Muskuloskeletal MR imaging at 3.0 T: current status and future perspectives

Magnetic resonance (MR) imaging has become an important diagnostic tool in evaluation of the musculoskeletal system. While most examinations are currently performed at magnetic field strengths of 1.5T or lower, whole-body MR systems operating at 3.0T have recently become available for clinical use. The higher field strengths promise various benefits, including increased signal-to-noise ratios, enhanced T2* contrast, increased chemical shift resolution, and most likely a better diagnostic performance in various applications. However, the changed T1, T2, and T2* relaxation times, the increased resonance-frequency differences caused by susceptibility and chemical-shift differences, and the increased absorption of radiofrequency (RF) energy by the tissues pose new challenges and/or offer new opportunities for imaging at 3.0T compared to 1.5T. Some of these issues have been successfully addressed only in the very recent past. This review discusses technical aspects of 3.0T imaging as far as they have an impact on clinical routine. An overview of the current data is presented, with a focus on areas where 3.0T promises equivalent or improved performance compared 1.5T or lower field strength

Synthesis and NMR Spectroscopic Characterization of Organometallics in the Laboratory of Wolfgang von Philipsborn: Reminiscences of Former Graduate Students

On the occasion of his 80th birthday, former graduate students from the group of Prof. Wolfgang von Philipsborn from the Institute of Organic Chemistry, University of Zurich, describe from a personal perspective the scientific achievements of his group in the field of nuclear magnetic resonance, mainly applied to transition metals and in the field of organometallic chemistry. Interest in metal chemical shifts is driven by the need to understand reactivity of organometallic compounds in catalysis. Progress in the field is very much related to the technical development of NMR instruments. The range of experiments spans from simple 1D experiments with direct metal detection to 2D NMR experiments, in which metal frequencies are encoded via their attached protons or phosphorous ligands. Other examples come from the structural biology of metal-containing proteins or form the measurement of scalar couplings to quadrupolar nuclei via lineshape analysis. A particular emphasis is presented on how collaborations from various groups at the campus have been fruitful to the scientific progress in the von Philipsborn group. The article also contains a number of personal anecdotes that document life of the graduate students in his group at that time

Two- versus three-dimensional dual gradient-echo MRI of the liver: a technical comparison

Objective: To compare 2D spoiled dual gradient-echo (SPGR-DE) and 3D SPGR-DE with fat and water separation for the assessment of focal and diffuse fatty infiltration of the liver. Methods: A total of 227 consecutive patients (141 men; 56 ± 14years) underwent clinically indicated liver MRI at 1.5T including multiple-breath-hold 2D SPGR-DE and single-breath-hold 3D SPGR-DE with automatic reconstruction of fat-only images. Two readers assessed the image quality and number of fat-containing liver lesions on 2D and 3D in- and opposed-phase (IP/OP) images. Liver fat content (LFC) was quantified in 138 patients without chronic liver disease from 2D, 3D IP/OP, and 3D fat-only images. Results: Mean durations of 3D and 2D SPGR-DE acquisitions were 23.7 ± 2.9 and 97.2 ± 9.1s respectively. The quality of all 2D and 3D images was rated diagnostically. Three-dimensional SPGR-DE revealed significantly more breathing artefacts resulting in lower image quality (P < 0.001); 2D and 3D IP/OP showed a similar detection rate of fat-containing lesions (P = 0.334) and similar LFC estimations (mean: +0.4%; P = 0.048). LFC estimations based on 3D fat-only images showed significantly higher values (mean: 2.7% + 3.5%) than those from 2D and 3D IP/OP images (P < 0.001). Conclusion: Three dimensional SPGR-DE performs as well as 2D SPGR-DE for the assessment of focal and diffuse fatty infiltration of liver parenchyma. The 3D SPGR-DE sequence used was quicker but more susceptible to breathing artefacts. Significantly higher LFC values are derived from 3D fat-only images than from 2D or 3D IP/OP images. Key Points: • Magnetic resonance imaging can assess focal and diffuse hepatic fatty infiltration • Both 2D and 3D dual-echo MRI techniques can be used for chemical shift imaging of the liver. • The single breath-hold 3D dual-echo technique is faster but more susceptible to breathing artefacts. • Three-dimensional fat-only images show higher fat estimates than in- and out-of-phase image

