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Radiation Dose Reduction Strategy for CT Protocols: Successful Implementation in Neuroradiology Section¹

¹ From the Department of Radiology, Neuroradiology Section, University of California, San Francisco, 505 Parnassus Ave, Box 0628, San Francisco, CA 94143-0628 (A.B.S., W.P.D., B.C.L., R.G., E.B.L., M.W.); and University Institute for Radiation Physics, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Switzerland (F.R.V.). Received June 16, 2007; revision requested August 22; revision received August 31; final version accepted October 4. Address correspondence to M.W. (e-mail: Max.Wintermark{at}radiology.ucsf.edu).

Purpose: To retrospectively quantify the effect of systematic use of tube current modulation for neuroradiology computed tomographic (CT) protocols on patient dose and image quality.

Materials and Methods: This HIPAA-compliant study had institutional review board approval, with waiver of informed consent. The authors evaluated the effect of dose modulation on four types of neuroradiologic CT studies: brain CT performed without contrast material (unenhanced CT) in adult patients, unenhanced brain CT in pediatric patients, adult cervical spine CT, and adult cervical and intracranial CT angiography. For each type of CT study, three series of 100 consecutive studies were reviewed: 100 studies performed without dose modulation, 100 studies performed with z-axis dose modulation, and 100 studies performed with x-y-z–axis dose modulation. For each examination, the weighted volume CT dose index (CTDI_vol) and dose-length product (DLP) were recorded and noise was measured. Each study was also reviewed for image quality. Continuous variables (CTDI_vol, DLP, noise) were compared by using t tests, and categorical variables (image quality) were compared by using Wilcoxon rank-sum tests.

Results: For unenhanced CT of adult brains, the CTDI_vol and DLP, respectively, were reduced by 60.9% and 60.3%, respectively, by using z-axis dose modulation and by 50.4% and 22.4% by using x-y-z–axis dose modulation. Significant dose reductions (P < .001) were also observed for pediatric unenhanced brain CT, cervical spine CT, and adult cervical and intracranial CT angiography performed with each dose modulation technique. Image quality and noise were unaffected by the use of either dose modulation technique (P > .05).

Conclusion: Use of dose-modulation techniques for neuroradiology CT examinations affords significant dose reduction while image quality is maintained.

Supplemental material:
http://radiology.rsnajnls.org/cgi/content/full/2472071054/DC1
http://radiology.rsnajnls.org/cgi/content/full/2472071054/DC2

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