SAGES Magazine

THE SOUTH AFRICAN GASTROENTEROLOGY REVIEW 2022 | VOLUME 20 | ISSUE 1 | 36 in their retrospective analysis of 278 DCBE examinations from January 2003 to December 2007. They did not provide the average number of DCBEs performed per week during the 59 months of the retrieved data nor did they provide details who analysed the retrieved data. Put differently it is unclear whether experienced DCBE radiologists interpreted the retrieved images or whether the analysis was based on retrieved reports. Barium enema is a time consuming and labour intensive examination; due to its very low sensitivity in detection of CRC the daily numbers of DCBE have continued to decrease thus radiologists are less experienced interpreting the images. 10 Following the 2003 ground breaking publication by Pickhardt et al 25 CTC is now performed in CRC screening and in failed or incomplete colonoscopy. 9,26-28 Barium enema versus computed tomographic colonography (CTC) Sensitivity of DCBE for detection of polyps >10 mm ranges from 50% to 75% 17 and 97% for CTC. 29 The findings of a multicenter randomised study on symptomatic patients for diagnosis of polyps and CRC were that CTC detected more polyps and cancer than DCBE. 30 Based on the findings of several DCBE and CTC studies the British Society of Gastrointestinal and Abdominal Radiology (BSGAR) and The Royal College of Radiologists (RCR) 31 stated in 2014 that BE should not be performed in patients with incomplete colonoscopy as CTC is the preferred radiology examination. Justi cation of radiology imaging in patients with failed or incomplete colonoscopy Informed consent underpins investigations, treatment and management of patients by healthcare practitioners. 32 In radiology an important ethical consideration in informed consent is ionising radiation dose to patients. There are published appropriateness criteria for selection of the most appropriate imaging examination. 33 The use of x-rays has grown exponentially over the years hence contributing to ionising radiation dose to patients with the result there is a worldwide campaign to reduce radiation dose to patients. 34-38 The findings of radiation doses to patients undergoing BE examinations showed an effective dose of 24±16mSv (milliSievert). 39 The effective dose in BE ranges from 7mSv to 11.4 mSv; in multidetector computed tomography (MDCT) CTC the range is from 0.5mSv to 8mSv. 40-45 The effective dose in BE includes fluoroscopy times and may vary in terms of the respective expertise of radiologists and radiology registrars. 47 Fluoroscopy was the focus of the study 47 therefore radiation dose of other radiographic exposures, such as a supine post evacuation radiograph, was not measured. Furthermore, possible pathology seen during a BE study may require additional fluoroscopy to allow for careful scrutiny of the area of interest which then will add to effective dose. 27 BE requires obtaining several projections of the colon hence a patient’s position is constantly changed during fluoroscopy for visualisation of large bowel segments; the range of positions of patients varies and impacts on effective dose. 27 The effective dose of a BE study tends to be much higher than that of a CTC study suggesting that the latter is the preferred imaging study. 27 The effective dose of CTC patients in a CRC screening programme was 2.17 ± 0.12 mSv, whereas the effective dose of DCBE patients was 1.9 times greater (4.12 ± 0.17 mSv) than CTC (p<0.0001). 31 Initially the radiation dose at CTC was of concern, but due to technological advances in radiation reduction tools such as automated tube current modulation, automated tube potential, and iterative reconstruction, in the latest generation scanners the effective dose can be sub- milliSievert (mSv). 41-45 The effective dose in CTC is the measurement of data acquisition of a routine two-position supine and prone study. 27 The acquired CT scans are automatically sent to the picture archival communication system (PACS) to view on the workstation. Advantages of CTC CT colonography is a fast, safe, socially distanced, minimally invasive, low dose examination which does not require sedation. 10,47-51 A CT scanner with special software produces a reconstruction of the carbon dioxide (CO2) filled colon. The software produces two-dimensional (2D) images and three-dimensional (3D) endoluminal views. 48,52 The software allows video viewing of a 3D virtual fly-through of the colon from the rectum to the caecum (retrograde navigation) and back to the rectum (antegrade navigation). This process takes approximately two minutes to perform; one is able to stop the fly-through at any stage for careful scrutiny of any part of the colon that may have a lesion. 52 In a routine supine and prone CTC examination a virtual fly-through is performed four times. The software also has a tool to produce a 3D surface- rendered image 53 (colon-map) of the entire colon as shown in Figures 1a, b and c. The software generates an automated centerline for endoluminal navigation. The automated centerline may be used for in vivo length measurements. Figures 1 d and e are examples of an automated green line. Figure 1a 3D surface-rendered image (colon-map) showing sigmoid in a normal appearing colon Figure 1b An oblique colon-map showing an ischaemic stricture (black arrow). Figure 1d Normal colon-map with automated centerline (green line) which allows for measurement of length of the colon. Figure 1c Colon-map showing extensive diverticular disease involving the sigmoid and distal descending colon (white circle). The rest of the colon is normal. Figure 1e Colon-map with green centerline. Red dot in the caecum indicates the site of a lesion observed in the CTC fly-through. CASE SERIES