MR-guided biopsy using a T2-weighted single-shot zoom imaging sequence (Local Look technique).
The purpose of this study was to demonstrate the utility of a T2-weighted single shot turbo spin-echo technique--the so-called "Local Look" (LoLo) and more recently renamed "Zoom Imaging" technique--for MR-guided percutaneous interventions. We performed 28 procedures on 22 patients using a 1.5-T system for MR guidance. All procedures were controlled with the LoLo technique, which acquires T2-weighted images in 600 msec. This is achieved by using a small field of view (250 x 125 mm) along with a maximum echo train length, the so-called "single shot method." To prevent backfolding artifacts, the 90 degrees and 180 degrees pulses were oriented orthogonally to each other. Because signal is created only in the region in which the pulses overlap, no backfolding can occur from outside this area. Half of the biopsies were additionally monitored using a fast gradient-echo sequence, which was compared with the LoLo technique. All of the procedures were technically successful, and there were no procedural complications. The LoLo technique produced images that had good contrast between the lesion and the needle artifact, and the artifact size was smaller than that produced by the gradient-echo technique. Subjective judgment of the ability to accurately delineate the needle tip indicated that the LoLo technique was either superior to (73%) or equal to (27%) the gradient-echo sequence in all cases. The LoLo technique is an accurate and effective method for MR guidance of percutaneous procedures, because it shows good lesion contrast and small needle artifacts. The additional use of a gradient-echo sequence during the procedure planning stage is advisable in more difficult cases, particularly when adjacent blood vessels are a concern. Monitoring of the needle tip is best performed with the LoLo technique.