MR colonography in patients with incomplete conventional colonoscopy

Alternatives to Incomplete Colonoscopy

A thorough and complete colonoscopy is critically important in preventing colorectal cancer. Factors associated with difficult and incomplete colonoscopy include a poor bowel preparation, severe diverticulosis, redundant colon, looping, adhesions, young and female patients, patient discomfort, and the expertise of the endoscopist. For difficult colonoscopy, focusing on bowel preparation techniques, appropriate sedation and adjunct techniques such as water immersion, abdominal pressure techniques, and patient positioning can overcome many of these challenges. Occasionally, these fail and other alternatives to incomplete colonoscopy have to be considered. If patients have low risk of polyps, then noninvasive imaging options such as computed tomography (CT) or magnetic resonance (MR) colonography can be considered. Novel applications such as Colon Capsule™ and Check-Cap are also emerging. In patients in whom a clinically significant lesion is noted on a noninvasive imaging test or if they are at a higher risk of having polyps, balloon-assisted colonoscopy can be performed with either a single- or double-balloon enteroscope or colonoscope. The application of these techniques enables complete colonoscopic examination in the vast majority of patients.

Bimodal visualization of colorectal uptake of nanoparticles in dimethylhydrazine-treated mice

AIM: To investigate colorectal uptake of solid lipid nanoparticles (SLNs) in mice receiving different doses of 1,2-dimethylhydrazine (DMH) using magnetic resonance (MR) and laser-scanning confocal fluorescence microscope (LSCFM) imaging.

METHODS: Eight mice were sacrificed in a pilot study to establish the experimental protocol and to visualize colorectal uptake of SLNs in normal mice. Gadopentetate dimeglumine and fluorescein isothiocyanate (FITC)-loaded SLN (Gd-FITC-SLN) enemas were performed on mice receiving DMH for 10 wk (group 1, n = 9) or 16 wk (group 2, n = 7) and FITC-SLN enema was performed on 4 DMH-treated mice (group 3). Pre- and post-enema MR examinations were made to visualize the air-inflated distal colorectum. Histological and LSCFM examinations were performed to verify colorectal malignancy and to track the distribution of SLNs.

RESULTS: Homogeneous enhancement and dense fluorescence (FITC) deposition in colorectal wall were observed in normal mice and 1 DMH-treated mouse (group 1) on fluid attenuated inversion recovery (FLAIR) and LSCFM images, respectively. Heterogeneous mural enhancement was found in 6 mice (4 in group 1; 2 in group 2). No visible mural enhancement was observed in the other mice. LSCFM imaging revealed linear fluorescence deposition along the colorectal mucosa in all groups. Nine intraluminal masses and one prolapsed mass were detected by MR imaging with different enhancement modes and pathologies. Interstitial FITC deposition was identified where obvious enhancement was observed in FLAIR images. Bladder imaging agent accumulations were observed in 11 of 16 DMH-treated mice of groups 1 and 2.

CONCLUSION: There are significant differences in colorectal uptake and distribution of SLNs between normal and DMH-treated mice, which may provide a new mechanism of contrast for MR colonography.

Benefits and challenges in bowel MR imaging at 3.0 T

Abdominal imaging at 3.0 T has shown to be challenging because of a number of artifacts and effects related to the physics at higher field strength. For bowel imaging at 3.0 T, artifacts due to magnetic field inhomogeneities, standing waves, increased susceptibility, and greater chemical shift effects are of particular concern because they are likely to affect the assessment of relevant structures and counterbalance the benefits of higher signal-to-noise ratio. Regarding small- and large-bowel magnetic resonance imaging, the benefits of higher field strengths translate mainly in better contrast-to-noise ratio of contrast-enhanced T1-weighted gradient echo and T2-weighted imaging, whereas steady-state free precession sequences seem to suffer from serious degradation of image quality. The present article summarizes the technical challenges in bowel imaging at 3.0 T, provides an overview of performance compared with 1.5 T in small- and large-bowel diseases including the rectum, and revises the current literature.

