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Purpose The aim of this study was to assess the distribution of CT dose index (CTDI) values reported by sites undergoing ACR CT accreditation between 2002 and 2004. Methods Weighted CTDI (CTDI w ) values were measured and reported by sites applying for ACR CT accreditation, and the percentage of scanners with values above the 2002 ACR diagnostic reference levels (DRLs) was determined. Acquisition parameters for a site's adult head, adult abdominal, and pediatric abdominal examinations were used to calculate volume CTDI (CTDI vol ), and the average and standard deviation were calculated by year. Histogram analysis was performed to determine 75th and 90th percentiles of CTDI vol . Results Between September 2002 and December 2004, 829 scanners underwent the accreditation process. Volume CTDI values (average ± SD) for 2002, 2003, 2004, and 2002 to 2004, respectively, were 66.7 ± 23.5, 58.5 ± 17.5, 55.8 ± 15.7, and 59.1 ± 18.6 mGy for adult head examinations; 18.7 ± 8.0, 19.2 ± 8.6, 17.0 ± 7.6, and 18.4 ± 8.3 for adult abdominal examinations; and 17.2 ± 9.7, 15.9 ± 8.6, 14.0 ± 7.0, and 15.5 ± 8.4 for pediatric abdominal examinations. For 2004 data, 23.8%, 2.3%, and 6.9% of sites reported doses above the 2002 CTDI w reference levels, compared with 49.6%, 4.7%, and 15% for 2002 data for adult head, adult abdominal, and pediatric abdominal examinations, respectively. Seventy-fifth percentiles of CTDI vol were 76.8 mGy (adult head, 2002 only), 22.2 mGy (adult abdominal), and 20.0 mGy (pediatric abdominal). Conclusions From 2002 to 2004, average CTDI vol values decreased by 10.9, 1.7, and 3.2 mGy for adult head, adult abdominal, and pediatric abdominal examinations. Effective January 1, 2008, the ACR program implemented United States-specific diagnostic reference levels of 75, 25, and 20 mGy, respectively, for the CTDI vol of routine adult head, adult abdominal, and pediatric abdominal CT scans.

Purpose The aim of this study was to determine, for 3 basic clinical examinations, whether blinded, experienced CT radiologists participating in the ACR's CT Accreditation Program could use scan parameters such as tube current–time product (mAs), tube voltage (kVp), and pitch to predict scanner output settings, expressed as weighted CT dose index (CTDIw) and volume CT dose index (CTDIvol), exceeding CTDIw diagnostic reference levels (DRLs) set by the ACR in 2002 and CTDIvol DRLs adopted by the ACR in 2008. Methods CT sites with 829 scanners submitted examinations to the ACR between 2002 and 2004, yielding 518 eligible examinations for analysis (138 adult head CT scans, 333 adult abdominal CT scans, and 47 pediatric abdominal CT scans). The sites' measured CTDIw values for each type of examination were compared with the ACR's CTDIw DRLs in effect from 2002 to 2004 and compared with comments regarding excessively high mAs or kVp made by radiologist clinical reviewers to determine if excessively high-dose index measurements could be predicted. The same analysis was repeated using CTDIvol DRLs adopted by the ACR in 2008 and compared with excessively high mAs or kVp and excessively low-pitch comments. Results Excessively high mAs or kVp comments yielded sensitivity of only 21.2% in predicting examinations above the CTDIw DRLs, with specificity of 87.6%. Using the 2008 CTDIvol DRLs, the corresponding sensitivity was 13.1% and specificity was 86.2%. Significance was not achieved for use of clinical parameters in predicting either the CTDIw or CTDIvol. Conclusion Experienced CT radiologists cannot reliably use scan parameters to predict examinations that exceed CTDIw or CTDIvol DRLs.

The ACR CT accreditation program, begun in 2002, requires the submission of approximately 20 images, several completed data sheets and printouts of three Excel worksheets. The procedure manual is very detailed, yet participants unfamiliar with the program or having minimal CT experience have needed to redo aspects of their submission, or in some cases do not receive accreditation, due to mistakes made by the physicist. This review of the phantom portion of the ACR CT accreditation program supplements the ACR provided instructions with additional photos of phantom setup, region-of-interest (ROI), and image placement on the film sheets, and examples of completed portions of actual (but anonymous) submissions. Common mistakes, as well as uncommon but interesting images, are shown and explanations are given as to what could have been done to avoid the problem. Additionally, a review of CT dose measurement techniques and calculations will enable the physicist to better assist sites where typical exam doses are above the ACR reference values.