7 T Musculoskeletal MRI: Fundamentals and Clinical Implementation

This review summarizes the current state-of-the-art of musculoskeletal 7 T magnetic resonance imaging (MRI), the associated technological challenges, and gives an overview of current and future clinical applications of 1 H-based 7 T MRI. The higher signal-to-noise ratio at 7 T is predominantly used for increased spatial resolution and thus the visualization of anatomical details or subtle lesions rather than to accelerate the sequences. For musculoskeletal MRI, turbo spin echo pulse sequences are particularly useful, but with altered relaxation times, B1 inhomogeneity, and increased artifacts at 7 T; specific absorption rate limitation issues quickly arise for turbo spin echo pulse sequences. The development of dedicated pulse sequence techniques in the last 2 decades and the increasing availability of specialized coils now facilitate several clinical musculoskeletal applications. 7 T MRI is performed in vivo in a wide range of applications for the knee joint and other anatomical areas, such as ultra-high-resolution nerve imaging or bone trabecular microarchitecture imaging. So far, however, it has not been shown systematically whether the higher field strength compared with the established 3 T MRI systems translates into clinical advantages, such as an early-stage identification of tissue damage allowing for preventive therapy or an influence on treatment decisions and patient outcome. At the moment, results tend to suggest that 7 T MRI will be reserved for answering specific, targeted musculoskeletal questions rather than for a broad application, as is the case for 3 T MRI. Future data regarding the implementation of clinical use cases are expected to clarify if 7 T musculoskeletal MRI applications with higher diagnostic accuracy result in patient benefits compared with MRI at lower field strengths

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

Lesion follows function: video-oculography compared with MRI to diagnose internuclear ophthalmoplegia in patients with multiple sclerosis

Background: Video-oculography (VOG) is used to quantify functional deficits in internuclear ophthalmoplegia (INO), whereas MRI can detect the corresponding structural lesions in the medial longitudinal fasciculus (MLF). This study investigates the diagnostic agreement of MRI compared to VOG measurements. Methods: We prospectively compared structural MRI findings and functional VOG measures of 63 MS patients to assess their diagnostic agreement for INO. Results: MRI detected 12 true-positive and 92 true-negative MLF lesions for INO compared to VOG (12 true-positive and 38 true-negative patients) but identified one-third of the MLF lesions on the wrong side. MRI ratings were specific (92.0%) to detect MLF lesions but not sensitive (46.2%) for diagnosing INO (86.4% and 63.2% by patient). Accordingly, MRI has a high positive likelihood ratio of 5.77 but a modest negative likelihood ratio of 0.59 for the probability of INO (4.63 and 0.43) with an accuracy of 82.5% (79.4%). Conclusion: MRI assessments are highly specific but not sensitive for detecting INO compared to VOG. While MRI identifies MLF lesions in INO, VOG quantifies the deficit. As a simple, quick, and non-invasive test for diagnosing and tracking functional INO deficits, it will hopefully find its place in the diagnostic and therapeutic pathways of MS. Keywords: Eye movements; Internuclear ophthalmoplegia; Magnetic resonance imaging; Multiple sclerosis; Video oculography

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

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

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 8,250 ms/74 ms, b values 0 and 500 s/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

Effects of pravastatin on the contraction and the PI3K-Akt signaling pathway in isolated rabbit and isolated failing human myocardium

