BMI-based radiation dose reduction in CT colonography

There is potential for x-ray dose reduction in computed tomography colonography (CTC) relative to body mass index (BMI). We evaluated the association between BMI and three-dimensional (3D) CTC image quality to assess the potential utility of BMI as the basis for radiation dose reduction in CTC.

Ninety-six consecutive patients underwent CTC and were randomized for scanning at 15 or 30 mAs. Extremely obese patients (BMI > 50) were excluded. Each patient was scanned supine and prone on a multidetector CT scanner. Postprocessing CTC visualization was performed on a dedicated workstation. Three independent observers assessed 3D image quality using a four-point scale. Image noise was measured in both the abdomen and pelvis. The association between BMI and image noise was examined using random-effects linear regression models. Logistic regression was used to examine the relationship between BMI, mAs, and conspicuity scores.

Statistically significant differences in image noise were observed between 15 and 30 mAs in both the abdomen and pelvis, and the difference was greater with increasing BMI. A positive relationship was detected between BMI and noise in the abdomen (P < .001) and pelvis (P < .001). Inverse correlation was identified between BMI and conspicuity scores in the abdomen (P = .01) and pelvis (P < .001). Overall conspicuity scores were reduced for both 15 and 30 mAs groups as BMI increased.

The radiation dose for CTC can be reduced by 40% and 70% below commonly employed doses for overweight and normal BMI patients, respectively, by using a BMI-adjusted dose reduction approach. Conspicuity scores dropped in obese patients with reduced dose suggesting that standard accepted doses should be utilized in that group.