Utility of low mA 1.5 pitch helical versus conventional high mA abdominal CT

The objective of this study was to evaluate the utility of a low mA 1.5 pitch helical versus conventional high mA conventional technique in abdominal computed tomography (CT). Twenty-five patients who had both a conventional high mA (> 300) and a 1.5 pitch low mA (80-125) helical CT within 3 months were selected for inclusion in the study. Patients were excluded who had a significant change in pathology between the two studies. The other parameters (injection rate, contrast type and volume, and filming window/level) were constant. The studies were randomized and blinded to five separate experienced readers who graded the studies by a variety of normal anatomical structures and pathological criteria. Overview questions also assessed noise, resolution, contrast, and overall quality. The abdominal wall/retroperitoneum and hiatal hernias were statistically better visualized on the conventional high mA studies. However, for all other normal anatomical and pathological sites, there was equivalent or better visualization on the helical versus the conventional CT examinations. The resolution of the helical studies was graded statistically better than the high mA conventional CT scans as was the amount of noise present on the images. While there was some advantage for conventional high mA CT with respect to contrast enhancement and low contrast sensitivity, these differences were not statistically significant. It appears from the data of this study that a low mA technique in evaluating the abdomen may be a useful option in performing routine abdominal CT. The radiation dose savings to the patient is significant and there appears to be little degradation of image quality using a low mA 1.5 helical versus mA conventional CT technique.