The ABCT’s of CT Imaging (Part I)

The Debrief

Pearl #1: CT relies on x-ray beams and various tissue impedance of these x-ray beams to create black-white images. Tissues with high attenuation (or high impedance of x-ray beams) are by convention WHITE, i.e. Bones. Tissues with low attenuation (or low impedance of x-ray beams) are by convention BLACK, i.e. Air. 

Pearl #2:  The Hounsfield unit of blood is approximately 50.

Pearl #3: The timing of CT scan in relation to the injection of contrast media is the basis for various phases of CT scans. Depending on your clinical question, the radiologist will protocol the CT scan to look at the pathology of interest in the non-contrast CT or CT timed for arterial, venous or delayed phase. The CT technologist will then perform the CT scan after specific time-delays after injection of contrast, basically timing the contrast to either be in arterial or venous circulation or excreted in ureters.