CT and MR enterography in evaluating small bowel diseases: when to use which modality?

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 advantages of these techniques over traditional barium fluoroscopic examinations due 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. 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. MRI has many properties that make it well suited to imaging of the small bowel: the lack of ionizing radiation, the improved tissue contrast that can be obtained by using a variety of pulse sequences, and the ability to perform real time functional imaging. Moreover, MR modalities allow visualization of the entire bowel, without overlapping bowel loops, as well as the detection of both intra- and extraluminal abnormalities.The intra- and extraluminal MR findings, combined with contrast enhancement and functional information, help to make an accurate diagnosis and consequently characterize small bowel diseases.     

Evaluation of small bowel tumors: MR enteroclysis

Magnetic resonance imaging (MRI) of the small bowel has become widely accepted at centers dedicated to the diagnosis and treatment of inflammatory bowel disease, due to the method’s diagnostic efficacy. MR enteroclysis is an imaging modality that combines the advantages of enteroclysis and multiplanar MR and allows the detection and the manifestations of small bowel diseases wherever they are located (intraluminal, intramural, or extramural). Magnetic resonance enteroclysis (MRE) is an emerging technique used for the detection and evaluation of small bowel neoplasms. This article illustrates the imaging appearances of small bowel tumors on MRI and the usefulness of MR enteroclysis in the diagnosis and categorization of these tumors, also discussing the role of MRE in comparison with other diagnostic modalities.     

Small bowel capsule endoscopy: a systematic review

Wireless capsule endoscopy offers a revolutionary diagnostic tool for small bowel diseases. Since its formal introduction, it has become an integral part of the diagnostic evaluation for obscure gastrointestinal bleeding. This relatively noninvasive imaging modality offered by small bowel capsule endoscopy is appealing to both patients and providers and consequently, the desire to expand its diagnostic role continues to grow. The use of CE in the diagnosis of Crohn disease and chronic diarrhea is being further investigated, as is the potential of employing this technique as a cancer surveillance mechanism in patients with hereditary polyposis syndromes which may involve the small bowel. This review article discusses the current indications for small bowel capsule endoscopy, the results of capsule endoscopy in patients with obscure gastrointestinal bleeding and small bowel diseases, and patient outcomes following capsule endoscopy. Capsule endoscopy is compared with traditional diagnostic modalities, including small bowel series, enteroclysis, CT, and push enteroscopy. Small bowel capsule endoscopy is the procedure of choice to evaluate obscure gastrointestinal bleeding, and is superior to radiographic procedures in detecting Crohn disease of the small bowel.     

Magnetic resonance enteroclysis compared with conventional enteroclysis and computed tomography enteroclysis: a critically appraised topic

Recent advances in CT and MR technology, particularly the advent of multidetector CT (MDCT), the advent of rapidly changing gradients in industry standard MRI scanners, enabling ultrafast sequences, have led to an expansion in the role of cross sectional imaging in the investigation of small bowel disorders. We conducted an evidence-based review of MR enteroclysis (MRE) and how it performs in comparison to CT enteroclysis (CTE) and the gold standard of conventional enteroclysis (CE) for diagnosis of small bowel Crohn’s disease and small bowel neoplasia. We used the standard 5 step evidence-based medicine method of ask, search, appraise, apply and evaluate. We found 3 relevant level 1B studies, and one level 3B study. No studies evaluating MRE in small bowel neoplasia were found. MRE does not perform as well as CE in evaluation of fine mucosal detail, but the additional extraluminal detail, and absence of ionising radiation enhances its overall performance. It was not possible to establish the relative diagnostic performances of MRE and CTE from existing literature. CTE does involve patient irradiation. For patients in whom jejunal intubation and enteroclysis is considered to evaluate the small bowel, MRE should be considered the first-line investigation, local resources and expertise permitting.     

Magnetic resonance imaging in gastroenterology: time to say good-bye to all that endoscopy?

Magnetic resonance imaging (MRI) has been described as the most important development in medical diagnosis since the discovery of the roentgen ray more than 100 years ago. The effectiveness of MRI has been extended to make it applicable in a wide variety of gastrointestinal disorders. The attention of gastroenterologists is currently focusing on pancreaticobiliary and bowel diseases. Magnetic resonance cholangiopancreatography (MRCP) has become a competitive alternative to diagnostic endoscopic retrograde cholangiopancreatography in a variety of hepatobiliary and pancreatic diseases. Magnetic resonance enteroscopy has the potential to become the preferable method for evaluating the entire small bowel; virtual colonoscopy, on the other hand, is far from the stage at which it could be promoted as a tool for general screening purposes in suspected colonic diseases. Its drawbacks include problems with standardization, implementation of the techniques in generalized settings, and patient acceptance.     