MR colonography and MR enterography

The bowel is a common site for pathologic processes, including malignancies and inflammatory disease. Colorectal cancer accounts for 10% of all new cancers and 9% of cancer deaths. A significant decrease in the incidence of colorectal cancer and cancer death rates has been attributed to screening measures, earlier detection, and improved therapies. Virtual colonoscopy (VC), also known as computed tomography colonography, is an effective method for detecting polyps. However, in light of increasing concerns about ionizing radiation exposure from medical imaging and potential increased risk of future radiation-induced malignancies, magnetic resonance imaging (MRI) is seen as an increasingly attractive alternative. Improvements in MRI technology now permit three-dimensional volumetric imaging of the entire colon in a single breath hold at high spatial resolution, making VC with MRI possible.

Magnetic resonance (MR) colonography in the detection of colorectal lesions: a systematic review of prospective studies

Objective

To determine the diagnostic accuracy of MR-colonography for the detection of colorectal lesions.

Methods

A comprehensive literature search was performed for comparative MR-colonography studies, published between May 1997 and February 2009, using the MEDLINE, EMBASE and Cochrane databases. We included studies if MR-colonography findings were prospectively compared with conventional colonoscopy in (a)symptomatic patients. Two reviewers independently extracted study design characteristics and data for summarising sensitivity and specificity. Heterogeneity in findings between studies was tested using I² test statistics. Sensitivity and specificity estimates with 95% confidence intervals (CI) were calculated on per patient basis and summary sensitivity on per polyp basis, using bivariate and univariate statistical models.

Results

Thirty-seven studies were found to be potentially relevant and 13 fulfilled the inclusion criteria. The study population comprised 1,285 patients with a mean disease prevalence of 44% (range 22–63%). Sensitivity for the detection of CRC was 100%. Significant heterogeneity was found for overall per patient sensitivity and specificity. For polyps with a size of 10 mm or larger, per patient sensitivity and specificity estimates were 88% (95% CI 63–97%; I² = 37%) and 99% (95% CI 95–100%; I² = 60%). On a per polyp basis, polyps of 10 mm or larger were detected with a sensitivity of 84% (95% CI 66–94%; I² = 51%). The data were too heterogeneous for polyps smaller than 6 mm and 6–9 mm.

Conclusion

MR-colonography can accurately detect colorectal polyps more than 10 mm in size

Annotation and retrieval of clinically relevant images

PURPOSE

Medical images are a significant information source for clinical decision-making. Currently available information retrieval and decision support systems rely primarily on the text of scientific publications to find evidence in support of clinical information needs. The images and illustrations are available only within the full text of a scientific publication and do not directly contribute evidence to such systems. Our first goal is to explore whether image features facilitate finding relevant images that appear in publications. Our second goal is to find promising approaches for providing clinical evidence at the point of service, leveraging information contained in the text and images.

METHODS

We studied two approaches to finding illustrative evidence: a supervised machine-learning approach, in which images are classified as being relevant to an information need or not, and a pipeline information retrieval approach, in which images were retrieved using associated text and then re-ranked using content-based image retrieval (CBIR) techniques.

RESULTS

Our information retrieval approach did not benefit from combining textual and image information. However, given sufficient training data for the machine-learning approach, we achieved 56% average precision at 94% recall using textual features, and 27% average precision at 86% recall using image features. Combining these classifiers resulted in improvement up to 81% precision at 96% recall (74% recall at 85% precision, on average) for the requests with over 180 positive training examples.

CONCLUSIONS

Our supervised machine-learning methods that combine information from image and text are capable of achieving image annotation and retrieval accuracy acceptable for providing clinical evidence, given sufficient training data.

Preoperative evaluation of synchronous colorectal cancer using MR colonography

RATIONALE AND OBJECTIVES

It is well known that synchronous cancers (incidence, 2%-11%) and polyps (incidence, 12%-58%) occur in patients with colorectal cancer. Magnetic resonance colonography (MRC) seems like the obvious choice as a diagnostic tool in preoperative evaluation, because it is noninvasive, and most of the colon can be evaluated. Furthermore, it has higher patient acceptance, and no sedation or radiation is used. The purpose of this study was to determine the feasibility of performing MRC preoperatively in an everyday clinical situation in a group of patients who were not offered a full conventional colonoscopy or in whom full conventional colonoscopy was not possible.

