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There are several CT colonography (CTC) com­ponents. Each one contributes to a successful examination: from patient preparation to perfor­mance and interpretation of the results [1]. Pickhardt [1] underscores that every part of the technical component of a CTC examination is interconnected. The nal outcome will therefore be negatively impacted if there is a weak link in a CTC examination chain.

During the Covid-19 pandemic, patients were assured that CTC, compared to colonoscopy, is a socially distanced and minimally invasive study with a very low risk of transmission of infection [12]: patients should always be told this when they make an appointment for CTC examinations.

• CRC: colorectal cancer

• OC: optical colonoscopy

• 2D: two-dimensional

the best preparation. When CTC was rst intro­duced in 1994, sodium phosphate (NaP) was the agent of choice. Patients were not adverse to its usage. The ndings of a 2007 study showed that effective bowel cleansing could be achieved using either 90mL or 45 mL sodium phosphate [19]. There were reports that its usage could have contributed to isolated cases of acute phosphate nephropathy [20]. A blinded study in 2010 that compared magnesium citrate (MgC) and sodium phosphate for catharsis resulted in the former being preferred for CTC bowel preparation [21]. A 2014 study undertaken to compare the efcacy of replacing sodium phosphate with magnesium citrate showed there had not been any compro­mise of the overall CTC examination quality [22]. Magnesium citrate remains the front-line CTC cathartic agent (see Fig.9.1a). The regimen consists of 2 × 296 mL bottles compared with only one bottle of sodium phosphate. Signicant clinical electrolyte imbalances are less likely with magnesium citrate compared to sodium phosphate. Fluid intake is essential to avoid dehydration [2].

1.6g magnesium sulphate, 3.1g potassium sul­phate, and avouring agents in an aqueous liquid form supplied in a 177 mL plastic bottle [24].

Sulphate is a poorly absorbed anion, and OSS does not alter electrolyte balance [25]. The rec­ommended OC regimen consists of 2 × 177mL bottles in a split dose to adequately cleanse the colon for OC examinations. Bannas et al. [26] undertook a trial using a single bottle regime (177mL) for colonic cleansing. They were of the opinion that a single-bottle regime, together with an ionic iodinated oral contrast medium of sodium diatrozoate/megulumine diatrozoate (Gastrogran), would act as an additional mild cathartic agent. Five different cathartic regimes were employed in the trial, namely

however reluctant to ingest the oral contrast medium for two reasons. It contains iodine and/ or they may have had a prior reaction to injected contrast media. Anaphylactoid reactions have been reported in the literature, especially when Gastrogran has been aspirated [31]. The main contraindications for its use would be known hypersensitivity to iodine. Asthmatic patients need to be careful as they may experience bron­chospasm. Patients with hyperthyroidism should avoid Gastrogran [30]. In the vast majority of patients, the contrast medium is administered without reported problems. However, it is essen­tial that cognisance should be taken of a patient’s history of allergy or previous reactions to con­trast media.

bre diet as well as barium and Gastrogran for stool and uid tagging. The study employed elec­tronic cleansing as well as CTC computer-aided detection (CAD) software, respectively. Electronic cleansing may cause signicant artefacts (see Chap. 12), and 2D (two- dimensional) reading is required. Feedback from the patients was positive in terms of a laxative- free CTC.A downside to a laxative-free study is that a same-day OC cannot be performed if the CTC ndings reveal an ade­noma ≥10 mm [33]. A cathartic-free regime would probably result in an increase in screening compliance. Furthermore, risks associated with purgative preparations would be avoided, particu-

day optical colonoscopy.

• Electronic cleansing produces its own arte­facts which further complicate reading of the CTC study.

Manual insufation requires the use of a hand­held air-bulb insufator. Room air and CO2 can both be used to distend the colon in a CTC study; room air is free whereas there are costs involved in the use of CO2. Irrespective of which negative

contrast medium is used the success of a CTC depends on an adequately distended and clean colon [39]. Introducing room air or CO2 into the colon requires many puffs of a handheld device. According to Sosna et al. [40], each puff of a device will introduce approximately 40cc of air; at least 50 puffs will be required to introduce 2L of air. Of importance is that the pressure at which the air is introduced is unknown [40]. The danger of perforating the bowel under these circum­stances far exceeds that of the gentle measured pressure and volume attained with an automated pressure-controlled CO2 insufator. The intraco­lonic pressure produced by manual insufation may vary greatly depending on the force used to compress the bulb of the puffer. Pressures varied from 41 to 148mmHg in an industrial study per­formed in 2002 [41]. An intracolonic pressure above 140mmHg can lead to perforation of the caecum [42]. During manual insufation, perfo­ration can be caused by the use of either room air or CO2. The medico-legal ramications of using manual insufation are self-evident.