Diffusion tensor imaging of the median nerve: intra-, inter-reader agreement, and agreement between two software packages

Objective: To assess intra-, inter-reader agreement, and the agreement between two software packages for magnetic resonance diffusion tensor imaging (DTI) measurements of the median nerve. Materials and methods: Fifteen healthy volunteers (seven men, eight women; mean age, 31.2years) underwent DTI of both wrists at 1.5T. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) of the median nerve were measured by three readers using two commonly used software packages. Measurements were repeated by two readers after 6weeks. Intraclass correlation coefficients (ICC) and Bland-Altman analysis were used for statistical analysis. Results: ICCs for intra-reader agreement ranged from 0.87 to 0.99, for inter-reader agreement from 0.62 to 0.83, and between the two software packages from 0.63 to 0.82. Bland-Altman analysis showed no differences for intra- and inter-reader agreement and agreement between software packages. Conclusion: The intra-, inter-reader, and agreement between software packages for DTI measurements of the median nerve were moderate to substantial suggesting that user- and software-dependent factors contribute little to variance in DTI measurement

7 T MRI of the Cervical Neuroforamen: Assessment of Nerve Root Compression and Dorsal Root Ganglia in Patients With Radiculopathy

OBJECTIVES: The aim of this study was to assess the diagnostic value of 3-dimensional dual-echo steady-state (DESS) magnetic resonance imaging (MRI) of the cervical spine at 7 T compared with 3 T in patients with cervical radiculopathy. MATERIALS AND METHODS: Patients diagnosed with cervical radiculopathy were prospectively recruited between March 2020 and January 2023 before undergoing surgical decompression and received 3-dimensional DESS imaging at 3 T and 7 T MRI. Cervical nerve root compression and the dimensions of the dorsal root ganglia were assessed by 2 radiologists independently. Signal intensity, visibility of nerve anatomy, diagnostic confidence, and image artifacts were evaluated with Likert scales. The degree of neuroforaminal stenosis was assessed on standard clinical 3 T scans. Statistics included the analysis of the diagnostic accuracy and interreader reliability. The Wilcoxon signed rank test was used to assess differences between the groups. RESULTS: Forty-eight patients (mean age, 57 ± 12 years; 22 women) were included in the study with the highest prevalence of severe neuroforaminal stenosis observed at C6 (n = 68) followed by C7 (n = 43). Direct evaluation of nerve root compression showed significantly higher diagnostic confidence and visibility of cervical nerve rootlets, roots, and dorsal root ganglia on 7 T DESS than on 3 T DESS (diagnostic confidence: P = 0.01, visibility: P < 0.01). Assessment of nerve root compression using 7 T DESS allowed more sensitive grading than standard clinical MRI (P < 0.01) and improved the performance in predicting sensory or motor dysfunction (area under the curve combined: 0.87). CONCLUSIONS: 7 T DESS imaging allows direct assessment of cervical nerve root compression in patients with radiculopathy, with a better prediction of sensory or motor dysfunction than standard clinical MRI. Diagnostic confidence and image quality of 7 T DESS were superior to 3 T DESS

Assessment of the abdominal aorta and its visceral branches by contrast-enhanced dynamic volumetric hepatic parallel magnetic resonance imaging: feasibility, reliability and accuracy

