Data Acquisition

Over the past decade, there have been three important advances in CTC data acquisition, including reduction in radiation exposure, improved CT slice profile, and shorter acquisition times. These advances have been facilitated by the development and installation of multi-detector row CT scanners. The scanners allow four to 64 slices to be obtained in a single rotation of the X-ray tube. Moreover, gantry rotation times have decreased so that now most CT scanners allow tube rotation in 0.5 seconds or less. Multidetector row CT scanners allow large volumes of near isotropic data to be acquired in a single breath-hold.

Utilizing a 16 slice multidetector row CT scanner with 0.75 mm thick collimation and a pitch of 1.5, the same Z-axis coverage can be obtained in 15-20 seconds. Data can be reconstructed as 1 mm thick sections overlapped every 0.75 mm. Using a 64-row multidetector CT scanner, acquisition times are routinely less than 10 seconds.

The optimal slice profile for CTC has not been determined, but it is likely that data acquired with thin sections, approximately 1 mm, will improve sensitivity for small polyps and specificity. Using a four-row scanner, a 1-1.25 mm detector configuration is recommended. Others have advocated a 4 x 2.5 mm detector configuration [12]. There are two benefits of the 2.5 mm detector configuration. First, the mAs can be lowered and there is an inherent decrease in radiation exposure at 2.5 mm, when compared to 1 mm collimation on a four-row detector system. In addition, there are fewer images that need to be acquired.

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