Fecal tagging: MR colonography without colonic cleansing

Colorectal cancer, mostly arising (>90%) from preexisting adenomatous polyps, continues to be the second leading cause of cancer death. Magnetic resonance colonography (MRC) permits accurate detection of colonic polyps with a diameter larger than 10 mm. Because residual colonic stool cannot be differentiated from polyps, MRC requires a clean colon. However, the rigors associated with colonic cleansing considerably reduce patient acceptance. The need for colonic cleansing could be eliminated, if stool were to acquire a signal intensity different from polyps and identical to the enema used to fill and distend the colon. In principle, there are two approaches to this concept of fecal tagging: dark polyps surrounded by bright stool and a bright enema, and bright polyps surrounded by dark stool and a dark enema. The first approach has been evaluated with some success. Gadolinium (Gd)-DOTA was administered as an oral contrast agent with meals preceding MRC based on the administration of a Gd-based enema. The high cost of Gd-based contrast has limited the clinical utility of this technique. In the second approach patients are provided with barium as an oral fecal tagging agent to render stool dark, and barium for the enema is used to distend the colon during MRC. The colonic wall and polyps arising from it can be made visible after intravenous administration of Gd-based extracellular contrast. This method provides sufficient contrast between the darkened colonic lumen and the brightly enhanced colonic wall to permit virtual endoscopic rendering. Preliminary results showed an exact correlation with findings of conventional endoscopy and surgery. Fecal tagging obviates bowel cleansing and therefore should enhance patient acceptance for MR colonoscopy. Barium as the tagging agent is promising because it is inexpensive, commercially available, and characterized by an excellent safety profile.     

Diagnostic accuracy of MR colonography with fecal tagging

Background  MR colonography (MRC) is a non-invasive method of examining the colon, but it is still only used in a few specialized centers on a daily basis. The purpose of this study was to evaluate the performance of MRC with improved fecal tagging vs. conventional colonoscopy (CC). Methods  Between March 2006 and February 2007, consecutive patients who received first-time referrals to CC were asked to participate in the study. Two days prior to MRC, a new contrast mixture (barium/ferumoxsil) was ingested together with four meals each day. Standard bowel cleansing was performed before CC. MRC was evaluated by two blinded observers. MRC results were compared with CC. Results  A total of 56 patients were included. The per-polyp sensitivity was 85.7% for polyps 6–10 mm and 81.3% for polyps >10 mm. The per-patient sensitivity/specificity was 100%/80% for polyps >6 mm and 100%/91.4% for polyps >10 mm. Conclusion  MRC showed acceptable per-patient sensitivities, but the per-polyp sensitivities are still compromised by the fecal tagging. MRC may be implemented, but at the present time MRC with fecal tagging is not ready for widespread use, although it remains a very promising diagnostic tool.     

Implementation of MR colonography

Background MR colonography (MRC) is a promising method of examining the colon, but is limited to a few specialist centres. The purpose of this article was to describe the implementation of MRC with fecal tagging. Materials and methods Patients referred for conventional colonoscopy (CC) were offered MRC with fecal tagging before CC. Two days before MRC patients ingested an oral contrast agent. Before and after MRC and CC a number of questions were addressed. MR images were rated by a blinded investigator. Results In 6 months, 30 consecutive patients were included. The median time in the MR suite was 44 min, 23 min for the MRC examination and 9 min for the evaluation. The median time for CC was 32 min. Sixty-six percent of the patients preferred MRC as the future method of examination, 10% preferred CC, 21% had no preferences. Of the oral contrast agents, barium sulphate with ferumoxsil was significantly better than barium sulphate alone. Conclusion The majority of the patients found MRC less unpleasant than CC and a majority would prefer MRC over CC as a future colon examination. MRC also appears to be less time consuming to the patients and medical personnel than CC with post-procedural monitoring.     

Comparison of routine and unprepped CT colonography augmented by low fiber diet and stool tagging: a pilot study

