title: Factors associated with successful magnetic resonance-guided focused ultrasound treatment: efficiency of acoustic energy delivery through the skull.
abstract: OBJECTIVE
  Magnetic resonance-guided focused ultrasound surgery (MRgFUS) was recently introduced as treatment for movement disorders such as essential tremor and advanced Parkinson's disease (PD). Although deep brain target lesions are successfully generated in most patients, the target area temperature fails to increase in some cases. The skull is one of the greatest barriers to ultrasonic energy transmission. The authors analyzed the skull-related factors that may have prevented an increase in target area temperatures in patients who underwent MRgFUS.
  
  
  METHODS
  The authors retrospectively reviewed data from clinical trials that involved MRgFUS for essential tremor, idiopathic PD, and obsessive-compulsive disorder. Data from 25 patients were included. The relationships between the maximal temperature during treatment and other factors, including sex, age, skull area of the sonication field, number of elements used, skull volume of the sonication field, and skull density ratio (SDR), were determined.
  
  
  RESULTS
  Among the various factors, skull volume and SDR exhibited relationships with the maximum temperature. Skull volume was negatively correlated with maximal temperature (p = 0.023, r(2) = 0.206, y = 64.156 - 0.028x, whereas SDR was positively correlated with maximal temperature (p = 0.009, r(2) = 0.263, y = 49.643 + 11.832x). The other factors correlate with the maximal temperature, although some factors showed a tendency to correlate.
  
  
  CONCLUSIONS
  Some skull-related factors correlated with the maximal target area temperature. Although the number of patients in the present study was relatively small, the results offer information that could guide the selection of MRgFUS candidates.
authors.affiliation: Department of Neurosurgery, Brain Research Institute, Yonsei University College of Medicine, Seoul, Korea; and.
authors.forename: Won Seok
authors.initials: WS
authors.lastname: Chang
authors.affiliation: Department of Neurosurgery, Brain Research Institute, Yonsei University College of Medicine, Seoul, Korea; and.
authors.forename: Hyun Ho
authors.initials: HH
authors.lastname: Jung
authors.affiliation: InSightec Ltd., Tirat Carmel, Israel.
authors.forename: Eyal
authors.initials: E
authors.lastname: Zadicario
authors.affiliation: InSightec Ltd., Tirat Carmel, Israel.
authors.forename: Itay
authors.initials: I
authors.lastname: Rachmilevitch
authors.affiliation: InSightec Ltd., Tirat Carmel, Israel.
authors.forename: Tal
authors.initials: T
authors.lastname: Tlusty
authors.affiliation: InSightec Ltd., Tirat Carmel, Israel.
authors.forename: Shuki
authors.initials: S
authors.lastname: Vitek
authors.affiliation: Department of Neurosurgery, Brain Research Institute, Yonsei University College of Medicine, Seoul, Korea; and.
authors.forename: Jin Woo
authors.initials: JW
authors.lastname: Chang
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D020329:Essential Tremor / Q000601:surgery; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D019635:Neurosurgical Procedures / Q000379:methods*; D009771:Obsessive-Compulsive Disorder / Q000601:surgery; D010300:Parkinson Disease / Q000601:surgery; D012189:Retrospective Studies; D012737:Sex Factors; D012886:Skull / Q000000981:diagnostic imaging* / Q000601:surgery*; D013238:Stereotaxic Techniques; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013696:Temperature; D013787:Thalamic Nuclei / Q000033:anatomy & histology / Q000601:surgery; D016896:Treatment Outcome; D059708:Ultrasonic Surgical Procedures / Q000379:methods*; D014463:Ultrasonography; D055815:Young Adult
keywords: ET = essential tremor; Emax = maximal energy required to achieve Tmax; MRgFUS = magnetic resonance-guided focused ultrasound surgery; OCD = obsessive-compulsive disorder; PD = Parkinson’s disease; RF = radiofrequency; SDR = skull density ratio; Tmax = maximum temperature; focused ultrasound; functional neurosurgery; magnetic resonance; skull; treatment