Abstract

Purpose: To compare the image quality on low-dose urinary tract multidetector CT examinations with 80 kVp and 120 kVp. Materials and Methods: Seventy-six patients with urinary tract symptoms were evaluated for urinary tract calculi by unenhanced multidetector CT. The examinations were performed with a four-row detector CT scanner. In all patients, two low-dose CT examinations with different kVp and mAs values (120 kVp, 30 mAs and 80 kVp, 95 mAs) were performed. The other scanning parameters were kept constant. Weighted-CT dose index was equal in both examinations. Both CT examinations were quantitatively compared with calculating the HU values of kidneys, subcutaneous fat, calculus, and phleboliths and the HU ratio of urinary calculi to the kidney. Both scans were also qualitatively compared for image quality of upper and lower abdomen. Results: One hundred and two calculi were detected in 50 of 76 patients. One or more phleboliths were present in 20 patients. HU values of the phleboliths and urinary calculi were higher on images obtained with 80 kVp than those obtained with 120 kVp. HU ratio of the calculi to the kidney was higher on scans with 80 kVp. Adipose tissue was less noisy and had lower HU value on 80 kVp images. Image quality of the upper abdomen and major pelvis were better on 80 kVp images, and the majority of these patients were normal (n=28) and overweight (n=20). Minor pelvis mostly (60%) revealed poorer image quality on 80 kVp images. However, the majority were overweight (n=22) or obese (n=6). In patients with osteoporosis, image quality was relatively better when compared with similar weighed patients without osteoporosis on 80 kVp images. Small renal, proximal and middle ureteral calculi were better demarcated on 80 kVp images. Conclusion: Low-dose urinary tract multidetector CT examination with 80 kVp, compared to 120 kVp provides better image quality in the upper abdomen and major pelvis. In overweight and obese patients, minor pelvis may not be evaluated thoroughly on 80 kVp images. Detection of small renal, proximal and middle ureteral calculi could be improved by using 80 kVp setting.

Keywords: urinary calculi, low-dose multidetector ct, lower kilovoltage, 80 kvp