MR imaging of the small bowel with increasing concentrations of an oral osmotic agent

The aim of this study was to assess the quality of MR imaging and level of adverse effects with increasing concentrations of gastrografin. This is a prospective study with 24 healthy volunteers which were randomised into four groups receiving 50%, 25%, 10% and 0% gastrografin. The endpoint was bowel image quality based on distension, signal homogeneity and wall delineation evaluated by three independent radiologists, and the maximum bowel diameter at three different levels. The subjects also scored any adverse events on a 1–5 scale. The interradiologist agreement was relatively good, with kappa values varying between 0.81 and 0.41. Improved bowel distension and image quality were achieved with increasing concentrations. But significant dose-response effects were found between increasing osmolalities and the bowel diameters and also versus the score of adverse events. The most frequent adverse reactions were diarrhea, nausea and lack of palatability. There is a gradient relationship between increasing osmolality of gastrografin and improved image quality and the score of adverse effects. The optimum concentration of gastrografin is dependent of the tolerance of the adverse events.     

Renal cancer staging: Comparison of contrast-enhanced CT and gadolinium-enhanced fat-suppressed spin-echo and gradient-echo MR imaging

Fifty-three consecutive patients with 61 solid or complex non-fat-containing renal masses compatible with renal cancer were examined with contrast-enhanced computed tomography (CT) and magnetic resonance (MR) imaging with pre- and postcontrast FLASH (fast low-angle shot) and fat-suppressed spin-echo sequences. CT and MR imaging were performed within a 1-month interval. CT and MR images were prospectively interpreted. Tumor detection and staging were determined in all patients. CT and MR imaging enabled detection of 54 and 58 of 61 renal tumors, respectively. CT and MR imaging showed 34 and 35 of 38 histologically proved renal tumors, respectively, in 31 patients. Tumor size on CT and MR images demonstrated good correlation and correlated well with the size of pathologic specimens of 34 of 38 resected tumors detected with CT and MR imaging (r =.99). Of the 31 tumors in 31 patients who underwent surgical resection, 24 were correctly staged with CT and 29 with MR imaging. CT and MR imaging both enabled correct staging of four of five additional tumors with biopsy proof of tumor stage. A moderate difference in staging was observed between CT and MR imaging (P =.05). CT showed 13 and MR imaging 15 of 15 tumor thrombi. CT and MR imaging both showed 11 of 11 cases of adenopathy. The results suggest that MR imaging is moderately better than CT for the detection and staging of renal cancer.     

MR imaging of the small bowel

Cross-sectional imaging techniques such as CT and MR imaging have advantages over traditional barium fluoroscopic techniques in their ability to visualize superimposed bowel loops better and to improve visualization of extraluminal findings and complications. This article discusses MR imaging of the small bowel with enterography and enteroclysis techniques. It reviews the advantages, limitations, technique, and indications and reviews the results that have been obtained in evaluating different disease processes.     

MR imaging of the small bowel

Small-bowel radiology has undergone dramatic changes in the past 2 decades. Despite important recent advances in small-bowel endoscopy, radiologic imaging remains important for patients suspected of having or with established small-bowel disease. Cross-sectional imaging techniques (computed tomography and magnetic resonance [MR] imaging), used to investigate both extraluminal abnormalities and intraluminal changes, have gradually replaced barium contrast examinations, which are, however, still used to examine early mucosal disease. MR imaging techniques clearly highlight endoluminal, mural and extramural enteric details and provide vascular and functional information, thereby enhancing the diagnostic value of these techniques in small-bowel diseases. Two MR imaging based techniques are currently utilized: MR enteroclysis and MR enterography. In enteroclysis, enteric contrast material is administered through a nasoenteric tube, whereas in enterography, large volumes of enteric contrast material are administered orally. MR enteroclysis ensures consistently better luminal distention than does MR enterography in both the jejunum and the ileum and more accurately depicts endoluminal abnormalities and early disease, particularly at the level of the jejunal loops. Moreover, MR enteroclysis provides a high level of accuracy in the diagnosis and exclusion of small-bowel inflammatory and neoplastic diseases and can be used for the first radiologic evaluation, while MR enterography may effectively be used to follow up both Crohn disease patients without jejunal disease and in pediatric patients where nasogastric intubation might be a problem. MR enteroclysis may also reveal subtle transition points or an obstruction in the lower small bowel, which may escape detection when more routine methods, including enterography, are used. MR imaging offers detailed morphologic information and functional data of small-bowel diseases and provides reliable evidence of normalcy, thereby allowing the diagnosis of early or subtle structural abnormalities and guiding treatment and decisions in patient care.     

