Small Animal Radiography Techniques

• These notes cover radiographic techniques and positioning for small animal (SA) abdominal and thoracic imaging, SA forelimb and hindlimb/pelvis imaging, vertebral column imaging, and basic equine imaging

Abdominal Radiography in Small Animals

• Abdominal radiographs should be taken at the end of expiration to maximize soft tissue contrast and prevent organ compression
• The thicker part of the abdomen goes under the cathode side of the X-ray tube to utilize the anode heel effect
• Use a low kVp and high mAs technique to maximize contrast
• Borders: Cranial ~1 inch cranial to the xiphoid process (T9), Caudal includes the greater trochanters/coxofemoral joints
• Modified lateral view is used for urethral imaging in male dogs, with borders from L4 to the caudal aspect of the rectum
• Use the right lateral view for best view of both kidneys, and the spleen
• Left lateral view is best for evaluating GI foreign bodies
• Left lateral recumbency will fill the pylorus and duodenum with air
• Right lateral recumbency fills the fundus of the stomach with air
• Ventral recumbency fills the fundus with air
• Dorsal recumbency fills the pylorus and duodenum with air
• In a right lateral radiograph, the right side is the "dependent" side
• Correct lateral positioning indicated by: superimposed rib heads; equal-sized intervertebral foramina; "Nike swoosh" transverse processes; superimposed coxofemoral joints and ilial wings
• Correct DV/VD positioning occurs when: spinous processes are centered/teardrop-shaped; ribs are symmetrical; ilium wings and obturator foramen are symmetrical
• Dog beam centering: Over the caudal aspect of 13th rib at L2-L3
• Cat beam centering: 2-3 finger widths caudal to the 13th rib
• Patient should be measured in the position they will be radiographed
• Sante's rule: kVp = (2 x thickness in cm) + 40
• Lateral marker placement goes on the ventral side of the abdomen
• VD/DV marker placement goes on the correct side of the abdomen
• Lateral radiograph display: cranial part on the left
• VD/DV radiograph display: cranial part up, patient’s left on viewer’s right
• DV preferred over VD if the patient has trouble breathing in dorsal recumbency
• Lateral decubitus view used to detect free gas or fluid in the abdomen; X-ray beam is horizontal with the receptor behind the patient
• Lateral oblique view used to avoid overlap of the os penis over the bladder in male dogs
• In a lateral abdominal radiograph, the down limb should be pulled cranially
• Fat provides contrast between structures in the abdomen

Thoracic Radiography in Small Animals

• Higher kVp and lower mAs technique used
• Take thoracic radiographs at peak inspiration to maximize lung inflation and improve contrast
• Overexposed radiographs: Lungs appear too dark, soft tissues harder to see
• Underexposed radiographs: Image appears too light, lung detail obscured
• Expiration increases heart-diaphragm contact
• Symmetrical thoracic image: sternum and spine are superimposed, and the ribs appear symmetrical
• Right lateral recumbency provides the best visualization of left lung fields
• If pneumonia is suspected take both laterals (right and left) and a VD or DV to assess different lung regions
• For heart evaluation, take a DV and right lateral
• To look for lung metastasis take VD and both laterals
• Do not radiograph a dyspneic cat
• Remove debris/collars to prevent artifacts
• In a left to right lateral image, the right side is the dependent side
• Measure at the caudal border of the scapula over the thickest portion of the thorax and center the Beam at caudal border of the scapula, midway between the spine and sternum (between ribs 5 & 6)
• The entire thorax/ribcage should be included in thoracic rads
• Lateral marker placement: ventral aspect of the abdomen
• VD/DV marker placement goes near the axilla
• Normal dog heart size: 2.5 to 3.5 intercostal spaces
• Normal cat heart size: 2 to 3 intercostal spaces
• Right lateral: Heart is more oval, diaphragmatic crura are parallel (right side slightly more cranial), caudal vena cava only visible between the heart and diaphragm
• Left lateral: Heart is more rounded, right and left crura separate (left is more cranial), right cranial lobar artery/vein is more visible
• Inspiration: Heart appears smaller, lungs clearer and more inflated, more space between heart and diaphragm
• Expiration: Heart appears larger, lungs appear more opaque, more contact between the heart and the diaphragm
• Measure: Over the caudal border of the scapula at the highest point. Beam placement: Midline over the spine/sternum at the caudal margin of the scapula
• The entire thorax should be included for borders
• Symmetry occurs when: sternum and spine should be superimposed, and the ribs should be symmetrical
• A VD view will make the heart look longer because the heart shifts slightly to the left and elongates
• DV is the best view for evaluating the heart as well as providing better visualization of caudal lobar vessels and being a more natural position for patients in respiratory distress
• The diaphragm appears as three humps in a VD view but in a DV view its a single convex shape
• Left atrium is NOT visible from 2-3 o’clock in dogs but IS visible in cats
• The 3-6 o’clock position contains the left ventricle
• A horizontal beam is used to identify free air or fluid in the thoracic cavity
• X-ray tube must be able to tilt and rotate for horizontal beam views
• The decubitus’ side in a horizontal view is closest to the table and the plate must be vertically placed, directly behind the patient
• For a VD Decubitus view, the patient is similar to a regular VD, the plate is placed behind the patient and the X-ray Beam is directed horizontally
• Standing lateral thoracic view is used for patients that can’t be placed in lateral recumbency and the marker tells which side is closest to the plate and goes cranial to the axilla
• Oblique views are to better visualize the thoracic wall and pleura by rotating the sternum 20-30 degrees
• Right lung lobes: Cranial, middle, caudal, and accessory versus, Left lung lobes: Cranial (cranial and caudal parts) and caudal

