Magnetic Resonance (MR) Cholangiography

Magnetic resonance imaging and other medical imaging techniques in the diagnosis of gallstones

Biliary diseases are one of the most common pathologies of the digestive system in the world. However, assessing the prevalence of biliary diseases is difficult, due to the asymptomatic course of the disease in some cases. Biliary diseases are a diagnostic problem, especially if a complicated course of the disease is suspected, and when the etiology cannot be established after laboratory examination and ultrasound imaging. Magnetic resonance imaging (MRI) is a highly specific non-invasive method for examining the gallbladder and imaging the bile ducts to identify gallstones, biliary strictures, tumors, and detect the level of obstruction. Magnetic resonance cholangiography/cholangiopancreatography (MRCP) is currently considered to be the most accurate non-invasive procedure for detecting bile duct stones, with high sensitivity, which allows to obtain a detailed image of the biliary tract. MRI is an established imaging technique for the biliary tract, has better contrast resolution, and is an excellent diagnostic tool. The choice of method to start the diagnosis with depends on many factors and requires careful interaction between the gastroenterologist and the radiologist to optimize the imaging technique.

Comparison of respiratory-triggered 3D MR cholangiopancreatography and breath-hold compressed-sensing 3D MR cholangiopancreatography at 1.5 T and 3 T and impact of individual factors on image quality

PURPOSE

To evaluate the image quality of an accelerated compressed-sensing single-breath-hold 3D magnetic resonance cholangiopancreatography (BH-CS-MRCP) prototype sequence compared to the standard 3D sequence with respiratory triggering (STD-MRCP) at 1.5 T and 3 T. To assess the individual factors that can affect image quality.

METHOD

This is a retrospective analysis. Both sequences (BH-CS-MRCP and STD-MRCP) were performed in 200 patients at 1.5 T and 200 patients at 3 T. Overall image quality and the visualization of the bilio-pancreatic ducts were rated on a 5-point scale. Image sharpness and background suppression were rated on a 4-point scale. A double reading was performed in 50 patients to assess the inter-observer reproducibility. Individual characteristics studied were gender, age, BMI, ascites, abdominal surface and breath-hold quality.

RESULTS

At 1.5 T, BH-CS-MRCP was inferior to STD-MRCP in terms of overall quality (p = 0.0046), background suppression (p < 0.0001), visualization of the cystic duct (p < 0.0001), the right bile duct (p = 0.0008), the left bile duct (p = 0.0152), and the main pancreatic duct (p < 0.0001). However, BH-CS-MRCP was sharper than STD-MRCP (p = 0.028). At 3 T, BH-CS-MRCP was superior to STD-MRCP for overall quality (p < 0.0001), sharpness (p < 0.0001), and visualization of the bilio-pancreatic ducts (p < 0.0001). Background signal was conversely better suppressed in STD-MRCP (p < 0.0001). At 1.5 T, the volume of ascites was inversely correlated with image quality for BH-CS-MRCP while BMI was inversely correlated with image quality for STD-MRCP. Breath-hold quality was correlated with image quality for BH-CS-MRCP at 1.5 T and 3 T.

CONCLUSION

BH-CS-MRCP is feasible in clinical routine at 1.5 and 3 T, yielding significantly better perceived image quality at 3 T but not at 1.5 T. BH-CS-MRCP appears to be influenced by ascites whereas STD-MRCP is influenced by BMI at 1.5 T. This study was approved by the Ethics Review Board for Research in Medical Imaging (IRB: CRM-2003-065).

A Nondestructive Method to Distinguish the Internal Constituent Architecture of the Intervertebral Discs Using 9.4 Tesla Magnetic Resonance Imaging

STUDY DESIGN

An in vitro study of the intervertebral disc (IVD) structure using 9.4T magnetic resonance imaging (MRI).

OBJECTIVE

Investigate the potential of ultrahigh-field strength MRI for higher quality 3-dimensional (3D) volumetric MRI datasets of the IVD to better distinguish structural details.

