title: Quantitative measurement and real-time tracking of high intensity focused ultrasound using phase-sensitive optical coherence tomography: Feasibility study.
abstract: Phase-sensitive optical coherence tomography (PhS-OCT) is proposed, as a new high intensity focused ultrasound (HIFU) imaging guidance to detect and track HIFU focus inside 1% agar samples in this work. The experiments studied the effect of varying HIFU power on the induction of shear wave, which can be implemented as a new technique to monitor focused ultrasound surgery (FUS).
  
  
  
  A miniature HIFU transducer (1.02 MHz, 20 mm aperture diameter, 15 mm radius of curvature) was produced in-house, pressure-field mapped, and calibrated. The transducer was then embedded inside a 1% agar phantom, which was placed under PhS-OCT for observation, under various HIFU power settings (acoustic power, and number of cycles per pulse). Shear wave was induced on the sample surface by HIFU and was captured in full under PhS-OCT. The lowest HIFU acoustic power output for the detection of shear wave was found to be 0.36 W (1.02 MHz, 100 cycles/pulse), or with the number of cycles/pulse as low as 20 (1.02 MHz, 0.98 W acoustic power output).
  
  
  
  A linear relationship between acoustic power output and the maximum shear wave displacement was found in the first study. The second study explores a non-linear correlation between the (HIFU) numbers of cycles per pulse, and the maximum shear wave displacement.
  
  
  
  PhS-OCT demonstrates excellent tracking and detection of HIFU-induced shear wave. The results could benefit other imaging techniques in tracking and guiding HIFU focus. Further studies will explore the relationship between the physical transducer characteristics and the HIFU-induced shear wave.
authors.affiliation: a Department of Mechanical Engineering , University of Dundee , Dundee , UK ;
authors.forename: Nhan
authors.initials: N
authors.lastname: Le
authors.affiliation: b Biophotonics and Imaging Laboratory , University of Washington , Seattle , USA ;
authors.forename: ShaoZhen
authors.initials: S
authors.lastname: Song
authors.affiliation: c Division of Cancer Research , University of Dundee, Angus , Dundee , UK ;
authors.forename: Ghulam
authors.initials: G
authors.lastname: Nabi
authors.affiliation: d Department of Bioengineering , University of Washington , Seattle , USA.
authors.forename: Ruikang
authors.initials: R
authors.lastname: Wang
authors.affiliation: a Department of Mechanical Engineering , University of Dundee , Dundee , UK ;
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Huang
mesh_terms: D005240:Feasibility Studies; D057086:High-Intensity Focused Ultrasound Ablation; D041623:Tomography, Optical Coherence; D014159:Transducers
keywords: Acoustic radiation force impulse; high intensity focused ultrasound; shearwave imaging; ultrasound