Low-dose CT Using Iterative Reconstruction in Patients With Inflammatory Bowel Disease

Study Overview
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Brief Summary
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The purpose of this study is to validate the use of a low-dose computed tomography (CT) protocol and facilitate reduced radiation doses in patients with inflammatory bowel disease (IBD). This is to be achieved using new computer software (Iterative Reconstruction and Automatic Tube Modulation) which will enable low-dose CT imaging at doses equivalent to that of an abdominal radiograph.

Detailed Description
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The increasing use of CT has prompted the development of new scanning protocols which reduce radiation doses to patients and minimise the likelihood of radiation related morbidity. The use of disease specific low-dose CT examinations is an emerging method of limiting radiation doses. Research conducted in Cork University Hospital(CUH) by the current authors has identified a pressing need to reduce radiation doses in patients with IBD. A retrospective study of radiation doses in patients with Crohn's disease demonstrated that increasing numbers of CT exams are performed with average cumulative effective doses rising from 7.9 to 25mSv when the first 5-years of the 15 year study period were compared with the final 5-years. Eight-five percent of the dose during the final 5-year period was due to CT. Younger patients with more severe disease requiring surgery or steroids were more likely to undergo an increased number of exams. 15.5% of patients received cumulative effective doses of greater than 75mSv. This quantity of radiation exposure is associated with a 7.3% increase in mortality from cancer. In addition, patients with Crohn's disease are inherently predisposed to gastrointestinal and hepatobiliary carcinoma and small bowel lymphoma. As an alternative to CT, IBD patients are frequently imaging with conventional abdominal radiography. The effective dose of a conventional abdominal radiograph (CAR) is approximately 10% that of a standard abdominal CT varying between 0.7 -0.1mSv. The current authors have also investigated the value of CAR. We retrospectively examined over 500 CAR's performed over a 16 year period in patients with IBD. Patients had an average of 3.5 CAR's performed but there were positive findings in less than 30% of exams. Many of these findings were non-specific requiring further investigation. For example separation of bowel loops on a plain radiograph has a wide differential diagnosis including abscess formation, presence of a phlegmonous mass, fibrofatty proliferation, bowel wall thickening and lymphadenopathy. Patients with inflammatory bowel disease referred to CUH will undergo a modified abdominal CT protocol. The radiation dose of a standard CT abdomen and pelvis will be divided into 2 quotients. Patients will have a low-dose CT scan requiring approximately 10% of the dose of a standard abdominal CT. This equates to the radiation dose of a conventional abdominal radiograph. Patients will be imaged with a second CT exam using 90% of the standard abdominal CT dose ensuring a diagnostic study is acquired. Patients will be given oral and intravenous contrast agents as for a standard CT. Patients will have a C-reactive protein measured on the day of CT and will have their heights and weights also measured at the time of scanning. Patients will have a plain film of abdomen performed prior to CT.

Conditions
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Inflammatory Bowel Disease, Crohn's Disease, Ulcerative Colitis

Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Adult patients requiring a CT abdomen for clinical purposes will be included Exclusion Criteria: Pediatric patients

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Inflammatory bowel disease<br>Patients with inflammatory bowel disease requiring CT for clinical purposes will be studied. | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The adequacy of low dose CT in patients with Inflammatory bowel disease compared with standard dose CT | Radiation dose of a standard CT abdomen and pelvis will be divided into 2 quotients. A low-dose CT scan acquired using automatic tube current modulation (ATM) requiring 10% the dose of a standard abdominal CT and equating to that of a conventional abdominal radiograph. High noise index will be used ensuring reduced mAs. Increased image noise will be overcome by the IR filter. A second CT using 90% of the standard abdominal CT dose will ensure a diagnostic study is acquired. | At the time of CT | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The correlation of C-reactive protein assay with CT disease severity in inflammatory bowel disease. | The severity of inflammatory bowel disease will also be quantified based on the CT appearances. The disease severity as measured by CT will be correlated with C-reactive protein measured on the day of imaging. | CRP sample on same day as CT | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Computed tomography, Iterative reconstruction, Automatic tube current modulation, Crohn's disease, Inflammatory bowel disease, Radiation dose optimization, C reactive protein