MR imaging of the bowel: pediatric applications

Pediatric Body Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a radiation-free imaging modality with excellent contrast resolution and multiplanar capabilities. Since ionizing radiation is an important concern in the pediatric population, MRI serves as a useful alternative to computed tomography (CT) and also provides additional clues to diagnosis, not discernible on other investigations. Magnetic resonance cholangiopancreatography (MRCP), urography, angiography, enterography, dynamic multiphasic imaging and diffusion-weighted imaging provide wealth of information. The main limitations include, long scan time, need for sedation/anesthesia, cost and lack of widespread availability. With the emergence of newer sequences and variety of contrast agents, MRI has become a robust modality and may serve as a one-stop shop for both anatomical and functional information.

Value of diffusion-weighted imaging when added to magnetic resonance enterographic evaluation of Crohn disease in children

BACKGROUND

MR enterography is increasingly utilized for noninvasive evaluation of disease activity in young patients with Crohn disease and has great impact on clinical management. Diffusion-weighted imaging (DWI) is a rapid MR imaging technique that measures molecular diffusion of water and is sensitive to the inflammatory process; however, its value to MR enterography has not been rigorously evaluated.

OBJECTIVE

To determine whether the addition of DWI to MR enterography is helpful in evaluating Crohn disease activity in young patients when compared to a histological reference.

MATERIALS AND METHODS

In this single-institution retrospective study, we searched an imaging database for the period January 2010 to December 2012 to identify patients age 19 years and younger who had MR enterography with diffusion-weighted imaging (DWI). We used an electronic medical record search to identify those who had MR enterography and colonoscopy performed within 28 days of each other. All MR enterography scans were performed on a 1.5-T or 3-T clinical MR scanner with phased-array torso coil configuration using standard pulse sequences as well as axial DWI with b values of 50, 400 and 800. Bowel segments were evaluated for disease activity based on standard MR enterography sequences; in addition, segmental apparent diffusion coefficient (ADC) values were calculated based on DWI. Histological reference for disease activity was based on assessment for mucosal inflammatory changes on endoscopic biopsy. MR enterography and DWI evaluation were performed in a blinded fashion with respect to histological results.

RESULTS

We included imaging of 78 bowel segments from 27 patients (mean age 14.5 ± 3.02 years) with known Crohn disease in the study. The mean ADC for bowel segments with active disease was 1.56 ± 0.7 × 10(3) mm(2)/s compared with 2.58 ± 1.4 × 10(3) mm(2)/s for segments without active disease, a difference that was statistically significant (P < 0.01, Student's t-test). Using a threshold value of 2.0 × 10(3) mm(2)/s, DWI demonstrated lower accuracy (64.1%) but higher sensitivity (78.8%) for detecting active disease compared with standard MR enterography (69.2% and 54.6%, respectively). Combining DWI with MR enterography, using DWI as the initial screen and MR enterography afterward to reduce false negativity, led to a significant increase in accuracy (76.9%; P = 0.03, McNemar's test) compared with either imaging technique alone.

CONCLUSION

Although DWI does not perform as well as standard MR enterography for detection of active Crohn disease, the combination of DWI and MR enterography increases imaging accuracy for determining disease activity compared with either technique alone. These results indicate that DWI adds value to MR enterography and supports the incorporation of DWI into MR enterography protocols for evaluation of Crohn disease in young patients.

Imaging in the evaluation of the young patient with inflammatory bowel disease: what the gastroenterologist needs to know

Imaging plays a pivotal role in the diagnosis and management of children and young adults with inflammatory bowel disease. The clinician is presented with numerous imaging options, and it can be challenging to decide which test is the best option. In this article we review the present imaging techniques available in the evaluation of inflammatory bowel disease, with emphasis on the advantages, disadvantages, and radiation burden of each test. Finally, we highlight a few common clinical scenarios and propose an imaging algorithm to approach these diagnostic challenges.

Magnetic resonance imaging of the gut: a primer for the luminal gastroenterologist

Magnetic resonance imaging (MRI) is well established for imaging the solid organs of the abdomen and pelvis. In recent years it has been having an increasingly important role in the evaluation of the gastrointestinal (GI) tract. Fluoroscopy and abdominal computed tomography, the traditional mainstays of bowel imaging, remain valuable; however, the contemporary emphasis on decreasing patient radiation exposure is driving practice toward non-ionizing modalities such as MRI. The inherent dynamic properties of MRI, its superior tissue contrast, and cross-sectional capabilities offer additional advantages. Here we review, from esophagus to anus, techniques and indications for MRI of the GI lumen with an emphasis on the normal MRI appearance of the GI tract and commonly encountered pathology.

