THE USEFULNESS OF A CONTRAST AGENT AND GRADIENT-RECALLED ACQUISITION IN A STEADY-STATE IMAGING SEQUENCE FOR MAGNETIC-RESONANCE IMAGING-GUIDED NONINVASIVE ULTRASOUND SURGERY

RATIONALE AND OBJECTIVES. The ability of magnetic resonance imaging to detect small temperature elevations from focused ultrasound surgery b eams was studied. In addition, the value of a contrast agent in deline ating the necrosed tissue volume was investigated. MATERIALS AND METHO DS. Gradient-recalled acquisition in a steady state (GRASS) TI-weighte d images were used to follow the temperature elevation and tissue chan ges during 2-minute sonications in the thigh muscles of 10 rabbits. Th e effects of the treatment on the vascular network was investigated by injecting a contrast agent bolus before or after the sonication. RESU LTS. The signal intensity decreased during the sonication, and the red uction was directly proportional to the applied power and increase in temperature. The signal intensity returned gradually back to baseline after the ultrasound was turned off. Injection of the contrast agent i ncreased the signal intensity in muscle, but not in the necrosed tissu e. The dimensions of the delineated tissue volume were the same as mea sured from the T2-weighted fast-spin-echo images and postmortem tissue examination. CONCLUSIONS. These results indicate that magnetic resona nce imaging can be used to detect temperature elevations that do not c ause tissue damage and that contrast agent can be used to delineate th e necrosed tissue volume.