Diagnostic Imaging Modalities of Medical Imaging Session 1 PDF

MODALITIES OF MEDICAL IMAGING Radiography  LECTURE OBJECTIVES Discriminate between the image generation process in Radiography, CT, Molecular Imaging (Nuclear Medicine/PET), MRI, and Ultrasound Define terminology used to describe the appearance of the different densities when interpreting the...

MODALITIES OF MEDICAL IMAGING Radiography  LECTURE OBJECTIVES Discriminate between the image generation process in Radiography, CT, Molecular Imaging (Nuclear Medicine/PET), MRI, and Ultrasound Define terminology used to describe the appearance of the different densities when interpreting the following imaging studies: Radiographs, CT, MRI, Ultrasound, and Nuclear Medicine/PET Describe the preferred clinical indications for selecting the following imaging studies as well as their strengths and weaknesses: Radiographs, CT, MRI, Ultrasound, and Nuclear Medicine/PET Distinguish between the most common contrast materials used in radiology and describe their indications/ contraindications Considerations when ordering imaging studies Radiography  Question 1 Mr. Smith is a 65-year-old male with a past medical history of hypertension, presents to the ER complaining of shortness of breath and chest pain which started while gardening. Which of the following is the initial study of choice? a. CT of chest b. MRI of chest c. Chest Radiograph d. Nuclear medicine V/Q scan e. Ultrasound of the heart (Echocardiogram) Radiography  Question 2. A 45-year-old male status post high-speed MVA involving blunt trauma to the chest complains of chest pain and hemoptysis. Which of the following is the modality of choice? a. CT of chest b. MRI of chest c. Chest Radiograph d. Nuclear medicine V/Q scan e. Ultrasound of the heart (Echocardiogram) Radiography Question 3. Which of the following is the normal image? a. Image #1 B. Image #2 #1 #2 Radiography  Image contrast The difference in brightness between an area of interest and its surroundings. The larger the difference in brightness between different tissue types, the easier it is to differentiate them from each other. Radiography  Artifacts and Interfaces An artifact is an imaging finding that does not directly correspond to the reality of the patient May mimic a clinical feature, degrade image quality, or obscure anatomy. Radiological interfaces are between different radiodensities The border of the heart against the lung Radiography  PLANAR VERSUS CROSS-SECTIONAL IMAGING Planar images are shadows of complex three-dimensional objects e.g. radiography Cross-sectional images show the three-dimensional reality of anatomy e.g. CT, ultrasound, and MRI. Radiography CATEGORIES Radiating imaging Modalities (use ionizing radiation to produce an image) Radiography Fluoroscopy Mammography Computed Tomography (CT) Nuclear Medicine Positron (positive electron) Emission Tomography (PET) Non-radiating imaging Modalities (do not use ionizing radiation to produce an image) Magnetic Resonance Imaging (MRI) Ultrasonography Radiography  Radiating Testing Modalities that use X-rays RADIOGRAPHY COMPUTED TOMOGRAPHY (CT) Radiography RADIOGRAPHY Radiography  RADIOGRAPHY https://www.merckmanuals.com/home/sp ecial-subjects/common-imaging-tests/plain -x-rays# Roentgen discovered x-rays in 1895. Referred to as x-ray, plain film, radiograph, and conventional radiograph Radiography refers to the medical images that are the “shadows” projected onto a flat plane (planar) when x-rays pass through a patient. Radiography  Five Basic Densities Seen on Conventional Radiography Radiography Radiography Radiopaque- Denser structures block x-rays better, appear white on radiograph Radiolucent- Less dense structures allow x-rays to pass through, appear gray to black on radiograph. Radiography  INDICATIONS Lung pathologies- Pneumonia, lung nodules, pneumothorax, COPD (chest film) Chest pain- aortic dissection, cardiomegaly and other findings may be seen on plain film (chest radiograph) Abdominal processes- pneumoperitoneum, obstruction, other causes of acute abdomen. You may need to use oral contrast when imaging the abdomen. C-spine- initial screen for fracture/injury that may threaten the spinal cord Bone and joint problems- fractures, deformities, infections, neoplasms, cartilage loss, derangement. radiographs remain the entrance-point for virtually all bone and joint assessments. Radiography RADIOGRAPHY Strengths Weaknesses Inexpensive Poor differentiation between different soft tissues Portable 2D image of a 3D object (frontal Low amount of ionizing radiation & lateral views needed) to patient Good contrast between bone, soft tissue, lung and air (in two dimensions) Contrast may be used to outline hollow viscera (gastrointestinal tract, urinary tract) Radiography  FLUOROSCOPY An application of