MATERIALS AND METHODS

In a 13-month period, 47 patients diagnosed with rectal or sigmoid colon cancer scheduled for operation were included in the study. MRC was performed with bowel purgation either the night before surgery or as ambulatory MRC the week before surgery.

RESULTS

Full MRC was performed in 98% of the patients. In four patients, 12 synchronous lesions (one cancer, two plaques of carcinosis, and nine adenomas) were found. One flat adenoma and five small polyps were missed by MRC and perioperative palpation but found on postoperative colonoscopy. The findings resulted in altered operative strategies in three patients.

CONCLUSION

This study shows the feasibility and potential gain of preoperative MRC in patients with sigmoid colon cancer or rectal cancer.

Second look colonoscopy: indication and requirements

BACKGROUND

There are circumstances when a colonoscopy should be repeated after a short interval following the first endoscopic procedure which has not completely fulfilled its objective.

REVIEW OF THE LITERATURE

A second look colonoscopy is proposed when there remains a doubt about missed neoplastic lesions, either because the intestinal preparation was poor or because the video-endoscope did not achieved a complete course in the colon. The second look colonoscopy is also proposed at a short interval when it is suspected that the endoscopic removal of a single or of multiple neoplastic lesions was incomplete and that a complement of treatment is required. When the initial endoscopic procedure has completely fulfilled its objective, a second look colonoscopy can be proposed at longer intervals in surveillance programs. The intervals in surveillance after polypectomy are now adapted to the initial findings according to established guidelines. This also applies to the surveillance of incident focal cancer in patients suffering from a chronic inflammatory bowel disease.

CONCLUSION

Finally, in most developed countries, a priority is attributed to screening of colorectal cancer and focus is given on quality assurance of colonoscopy which is considered as the gold standard procedure in the secondary prevention of colorectal cancer.

Role of 3.0-T MR colonography in the evaluation of inflammatory bowel disease

Conventional colonoscopy combined with histologic analysis represents the standard of reference for the evaluation of colorectal disease and is usually the initial examination in patients with a suspected or established diagnosis of inflammatory bowel disease (IBD). However, it is increasingly being recognized that colonoscopy is limited to providing information regarding mucosal alterations. Colonoscopy cannot help estimate the depth of involvement of colonic lesions and does not provide information regarding the presence of extraluminal complications such as abscesses or fistulas. Recent technologic advances in magnetic resonance (MR) imaging, with its high spatial and tissue resolution, have raised expectations as to the potential role of this modality in the evaluation of colonic lesions in patients with IBD, as either a complement or an alternative to colonoscopy. MR colonography allows the characterization of colonic changes in acute and chronic IBD and can depict a wide spectrum of related lesions, including ulcers, edema, wall thickening, hyperemia, and fistulas, as well as potential extraluminal complications. The bulk of available evidence indicates that MR colonography can be useful as a problem-solving tool in the evaluation of IBD, as an alternative to colonoscopy whenever tissue sampling is not required, and for the assessment of the entire colon in cases of incomplete colonoscopy.

Advances in radiological imaging of gastrointestinal tumors

This article summarizes the recent advances in radiological imaging in the hepatogastrointestinal field in terms of detection, characterization and staging of tumors. Introduction of multidetector row computed tomography technology has helped computed tomography to excel in its already established indications, and has expanded its capabilities by adding new clinical applications, such as computed tomography angiography, liver perfusion, computed tomography enterography or enteroclysis, and virtual colonoscopy. Contrast-enhanced ultrasound has dramatically changed the role of ultrasound in liver tumor characterization, detection, and other applications. Combining the advantages of unsurpassed soft tissue contrast and lack of ionizing radiation, magnetic resonance imaging of the gastrointestinal tract has become increasingly used clinically. Moreover, substantial progress in molecular and cellular magnetic resonance imaging has been achieved in the past few years. Particularly, the increasing number of available specific contrast agents dedicated to the evaluation of the liver and lymph nodes shows promises in the area of oncologic abdominal imaging.