The purpose of this study was to evaluate a new three-dimensional gradient-echo (GRE) MR sequence performed with a parallel acquisition technique to shorten breath-hold times (parallel GRE MRI) in the detection of arterial variants and stenosis of the abdominal aorta and its visceral branches. A total of 102 patients underwent dynamic parallel GRE MRI, timed to the arterial phase by a test bolus (mean breath-hold time, 17s). For both quantitative and qualitative analysis, the abdominal aorta and its visceral branches were divided into 13 arterial segments. In a subanalysis of 55/102 patients, the accuracy of parallel GRE MRI compared to MDCT in the detection arterial variants and stenosis was calculated for two independent readers. Mean SNRs and CNRs were 47.2 and 35.6, respectively. Image quality was rated good or excellent in 1,234/1,326 segments (93%). Hepatic and renal arterial variants were identified with an accuracy of 93 and 95%, respectively (reader 1) and 98 and 100%, respectively (reader 2). Both readers detected arterial stenosis with an accuracy of 98%. Interobserver agreement was good to excellent for the detection of hepatic (κ=0.69) and renal (κ=0.92) variants and for the diagnosis of stenosis (κ=0.96). Dynamic three-dimensional parallel GRE MRI is feasible and allows a reliable and accurate diagnosis of arterial variants and stenosis of the abdominal aorta and its visceral branches in a short breath-hold-tim

Magnetization transfer for the assessment of bowel fibrosis in patients with Crohn's disease: initial experience

Object: To assess the feasibility of magnetization transfer (MT) imaging of the bowel wall in patients with Crohn's disease (CD), and to evaluate its utility for the detection of intestinal fibrosis. Materials and methods: In this prospective study, 31 patients (age 39.0±13.2years) with CD were examined in a 1.5T MR scanner. To establish a standard of reference, two independent readers classified the patients in different disease states using standard MR enterography, available clinical data and histological findings. In addition to the standard protocol, a 2D gradient-echo sequence (TR/TE 32ms/2.17ms; flip angle 25°) with/without 1,100Hz off-resonance prepulse was applied. MT ratios (MTR) of the small bowel wall were computed off-line on a pixel-by-pixel basis. Results: The MT sequences acquired images of sufficient quality and spatial resolution for the evaluation of the small bowel wall without detrimental motion artefacts. In normal bowel wall segments, an intermediate MTR of 25.4±3.4% was measured. The MTR was significantly increased in bowel wall segments with fibrotic scarring (35.3±4.0%, p<0.0001). In segments with acute inflammation, the mean MTR was slightly smaller (22.9±2.2%). Conclusion: MT imaging of the small bowel wall is feasible in humans with sufficient image quality and may help with the identification of fibrotic scarring in patients with C

Diagnostic Accuracy of a MR Protocol Acquired with and without Endorectal Coil for Detection of Prostate Cancer: A Multicenter Study

Introduction The purpose of this study was to compare diagnostic accuracy of a prostate multiparametric magnetic resonance imaging (mpMRI) protocol for detection of prostate cancer between images acquired with and without en-dorectal coil (ERC). Materials This study was approved by the regional ethics committee. Between 2014 and 2015, 33 patients (median age 51.3 years; range 42.1-77.3 years) who underwent prostate-MRI at 3T scanners at 2 different institutions, acquired with (mpMRI) and without (mpMRI) ERC and who received radical prostatectomy, were included in this retrospective study. Two expert readers (R1, R2) attributed a PI-RADS version 2 score for the most suspect (i. e. index) lesion for mpMRI and mpMRI. Sensitivity and positive predictive value for detection of index lesions were assessed using 2 × 2 contingency tables. Differences between groups were tested using the McNemar test. Whole-mount histopathology served as reference standard. Results On a quadrant-basis cumulative sensitivity ranged between 0.61-0.67 and 0.76-0.88 for mpMRI and mpMRI protocols, respectively (p > 0.05). Cumulative positive predictive value ranged between 0.80-0.81 and 0.89-0.91 for mpMRI and mpMRI protocols, respectively. The differences were not statistically significant for R1 (p = 0.267) or R2 (p = 0.508). Conclusion Our results suggest that there may be no significant differences for detection of prostate cancer between images acquired with and without an ERC