projectional radiography that allows real-time observation The digital images are displayed on a television monitor and are recorded as a movie clip or as a series of images Uses: Barium X-rays and enemas (to view the gastrointestinal tract) Catheter insertion and manipulation (to direct the movement of a catheter through blood vessels, bile ducts or the urinary system) Placement of devices within the body, such as stents (to open narrowed or blocked blood vessels) Angiograms (to visualize blood vessels and organs) Orthopedic surgery (to guide joint replacements and treatment of fractures) https://www.merckmanuals.com/home/multimedia/video/barium-sw allow-fluoroscopy Fluoroscopy  MAMMOGRAPHY A mammographic unit is installed with a special x-ray tube and a plastic breast-compression device. Only method of screening for breast cancer shown to decrease mortality. Digital breast tomosynthesis (DBT) also referred to as three-dimensional (3D) mammography allows the breast to be viewed in a 3D format as multiple thin-slice images spanning the entire breast. MAMMOGRAPHY MAMMOGRAPHY IMAGES MAMMOGRAPHY COMPUTED TOMOGRAPHY COMPUTED TOMOGRAPHY https://www.merckmanuals.com/home/multimedia/video/computed-tomo graphy-ct-scan An x-ray beam that rotates along a 360°circle circular pattern with detectors rotating along the opposite side CT descriptors are “high attenuation” (radiodense or whiter) and “low attenuation” (radiolucent or blacker) CT images are viewed in sequential anatomic order, examining each slice with reference to slices above and below. COMPUTED TOMOGRAPHY  CT VIEWS AND CT WINDOWS The appearance of CT images depends on the window and level set by user. By “altering the window settings” within the same area being scanned different details can be seen. COMPUTED TOMOGRAPHY CT RECONSTRUCTION IMAGES 3D Surface Rendering- Useful for evaluating 3D Volume Rendering-A method for bone surfaces and surfaces of tubular displaying the anatomy in a life-like, Dynamic contrast-enhanced (multi-phase) CT- structures three-dimensional format. Most commonly used in liver, adrenal, and pancreatic imaging, as well as CT arteriography and venography. MIP of Aorta - maximum intensity projection is very CT Angiography- makes use of useful in evaluating the vasculature precise contrast timing to image vascular anatomy COMPUTED TOMOGRAPHY CT INDICATIONS Bone: useful for characterization of fractures or other local changes in bone such as neoplasm or infection Anything well-calcified: such as lung nodules Blood: in trauma situations when acute hemorrhage is suspected. Head injury or possible hemorrhagic stroke patients, for example, can get rapid assessment for intracranial bleeding with non-contrast CT. Chest and Abdomen: useful for visualizing internal organs (with and/or without contrast) Pelvis: Pelvic fractures/trauma (which are often acute emergencies) usually best seen on CT-which will depict not just bone but all the tissues, structures, and organ systems (GI, GU, neurovascular..) involved. Usually not used first in children/young adults due to risk of radiation to reproductive organs. Consider ultrasound or MRI as initial COMPUTEDimaging TOMOGRAPHY alternatives with no radiation risk.  COMPUTED TOMOGRAPHY Strengths Weaknesses Speed: The ability to provide very rapid Relatively high amount of ionizing radiation acquisition of images with a large area of per scan – 10-100 times more radiation than coverage in patients with severe/multisystem conventional x-rays acute trauma. Subject to artifacts due to patient movement Contrast resolution between different tissues: Allows for superior evaluation of abnormalities Hazards of IV contrast materials involving hemorrhage, calcium, or gas. Cannot be done at the bedside therefore Post-processing: The ability to obtain not for patients who have reformations in multiple planes unstable vital signs are in traction in spinal immobilization frames cannot leave the floor for other reasons. COMPUTED TOMOGRAPHY NUCLEAR (MOLECULAR) MEDICINE MOLECULAR IMAGING: NUCLEAR MEDICINE The only imaging technique entirely dependent on contrast agents Uses radioactive compounds called radiopharmaceuticals or radiotracers After the radiopharmaceutical is carried to a tissue or organ in the body, usually via the bloodstream, its radioactive emissions allow it to be measured and imaged with a detection device called a gamma camera. Provide targeted therapy for a variety of diseases (Radiotherapy). NUCLEAR (MOLECULAR) MEDICINE  NUCLEAR MEDICINE Single photon emission computed tomography (SPECT) imaging Acquires many 2D images from multiple angles, which are then reconstructed by computer into a 3D data set that can be manipulated to demonstrate thin slices in any projection. NUCLEAR (MOLECULAR) MEDICINE POSITRON EMISSION TOMOGRAPHY (PET) SCANS