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To evaluate the potential of magnetic resonance imaging (MRI) for evaluation of velocity fields downstream of prosthetic aortic valves. Furthermore, to provide comparative data from bileaflet aortic valve prostheses in vitro and in patients.

The quantitative assessment of velocity fields can help to get a better understanding of complicated flow patterns which are considered to play an important role in atherosclerotic plaque formation. Magnetic resonance imaging offers the possibility of non-invasive visualization and quantification of blood flow in many larger human arteries and veins. However, the assessment of complex blood flow patterns with conventional gradient echo flow sequences sutler from severe image artifacts. In order to overcome these problems, a partial echo signal acquisition technique which strongly reduces such artifacts may be applied. Using this technique, three dimensional velocity fields were measured in a bifurcation model, in the human carotid bifurcation and in the human aorta, right downstream of the aortic valve.

Abstract.: The purpose of this study was to perform percutaneous laser disc decompression (PLDD) under MR guidance in an open configuration 0.5-T MR system. Following failed conservative treatment for 6 months, eight patients with contained disc herniations were enrolled in the study. Following MR guided introduction of the laser fiber into the targeted disc space, the laser-induced temperature distribution was visualized using a color-coded subtraction technique based on a T1-weighted GRE sequence. In seven patients PLDD could be performed. In all cases laser effects were depicted by MR. In this regard the color-coded technique was found to be superior to conventional magnitude images. Whereas no apparent decrease in the extent of herniation was discovered immediately following PLDD, T2-weighted FSE images showed signal intensity alterations in two of the seven patients. Clinical evaluation, obtained 3–4 months after PLDD, revealed a fair (n = 2) or good (n = 4) response to the treatment. One patient showed no change in symptoms. MR guidance and monitoring of PLDD is feasible within an open 0.5-T system and seems to render PLDD more safe and controllable.