RSNA 2012 

Abstract Archives of the RSNA, 2012


SSK16-05

Automated Extraction of Patient Size from Axial Computed Tomography (CT) Images as a Water-Equivalent Diameter for Use in Size-Specific Dose Estimates (SSDE)

Scientific Formal (Paper) Presentations

Presented on November 28, 2012
Presented as part of SSK16: Physics (CT Dose Optimization)

Participants

Ichiro Ikuta MD, MMSc, Presenter: Nothing to Disclose
Katherine P. Andriole PhD, Abstract Co-Author: Nothing to Disclose
Graham Ingersoll Warden MD, Abstract Co-Author: Nothing to Disclose
Leena M. Hamberg PhD, Abstract Co-Author: Nothing to Disclose
Ramin Khorasani MD, Abstract Co-Author: Stockholder, Medicalis Corp Royalties, Medicalis Corp Advisory Board, General Electric Company
Aaron D. Sodickson MD, PhD, Abstract Co-Author: Consultant, Siemens AG Consultant, Bayer AG

PURPOSE

Patient size is an essential parameter to adjust radiation exposure metrics such as volume computed tomography dose index (CTDIvol), as demonstrated by the American Association of Physicists in Medicine (AAPM) Task Group Report 204. We present an automated method to consistently and efficiently extract patient size, without requiring manual measurements that are prone to variation or susceptible to irregular patient contours.

METHOD AND MATERIALS

Fifty CT scans of the thorax and abdomen/pelvis performed in the emergency department in January 2012 were reconstructed with full field of view (500 mm) to visualize all skin contours. The open source Generalized Radiation Observation Kit (GROK) application automatically calculates the total attenuation-area product for an entire axial CT image based on pixel attenuation and area data, producing a water-equivalent diameter (DW). The effective diameter Deff = sqrt(Anterior-Posterior Diameter X Lateral Diameter) as defined by AAPM Task Group Report 204 was manually determined for these same images. DW was plotted against Deff at several anatomic locations in the thorax (lung apex, aortic arch, carina, diaphragmatic dome) and abdomen/pelvis (superior mesenteric artery, iliac crest, and L5-S1 intervertebral disc), and linear regression performed separately for the thorax and abdomen/pelvis.

RESULTS

For the thorax with Deff range 21.3-33.6 cm, R2 = 0.46, p < 0.0001, n = 200. For the abdomen/pelvis with Deff range 24.8-36.5 cm, R2 = 0.87, p < 0.0001, n = 150. Applying the regression models, we produced tables of the AAPM Task Group Report 204 SSDE conversion factors as a function of DW rather than Deff, separately for the thorax and abdomen/pelvis. For fixed physical dimensions, variations in patient anatomy and density may produce wide variability in the associated DW, with poorer correlation in the thorax from these effects.

CONCLUSION

The automatically extracted water-equivalent diameter (DW) from axial CT images is a predictor of manually measured effective diameter (Deff), allowing DW to select SSDE conversion factors.

CLINICAL RELEVANCE/APPLICATION

Automated extraction of patient size is possible from axial CT images, and may enable large-scale size-adjustment of CT exposure metrics such as CTDIvol.

Cite This Abstract

Ikuta, I, Andriole, K, Warden, G, Hamberg, L, Khorasani, R, Sodickson, A, Automated Extraction of Patient Size from Axial Computed Tomography (CT) Images as a Water-Equivalent Diameter for Use in Size-Specific Dose Estimates (SSDE).  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12025110.html