AJR: Low-dose CT for Crohn's disease maintains image quality, lowers rad dose

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Substantial dose reduction for CT examinations in patients with Crohn's disease can be achieved with simulated low-dose MDCT examinations, without compromising diagnostic information and image quality, according to the results of a study published in the July issue of the American Journal of Roentgenology ( AJR).

Avinash R. Kambadakone, MD, and colleagues from the department of radiology within the division of abdominal imaging and interventional radiology at Massachusetts General Hospital in Boston, evaluated the image quality and diagnostic performance of MDCT examination images that had been introduced to noise index (NI) levels of 18–25 in order to simulate low-dose MDCT examinations for the evaluation of Crohn’s disease.

The researchers retrospectively evaluated 25 patients (14 males and 11 females, with an age range of 16–86 years) who underwent 35 contrast-enhanced MDCT exams of the abdomen and pelvis for initial diagnosis of Crohn's disease. Each of the 175 images were then artificially modified by the introduction of noise using volume CT noise simulation software to simulate low-dose MDCT data acquired with noise indexes (NIs) of 18–35. Next, the images were then randomized and reviewed by two readers who assessed the subjective image quality and diagnostic accuracy for the confident detection of Crohn's disease using a five-point scale (1, definitely absent; 5, definitely present).

Kambadakone and colleagues compared the image quality, diagnostic performance and radiation dose of the modified MCCT images to the original MDCT examinations.

The authors determined that based on the comparison with the original images, the simulated low-dose CT images with elevated NIs of 18–25 yielded optimal image quality and concordant diagnostic accuracy. The image quality score for the original images was in the range of 4–4.9, compared to that of the modified images, with an average image quality score of 4.95.

In addition, increases in the NI levels of the MDCT examinations resulted in a proportionate fall in estimated radiation doses, noted the researchers. “For NI of 18, the average dose reduction was found to be 31 percent; for NI of 20, 44 percent; and for NI 25, 64 percent.” For NIs of 30 and 35, average dose reductions of 75 and 82 percent, respectively, were achieved, the authors wrote. 

However, Kambadakone cautioned that images simulating NIs of 30–35 were degraded because of excessive image noise and presented lower diagnostic performance, resulting in an image quality score range of 3–3.6.

“An increase in NI will allow a significant reduction in the radiation dose—particularly for young patients who undergo multiple examinations—while maintaining the diagnostic accuracy,” stated the researchers.

The authors concluded that they intend to determine if further dose reductions might be possible for CT examinations in future studies.