The double-contrast barium enema (DCBE) has existed as a radiologic alternative for CRC screening for decades, but interest has faded in light of the emergence of imaging alternatives yielding improved detection rates, such as VC [6, 10]. Despite its documented value in the detection of colonic polyps, DCBE is widely perceived as time-consuming and technically demanding. Traditional indications for single- and double-contrast barium imaging include diagnoses of large bowel symptoms and the identification of complications such as leak or fistula, as well as intussusception [10].

The contrast agent used in the single-contrast barium enema (SCBE ) technique is a solid column of low-density, low-viscosity barium-administered retrograde from the rectum [7]. This is performed under fluoroscopic guidance and requires manual manipulation by the radiologist in order to thin the barium in order to contrast potential lesions as radiolucent defects against barium [7]. This process is rather challenging and requires considerable training and practice. In contrast, DCBE utilizes both a high-density, high-viscosity barium and air or carbon dioxide insufflation to visualize the mucosa [7]. Once both agents are instilled into the rectum, the mucosa is coated by a thin layer of barium against the gas-distended bowel, which creates the double contrast effect. Although this technique has been reported to be technically simpler than SCBE , the entire colon cannot be imaged in a single radiograph due to overlapping colon loops with residual barium pools, thus requiring a series of spot images. Various literature reviews have reported DCBE to be superior to SCBE in routine surveillance and detection of colonic polyps [7].

Some authors have questioned the accuracy of DCBE such that several comparative studies have emerged contrasting the stage and outcome for patients with CRC diagnosed by DCBE versus other imaging modalities and traditional colonoscopy [10, 19–22]. In a study by Kao et al., 22,000 colonoscopies were performed within a year, wherein 67% of patients underwent an incomplete initial colonoscopy and subsequently underwent DCBE [19]. Among those patients who underwent DCBE as a secondary study, 13% of DCBEs were deemed uninterpretable and of suboptimal quality. Furthermore, 50% of patients who underwent a repeat colonoscopy after DCBE demonstrated non-concordant findings [19]. Additionally, the primary reasons for incomplete colonoscopy were largely limited to incomplete bowel preparation or patient discomfort, which the authors believed were amenable causes on subsequent colonoscopy. Various reports have suggested similar findings, with reports of DCBE sensitivities ranging from 33% to up 89.8% for CRC screening and 20–50% for detection of adenoma [20–23]. In a Canadian study by Toma et al., factors associated with missed or new CRC undetected by DCBE included older age, female gender, a positive history of abdominal or pelvic surgery, a history of diverticular disease, and right-sided neoplasm, comprising 22% of the study population [23]. Altogether, various authors have identified significant miss rates for CRC ranging from 15 to 22% [8, 23]. With this data in mind, it is critical to counsel patients on the chances of missing a CRC to be one in five. These figures serve as a greater impetus to reevaluate the role of DCBE in an era of improving imaging modalities with higher sensitivities for disease detection (Fig. 21.2).

In an era of increased utilization of medical imaging, the potential risks of future radiation-induced malignancies has led to intensified attractiveness of magnetic resonance imaging (MRI) . Magnetic resonance enterography (MRE) has been reported to offer high diagnostic accuracy for detection of distal ileal and colorectal inflammatory conditions (24). Magnetic resonance offers a myriad of benefits and has emerged as a preferred method of noninvasive imaging for inflammatory bowel diseases, using enterography technique . The superiority of MR imaging among other imaging options is well established in revealing superior soft-tissue contrast as well as the absence of ionizing radiation [24]. This is particularly important for patients requiring frequent imaging follow-up in IBD and carcinoma. Advantages of MR imaging include visualization of the entire colon, including intraluminal, extraluminal, and mural definition, permitting detection of complications such as fistulas and abscesses, in addition to the lack of requiring bowel preparation. Magnetic resonance colonography (MRC) utilization , however, has been largely limited to a few centers of excellence, as most radiologists feel that CTC is a more reliable, reproducible, available, and overall easier technique to employ.

There are two principle MR techniques, dark-lumen MRC and bright-lumen MRC [25, 26]. For both approaches, adequate colonic distension is a prerequisite for accurate evaluation. In the dark-lumen approach, colonic distension is achieved with instilling 2 L of normal saline. Alternatively, room air and CO₂ have been utilized with comparable results [25]. Dark-lumen MRC involves the administration of intravenous (IV) gadolinium (Gd) contrast agents, which illuminate the bowel wall, thus differentiating mural abnormalities from stool, which does not enhance [25–27]. In contrast, bright-lumen MRC involves enhancement of the intraluminal space via administration of MRI contrast agents mixed with water enemas [27]. Alternatively, T2-weighted images will also enhance intraluminal content with water enemas (Fig. 21.3a–c). Lauenstein and colleagues contrasted the benefits of dark-lumen to bright-lumen MRC and found the overall cost of dark-lumen MRC to be lower due to smaller amounts of contrast used for IV administration, compared with contrast-enhanced water enemas in bright-lumen MRC [28]. The basis of bright-lumen MRC relies on visualization of filling defects or the presence of mucosal thickening. As a result, air may be confused as defects, whereas dark-lumen imaging relies on directly evaluating mucosal enhancement [27].