Optimization of oral contrast agents for MR imaging of the small bowel

Effect on small-bowel distention of additives to water as contrast agents for magnetic resonance (MR) imaging was assessed. Oral contrast agents included water and water in combination with mannitol, a bulk fiber laxative, locust bean gum, and a combination of mannitol and locust bean gum. Filling of the small bowel was quantified on coronal images obtained with two-dimensional true fast imaging with steady-state precession sequence; bowel diameters were measured. Ingestion of water with locust bean gum and mannitol provided the best distention of the small bowel. MR imaging of the small bowel with oral administration of water can be improved with addition of osmotic and nonosmotic substances that lead to decreased water resorption.     

Breathhold MRI of the small bowel in Crohn's disease after enteroklysis with oral magnetic particles

Purpose: To evaluate the efficacy of breathhold MRI following enteroclysis with addition of oral magnetic particles to study the extension, detection of stenoses and extraluminal manifestations in Crohn's disease. Material and Methods: 18 patients with Crohn's disease and potential of surgical intervention were studied with enteroclysis with addition of oral magnetic particles. T1-/T2-weighted breathhold MRI w/o spectral fat suppression w/o i. v. Gd-DTPA was applied. Results: Typical findings were marked bowel wall thickening with strong contrast enhancement. 95.8 % of affected small bowel segments and 94.7 % of stenoses were correctly detected by MRI. All four fistulas were detected and important extraluminal findings were seen in 6/18 patients. Additionally, one ileoileal and two ileosigmoidal adhesions, two extraluminal abscesses and affection of the right ureter were delineated. Conclusion: MRI in Crohn's disease offers the potential to avoid radiation exposure in this relatively young patient group. Important additional findings relevant to indication of surgery are seen in approximately one third of cases. The replacement of transduodenal intubation by oral contrast application remains to be further studied.      

Pituitary adenoma: correlation of half-dose gadolinium-enhanced MR imaging with surgical findings in 26 patients

Sellar magnetic resonance imaging studies obtained with half doses of gadopentetate dimeglumine (0.05 mmol/kg) were prospectively interpreted and retrospectively rated in 26 patients who subsequently underwent transsphenoidal sellar surgery for suspected pituitary adenoma. Studies included a sagittal scout view followed by a non-contrast-material-enhanced, an immediate postcontrast, and a delayed postcontrast T1-weighted image (obtained at 1.0 or 1.5 T). Ten of 11 confirmed microadenomas were identified prospectively; all were identifiable in retrospect. Macroadenomas (12 cases) were well demonstrated. The high signal intensity of the posterior pituitary and of intrasellar hemorrhage was obscured on postcontrast studies. Delayed images proved unnecessary. This prospective evaluation suggests that a half-dose study is comparable to retrospective studies in which full-dose techniques were used for detection of micro- and macroadenomas. Imaging times are reasonably short, and cost of contrast material is potentially reduced. Confirmation with larger studies is required, and careful endocrinologic and clinical follow-up of nonsurgical patients is necessary.     

MR imaging of small bowel with water administration

We performed MR imaging of the small bowel (MRSB) in 20 patients using water as an oral contrast agent, to improve the demonstrability of pathologic conditions without a large amount of intestinal fluid. Bowel lumen and folds were clearly visualized: duodenum in 13(65%), jejunal loops in 14 (70%), ileal loops in 15(75%), and ileocecum in 8 (40%) cases. Furthermore, conventional enteroclysis was performed in 16 of 20 patients, and the MRSB findings were comparable with those of conventional enteroclysis. If conventional enteroclysis is used as the gold standard, MRSB visualized luminal stenosis in 11 of 13(84.6%), displacement or extrinsic compression in 4 of 5(80%), polypoid lesion in 3 of 4(75%), and fistula formation in one of one cases. None of four ulcerative lesions could be visualized by MRSB. Our MRSB technique is a noninvasive, easy method that does not require a long time. Accordingly, MRSB can be used in addition to the conventional MR sequence. MRSB has potential usefulness for evaluating small-bowel disease without radiation exposure.     