Statine besitzen neben der lipidsenkenden Wirkung eine Reihe von pleiotropen Effekten, die von zusätzlichem therapeutischen Nutzen sein könnten. In der vorliegenden Arbeit wurden direkte Wirkungen von Pravastatin auf das Myokard untersucht, die bei der Herzinsuffizienz von therapeutischer Relevanz sein könnten. Die Experimente wurden an isolierten insuffizienten humanen Trabekelpräparaten oder an isolierten adulten Kaninchen-Kardiomyozyten durchgeführt. Die Ergebnisse zeigen für Pravastatin in therapeutischer Konzentration keinen akuten oder mittelfristig messbaren Einfluss auf die Kontraktilität in isolierten humanen Herzmuskelstreifen. Ein längerfristiger Effekt kann aber nicht ausgeschlossen werden. Mit Hilfe von Western-Blot-Analysen haben wir die kardiale, antiapoptotische Akt-GSK3-Signalkaskade in insuffizientem Myokard sowie den Einfluss von Pravastatin auf diesen „Cell-survival-pathway“ untersucht. Dabei wurden das Expressionsniveau und der Phosphorylierungsgrad von Akt und GSK3 bestimmt. Unsere Daten deuten auf eine verminderte Aktivierung dieser Signalkaskade in terminal insuffizientem humanen Herzventrikelgewebe im Vergleich zu nicht-insuffzienten Kontrollherzen hin. Pravastatin aktiviert die Akt-GSK3-Signalkaskade über die PI3-Kinase in humanen insuffizienten Ventrikelpräparaten sowie in isolierten Kaninchen-Kardiomyozyten, was der erhöhten Apoptoserate im Rahmen einer Herzinsuffizienz entgegenwirken könnte. Die erhöhte Aktivität dieser Signalkaskade zieht möglicherweise auch eine Induktion der SERCA2a-Expression nach sich, die bei der Herzinsuffizienz charakteristisch erniedrigt ist. Zur Klärung der klinischen Relevanz dieses Effektes sind weiterführende Untersuchungen erforderlich. Als weiterer Effekt einer Pravastatin-vermittelten Aktivierung der PI3K-Akt- Signalkaskade konnte mittels Konfokalmikroskopie ein akuter Anstieg der zytosolischen NO-Produktion in Kardiomyozyten nachgewiesen werden. Aus den Ergebnissen der vorliegenden Arbeit lässt sich schlussfolgern, dass Pravastatin direkte Einflüsse auf das Myokard besitzt, die möglicherweise akute sowie chronische kardioprotektive Eigenschaften bewirken und bei der Herzinsuffizienz von therapeutischem Nutzen sein könnten

MRI of the Elbow: How to Do It

The diagnostic cascade for elbow complaints starts with the physical examination and radiographs that already can clarify or rule out many causes. Depending on the suspected pathology, additional imaging is necessary. Magnetic resonance imaging (MRI) has the advantage of accurately demonstrating a broad spectrum of diseases. The main indication for noncontrast MRI of the elbow is chronic epicondylitis. For magnetic resonance (MR) arthrography, it is suspected chondral and osteochondral abnormalities. Indirect MR arthrography is an option when direct arthrography is not practicable. MR arthrography of the elbow with traction is feasible, with promising results for the assessment of the radiocapitellar cartilage

Measurement variations of MRI and CT in the assessment of tumor depth of invasion in oral cancer: A retrospective study

Purpose In oral squamous cell carcinoma (OSCC), depth of invasion (DOI) is an important predictive, prognostic, and staging parameter. While it is known that DOI can be estimated from preoperative imaging, an analysis of measurements variations according to imaging modality and to depth of tumor itself is lacking. The aim of the study was to assess the accuracy of imaging-based estimation of DOI in relation with the tumor histological DOI. Methods We retrospectively reviewed 121 patients with OSCC treated at University Hospital Zurich. The radiologic DOI of CT, T1-weighted, and T2-weighted MRI were compared with histological DOI. Frequency of relevant imaging artifacts was assessed as well. Results A total of 110 CT (90.9 %) and 90 MRI (74 %) were analyzed. Both modalities were available for 79 patients (65.3 %). The median histological depth of invasion was 9 mm (IQR 4.5–14). The median depth of invasion was 14 mm (IQR 10–20) on CT, 13 mm (IQR 8.25–18) on T1-weighted MRI, and 13 mm (IQR 9–18.75) on T2-weighted MRI. All diagnostic modalities tended towards an overestimation of the histopathologic DOI from about 5–15 %. This trend was most pronounced for thin tumors, for which both CT and MRI lead to upstaging in over 50 % of the cases. For 25 (22.7 %) patients, dental scattering on CT rendered DOI not estimable. For MRI, 18 patients (20 %) had artifacts (blooming, motion artifacts) rendering DOI not estimable. Conclusion CT and MRI measurements of DOI in OSCC lead to an overestimation of histological DOI, especially in tumors with DOI<5 mm, with upstaging by imaging in over 50 % of the cases. Artifacts were present in more than 20 % of performed images

Blood oxygen level-dependent magnetic resonance imaging of the Kidneys: Influence of spatial resolution on the apparent R2* transverse relaxation rate of renal tissue

