CT Imaging Procedures and Cross-Sectional Anatomy
Protocol selection and timing
Head, chest, abdomen/pelvis, CTA, and extremity protocols differ in slice thickness, pitch, kVp, and contrast timing. Bolus tracking or a test bolus ensures arterial opacification. Breath-hold instructions include inspiration for chest and quiet breathing or expiration for some abdominal studies. Position the patient at isocenter and raise the arms for chest and abdominal scans when possible.
Cross-sectional anatomy
Know axial landmarks. At the level of the carina, the ascending aorta is anterior and the descending aorta is posterior-left. At T12/L1, the aorta lies left of the spine and the IVC lies right. The liver is right, the spleen left, and the pancreas central. Hounsfield units: water 0, air −1000, fat −50 to −100, soft tissue 20–60, and bone greater than 300. Contrast phases include arterial (aorta bright, organs not yet enhancing), portal venous (liver bright, hepatic veins opacified), and delayed (collecting system opacified).
Traps
Right/left confusion, unopacified bowel mistaken for mass, incorrect phase timing, and inappropriate window settings are common. Practice identifying structures on coronal and sagittal reformats, not just axial images.
Rule of thumb
At an upper abdominal level, when two large vessels are seen, the more anterior/right vessel is the IVC and the left/posterior vessel is the aorta.