Operate on a molecular level to produce 3D images that depict the body's biochemical and metabolic processes. The most commonly used target molecule in PET scanning is an analog of glucose called fluorodeoxyglucose (FDG). Most often used in the diagnosis and treatment follow-up of cancer. Radiography Videos https://www.youtube.com/watch?v=U0SZHGfP_1A https://www.youtube.com/watch?v=TresR2wSw40 NUCLEAR (MOLECULAR) MEDICINE FUSION IMAGING Fusion imaging combines anatomic images with metabolic function images. PET scanning can be used in conjunction with a CT scan to give a more accurate localization of an abnormality or lesion for surgery or biopsy, or to identify suspected metastasis. increased specificity and sensitivity in the cardiac, neural, and oncological identification of abnormalities. NUCLEAR (MOLECULAR) MEDICINE MOLECULAR IMAGING Strengths Weaknesses Highly sensitive Non-specific Functional and anatomical Uses ionizing radiation information Cost of equipment Extra care in handling of radioactive material NUCLEAR (MOLECULAR) MEDICINE Non-radiating imaging Modalities MAGNETIC RESONANCE IMAGING (MRI) ULTRASONOGRAPHY  MAGNETIC RESONANCE IMAGING https://www.youtube.com/watch?v=FvOe zMIL9BU Patient is placed inside the gantry of an MRI Machine with a strong magnetic field Hydrogen protons inside the body (act as tiny magnets) will align in the same direction as the main magnetic field. Depending on the composition/pathology of the tissue, these protons relaxes at different speed. MR signal is captured and processed by the computer to form the image. High quality cross-sectional images (in any plane) MAGNETIC RESONANCE IMAGING  TISSUE DENSITIES Compact bone and air appear black on all sequences as no signal is emitted Proton density- Brighter area- the greater the concentration of hydrogen protons. Darker the area - the fewer the number of hydrogen protons. T1 weighting- fatty tissues appear bright (adipose, yellow marrow, CNS white matter) T2 weighting- fluids appear bright (CSF, mucus, urine, bile, edema and non-clotted blood) MAGNETIC RESONANCE IMAGING  MRI INDICATIONS Brain tumors or ischemic stokes Tumors more visible with gadolinium Any soft tissue pathology- ligament or meniscal tears in the knee, spinal disc herniation, nerve root impingement, bone marrow changes Pelvic imaging (both because of the lack of radiation exposure to reproductive organs and because of good soft tissue discrimination)- uterine fibroids MRI angiograms can be useful in the study of coronary or cerebral vasculature MAGNETIC RESONANCE IMAGING  MRI Strengths Weaknesses Machines are more expensive than CT Superb contrast between different soft Some patients are unable to have MRI due to : tissues claustrophobia Lack of artifact from adjacent bone presence of sensitive equipment Higher resolution than CT Internal (implanted) defibrillator or Highlights pathological changes pacemaker. No ionizing radiation Cochlear (ear) implant. 3D data acquisition/multiplanar Surgical clips such as those used on brain aneurysms. May be fused with CT scans Artificial heart valves. Implanted drug infusion ports. Artificial limbs or metallic joints. Implanted nerve stimulators. Pins, screws, plates, stents or surgical staples. Reduced sensitivity for small calcification and acute hemorrhage MAGNETIC RESONANCE IMAGING MAGNETIC RESONANCE IMAGING ULTRASONOGRAPHY A signal generator is combined with a transducer. Piezoelectric crystals in the signal generator convert electricity into high-frequency sound waves, which are sent into tissues. The tissues scatter, reflect, and absorb the sound waves to various degrees. The sound waves that are reflected back (echoes) are converted into electric signals. A computer analyzes the signals and displays an anatomic image on a screen. The machine displays the distances and intensities of the echoes on the screen, forming a 2D image. The body surface that is scanned may be: External transabdominal sonography Internal transvaginal, transrectal, and transesophageal ULTRASONOGRAPHY IMAGING PLANES Refers to adjustment in the direction of the probe The sagittal or longitudinal plane is viewed with the patient's head toward the left and feet toward the right The transverse plane is conventionally viewed with the patient's right on your left side and the patient's left on your right side ULTRASONOGRAPHY ULTRASOUND INTERPRETATION Echogenicity of the tissue - the ability to reflect or transmit us waves in the context of surrounding tissues. Bones, fat and stones Bones, fat and stones produce a hyperechoic signal. A hyperechoic signal is bright as most ultrasound waves are reflected. Cartilage and muscle Cartilage and muscle produce a hypoechoic signal. A hypoechoic signal appears dark as most waves pass through the tissue. Fluid and fluid-filled