<title>Effect of pitch, collimation, and reconstruction interval on low-contrast detectability in spiral computed tomography</title>

Abstract

Image quality characteristics of spiral CT are similar to conventional CT except for image noise and slice sensitivity profile. While these factors have been studied for high contrast, low contrast detectability in spiral CT has not yet been fully explored. Low contrast simulations that have been performed demonstrate the behavior of contrast sensitivity as related to the parameters of pitch, collimation, size of the object, alignment between the object and reconstructed slice, and reconstruction algorithm. The effect of spiral CT parameters on contrast to noise ratio (CNR), one component of low contrast detectability, is the focus of this study. A 9.5 mm diameter object was scanned using different collimations and pitches and reconstructed with different intervals. Results showed that low contrast detectability is optimized with collimations 7 mm and 10 mm at a pitch of 1 and the lowest CNR values were at a 1 mm collimation. A pitch of 1 had the highest CNR values while a pitch of 3 had the lowest CNR values. For similar table speeds selection of a lower pitch will improve CNR. The effect of object-slice alignment on CNR indicates no significant difference at a pitch of 3, but it had the lowest CNR values. For a pitch of 1 or 2, a small reconstruction interval is preferred over a large reconstruction interval.