrasound uses high-frequency sound waves to measure blood flow in the arteries and veins. The change in pitch, sound-wave frequency is called the Doppler shift. The Doppler effect is named after an Austrian mathematician and physicist, who first introduce the said effect in 1842. He is Sir Johann Christian Andreas Doppler (Thrall, 2017). In this lesson, we will discuss the four Doppler modes, namely: (1) continuous-wave Doppler, (2) pulse-wave Doppler, (3) color Doppler, and (4) power Doppler. Continuous-wave Doppler It is performed by using two separate crystals housed in one transducer. One crystal emits sound continuously, and the second receives echoes continuously. Compared with pulsed-wave Doppler, much higher velocities can be recorded with continuous-wave Doppler because of the continuous signal sampling. The crystal emitting the sound does not have to wait to receive echoes because the second crystal handles the echo-receiving task. However, with continuous-wave Doppler, all Doppler shifts along the sound wave path are measured, making differentiation of blood-flow velocity from two blood vessels in the path of the sound wave impossible (Thrall, 2017). Pulse-wave Doppler It is performed using the same crystal for sending and receiving sound. Pulse-wave Doppler is used in combination with B-mode imaging; this is termed duplex Doppler. A blood vessel is selected in the B-mode image for Doppler interrogation, and an electronic region of frequency sampling, called the gate, is positioned in the blood vessel. The electronic gate is the only area from which echoes are accepted for flow quantification. Being able to select a blood vessel for evaluation visually is a benefit of pulsed-wave Doppler (Thrall, 2017). Spectral Tracing A spectral tracing is produced with both continuous- and pulsed-wave Doppler. It records the direction and velocity of the blood flow as a function of time. Tracing the blood flow: if above the baseline, the blood flows toward the transducer; if below the baseline, the blood flows away from the transducer. The thickness of the spectral tracing is known as spectral broadening, so when a large volume or range of blood flow velocity is present with the area of interest, the spectral tracing will appear broad. If the blood-flow velocity within the sample area is homogenous, the spectral tracing will be thin (Thrall, 2017). Color Doppler It is a variation of pulsed-wave Doppler. Blood-flow velocity is recorded in multiple regions within an image, and the velocities are color-coded. The user determines the color Doppler region of interest's size and location, which can be much larger than the sample gate used for pulsed-wave Doppler. Color-coded information is superimposed on the grayscale B-mode image within the region of interest. The commonly used colors in the Doppler is the blue and red hues. These colors are assigned individually to the blood flow: one color indicates the blood flow toward the transducer and the other away from the transducer. The intensity of the color indicates the velocity of the blood flow. The color Doppler is indicated in determining the speed, direction, character, presence, and or absence of blood flow within an area. One of the limitations of the color Doppler is that it is angle-dependent so that when the blood flow is 90 degrees to the transducer, no Doppler shift is recorded (Thrall, 2017). Power Doppler It is a signal-processing method that analyzes the total strength of the Doppler signal while ignoring direction. It is determined through the concentration of the moving blood (red blood cells). With the use of power Doppler, a Doppler shift color map will be created, wherein the hues and brightness of the color represent the power of the Doppler signal (Thrall, 2017). Discussion Echocardiography To evaluate cardiac diseases such as myocardial and valvular disease and congenital anomalies, M-mode and two-dimensional B-mode are used (Lavin, 2003; Thomas et al., 1993; Thrall, 2017). Patient Preparation No specific preparation is needed when conducting an echocardiogram. To protect the personnel conducting the test and the machine itself, aggressive patients should be restrained (physical or chemical). The hair at the area of interest must be clipped, and an acoustic gel is applied over the area. In small animal practice, the left and right cardiac windows are located by bending the elbow caudally. The intercostal space marked by the elbow will serve as our landmark for the placement of the transducer (Figure 18). The forelimbs are flexed cranially to give a free space for manipulating the transducer and preventing the appendage bone's superimposition to the thoracic organs. A rolled-up towel or sponge can be placed beneath the feline patient since their ribs are closer together, making the intercostal space window narrower. In normal ultrasound operation, the patient is approached from the dependent side by directing the transducer upward beneath the table level. In deep-chested breeds of dogs such as the Borzoi or Irish wolfhound and barrel-chested dogs (e.g., bulldog), a standing or sternal positioning can be used the ultrasonography of the thorax (Lavin, 2003; Thomas et al., 1993; Thrall, 2017). Imaging To improve the understanding of the cardiac and mediastinal anatomy, two-dimensional echocardiography can be used. Long-axis and short-axis scans are commonly used to obtain standard views of the heart. The long-axis scans normally include the left atrium, mitral valve, interventricular septum, and the left ventricular free wall (Figure 18). The aortic root and valve can be seen by slightly tipping the transducer (Estrada, 2017; Lavin, 2003; Thomas, 1993). In cats, the heart's right chamber (right ventricle and right atrium) is difficult to examine on the long-axis view, especially when approached in the parasternal position. This is due to the natural