Vascular Enhancement and Image Quality of CT Venography: Comparison of Standard and Low Kilovoltage Settings

Abstract

The objective of our study was to investigate the vascular enhancement and image quality of CT venography (CTV) with a lower peak kilovoltage (kVp) setting than the standard setting. In this retrospective study, the clinical records of 100 consecutive patients with suspected pulmonary embolism were analyzed. All patients underwent pulmonary CT angiography and CTV of the abdomen, pelvis, and lower extremities using 64-MDCT with automatic tube current modulation: 50 patients underwent CT at 120 kVp, the standard kVp setting, and 50 patients were scanned at 100 kVp; we refer to these groups as the "standard-kVp group" and the "low-kVp group," respectively. Vessel enhancement and image noise were assessed in the inferior vena cava (IVC), femoral vein, and popliteal vein. Two radiologists who were blinded to the kVp setting placed the regions of interest on vessels by consensus and assessed image quality using a 5-point visual scale. Effective dose was estimated using the dose-length product. The Wilcoxon rank test was used to evaluate differences between the two groups using statistics software (JMP, version 5.1). A p value of less than 0.05 was considered to indicate statistical significance. Mean vascular enhancement was significantly higher in the low-kVp group than in the standard-kVp group: IVC, 138.4 ± 12.2 (SD) HU versus 164.5 ± 17.4 HU, respectively; femoral vein, 130.2 ± 18.0 HU versus 152.0 ± 24.5 HU; and popliteal vein, 136.7 ± 17.5 HU versus 158.3 ± 26.0 HU. Although the images of the low-kVp group had significantly higher image noise, there were no significant differences in image quality in the IVC and popliteal vein. The mean effective dose for the low-kVp protocol was significantly lower than that for the standard-kVp protocol. Lowering the kVp setting for CTV examinations improved vascular enhancement while providing sufficient image quality.