Purpose: The purposes of the study were to determine the frequency and magnitude of extension of computed tomographic (CT) scans performed for the evaluation of urolithiasis, to investigate the potential contributing factors for overscanning, and to establish potential landmarks to assist in estimating the location of the superior margin of the kidneys.
Materials and Methods: This is a retrospective review of 300 CT studies performed for evaluation of urolithiasis. The total length of the scanned area, performing technologist, and the patient demographics were collected.
Results: We found that scanning beyond the defined z-axis boundaries is a common phenomenon in CT examinations in patients with suspected urolithiasis with a magnitude that correlates (P < 0.0001) with patient time and setting: greater in the emergent (78.3 mm) and inpatient (79.8 mm) settings as well as on-call hours (80.4 mm). Our study also shows the superior margin of T11 to be consistently within 3 mm of the superior margin of the kidney but not below it.
Conclusions: Overextension along the z axis is a ubiquitous phenomenon. The appropriate prescription of scan length, however, is an easy, efficient, costless, and universally applicable strategy. In patients with suspected urolithiasis, the superior margin of T11 represents a potential landmark to assist in estimating the upper margin of the kidneys.