Sub-milliSievert ultralow-dose CT colonography with iterative model reconstruction technique

Abstract

Purpose. The purpose of this study was to evaluate the technical and diagnostic performance of sub-milliSievert ultralow-dose (ULD) CT colonograpy (CTC) in the detection of colonic and extracolonic lesions.Materials and Methods. CTC with standard dose (SD) and ULD acquisitions of 64 matched patients, half of them with colonic findings, were reconstructed with filtered back projection (FBP), hybrid (HIR) and iterative model reconstruction techniques (IMR). Image noise in six colonic segments, in the left psoas muscle and aorta were measured. Image quality of the left adrenal gland and of the colon in the endoscopic and 2D view was rated on a five point Likert scale by two observers, who also completed the reading of CTC for colonic and extracolonic findings.Results. The mean radiation dose estimate was 4.1 ± 1.4 mSv for SD and 0.86 ± 0.17 mSv for ULD for both positions (p < 0.0001). In ULD-IMR, SD-IMR and SD-HIR, the endoluminal noise was decreased in all colonic segments compared to SD-FBP (p < 0.001). There were 27 small (6–9 mm) and 17 large (≥10 mm) colonic lesions that were classified as sessile polyps (n = 38), flat lesions (n = 3), or as a mass (n = 3). Per patient sensitivity and specificity were 0.82 and 0.93 for ULD-FBP, 0.97 and 0.97 for ULD-HIR, 0.97 and 1.0 for ULD-IMR. Per polyp sensitivity was 0.84 for ULD-FBP, 0.98 for ULD-HIR, 0.98 for ULD-IMR. Significantly less extracolonic findings were detected in ULD-FBP and ULD-HIR, but in the E4 category by C-RADS (potentially important findings), the detection was similar.Conclusion. Both HIR and IMR are suitable for sub-milliSievert ULD CTC without sacrificing diagnostic performance of the study.

Ultra‐low dose CT colonography with automatic tube current modulation and sinogram‐affirmed iterative reconstruction: Effects on radiation exposure and image quality

“…Lambert et al 29 demonstrated that iterative reconstructions are suitable for sub-milliSievert ultralow-dose CTC without sacrificing diagnostic performance of the study. Shin et al 30 stated that the per-polyp sensitivity of one-mSv CTC can be improved with the application of iterative reconstruction algorithms, when compared with the standard FBP algorithms.…”

Hybrid and Model‐Based Iterative Reconstruction Influences the Volumetry of Visceral and Subcutaneous Adipose Tissue on Ultra‐Low‐Dose CT

“…These algorithms are still undergoing development—from image‐based, hybrid, to model or convolutional network‐based being the latest (22). This technology allows decrease of the radiation dose by more than 60% while maintaining image quality and diagnostic performance (7,9). The reduction of radiation burden from a single thin slice also requires a collimator to reduce the unnecessary exposure of the surrounding tissue by overranging.…”

“…These settings were based on our previous experience with ultra‐low‐dose CT imaging of the abdomen in CT colonography (7,9). The radiation dose, E , was estimated using a conversion coefficient ( k ‐factor) of 0.015 and the dose length product (DLP) as E = k × DLP [mSv] (5).…”

Can fully iterative reconstruction technique enable routine abdominal CT at less than 1 mSv?

“…Previous studies have described use of IR techniques to enable radiation dose reduction below 1 mSv for abdomen CT [[21], [22], [23], [24], [25], [26]]. However, most successful studies with sub-mSv radiation doses using IR techniques were performed for evaluation of kidney stones and CT colonography [[22], [23], [24], [25], [26]]. Kidney stones are high contrast findings are not as much affected by high image noise at sub-mSv radiation doses [22].…”