Distinguishing benign from malignant bowel obstruction in patients with malignancy: findings at MR imaging

PURPOSE: To retrospectively evaluate the features of benign versus malignant bowel obstruction on unenhanced and gadolinium-enhanced spoiled gradient-echo magnetic resonance (MR) images in patients with malignancy. MATERIALS AND METHODS: Forty-eight patients with malignancy and bowel obstruction underwent abdominal and pelvic MR imaging. Two blinded radiologists independently evaluated each study for dilated bowel, transition point, level of obstruction, obstructing mass, mural thickening and enhancement, and peritoneal disease. Benign obstruction was recorded if no mass was present and if mural thickening (when present) was segmental or diffuse. Malignant bowel obstruction was recorded if there was a mass, a disseminated abdominal tumor, or focal mural thickening. MR images were compared with surgical findings, follow-up imaging studies, and clinical outcome. chi2 test and Fisher exact test were used to assess the relationship between the MR features and benign versus malignant obstruction. RESULTS: Bowel obstruction had a benign cause in 19 patients and a malignant cause in 29 patients. Observer 1 correctly characterized benign bowel obstruction in 17 of 19 patients and malignant bowel obstruction in 27 of 29 patients. The sensitivity of observer 1 for characterizing malignant obstruction was 93%, specificity was 89%, and accuracy was 92%. Observer 2 correctly characterized benign bowel obstruction in 18 of 19 patients and malignant bowel obstruction in 26 of 29 patients. The sensitivity of observer 2 for characterizing malignant obstruction was 90%, specificity was 95%, and accuracy was 92%. Malignant bowel obstruction was present in 24 of 25 patients with an obstructing mass (P <.001). All 16 patients with focal mural thickening had malignant obstruction. Benign obstruction was present in four of five patients with diffuse mural thickening. Segmental mural thickening occurred in four patients with serosal metastases and in 11 patients with benign bowel obstruction. More extensive peritoneal thickening and enhancement correlated with malignant obstruction. CONCLUSION: In patients with malignancy who have symptoms indicative of bowel obstruction, gadolinium-enhanced MR imaging can help distinguish benign from malignant causes of bowel obstruction.     

Gallbladder carcinoma: findings at MR imaging with MR cholangiopancreatography

PURPOSE: To describe magnetic resonance (MR) imaging and MR cholangiopancreatography (MRCP) findings in gallbladder carcinoma, and to correlate these findings with available surgical and biopsy information. METHODS: Preoperative MR images (T1-weighted spin-echo, T2-weighted fast spin-echo, single shot fast spin-echo, and dynamic gadolinium-enhanced gradient echo) in 34 patients with gallbladder carcinoma were retrospectively reviewed for appearance of the primary neoplasm and for demonstration of hepatic, peritoneal, duodenal, and nodal involvement. Imaging findings were then compared with surgical findings (n = 19 patients) and histologic findings (n = 15 patients). RESULTS: Gallbladder carcinoma manifested at MR imaging as focal gallbladder wall thickening with an eccentric mass in 76% (26/34) of cases. The most common types of regional spread demonstrated were direct liver invasion in 91% (31/34), lymphadenopathy in 76% (26/34), and biliary tract invasion in 62% (21/34). Sensitivity for direct hepatic invasion was 100%, and was 92% for lymph node metastasis. CONCLUSION: MRI and MRCP can provide information relevant to preoperative staging of gallbladder carcinoma.     

MR imaging of the small bowel in Crohn's disease

MR and CT techniques optimized for small bowel imaging are playing an increasing role in the evaluation of small bowel disorders. Several studies have shown the advantage of these techniques over tradition barium fluoroscopic examinations secondary to improvements in spatial and temporal resolution combined with improved bowel distending agents. The preference of MR vs. CT has been geographical and based on expertise and public policy. With the increasing awareness of radiation exposure, there has been a more global interest in implementing techniques that either reduce or eliminate radiation exposure [Brenner DJ, Hall EJ. Computed tomography—an increasing source of radiation exposure. N Engl J Med 2007;357:2277–84]. This is especially important in patients with chronic diseases such as inflammatory bowel disease who may require multiple studies over a lifetime or in studies that require sequential imaging time points such as in assessment of gastrointestinal motility [Froehlich JM, Patak MA, von Weymarn C, Juli CF, Zollikofer CL, Wentz KU. Small bowel motility assessment with magnetic resonance imaging. J Magn Reson Imaging 2005;21:370–75]. A recent study showed that certain subgroups of patients with Crohn's disease may be exposed to higher doses of radiation; those diagnosed at an early age, those with upper tract inflammation, penetrating disease, requirement of intravenous steroids, infliximab or multiple surgeries [Desmond AN, O’Regan K, Curran C, et al. Crohn's disease: factors associated with exposure to high levels of diagnostic radiation. Gut 2008;57:1524–29]. Therefore it has been suggested that techniques that can reduce or eliminate radiation exposure should be considered for imaging [Brenner DJ, Hall EJ. Computed tomography—an increasing source of radiation exposure. N Engl J Med 2007;357:2277–84]. Owing to the excellent softtissue contrast, direct multiplanar imaging capabilities, new ultrafast breath-holding pulse sequences, lack of ionizing radiation and availability of a variety of oral contrast agents, MR is well suited to play a critical role in the imaging of small bowel disorders. In this article we will review the technical issues related to the performance of MR enterography and enteroclysis and discuss the role and controversies of using MR in the assessment of inflammatory bowel disease.     

