Visualization of cardiac involvement in patients with systemic sarcoidosis applying contrast-enhanced magnetic resonance imaging

5. Summary Contrast-enhanced MRI may serve as a sensitive noninvasive tool for the detection and follow-up of myocardial involvement in patients with systemic sarcoidosis.     

Semi-quantitative approach to estimating GFR by magnetic resonance imaging

Objective: The purpose of this study was to compare a semi-quantitative approach to estimating glomerular filtration rate (GFR) by magnetic resonance imaging with radionuclide calculation of GFR, and to investigate whether spin echo or gradient echo is more suitable for estimating GFR.Methods and patients: Fourteen kidneys of seven patients (GFR ranging from 26 to 57 ml/min) were studied. Spin echo and gradient echo sequences interleaving each other at every excitation were used. After intravenous injection of gadopentetate dimeglumine, serial scans were performed. The signal intensities measured in the regions of interest were converted to time-transverse relaxation rate changes for both spin echo (ΔR2) and gradient echo (ΔR2^*). The areas under the time-ΔR2 and time-ΔR2^* curves were calculated as a semi-quantitative index of GFR for both spin echo and gradient echo images, and the results were compared by GFR measured by radionuclide imaging.Results: The semi-quantitative index of the GFR calculated from spin echo images showed a significant correlation with the GFR measured by radionuclide imaging (r=0.85,P<0.001). On the other hand, the semi-quantitative index of the GFR calculated from gradient echo images showed no such correlation (r=0.46,P=0.10).Conclusion: Spin echo sequences may be more suitable than gradient echo sequences for the evaluation of GFR.     

Volumetric analysis of mice lungs in a clinical magnetic resonance imaging scanner

Small animal models are widely used to study various pathologies. Magnetic resonance imaging (MRI) allows investigation of these animals in a non-invasive way. Therefore, the aim of our study was to develop and evaluate a low-cost approach to measure lung volumes in small animal MRI using a clinical scanner and a specially designed RF coil. Five mice (three of an established emphysema model and two controls) were investigated in a 1.0-T clinical scanner using a specially built small animal saddle coil and three different three-dimensional sequences; overall imaging time was approximately 16 min. Lung volumes were calculated from these images using an interactive watershed transform algorithm for semi-automatic image segmentation. The gold standard for the volume measurement was water displacement after surgical explantation. MRI measured volumes correlated significantly with ex vivo measurements on the explanted lungs (r = 0.99 to 0.89; p < 0.05). Mean lung volume in emphysema model mice was larger than in controls. High-resolution, small animal MRI using a clinical scanner is feasible for volumetric analysis and provides an alternative to a dedicated small animal scanner.     

Detection of myocardial viability in acute infarction using contrast-enhanced <Superscript>1</Superscript>H magnetic resonance imaging

Background Reperfusion strategies salvage myocardium at risk in acute myocardial infarction (MI). This clinical study was performed to determine whether areas without evidence of delayed MRI contrast enhancement in MI correspond to viability by means of percent systolic wall thickening (%SWT) and enddiastolic wall thickness (EDWT) in chronic infarction. Methods Twenty MRI studies were performed in ten patients within 6 days of MI and 3 months post-MI. On a segmental basis the percentage of viable myocardium as defined by contrast-enhanced MRI (no delayed MRI contrast enhancement) in acute MI was measured and was compared with %SWT and EDWT in chronic MI. Results Of the 1718 segments in acute infarction in which the percentage of viable myocardium was measured 1333 were found to be completely viable by means of contrast-enhanced MRI (no delayed MRI contrast enhancement). All of these segments revealed %SWT on day 90 post-MI, and 97% of segments were viable by means of an EDWT of more than 5.5 mm. In 85 segments the proportion of viable myocardium was 50–99% (mean 56±8%), with 92% segments found to be viable by means of %SWT and 92% by EDWT, and of 156 segments with viable myocardium between 1–49% (36±8%) 79% were found to be viable by means of %SWT and 82% by EDWT. Corresponding proportions of 144 segments with transmural delayed MRI contrast enhancement in acute MI were 45% and 17%. Conclusions In acute reperfused MI viable myocardium as delineated by contrast-enhanced MRI is correlated with clinical parameters of viability. Delayed MRI contrast enhancement resolves nontransmural MI and may become a valuable clinical tool when planning revascularization procedures.     