Magnetic resonance enterography: inflammatory bowel disease and beyond

This article addresses the current technique and protocols for magnetic resonance (MR) enterography, with a primary focus on inflammatory bowel disease (IBD) and a secondary detailed discussion of other diseases of the small bowel beyond IBD. A brief discussion of MR imaging for appendicitis is included, but the evaluation of appendicitis does not require an enterographic protocol. The focused key points and approach presented in this article are intended to enhance the reader's understanding to help improve patient compliance with the MR enterographic studies, overcome challenges, and improve interpretation.

An MRI system for imaging neonates in the NICU: initial feasibility study

BACKGROUND

Transporting premature infants from a neonatal intensive care unit (NICU) to a radiology department for MRI has medical risks and logistical challenges.

OBJECTIVE

To develop a small 1.5-T MRI system for neonatal imaging that can be easily installed in the NICU and to evaluate its performance using a sheep model of human prematurity.

MATERIALS AND METHODS

A 1.5-T MRI system designed for orthopedic use was adapted for neonatal imaging. The system was used for MRI examinations of the brain, chest and abdomen in 12 premature lambs during the first hours of life. Spin-echo, fast spin-echo and gradient-echo MR images were evaluated by two pediatric radiologists.

RESULTS

All animals remained physiologically stable throughout the imaging sessions. Animals were imaged at two or three time points. Seven brain MRI examinations were performed in seven different animals, 23 chest examinations in 12 animals and 19 abdominal examinations in 11 animals. At each anatomical location, high-quality images demonstrating good spatial resolution, signal-to-noise ratio and tissue contrast were routinely obtained within 30 min using standard clinical protocols.

CONCLUSION

Our preliminary experience demonstrates the feasibility and potential of the neonatal MRI system to provide state-of-the-art MRI capabilities within the NICU. Advantages include overall reduced cost and site demands, lower acoustic noise, improved ease of access and reduced medical risk to the neonate.

Feasibility of using MR enterography for the assessment of terminal ileitis and inflammatory activity in children with Crohn disease

BACKGROUND AND OBJECTIVE

Radiation exposure increases cancer risk in children with Crohn disease (CD). Magnetic resonance enterography (MRE) can image the gastrointestinal tract without exposure to radiation. The aim of the present study was to determine whether our MRE protocol could diagnose terminal ileitis and the degree of inflammatory activity in children with CD.

METHODS

Retrospective review of patients 18 years of age or younger who underwent MRE for known or suspected CD from June 15, 2007 to April 1, 2010. MRE was performed with Volumen and water as oral contrast and gadolinium-based intravenous contrast. No antiperistaltic agent was used. Each MRE was compared with ileal biopsies obtained within 90 days. Severity of inflammation on MRE was scored and compared with the Pediatric Crohn Disease Activity Index (PCDAI).

RESULTS

Seventy-two patients underwent 80 MREs during the study period. Forty-two of the 72 patients (58.3%) underwent colonoscopy within 90 days of MRE, and the terminal ileum was intubated in 33. Compared with histology, MRE had a sensitivity of 71.4% and a specificity of 100% for terminal ileitis. The positive and negative predictive values were 100% and 70%, respectively. PCDAI was calculated in 39 of the 72 patients (54.2%) and had a statistically significant positive correlation with MRE score of 0.37 (P = 0.020426).

CONCLUSIONS

In children with known or suspected CD, our MRE protocol has a high specificity and positive predictive value for terminal ileitis. Severity of inflammation on MRE had a statistically significant positive correlation with PCDAI.

Comparison of MR enterography and histopathology in the evaluation of pediatric Crohn disease

BACKGROUND

While MR enterography (MRE) is commonly used to identify segments of bowel affected by Crohn disease in children, there is little data to support this practice.

OBJECTIVE

To assess the ability of MRE to identify segments of small bowel and colon affected by pediatric Crohn disease using histopathology as the reference standard.

MATERIALS AND METHODS

Pediatric MRE examinations performed between April 2009 and December 2010 were identified. Subjects were excluded if they did not have Crohn disease, if they had Crohn disease but no correlative histopathology within 2 months of imaging, or if they had undergone prior bowel resection. Pertinent MRE and histopathology reports were reviewed, and normal and abnormal bowel segments were documented.

RESULTS

Thirty-two pediatric MRE examinations were identified with correlative histopathology. MRE had an overall sensitivity of 94% for detecting the presence of Crohn disease, in general. At the bowel segmental level, MRE had a sensitivity of 66%, specificity of 90%, positive predictive value of 85% and negative predictive value of 76%. The terminal ileum was abnormal by MRE in 11 of 15 (73%) subjects lacking a diagnostic biopsy of this bowel segment.

CONCLUSION

MRE successfully identifies small bowel and colon segments affected by pediatric Crohn disease.

