title: Magnetic resonance imaging-guided focused ultrasound for thermal ablation in the brain: a feasibility study in a swine model.
abstract: BACKGROUND
  Magnetic resonance imaging (MRI)-guided focused ultrasound is a novel technique that was developed to enable precise, image-guided targeting and destruction of tumors by thermocoagulation. The system, ExAblate2000, is a focused ultrasound delivery system embedded within the MRI bed of a conventional diagnostic MRI scanner. The device delivers small volumetric sonications from an ultrasound phased array transmitter that converge energy to selectively destroy the target. Temperature maps generated by the MRI scanner verify the location and thermal rise as feedback, as well as thermal destruction. To assess the safety, feasibility, and precision of this technology in the brain, we have used the ExAblate system to create predefined thermal lesions in the brains of pigs.
  
  
  METHODS
  Ten pigs underwent bilateral craniectomy to provide a bone window for the ultrasound beams. Seven to 10 days later, the animals were anesthetized and positioned in the ExAblate system. A predefined, 1-cm frontal para ventricular region was delineated as the target and treated with multiple sonications. MRI was performed immediately and 1 week after treatment. The animals were then sacrificed and the brains removed for pathological study. The size of individual sonication points and the location of the lesion were compared between the planned dose maps, posttreatment MRI scans, and pathological specimen.
  
  
  RESULTS
  High-energy sonications led to precise coagulation necrosis of the specified targets as shown by subsequent MRI, macroscopic, and histological analysis. The thermal lesions were sharply demarcated from the surrounding brain with no anatomic or histological abnormalities outside the target.
  
  
  CONCLUSIONS
  MRI-guided focused ultrasound proved a precise and an effective means to destroy anatomically predefined brain targets by thermocoagulation with minimal associated edema or damage to adjacent structures. Contrast-enhanced T1-, T2-, and diffusion-weighted MRI scans may be used for real-time assessment of tissue destruction.
authors.affiliation: Department of Neurosurgery, Sheba Medical Center, Tel Aviv, Israel.
authors.forename: Zvi R
authors.initials: ZR
authors.lastname: Cohen
authors.forename: Jacob
authors.initials: J
authors.lastname: Zaubermann
authors.forename: Sagi
authors.initials: S
authors.lastname: Harnof
authors.forename: Yael
authors.initials: Y
authors.lastname: Mardor
authors.forename: Dvora
authors.initials: D
authors.lastname: Nass
authors.forename: Eyal
authors.initials: E
authors.lastname: Zadicario
authors.forename: Arik
authors.initials: A
authors.lastname: Hananel
authors.forename: David
authors.initials: D
authors.lastname: Castel
authors.forename: Meir
authors.initials: M
authors.lastname: Faibel
authors.forename: Zvi
authors.initials: Z
authors.lastname: Ram
mesh_terms: D000818:Animals; D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology*; D001927:Brain Diseases / Q000473:pathology / Q000628:therapy; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005240:Feasibility Studies; D006979:Hyperthermia, Induced / Q000295:instrumentation / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D013552:Swine; D014464:Ultrasonic Therapy / Q000295:instrumentation* / Q000379:methods*