Radiation dose optimization for the bolus tracking technique in abdominal computed tomography: usefulness of real-time iterative reconstruction for monitoring scan.

The purpose of this study was to optimize the monitoring dose, obtained using the conventional filtered back projection (FBP) method and iterative reconstruction algorithms, for the bolus tracking technique. A phantom study was performed to assess the effect of the scan start time in patients grouped according to different body weights. An oval torso phantom was used for simulating the time enhancement curve of the bolus tracking technique. To reproduce image noise levels in the two body weight groups, the phantom diameter was adjusted with a water-equivalent material. The tube currents were 10, 20, 30, and 50 mA. The monitoring scan was performed with the conventional FBP method and real-time adaptive iterative dose reduction by three-dimensional processing (AIDR 3D). The results at different doses were compared with those at 50 mA. The volume computed tomography dose index was 1.31, 2.65, 3.93, and 6.56 mGy at tube currents of 10, 20, 30, and 50 mA, respectively. The scan start time, reconstructed using FBP, was significantly faster at 10 and 20 mA in group A (50-59 kg) and at 20 mA in group B (≥80 kg). The CT values in the region of interest could not be measured at 10 mA because of artifacts. With real-time AIDR 3D, both groups showed no significant differences between the measurements obtained at 30 or 20 mA and those obtained at 50 mA. Our study demonstrated that the real-time AIDR 3D algorithm improved the accuracy of the CT measurements with the bolus tracking technique.