MRI of the small bowel: can sufficient bowel distension be achieved with small volumes of oral contrast?

Sufficient luminal distension is mandatory for small bowel imaging. However, patients often are unable to ingest volumes of currently applied oral contrast compounds. The aim of this study was to evaluate if administration of low doses of an oral contrast agent with high-osmolarity leads to sufficient and diagnostic bowel distension. Six healthy volunteers ingested at different occasions 150, 300 and 450 ml of a commercially available oral contrast agent (Banana Smoothie Readi-Cat, E-Z-EM; 194 mOsmol/l). Two-dimensional TrueFISP data sets were acquired in 5-min intervals up to 45 min after contrast ingestion. Small bowel distension was quantified using a visual five-grade ranking (5 = very good distension, 1 = collapsed bowel). Results were statistically compared using a Wilcoxon-Rank test. Ingestion of 450 ml and 300 ml resulted in a significantly better distension than 150 ml. The all-over average distension value for 450 ml amounted to 3.4 (300 ml: 3.0, 150 ml: 2.3) and diagnostic bowel distension could be found throughout the small intestine. Even 45 min after ingestion of 450 ml the jejunum and ileum could be reliably analyzed. Small bowel imaging with low doses of contrast leads to diagnostic distension values in healthy subjects when a high-osmolarity substance is applied. These findings may help to further refine small bowel MRI techniques, but need to be confirmed in patients with small bowel disorders.

MR colonography vs. optical colonoscopy: comparison of patients' acceptance in a screening population.

The aim of this study was to compare optical colonoscopy to fecal-tagging-based MR colonography in a screening population in terms of comfort and acceptance ratings as well as for future preferences as colorectal cancer screening examinations. Two hundred eighty-four asymptomatic patients (mean age 59 years) underwent MRC and OC within 4 weeks. While MRC was based on a fecal tagging technique, OC was performed after bowel cleansing. For OC, sedatives and analgesics were used. Patients evaluated both modalities and certain aspects of the examination according to a 10-point-scale with higher scores denoting a worse experience. Furthermore, preferences for future examinations were evaluated. No significant difference was noted for the overall acceptance of OC (mean value 3.0) and MRC (mean value 3.4). For MRC, the placement of the rectal tube was rated as the most unpleasant part, whereas bowel purgation was regarded most inconvenient for OC. Patients aged 55 years and older perceived most aspects less unpleasant than younger patients. Of the patients, 46% preferred MRC for future screening examinations (OC: 44%). OC and MRC have comparable general acceptance levels in a screening population. Especially for patients declining endoscopy as a screening method MRC may evolve as an attractive alternative.

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.

Magnetic resonance colonography without bowel cleansing: a prospective cross sectional study in a screening population.

BACKGROUND AND AIMS: To evaluate the diagnostic accuracy of magnetic resonance colonography (MRC) without bowel cleansing in a screening population and compare the results to colonoscopy as a standard of reference. METHODS: 315 screening patients, older than 50 years with a normal risk profile for colorectal cancer, were included in this study. For MRC, a tagging agent (5.0% Gastrografin, 1.0% barium sulphate, 0.2% locust bean gum) was ingested with each main meal within 2 days prior to MRC. No bowel cleansing was applied. For the magnetic resonance examination, a rectal water enema was administered. Data collection was based on contrast enhanced T1 weighted images and TrueFISP images. Magnetic resonance data were analysed for image quality and the presence of colorectal lesions. Conventional colonoscopy and histopathological samples served as reference. RESULTS: In 4% of all colonic segments, magnetic resonance image quality was insufficient because of untagged faecal material. Adenomatous polyps >5 mm were detected by means of MRC, with a sensitivity of 83.0%. Overall specificity was 90.2% (false positive findings in 19 patients). However, only 16 of 153 lesions <5 mm and 9 of 127 hyperplastic polyps could be visualised on magnetic resonance images. CONCLUSIONS: Faecal tagging MRC is applicable for screening purposes. It provides good accuracy for the detection of relevant (ie, adenomatous) colorectal lesions >5 mm in a screening population. However, refinements to optimise image quality of faecal tagging are needed.

Diagnostic accuracy of colorectal cancer staging with whole-body PET/CT colonography.

