Flash scanner

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.

Two state-of-the-art MDCT scanners—Scanner 1: Siemens SOMATOM Definition Flash (briefly Flash), Forchheim, Germany; Scanner 2: Siemens SOMATOM Force (briefly Force), Forchheim, Germany—were used. For both scanners, imaging experiments were performed at the ICLIC. The UHR scan mode was used and a scan-length of 10 cm beginning at the distal tibia end-plateau was used; an anterior-posterior (AP) projection scout scan of the entire tibia was acquired to locate the field of view (FOV). A Gammex RMI 467 Tissue Characterization Phantom (Gammex RMI, Middleton, WI) was scanned to calibrate CT Hounsfield units into BMD (mg/cm³). In vivo ankle scan setup for a Siemens Force MDCT scanner along with the FOV selection on a scout scan and a reconstructed axial image slice are illustrated in Figure 1; a similar setup was used for the Siemens Flash scanner. Scanner-specific CT parameters are detailed in the following.