Photon-counting CT urogram: optimal acquisition potential (kV) determination for virtual noncontrast creation.

Abstract

To quantitatively and qualitatively compare the degree of iodine removal in the collecting system from PCCT urographic phase-derived virtual noncontrast (VNC) images obtained at 140 kV versus 120 kV. A retrospective PACS search identified adult patients (>18 years) who underwent a PCCT urogram for hematuria from 4/2022 to 4/2023 with available urographic phase-derived VNC images in PACS. Tube voltage (120kV, 140kV), body mass index, CTDIvol, dose length product (DLP), and size-specific dose estimate (SSDE) were recorded. Hounsfield Unit (HU) in both renal pelvises and the urinary bladder on urographic-derived VNC were recorded. Three radiologists qualitatively assessed the degree of iodine removal (renal pelvis, urinary bladder) and diagnostic confidence for urinary stone detection. Continuous variables were compared for 140 kV versus 120 kV with the Wilcoxon rank sum test. A p<.05 indicated statistical significance. 63 patients (34 male; median (Q1, Q3) age: 30 (26, 34) years; 140kV/120kV: 30 patients/33 patients) were included. BMI, CTDIvol, DLP, and SSDE were not different for 140kV and 120kV (all p>.05). Median (Q1, Q3) collecting system HU (renal pelvis and bladder) was 0.9 (-3.6, 4.4) HU at 140kV and 10.5 (3.6, 26.7) HU at 120kV (p=.04). Diagnostic confidence for urinary calculi was 4.6 [1.1] at 140kV and 4.1 [1.4] at 120kV (p=.005). Diagnostic confidence was 5/5 (all readers) in 82.2% (74/90) at 140kV and 59.6% (59/99) at 120kV (p<.001). PCCT urographic phase-derived VNC images obtained at 140kV had better collecting system iodine removal than 120kV with similar patient radiation exposure. With excellent PCCT urographic phase iodine removal at 140kV, consideration can be made to utilize a single-phase CT urogram in young patients.