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October 28, 2009

Radiation Dose-Reduction Program for Cardiac Computed Tomography Angiography—Reply

JAMA. 2009;302(16):1753. doi:10.1001/jama.2009.1513

In Reply: Dr Torres and colleagues convey an important concern regarding the potential degradation of CCTA image quality as a consequence of decreased radiation dose. We agree that applying best-practice guidelines to decrease radiation exposure should not come at the expense of reduced scan quality.

Their suggestions of potential causes of increased numbers of poor or nondiagnostic quality scans are very reasonable. There is another potential cause that we did not quantify but might have been operative. The proportion of scans done at lower tube voltage (100 kVp) significantly increased during the course of our study (from 13% to 43%; P < .001). This had a beneficial effect on radiation dose, but due to the absorption spectrum of iodine would tend to increase the efficiency of absorption of photons at the lower voltage. The result is CT angiograms with a higher mean contrast level than scans done at 120 kVp. This requires adjustment of the window level and window width of the display monitor from the customary settings for 120 kVp. If this is not done, calcium deposits would tend to appear larger and other image distortions occur. Display adjustment was not taught as part of our best-practice guidelines and in retrospect it should have been. We have subsequently added this to the program and the current nondiagnostic scan rate is approximately 5%.

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