placement of the heart of the cat since it is so close to the thorax walls that it does not align or fall in the transducer's focal zone. In dogs, using the long-axis scan, the right chamber of the heart can be examined. The short-axis scans are used to assess the structures of the cardiac base and apex. The following structures are seen at the base of the heart: aortic and pulmonic valve, pulmonary trunk, and the left atrium. When the transducer is moved toward the heart's apex part, the mitral valve can be seen and below it is the interventricular septum and the right and left ventricle. Using the left parasternal position, the four-chamber view of the heart can be obtained (Figure 18) (Estrada, 2017). Basic knowledge of the heart's morphological appearance and function allows a rapid assessment and detection of cardiac abnormalities and disease. The two-dimensional scans are indicated in identifying pathological (e.g., pericardial and pleural effusion, cardiac masses such as clots) and congenital anomalies (e.g., defects in the interventricular septum). To measure the size of the cardiac chamber and thickness of the wall, and also detect abnormal valvular motion (e.g., prolapse, fluttering, or insufficient closure), an M-mode ultrasound is used. With this examination mode, the aortic and mitral valvular motion and thickness can also be assessed (Estrada, 2017; Lavin, 2003; Thomas, 1993). Horses are scanned in a standing position, usually confined in stocks. Indications for echocardiography of the horses are congenital heart disease and acquired valvular disease. Ventricular septal defect (VSD) is the most commonly diagnosed lesion. Acquired valvular disease is commonly seen in middle-aged to older horses. Myocardial disease and pericardial effusion are uncommon in horses. We have already discussed the Doppler and the Doppler shift in our previous lesson. For additional information, the Doppler studies are pulmonic, aortic, mitral, and tricuspid valvular insufficiencies and stenosis and congenital heart defects such as VSD and persistent ductus arteriosus (PDA) (Estrada, 2017; Lavin, 2003; Thomas, 1993). Abdominal Ultrasonography To prepare a small animal for an abdominal scan, the nonemergency patient may be faster for 12 hours to reduce intestinal gas. A full urinary bladder is optimal for scanning the bladder or prostate. The hair coat is clipped around the margins of the costal arch, flank, and caudally to the bladder. A coupling gel is applied. The animal is positioned in ventrodorsal or lateral recumbency; several different positions may be used to obtain optimal B-mode images (Lavin, 2003). Liver and Biliary Tract On an ultrasound, the normal liver has a uniform but slightly coarse echotexture; it is less echogenic than the spleen and more echogenic than the renal cortex. Typically, the larger vessels and the gallbladder are visible. The normal gallbladder has a smooth wall and anechoic contents. The visibility of the common bile duct is variable in animals. The portal veins are clearly defined by echogenic walls resulting from adjacent fat. Hepatic veins, in contrast, have poorly defined walls. Bile ducts and hepatic arteries are not well visualized in small animals, and in normal animals, separate lobes can be identified. Primary indications for liver scanning are abnormalities seen on survey radiographs (hepatomegaly or a liver mass). A liver scan is also indicated in cases of elevated liver enzymes, ascites, or suspected hepatic metastases. Ultrasound-guided biopsy or fine-needle aspiration is often performed in conjunction with liver scanning. Heavy sedation or general anesthesia is required for biopsy, but sedation is not required for fine-needle aspiration unless the patient is very active. For this procedure, the animal is placed in dorsal or lateral recumbency, and the area is surgically prepared (Lavin, 2003). Spleen The normal spleen is elliptic, flat, and smoothly contoured. Echogenically, it is homogenous, finely grained, and more echogenic than the liver. Small vessels are seen at the hilus. Indications for scanning are a mass, diffuse enlargement or an abnormal position of the spleen, identified on survey radiographs or during abdominal palpation. Abdominal trauma with bleeding, acute abdominal pain, or signs of anemia and collapse also indicate a splenic scan. In cases of hemangiosarcoma, the liver is scanned to search for metastases (Lavin, 2003). Pancreas The normal pancreas is narrow, smoothly marginated, and hypoechoic. The right pancreatic lobe is imaged best from the abdomen's right side with the animal in the left lateral recumbency. It is important to identify the descending duodenum because the pancreas' right limb lies along with it. The left pancreatic lobe is more difficult to image because of gas in the adjacent stomach and transverse colon. Usually, the animal is placed in right lateral recumbency. Landmarks include a triangular area bounded by the stomach's caudal margin, the cranial margin of the left kidney, and the area medial to the spleen. Pancreatitis is the most common indication for scanning. Neoplasms, cysts, and abscesses are rare (Lavin, 2003). Gastrointestinal Tract Gastrointestinal sonography can be difficult due to variable amounts of gas within the lumen, which reflect sound and prevent the imaging of deeper structures. Also, feces within the colon cause shadows. The normal bowel has different layers (lumen, mucosal surface and mucosa, submucosa, muscular, and subserosa-seros). The normal intestinal wall is 3 mm thick. Ultrasound can be used to identify gastrointestinal mural masses, assess bowel peristalsis, locate intraluminal masses and foreign bodies, and confirm intussusception (Lavin, 2003). Kidneys and Adrenal Glands To prepare for renal and adrenal scanning, the abdomen is clipped wide enough in the flank area to allow easy visualization. The left