Comparison of 0.625-mm source computed tomographic images versus 5-mm thick reconstructed images in the evaluation for renal calculi in at-risk patients.

Background and Purpose: CT has become a well-established modality in the evaluation of urinary calculi. The advent of multidetector CT (MDCT) scanners and submillimeter thick slice acquisitions has yielded CT images with even greater resolution. MDCT scanners allow for source data slice acquisition with submillimeter slice thickness. These source images can then be reconstructed to thicker slices for more convenient interpretation of the CT scan. Previous authors have looked at the effect of slice thickness on detection of urinary calculi. We investigated whether the thin slice source images yielded detection of additional stones and the potential significance of detecting these additional stones. Patients and Methods: Ninety-five consecutive patients who were referred to our outpatient imaging center for CT, with a clinical history placing them at risk for urinary calculi, were included in the study. Results: In 49 (52%) of the 95 patients, more calculi were visualized using the 0.625-mm thick images than with the 5-mm thick images. In 34 (69%) of these 49 patients, the additional findings were thought to be "clinically significant," while in the remaining 15 (31%) patients, the additional findings were not thought to be clinically significant. In 46 (48%) of the 95 patients, there were no additional urinary calculi identified on the 0.625-mm thick images compared with that observed on 5-mm thick images. Conclusion: The results from this study encourage reviewing the thin slice source images of MDCTs in patients at risk for urinary calculi, because important clinical decisions may hinge on the additional findings made on these images.