Background We performed a pilot study examining the feasibility of a new unprepped CT colonography (CTC) strategy: low fiber diet and tagging (unprepped) vs. low fiber diet, tagging and a magnesium citrate cleansing preparation (prepped). Prior reports of tagging were limited in that the residual stool was neither measured and stratified by size nor did prior reports subjectively evaluate the ease of interpretation by a reader experienced in interpreting CTC examinations. Methods Prospective randomized to unprepped n = 14 and prepped n = 14. Colonic segments were subjectively evaluated for residual stool that would potentially interfere with interpretation. Scores were given in the following categories: percentage of residual stool that was touching or nearly touching mucosa, the largest piece of retained stool, effectiveness of tagging, height of residual fluid, degree of distention, ease of interpretation, and reading time. Results Ease of the CT read (scale where 4 = optimal read) averaged 1.3 for the unprepped group and 2.3 for the prepped group. The mean read time averaged 17.5 min for unprepped and 17.9 min for prepped. The degree of distention (scale where 4 = well distended) averaged 3.7 for unprepped and 3.6 for prepped. Supine and prone images combined, the unprepped group had 160 segments with stool; prepped group had 58 segments. The amount of stool covering the mucosa in all segments averaged 1.6 (33%–66% coverage) in the unprepped group and 0.35 (<33% mucosal coverage) in the prepped group. The mean size of the largest piece of stool was 33.67 mm for unprepped and 4.01 mm for prepped. Percentage of tagged stool was not significantly different between the groups (range of 94–98%). The height of residual fluid averaged 8.37 mm for unprepped and 13.4 mm for prepped. Three polyps in three patients were found during optical colonoscopy (OC) in the unprepped group (5, 6, and 10 mm), none of which were prospectively detected at CTC. Three polyps in three patients were detected during OC in the prepped group (5, 10, and 15 mm), two of which were prospectively detected at CTC. Two false-positive lesions were observed at CTC in one patient in the prepped group. Conclusion There was more stool in the unprepped group and while this factor did not slow down the reading time, it made the examination subjectively harder to interpret and likely caused the three polyps in this group to be missed. We conclude that a truly unprepped strategy that leaves significant residual stool, even if well tagged, is not desirable.     

Magnetic resonance colonography with fecal tagging: an innovative approach without bowel cleansing

To date, virtual colonography mandates bowel cleansing in a manner similar to colonoscopy. Because more than half of patients undergoing bowel preparation complain about negative side effects, patient acceptance is negatively impacted. To assure high patient acceptance of MR colonography, bowel cleansing needs to be eliminated. This can be accomplished by fecal tagging, a concept based on altering the signal intensity of stool by adding contrast-modifying substances to regular meals. This article describes different fecal tagging approaches and points out both advantages and limitations of these strategies.     

Magnetic resonance colonography for colorectal cancer screening

Colorectal cancer screening has vast potential. Beyond considerations of cost and diagnostic accuracy, the effectiveness of any colorectal screening strategy will be dependent on the degree of patient acceptance. Magnetic resonance (MR) colonography has been shown to be accurate regarding the detection of clinically relevant colonic polyps exceeding 10 mm in size, with reported sensitivity and specificity values exceeding 95%. To further enhance patient acceptance, strategies for fecal tagging have recently been developed. By modulating the signal of fecal material to be identical to the signal characteristics of the enema applied to distend the colon, fecal tagging in conjunction with MR colonography obviates the need for bowel cleansing. This article will describe the techniques underlying MR colonography and early clinical experience with fecal tagging techniques.     

Virtual endoscopic colonography based on 3D MRI

Background: To evaluate the potential of magnetic resonance colonography (MRC) in detecting colorectal mass lesions. Methods: Twenty patients underwent MR imaging (MRI) before colonoscopy. The colon was filled with a gadolinium (0.5 mol):water mixture (1:100) under MRI control, and patients were imaged while breath-holding imaged with a three-dimensional spoiled gradient echo sequence in the prone and supine positions. Images were interactively analyzed based on the combination of multiplanar reconstruction and virtual colonoscopy by a radiologist blinded to colonoscopic findings and the patient's history. MRC interpretations were correlated with colonoscopic results. Results: Polyps smaller than 5 mm could not be identified with MRC. The sensitivity for detecting polyps of 5–10 mm was 70%, whereas mass lesions larger than 10 mm were all detected (sensitivity = 100). The sensitivity, specificity, and accuracy for identifying polyp-positive patients including the three patients with small (<5 mm) polyps were 64%, 89%, and 75%, respectively. Conclusion: Virtual colonoscopy based on MRI data is feasible and should be evaluated in a larger sample of patients.     

空气灌肠MR结肠成像检测结、直肠息肉及癌

目的 评价空气灌肠三维Fourier变换快速扰相梯度回波(FSPGR)序列MR结肠成像检测结直肠息肉及癌的灵敏度.方法 对30例因便血、大便隐血试验阳性或大便习惯改变而拟接受光学结肠镜检查者进行空气灌肠三维Fourier变换FSPGR序列MR结肠成像及光学结肠镜检查.以光学结肠镜及组织病理学检查为标准,按息肉及癌的大小统计分析MR结肠成像检测结直肠息肉及癌的灵敏度.结果 光学结肠镜共检出76枚结直肠息肉及癌,其中1～5 mm息肉11枚、6～9 mm息肉29枚、≥10 mm息肉及癌36枚.MR结肠成像对1～5 mm息肉、6～9 mm息肉、≥10 mm息肉及癌、≥6 mm息肉及癌的检测灵敏度分别为9.09%、75.86%、100%及89.23%,总体检测灵敏度为77.63%.结论 空气灌肠三维Fourier变换FSPGR序列MR结肠成像对1～5 mm结直肠息肉检测灵敏度低,但对≥6 mm息肉及癌的检测灵敏度较高,并能够检出全部≥10 mm的息肉及癌.     

