John Kook

Acoustic hemostasis of porcine superficial femoral artery: Simulation and in-vivo experimental studies

In-vivo focused ultrasound studies were computationally simulated and conducted experimentally with the aim of occluding porcine superficial femoral arteries (SFA) via thermal coagulation. A multi-array HIFU applicator was used which electronically scanned multiple beam foci around the target point. The spatio-temporally averaged acoustic and temperature fields were simulated in a fluid dynamics and acousto-thermal finite element model with representative tissue fields, including muscle, vessel and blood. Simulations showed that with an acoustic power of 200W and a dose time of 60s, perivascular tissue reached 91°C; and yet blood reached a maximum 59°C, below the coagulation objective for this dose regime (75°C). Per simulations, acoustic-streaming induced velocity in blood reached 6.1cm/s. In in-vivo experiments, several arteries were treated. As simulated, thermal lesions were observed in muscle surrounding SFA in all cases. In dosing limited to 30 to 60 seconds, it required 257W to provide occlusion (o...

A method for automated detection of high intensity focused ultrasound (HIFU) beams in 3D space

In HIFU therapy, it is critical to determine the HIFU beam path and its focus before the therapy-level dose is administered into tissue. In this work, we adapted echo-strain methods to construct the HIFU beam information and developed an automated detection method using 3D data segmentation, beam trajectory estimation, and focal point localization. A series of 3D volume ultrasound data acquisitions was interleaved in time with a testing pulse with low intensity (Isppa ∼200 W/cm2) and small duty cycle (4.7%). 3D echo-strain was derived from tissue apparent displacement and was segmented based on a volume growing technique. Our methods were tested on tissue mimicking phantom materials with acoustic properties similar to human muscle. Testing was done to show repeatability and accuracy for HIFU beams focused at varying depths and steering angles. The error from thirteen (13) different focal positions was 5.7 ± 2.3 mm (mean ± std) in 3D space, with error defined as the Euclidian distance between the estimated focal location and the experimentally determined focal location. Experimental location was determined via a thermocouple embedded in the phantom, and the location of the thermocouple was determined by the highest temperature rise location when moving the HIFU 2D array transducer through a 3D volume using a short (1 second) and low power (Isppa ∼40W/cm2) focused beam sonication. It was concluded that an automated HIFU beam focal point detection method was developed and provides accurate localization of the HIFU beam focus.

Acoustic hemostasis device for automated treatment of bleeding in limbs

A research prototype automated image-guided acoustic hemostasis system for treatment of deep bleeding was developed and tested in limb phantoms. The system incorporated a flexible, conformal acoustic applicator cuff. Electronically steered and focused therapeutic arrays (Tx) populated the cuff to enable dosing from multiple Txs simultaneously. Similarly, multiple imaging arrays (Ix) were deployed on the cuff to enable 3D compounded images for targeting and treatment monitoring. To affect a lightweight cuff, highly integrated Tx electrical circuitry was implemented, fabric and lightweight structural materials were used, and components were minimized. Novel cuff and Ix and Tx mechanical registration approaches were used to insure targeting accuracy. Two-step automation was implemented: 1) targeting (3D image volume acquisition and stitching, Power and Pulsed Wave Doppler automated bleeder detection, identification of bone, followed by closed-loop iterative Tx beam targeting), and 2) automated dosing (auto-selection of arrays and Tx dosing parameters, power initiation and then monitoring by acoustic thermometry for power shut-off). In final testing the device automatically detected 65% of all bleeders (with various bleeder flow rates). Accurate targeting was achieved in HIFU phantoms with end-dose (30 sec) temperature rise reaching the desired 33-58°C. Automated closed-loop targeting and treatment was demonstrated in separate phantoms.A research prototype automated image-guided acoustic hemostasis system for treatment of deep bleeding was developed and tested in limb phantoms. The system incorporated a flexible, conformal acoustic applicator cuff. Electronically steered and focused therapeutic arrays (Tx) populated the cuff to enable dosing from multiple Txs simultaneously. Similarly, multiple imaging arrays (Ix) were deployed on the cuff to enable 3D compounded images for targeting and treatment monitoring. To affect a lightweight cuff, highly integrated Tx electrical circuitry was implemented, fabric and lightweight structural materials were used, and components were minimized. Novel cuff and Ix and Tx mechanical registration approaches were used to insure targeting accuracy. Two-step automation was implemented: 1) targeting (3D image volume acquisition and stitching, Power and Pulsed Wave Doppler automated bleeder detection, identification of bone, followed by closed-loop iterative Tx beam targeting), and 2) automated dosing (auto-...