structures Fluid and fluid-filled structures produce an anechoic signal. An anechoic signal appears black as there is no reflection of ultrasound waves. ULTRASONOGRAPHY US ARTIFACTS ARE DIAGNOSTICALLY USEFUL: ACOUSTIC SHADOWING When a hypoechoic area is located behind a hyperechoic structure ACOUSTIC ENHANCEMENT When structures located behind fluid and homogeneous tissues generally appear brighter (whiter) than other structures typical feature of cysts and homogeneous solid masses, such as lymphomas. ULTRASONOGRAPHY DOPPLER SONOGRAPHY Provides valuable information regarding the presence, direction, and velocity of blood flow. DOPPLER DISPLAYS: Color Doppler Velocity and direction are color-coded. The color above the black bar - flow toward the Doppler beam The color below the black bar - flow away from the Doppler beam. By convention flow within arteries are red and veins are blue The brighter colors correspond to higher mean velocities and the darker colors indicate lower mean velocities. Doppler spectral velocity is plotted on the vertical scale (y axis) and time is plotted on the horizontal scale (x axis). The directions towards the transducer is above the baseline and the direction away from the transducer is below the baseline Doppler Sonography ULTRASOUND IMAGING: CAROTID ARTERY Doppler imaging looks at artery This is a healthy artery. The flow is smooth and all in the same direction, like water in a large, slow river This is also a carotid artery. The flow is not all in the same direction. It is turbulent, like rapids in a river. This is usually due to a build-up of fatty deposits in the artery Doppler Sonography CLINICAL INDICATIONS US Gynecologic exams- the lack of radiation makes ultrasound one of the most frequently used imaging tests in both pregnancy and other gynecologic exams Echocardiography- this very common test used to detect wall motion abnormalities in the heart is actually a form of ultrasound. Abdominal exams- useful to examine for cysts, bleeding, or inflammation of organs. Checking for deep venous thromboses in the extremities, especially proximally; Doppler effects can be used to assess volume, speed, and direction of flow Using Doppler ultrasound to examine the severity of carotid artery blockage Procedures- to guide procedures like biopsies, line placements, and thoracentesis/paracentesis (removing excess fluid from the thorax or abdomen without injuring other structures). Examining breast masses to further distinguish cyst/fluid from focal fat or tissue Focused assessment with sonography for trauma (FAST) –for evaluation of the torso for free fluid suggesting injury to the peritoneal, pericardial, and pleural cavities, particularly in cases of trauma. SONOGRAPHY ULTRASOUND Strengths Weaknesses Lack of ionizing radiation Cannot penetrate gas or bone so lesions within/behind/ above Low cost cannot be visualized Portability Obese patients may be difficult to Lack of use of contrast penetrate Dependent on the skills of the operator scanning SONOGRAPHY CONTRAST AGENTS  CONTRAST AGENTS FOR RADIOGRAPHY AND CT To distinguish adjacent tissues in imaging, the tissues must have different densities. An oral or IV administration of a contrast agent is often used to create a temporary, artificial density difference between objects. Intravascular iodinated contrast material excreted through the renal system In patients with normal renal function, the kidneys eliminate almost all the contrast agent. The half-time in patients with normal renal function is 1 to 2 hours, compared with 2 to 4 hours in dialysis patients. CONTRAST AGENTS  CONTRAST REACTIONS Contrast reactions can be anaphylactoid or chemotoxic reactions. Reactions may be: Minor- heat sensation, nausea, and mild urticaria. Intermediate- vasovagal reaction, bronchospasm, and generalized urticaria Severe- profound hypotension, pulmonary edema, and cardiac arrest In patients with a history of contrast allergy, pretreatment on re-exposure is usually recommended. Various protocols are used but typically include antihistamines and corticosteroids. CONTRAST AGENTS  MAGNETIC RESONANCE CONTRAST AGENTS The two classes of MRI contrast agents are diffusion and non-diffusion agents. Diffusion agents, with appropriate timing of imaging sequences, can delineate vessels as well as parenchymal tissues. Non-diffusion agents remain in the bloodstream and are primarily useful for MRA. All the contrast agents are based on the paramagnetic properties of gadolinium. Minor reactions such as headache and nausea occur in 3% to 5% of patients In patients with renal impairment, a rare severe reaction, nephrogenic systemic fibrosis (NSF), has been described The most recent guidelines gadolinium is contraindicated in patients with AKI and in those with chronic kidney disease stages 4 and 5 (i.e., GFR