Magnetic resonance imaging-guided focused ultrasound thermal therapy in experimental animal models: Correlation of ablation volumes with pathology in rabbit muscle and VX2 tumors

Purpose: To further investigate the use of magnetic resonance-guided focused ultrasound therapy (MRgFUS) as a noninvasive alternative to surgery in the local control of soft-tissue tumors by ablating prescribed volumes of VX2 rabbit tumors and comparing with ablation of normal tissue volumes. Materials and Methods: Small, ellipsoidal ablations at shallow depth were created using 5- to 15-second sonication pulses at radio frequency (RF) powers of 50-125 W using a spherical, air-backed transducer operating at 1.463 MHz under MR guidance in a 1.5-T clinical scanner. Results: Excellent correlation was observed between prescribed treatment volumes, MR thermal dosimetry, post-treatment verification MRI, and histopathology. Multifocal ablations of VX2 tumors in rabbits at depths of up to 2.5 cm resulted in complete ablation of the prescribed treatment volume. Conclusion: MRgFUS is an effective technique for treating tumors in vivo. Techniques developed for treatments in homogeneous tissue volumes are applicable in the more complicated tumor environment if MR temperature feedback is available to modify treatment delivery parameters.