CONTEXT: Staging of patients with colorectal cancer often requires a multimodality, multistep imaging approach. Colonography composed of a combined modality of positron emission tomography (PET) and computed tomography (CT) provides whole-body tumor staging in a single session. OBJECTIVES: To determine the staging accuracy of whole-body PET/CT colonography compared with the staging accuracies of CT followed by PET (CT + PET) and CT alone and to evaluate the effect of PET/CT colonography on therapy planning compared with conventional staging (CT of the abdomen and thorax and optical colonoscopy). DESIGN, SETTING, AND PATIENTS: Prospective study of 47 patients enrolled between May 2004 and June 2006 with clinical findings and optical colonoscopy that suggested primary colorectal cancer (mean [SD] age, 71 [11] years; range, 47-92 years). Patients underwent whole-body PET/CT colonography 1 day after colonoscopy. The study was conducted at a university hospital with a mean (SD) follow-up of 447 (140) days (range, 232-653 days). MAIN OUTCOME MEASURES: Correct classification of overall TNM stage using PET/CT colonography compared with CT + PET and CT alone. Secondary outcome measures were the accurate assessment of T-stage, N-stage, and M-stage by PET/CT colonography compared with CT + PET and CT alone and the effect of PET/CT colonography on therapy planning. RESULTS: Of the 47 patients with a total of 50 lesions, the overall TNM stage was correctly determined for 37 lesions with PET/CT colonography (74%; 95% confidence interval [CI], 60%-85%), 32 lesions with CT + PET (64%; 95% CI, 49%-77%), and 26 lesions with CT alone with a 0.7-cm node threshold (52%; 95% CI, 37%-66%). Compared with optimized abdominal CT staging alone, PET/CT colonography was significantly more accurate in defining TNM stage (difference, 22%; 95% CI, 9%-36%; P=.003), which was mainly based on a more accurate definition of the T-stage. Differences were not detected for defining N-stage between PET/CT colonography and CT alone with a threshold of 0.7 cm for malignant nodes but were detected with a threshold of 1 cm. Differences were not detected in defining M-stage separately or when comparing the accuracies of PET/CT colonography with CT + PET. PET/CT colonography affected consecutive therapy decisions in 4 patients (9%; 95% CI, 2.4%-20.4%) compared with conventional staging (CT alone and colonoscopy). CONCLUSIONS: In this preliminary study, PET/CT colonography is at least equivalent to CT + PET for tumor staging in patients with colorectal cancer. Thus, PET/CT colonography in conjunction with optical colonoscopy may be a suitable concept of tumor staging for patients with colorectal cancer.

Hydro-MRI of the small bowel: effect of contrast volume, timing of contrast administration, and data acquisition on bowel distention.

OBJECTIVE: The purpose of this study was to assess oral contrast agents, volumes of the agents, and time points of data acquisition in regard to small-bowel distention and patient acceptance. SUBJECTS AND METHODS: Six healthy volunteers underwent imaging on 16 different days. Four volumes (450, 900, 1,350, and 1,800 mL) of each of the four contrast compounds (0.2% locust bean gum plus 2.5% mannitol, VoLumen containing 2.0% sorbitol, VoLumen containing 1.4% sorbitol, and tap water) were used. Two-dimensional true fast imaging with steady-state free precession data sets were acquired at 5-minute intervals after contrast ingestion. Distention values for small-bowel segments (duodenum, proximal and distal jejunum, ileum) and occurrence of side effects were documented. RESULTS: Analysis of bowel distention revealed significantly greater distention for all carbohydrate sugar alcohol-containing solutions compared with water but no significant difference among the three contrast agents. Sufficient duodenal distention was achieved with 900 mL of any of the contrast agents, but imaging had to be performed soon after ingestion. For MRI of the distal jejunum and ileum, a volume of 1,350 mL is preferable, and the time point of data acquisition plays a minor role. Ingestion of 1,800 mL of the carbohydrate sugar alcohol solutions led to a significantly higher rate of side effects such as abdominal cramps than did ingestion of smaller volumes. CONCLUSION: The data indicate that sufficient contrast consumption and optimal timing of data acquisition are essential to distention of the small bowel. Oral contrast agent protocols should be adapted to the bowel region in question.

Accuracy of combined PET/CT in image-guided interventions of liver lesions: an ex-vivo study.

AIM: Positioning of interventional devices in liver lesions is a challenging task if only CT is available. We investigated the potential benefit of combined PET/CT images for localization of interventional devices in interventional liver studies. METHODS: Thirty lesions each of hyperdense, isodense and hypodense attenuation compared to normal liver parenchyma were injected into 15 ex-vivo pig livers. All lesions were composed of the same amounts of gelatine containing 0.5 MBq of (18)F-FDG. Following lesion insertion, an interventional needle was placed in each lesion under CT-guidance solely. After that, a PET/CT study was performed. The localization of the needle within the lesion was assessed for CT alone and PET/CT and the root mean square (RMS) was calculated. Results were compared with macroscopic measurements after lesion dissection serving as the standard of reference. RESULTS: In hypo- and isodense lesions PET/CT proved more accurate in defining the position of the interventional device when compared with CT alone. The mean RMS for CT and PET/CT differed significantly in isodense and hypodense lesions. No significant difference was found for hyperdense lesions. CONCLUSION: Combined FDG-PET/CT imaging provides more accurate information than CT alone concerning the needle position in FDG-PET positive liver lesions. Therefore combined PET/CT might be potentially beneficial not only for localization of an interventional device, but may also be beneficial for guidance in interventional liver procedures.