Transabdominal sonographic appearance of adult colonic polyps

Purpose To assess the ability of transabdominal ultrasound to detect adult colonic polyps and to describe their ultrasonographic appearance. Methods Total colonoscopy was carried out for 729 consecutive patients over a 39-month period. Ultrasonographic examination of the abdomen was followed by specific examination of the colon. Colorectal ultrasound was carried out for patients with colonic polyps of the protruded type (exclusive of advanced cancers and polyps of the flat or depressed types), and cleansing liquid was administered preparatory to colonoscopic examination. In examining colonic polyps we wanted to determine the sensitivity and specificity of ultrasound for detecting colonic polyps, and the presence of power-Doppler flow signals, location, morphologic classification, and size of the polyps. Results Ultrasound identified no colonic polyps less than 10 mm in diameter in any of the 729 patients. Of the 732 deternimation (three patients had two polyps greater than 10 mm in diameter), ultrasound yielded a positive diagnosis in 16 cases, false-positive in four cases, false-negative in 40 cases, and negative in 672 cases. Sensitivity of the technique was 28.6% and specificity was 99.4% for detection of polyps greater than 10 mm in diameter. Doppler signals were detected in all positive cases. Most polyps that were false-negatives on ultrasound examination occurred in the rectum and sigmoid colon. Sensitivity increased with tumor size, and was as high as 82% (9/11) for polyps exceeding 25 mm in diameter. Fifty-seven percent of pedunculated polyps (type Ip) but no sessile polyps (type Is) were found using ultrasound. Conclusion Colorectal ultrasound detected adult colonic polyps greater than 10 mm in diameter 16 of the 56 in present 729 patients, suggesting that this method may be of limited value in screening for colonic polyps.     

Computed tomographic colonography (virtual colonoscopy): blinded prospective comparison with conventional colonoscopy for the detection of colorectal neoplasia

BACKGROUND AND STUDY AIMS: Computed tomographic colonography (CTC), also known as virtual colonoscopy, is a recently introduced imaging modality for the detection of colorectal neoplasia. The aim of our study was to evaluate the performance of CTC in a blinded comparison with conventional colonoscopy. PATIENTS AND METHODS: A total of 66 consecutive, symptomatic patients underwent spiral computed tomography (CT) examination after standard bowel preparation. CT images were analyzed and subsequently compared with conventional colonoscopy findings. RESULTS: Conventional colonoscopy detected 15 colorectal carcinomas and 52 polyps. CTC correctly identified all carcinomas, 13 of 14 polyps greater than 10.0 mm (sensitivity 92.8 %; 95 % confidence interval (95 % CI); 77 - 100), 11 of 13 polyps between 6.0 and 9.0 mm (sensitivity 84.6 %; 95 % CI; 62 - 100), and six of 25 polyps smaller than 5.0 mm (sensitivity 24 %; 95 % CI; 6 - 42). The per-patient sensitivity and specificity were 93.7 % and 94.1 %, respectively. CONCLUSIONS: Computed tomographic colonography is an accurate imaging modality for the detection of colorectal neoplasia, especially for lesions larger than 6.0 mm in diameter.     

Extracolonic findings at CT colonography

This review focuses on the detection of extracolonic findings at CT colonography (CTC). Since its introduction, it has been regarded as a promising alternative to conventional colonoscopy for the detection of colorectal polyps and cancers. Unlike conventional colonoscopy and barium enema, CTC allows evaluation not only of the colon but also visualization of the lung bases, the abdomen, and the pelvis. CTC is performed with thin sections (1–5 mm) and small intervals (0.5–2 mm), enabling superb image reconstruction. The ability to evaluate the extracolonic structures can present a clinical dilemma. On the one hand, CTC may incidentally demonstrate asymptomatic malignant diseases or other clinically important conditions, thus possibly reducing morbidity or mortality. On the other hand, CTC may reveal numerous findings of no clinical relevance; this could result in costly additional diagnostic examinations with an increase in morbidity and overall negative impact on patients' health. In this article, extracolonic findings at CTC will be reviewed and the potential benefits and disadvantages will be presented.     