MR imaging of the abdomen and pelvis in infants, children, and adolescents

Recent developments in magnetic resonance (MR) imaging have profoundly changed the investigation of abdominal and pelvic disease in pediatrics. Motion reduction techniques, such periodically rotated overlapping parallel lines with enhanced reconstruction, or PROPELLER, have resulted in reliable imaging with quiet breathing. Faster imaging sequences minimize artifact and allow for more efficient studies. Diffusion-weighted imaging has become increasingly important in the evaluation of neoplastic disease, depicting disease with increased cellularity and helping to differentiate benign from malignant masses. MR enterography helps visualize intra- and extraluminal bowel pathologic conditions. MR cholangiopancreatography can depict congenital and acquired causes of pancreatic and biliary abnormalities. MR urography is an effective technique for a one-stop-shop evaluation of structural urinary tract abnormality and renal function. Three-dimensional acquisitions allow volumetric display of structures from multiple angles. Specialized techniques allow quantification of iron and fat in the viscera in children with hemolytic anemia and obesity, respectively. This article covers current techniques and strategies to perform and optimize MR imaging of the abdomen and pelvis in infants, children, and adolescents and describes important practical applications.

Pause and pulse: ten steps that help manage radiation dose during pediatric fluoroscopy

OBJECTIVE

The Image Gently Campaign of The Alliance for Radiation Safety in Pediatric Imaging seeks to increase awareness of opportunities to lower radiation dose in the imaging of children. Pause and Pulse is the most recent phase of the campaign, addressing methods of dose optimization in pediatric fluoroscopy.

CONCLUSION

This article discusses 10 steps that can be taken for fluoroscopic dose optimization in pediatric diagnostic fluoroscopy.

Acute colonic pseudo-obstruction complicating chemotherapy in paediatric oncohaematological patients: clinical and imaging features

OBJECTIVE

Although acute colonic pseudo-obstruction (ACPO) complicating chemotherapy is still a controversial entity, it is one with which radiologists should be familiar. We describe the imaging features of ACPO in children following chemotherapy for treatment of a haematological malignancy.

METHODS

We retrospectively reviewed the imaging features of eight children (age 3-14 years) with chemotherapy-related ACPO, all of whom had undergone plain radiography and CT examinations. The diagnosis of ACPO was based on both clinical features and imaging findings.

RESULTS

Abnormalities noted on plain radiography included faecal gaseous distension of the transverse colon (4/8), faecal gaseous distension of the ascending colon (3/8), gaseous distended transverse colon (3/8) and gaseous small bowel loops (6/8). As seen on CT scans, findings of faecal fluid distended the ascending and transverse colon (5/8), faecal gas distended the transverse and ascending colon (3/8), and small bowel dilatation (5/8) and pneumatosis intestinalis (2/8) were noted. Seven of the eight patients had colonic dilatation from the caecum to the transverse colon with the transition zone near the splenic flexure.

CONCLUSION

In children presenting with abdominal pain and constipation following chemotherapy, imaging features of progressive colonic dilatation seen on radiography and dilatation from the caecum to the transverse colon with the transition zone near the splenic flexure, as noted on CT, are suggestive of ACPO. CT is more successful than plain radiography for evaluating this finding, particularly in colonic segments filled primarily with fluid, but CT should not be necessary for making the diagnosis as plain radiographs and clinical evaluation should be adequate.

Magnetic Resonance Enterography Findings in Crohn's disease in the Pediatric Population and Correlation with Fluoroscopic and Multidetector Computed Tomographic Techniques

Traditionally, fluoroscopic examinations such as enteroclysis, upper GI studies, and small bowel follow through exams have been the procedures of choice in evaluating inflammatory bowel disease (IBD) in pediatric populations. With the advent of multidetector computed tomography (MDCT), it has subsequently become a complementary examination in imaging inflammatory bowel disease. A major advantage of MDCT over fluoroscopic examination is its ability to directly visualize bowel mucosa, as well as demonstrate extra-enteric complications of IBD such as abscesses, fistulae, and sinus tracts. The major disadvantage of CT however is exposure to ionizing radiation, especially in IBD patients of the pediatric age group who maybe repeatedly imaged due to exacerbations. As a result, magnetic resonance enterography (MRE) is becoming increasingly important in the evaluation and follow-up of pediatric patients with IBD. This pictorial essay will summarize the multi-modality imaging findings of IBD with emphasis on MRE including the imaging protocol and procedure. For the purposes of this article, patients less than 17 years of age have been considered to represent the pediatric population.

Chronic inflammatory diseases of the bowel: diagnosis and follow-up

Approximately one fourth of cases of inflammatory bowel disease (IBD) occur during childhood and children are more prone than their adult counterparts to have severe disease at presentation. To investigate these diseases MR imaging is no longer an emerging tool. Numerous reviews and articles have been published on this topic underlying the advances of imaging but also the complexity and the financial impact on management of such diseases. In children it seems reasonable to consider US as the first imaging examination to perform, especially when the diagnosis of IBD is unknown. However, we believe that recent and future technical progress, especially the ability of MR to display reproducible data, and the need for gold standard evaluation of new medical therapies will increase the role of MR enterography.