Colonography by CT, MRI and PET/CT combined with conventional colonoscopy in colorectal cancer screening and staging

Colorectal cancer (CRC) remains a leading cancer killer worldwide. But the disease is both curable and preventable at an early stage. Regular CRC cancer screening has been shown to reduce the risk of dying from CRC. However, the importance of large-scale screening is only now starting to be appreciated. This article reviews a variety of imaging procedures available for detecting ulcerative colitis (UC) and Crohn’s disease (CD), polyps and CRC in their early stage and also presents details on various screening options. Detecting, staging and re-staging of patients with CRC also require multimodality, multistep imaging approaches. Staging and re-staging with conventional colonoscopy (CC), computer tomography colonography (CTC), magnetic resonance colonography (MRC) and positron emission tomography/computer tomography colonography (PET/CTC) are of paramount importance in determining the most appropriate therapeutic method and in predicting the risk of tumor recurrence and overall prognosis. The advantages and limitations of these modalities are also discussed.

MR colonography: 1.5T versus 3T

MR colonography is a powerful noninvasive method to image colorectal masses and inflammatory bowel disease. This article describes current techniques of MR colonography and compares its implementation at 1.5T and 3T.

Incomplete colonoscopy in patients with occlusive colorectal cancer: usefulness of CT colonography according to tumor location

PURPOSE

We sought to evaluate the clinical usefulness of CT colonography (CTC) after incomplete conventional colonoscopy (CC) for occlusive colorectal cancer (CRC) according to the tumor location.

MATERIALS AND METHODS

Seventy-five patients with occlusive CRC underwent subsequent CTC immediately after incomplete CC. Fifty-nine patients had distal CRC and 16 had proximal colon cancer. Experienced radiologists prospectively analyzed the location, length, and TNM staging of the main tumor. The colorectal polyps in the remaining colorectum and additional extraluminal findings were also recorded. Sixty-seven patients underwent colorectal resection. We retrospectively analyzed the surgical outcome and correlated CTC and CC findings.

RESULTS

The overall accuracies of tumor staging were: T staging, 86%; N staging (nodal positivity), 70% (80%); and intra-abdominal M staging, 94%. Additional colonic polyps were found in 23 patients. Six synchronous carcinomas were detected (9%); three in the proximal colon and three in the distal colon of occlusion. Clinically significant localization errors at CC were noted in 8 patients (12%, 5 proximal colon cancers and 3 distal CRCs) and were corrected by CTC. After CTC, the surgeons modified the initial surgical plan in 11 cases (16%).

CONCLUSION

In occlusive CRC, CTC is not only useful in the evaluation of the proximal bowel, but can also provide surgeons with accurate information about staging and tumor localization. CTC is recommended when endoscopists encounter occlusive CRC, regardless of tumor location.

[MR colography: technique, indications, and findings]

Magnetic resonance imaging (MRI) has evolved as a powerful tool that has been applied more and more in recent years for the assessment of gastrointestinal structures, owing to its unsurpassed soft tissue contrast, lack of radiation exposure, and implementation of fast scanning techniques. As a virtual endoscopic technique, MR colography (MRC) makes it possible to image inflammatory processes and tumor disease of the large intestine with a high degree of accuracy. In this article we describe current techniques and applications of MRC and give an overview of clinical studies comparing MRC with other diagnostic procedures.

Colorectal neoplasm: Magnetic resonance colonography with fat enema-initial clinical experience

AIM: To assess Magnetic resonance colonography with fat enema as a method for detection of colorectal neoplasm.