kidney is mobile, especially in cats. The normal kidney has a hyperechogenic capsule. The cortex is less echogenic than the liver or spleen and more echogenic than the almost anechoic medullary papillae. The renal sinus area is hyperechogenic due to fat and vascular interfaces. The renal pelvis is not identified as an anechoic cavity except when dilation is present. Evaluation of renal size based on sonographic assessment is less accurate than size determined by radiographs because of the falloff of the beam's sound at the round edges of the cranial and caudal poles (Lavin, 2003). Sonography is used to identify kidneys not visualized on survey radiographs, characterize a mass seen on radiographs, assess the location and distribution of disease in enlarged kidneys, determine mineralization, and confirm pelvic and perinephric fluid accumulations. Ultrasonography does not assess kidney function unless Doppler techniques are applied. Sonography in renal disease helps identify fluid-filled, cystlike lesions of solid masses (Lavin, 2003). Normal adrenal glands are small (less than 1.0 cm in height) and are located in perirenal fat medial to each kidney's cranial pole. The left adrenal gland has a dumbbell-like shape with widened cranial and caudal poles, whereas the right one is more triangular, and the cranial third of the gland is widened. Indication for imaging is to determine bilateral or unilateral enlargement. In pituitary-dependent hyperadrenocorticism, both glands become symmetrically enlarged, and there is no change in shape. An adrenal mass such as adenocarcinoma, adenoma, or pheochromocytoma usually is unilateral and alters the shape of the gland (Lavin, 2003). Prostate The normal prostate gland has homogenous echogenicity and fine texture. Ultrasound is indicated in cases of prostatomegaly, signs of lower urinary tract disease, constipation, or caudal abdominal pain. Prostatic and para prostatic cysts, focal and multifocal masses, and sublumbar lymph nodes can be identified. Ultrasound is not specific enough to differentiate benign prostatic hyperplasia from neoplasia or infection, and biopsy is recommended (Lavin, 2003). Urinary Bladder The normal urinary bladder contains anechogenic urine. The bladder mucosa is smooth, and the thickness of the bladder wall is uniform. Indications for bladder scanning are signs of lower urinary tract disease. Calculi, blood clots, and masses arising from the bladder wall are identified. It is necessary to scan with the bladder filled. Tumors in the bladder area can be difficult to see, and urethral masses are not visible because of their intrapelvic location (Lavin, 2003). Reproductive Tract The normal non-pregnant reproductive tract is not commonly seen in small animals. Indication for ultrasound is to diagnose pregnancy, pyometra, stump granuloma, or ovarian neoplasia. The optimal time for pregnancy detection in small animals is 30 days after the last breeding. Ultrasound is not accurate for determining the numbers of fetuses because of the superimposition of bowel gas and also because only a small segment of the uterus can be imaged at one time. However, ultrasound is very effective in detecting enlargement of the uterine horn in cases of pyometra. Ultrasonography is also an important tool to evaluate the mare's reproductive tract; the optimal time to detect pregnancy is day 11 of gestation (Lavin, 2003). Ultrasound Examination of the Eyes A 7.5 MHz transducer may be placed directly on the cornea after the application of the topical anesthetic. It can also be placed on the eyelid, although with this technique, the hair must be clipped, or coupling gel must be applied liberally. The cornea, anterior chamber, ciliary body and lens, vitreous chamber, optic disk, optic nerve, extraocular muscle, and retrobulbar fat can be seen. Indications for scanning the orbital region are intraocular masses such as melanoma or ciliary body tumors. Intraocular hemorrhage and inflammatory masses may also be seen (Lavin, 2003). Ultrasound Examination of the Extremities Ultrasound examination of extremities has focused primarily on the equine limb below the carpus and tarsus. Sonography plays an important role in diagnosing traumatic injury, infection, and inflammation of the equine extremities. Indications in thoroughbred horses are "bowed tendons," tenosynovitis, and suspensory ligament tear. It is important to monitor the healing process of acute injury and determine when the horse can begin rehabilitation and return to work. Consistently identified structures are skin, superficial and deep digital flexor tendons, inferior check ligament, and suspensory ligament, including medial and lateral branches. The inferior check ligament and the suspensory ligament are the most echogenic because of their dense fibrous composition. The superficial and deep flexor tendons have a medium echogenicity but are distinguishable from one another because of a slight difference in echo intensity and their differing shapes (Lavin, 2003). Discussion Contrast Media As mentioned earlier, contrast media helps to increase the radiographic contrast of an organ or system, thus increasing its visualization and examination. There are two basic categories of contrast media: the negative and positive. Elements with a high atomic number, such as the iodine compounds of barium, are classified as positive-contrast agents. These agents absorb more X-rays than the soft tissues or bones; they are radioopaque and appear white in a radiograph. It is also used to fill or outline a hollow organ (e.g., alimentary tract and the urinary bladder) or administered into the blood vessel for visualization and assessment of the vascular supply. Meanwhile, negative-contrast agent consists of gases of low specific gravity such as oxygen and carbon dioxide. These substances appear black or radiolucent than soft tissues on a radiographic