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.

Contrast-enhanced dark lumen PET/CT and MR colonography in a rodent polyp model: initial results with histopathologic correlation.

OBJECTIVE: The objective of this study was to assess the feasibility of PET/CT for the detection of colorectal masses in a rodent polyp model in an intraindividual comparison with dark-lumen MR colonography. CONCLUSION: Detection of small tumors with PET/CT and MR colonography is possible in a rodent model. The technique thus warrants further evaluation in animal studies as well as in patients with suspected colorectal disease.

Dark-lumen magnetic resonance colonography in patients with suspected sigmoid diverticulitis: a feasibility study.

To assess dark-lumen magnetic resonance colonography (MRC) for the evaluation of patients with suspected sigmoid diverticulitis. Forty patients with suspected sigmoid diverticulitis underwent MRC within 72 h prior to conventional colonoscopy (CC). A three-dimensional T1-weighted volumetric interpolated breath-hold examination sequence was acquired after an aqueous enema and intravenous administration of gadolinium-based contrast agents. All MRC data were evaluated by two radiologists. Based on wall thickness and focal uptake of contrast material and pericolic reaction including mesenteric infiltration on T1-weighted sequence the sigmoid colon was assessed for the presence of diverticulitis. MRC classified 17 of the 40 patients as normal with regard to sigmoid diverticulitis. However, CC confirmed the presence of light inflammatory signs in four patients which were missed in MRC. MRC correctly identified wall thickness and contrast uptake of the sigmoid colon in the other 23 patients. In three of these patients false-positive findings were observed, and MRC classified the inflammation of the sigmoid colon as diverticulitis whereas CC and histopathology confirmed invasive carcinoma. MRC detected additionally relevant pathologies of the entire colon and could be performed in cases where CC was incomplete. MRC may be considered a promising alternative to CC for the detection of sigmoid diverticulitis.

Magnetic resonance colonography without bowel cleansing using oral and rectal stool softeners (fecal cracking)--a feasibility study.

The aim of our study was to assess the effect of oral and rectal stool softeners on dark-lumen magnetic resonance (MR) colonography without bowel cleansing. Ten volunteers underwent MR colonography without colonic cleansing. A baseline examination was performed without oral or rectal administration of stool softeners. In a second set, volunteers ingested 60 ml of lactulose 24 h prior to MR examination. In a third examination, water as a rectal enema was replaced by a solution of 0.5%-docusate sodium (DS). A fourth MR examination was performed, in conjunction with both oral administration of lactulose and rectal application of DS. A T1-weighted data set was acquired at scanning times of 0, 5 and 10 min after colonic filling. A fourth data set was acquired 75 s after i.v. injection of contrast agent. Signal intensity of stool was calculated for all colonic segments. Without oral ingestion of lactulose or rectal enema with DS stool signal intensity was high and did not decrease over time. However, lactulose and DS caused a decrease in stool signal intensity. Both substances together led to a decreasing signal intensity of feces. Combination of lactulose and DS provided the lowest signal intensity of stool. Thus, feces could hardly be distinguished from dark rectal enema allowing for the assessment of the colonic wall.

Small bowel hydro-MR imaging for optimized ileocecal distension in Crohn's disease: should an additional rectal enema filling be performed?

PURPOSE: To assess the impact of an additional rectal enema filling in small bowel hydro-MRI in patients with Crohn's disease. MATERIALS AND METHODS: A total of 40 patients with known Crohn's disease were analyzed retrospectively: 20 patients only ingested an oral contrast agent (group A), the other 20 subjects obtained an additional rectal water enema (group B). For small bowel distension, a solution containing 0.2% locust bean gum (LBG) and 2.5% mannitol was used. In all patients, a breathhold contrast-enhanced T1w three-dimensional volumetric interpolated breathhold examination (VIBE) sequence was acquired. Comparative analysis was based on image quality and bowel distension as well as signal-to-noise ratio (SNR) measurements. MR findings were compared with those of conventional colonoscopy, as available (N = 25). RESULTS: The terminal ileum and rectum showed a significantly higher distension following the rectal administration of water. Furthermore, fewer artifacts were seen within group B. This resulted in a higher reader confidence for the diagnosis of bowel disease, not only in the colon, but also in the ileocecal region. Diagnostic accuracy in diagnosing inflammation of the terminal ileum was 100% in group B; in the nonenema group there were three false-negative diagnoses of terminal ileitis. CONCLUSION: Our data show that the additional administration of a rectal enema is useful in small bowel MRI for the visualization of the terminal ileum. The additional time needed for the enema administration was minimal, and small and large bowel pathologies could be diagnosed with high accuracy. Thus, we suggest that a rectal enema in small bowel MR imaging be considered.

