Low-dose MSCT tops x-ray for renal calculi diagnosis

New low-dose multislice CT protocols offer a reliable and safer alternative to x-rays in the diagnosis and management of kidney stones, according to European and U.S. researchers.

Abdominal radiography and excretory urography remain the diagnostic standard in patients with stone disease. Excretory urography has limitations, however, including high radiation dosage (mean, 1.5 mSv), possible allergic reactions to contrast agents, and low throughput. Ultrasound offers an alternative, but its detection rates are low.

German researchers led by Dr. Claudia Kluner, a radiologist at the Charité University Hospital in Berlin, proposed an MSCT protocol that provides diagnosis of stone disease with an effective whole-body dose of 0.5 to 0.7 mSv.

Her group evaluated 30 patients presenting with renal colic using a 16-slice scanner and compared the CT findings with ultrasound scans. The investigators found the dose-reduced CT scans detected all renal calculi identified by ultrasound and more urethral calculi than ultrasound revealed. Low-dose MSCT detected 69% of calculi in all cases, with a 78% detection rate in the presence of hematuria. Findings were presented at the 2004 RSNA meeting.

Low-dose MSCT's sensitivity and specificity compared favorably with those of conventional CT and topped those of ultrasound and conventional x-rays. The application of this protocol nullifies the main disadvantage of MSCT while retaining all of its advantages, Kluner said.

Other studies reported at the RSNA meeting bear out Kluner's findings.

Dr. Pierre-Alexandre Poletti and colleagues from Geneva University Hospital in Switzerland reported on 139 patients with renal colic who were randomized into two groups. Seventy-one underwent conventional abdominal x-ray, and 68 underwent nonenhanced low-dose CT. Low-dose CT delivered the same radiation dose as abdominal film radiography while reducing the need for further imaging.

Harvard researchers led by Dr. Vassilios Raptopoulos, a professor of radiology at Beth Israel Deaconess Medical Center, found that nearly all stones smaller than 5 mm detected in 34 patients could be seen on noncontrast MSCT with an imaging protocol set at 25 mAs.

Low-dose protocols may miss stones smaller than 4 mm. Small calculi, however, can be diagnosed and managed without the need for invasive procedures, researchers said.

For more information from the Diagnostic Imaging archives:

Multislice CT urography garners support but needs refining

Dose concerns get short shrift from non-rads in ER

Spiral CT pinpoints causes of renal colic

Spiral CT replaces IVP and KUB for renal stone disease