Urinary stone disease: comparison of standard-dose and low-dose with 4D MDCT tube current modulation.

OBJECTIVE: The purpose of this prospective study was to compare the performance of standard-dose MDCT with that of low-dose MDCT with tube current modulation in patients with renal colic.

SUBJECTS AND METHODS: Three hundred patients underwent 6- and 16-MDCT in 150 standard-dose examinations (6-MDCT effective tube current, 95 mAs at 130 kV; 16-MDCT effective tube current, 120 mAs at 120 kV) and 150 low-dose examinations (6-MDCT effective tube current, 51 mAs at 110 kV; 16-MDCT effective tube current, 70 mAs at 120 kV), all performed with 4D tube current modulation. Two experienced radiologists using a clinical workstation and blinded to scan parameters prospectively viewed the images from the 300 examinations. In a second session, one experienced radiologist and two first-year residents using a clinical workstation retrospectively reviewed images from 100 randomly selected standard-dose and 100 randomly selected low-dose examinations.

RESULTS: Tube current modulation reduced effective tube current 25-31% in all examinations. Mean effective dose was 1.41-1.58 mSv for low-dose examinations, which reached additional dose reduction of 51.2-64.3% in comparison with standard-dose examinations. Excellent correlation existed between mean tube current and body mass index of the patients. Spearman's correlation coefficient was 0.85-0.88 for all examinations. The sensitivity of low-dose examinations interpreted by two experienced reviewers was 97.3-98.6%; specificity, 93.5%; and accuracy, 95.3%. These findings were comparable with those for standard-dose examinations. Sensitivity, specificity, and accuracy of low-dose examinations of overweight and obese patients reached similar high values: 97-100%, 100%, and 98-100%, respectively. Interobserver agreement for urinary stone detection was excellent between the two reviewers, with kappa values of 0.98 for the low-dose and 0.96 for the standard-dose examinations. An alternative diagnosis was identified in 15% and 16% of cases by two experienced radiologists in the two examinations groups. In the second interpretation session, the residents found an alternative diagnosis in only 10-12% of standard-dose examinations and only 4-5% of low-dose examinations.

CONCLUSION: Low-dose MDCT with tube current modulation can be used as standard procedure in evaluation for urolithiasis, even in overweight and obese patients.