METHODS: Consecutive twenty-two patients underwent MR colonography with fat enema before colonoscopy. T1-weighted three-dimensional fast spoiled gradient-echo with inversion recovery sequence was acquired with the patient in the supine position before and 75 s after Gadopentetate Dimelumine administration. Where by, pre and post MR coronal images were obtained with a single breath hold for about 20 s to cover the entire colon. The quality of MR colonographs and patients' tolerance to fat contrast medium was investigated. Colorectal neoplasms identified by MR colonography were compared with those identified on colonoscopy and sensitivity of detecting the lesions was calculated accordingly.

RESULTS: MR colonography with fat enema was well tolerated without sedation and analgesia. 120 out of 132 (90.9%) colonic segments were well distended and only 1 (0.8%) colonic segment was poor distension. After contrast enhancement scan, mean contrast-to-noise ratio (CNR) value between the normal colonic wall and lumen was 18.5 ± 2.9 while mean CNR value between colorectal neoplasm and lumen was 20.2 ± 3.1. By Magnetic resonance colonography, 26 of 35 neoplasms (sensitivity 74.3%) were detected. However, sensitivity of MRC was 95.5% (21 of 22) for neoplasm larger than 10 mm and 55.6% (5 of 9) for 5-10 mm neoplasm.

CONCLUSION: MR colonography with fat enema and T1-weighted three-dimensional fast spoiled gradient-echo with inversion recovery sequence is feasible in detecting colorectal neoplasm larger than 10 mm.

MR colonography without bowel purgation for the assessment of inflammatory bowel diseases: diagnostic accuracy and patient acceptance

BACKGROUND

The purpose of this pilot study was to assess the diagnostic accuracy of MR colonography (MRC) without bowel cleansing regarding its ability to quantify inflammatory bowel disease (IBD). In addition, patient acceptance was compared with conventional colonoscopy (CC).

METHODS

In all, 29 patients with IBD (17 ulcerative colitis; 12 Crohn's disease) were included. While CC was performed after bowel cleansing as the gold standard, MRC was based on a fecal tagging technique and performed 48-72 hours prior to CC. The presence of inflammation in each of 7 ileocolonic segments was rated for every procedure. Patients evaluated both modalities and dedicated aspects of the examination according to a 10-point-scale (1 = good, 10 = poor acceptance). Furthermore, preferences for future examinations were investigated.

RESULTS

Inflammatory segments were found by means of CC in 23 and by MRC in 14 patients. Overall sensitivity and specificity of MRC in a segment-based detection were 32% and 88%, respectively. Concerning severely inflamed segments, sensitivity increased to 53% for MRC. Overall acceptance of CC was significantly higher compared to MRC (mean value (mv) for MRT = 6.0; CC = 4.1; P = 0.003). For MRC, the placement of the rectal tube (mv = 7.3), and for CC bowel purgation (mv = 6.5), were rated as the most unpleasant. A total of 67% of patients voted for CC as the favorable tool for future examinations.

CONCLUSIONS

The presented data indicate that 'fecal tagging MRC' is not suitable for an adequate quantification of inflammatory diseases of the large bowel. Furthermore, overall acceptance of endoscopic colonoscopy was superior to MRC.

MR colonography

Combining the advantages of unsurpassed soft tissue contrast and lack of ionizing radiation, MR imaging of the gastrointestinal tract has become increasingly used clinically. Both bowel inflammation and tumor disease of the large bowel can be well visualized by means of MR colonography (MRC). This article describes current techniques of MRC and gives an overview of its clinical outcome. Special focus is directed toward the evaluation of patients' acceptance of MRC.

MR colonography with fecal tagging: do individual patient characteristics influence image quality?

PURPOSE

To evaluate if different patient characteristics influence performance of fecal tagging (a new MR colonography (MRC) technique to label stool to avoid bowel cleansing) and, consecutively, MR image quality.

MATERIALS AND METHODS

A total of 333 patients (mean age = 61 years) underwent MRC with fecal tagging. Four segments of the large bowel (ascending, transverse, descending, and sigmoid colon) were assessed as for the presence of nontagged stool particles, which can impede an assessment of the colonic wall. Ratings were correlated with patients' characteristics including patient age (<55 vs. > or =55 years), body mass index (BMI) (<25 vs. > or =25), gender, and acceptance levels for fecal tagging. Statistical analysis was performed using a Mann-Whitney U-test.

