Baojun Li PhD, Presenter: Nothing to Disclose

Richard H. Behrman PhD, Abstract Co-Author: Nothing to Disclose

Alexander M. Norbash MD, Abstract Co-Author: Stockholder, Boston Imaging Core Laboratories, LLC

To retrospectively compare different topogram-based patient body size indices and to determine the optimal topogram-based body size index as a basis for optimizing scan protocol and minimizing patient dose in body CT of adults.

Thirty-seven non-contrast CT scans of thorax or abdomen exam were studied retrospectively, with patient age ranging from 21 to 67 years old. The individual patient body attenuation of the scanned region was computed from reconstructed images as the gold standard, after first converting image pixel values from HU values to μa values, where μ is the attenuation coefficient and a is the area per pixel. Four topogram-based body size indices [diameter (D), girth (G), projection area (sqrtPA), and attenuation-area product (AAP)] were computed and correlated with the gold standard using regression analysis. Specifically, D was calculated by averaging the coronal and sagittal diameters; G was computed by modeling the patient cross-section as an ellipsoid; sqrtPA was the square root of the summation of the detector channel data; and AAP was the square root of the summation of detector channel data times detector channel width (cross-table direction) products. The AAP summation was performed after correction of patient mis-centering, table attenuation, scanner geometry and detector pitch angle. The accuracy of these four approaches for estimating body attenuation was assessed by goodness of fit using linear regression models. Results are given in terms of 95% confidence intervals (CIs).

Regression analysis resulted in different linear models. Preliminary results showed diameter and girth had comparable accuracies with 95% CIs of ±2.8cm and 3.1cm, respectively. PA was better than both D and G with 95% CI of 2.1cm; however, AAP was most accurate with a 95% CI of 1.3cm.

AAP is the most accurate body size index based on our retrospective in vivo study, and may be valuable as a prospective tool for protocol optimization and dose minimization in adult body CT.

Attenuation-Area Product In-Vivo is more accurate and a potentially superior tool for detemining CT dose than other body size indices such as diameter, girth and projection area.

Li, B, Behrman, R, Norbash, A, In Vivo Attenuation Area Product Is an Optimized Topogram-based Body Size Index for Body CT Dose Consideration and Scan Protocol Optimization.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11006098.html