picture (Table 9) (Lavin, 2003). In the advancement of radiography, many different compounds are manufactured and now available in the market. Because of this, some identical products are named differently, and the concentration of the substance varies. To make it easier for us to understand the different contrast media, we will place them into three general categories: (1) positive contrast iodinated preparations, (2) positive-contrast barium sulfate preparations, (3) negative-contrast gases (Lavin, 2003; Bassert et al., 2017). Iodine Preparations The iodine compounds are divided into two subcategories: the water-soluble agents and the oily/viscous agents. Water-Soluble Agents The water-soluble preparations make up the largest group of the contrast agents. The following are properties of these agents: it is opaque (white) in x-rays, low in viscosity for rapid intravenous injection, it is pharmacologically inert with low toxicity tendency, and it is chemically stable and rapidly excreted by the kidneys. One of the commonly known water-soluble agents that provides excellent contrast is the tri-iodinated compounds. The tri-iodinated compounds contain three atoms of iodine per molecule. They are supplied as sodium or meglumine salts of iothalamic diatrizoic or metrizoic acids or a mixture of these two salts. In general, sodium salts are less dense. The meglumine salts reduce toxicity, minimize high sodium concentration, and lessen tissue irritability. These contrast agents are usually injected into a vascular system for immediate visualization of the system or subsequent demonstration of the excretory system. Water-soluble agents can also be infused into the bladder via a urinary catheter to show the urinary mucosa and bladder shape and size (Lavin, 2003). Iodine agents are contraindicated for myelography and arthrography since ionic salt preparations all have a local irritant. Intravenous administration of an iodinated contrast agent can also cause mild discomfort and nausea in an animal patient. In rare cases, cardiac arrest, hypovolemia, and anaphylaxis have been observed. In general, sodium salts are more toxic than meglumine salts but are included in the compound to reduce viscosity for easier administration (Lavin, 2003). In patients with a suspected gastrointestinal perforation, water-soluble contrast agents are used. The drawback of these agents is that; upon administration, it enters the alimentary tract through the lesion/perforation and is rapidly absorbed by the body (Lavin, 2003). Oily/Viscous Agents In veterinary medicine, oily/viscous agents are used only in lymphography. These agents consist of iodized oils. The oil contains a suspension of propyliodone in either water or arachidic oils. Because of their vicious nature and insolubility in water, they are not resorbed in the body, and they produce fat embolism. Since it is an oil-based compound, it cannot be administered intravascularly. And during myelography, the agent does not mix with the cerebrospinal fluid. The recorded absorption rate of these contrast media is estimated at approximately 1 mL/year (Lavin, 2003). Barium Preparations Barium sulfate is a positive-contrast suspension and is the medium of choice for radiographic studies of the gastrointestinal tract. These contrast media are completely insoluble; they are not diluted by alimentary secretions and are not absorbed through the intestines. Barium is available in various forms (e.g., liquid, paste, and powder for reconstitution with water). The primary disadvantage of barium sulfate is that if it passed through a perforation in the alimentary tract into the thorax or abdomen, it would not be absorbed or eliminated. The barium can remain in the body indefinitely and could potentially produce a granulomatous reaction. In cases in which perforation is suspected, it is advisable to use a water-soluble contrast medium. However, if the water-soluble study is negative, a barium study should follow to avoid missing a perforation (Lavin, 2003). Negative-Contrast Agents: Gases Oxygen, nitrogen, nitrous oxide, and carbon dioxide are the most common negative- contrast gases used in radiographic studies. The most frequently used gas is oxygen, room air, and carbon dioxide. The advantage of carbon dioxide over room air is that it is absorbed into the body when administered into a hollow organ, while room air can cause air emboli formation. Gases, compared to other contrast media, are inexpensive, relatively safe, and easily administered (Lavin, 2003). Negative-contrast media enhance the contrast between various soft tissues but produce less mucosal detail than positive-contrast media. Some special procedures call for the use of both negative- and positive-contrast media, or double contrast. A double-contrast study gives optimum mucosal detail and voids masking small anomalies by large volumes of positive-contrast media (Lavin, 2003). Patient Preparation Proper patient preparation is vital to a diagnostic radiographic study. Before the study, the patient's gastrointestinal tract be emptied by withholding food for 12 to 24 hours and, if necessary, administering a cleansing enema. The presence of any gastrointestinal contents can detract from a quality study and may obstruct certain areas of interest due to superimposition. Keep in mind that cathartics and enemas often produce in the gastrointestinal tract during a study, the cathartic should be administered 4 to 12 hours before the radiographic procedure, and a radiographic study should not be administered within 1 hour of enema administration (Lavin, 2003). Evacuation of the gastrointestinal tract should be as atraumatic as possible, especially when working with an acutely ill patient. When an enema is contraindicated because of the poor condition of the patient, it is usually sufficient to fast the animal. However, if fasting would further compromise