RESULTS

A total of 1332 colonic segments were evaluated. Among them, 327 segments (25%) did not contain any visible stool particles. Considerably reduced image quality was found in 61 segments (5%). Best image quality was found in the sigmoid colon (mean value = 1.9), while image quality of the ascending colon turned out to be worst (mean value = 2.6). Fecal tagging effectiveness showed a reverse correlation with patient age. However, all other characteristics did not have a statistically significant influence on fecal tagging outcome.

CONCLUSION

MRC in conjunction with barium-based fecal tagging led to diagnostic image quality in 95% of all colonic segments. Since tagging results were significantly decreased in patients > or =55 years, tagging protocols should to be modified in this group, i.e., by increasing the time interval of tagging administration.

Prospective study on bright lumen magnetic resonance colonography in comparison with conventional colonoscopy

The aim of this prospective trial was to evaluate sensitivity and specificity of bright lumen magnetic resonance colonography (MRC) in comparison with conventional colonoscopy (CC). A total of 120 consecutive patients with clinical indications for CC were prospectively examined using MRC (1.5 Tesla) which was then followed by CC. Prior to MRC, the cleansed colon was filled with a gadolinium-water solution. A 3D GRE sequence was performed with the patient in the prone and supine position, each acquired during one breathhold period. After division of the colon into five segments, interactive data analysis was carried out using three-dimensional post-processing, including a virtual intraluminal view. The results of CC served as a reference standard. In all patients MRC was performed successfully and no complications occurred. Image quality was diagnostic in 92% (574/620 colonic segments). On a per-patient basis, the results of MRC were as follows: sensitivity 84% (95% CI 71.7-92.3%), specificity 97% (95% CI 89.0-99.6%). Five flat adenomas and 6/16 small polyps (< or =5 mm) were not identified by MRC. MRC offers high sensitivity and excellent specificity rates in patients with clinical indications for CC. Improved MRC techniques are needed to detect small polyps and flat adenomas.

Air-inflated magnetic resonance colonography in patients with incomplete conventional colonoscopy: Comparison with intraoperative findings, pathology specimens, and follow-up conventional colonoscopy

BACKGROUND

To assess the usefulness of air-inflated magnetic resonance colonography (MRC) in patients with incomplete conventional colonoscopy (CC).

METHODS

From September 2001 to December 2004, 51 patients (25 male and 26 female, age range 32 to 85 years) with incomplete colonoscopy were recruited to have MRC performed. Half-fourier single short turbo spin echo (HASTE) axial, coronal, and three dimensional fat suppressed gradient echo sequence (VIBE) coronal images in both the prone and supine positions were performed for each patient. MRC was reviewed by two radiologists for detection of synchronous colonic lesion. The location and size of lesions were recorded and were compared with the findings of CC. Patients were managed according to the clinical situation and intraoperative findings were compared with MRC findings. Follow-up colonoscopy was performed in 29 patients. The follow-up colonoscopy findings were then compared with the MRC findings.

RESULTS

Forty-four patients had incomplete colonoscopy because of an obstructing tumor. The other seven patients had incomplete colonoscopy because of excessive bowel looping. Apart from one patient suffering from chronic obstructive airway disease with resulting nondiagnostic MRC, all other patients had MRC successfully performed. Each colon was divided into six bowel segments for analysis. All 300 segments were of diagnostic quality and were assessed by the MRC. MRC correctly identified all 44 obstructing tumors demonstrated by initial CC. Synchronous tumors in proximal colonic segments were identified in two patients by MRC. In addition, MRC identified two colonic tumors located in bowel segments inaccessible by CC because of excessive looping.

CONCLUSIONS

MRC is useful for detection of colonic pathology and assessment of proximal colon in patients with colonic cancer after incomplete colonoscopy.