OBJECTIVES: The aim of this study was to quantify the influence of image resolution on the apparent transverse relaxivity (R2*) of the magnetic resonance (MR) signal in human renal tissue in vivo and in phantom measurements. MATERIALS AND METHODS: This prospective study included 17 healthy volunteers (age, 32 ± 8 years, 6 women). Parametrical R2* maps were computed via monoexponential fitting of multiecho 2-dimensional fast-field echo data measured at 1.5 T (repetition time [TR], 150 milliseconds; flip angle [FA], 40°; minimum echo time [TE], 4.6 milliseconds; ΔTE, 5 milliseconds; 16 echoes) and at 3 T (TR, 140 milliseconds; FA, 70°; minimum TE, 2 milliseconds; ΔTE, 5 milliseconds; 16 echoes) with varying nominal volumes of the encoded voxels (from 5.76 to 36.0 mm). For each voxel size, mean R2* values were computed in regions of interest drawn in the left and right renal parenchyma. For data acquired using minimum voxel size, the mean R2* values were computed over the cortex and medulla separately. The squared 2-norm of the residuals was computed to evaluate the goodness of the pixel-wise exponential fits. Six multiecho MR images of a water phantom were acquired using a 2-dimensional fast-field echo sequence (FA, 50°; TR, 108 milliseconds; TE, 4 milliseconds; ΔTE, 20 milliseconds) at 3 T after shim adjustment and in the presence of a uniform background gradient of 40 μT/m. The nominal voxel size was varied in a range between 2 and 12.5 mm. RESULTS: Mean R2* values of 13.04 ± 0.71 s (right renal cortex) and 16.47 ± 1.92 s (right renal medulla) were computed at 1.5 T. At 3 T, the R2* of the right medulla was 28.27 ± 1.52 s and the cortical R2* was 19.22 ± 2.32 s. Comparable relaxivity values were found over the left kidney at both field strengths. Increasing R2* values were observed for increasing voxel volume in both the water phantom and renal tissue data. At a constant slice thickness of 4 mm, the decrease in the in-plane resolution from 1.2 × 1.2 mm to 3.0 × 3.0 mm led to a maximum increase of the renal R2* of 15% at 1.5 T and of 12% at 3 T. Increasing the slice thickness from 3 to 8 mm at a constant in-plane resolution of 1.5 × 1.5 mm resulted in a maximum increase of the renal R2* of 30% at 1.5 T and of 26% at 3 T. On the other hand, increasing the voxel size improved the goodness of the fit implied by the smaller residuals. CONCLUSIONS: The phantom experiments and in vivo acquisitions of healthy renal tissue documented a significant dependence of the apparent R2* relaxation rate on the spatial resolution of the MR imaging data. In clinical practice, the voxel volume for the quantification of renal R2* should be optimized in a compromise between minimizing the effects of macroscopic field inhomogeneity and maintaining a sufficiently high signal-to-noise ratio and goodness of fit. When comparing quantitative R2* among different publications, the influence of the spatial resolution should be taken into account

Diagnostic accuracy of computed tomography and magnetic resonance imaging compared to surgical exploration for anterior skull base and medial orbital wall infiltration in advanced sinonasal tumors

BACKGROUND Knowledge of medial orbital wall (MOW) and anterior skull base (ASB) infiltration is of uttermost importance for staging and therapy planning of advanced sinonasal tumors. METHODS We assessed the diagnostic performance of preoperative computed tomography (CT) and magnetic resonance imaging (MRI) for MOW and ASB infiltration compared to intraoperative exploration. RESULTS Both CT and MRI yielded higher diagnostic accuracy for MOW infiltration (Reader 1: 83.6% CT; 89.0% MRI, Reader 2: 91.8% CT, 93.2% MRI) than for ASB infiltration (Reader 1: 82.2% CT, 82.2% MRI, Reader 2: 67.7% CT, 67.7% MRI). Both modalities were equal to the gold standard, except for ASB assessment by Reader 2 with MRI. A postoperative change of T classification is common (Reader 1: 28.8%, Reader 2: 31.5%). CONCLUSIONS CT and MRI are accurate methods for the assessment of MOW infiltration. ASB assessment is challenging and false-positive and false-negative findings are common with both methods, emphasizing the need for intraoperative exploration