SUMMARY OF BACKGROUND DATA

MRI has the advantages of being nondestructive and 3D in comparison to most techniques used to obtain the structural details of biological tissues, however, its poor image quality at higher resolution is a limiting factor. Ultrahigh-field MRI could improve the imaging of biological tissues but the current understanding of its application for spinal tissue is limited.

METHODS

2 ovine spinal segments (C7-T1, T2-T3) containing the IVD were separately imaged using 2 sequences; 3D spin echo (multislice-multiecho) pulse sequence for the C7-T1 sample and 3D gradient echo (fast-low-angle-shot) pulse sequence for the T2-T3 sample. The C7-T1 sample was subsequently decalcified and imaged again using the same scanning parameters. Histological sections obtained from the decalcified sample were stained followed by digital scanning. Observations from corresponding MRI slices and histological sections were compared as a method of confirmation of morphology captured under MRI. The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and relative-contrast values were calculated for quantitative evaluation of image quality.

RESULTS

Measurements from histology sections and corresponding MRI slices matched well. Both sequences revealed finer details of the IVD structure. Under the spin echo sequence, the annulus lamellae architecture was distinguishable and the SNR and CNR values were higher. The relative contrast was considerably higher between high (nucleus) and low (bone) signal constituents, but between the nucleus and the annulus the relative contrast was low. Under the gradient echo sequence, although the relative contrasts between constituents were poor, the fiber orientation was clearly manifested.

CONCLUSION

The obtained positive results demonstrate the potential of ultrahigh-field strength MRI to nondestructively capture the IVD structure.

LEVEL OF EVIDENCE

N/A.

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.

Biliary tract depiction in living potential liver donors: intraindividual comparison of MR cholangiography at 3.0 and 1.5 T

PURPOSE

To intraindividually compare the accuracy of magnetic resonance (MR) cholangiography at 3.0 and 1.5 T for depicting biliary anatomy with intraoperative cholangiography as the reference standard and to compare the image quality for biliary tract visualization at these two field strengths.

MATERIALS AND METHODS

After obtaining institutional review board approval and informed consent, 52 living potential liver donors underwent MR cholangiography at both 1.5 and 3.0 T. The protocol included projectional single-section rapid acquisition with relaxation enhancement (RARE) and respiratory-triggered three-dimensional (3D) fast spin-echo (SE) T2-weighted sequences. Two readers independently analyzed images, scoring the visualization of all first- and second-order biliary branches on a four-point scale and determining the number of visible third-order branches.

RESULTS

MR cholangiography at 3.0 T correctly depicted biliary anatomy in 90.4% of subjects on combined analysis of both sequences by both readers, in 88.5% with projectional RARE images for both readers, and in 84.6% and 88.5% with 3D fast SE images for readers 1 and 2, respectively. MR cholangiography at 1.5 T showed 86.5% and 84.6% accuracy on combined analysis for readers 1 and 2, respectively; 78.8% and 75.0% accuracy on projectional RARE images for readers 1 and 2, respectively; and 84.6% and 86.5% accuracy with 3D fast SE images for readers 1 and 2, respectively. With the projectional RARE sequence, 3.0-T MR cholangiography demonstrated significantly higher mean visualization scores for second-order branches (reader 1: 2.29 vs 1.78, P = .01; reader 2: 2.52 vs 2.10, P < .01) and mean numbers of visible third-order branches (reader 1: 5.53 vs 4.21, P < .01; reader 2: 5.91 vs 3.74, P < .01) than did 1.5-T MR cholangiography.

CONCLUSION

Compared with 1.5-T MR cholangiography, 3.0-T MR cholangiography did not significantly increase accuracy for identification of biliary anatomy. Projectional RARE images at 3.0 T enabled better visualization of second- and third-order branches than did those at 1.5 T.

Optimization of the contrast dose and injection rates in whole-body MR angiography at 3.0T

PURPOSE

To optimize the contrast agent dose and delivery rate used in a novel whole-body magnetic resonance angiography (MRA) protocol using a 3.0T MR scanner.