Virtual endoscopy--comparison with colonoscopy in the detection of space-occupying lesions of the colon

BACKGROUND AND STUDY AIMS: A new technique has been described which combines abdominal helical computed tomography (CT) scanning and virtual reality computer technology, known as virtual colonoscopy (VC); the reconstructed images provide a simulation of the interior of the colon as viewed by endoscopy. We compared VC with conventional colonoscopy in patients with suspected or known colonic neoplasia. PATIENTS AND METHODS: A total of 38 patients, in whom there was a high likelihood of colonic polyps or cancer, underwent a noncontrast helical CT scan of the abdomen and pelvis after regular colonoscopy bowel preparation.The images were reconstructed into a VC presentation and compared with the subsequent conventional colonoscopy in a blinded manner. RESULTS: Conventional colonoscopy identified a total of 24 polyps 5 mm or greater. VC correctly identified five of 13 polyps 5-9 mm in size, and ten of 11 lesions greater than or equal to 10 mm in diameter. The reasons for four missed lesions were identified as being secondary to a collapsed rectum in two patients and stool in the right colon in two patients. The sensitivity and specificity per patient of VC for lesions greater than or equal to 5 mm were 66.7% and 75.0% respectively, and for lesions greater than 1 cm were 90.0% and 82.1%, respectively. CONCLUSIONS: Virtual colonoscopy is feasible, well tolerated, and capable of detecting most lesions greater than 10 mm in diameter. This technique is continuing to be developed and warrants further evaluation as a diagnostic and screening tool in colorectal neoplasia.     

CT colonography: contrast enhancement of benign and malignant colorectal lesions versus fecal residuals

We retrospectively reviewed the computed tomographic colonographic datasets of 22 patients. Mean attenuation values of benign polyps before and after contrast administration were 30 ± 15 HU and 90 ± 18 HU, respectively. Mean attenuation values of colorectal cancer before and after contrast administration were 43 ± 15 HU and 124 ± 18 HU, respectively. The mean attenuation value of solid fecal residuals was 43 ± 15 HU. The difference in attenuation value between precontrast and postcontrast studies of polyps was statistically significant (mean 60 HU, p < 0.01); the same was true for colorectal cancer (mean 81 HU, p < 0.01). The difference between postcontrast density of polyps and cancer with respect to density of solid fecal residuals was statistically significant (p < 0.01). The use of contrast medium could be of help in computed tomographic colonography for discriminating polypoid benign lesions and colorectal cancer from fecal residuals.     

Diagnostic performance of virtual colonoscopy

The most important diagnostic performance of virtual colonoscopy is the ability to detect colorectal polyps. However, its diagnostic value for evaluation of patients undergoing incomplete colonoscopy and the ability to detect unsuspected extracolonic findings are also important diagnostic features. Because of important differences between published patient populations, a meta-analysis combining data from different studies would not provide a reliable statistic. The by-patient sensitivity for patients with polyps 10 mm and larger ranges from 75% to 100% in most series and was 100% in the two largest series published to date. By-polyp sensitivity for polyps 10 mm and larger ranges from 50% to 100% and was 89–90% in the two largest series. Detailed data on smaller polyps are summarized. Virtual colonoscopy is an excellent test for evaluation of patients with incomplete colonoscopies. The incidence of significant extracolonic findings is 7–13%.     

Recent developments in colorectal cancer screening and prevention

Colorectal cancer is a significant contributor to morbidity and mortality in the United States. Studies published in the early 1990s, showing that screening for colorectal cancer can reduce colorectal cancer-related mortality, led many organizations to recommend screening in asymptomatic, average-risk adults older than 50 years. Since then, however, national screening rates remain low. Several important studies published over the past four years have refined our understanding of existing screening tools and explored novel means of screening and prevention. The most important new developments, which are reviewed in this article, include the following: Additional trial results support the effectiveness of fecal occult blood testing in reducing the incidence of, and mortality from, colorectal cancer. New studies document the sensitivity of fecal occult blood testing, sigmoidoscopy, and double-contrast barium enema compared with colonoscopy. Cost-effectiveness models show that screening by any of several methods is cost-effective compared to no screening. Randomized trials show that calcium is effective but fiber is not effective in preventing reoccurrence of adenomatous polyps. Preliminary data suggest that nonsteroidal anti-inflammatory drugs may prevent adenomatous polyps and that DNA stool tests and virtual colonoscopy may show promise as screening tools. This new information provides further support for efforts to increase the use of colorectal cancer screening and prevention services in adults older than 50 years.     