High-resolution magnetic resonance imaging of iron-labeled myoblasts using a standard 1.5-T clinical scanner

Myoblast transplantation is a promising means of restoring cardiac function in infarcted areas. For optimization of transplant protocols, tracking the location and fate of the injected cells is necessary. An attractive imaging modality for this is magnetic resonance imaging (MRI) as it is noninvasive and as iron-labeled myoblasts provide a signal attenuation in T2*-weighted protocols. The aim of this study was to develop an efficient iron-labeling protocol for myoblasts and to visualize single-labeled cells using a clinical 1.5-T scanner. Pig myoblasts were labeled with a superparamagnetic iron oxide (SPIO) agent using a liposome transfection agent. Labeling efficiency, toxicity, cell viability, and proliferative capacity were measured for 10 days. Magnetic resonance (MR) of myoblast cultures used a T2*-weighted three-dimensional protocol with a maximum in-plane resolution of 19.5 × 26.0 m² and 50 m slices. Use of liposomes improved SPIO labeling efficiency. Labeling did not induce toxicity or affect cell viability or proliferation. The cell distribution as observed with light and fluorescence microscopy matched the signal voids observed in the MRI datasets. Liposomes promote fast, nontoxic and efficient SPIO labeling of myoblasts that can be tracked by MRI microscopy in clinical scanners using susceptibility-weighted protocols.     

Magnetic resonance imaging of rodent teeth

In this paper, the anatomical structures of rat jaws are studied using magnetic resonance imaging (MRI) with high spatial resolution. In vivo microimages of teeth from 3- and 12-week-old (young and adult) rats have been performed. A 2 T nuclear magnetic resonance microscope was used to collect, with multiple orientations, non-invasive 2D data images using the spin-echo technique. MRI appears well suited to give images of the oral area and may represent a useful tool for diagnosis of dental diseases and more particularly of pulp pathologies. This work was presented at the ESMRMB meeting in Brussels, September 1997.     

Low-field magnetic resonance imaging of the pelvis in patients with anal dynamic graciloplasty: initial experience

The aim of this study was to determine whether low-field magnetic resonance (MR) imaging can safely and accurately depict inflammatory changes in patients with anal dynamic graciloplasty, in whom high-field MR imaging is contraindicated and ultrasonography and computed tomography are inadequate. A 0.2-T field-strength MR examination was performed in six patients with anal dynamic graciloplasty malfunction in whom reoperation was contemplated. The following sequences were applied:T ₂-weighted turbo spinecho with fat saturation,T ₁-weighted conventional spin-echo, and contrastenhancedT ₁-weighted conventional spin-echo with fat saturation. Results indicated that none of the patients experienced relevant discomfort, pacemaker malfunction, or electrode dislocation with low-field MR imaging. Inflammatory pelvic changes were visualized in four patients and atrophy of the transposed gracilis muscle in another. Surgery was thus avoided in the four, who underwent conservative treatment for their pelvic inflammation. It was concluded that these prelininary results demonstrate the feasibility of MR imaging with a low field strength in patients with anal dynamic graciloplasty. In such patients, in whom diagnostic imaging had been problematic, the potential for safe and accurate visualization will be a boon to treatment planning.     

MR imaging of the prostate in clinical practice

Magnetic resonance imaging (MRI) is the imaging tool of choice in the evaluation of prostate cancer. The main applications of MR imaging in the management of prostate cancer are: (1) to guide targeted biopsy when prostate cancer is clinically suspected and previous ultrasound-guided biopsy results are negative; (2) to localize and stage prostate cancer and provide a roadmap for treatment planning; and (3) to detect residual or locally recurrent cancer after treatment. Other MR techniques such as proton MR spectroscopic imaging (MRSI), diffusion-weighted imaging (DWI), and contrast-enhanced MRI (CE-MRI) complement conventional MR imaging by providing metabolic and functional information that can improve the accuracy of prostate cancer detection and characterization. In everyday clinical practice, and to account for patient comfort, MR imaging studies are limited to 1 h. To obtain consistently high-quality images, a well-designed protocol is necessary. Routine MR imaging can be supplemented by other MR techniques such as MRSI, DWI or CE-MRI depending on the expertise available and the clinical questions that need to be answered. This review summarizes the role of MR imaging in the management of prostate cancer and describes practical approaches to implementing anatomic, metabolic and functional MR imaging techniques in the clinic.     