高频超声在细小神经诊疗中的临床应用

目前CT、MRI等影像技术均难以对细小周围神经进行实时动态观察。随着超声技术的快速发展,超声分辨率不断提高,应用高频超声对一些细小神经进行观察成为可能,并逐渐应用于多种疾病的诊断与鉴别诊断。通过超声显像确定细小神经的解剖位置可以精准地引导神经阻滞,通过观测神经的横截面积、回声及血流信号等参数的变化,可为多种疾病的诊断及疗效评估提供参考依据。本文就高频超声对各细小神经显像和相关诊断,以及其在神经阻滞中的应用现状进行综述。     

肝硬化背景下小肝癌MRI影像评价研究进展

肝硬化背景下小肝癌是一种常见的恶性肿瘤疾病,受疾病早期症状不典型的的影响,常常使得疾病的检出率低,因此探讨一种有效的诊断方法也是临床中关注的重点话题。磁共振成像(MRI)技术的发展,为肝硬化肝癌的诊断提供可靠基础,MRI诊断疾病上,各种各样的影像评价方式使得小肝癌的检出率大大提高。本文就MRI影像评价肝硬化背景下小肝癌的相关研究做一综述,报告如下。     

The role of endoscopic ultrasound in inflammatory bowel disease

Ultrasonography has been applied to the diagnosis and management of inflammatory bowel disease for over 20 years. The combination of endoscopy with ultrasound has resulted in the application of intraluminal sonographic imaging to multiple diseases, including inflammatory bowel disease. Initial efforts were focused on the sonographic assessment of disease severity as based on bowel wall thickness, but this has been inconsistently demonstrated. Furthermore, disease severity is a clinical assessment that is based on both clinical and imaging studies. Recognizing that Crohn's disease tends to be transmural and ulcerative colitis a superficial mucosal inflammatory process, hopes were raised that endosonography would be effective in discriminating cases of otherwise indeterminate colitis. Efforts to demonstrate this, however, have been largely disappointing, and EUS plays a limited role in discriminating ulcerative colitis from Crohn's disease. On a more positive note, EUS evaluation of perirectal and perianal complications of Crohn's disease has been demonstrated to be superior to fistulography, CT, and equal to or superior to MRI. Because accurate anatomic information is required to guide surgical therapy of these lesions, EUS has the potential to emerge as a powerful imaging tool in the management of perianorectal Crohn's disease.     

无肠道准备的磁共振成像对胃肠道间质瘤的诊断价值初探

目的探讨无肠道准备的磁共振成像对胃肠道间质瘤(GISTs)的诊断价值。方法对7例不能耐受肠道准备或不愿接受辐射检查的GISTs患者进行无肠道准备的腹部磁共振常规扫描及弥散加权成像。结果 7例GISTs中发生于胃3例,腹膜后2例,小肠及肠系膜各1例;良性1例,恶性6例;7例GISTs于DWI像均呈高信号,与邻近正常组织对比明显。结论无肠道准备的磁共振成像检查简便、无X线辐射,结合弥散加权成像,有助于GISTs的检出及定位。     

Imaging the pregnant patient with abdominal pain

Imaging of pregnant patients with non-obstetric abdominal pain is reviewed, with an accompanying pictorial essay of cases with concentration on magnetic resonance imaging. Non-obstetric causes of abdominal pain during pregnancy are similar to those of non-pregnant patients. The most common causes are appendicitis and cholecystitis. Other causes are myriad and include biliary, gastrointestinal, infectious, inflammatory, and malignant etiologies, among others. The approach to imaging in pregnant patient is unique, as it is imperative to minimize potentially harmful radiation exposures to the fetus. Ultrasound and MRI are the primary modalities for evaluation of the pregnant patient with abdominal pain. The use of intravenous contrast is discouraged, except in highly-selected patients where there is no other way to obtain vital diagnostic information. CT is still used as the mainstay of evaluation of blunt abdominal trauma and is commonly used for diagnosis of small bowel obstruction, stone disease, and work-up of malignancy during pregnancy. A discussion of test selection and underlying rationale is presented.     

