title: In silico study of low-frequency transcranial ultrasound fields in acute ischemic stroke patients.
abstract: Ultrasound in the sub-megahertz range enhances thrombolysis and may be applied transcranially to ischemic stroke patients. The consistency of transcranial insonification needs to be evaluated. Acoustic and thermal simulations based on computed-tomography (CT) scans of 20 patients were performed. An unfocused 120-kHz transducer allowed homogeneous insonification of the thrombus, and positioning based on external landmarks performed similarly to an optimized placement based on CT data. With a weakly focused 500-kHz transducer, the landmark-based positioning underperformed. The predicted inter-patient variation of in situ acoustic pressure was similar with both the 120 and 500-kHz transducers for the optimized placement (18.0-26.4% relative standard deviation). The simulated maximum acoustic pressure in intervening tissues was 2.6 ± 0.6 and 2.0 ± 0.7 times the pressure in the thrombus for the 120-kHz and 500-kHz transducers, respectively. A 1 W/cm(2) insonification of the thrombus caused a 3.8 ± 2.2 °C increase in the bone for the 120-kHz transducer, and a 13.4 ± 3.3 °C increase for the 500-kHz transducer. Contralateral local maxima up to 1.1 times the pressure amplitude in the targeted zone were predicted for the 120-kHz transducer. We established two transducer placement approaches, one based on analysis of a head CT and the other using simple external, visible landmarks. Both approaches allowed consistent insonification of the thrombus.
authors.affiliation: Division of Cardiovascular Health and Disease, Department of Internal Medicine, College of Medicine, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Bouchoux
authors.affiliation: Department of Neurosurgery, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: Ravishankar
authors.initials: R
authors.lastname: Shivashankar
authors.affiliation: Department of Neurosurgery, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: Todd A
authors.initials: TA
authors.lastname: Abruzzo
authors.affiliation: Division of Cardiovascular Health and Disease, Department of Internal Medicine, College of Medicine, University of Cincinnati, Cincinnati, OH, USA; Biomedical Engineering Program, College of Engineering and Applied Sciences, University of Cincinnati, Cincinnati, OH, USA. Electronic address: Christy.Holland@uc.edu.
authors.forename: Christy K
authors.initials: CK
authors.lastname: Holland
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002545:Brain Ischemia / Q000000981:diagnostic imaging / Q000628:therapy*; D005260:Female; D006801:Humans; D006979:Hyperthermia, Induced / Q000379:methods*; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D011857:Radiographic Image Interpretation, Computer-Assisted; D015641:Radiography, Interventional; D012189:Retrospective Studies; D012984:Software; D020521:Stroke / Q000000981:diagnostic imaging / Q000628:therapy*; D015912:Thrombolytic Therapy / Q000379:methods*; D014057:Tomography, X-Ray Computed; D014159:Transducers; D016896:Treatment Outcome; D014464:Ultrasonic Therapy / Q000379:methods*
keywords: Acute ischemic stroke; Finite-difference simulation; Thermal simulation; Thrombolysis; Transcranial ultrasound