The protein and contrast agent-specific influence of pathological plasma-protein concentration levels on contrast-enhanced magnetic resonance imaging

OBJECTIVE: The objective of this study was to measure the protein-specific response of r1 and r2 relaxivities of commercially available gadolinium-based magnetic resonance imaging contrast agents to variation of plasma-protein concentrations. MATERIALS AND METHODS: In this in vitro study, contrast agent (gadofosveset trisodium, gadoxetate disodium, gadobutrol, and gadoterate meglumine) dilution series (0-2.5 mmol Gd/L) were prepared with plasma-protein (human serum albumin [HSA] and immunoglobulin G [IgG]) concentrations at physiological (42 and 10 g/L HSA and IgG, respectively, Normal) and at 3 pathological levels with HSA/IgG concentrations of 10/10 (solution Alb low), 42/50 (IgG mild), and 42/70 (IgG severe) g/L. Contrast-agent molar relaxivities and relaxivity-enhancing protein-contrast-agent interaction coefficients were determined on the basis of inversion-recovery and spin-echo data acquired at 1.5 and 3.0 T at 37°C. Protein-induced magnetic resonance imaging signal changes were calculated. RESULTS: The effective r1 and r2 molar relaxivities consistently increased with albumin and IgG concentrations. At 1.5 T, the r1 values increased by 10.2 (gadofosveset), 4.3 (gadoxetate), 1.3 (gadobutrol), and 1.1 L s mmol (gadoterate), respectively, from the Alb low to the IgG severe solution. At 3.0 T, the r1 values increased by 2.9 (gadofosveset), 2.3 (gadoxetate), 0.7 (gadobutrol), and 0.9 (gadoterate) L s mmol, respectively. An excess of IgG most strongly increased the r1 of gadoxetate (+40 and +19% at 1.5 and 3.0 T, respectively, from Normal to IgG severe). An albumin deficiency most strongly decreased the r1 of gadofosveset (-44% and -20% at 1.5 and 3.0 T, respectively, from Normal to Alb low). The modeling confirmed a strong gadofosveset r1 enhancement by albumin and suggested stronger IgG than albumin effects on the apparent molar relaxivity of the other agents per protein mass concentration at 1.5 T. CONCLUSIONS: Pathological deviations from normal plasma-protein concentrations in aqueous solutions result in changes of effective r1 and r2 contrast-agent relaxivities and projected signal enhancements that depend on the contrast agent, the blood-serum protein profile, and the field strength

Quantitative breast MRI: 2D histogram analysis of diffusion tensor parameters in normal tissue

Abstract : Object: Diffusion tensor imaging (DTI) of the breast may provide a powerful new approach for the detection of intraductal processes. The aim of this investigation was to characterize the relation between diffusion tensor parameters [fractional anisotropy (FA), mean diffusivity (MD)] in normal breast tissue to obtain information on the microenvironment of the diffusing water molecules and to provide a systematic approach for DTI analysis. Materials and methods: Seven female, healthy volunteers underwent prospective double-spin-echo prepared echo-planar diffusion-weighted sequence (TR/TE 8,250ms/74ms, b values 0 and 500s/mm (2), six encoding directions, 12 averages, 35 slices) in 4 consecutive weeks (3.0 T). Quantitative maps of diffusion tensor parameters were computed offline with custom routines. The interdependence of MD and FA in different voxels was analysed by linear and exponential regression. Results: All MD and FA maps were of excellent quality. A consistent pattern was observed in that lower fractional anisotropy values were more likely associated with higher mean diffusivity values. The dependence exhibited an exponential behavior with a correlation coefficient R=0.60 (R linear=0.57). Conclusion: The likelihood with which FA and MD values are observed in a voxel within normal breast tissue is characterized by a specific pattern, which can be described by an exponential model. Moreover, we could show that the proposed technique does not depend on the menstrual cycle