[Comparison of various parameters (pitch 1 and 2) in the study of the lung with spiral computerized tomography]

In Spiral CT, the pitch is the ratio of the distance the tabletop travels per 360 degrees rotation to nominal slice width, expressed in mm. Performing Spiral CT examinations with pitch 2 allows to reduce examination time, exposure and contrast dose, and X-ray tube overload. We investigated the yield of pitch 2 in lung parenchyma studies, particularly relative to diagnostic image quality.

Thirty patients were submitted to Spiral CT with pitch 1 [10 mm slice thickness, 10 mm/s table feed; 10 mm (a') and 5 mm (a") reconstruction index: protocol A] and with pitch 2 [10 mm slice thickness, 20 mm/s table feed; 10 mm (b') and 5 mm (b") reconstruction index: protocol B]. Five expert radiologists evaluated the images separately and blindly, grading noise, bronchial wall resolution and diagnostic yield on a 0-5 point scale. The results of protocol A versus protocol B images were analyzed statistically using the Mann-Whitney U-test.

The mean scores for each parameter ranged 4.13 (.70 standard deviation) for protocol B with 5 mm reconstruction index (b") to 4.81 (.44 standard deviation) for protocol A with 10 mm reconstruction index (a'). These values (max: 5) indicate very positive results on both protocol A and B images. There were no statistically significant interprotocol differences, except for bronchial wall resolution, in favor of protocol A with 5 mm reconstruction index (a") (p = .025), and for diagnostic yield, in favor of protocol A with 10 mm reconstruction index (a') (p = .018).

Spiral CT with pitch 2 is a reliable tool for lung parenchyma studies which permits to reduce examination time and contrast dose, as well as X-ray tube overload and exposure dose.