Reducing the radiation dose for computed tomography colonography using model-based iterative reconstruction.

PURPOSE: To determine whether radiation doses during computed tomography (CT) colonography (CTC) can be further reduced while maintaining image quality using model-based iterative reconstruction (MBIR). METHODS: Twenty patients underwent CTC at a standard dose in supine and prone positions and at a reduced dose in the supine position. All other scan parameters (except noise index) were held constant. Acquisitions were reconstructed using 3 algorithms: filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and MBIR. Noise was assessed quantitatively by comparing the SD in Hounsfield units at 5 standard locations. Qualitative assessment was made by 2 experienced radiologists blinded to technique who subjectively scored image quality, noise, and sharpness (from 0 to 4). RESULTS: The standard-dose and reduced-dose CT dose index/dose-length product were 6.7/328 and 2.7 mGy/129 mGy-cm, respectively (60% reduction). Measured mean noise level increased from the standard to the reduced dose (FBP, from 58.6 to 97.2; ASIR from 35.8 to 60.6; and MBIR from 16.6 to 21.9). MBIR had significantly less noise than ASIR on 2-dimensional images at both standard and reduced doses (P < .01). CONCLUSIONS: Radiation dose in CTC using MBIR can be reduced by 60% while maintaining image quality and reducing image noise.

Partial preparation computed tomographic colonography: a feasibility study.

We retrospectively evaluated computed tomographic colonography examinations of patients who have had a partial bowel preparation and compared the quality of their preparation with patients who have had a full bowel preparation. In total, 27 patients undergoing computed tomographic colonography examination (10 patients with partial bowel preparation and 17 with full bowel preparation) had their examinations retrospectively reviewed by three independent radiologists in a blinded manner, with evaluation of residual stool, distention, residual fluid, and overall bowel preparation quality. Six colon segments were evaluated individually and independently for these four variables (a total of 161 segments tested). Comparisons were made with the Mann-Whitney test between the partial preparation group and the full preparation group. Partial preparation included stool and fluid tagging plus 20 mg of bisacodyl orally; full preparation included stool and fluid tagging plus 2 L of polyethylene glycol solution. No significant clinical difference was found in colon preparation between the partial and full bowel preparation groups--when evaluated with individual colon segments or by independent readers. Interreader correlation was high. This pilot study indicates that full bowel preparation is not required for diagnostic-quality computed tomographic colonography examination. Further evaluation of this partial bowel preparation regimen is warranted.

Large sample of nephrogenic systemic fibrosis cases from a single institution.

OBJECTIVES: To estimate and stratify the risk of development of nephrogenic systemic fibrosis (NSF) in well-defined at-risk subpopulations from a large single institution, and to perform a single-institution case series study of patients with biopsy-proven NSF. DESIGN: Retrospective cohort of patients exposed to gadolinium-based contrast agents (GBCAs) at a single institution during an 8-year period (January 1, 1999, to December 31, 2006), and a case series study of patients with biopsy-proven NSF. SETTING: A primary, secondary, and tertiary health care center that treated more than 2.2 million outpatients and had 135 000 hospital admissions in 2007. Patients A total of 94 917 patients exposed to GBCAs; patients at risk for NSF (3779 patients on hemodialysis, 1694 patients with renal transplants, and 717 patients with liver transplants, a well-defined subgroup that includes patients at risk for reduced renal function); and 61 patients with a clinical diagnosis of NSF. MAIN OUTCOME MEASURE: Risk estimate for NSF. RESULTS: The risk of development of NSF is 1.0% for patients who undergo hemodialysis (8 of 827), 0.8% for patients with renal transplantation (4 of 527), and 0% for patients with liver transplantation at our institution (0 of 327). CONCLUSIONS: Despite the limitations, this study, which reviewed a large number of patients who underwent intravascular GBCA injections, demonstrates a 77-fold higher risk of NSF among patients who undergo hemodialysis and a 69-fold higher risk in patients with renal transplantation. This increased risk is thought to be associated with poor clearance of most GBCAs.