Distributed large-scale simulation of magnetic resonance imaging

The concept and the implementation of a parallelized and spin-based simulator for magnetic resonance (MR) imaging is presented. The dynamics of magnetization are modeled using the Bloch equation covering arbitrary radiofrequency (RF) pulses, gradients, main-field inhomogeneity, and relaxation. A temporal decomposition of a given sequence is introduced, leaning to basic sequence elements called atoms. A concept of spatial sampling of the object by spins is proposed, in the course of which Shannon's sampling theorem must be respected. In biomedical MR imaging, spins can be modeled as noninteracting entities, permitting an efficient parallelization of the simulation. The simulator ParSpin was implemented on a heterogeneous, interconnected cluster of workstations based on existing message passing libraries. The communication overhead has been kept moderately small. The aggregate computing performance of many processors enables the research into very complex problems (e.g., three-dimensional or steady-state MR experiments requiring up to 10⁶ spins). Additionally, ParSpin allows a comprehensive visualization for educational purposes.     

Application of magnetic resonance imaging in reptile medicine

Clinical examinations of reptiles are physically limited and therefore usually have to be complemented by other methods. This is especially true for Chelonians. A modern imaging technique like magnetic resonance imaging is well suited for this purpose. Its application and practical experiences with tortoises are presented.     

Transient global brain ischemia in young and aged rats: differences in severity and progression, but not localisation, of lesions evaluated by magnetic resonance imaging

A model of transient global brain ischemia consisting of bilateral occlusion of common carotid arteries for 10 min and mild hypoxia (15% O₂−85% N₂) for 20 min was studied by means of MRI in young and aged Fischer 344 rats (3–4 and 24–26 months, respectively). Ischemia was assessed by full suppression of spontaneous EEG activity, which reappeared and normalized similarly in the two age-groups. The survival of young with respect to aged rats was considerably higher both at 24 h (20/20, i.e. 100% vs 12/16, i.e. 75%) and at 48 h (16/20, i.e. 80% vs 6/16, i.e. 38%). The localisation of brain lesions, their severity and progression were evaluated by a diffusion-weighted MRI (DWI) sequence at 24 and 48 h post-ischemia. There were no DWI-detectable lesions in eight out of 20 young and two out of 12 aged rats. The localisation of DWI-detected lesions was rather similar in rats of the two age-groups. In fact, the cerebral cortex, mainly parietal, occipital and temporal lobes were damaged in 83% of young and 90% of aged rats. The respective percentages for the thalamus were 83 and 60%, for the striatum 58 and 50%, and for the hippocampus 25 and 30%. The lesions present in the cerebral cortex and the thalamus were considerably more severe in aged than in young rats. In conclusion, in spite of similar localisation of ischemic lesions in the two age-groups, their incidence was higher, appearance more rapid and severity more pronounced in aged with respect to young rats. This resulted in a considerably higher mortality of the former. The overall data indicate that the age issue is very important in experimental ischemia research.     

Assessment of prosthetic aortic valve performance by magnetic resonance velocity imaging

Objectives Magnetic resonance (MRI) velocity mapping was used to evaluate non-invasively the flow profiles of the ascending aorta in normal volunteers and in patients with an aortic (mechanical) valve prosthesis. Background In patients with artificial aortic valves the flow profile in the ascending aorta is severely altered. These changes have been associated with an increased risk of thrombus formation and mechanical hemolysis. Methods Velocity profiles were determined 30 mm distal to the aortic valve in six healthy volunteers and seven patients with aortic valve replacement (replacement within the last 2 years) using ECG triggered phase contrast MRI. Peak flow, mean flow and mean reverse flow were measured in intervals of 25 ms during the entire heart cycle. Systolic reverse flow, end-systolic closing and diastolic leakage volume were calculated for all subjects. Results Peak flow velocity during mid-systole was significantly higher in patients with valvular prosthesis than in normals (mean±SD, 1.9±0.4 m/s vs. 1.2±0.03 m/s,P<0.001) with a double peak and a zone of reversed flow close to the inner (left lateral) wall of the ascending aorta of the patients. Closing volume was significantly larger in patients than in controls (−3.3±1.2 ml/beat vs. −0.9±0.5 ml/beat;P<0.001). There was reverse flow during systole in valvular patients amounting to 15.7±6.7% of total cardiac output compared to 2.3±1.2% in controls (P<0.001). Diastolic mean flow was negative in patients after valve replacement but not in controls (−11.0±15.2 ml/beat vs. 6.8±3.2 ml/beat;P<0.01). Conclusions The following three major quantitative observations have been made in the present study: (1) Mechanical valve prostheses have an increased peak flow velocity with a systolic reverse flow at the inner (left lateral) wall of the ascending aorta. (2) A double peak flow velocity pattern can be observed in patients with bileaflet (mechanical) prosthesis. (3) The blood volume required for leaflet closure and the diastolic leakage blood volume are significantly higher for the examined bileaflet valve than for native heart valves.     