Small Animal Forelimb Radiography

• The forelimb is part of the appendicular skeleton
• Joints are imaged while non-weight-bearing Major Bone Parts & Terms
• Fossa: A depression or hollow in a bone
• Condyle: A rounded articular surface at the end of a bone
• Diaphysis: The shaft or central part of a long bone
• "Contralateral" limb refers to the opposite limb
• Imaging technique: Low kV and high mAs, small focal spot, tight collimation
• Long bone borders involves the joint above and below
• Joint borders involves at least 1/3 of each long bone on either side of the joint
• Caudocranial views: Scapula, humerus, shoulder
• Craniocaudal views: Elbow, radius/ulna, carpus, foot
• Patients placed in dorsal recumbency for caudocranial limbs but sternal recumbency for craniocaudal
• Dorsopalmar view also called dorsoventral (DV) of the foot
• In a lateromedial view of the scapula, place the affected side UP instead of DOWN
• Scapula border: Proximal to the shoulder (cranial), beyond the caudal border of the scapula (caudal) with measuring at the cranial border of the scapula (~T1-2)
• Lateral side marker placement if caudocranial on the scapula
• Caudocranial: The patient is in dorsal recumbency. Craniocaudal: The patient is in sternal recumbency
• Skyline view assesses biceps tendon issues and humeral head pathology also called Cranioproximal-craniodistal view.
• Flexed mediolateral (hyperflexed lateral) view evaluates for elbow dysplasia
• Measure: Toward the proximal humerus at the shoulder joint. Beam centering: Middle of the humerus (when using the humerus)
• A craniocaudal view of the elbow best demonstrates the ossifications of the humeral condyle
• Oblique view of the elbow best demonstrates a fractured coronoid process
• Position a dogs head and neck away from the limb utilizing foam pads
• Central ray should be angled 10-20 degrees toward the joint for craniocaudal view of the elbow
• For a hyperflexed lateral, measure the distal humerus but measure the distal elbow when flexed
• Oblique view of the elbow for better visualization of the coronoid process and humeral condyle
• Measure: Distal humerus but center beam at misdhaft when using the radius/ulna
• For a lateral view of the foot, measure where the carpal joint and phalangeal-metacarpal articulate
• Bending the toes upward to hyperextend when hyperexending the carpus and foot, bending the toes upward is how it is completed
• To center medially or laterally without moving the X-ray tube, rotate the patients limb instead

Small Animal Hindlimb/Pelvis/OFA Radiography

• Evaluation purposes: fractures, hip dysplasia, luxation etc
• Assess the proximal pelvis/femur with dorsal recumbency, evaluate the distal pelvic limbs while in sternal recumbency
• Normals: The cranial 1/3 of each coxofemoral space should be equal in width; At least ½ of the femoral head should be in the acetabulum; Femoral neck angle should be ~130 degrees
• Low kV and high mAs technique used with lateral marker placement of the dorsal/craniad line and VD/DV done laterally
• Views: lateral, VD extended-leg, VD frog-leg
• A down (dependent) limb should be pulled cranially for a lateral pelvis image
• Symmetrical view indicates that the joint are superimposed: Femoral heads, iliac wings, and transverse processes of the caudal lumbar
• Use a lateral oblique view to image hips seperate
• Measure: At the level of the trochanter. Central Ray: Greater trochanter of the femur (lateral pelvis)
• Wing of ilium to at least one lumbar vertebra (cranial), caudal ischium (caudal), to dorsum, 1/3 of the femur (general pelvic)
• Extend limbs caudally and rotate femurs inward for VD extended leg pelvic
• Midline between the ischial tuberosities (VD extend)
• View border: Tip of iliac wings to distal patella (VD extend)
• For OFA evaluation, use VD extended-leg view
• Hip dysplasia may lead to arthritis formation, resulting it being the most common inherited orthopedic disease of dogs

