[en] The effects of myocardial anisotropy on the torso current flow patterns, voltage and the magnetic field were examined using an anatomically realistic torso model of an adult male subject. A finite element model of the torso was built with 19 major tissue types identified. The myocardial fibre orientation in the heart wall was included with a voxel resolution of 0.078x0.078x0.3cm. The fibre orientations from the canine heart which are available in the literature were mapped to our adult male subject's human heart using deformable mapping techniques. The current and potential distribution in the whole torso were computed using an idealized dipolar source of ±1.0 V in the middle of the septum of the heart wall as a boundary condition. An adaptive finite element solver was used. Two cases were studied. In one case the myocardium was isotropic and in the other it was anisotropic. It was found that the current density distribution shows a very noticeable difference between the isotropic and anisotropic myocardium. The resultant magnetic field in front of the torso was computed using the Biot-Savart law. It was found that the magnetic field profile was slightly affected by the myocardial anisotropy. The potential on the torso surface also shows noticeable changes due to the myocardial anisotropy. (author)

No abstract available

[en] The application of steady-state-free-precession (SSFP) techniques at 3 T systems is still limited by their sensitivity to magnetic field inhomogeneities. Especially during imaging of the heart, the arising signal voids and distortions in the myocardium currently often limit the diagnostic value of the resulting images. Dedicated shim systems providing higher order shimming capabilities have been applied to improve the field homogeneity across the heart. In this study, the potential benefit of applying a cardiac phase-specific shim (CPSS) was investigated. The cardiac phase dependence of the magnetic field distortions over the heart was assessed and the potential gain in field homogeneity by CPSS was evaluated. CPSS was successfully applied in volunteers and yielded significant improvement in the main magnetic field homogeneity over the entire cardiac cycle. (note)

[en] This study used MR perfusion imaging to detect and quantify reperfused ischemic myocardium during a brief coronary occulusion and reperfusion, and to characterize the spatial extent of ischemic and reperfused ischemic myocardium relative to the 'true' size of the area at risk as defined in histochemical morphometry at post mortem. The left circumflex (LCX) coronary artery in 8 dogs was occluded for 15 min followed by reperfusion in order to produce regional reversible myocardial ischemia. Perivascular Doppler probes were used to measure blood flow in the left anterior descending (LAD) and LCX coronary arteries. Fast inversion recovery-prepared gradient-recalled-echo images were acquired to delineate the ischemic area during occlusion, and the area of reversible ischemic injury at 1 and 30 min of reperfusion. The size of ischemic and reperfused ischemic myocardium were compared with the area at risk as determined by histochemical morphometry at post mortem. During LCX occlusion, LCX flow decreased from 16±1 to 0.2±0.1 ml/min. On contrast-enhanced images, ischemic myocardium was evident as a zone of relatively low signal intensity (SI) compared to normal myocardium. The size of the ischemic region was significantly smaller (30±2%) than at post mortem (36±3%; p<0.05). Immediately after reperfusion, LCX flow increased to 83±11 ml/min and the contrast medium caused greater enhancement in the reperfused ischemic region than in the normal myocardium (69±3 vs 42±3 arbitrary units; p<0.05). The increase in regional SI correlated closely with the increase in regional blood flow (r=0.73). At 1 min of reperfusion, the size of the reperfused ischemic myocardium was larger (48±3%, p<0.05) than the area at risk measured at post mortem. At 30 min of reperfusion, when the flow returned to baseline values (16±2 ml/min), contrast bolus produced no differential enhancement between the 2 myocardial territories. (orig./AJ)

[en] Purpose: To identify the normal performance of left ventricular (LV) regional contraction using cine MR imaging with presaturation myocardial tagging. Material and Methods: Sixteen normal volunteers were examined on a 1.5 T MR system with tagging cine sequences. Tags were applied at end-diastole as 2 parallel black lines on short-axis and 4-chamber sections, and the fractional shortenings were calculated at 7 LV locations. Results: The following results were obtained with significance: A transmural gradient of contractility in the short-axis section; prolonged late-systolic endocardial shortening and epicardial early termination in the free wall; initial delay of shortening in the anterior wall; apical predominance of contractility; predominance of circumferential shortening in the free wall and of meridional shortening in the septum. These findings could be associated with myocardial fiber architecture, presumed wall stress and temporal asynergy of excitation. Conclusion: Cine MR imaging with myocardial tagging proved to be useful in assessing the nonuniformity of LV contraction. (orig.)

[en] Left ventricular (LV) long-axis shortening produces cardiac motion through fixed short-axis sections, complicating accurate quantification of myocardial and wall-motion parameters with MRI. Therefore, LV long-axis length and shortening was studied in both long- and short-axis end-diastolic (ED) and end-systolic (ES) MRI scans. A group of 38 male volunteers underwent gradient-echo cine-MRI: single-slice long-axis and multi-slice short-axis. The LV dimensions were directly measured in the long-axis images using epicardial and endocardial contours. The position of the apex and the base (aortic valve) were assessed in the sections of the short-axis scan. The LV dimensions as measured on both long- and short-axis scans showed a correlation of r = 0.62 for ED and r = 0.69 for ES. Relative LV shortening between long- and short-axis scans showed a poor correlation (r = 0.22). These results suggest that short-axis MRI is not sufficient to accurately assess through-plane motion. Therefore, long-axis images are needed for optimal quantification of myocardial and wall-motion parameters. (orig.)

[en] MR images in cardiac function studies allow for precise alignment in reproducible axial planes, with excellent resolution and without areas of signal loss, so that highly accurate measurements can be made. This is important particularly in patients with regional functional deficits, in whom precise depiction of function in each myocardial region without overlap or signal 'drop-out' is critical. Also, MR tomograms make possible the elimination of geometric assumptions, which lead to errors when regional dysfunction is present, in assessment of ventricular volume and ejection fraction. The development of improved temporal resolution and motion display by cine MRI and, in particular, echo-planar techniques has made the measurement of function MRI a valuable clinical method. (author). 36 refs.; 7 figs.; 1 tab

No abstract available

[en] As the result of recent improvements in catheter design and pathologic interpretation, transvascular endomyocardial biopsy has become an important component in the invasive evaluation of patients with known or suspected primary myocardial dysfunction. Because significant controversy remains about the definition, frequency, natural history, and optimal treatment, of many of these myocardial disorders, however, use of the endomyocardial biopsy in the routine evaluation of patients with myocardial disease varies from center to center. This chapter focuses on the currently available techniques for endomyocardial histology appears most valuable, rather than on a precise listing of current indications for this procedure

[en] An integral method was developed for the evaluation of MR images of the coronary vessels, cardiac wall, and the ventricle. The method enables a three-dimensional analysis of the spatial relationships at a resolution of up to 140 μm. An isolated perfused rat heart prepared by the Langendorf method was used to model the human heart. Semiautomatic segmentation tools based on new image processing algorithms were employed for the segmentation of the myocardium and coronary vessel images. The 3D images were visualized by using the optimized ''Marching Cubes'' algorithm. 2 figs., 9 refs