Colorectal cancer: the case for barium enema.

Both colonoscopy and barium enema are important techniques for examining the colon for polyps and cancer. They are approximately equally sensitive in detecting polypoid lesions of 7 to 10 mm or larger. A major limitation of colonoscopy is that the cecum cannot be visualized in 10 to 36% of cases. The comparable accuracy for detecting significant lesions, greater safety, and greater cost-effectiveness of barium enema favor its use in most patients.     

粪便SDC2基因甲基化检测联合结肠镜在早期结直肠癌筛查中的意义

目的探讨粪便SDC2基因甲基化检测联合结肠镜在早期结直肠癌(CRC)筛查中的意义。方法选择2018年1月-2019年10月在深圳市宝安区中心医院体检的1 000例体检者作为研究对象,使用试剂盒分别检测粪便SDC2基因甲基化和血浆SEPT9基因甲基化,对两者任一结果为阳性者再行结肠镜检查。比较SDC2和SEPT9基因甲基化检测的阳性率以及两者联合结肠镜对进展性腺瘤和CRC的检出率。结果在1 000例筛查对象中,粪便SDC2基因甲基化检测阳性率明显高于血浆SEPT9基因甲基化〔18.10%(181/1 000)比9.80%(98/1 000)〕,差异有统计学意义(P<0.05);粪便SDC2基因甲基化检测联合结肠镜对进展性腺瘤和CRC的检出率均明显高于血浆SEPT9基因甲基化检测联合结肠镜筛查〔进展性腺瘤检出率:2.50%(25/1 000)比1.00%(10/1 000),CRC检出率:1.50%(15/1 000)比0.50%(5/1 000)〕,差异均有统计学意义(均P<0.05)。结论粪便SDC2基因甲基化检测是一种简单无创的CRC筛查新技术,患者接受程度更高,能够避免大规模肠镜筛查带来的弊端,联合结肠镜检测可作为CRC早期筛查的首选策略。     

CT仿真结肠镜在结直肠病变认断中的临床应用

目的：与纤维结肠严格对比客观评价螺旋CT仿真肠镜诊断结肠病变的价值和限度。方法：采用CTVE技术与纤维结肠镜对照,前瞻性研究一组55例结肠病变,评价CTVE对结肠病变检出的敏感性和准确性。结果：35例结直肠癌患者CTVE成功检查33例,有31例（88.6％）诊断正确,得到手术病理证实。对于10mm以上息肉样病变,CTVE和结肠镜都能正确的诊断,5－10mm息肉样病变,CTVE检出率为81％,5mm以下病灶检出率为25％。结论：CTVE是一种非侵入性、简便、安全有效的结肠病变的检查手段,对于5mm以上的息肉样病变有较高的诊断价值,对由于各种原因引起的肠管狭窄内镜无法通过及不能耐受全结肠检查的病例,CTVE更有诊断价值。缺点为对小于5mm的病灶以及较平坦表浅的病灶检出率不高,无法显示粘膜色泽变化,不能直视下活检,对肠道准备要求较高等。CTVE虽然无法完全取代纤维肠镜,但可作为结肠镜一项很好的补充检查手段。     

Prolonged rectal bleeding associated with hemorrhoids: the diagnostic contribution of colonoscopy

We studied 387 patients with prolonged rectal bleeding and hemorrhoids (grades 2 and 3) routinely examined by anoscopy, proctoscopy, single contrast barium enema, and hemoglobin measurements. Normal results were obtained in 86 patients above the age of 40. Total colonoscopy in these patients revealed one patient (1.2%) with cancer, 19 (22.1%) with colorectal polyps, and one (1.2%) with angiodysplasia. These findings indicate that in patients above age 40, a full investigation of the large bowel should be done in every case of prolonged rectal bleeding despite the presence of substantial hemorrhoids. Double contrast barium enema or colonoscopy must be used, rather than single contrast barium enema, which proved to be an inaccurate method of investigating prolonged rectal bleeding.     

The virtual colonoscopy study: a large multicenter clinical trial designed to compare two diagnostic screening procedures

This paper reviews the design of a large multicenter clinical trial currently being conducted to test the equivalence of two screening procedures for colorectal polyps. The primary outcome is the sensitivity and specificity of the new and standard procedures for detecting subjects with and without polyps of a size > or =6 mm, respectively. An important secondary outcome is the accuracy of these procedures in detecting individual polyps. A total of 619 participants underwent virtual colonoscopy, the new procedure, followed by conventional colonoscopy, the standard procedure. Strategies for the design and implementation of the study are shared as well as the challenges encountered.