Temperature elevation by HIFU in ex vivo porcine muscle: MRI measurement and simulation study.
OBJECTIVE
High-intensity focused ultrasound is a rapidly developing medical technology with a large number of potential clinical applications. Computational model can play a pivotal role in the planning and optimization of the treatment based on the patient's image. Nonlinear propagation effects can significantly affect the temperature elevation and should be taken into account. In order to investigate the importance of nonlinear propagation effects, nonlinear Westervelt equation was solved. Weak nonlinear propagation effects were studied. The purpose of this study was to investigate the correlation between the predicted and measured temperature elevations and lesion in a porcine muscle.


METHODS
The investigated single-element transducer has a focal length of 12 cm, an aperture of 8 cm, and frequency of 1.08 MHz. Porcine muscle was heated for 30 s by focused ultrasound transducer with an acoustic power in the range of 24-56 W. The theoretical model consists of nonlinear Westervelt equation with relaxation effects being taken into account and Pennes bioheat equation.


RESULTS
Excellent agreement between the measured and simulated temperature rises was found. For peak temperatures above 85-90 °C "preboiling" or cavitation activity appears and lesion distortion starts, causing small discrepancy between the measured and simulated temperature rises. From the measurements and simulations, it was shown that distortion of the lesion was caused by the "preboiling" activity.


CONCLUSIONS
The present study demonstrated that for peak temperatures below 85-90 °C numerical simulation results are in excellent agreement with the experimental data in three dimensions. Both temperature rise and lesion size can be well predicted. Due to nonlinear effect the temperature in the focal region can be increased compared with the linear case. The current magnetic resonance imaging (MRI) resolution is not sufficient. Due to the inevitable averaging the measured temperature can be 10-30 °C lower than the peak temperature. Computational fluid dynamics can provide additional important information that is lost using a state of the art MRI device.
Center for Advanced Study in Theoretical Sciences (CASTS), National Taiwan University, Taipei 10617, Taiwan.
Maxim A
MA
Solovchuk
Medical Engineering Research Division, National Health Research Institute, Miaoli 35053, Taiwan.
San Chao
SC
Hwang
Medical Engineering Research Division, National Health Research Institute, Miaoli 35053, Taiwan.
Hsu
H
Chang
Sorbonne Universités, UPMC Univ Paris 06, UMR 7598, Laboratoire Jacques-Louis Lions, F-75005, Paris, France.
Marc
M
Thiriet
Department of Engineering Science and Ocean Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, Republic of China and Center for Advanced Study in Theoretical Sciences (CASTS), National Taiwan University, Taipei 10617, Taiwan.
Tony W H
TW
Sheu
D000465:Algorithms; D000818:Animals; D003198:Computer Simulation; D057446:Hydrodynamics; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000502:physiology*; D017711:Nonlinear Dynamics; D011312:Pressure; D034421:Sus scrofa; D013696:Temperature; D014463:Ultrasonography