Accuracy of computed tomography and magnetic resonance imaging in staging bronchogenic carcinoma

Sixty-three patients with non-small cell bronchogenic carcinoma were prospectively and independently assessed by computed tomography (CT) and magnetic resonance imaging (MRI) before surgery. Images were interpreted by four radiologists who had no knowledge of other imaging studies, except chest x-ray, and were blinded to surgical findings. The data were compared with pathologic and histologic findings. The accuracies of CT and MRI in determining tumor classification and assessing mediastinal and hilar lymph node metastases were compared. Sensitivity of CT in determining T factor was 78%, and specificity was 96%. The values for MRI were 84% and 96%, respectively. There was no significant difference between CT and MRI in staging tumors. MRI is more accurate than CT in diagnosing mediastinal invasion in staging superior sulcus tumors and complex tumors. There was no significant difference between the accuracies of CT and MRI in detecting mediastinal node metastases; the sensitivities were 82% and 90%, respectively, and specificities were 88% and 93%, respectively.     

Role of magnetic resonance methods in the evaluation of prostate cancer: an Indian perspective

The challenges in detection, localization, and staging of prostate cancer have prompted the investigation of the role of various magnetic resonance (MR) methodologies in a large cohort of men prior to biopsy. The identification of suspicious areas of malignancy was carried out using magnetic resonance imaging (MRI), magnetic resonance spectroscopic imaging (MRSI) and diffusion-weighted imaging (DWI). Our data shows that apparent diffusion coefficient (ADC) may be a reliable marker to differentiate normal, benign, and malignant prostate tissues similar to the metabolite ratio. Also, the combined use of MRSI and DWI improves the diagnosis of prostate cancer. In this review, we present our experience on the use of MRI, MRSI and DWI methods in the assessment of prostate cancer in Indian men. Further, analysis of the comparison of the ADC and the metabolite ratio values reported in the literature across various patient populations are presented. An erratum to this article can be found at     

Exponential wavelet iterative shrinkage thresholding algorithm with random shift for compressed sensing magnetic resonance imaging

We propose the use of exponent of wavelet transform (EWT) coefficients as a sparse representation which is combined with the iterative shrinkage/threshold algorithm (ISTA) for the reconstruction of compressed sensing magnetic resonance imaging. In addition, random shifting (RS) is employed to guarantee the translation invariance property of discrete wavelet transform. The proposed method is termed the exponential wavelet iterative shrinkage/threshold algorithm with random shifting (EWISTARS), which takes advantages of the sparse representation of EWT, the simplicity of ISTA, and the translation invariance of RS. Simulation results on brain, vertebrae, and knee MR images demonstrate that EWISTARS is superior to existing algorithms with regard to reconstruction quality and computation time. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Gadolinium-enhanced magnetic resonance angiography of the pelvis in patients with erectile impotence

