Avinash Kambadakone Ramesh MD, FRCR, Presenter: Nothing to Disclose

Priyanka Prakash MBBS, Abstract Co-Author: Nothing to Disclose

Ashish Sharma MBBS, Abstract Co-Author: Nothing to Disclose

Mehdi Khawaja MBBS, Abstract Co-Author: Nothing to Disclose

Dushyant V. Sahani MD, Abstract Co-Author: Researcher, General Electric Company

To study the impact of low dose CT examinations on image quality and diagnostic accuracy in patients with Crohns disease using a noise simulation software and to study their radiation dose benefits.

25 patients (14M: 11F, Age 16-76yrs) of Crohn’s disease who underwent contrast enhanced MDCT examination for evaluation of disease activity were included. The CT images were then modified using noise insertion software (GE healthcare) to generate low dose images of varying noise indices (NI) (15, 18, 20, 25, 30 and 35). The images were reviewed by 2 readers who recorded their confidence level for determination of enhancement, detection and conspicuity of complications on a 5-point scale (1-definitely absent & 5-definitely present). The original images served as the reference standard. The radiation dose for the original study and for modified images was estimated and the dose reduction achieved calculated. The final confirmation of disease activity and complications was based on clinical evaluation /follow up imaging/endoscopy and surgery.

21/25 patients (84%) had active disease and 7/25 (28%) patients had complications (abscess-4, strictures-3, fistula-1) detected on standard CT exam for which the readers had the highest confidence. Accuracy of detection of enhancement with increasing NI of 15, 18, 20, 25, 30, 35 were 100%, 100%, 100%, 100%, 90% & 85% respectively. The reader confidence for detection of enhancement was high (4.8) for NI ≤25 and reduced for NI ≥30 (3.9). Accuracy of detection of complications for NI of 15, 18, 20, 25, 30, 35 were 100%, 100%, 100%, 85%, 71% and 71% respectively. The reader confidence for detection of complications was highest for strictures at all NI levels. Reduced image quality with image degradation was reported at NI level ≥30 in 67-89% of cases. Average radiation dose per exam was 13.7mSv (4.1-22.8). The radiation dose reduction achieved by the noise simulation for NI of 18, 20, 25, 30 and 35 were 20-28%, 32-42%, 41-56%, 66-70% and 75-80% respectively.

Low dose CT examinations with NI levels up to 25-30 provide substantial radiation dose reduction while maintaining diagnostic accuracy. This has immense benefits in follow up imaging of young patients.

Performing low dose CT examinations has considerable radiation dose benefits with comparable diagnostic accuracy particularly in young patients who undergo multiple examinations

Kambadakone Ramesh, A, Prakash, P, Sharma, A, Khawaja, M, Sahani, D, Simulated Low Dose CT Examinations in Crohns’ Disease: From the Standpoint of Diagnostic Quality and Radiation Dose Reduction.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6022303.html