MR imaging of the colon: "technique, indications, results and limitations"

In the last few years virtual colonography using MR imaging has shown a proceeding development regarding detection and quantification of colorectal pathologies. Dark-lumen MR colonography (MRC) has been a leading tool for the diagnosis of the entire colon and their pathologies. This review article describes some of the underlying techniques of MRC concerning data acquisition, the need for intravenously applied paramagnetic contrast agent, as well as indications, results and limitations of MRC for the detection of colorectal pathologies. In addition, new techniques to improve patient acceptance are discussed.

MR colonoscopy at 3.0 T: comparison with 1.5 T in vivo and a colon model

PURPOSE

Retrospectively, magnetic resonance (MR) colonography images obtained from a colon model and in routine examinations of patients screened for polyps were compared in terms of whether, and to what degree, image quality improved at a higher field strength of 3.0 T compared to 1.5 T.

MATERIALS AND METHODS

One hundred twenty-eight MR colonography images from 40 patients, of whom 20 had each been scanned at 1.5 and 3.0 T, respectively, using a four-element phased-array torso coil, were compared. At both field strengths, imaging included T1-weighted fat-suppressed spoiled gradient-echo (T1-fs-GE), T2/T1-weighted fast imaging employing steady-state acquisition (FIESTA), and T2-weighted single-shot fast spin-echo (T2-SSFSE), with breath-hold technique. Using receiver operating characteristic analysis performed by seven readers, the three types of images from the colon model and from 20 patients each at 1.5 and 3.0 T were compared. While a time window of 20 s was allowed for picture assessment in a chance-generated succession of images on a monitor, image quality was rated with a score of 1-5 (1=very good; 5=very bad). Statistical significance was calculated with Mann-Whitney U test.

RESULTS

At both field strengths, T2-SSFSE images received the best ratings, followed by FIESTA images (P=.001). Although, overall, the 3.0-T images obtained scores worse than those of the 1.5-T images, a better detection of phantom polyps was noted in the colon model (P=.001).

CONCLUSION

Although MR colonography with the breath-hold technique using the same four-element phased-array coil at 3.0 and 1.5 T does not perform better at a higher field strength in general, an improved detection of small polyps may be obtained.

Colorectal cancer screening and surveillance

Screening and surveillance substantially reduce both the incidence and mortality of colorectal cancer. Screening of normal-risk individuals may be accomplished by several methods, including fecal occult blood testing, fiberoptic sigmoidoscopy, double contrast barium enema, and colonoscopy. New technologies for screening are being developed, such as fecal immunochemical testing for blood,fecal DNA testing, and virtual colonoscopy. Patients at increased risk for colorectal cancer, such as those with a positive family history, previous adenomatous polyps or cancer, and inflammatory bowel disease, should be offered more intensive evaluation and surveillance.

MR colonography: current status

Magnetic resonance colonography (MRC) has gained access into clinical routine as a means for the assessment of the large bowel. There are widely accepted indications for MRC, especially in patients with incomplete conventional colonoscopy. Furthermore, virtual MRC is more and more propagated as a screening tool, with advantages especially inherent to the non-invasive character of this procedure and the lack of ionizing radiation exposition. Beyond a sufficiently high diagnostic accuracy, outstanding patient acceptance is a major advantage of MRC as a diagnostic modality. This review article describes indications, techniques and clinical outcome of current MRC approaches. Furthermore, the impact of fecal tagging concepts is discussed.

Virtual colonoscopy by MRI: state-of-the-art and future directions

MR colonography has been shown to be an appropriate diagnostic tool for the detection of colorectal lesions. The technique is based on the acquisition of T1-weighted sequences after the administration of water enema and the intravenous administration of paramagnetic contrast. This article describes the technical requirements for MR colonoscopy and the procedures of data acquisition and image interpretation. The advantages and drawbacks of MR colonoscopy also are outlined.

MR Imaging of the Large Bowel

MR colonography (MRC) is an accurate diagnostic tool for the detection of colorectal masses and inflammatory diseases. This article describes the underlying techniques of MRC that concern data acquisition and image interpretation. Indications for MRC are discussed, and technical developments are explained.