Biomedical subjects

F Wiesmann

Publications and source records attributed to F Wiesmann.

22 records · Page 2Linked to original sources

PubMed1997

[Current value of magnetic resonance imaging for diagnosis of coronary heart disease].

Magnetic Resonance Imaging (MRI) is a non-invasive imaging technique with increasing importance in clinical medicine. It has become a valuable and reliable imaging tool in the diagnosis and management of many medical and surgical conditions. Important advantages of MRI are its flexibility in orientation of imaging plane and the possibility of both anatomical and functional imaging. MRI is based on the application and detection of radio signals and works without any exposure to ionizing radiation, and therefore it is regarded as a safe imaging technique. In the heart there are well established imaging indications such as in acquired and congenital heart disease, pericardial and aortic disease and visualisation of cardiac masses and hypertrophy. Its applications in coronary artery disease (CAD) have been relatively limited, but recent developments in ultrafast imaging sequences and computer hardware have led to a considerable improvement in spatial and temporal image resolution. This has made applications in CAD a possibility, particularly coronary imaging and myocardial perfusion imaging. Recent clinical studies report good correlation between Magnetic Resonance Coronary Angiography (MRCA) and conventional x-ray contrast angiography in the detection of coronary lesions. In the assessment of coronary artery bypass graft (CABG) patency and the definition of anomalous coronary arteries, MRI showed good sensitivity and specificity. The first results of coronary artery flow measurements have now been reported. Myocardial perfusion imaging and stress-ventriculography for detection of wall motion abnormalities are reported as indirect imaging methods with high reliability and clinical value in the diagnosis of CAD. This overview describes recent developments in cardiac MRI and assesses the current and future value of MRI for clinical cardiology.

Coronary Artery Bypass↗

PubMedDate not supplied

MR navigator-echo monitoring of temporal changes in diaphragm position: implications for MR coronary angiography.

Temporal changes in respiration could influence navigator-echo (NE)-gated MR coronary angiography (MRCA), but systematic investigation of the effects of such variations and how to limit them has not been performed. We addressed these issues by studying the influence of time in the magnet on diaphragm position and respiratory patterns using NE diaphragm monitoring in volunteers and a phantom model. NE diaphragm monitoring was performed at .5 T in 10 subjects over a total period of 35 minutes. The end-expiratory position was sustained for longer (1.1 vs .4 seconds, P < .001) and with greater position stability (SD 1.9 vs 5.9 mm, P = .01) than the end-inspiratory position. Drift of the end-expiratory position occurred over time, causing a fall in scan efficiency (44-28%, P = .01). Up-drift of the end-expiratory position was most common. Loss of scan efficiency was worse with up-drift because of loss of the end-expiratory pause from the NE window (up-drift 10% mm-1, down-drift 7% mm-1, both P = .03). Scan efficiency also was reduced during sleep (to a nadir of 0%), secondary to loss of the end-expiratory pause, periodic breathing with oscillating end-expiratory position, and periods of apnea. The phantom model used actual diaphragm traces to evaluate the artifact resulting from diaphragm motion during acquisition. Artifact was considerably reduced by NE adaptive motion correction compared with NE gating alone (ghosting ratio 2.0 vs 2.8, P < .01). Artifact also was significantly reduced with up-drift if scan efficiency was maintained above 35% (P = .05). For optimal NE-gated MRCA, the following features are important: the NE window should be placed around the end-expiratory position; subjects should not sleep; scan efficiency should be monitored and the NE window should be repositioned if scan efficiency falls below 35%; and adaptive motion correction should be used.

Adult↗

PubMedDate not supplied

Hybrid ordered phase encoding (HOPE): an improved approach for respiratory artifact reduction.

Respiration causes continuous change in cardiac position, which leads to image degradation. Phase-encode reordering methods are often used to reduce these artifacts. An improved method for suppressing motion artifacts by reordering the acquisition of k space has been developed that is less sensitive to change of breathing patterns and bulk movement. We describe the theory behind the new approach and compare its results with those of existing methods by use of a phantom with simulated and actual acquired breathing patterns. The comparison was also made in vivo; cardiac scans were performed in 15 subjects with image planes that are known to be particularly susceptible to respiratory artifact. A significant improvement in image quality was achieved compared with conventional nonreordered and existing reordering methods.

Algorithms↗

PubMedDate not supplied

Comparison of fast spiral, echo planar, and fast low-angle shot MRI for cardiac volumetry at .5T.

The application of fast imaging is necessary to reduce the scanning time for cardiac volumetric MRI. Fast spiral, echo planar imaging (EPI), and fast low-angle shot (FLASH) imaging are rapid MRI techniques that allow image acquisition within a fraction of a second. Performed as a multi-shot technique, breath-hold imaging with high temporal and spatial resolution is feasible. This study evaluated the accuracy of interleaved spiral, EPI, and FLASH imaging for measuring ventricular volume and mass at .5T. Breath-hold short-axis cines in parallel planes covering both ventricles were acquired in 16 volunteers with all three fast methods, as well as with conventional gradient-echo imaging for comparison. All fast techniques showed good agreement with conventional imaging. Despite its lower temporal resolution, FLASH imaging yielded higher image quality than EPI and spiral, making FLASH more reliable and suggesting that at .5T, it is the method of choice for rapid cardiac volumetric imaging.

Adult↗