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.

Digital subtraction dark-lumen MR colonography: initial experience.

PURPOSE: To evaluate image subtraction for the detection of colonic pathologies in a dark-lumen MR colonography exam. MATERIALS AND METHODS: A total of 20 patients (12 males; 8 females; mean 51.4 years of age) underwent MR colonography after standard cleansing and a rectal water enema on a 1.5-T whole-body MR system. After suppression of peristaltic motion, native and Gd-contrast-enhanced three-dimensional T1-w gradient echo images were acquired in the coronal plane. Two radiologists analyzed the MR data sets in consensus on two separate occasions, with and without the subtracted images for lesion detection, and assessed the value of the subtracted data set on a five-point Likert scale (1=very helpful to 5=very unhelpful). All imaging results were compared with endoscopy. RESULTS: Without subtracted images, MR-colonography detected a total of five polyps, two inflammatory lesions, and one carcinoma in eight patients, which were all verified by endoscopy. Using subtraction, an additional polyp was found, and readout time was significantly shorter (6:41 vs. 7:39 minutes; P<0.05). In two patients, endoscopy detected a flat adenoma and a polyp (0.4 cm) that were missed in the MR exam. Sensitivity and specificity without subtraction were 0.67/1.0, and 0.76/1.0 with the subtracted images, respectively. Subtraction was assessed as helpful in all exams (mean value 1.8+/-0.5; Likert scale). CONCLUSION: We consider subtraction of native from contrast-enhanced dark-lumen MR colonography data sets as a beneficial supplement to the exam.

Oral contrast agents for small bowel distension in MRI: influence of the osmolarity for small bowel distention.

To assess the effect of the osmolarity for small bowel distension in MRI, ten volunteers ingested at two separate occasions negative oral contrast agents with different quantity and osmolarity: (1) a water solution combined with 2.0% sorbitol and 0.2% locus bean gum (LBG) with a quantity of 1500 ml and an osmolarity of 148 mOsmol/l, (2) a water solution combined with 2.0% sorbitol and 2.0% barium sulphate with a quantity of 1000 ml and an osmolarity of 194 mOsmol/l. Small bowel distension was quantified on coronal 2D-TrueFISP images by measuring the small bowel diameters. There were no statistically significant differences in mean small bowel diameter between both contrast agents. The mean small bowel distension was 19.2 mm after ingestion of 1500 ml of sorbitol-LBG solution and 19.0 mm after ingestion of 1000-ml sorbitol-barium sulphate solution. Furthermore, all volunteers found the ingestion of 1000-ml solution more pleasant than the 1500-ml solution. The ingestion of 1000 ml of sorbitol-barium sulphate solution led to a sufficient small bowel distension compared to 1500 ml of sorbitol-LBG solution. The side effect rate of both solutions was low. Based on these data, we recommend a quantity of 1000 ml of sorbitol-barium sulphate solution as an alternative for 1500-ml sorbitol-LBG solution for optimal bowel distension.

Magnetic resonance colonography: comparison of contrast-enhanced three-dimensional vibe with two-dimensional FISP sequences: preliminary experience.

PURPOSE: The purpose of this study was to compare a dark-lumen magnetic resonance colonography (MRC) approach with a True FISP-based bright-lumen technique concerning presence of artifacts and the detection rate of colorectal pathologies. MATERIALS AND METHODS: Thirty-seven patients with suspected colorectal lesions were included in this trial. The colon was filled with 2500 mL of tap water. Two-dimensional True FISP datasets as well as T1-weighted GRE sequences (pre- and post intravenous contrast) were acquired. The detection rate of colorectal masses and inflammatory lesions was determined for both techniques separately. Besides, image quality was assessed. All patients underwent conventional colonoscopy as the standard of reference. RESULTS: By means of dark-lumen MRC datasets, all polyps >5 mm were correctly diagnosed, whereas 4 polyps <5 mm were missed. Sensitivity of dark-lumen MRC amounted to 78.9%. There were no false-positive results: residual stool could correctly be differentiated from colorectal masses. The True FISP-based bright-lumen MRC, however, failed to detect 2 additional polyps resulting in a sensitivity of 68.4%. Furthermore, bright-lumen MRC led to false-positive results in 5 patients. Both techniques visualized inflammatory bowel disease in 5 patients. However, image quality of True FISP was rated superior to that of dark-lumen MRC. CONCLUSION: Dark-lumen MRC proved to be superior over bright-lumen MRC regarding the detection of colorectal masses. However, True FISP imaging can turn out to be helpful as a result of high image quality and motion insensitivity.