the patient's health, mild nongranular nourishment such as baby food or other commercially available foods. The anesthetic does not compromise many special radiographic procedures. For example, general anesthesia is contraindicated for a gastrointestinal study due to subsequently slowed motility. If sedation is necessary, it should be limited to phenothiazine tranquilizers such as acepromazine maleate. Phenothiazine tranquilizers have only minimal effects on gastrointestinal motility or transit time. The use of parasympatholytic agents such as atropine should be avoided for certain studies because of their anticholinergic effect (Lavin, 2003). Angiography and Angiocardiography Brief Overview Angiography consists of a bolus injection of an iodinated positive-contrast medium into a vascular system (e.g., cardiac, extremity), which is immediately followed by radiographic exposure. An angiogram may not be used to demonstrate occlusion of a particular blood vessel, to demonstrate pathologic lesions of the vascular system, or to provide evidence of a tumor that was undefinable on survey radiographs. A water-soluble iodine compound is the contrast medium of choice for angiography. For most procedures (e.g., angiography and angiocardiography), the contrast medium can be injected into a blood vessel proximal to the interest region. Because circulating blood rapidly transports the contrast agent away from the area under examination, it is necessary to expose the radiographs during or immediately after the injection. Ideally, the progress of a bolus injection of contrast medium should be followed by a series of radiographs exposed in rapid succession. This can be accomplished with commercially available rapid film changers, or in a small veterinary practice, it can be conveniently done with a sheet of sturdy clear plastic and several loaded cassettes. The sheet of clear plastic is positioned on top of small wood blocks, and the patient is centered on top of the glass sheet. The cassettes are numbered, placed under the plastic sheet, and positioned in a single-file line, with each cassette abutting the next. As the contrast medium is injected, the exposure is taken. The cassettes are advanced as each exposure is made (Lavin, 2003). Cystography Brief Overview Cystography is one of the contrast studies for the urinary system, especially the bladder. The contrast medium is introduced through the urinary catheter. Positive-, negative-, and double-contrast studies can be used for cystography. A cystogram can also be performed in conjunction with an upper urinary tract study (e.g., excretory urography). A contrast study of the bladder is beneficial for investigating cystic calculi, mural lesions, bladder rupture, and other bladder wall abnormalities. A cystogram is indicated for an animal exhibiting unresponsive clinical signs such as hematuria, crystalluria, bacterial infection, dysuria, anuria, and incontinence. At no time should cystography replace a clinical evaluation of the patient history, physical examination, and laboratory data. Radiographic findings from cystography can confirm, refute, or correct diagnoses formulated by earlier clinical evaluation. Sedation is recommended for cystography because the urinary bladder's distention can be uncomfortable, especially for a patient with cystitis (Lavin, 2003). Precautions Any urine samples needed for laboratory data should be obtained before the injection of contrast medium. Iodinated contrast agents increase urine-specific gravity to a variable degree and induce a false-positive reaction for protein detected by sulfosalicylic acid. Procedures using contrast agents can influence laboratory data obtained from the upper and lower urinary tracts for as long as 24 hours (Lavin, 2003). The use of barium sulfate and sodium iodide is contraindicated for cystography. Although they are rare, barium sulfate complications include barium casts and interstitial fibrosis secondary to vesicoureteral reflux. Barium also serves as a nidus for the formation of uroliths. Also, the granulomatous disease may occur secondary to a rupture of the bladder or urethra. Sodium iodine solution is not recommended for cystography because of its irritating effect on the bladder and urethra mucosa. Sodium iodide solution has been known to produce acute hemorrhagic cystitis, epithelial ulcerations, and submucosal hemorrhage (Lavin, 2003). Leakage of urine and contrast medium around or through the catheter may occur during the procedure. Any spill must be cleared off the equipment and patient immediately; contrast contaminants can confuse artifacts on a radiograph. Some indications that the injection of room air into the lower urinary tract can cause a fatal air embolism. This has been noted in patients with active bladder hemorrhage. The air can enter the low-pressure venous system via bleeding capillaries. Although this occurrence is rare, carbon dioxide or nitrous oxide should be used for macroscopic hematuria. Carbon dioxide and nitrous oxide are 20 times more soluble in serum than air or oxygen and are better absorbed in the body (Lavin, 2003). Cholecystography Brief Overview Colecystography consists of oral or intravenous administration of a positive-contrast medium that is excreted through the biliary system. The degree of opacification of the gallbladder and bile ducts can help evaluate gallbladder after injection of the contrast medium indicates possible gallbladder disease, biliary obstruction, gallstone, hepatocellular dysfunction, or failure to absorb the contrast agent if orally administered. Although opinions vary, the intravenous route of administration is most predictable and most rapid. Injectable contrast cholecystographic agents are recommended for the dog because the oral preparations have variable absorption and do not always provide a satisfactory study (Lavin, 2003). After the