Contrast medium administration and scan timing for MDCT

As computed tomography (CT) technology has evolved from single-slice imaging to 4- and 16-slice scanners, the speed at which the patient is passed through the gantry has increased up to eight-fold, depending on the technique used (Table 1). Therefore, the time to scan a body part or the entire body has been reduced substantially. For example, a chest scan that used to require 36 s on a singleslice scanner with 3-mm collimation now takes 5-10 s on a 16-slice scanner with 0.625 - 1.5 mm detector collimation; a chestabdomen-pelvis examination, which was not really feasible with singleslice scanners (requiring 80 s), is now possible in 10-20 s. The markedly reduced scan durations for multidetector-row CT (MDCT) examinations have made scan timing more critical than for single-detector CT.At the same time, these short scan times have provided radiologists with an opportunity to improve contrast enhancement with MDCT. It is therefore important for radiologists and technologists to: (1) understand the factors that determine both the timing and magnitude of arterial and hepatic parenchymal contrast enhancement for CT, and (2) identify the modifications needed to optimize contrast enhancement for 4-, 8-, 16-, and the new 64-row MDCT scanners.