Diagnostic Imaging
Core concepts
Candidates must understand radiographic principles: X-ray production, attenuation (bone white, air black, fat and soft tissue gray), and the five radiographic opacities (air, fat, soft tissue/fluid, bone/mineral, metal). Know positioning and the two orthogonal views rule, radiation safety (ALARA, collimation, PPE, dosimetry badges), and film/sensor handling. Understand contrast studies (barium vs. iodine, GI vs. urinary) and their contraindications. Know ultrasound basics: probe selection, acoustic windows, echogenicity, and the difference between radiography (screening, bone) and ultrasound (soft tissue, real-time). Recognize common artifacts and their causes.
Traps
Questions test opacity identification and whether a structure is silhouetted. Distinguish barium from iodinated contrast (barium is contraindicated with suspected GI perforation). Watch for "two views" necessity - a single view can miss or mislocalize a lesion. Do not confuse radiation safety for the patient vs. personnel.
Worked example / rule of thumb
Use the "two views, orthogonal" rule: always obtain at least two perpendicular views to localize a lesion in three dimensions. Rule of thumb for opacity: air is blackest; metal is whitest. If you see gas where it shouldn't be (e.g., free abdominal gas), consider perforation and avoid barium.
Study focus
Prioritize the five opacities, positioning, radiation safety, contrast media selection, and radiography vs. ultrasound indications. Know ALARA and PPE requirements.