cholecystographic agent's injection, radiographs should be taken at 15, 30, 60, and 120 minutes. The time required for complete opacification of the gallbladder varies with each patient. Once the gallbladder is identified radiographically, a small, preferably fatty meal may be given to the patient and the second set of radiographs. Feeding the patient small meals allow the evaluation of the emptying of the gallbladder (Lavin, 2003). Other Special Procedures Contrast media are used in the examination of luminal organs for the observation of the organ lining, detection of foreign body, evaluation of neoplastic growths and inflammation. Below are the special procedures for contrast examination (Table 9): Table 9. Different contrast media procedure and its indications. Contrast Media Indication Procedure GASTROINTESTINAL TRACT Esophagography Evaluation of the esophageal function and morphology -for patients with a history of regurgitation of undigested food, acute gagging, or dysphagia. Upper GastrointestinalEvaluation of the stomach and small intestine (UGI) Study -for patients with recurrent unresponsive vomiting, abnormal bowel movements, suspected foreign body or obstruction, chronic weight loss, or persistent abdominal pain. Gastrography Evaluation of the stomach -for patients experiencing acute or chronic vomiting, blood in the vomitus, or cranial abdominal pain. Lower GastrointestinalEvaluation of the rectum, colon, and cecum (LGI) Study  -for patients with abnormal bowel movements characterized by excessive mucus, bright-red blood in feces, pain during defecation, or diarrhea in high frequency. URINARY TRACT Excretory Urography Evaluation of the kidney structure and collection system Cystography *discussed previously Urethrography Evaluation of the urethra -for patients with urethral trauma, stricture, obstruction, and other pathologic disturbances such as tumor invasion. Other techniques Arthrography Evaluation of the joint spaces -for a patient that is lame or has pain associated with a joint. Evaluation of a ruptured joint capsule, presence of cartilaginous flap, and mechanical injuries. Fistulography Evaluation of fistula formation in the body of the patient. Lymphography Evaluation of the lymphatic system -indicated to evaluate the cause of edema in the forelimb or hindlimb of an animal. Myelography Evaluation of the subarachnoid space of the spine -indicated to highlight a lesion that is undetectable on survey radiographs. Pneumoperitoneography Evaluation of the peritoneal cavity, abdominal organs, and the abdominal wall. Sialography Evaluation of the salivary duct and glands =The parotid, zygomatic, mandibular, and sublingual salivary ducts can be examined with this technique. Vaginography Evaluation of the vagina and cervix -used to evaluate the morphology of the vaginal vault and the reproductive tract. Note. Adapted from Radiography in veterinary technology (3rd ed) (p. 238-252), by L.M. Lavin, 2003. Elsevier Health Sciences Discussion Fluoroscopy Fluoroscopy uses the concept of radiography. But in comparison to radiography, which produces a singular non-moving picture, fluoroscopy presents a continuous image of the area of interest. It uses a subsequent amount of low-dose radiation directed to the area of interest and receives by intensifying monitor. The fluoroscopy unit consists of an x-ray tube (same with the x-ray machine) and an intensifying image monitor. The two components are mounted in a "C" shaped frame wherein the patient is placed in the middle. The exposure settings (kVp, mAs, and time) are also needed to be manipulated before doing the imaging. The resulting image or video clip is recorded and used as a permanent medical record (Bassert et al., 2017). Indications of Fluoroscopy Fluoroscopic captures are usually indicated for gastrointestinal evaluation, tracheal assessment, and myelography, which is important for cardiac and vascular examination (Bassert et al., 2017): Fluoroscopy is commonly used to view the trachea's changing diameter during inspiration and expiration in patients with tracheal collapse. Viewing the motility of the esophagus in animals that have regurgitation. Fluoroscopy can also be used in surgical situations, such as fracture reductions and catheter placement and stents. Implantation of a pacemaker, tissue biopsy and fine-needle aspiration is also indicated for this imaging technique. Contrast agents may also be added to better view anatomic structures and their movement during the study. Computed Axial Tomography The Computed Tomography (CT) has a major advantage in acquiring information not available from radiographs, contrast studies, or ultrasound examination. The primary indications for CT are central and peripheral nervous system diseases of the brain, spinal cord, and lumbosacral spine. It is also useful for obscure masses in the mediastinum, axillary, and retroperitoneal spaces (Lavin, 2003). Technical Aspects of Computed Tomography CT uses x-rays (about 120kVp with variable mAs) and computers to produce images that show anatomy in cross-section. CT allows visualization of structures in sagittal, dorsal, transverse, and oblique planes without superimposition artifact from fat, ribs, spine, pelvis, or any organs that may mask detail on a survey radiograph. Objects imaged by CT appear more clearly than those on conventional survey radiographs because the tomographic technology blurs the superimposed tissues. This is a static imaging modality, with images captured at a fixed moment in time. Images are saved and formatted to a smaller size to appear in sequence on a single piece of film (Lavin, 2003; Thrall, 2017) The CT unit consists of a moveable bed or cradle on which the patient lies and a gantry that contains the x-ray tube and detectors. The cradle moves through the opening (portal) in the doughnut-shaped gantry at specific distance increments (in millimeters) during