Are there any possible dose reduction strategies for CT Colonography?

Yes. There are clear opportunities for dose reduction with almost any type of CT scan. Of importance are using the highest pitch and lowest tube current (mAs) consistent with acceptable images. Increasing the pitch from 1.0 to 2.0 usually reduces the dose by half. The patient must be carefully centred at the isocentre of the scanner. Tube current should be set at the lowest level that allows adequate visualization of the colonic wall , or tube current modulation (TCM), a technique that adapts tube current to the morphology of the patient, can be used to achieve dose reductions of about 35%.Most protocols use kVp between 110-120. A number of authors have developed innovative colonic phantoms to help optimize CTC protocols.

Ultra-low dose protocols result in an effective dose of 0.5 to 2 mSv using 10 mAs and 120 kVp These have been shown to be capable of a sensitivity of over 80% for polyps > 5 mm and specificity in excess of 95%. Imaging of polyps with doses as low as 0.05 mSv has been shown to be feasible. When compared with results from 8-12 mSv scans, the lesion detectability did not change significantly although image noise increased substantially. The latter problem can be ameliorated through use of noise reduction filters and image smoothing.This adds to the widely shared opinion that there is much scope for dose reduction, with some loss of image quality, but without significant reduction in lesion detectability.