Prior to any imaging application, metallic implants or pacemakers should be identified in order to perform MRC successfully. Caution is advised for patients with claustrophobia, and impaired renal function must be identified prior to administration of IV gadolinium, which increases the risk of nephrogenic systemic fibrosis [29]. The standard bowel preparation prior to MRC generally mandates the elimination of stool via cathartics. The presence of stool may alter image interpretation leading to increased false-positive rates on bright-lumen MRC , in which stool may appear as filling defects. Conventional bowel-cleansing regimens are consistent with traditional colonoscopy and require ingestion of 2–3 L of polyethylene glycol solution the day prior to evaluation.

The hindrance of stool evidenced on exam has led to the development of various stool-tagging techniques , which deliberately alters the signal of stool so that it becomes no longer visible [30]. Stool-tagging techniques obviate the need for arduous cathartic preparation, and various authors have shown improvements in compliance rates [31, 32]. Tagging is accomplished by ingestion of contrast agents that cause stool to match the signal of the enema, whether bright of dark. Although improvements in false-positive and false rates have been reported, inadequate tagging has also been shown to result in nondiagnostic evaluations [33]. Various tagging agents have been used. The ideal tagging agent will be inexpensive, well tolerated, and robust, generating uniform tagging signals without compromising artifacts. Tagging agents are ingested with low-fiber and low-manganese-containing meals for 2 days priors prior to examination [30]. Manganese-rich foods , such as chocolate and fruits, have the potential to cause bright signal stool artifacts on dark-lumen MRC [27, 34]. A less expensive alternative is barium oral contrast, which renders the stool dark on MRC, hence may be applied in dark-lumen MRC. Ferumoxsil is a dark-lumen agent consisting of small iron particles that may also be used in dark-lumen MRC [27].

The accuracy of detection is of importance as it directly affects therapeutic decisions and patient prognoses in specific clinical scenarios. Numerous studies have evaluated the performance of MRC in contrast to the findings on traditional colonoscopy, surgery, or both with overall sensitivities and specificities to be 91–92.1% and 71.0–72.0%, respectively [24, 35]. Commonly, segment specific detection has been evaluated, which independently evaluates the accuracy of detection at different levels of the colon, including the terminal ileum, ascending colon, descending colon, transverse colon, sigmoid, and rectum. Segment-based sensitivities have been reported to range from 55.1 to 79.1% and specificity of 93.6 to 98.2% [24, 36, 37]. In a study by Jiang and colleagues, MRC identified a greater overall number of fistulas in the distal ileum and associated abscesses among patients with known or suspected IBD, compared to traditional colonoscopy [24]. MRC has been shown to be inferior to colonoscopy under specific conditions, such as low-grade or mild inflammation , and following same-day colonoscopy [36]. These MRC have shown thickened mucosal enhanced with pronounced signal increased on T2-weighted images mimicking active inflammation, which have been attributed to instrumented areas during colonoscopy [24]. As a result, some authors do not recommend performing MRC following colonoscopy on the same day.

MRC is an effective, low-risk, and reliable alternative to standard colonoscopy in the detection of colorectal disease and complications , also serving as a salvage modality following incomplete colonoscopy. Ajaj et al. evaluated 37 patients following incomplete colonoscopies and successfully identified 35 lesions [38]. In another study, investigators identified 51 patients with incomplete colonoscopies and performed air dark-lumen MRC without fecal tagging and successfully completed 50 cases [38, 39]. Overall, MRC is comparable to that of traditional colonoscopy offering the greatest benefit to patients with elevated risk associated with additional exposure to ionizing radiation and may be considered. Large, prospective, randomized trials are required for definitive recommendations for MRC over traditional colonoscopy in an otherwise symptomatic or asymptomatic patient with suspected colorectal lesions.

Capsule endoscopy (CE) is a relatively new technique for imaging for the gastrointestinal tract . First introduced in the United States and Europe in 2000, CE was primarily used for evaluation of the small bowel [40–42]. Fifteen years later, CE is widely used across the world, serving as a highly revolutionized method of direct endoscopic imaging and the first-line investigation for disease of the small bowel [41]. The most common indications for small bowel CE include suspected bleeding , Crohn’s disease , celiac disease , and even small bowel tumors [40, 41, 43]. Various capsule endoscopy systems are now available and differ with respect to the field view, dimensions, additional optical enhancements, and image acquisition rates [40, 41]. Examples of small bowel CE devices include PillCam (Given Imaging^®; Yoqneam, Israel) , EndoCapsule (Olympus; Center Valley, PA, United States) , MicroCam (IntroMedic; Seoul, South Korea) , OMOM capsule (Jinshan Science and Technology; Chongqing, China) , and CapsoCam (CapsoVision; Saratoga; United States) [41]. Several newer generations of small bowel CE have emerged on the market, offering greater versatility in a variety of applications such that its role and application have expanded to detect esophageal and colonic lesions [40–48].