Force scanner

The phantom was scanned with the abdomen protocol in a Siemens Force scanner. We scanned using an abdomen protocol from 40 to 240 mAs with 20 mAs increments. All scans were performed at a peak voltage of 140 kV, where we found the best match between saline and nylon. The scans at 60, 120, and 180 mAs were repeated three times to estimate the repeatability. The phantom was also scanned twice at 375 mAs; these scans were averaged together to serve as a high-dose reference scan, effectively at 750 mAs. We used a slice thickness of 3 mm with increments of 1.5 mm. The FBP reconstructions were performed using a B44 kernel, and IR reconstructions also included ADMIRE strength 3. This ensured that the signal from an acrylic bead (1.6 mm) would be almost entirely contained in one slice, so that a 2D analysis could be applied directly to detect the beads. If the slice thickness was comparable to the bead diameter and a 2D analysis was still used, beads that were centered on a slice would have been easier to detect than beads that were split between two slices. While some evidence has pointed to the validity of 2D anthropomorphic model observers in a multi-slice environment,^{23 (link)} we felt that the simplest solution was to avoid this complication using a thicker slice.

Matching HR and LR ankle CT scans of human volunteers acquired on two different CT scanners with significantly different spatial resolution were used for training, validation, and testing of the GAN-CIRCLE-based HR reconstructor described in the previous section. Specifically, nineteen healthy volunteers (age: 26.2 ± 4.5 Y; 10 F) were recruited and the distal tibia of their left legs were scanned on two MDCT scanners. The study was conducted around the transition period of the MDCT scanner upgrade at the University of Iowa Comprehensive Lung Imaging Center (I-CLIC). The first MDCT distal scan on each volunteer was performed on a LR Siemens FLASH scanner, and then they were recalled and rescanned on a HR Siemens FORCE scanner after upgrade. The average time gap between the LR and HR scans was 44.6 ± 2.7 days, with the minimum and maximum gaps of 40 and 48 days, respectively. The human study was approved by The University of Iowa Institutional Review Board and all participants provided written informed consent. The CT scan protocols on the two scanners are described here.