Small bowel magnetic resonance imaging for inflammatory bowel disease

The presented concept of hydro-magnetic resonance imaging (MRI) using a 2.5% mannitol solution as an orally applicable intraluminal contrast agent is a meaningful, reproducible, and reliable imaging method for the depiction of the small bowel. Especially in patients with Crohn's disease, hydro-MRI is the imaging method of first choice because hydro-MRI offers the advantage of a superior depiction of the inflamed bowel wall and the extramural complications of this disease without radiation exposure. In addition, hydro-MRI allows for a reliable assessment of the inflammatory activity, especially for the differentiation between an active and an inactive (scarred) stenosis. In particular, the mural enhancement, the length as well as the wall thickness of inflamed bowel segments, are considered to be significant MR parameters for the determination of the activity of Crohn's disease. Hydro-MRI of the colon is suitable for the depiction of pathologic changes in ulcerative colitis, but in contrast to Crohn's disease, the assessment of disease activity by hydro-MRI is unreliable in ulcerative colitis, probably because of the low spatial resolution (mucositis in ulcerative colitis vs. transmural inflammation in Crohn's disease). Hydro-MRI does not allow a reliable classification of inflammatory bowel diseases, but in ambiguous cases, hydro-MRI may provide helpful information for the differentiation of Crohn's disease and ulcerative colitis. There are no data of larger patient groups published regarding MR findings in inflammatory bowel diseases besides Crohn's disease and ulcerative colitis, but hydro-MRI is a promising imaging tool for these entities, which should be assessed in additional studies.     

Contrast-enhanced MRI of the small bowel in Crohn��s disease

Recently, magnetic resonance imaging has emerged as a valuable tool in evaluation of small bowel Crohn’s disease. MRI provides several advantages to other imaging modalities, including the lack of ionizing radiation, multiplanar capability, and functional information. Intravenous contrast administration is a routine portion of MR enterography protocol, and aids in detection of disease extent, extramural complications such as fistula and abscess, and assessment of activity. Additionally, promising techniques such as dynamic contrast-enhanced MRI may provide quantitative measures to assess bowel perfusion, which may enhance evaluation of disease activity. This article will provide an overview of the technical aspects of contrast-enhanced MR enterography, describe common pathologic findings involving the small bowel in Crohn’s disease, summarize its role in determination of activity with an emphasis on endoscopic and histologic correlation, and compare its efficacy with other imaging modalities.     

Technical challenges and clinical applications of magnetic resonance enteroclysis

With the advent of gradient systems the image quality of ultrafast pulse sequences, i.e., half Fourier acquisition single shot turbo spin echo (HASTE), true fast imaging with steady-state processing and fast low angle shot (FLASH), improved substantially and clinical applications including small bowel imaging became feasible. Within this context, magnetic resonance enteroclysis was developed as a comprehensive examination of the small bowel, providing luminal, transmural, and exoenteric diagnostic information of small bowel abnormalities. Clinical applications of magnetic resonance enteroclysis include diagnostic evaluation and follow-up of patients with inflammatory or neoplastic diseases and small bowel obstruction.     

MRI of the abdomen with positive oral contrast agents for the diagnosis of inflammatory small bowel disease

Magnetic resonance imaging (MRI) is being used more often in the evaluation of inflammatory bowel diseases. A prerequisite for adequate image quality is the oral application of contrast medium, which can be administered with different modalities. Positive and negative oral contrast media can be used; in terms of diagnostic efficacy, there appears to be no relevant differences between them. Sequences usually are acquired using breath-hold or respiration-triggered protocols. The underlying principle is visualization of circumscribed thickening of the intestinal wall, which shows a pathologic pattern of contrast medium uptake. The available data suggest that MRI is equally as effective as enteroclysis in the primary diagnosis of Crohn's disease and actually more sensitive in the detection of extraintestinal manifestations such as fistulae or abscesses. Supporters of the method predict that MRI will replace enteroclysis in the long term.     

Air or methylcellulose as a double contrast medium in x-ray studies of the small intestine?

The value of enteroclysma in comparison to peroral roentgenologic imaging of the small bowel is beyond doubt. For the use of applicable double contrast media we carried out comparative investigations in 118 patients with inflammable diseases of the small bowel. 92 patients were investigated with air and 26 with 1% methylcellulose solution in double contrast. Advantages and shortcomings of both methods are discussed. For the diagnostic results as well as for the application of complementing techniques air seems to be better for double contrast studies than methylcellulose.     