OFA requirements

• At least 24 months old
• Hospital/DVM name, date, registration number or patient name, permanent ID are included on the radiograph
• Result options: Excellent, Good, Fair, Borderline, Mild, Moderate, Severe
• Minimum age for PennHIP is 16 weeks (4 months)
• PennHIP rads: VD extended-leg view, Distraction view, Compression view
• < 0.3 DI is considered low risk for arthritis development
• Legg-Calvé-Perthes database is for toy breeds >12 months of age. Screens for avascular necrosis of the femoral head
• Hallmarks of Hip Dysplasia: Subluxation/luxation, increased joint space width, shallow acetabulum, DJD, subchondral bone sclerosis, exostosis on acetabular rim, remodeling of femoral neck, femoral neck angle 130°

Femur, Stifle, and Tibia/Fibula Positioning

• Place a wedge/lead blocker to thinner parts and is also place over the distal end of the legs
• In a craniocaudal view of the femur, the patellas should be over the grooves
• Affected limb should be up and supported, with a cassette against the cranial aspect of the affected limb (caudocranial) with markers laterally
• Lateral stifle is completed when femoral condyles are superimposed
• A craniocaudal view magnifies the stifle
• Skyline view allows for assessment towards patellar and trochlear groove abnormalities (proximodistal/Cranioproximal-craniodistal). The affected limb should be up while the cassette goes against the cranial surface, alternatively use horizontal beam with limb flexed
• Evaluated lateral (mediolateral) tibia/fibula with the stifle and tarsal joints flexed at 90 degrees if TPLO surgery may occur
• Calcaneus vertical when taking the plantarodorsal on the foot

Vertebral Column Radiography

• Assess patients that are weak, paralyzed, and show signs of intervertebral disk disease (Used to access as it is the most broad)
• Evaluations should consider the intervertebral disc disease, congenital abnormalities and trauma
• Types: Cervical, Thoracic, Lumbar, Sacral, Caudal
• Canine/Feline vertebral formula: C7-T13-L7-S3-Ca (variable) Centering
• Primary view of focus of which the vet is looking between
• Limiting the number of vertebrae examined for better image detail and accuracy Markers
• Lateral views: Along the dorsum
• VD views: Side placed cranially
• The spine and sternum should be superimposed in a straight line from nose to tail
• Low kV and high mAs, but with enough kV to penetrate the tissue

Specific Vertebrae Positioning

• Yes, the whole body should be in a true lateral position even if only imaging a section of the spine
• Shoulder at C6 to the lateral cervical vertebrae
• Imaginary line drawn between the medial canthi of the eyes.
• C1 is also called Atlas and C2 is the Axis
• Sternum and vertebrae should be superimposed in a VD on the cervical vertebrea
• Move nose upward and secure with sandbags (occipital)
• Hyperextended view first to determine if a hyperflexed view is necessary and only done if necessary. Improper manipulation can cause an atlantoaxial dislocation.
• Hyperextendes/center at C3-C4
• Odentoid process can be better seen with an oblique view, measure and center at C1
• Pelvis should be in a ventral position to straighten the thorax
• Lateral: Shoulder joint (cranial) to L1 (caudal).
• VD view: The same
• Measure: At the highest point of the ribs and center the beam 4 vertebrea outside
• Whole body is truly needed when imagining the lumbar vertebrae

Lumbar, Lumbosacral, and Caudal Vertebrae Imaging

• Transverse processes should look like "nike swoosh"
• Consider giving them a enema 1-2 Hours before the imaging to reduce contamination
• Lumbar: Cranial (T12) to S1 which is Caudal and L4 at cranial to LS Juncture
• Borde: Femoral Head
• Hyperextended and hyperflexed lateral views.
• Thickest of the tail when measuring the caudal region
• Lateral decubitus view: VD

Equine Radiography

• Bones: The cannon bone with 3rd metacarpus/tarsus, 2nd and 4th Met
• Joints: FETLOCK, Pastern and Coffin joint, Carpys, Hock and Stiffle
• Weight bearing unless specified
• Clear foot for imaging purposes to not interfere with markers
• Should be on block for proper imagery
• Source-image-distance = 26-30 inches.
• Keep the plate as close as possible to the plates
• Center based on interested area and collimate there
• Evaluate indications such as lameness, pain, laminitis wounds and perurchase exams
• Dorsal or lateral aspect of the limb.
• Lateral aspect for CrCd and oblique views.
• Dorsal/cranial aspect for lateromedial views.
• Proximal view up for lateral/oblique also left is where dorsal ends
• At least 4 views in different planes is desired
• Pastern joint: Proximal interphalangeal joint.
• Coffin joint: Distal interphalangeal joint.
• Sesamoid bone, should be superimposed while imaging

Foot and Cannon Bone Imaging

• Dorsal or lateral aspect of the limb for labeling with proximal end up
• The limbs need Dorsoproximal views of the foot at the top portion
• Medial aspect view for lateral/oblique
• Look at lateral while doing a DMPLOs
• The medial bone is what can be seen if the DMLPOs in the cannon