Optimization of scanning parameters for CT colonography

Abstract

To determine the optimal collimation, pitch and reconstruction interval for CT colonography, 10 spherical polyps between 1 mm and 10 mm diameter and made of tissue equivalent material with a CT number of 40 Hounsfield units (HU) were placed in the colon of an anthropomorphic phantom. The phantom was scanned at slice thicknesses of 3 mm, 5 mm and 7 mm and pitches of 1.0, 1.3, 1.5, 1.7 and 2.0 on an IGE Hispeed advantage system. Images were reconstructed for each scanning parameter at the minimum intervals allowed along the z-axis. The optimum scanning protocol was assessed by measuring maximum contrast between the polyp and air, sensitivity for detection of each polyp along the z-axis, and relative radiation dose. In addition, images were reviewed separately by two radiologists who graded polyp conspicuity as: 0, not seen; 1, faintly seen; 2, well seen. It was found that varying the scanning parameters caused a marked alteration in the maximum contrast between each polyp and air. For example, for the 5 mm polyp, the range of contrasts from best to worst case was 910-490 HU. It was noted that with contrasts of less than 500 HU, polyps were only faintly seen. A slice thickness of 3 mm with a pitch of 2 offers optimal polyp conspicuity with a relatively low radiation dose, we conclude that scanning parameters can be optimized for threshold contrast, radiation dose and subjective conspicuity. We propose an optimal parameter of 3 mm slice thickness and pitch 2.

Low-Dose Brain Computer Tomography Sensitivity: A Comparative Study with a Conventional Technique

“…The low-dose technique differed from the conventional one for mAs reduction. The same results were also reported in another two similar papers 18,19 . Therefore even in the case of diverticulitis as for appendicitis the low-dose CT showed high diagnostic capacity by identifying any significant pathological specimen viewed with the standard technique.…”

CT Colonography: Protocol Optimization with Multi–Detector Row CT—Study in an Anthropomorphic Colon Phantom

“…Hara et al (8) reported no change in the diagnostic efficacy between CT settings of 140 mA and 70 mA for singledetector row CT, which resulted in an effective dose equivalent for the acquisition of a single supine study of 1.87 mGy for men and 2.85 mGy for women. Van Gelder et al (21) found comparable sensitivity and specificity for polyp detection at 30 mAs (3.6 mSv) and 100 mAs (5.9 mSv), although the image quality decreased. Our results show that lowdose thin-section imaging is feasible.…”

Virtuelle Zystoskopie mit reduziertem Röhrenstrom: Eine Alternative zur Zystoskopie?

“…Beim Somatom-Plus-4-Scanner mit seinem neu entwickelten Filter und Detektor konnte eine weitere Dosisreduktion bis zu 40 % erzielt werden [22]. Power et al zeigten für die virtuelle Kolonoskopie in einer Phantomstudie, dass eine Schichtdicke von 3 mm und ein Pitch von 2 zu einem optimalen Kontrast von polypösen Tumoren führt [23]. Die bei diesem Protokoll verwandte Dosis liegt um 50 % unterhalb derjenigen eines Protokolls von 3 mm Schichtdicke und einem Pitch von 1, wie wir es gewählt hatten.…”