MATERIALS AND METHODS

Six groups of 20 consenting volunteers underwent whole-body MRA, with each group receiving a different contrast dose and contrast delivery rate. The arterial tree was divided into 16 segments and the image quality at each of the anatomical locations, covering the whole body, was assessed. Qualitative analysis was carried out using a scoring assessment of image quality, and quantitative assessments were performed by measuring contrast-to-noise (CNR) and a signal-to-noise (SNR) index.

RESULTS

Reducing the contrast dose from 40 mL to 25 mL was found to significantly increase the CNR in several vessels of interest in the arterial tree. There was also a significant increase in the qualitative image quality score (P < 0.001).

CONCLUSION

This study demonstrates that reducing the contrast dose at 3.0T can result in an increase in the CNR in the vessels of interest without significantly affecting the SNR.

Advances in magnetic resonance (2008)

Current advances in magnetic resonance, as a diagnostic modality, are discussed in the context of publications from Investigative Radiology during 2007 and 2008. The articles relating to this topic, published during the past 2 years, are reviewed by anatomic region. The discussion concludes with a consideration of magnetic resonance contrast media, focusing on studies published in the journal, and examining in particular the potential impact of nephrogenic systemic fibrosis.

High spatial resolution 3D MR cholangiography with high sampling efficiency technique (SPACE): comparison of 3T vs. 1.5T

PURPOSE

The aim of this study was to evaluate image quality of 3D MR cholangiography (MRC) using high sampling efficiency technique (SPACE) at 3T compared with 1.5T.

METHODS AND MATERIALS

An IRB approved prospective study was performed with 17 healthy volunteers using both 3 and 1.5T MR scanners. MRC images were obtained with free-breathing navigator-triggered 3D T2-weighted turbo spin-echo sequence with SPACE (TR, >2700ms; TE, 780ms at 3T and 801ms at 1.5T; echo-train length, 121; voxel size, 1.1mmx1.0mmx0.84mm). The common bile duct (CBD) to liver contrast-to-noise ratios (CNRs) were compared between 3 and 1.5T. A five-point scale was used to compare overall image quality and visualization of the third branches of bile duct (B2, B6, and B8). The depiction of cystic duct insertion and the highest order of bile duct visible were also compared. The results were compared using the Wilcoxon signed-ranks test.

RESULTS

CNR between the CBD and liver was significantly higher at 3T than 1.5T (p=0.0006). MRC at 3T showed a significantly higher overall image quality (p=0.0215) and clearer visualization of B2 (p=0.0183) and B6 (p=0.0106) than at 1.5T. In all analyses of duct visibility, 3T showed higher scores than 1.5T.

CONCLUSION

3T MRC using SPACE offered better image quality than 1.5T. SPACE technique facilitated high-resolution 3D MRC with excellent image quality at 3T.

How is magnetic resonance imaging used in Iran?

Objectives:Analysis of and understanding the utilization patterns of diagnostic imaging technologies is important for planning health systems especially in middle- and low-income countries. Almost all published studies have been focused on utilization trends or utilization rates of magnetic resonance imaging (MRI) over time and little has been published about utilization patterns of MRI. This study aims to identify and describe the utilization pattern of MRI in Iran.

Methods:Data was collected from referrals and MRI reports of the population covered by one of the largest insurance organizations (Social Security Organization [SSO]) with more than 27 million beneficiaries in the Country. We focused on patients who had undergone an MRI examination during 1 month (October 13 to November 12), 2005. The data collected consisted of 1,656 referrals for MR imaging and 1,547 MRI reports.

Results:No clear association was found between the number of referrals per 100,000 population and the number of MRI machines per 100,000 population (r = 0.30;p= .13). Neurosurgeons, orthopedists, and neurologists contributed to more than 88 percent of MRI utilization. The Spinal column (55 percent), brain (25.5 percent), and knee (11.0 percent) were the most common parts of the body scanned by MRI.