Cine magnetic resonance imaging of the small bowel: comparison of different oral contrast media

PURPOSE: To evaluate several substances regarding small bowel distension and contrast on balanced steady-state free precession (bSSFP) cine magnetic resonance (MR) images. MATERIAL AND METHODS: Luminal contrast was evaluated in 24 volunteers after oral application of two different contrast agent groups leading to either bright lumen (pineapple, blueberry juice) or dark lumen (tap water, orange juice) on T1-weighted images. Bowel distension was evaluated in 30 patients ingesting either methylcellulose or mannitol solution for limiting intestinal absorption. Fifteen patients with duodeno-jejunal intubation served as the control. Quantitative evaluation included measurement of luminal signal intensities and diameters of four bowel segments, qualitative evaluation assessed luminal contrast and distension on a five-point scale. RESULTS: Quantitative and qualitative evaluation of the four contrast agents revealed no significant differences regarding luminal contrast on bSSFP images. Quantitative evaluation revealed significantly lower (P<0.05) small bowel distension for three out of four segments (qualitative evaluation: two out of four segments) for methylcellulose in comparison to the control. Mannitol was found to be equal to the control. CONCLUSION: Oral ingestion of tap water or orange juice in combination with mannitol is recommended for cine MR imaging of the small bowel regarding luminal contrast and small bowel distension on bSSFP sequences.     

Ovarian lesions: detection and characterization with gadolinium-enhanced MR imaging at 1.5 T

Magnetic resonance (MR) imaging for detection and characterization of ovarian masses was assessed in 33 patients with a total of 60 lesions. Lesions were characterized prospectively as benign or malignant by using T2-weighted MR images and unenhanced and gadolinium-enhanced T1-weighted MR images. MR imaging findings were compared with results of surgical laparotomy performed for staging of lesions. When malignancy was suspected, staging with MR imaging was performed. MR imaging demonstrated 57 of 60 (95%) surgically proved ovarian masses (34 of 36 were benign, 23 of 24 were malignant). Five significant primary criteria and four ancillary criteria for malignancy were established. For all MR pulse sequences combined, characterization of either type of lesion was correct in 84% of cases (48 of 57) when the five primary criteria were used and 95% (54 of 57) were correct when the four ancillary criteria were added. With gadolinium-enhanced images, correct characterization of malignant lesions increased from 56% to 78% with use of the five primary criteria and from 83% to 100% with use of both sets of criteria. Malignancies were correctly staged with MR imaging in 12 of 16 patients. Staging accuracy was 63% with unenhanced images and 75% with the addition of enhanced images.     

Low-grade fibromyxoid sarcoma of the small bowel mesentery: computed tomography and magnetic resonance imaging findings

Low-grade fibromyxoid sarcoma (LGFMS) is a rare tumor that commonly arises in the lower extremities but rarely in the mesentery. We report computed tomography (CT) and magnetic resonance imaging (MRI) findings of LGFMS of the small bowel mesentery. On CT, the mass was composed of two components. One component, on its right side, appeared to have isointense attenuation relative to muscle, whereas the other component, on its left side, appeared to have low attenuation. On MRI the mass on the right side showed hypointensity similar to muscle on both T1-and T2-weighted images as well as mostly slight enhancement on contrast-enhanced T1-weighted images. On the other hand, the mass on the left side showed relative hypointensity on T1-weighted images and hyperintensity on T2-weighted images as well as intense enhancement on contrast-enhanced T1-weighted images, suggesting that the tumor contained myxoid tissue. The myxoid area of LGFMS may have a tendency to reveal intense enhancement on contrast-enhanced images.