scanning. The cradle in standard CT units can support approximately 300 pounds. The cradle in standard CT for horses requires a specialized table to support and maneuver the larger patients into the gantry. Because of the small portal diameter of the gantry (20 to 25 inches), only the skull, neck, and distal parts of horses' extremities can be scanned (Figure 19) (Lavin, 2003; Thrall, 2017). Within the gantry are the x-ray tube, x-ray detectors, and x-ray collimators. The x-rays tube is positioned opposite the detectors. The x-ray tube and detectors can be moved 360 degrees around the patient. X-ray detectors absorb the photons emerging from the patient and convert them to electronic signals assigned a number, representing their intensity as they emerge from the patient. The computer reconstructs the information into a picture displayed on a television screen. A set of images or slices is acquired at each interval of movement through the gantry. The computer can further reconstruct the internal structure of an organ from several projections of the organ (Lavin, 2003; Thrall, 2017). This examination requires general anesthesia to avoid excessive motion, which degrades the image more than conventional radiography. The animal is placed on the cradle in dorsoventral, ventrodorsal, or lateral recumbency. A survey radiograph is taken with the animal positioned in the gantry to localize regional anatomic landmarks so that when the CT is programmed, the patient movement will cover the appropriate region, and slices can be obtained through the area of interest. The limits for cradle movement through the gantry are set to cover the area to be scanned (Lavin, 2003; Thrall, 2017). Image Appearance In this imaging technique, the computer's image is perceived and interpreted similarly to our previously discussed imaging techniques. It uses the varying gray to the white color scheme in describing the different organs of the body. Different structures and matter (e.g., liquid, gas) present in the body appears differently in the CT scan depending on its density. The Radiodensity of the CT scan is measured in Hounsfield Units (HU). The HU ranges from -1000 to +1000 (Figure 20). Based on this, the following structure/matter is measured (Learning Neuroradiology, 2011): Water component such as the Cerebrospinal Fluid = 0 Air component as a least dense matter = -1000 Bone as the densest structure = +1000 Fat, in comparison to water, is less dense = -100 Brain parenchyma is denser than water, and it ranges = +20 to +40 Acute blood formation/coagulated blood is bright = +55 to +75 Brain white matter = +20 to +30 Brain grey matter = +37 to +45 Calcification is denser than blood = low 100’s In a brain CT scan, the following image display is used to describe tissue density (Thrall, 2017): Hypodense – seen in abnormalities that are less dense than the reference structure of interest, and it appears as a dark area. Isodense – seen in abnormalities that are the same density as the reference structure of interest and appear gray or similar to the surrounding tissues. Hyperdense – seen in abnormalities that are denser than the reference structure and appear as brighter or white compared to the surrounding tissues. Indications of Computed Tomography In small animals, the use of CT is most commonly indicated in patients with thoracic and abdominal disease, intracranial and extracranial lesions, and disorders of the musculoskeletal system, including the appendicular skeleton and spine. As the generation of images in CT is so rapid, this diagnostic modality is important in cases where anesthesia and sedation are not an option. CT is, therefore, useful in emergency critical cases or disorders, which may be compromised by anesthesia or sedation (Table 10) (Keane et al., 2017). In equine practice, the use of CT is most appropriate in the assessment of structures with mixed tissue thickness and, thus, different levels of tissue absorption of x-rays. Therefore, the most commonly assessed structures are the appendicular skeleton for diagnostic lameness workups, the dental arcade, paranasal sinuses, and the skull. The application of CT in a clinical setting to produce diagnostic images in cattle is not common. CT is often reserved for valuable cattle, primarily due to its expense and the use of general anesthetics and off-label drugs. The most common indications for its use are the central nervous system's disease, otitis media, and dental disease (Lavin, 2003). Table 10. Clinical applications of the computed tomography (CT) scan. Body Parts Indications Skull CT easily demonstrates intracranial lesions. -Indications of skull CT are seizure, blindness, vestibular signs, and change in disposition, which may be caused by brain masses, hydrocephalus, or trauma. Scanning of localized nasal, sinus, and periorbital masses. Malignant nasal tumors are scanned to assess invasion into the frontal sinus and skull. -The primary indications for CT in horses are to detect evidence of trauma; to assess the extent of nasal, sinus, and guttural pouch masses; and to identify congenital anomalies such as hydronephrosis. Spine CT is very helpful when myelography and standard radiographic procedures cannot completely outline a spinal lesion. -CT is the modality of choice for imaging the spine caudal to L4-5, especially in the paravertebral areas and lateralized spinal canal disease. -It allows visualization of intervertebral disk protrusion at C6-7 and C7-S1 and nerve root compression by stenotic foramina and intraspinal fibrous tissue. Extremities -Used in assessing the ulnar coronoid process in cases of the fragmented medial coronoid process in dogs. Also helpful for meniscal disease assessment. -In horses, it is used to assess fractures, especially the third carpal bone, supracondylar fractures of the distal third metacarpal, third phalanx fractures, and stress