Adequacy of low dose computed tomography in patients presenting with acute urinary colic

Noncontrast abdominal/pelvic CT is the current imaging standard for patients who present with acute urinary colic. Conventional CT, however, exposes the patient to significant amounts of ionizing radiation, which is cumulative when additional CTs are used to monitor stone migration, outcomes, etc. We sought to maintain diagnostic adequacy while decreasing our patients' radiation exposure from CT by using a reduced tube current, an abbreviated scanning area, and the use of coronal reformatted images.

Between March 3, 2011 and October 31, 2011, 101 consecutive adult patients with suspected urinary colic were evaluated with a "low" dose CT. If the suspected calculus(i) was not seen, the patient underwent immediate conventional CT imaging customized to their body habitus. Radiation exposure for each patient was calculated using an established formula of dose length product and scan length. The effective total radiation dose was measured in millisieverts (mSv).

Overall, 84 patients had an upper tract calculus(i) consistent with the clinical suspicion. Of these, 76 (90%) were adequately imaged with low dose and 8 (10%) with conventional noncontrast CTs. The mean effective radiation dose in the 76 low dose stone-positive CTs was 2.14 mSV (median 2.10 mSv). This was almost seven-fold lower than the mean conventional stone-positive CT dose of 14.5 mSv (median 13.1 mSv).

Low dose noncontrast CT provided adequate imaging to guide optimal urologic management in the majority of our patients. This modality offered a significantly lower ionizing radiation dose and should be considered in patients who present with acute urinary colic.