Conclusions:Having identified some of the most frequent users of MRI technology, any plan for modifying or improving MRI use should focus mainly on these specialties. International evidence on using the technology for examining brain and spine indicate that MRI is mainly used in diagnosing the central nervous system (CNS) diseases.

Biliary tract depiction in living potential liver donors at 3.0-T magnetic resonance cholangiography

OBJECTIVES

To prospectively evaluate accuracy of biliary anatomy depiction and quality of biliary tract visualization of magnetic resonance cholangiography (MRC) at 3.0 T in living potential liver donors (LPLDs).

MATERIALS AND METHODS

Our institutional review board approved this study and did not require patient's informed consent. Thirty-three LPLDs underwent MRC at 3.0-T magnetic resonance and intraoperative cholangiography as the reference standard. MRC protocol included breath-hold rapid acquisition with relaxation enhancement (RARE) and respiratory-triggered 3-dimensional turbo spin-echo (TSE) T2-weighted sequence. Two readers independently analyzed 2 MRC image sets with a 2-week interval for delineating biliary anatomy and scoring degree of visualization of biliary branches with a 4-point scale, and recorded the number of visible third-order branches. One month later, both readers independently evaluated combined both MRC image set to assess biliary anatomy.

RESULTS

Biliary anatomy was correctly depicted by RARE sequence in 28 (84.8%) and 26 LPLDs (78.8%), by TSE sequence in 27 (81.8%) and 26 (78.8%), and by combined both sequences in 27 (81.8%) and 28 (84.8%), for readers 1 and 2, respectively. The mean second-order branch visualization scores for 2 readers were significantly higher for RARE images than for TSE (2.23 vs. 1.68, P = 0.02; 2.05 vs. 1.54, P = 0.02, respectively). The mean numbers of visible third-order branches were significantly higher for RARE images than TSE for both readers (4.36 vs. 3.04, P = 0.03; 4.72 vs. 3.32, P = 0.03, respectively).

CONCLUSIONS

In LPLDs, MRC at 3.0 T with both RARE and TSE sequences enables accurate depiction of biliary anatomy. RARE sequence more clearly visualizes second- and third-order biliary branches than TSE sequence.

MR cholangiopancreatography: 1.5T versus 3T

Soon after its introduction in 1991, MR cholangiopancreatography has become an established diagnostic tool for the evaluation of the pancreaticobiliary ductal system at a field strength of 1.5T. It remains unclear whether MR cholangiopancreatography performed at 3T will benefit from the higher magnetic field strength or whether a field strength of 1.5T should continue to be considered the gold standard for MR cholangiopancreatography. This article reviews the current literature on the benefits and drawbacks of MR cholangiopancreatography at 3T compared with a standard field strength of 1.5T. Field strength-related artifacts that affect MR cholangiopancreatography at 3T also are discussed.

Clinical advantages of 3.0 T MRI over 1.5 T

Since approval by the FDA in 2000, human MR imaging (MRI) at 3.0 T has been increasingly used in clinical practice. In spite of the potential technical challenges, a number of clinical advantages of 3.0 T MRI over 1.5 T have been identified in the recent years. This article reviews the benefits and the current knowledge of 3.0 T whole-body MRI from an evidence-based perspective and summarizes its clinical applications.

Advances in magnetic resonance (2007)

Advances in clinical magnetic resonance (MR) are discussed in this review in the context of publications from Investigative Radiology during 2006 and 2007. The articles relevant to this topic, published during this 2 year time period, are considered as organized by anatomic region. An additional final focus of discussion is in regards to those studies involving MR contrast media.

Kidneys and MR Urography

Clinically useful images of the kidneys, ureters, and bladder can be generated routinely on a 3T MR scanner. Although little has been published directly comparing 3.0-T MR imaging of the urinary tract with 1.5T imaging, the same benefits and limitations that apply to other areas of the body apply to urinary tract imaging at 3T. The potential benefits of improved signal-to-noise ratio and conspicuity of gadolinium enhancement and the potential for functional MR imaging of the kidneys at 3T are compelling, but need to be investigated further.