fractures in  the middle third metacarpal. It is also valuable for focal lesions such as infarct, osteochondrosis, and sequestra. Thorax -Indications for CT in the thorax include pulmonary and mediastinal masses, mediastinal lymphadenopathy, thoracic mass invasion into the spine or ribs, and detection of pulmonary metastases. There may be some advantages over ultrasonography for the detection of pericardial effusion and heart base masses. Abdomen The liver, gallbladder, stomach, small intestine, pancreas, spleen, adrenal glands, kidneys, ureters, urinary bladder, prostate, ovary, colon, and major vessels are easily identified on CT scans. -It is useful for canine adrenal masses. Note. Adapted from Radiography in veterinary technology (3rd ed) (p. 324-325), by L.M. Lavin, 2003. Elsevier Health Sciences. Nuclear Scintigraphy Nuclear scintigraphy is a non-invasive imaging procedure that uses a small amount of radioactive material (radionuclide) administered intravenously, transcolonically, or aerosol insufflation. Scintigraphy is more sensitive but less specific than standard radiographs or CT. Images do not provide anatomic detail of radiographs or CT, but they provide physiologic information about the specific organs' function (Table 6). The studies are complementary to those of other imaging modalities (Lavin, 2003). Technical Aspects of Nuclear Scintigraphy Nuclear scintigraphy, also known as isotope diagnostic procedure, employs radioactive labels that are a product of radiopharmaceutical product. Various physiochemical forms are formulated to deliver the radioactive atoms to specific body parts of a living animal. Once the substance is localized to the organ of interest, gamma radiation is emitted by the radiopharmaceutical substance will be available externally for detection and measurement (Balogh et al., 1999). Technetium 99m is the common radioactive isotope that emits gamma rays predominantly. Technetium radioactive pharmaceuticals are the most commonly used labeled compounds for imaging in veterinary medicine. The ideal radiopharmaceutical has a relatively short half-life, emits a low radiation dose to the patient and personnel, is readily available from commercial producers, and inexpensive. The radionuclide may be used alone or tagged to other compounds to absorb preferentially in a specific target organ (Lavin, 2003). A gamma scintillation camera (gamma camera) detects the gamma emission (counts) from the radionuclide and forms a black-and-white image of the selected organ printed on x-ray film. Animals are sedated for the procedure. Horses may be placed in stocks. The animal is positioned so that the detector's face is as close as possible to the suspected abnormality area to detect the maximum number of counts. It takes about 1 to 2 minutes to detect enough emissions to produce an image (Balogh et al., 1999; Lavin, 2003). Proper radiation protections, such as limited contact time with the patient, increased distance from the patient during scanning, and protective attire (lab coat, latex gloves), reduce personnel exposure. The radiopharmaceutical is excreted through urine and feces, so it is important to take precautions to avoid contamination during both the scanning and post-scanning decay phase. Technetium 99m is a convenient isotope for veterinary practice because of the short half-life (6 hours). Animals can usually be released 24 to 72 hours after administration of the radiopharmaceutical, depending on the radiation safety and protection laws of the state in which the procedure is performed (Balogh et al., 1999; Lavin, 2003). Indications of Nuclear Scintigraphy Nuclear Scintigraphy is used to examine neoplastic growth, inflammation of a certain organ, and the assessment of the organ function. Below are the different indications of nuclear scintigraphy per organ (Table 11). Table 11. Indications of Nuclear Scintigraphy.  Arterial balloon angiography  Arterial stenting  Emboli evaluation  Infarction and ischemia assessment  Endovascular embolization  Thrombectomy Bone Densitometry Bone densitometry is a technique that is used to measure the mineral content and density of the bone. It employs x-rays, dual-energy x-ray absorptiometry (DEXA or DXA), or special CT scan machines that use specialized computer software that measures bone density. Based on many studies, the DEXA is the "gold standard" approach for bone densitometry. The result of the said imaging technique could indicate if there has been a decrease in bone mass in a patient. In veterinary medicine, this technique is not usually performed in the field and even in small animal practice, due to the expense that it will cover and other technicalities (John Hopkins Medicine, n.d.). Indications of Bone Densitometry Bone densitometry is indicated primarily in assessing bone and bone diseases such as osteopenia and osteoporosis (John Hopkins Medicine, n.d.). Discussion Endoscopy Endoscopy is one of the minimally invasive procedures that does not employ the use of radiation. This procedure allows the examiner to gain visual access within a body cavity or an organ. It is used to gain diagnostic information, assesses the organ's function or interest, obtains tissue samples for histopathological examination, and evaluate the extent of an occurring lesion or metastasis. Gastrointestinal endoscopy is the most commonly used imaging technique in veterinary medicine. Endoscopic techniques can also be utilized to investigate multiple body systems. Endoscopy can be used as therapy, especially when used in the retrieval of foreign body, stone removal, and even in the placement of a feeding tube. Generally, endoscopic imaging is grouped into two categories; this is flexible endoscopy and rigid endoscopy (Table 12) (Clark, 2012; Tams, 2003). Flexible endoscopy uses flexible endoscopes such as the fiberscope and the video endoscope. Since it is easily mani