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Low-dose CT examinations in Crohn's disease: Impact on image quality, diagnostic performance, and radiation dose.

OBJECTIVE: The objective of this study was to evaluate the image quality and diagnostic performance of simulated low-dose MDCT examinations in patients with Crohn's disease.

MATERIALS AND METHODS: Thirty-five MDCT examinations from 25 patients (14 males and 11 females; age range, 16-86 years) with known or suspected Crohn's disease were retrospectively evaluated. The MDCT images (5 mm thickness) were modified by artificially introducing noise using volume CT noise simulation software to simulate low-dose MDCT data acquired with noise indexes (NIs) of 18-35. The 175 MDCT image data sets generated were then randomized and reviewed by two readers to assess the subjective image quality and diagnostic accuracy for confidently detecting Crohn's disease findings on a 5-point scale (1, definitely absent; 5, definitely present). The image quality, diagnostic performance, and radiation dose from the original MDCT examinations served as a reference standard for comparison.

RESULTS: The simulated low-dose CT images with elevated NIs of 18-25 yielded optimal image quality and concordant diagnostic accuracy with standard-dose scans with a mean baseline volume CT dose index of 16 +/- 3.34 (SD) mGy (image quality score, 4-4.9 vs 4.95, respectively; p = 0.4). Images simulating NIs of 30-35 were considered degraded because of excessive image noise and presented lower diagnostic performance (range of image quality score, 3-3.6; weighted kappa = 0.25-0.37; p < 0.001). Diagnostic performance and reader confidence for the determination of Crohn's disease manifestations in cases in which the reference standard was positive were higher at NIs of < or = 25 compared with NI of 30 (reader confidence score, 4.5 vs 3.6, respectively; p < 0.05) and an NI of 35 (3.2, p < 0.05). Compared with the standard-dose examination, a 31-64% reduction in radiation dose was estimated for NI levels of 18-25, which corresponds to image noise of 19-27 HU in subcutaneous fat.

CONCLUSION: Processed MDCT images with the introduction of noise to simulate low-dose MDCT examinations with NI levels of 18-25 allows substantial dose reduction for CT examinations in Crohn's disease without compromising diagnostic information.

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