Anatomy and Physiology Relevant to Imaging
Regional anatomy for imaging
A candidate should be able to localize major structures on plain film, CT, and cross-sectional images: the mediastinal compartments, the lobes of the lung, the abdominal organs and their relationships, and the bony landmarks of the spine and pelvis. Understand how patient positioning changes the projection of structures-for example, why an AP versus PA chest alters cardiac magnification. Know vascular anatomy relevant to contrast studies and the lymphatic drainage patterns that explain metastatic spread.
Physiology that affects image appearance
Understand how respiration, cardiac motion, and peristalsis create motion artifact and how breath-hold and gating mitigate it. Know how contrast agents behave physiologically-iodinated contrast clearance by the kidneys, barium in the GI tract, and gas as a negative contrast agent. Understand how fat, fluid, and bone differ in attenuation and why windowing reveals different tissues.
Traps to watch
Questions often test that magnification increases with object-to-detector distance and decreases with source-to-object distance, or that the same structure appears differently on different projections. Watch for items confusing left and right on cross-sectional images (radiological convention: patient's left is on the viewer's right) and for confusion between anatomical and functional descriptions.
Worked example / rule of thumb
Magnification factor = SID / SOD. If SID = 100 cm and SOD = 80 cm, magnification = 1.25, so a 4 cm object appears 5 cm. Rule of thumb: bring the object closer to the detector to reduce magnification.
Study guidance
Practice identifying structures on multiple planes and predicting how positioning changes projection and magnification.