CT Colonography Practice
The sensitivity and specificity of CT Colonography (CTC)
International CT Colonography standards have been agreed and published.(Ref 1).Colonoscopy is currently the gold standard investigation for large bowel pathology. However, approximately 5% of colonoscopies are incomplete and there is a subset of patients who cannot tolerate endoscopic investigation. In these circumstances CTC can provide an alternative investigation. It has also been approved for screening applications. It is therefore essential to have in place mechanisms for ensuring that CTC is performed to an appropriate standard.
CTC should demonstrate a greater than 75% sensitivity and greater than 95% specificity for detecting polyps greater than 1cm in size [2,3]. Outside of the context of a clinical trial, and during routine normal working practice within a teaching hospital, a sensitivity of 89% and specificity of 94% has been reported for polyps larger than 5mm in size .
>75% sensitivity and > 95% specificity for detecting polyps greater than 1cm in size [2,3].
•The number of negative CTC examinations that did not have a lesion identified at subsequent colonoscopy (specificity)
•The number of positive CTC examinations that were subsequently found at colonoscopy to be positive for disease (sensitivity)
Data items to be collected
•The number of patients with positive CTC findings (e.g. polyp or tumour)
•The number of these patients that have had subsequent positive histological confirmation
•The number of patients with negative CTC findings that have subsequently been found to have a polyp or tumour by alternative diagnostic means (e.g. colonoscopy or cross sectional imaging)
Retrospective patient data for the proceeding 1- 2 years for all patients who have undergone both CTC and subsequent endoscopy +/- biopsy, or 50 consecutive patients (whichever is greater).
•Present results at audit meeting, ensure standards meet those set by The International CT Colonography Standards Collaboration, and ESGAR [1,5]
1. Oral tagging agents should be considered in patients undergoing colorectal cancer screening with CTC
2. Symptomatic patients should receive full bowel purgation (if tolerated)
On the Scanner Table:
3. Spasmolytics such as Buscopan should be routinely used.(Glucagon not recommended)
4. Automated colonic distension with carbon dioxide is preferred
5. Supine and prone imaging should be routine unless prevented by patient's condition.
6. IV contrast medium should be routinely administered to symptomatic patients, but not to asymptomatic patients.
7. Datasets be should be analysed by a combination of 2D axial images, 2D MPRs and 3D rendering
8. Only experienced readers who have undergone approved training should be employed.
9. Consider double reading.
•CTC patient database generated from the appropriate RIS service
Radiologist: 6-12 hours to undertake
•Correlation with the relevant CTC reports
•Correlation with available histological reports
•Correlation with any subsequent colonoscopy report or cross sectional imaging report
1. Burling D. on behalf of the International Collaboration for CT Colonography Standards. CT Colonography Standards. Clin Rad 2010;65:474-480
2.Pickhardt PJ, Choi JR, Hwang I et al. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. N Engl J Med 2003;349:2191-2200
3.Macari M, Bini EJ, Xue X et al. Colorectal neoplasms: prospective comparison of thin section low dose multi detector row CT colonography and conventional colonoscopy for detection. Radiology 2002;224(2):383-392
4.Grant LA, Griffin N, Shaw AS. Two year audit of computed tomographic colonography in a teaching hospital: are we meeting the standard? Colorectal Dis 2009 Mar 5 [Epub ahead of print].
5.Taylor SA, Laghi A, Lefere P, Halligan S, Stoker J. European society of gastrointestinal and abdominal radiology (ESGAR): Consensus statement on CT Colonography. Eur Radiol 2007;17:575-579
If results are analysed by individual reporting radiologist this data can be used for revalidation purposes.
Lee Grant, Sona Biswas, Nyree Griffin, updated by Sue Barter on behalf of the Clinical Radiology Audit Committee.
19 March 2010