Predicting variation in subject thermal response during transcranial magnetic resonance guided focused ultrasound surgery: Comparison in seventeen subject datasets. Issue 9 (24th August 2016)

• Record Type: Journal Article
• Authors: Vyas, Urvi; Ghanouni, Pejman; Halpern, Casey H.; Elias, Jeff; Pauly, Kim Butts
• Is Part Of: Medical physics. Volume 43:Issue 9(2016)
• Page Start: 5170
• Page End: 5180
• Publication Date: 2016-08-24
• Subjects: biomedical transducers -- biomedical ultrasonics -- biothermics -- bone -- computerised tomography -- image reconstruction -- medical image processing -- physiological models -- surgery -- transcranial magnetic stimulation -- ultrasonic therapy; Biological effects of acoustic and ultrasonic energy -- Biothermics and thermal processes in biology -- Reconstruction -- Computed tomography; Computerised tomographs -- Diagnosis using ultrasonic, sonic or infrasonic waves -- Surgical instruments, devices or methods, e.g. tourniquets -- Ultrasound therapy -- Biological material, e.g. blood, urine; Haemocytometers -- Digital computing or data processing equipment or methods, specially adapted for specific applications -- Image data processing or generation, in general; transcrania ultrasound -- therapeutic ultrasound -- acoustic simulation -- tcMRGFUS -- MRgFUS; Computed tomography -- Ultrasonography -- Brain -- Transducers -- Acoustic scattering -- Acoustic absorption -- Acoustic modeling -- Speed of sound -- Tissues; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4955436
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: In transcranial magnetic resonance‐guided focused ultrasound (tcMRgFUS) treatments, the acoustic and spatial heterogeneity of the skull cause reflection, absorption, and scattering of the acoustic beams. These effects depend on skull‐specific parameters and can lead to patient‐specific thermal responses to the same transducer power. In this work, the authors develop a simulation tool to help predict these different experimental responses using 3D heterogeneous tissue models based on the subject CT images. The authors then validate and compare the predicted skull efficiencies to an experimental metric based on the subject thermal responses during tcMRgFUS treatments in a dataset of seventeen human subjects. Methods: Seventeen human head CT scans were used to create tissue acoustic models, simulating the effects of reflection, absorption, and scattering of the acoustic beam as it propagates through a heterogeneous skull. The hybrid angular spectrum technique was used to model the acoustic beam propagation of the InSightec ExAblate 4000 head transducer for each subject, yielding maps of the specific absorption rate (SAR). The simulation assumed the transducer was geometrically focused to the thalamus of each subject, and the focal SAR at the target was used as a measure of the simulated skull efficiency. Experimental skull efficiency for each subject was calculated using the thermal temperature maps from the tcMRgFUS treatments. Axial temperature images (with no artifacts) were reconstructed with a single baseline, corrected using a referenceless algorithm. The experimental skull efficiency was calculated by dividing the reconstructed temperature rise 8.8 s after sonication by the applied acoustic power. Results: The simulated skull efficiency using individual‐specific heterogeneous models predicts well ( R 2 = 0.84) the experimental energy efficiency. Conclusions: This paper presents a simulation model to predict the variation in thermal responses measured in clinical ctMRGFYS treatments while being computationally feasible.