Small‐bowel dislocation during long‐term MRI observation – insights in intestinal physiology

Magnetic resonance imaging (MRI) of the abdomen is a widely established imaging modality in the diagnostic workup of patients suffering from abdominal disorders. Small‐bowel motility analyses using MRI have recently been introduced to provide functional information about the intestine not provided by morphological analyses. This is of clinical importance as motility disorders correlate with inflammation. Yet motility analyses mainly rely on a series of acquisitions in coronal orientation. Temporal displacement of small‐bowel loops out of the coronal slice could falsify qualitative and quantitative motility analyses. Thus, our study quantified three‐dimensional (3D) dislocation of small‐bowel loops during abdominal MRI examinations with the patient lying in prone position to investigate its influence on motility analyses. Our study revealed segmental small‐bowel displacement during MRI examinations in prone position to predominantly occur in craniocaudal orientation and in a smaller extent in lateral and ventrodorsal orientation. However, the displacement amplitudes are rather small and might not significantly influence small‐bowel motility analyses in 2D coronal plane in general.     

Role of computed tomography enterography/magnetic resonance enterography: is it in prime time?

Today, cross-sectional imaging modalities, such as computed tomography enterography (CTE) and magnetic resonance enterography (MRE), are particularly suited to evaluate small bowel diseases, especially Crohn's disease (CD). It is well known that CTE/MRE can provide excellent assessment of disease activity as well as the macroscopic features, extramural abnormalities, and complications of the small intestine in patients with CD. In general, CTE is considered as the first-line modality for the evaluation of suspected inflammatory bowel disease and for long-term assessment or follow-up of these patients. Because of the advantage of lack of radiation, MRE is being used more frequently, especially in children or young patients with CD.     

MR colonography in inflammatory bowel disease

Colonography based on magnetic resonance imaging (MRI) appears to be a promising technique for polyp assessment in the colon. Several studies have evaluated this method for colonic assessment in patients with inflammatory bowel disease. We briefly review different methodologies such as dark lumen and bright lumen techniques for abdominal MRI. In addition, recently published studies concerning the sensitivity and accuracy in detecting inflammatory bowel changes in inflammatory bowel disease using MRI are discussed.     

小肠MR造影

MR小肠造影以其完全没有辐射、良好的软组织分辨率、能够清楚显示小肠腔内外情况而在临床上应用越来越多。作者介绍2种MR小肠造影方法:口服法MR小肠造影检查(MR enterography)和插管法MR小肠造影检查(MR enteroclysis),其中尤以口服法MR小肠造影简单、易行、无痛苦。用对比剂填充小肠、使小肠充分扩张是保证小肠造影取得成功的关键。作者经验是2.5%(等渗)甘露醇溶液为较理想的对比剂。简要归纳了一些常见小肠病变的MRI诊断要点并图示。     

儿童小肠MR成像临床应用评价

目的分析儿童小肠病变MRI表现,评价小肠MR成像在儿科中的临床应用价值。方法对12例经手术和病理证实的小肠病变患儿进行回顾性分析,检查前让患儿口服2.5%的等渗甘露醇溶液后,静脉注射山莨菪碱0.3mg/kg,随后行MR扫描,扫描方法包括冠状面真稳态进动快速成像(TrueFisp)序列,横断面及冠状面T1WI、T2WI脂肪抑制序列、vibe超薄容积扫描(压脂)序列,然后行带脂肪饱和技术的T1WI横断面及冠状面增强扫描。结果 12例患儿均能接受等渗甘露醇溶液,未发现并发症,其中Crohn病6例,共显示16段炎症肠管,MRI表现为增强后病变肠壁强化明显,病变肠段肠壁增厚(厚度为5～14mm),且多表现环形增厚,肠壁厚薄不均,肠腔变窄。十二指肠球部慢性溃疡、十二指肠球部穿孔、胃肠吻合口溃疡、小肠梗阻(柿石症)、小肠淋巴瘤、肠套叠各1例。小肠MR成像不仅显示了病变本身,还显示了肠壁、肠外血管及肠系膜脂肪的情况。结论小肠MR成像安全、有效、无创、无电离辐射,能全方位多维显示儿童小肠疾病的方法。