This study evaluted the potential of contrast-enhanced digital-subtraction magnetic resonance angiography (CE-DS-MRA) for noninvasive angiographic delineation of the arterial supply of the penis in patients with erectile dysfunction. After induction of an erection with prostaglandin E, a three-dimensional fast imaging with steady-state precision (FISP) sequence with TE of 1.8–2 milliseconds, TR of 4.4–5 milliseconds, and flip angle of 40°–60° was used to obtain high-resolution angiograms of the pelvis and penis during the injection of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) 0.3 mmol/kg body weight, within 30–50 seconds. DS maximum intensity projections (MIPs) and multiplanar reconstructions (MPRs) were compared with clinical work-up and directional Doppler ultrasound in 11 patients. In all 11 patients (100%), the arterial supply of the penis could be delineated from the aortic bifurcation via the iliac and internal pudendal arteries to the dorsal and deep penile arteries. Of the 22 internal pudendal arteries, 6 (27%) were occluded on CE-DS-MRA and 5 (23%) had stenoses, of which 4 (18%) were greater than 50%. In 7 patients (64%) good correlation between CE-DS-MRA and clinical findings and/or Doppler ultrasound was found; in 2 patients (18%), the correlation was moderate, and in 2 patients (18%) results were discrepant. In 6 patients (55%), MRA provided additional information to the clinical and Doppler ultrasound work-up. CE-DS-MRA can delineate small sessels such as the internal pudendal and penile arteries and thus has the potential to become a noninvasive angiography method in the work-up of erectile impotence. Supported by Siemens Medical Systems, Erlangen; Schering AG, Berlin; and Agfa-Gevaert AG, Leverkusen.     

Real-time direct volume rendering in functional magnetic resonance imaging

Direct volume rendering is a visualization method that allows display of all information hidden in three-dimensional data sets of, for example, computed tomography or magnetic resonance imaging (MRI). In contrast to commonly used surface rendering methods, these algorithms need no preprocessing but suffer from a high computational complexity. A real-time rendering system, VIRIM (Vitec: Visualization Technology GmbH, Mannheim, Germany), cuts down rendering times of minutes on normal workstations to an interactive rate of 1 second or less. The immediate visual feedback allows interactive steering of the visualization process to achieve insight into the internal three-dimensional structure of objects. Additional information is obtained by using an interactive gray-value segmentation tool that both allows segmentation of the data set according to bone, tissue, and liquor and display of multifunctional data sets (e.g., functional MRI [fMRI] data sets). Thus, real-time direct volume rendering allows segmentation and volume data processing of functional and anatomical MR data sets simultaneously. As this method can be integrated in the clinical routine, it is of great importance for real-time motion artifact detection and the interpretation of fMRI data acquired during cognitive experiments with normal subjects and psychiatric patients. Because of the free programmability of VIRIM, more complex matching procedures are currently being investigated for future implementation.     

Measurements of left ventricular dimensions using real-time acquisition in cardiac magnetic resonance imaging: comparison with conventional gradient echo imaging

This study investigates the use of real-time acquisition in cardiac magnetic resonance imaging (MRI) for measurements of left ventricular dimensions in comparison with conventional gradient echo acquisition. Thirty-one subjects with a variety of left ventricular morphologies to represent a typical clinical population were studied. Short-axis data sets of the left ventricle (LV) were acquired using a conventional turbo-gradient echo and an ultrafast hybrid gradient echo/echo planar sequence with acquisition in real-time. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF) and left ventricular mass (LV mass) were measured. The agreement between the two acquisitions and interobserver, intraobserver and interstudy variabilities were determined. The bias between the two methods was 5.86 ml for EDV, 0.23 ml for ESV and 0.94% for EF. LV mass measurements were significantly lower with the real-time method (mean bias 14.38 g). This is likely to be the result of lower spatial resolution and chemical shift artefacts with the real-time method. Interobserver, intraobserver and interstudy variabilities were low for all parameters. In conclusion, real time acquisition in MRI can provide accurate and reproducible measurements of LV dimensions in subjects with normal as well as abnormal LV morphologies, but LV mass measurements were lower than with conventional gradient echo imaging. Presented in abstract form at the International Society of Magnetic Resonance in Medicine meeting in Denver, Colorado in April 2000.     

Effects of riluzole on the evolution of focal cerebral ischemia: a magnetic resonance imaging study

The aim of this study was to investigate the effects of riluzole on the lesion induced by a permanent middle cerebral artery occlusion (MCAO) in rats. Riluzole at 4 or 8 mg/kg i.v. significantly reduced the cortical ischemic brain damage. With the most effective dose of 8 mg/kg, the time evolution of the lesion was assessed by T₂-weighted magnetic resonance imaging (MRI) repeated on the same animals after MCAO. MRI obtained at 24, 48, and 72 hours after MCAO showed a progressive increase of the ischemic lesion, except in the cortex of the riluzole-treated rats (8 mg/kg i.v.). Furthermore, there was no difference between lesion volumes as measured by MRI or by histology. This study indicates that MRI may be a valuable method to quantifyin vivo the neuroprotective profile of a drug.