Locally focused MRI of interventions

Certain interventional MR procedures would benefit from T2-weighted imaging because of the sensitivity of T2-weighted images to tissue damage and targ et lesion contrast. To acquire such images with reasonable temporal resolut ion, a single-shot acquisition should be used because of the inherently lon g TR needed for T2 weighting. Unfortunately, most scanners require long rea dout times (eg, greater than 150 msec) and high bandwidths (eg, greater tha n 120 kHz) to perform conventional single-shot imaging with high spatial re solution. The resulting images are thus degraded by unacceptable artifacts and noise levels. This study illustrates how to create locally focused MR i mages that have high spatial resolution in a region of interest and lower s patial resolution elsewhere in the image. Because these images can be creat ed from sparse k-space data, a scanner with modest gradients (eg, 10 mT/m m aximal amplitude, 500 mu sec minimal rise time) can acquire them after a si ngle excitation with relatively short readout time and low bandwidth. This technique may make it practical to monitor interventions with T2-weighted i maging. The method was illustrated by reconstructing dynamic changes, which were simulated experimentally by moving objects in the vicinity of a norma l human head.