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We present the first transcranial mapping of temperature with Dual-Mode Ultrasound Arrays (DMUAs), with subsequent validation of transskull ultrasound therapy guidance and monitoring in a small rodent model. Experiments were conducted in sacrificed rats, utilizing the custom designed DMUA platform manufactured in our laboratory. First, careful examination of DMUA imaging through the skull was conducted, where a fine 50μm wire was embedded within the brain tissue. Second, anatomical landmarks were visualized by co-registering two volumes, volume of synthetic aperture (SA) images acquired with DMUA and a 9.4T MRI volume acquired in live rats prior to the sacrifice. Third, subtherapeutic shot delivery through the skull was tested, where a set of five varying intensity shots were deposited below the skull surface. Shot delivery and temperature monitoring were performed with DMUA, and compared with the thermocouple data acquired close to the therapeutic focus. This study was an exploratory effort to validate u...

The recursive echo strain filter (RESF) model is presented as a new echo shift-based ultrasound temperature estimation model. The model is shown to have an infinite impulse response (IIR) filter realization of a differentitor-integrator operator. This model is then used for tracking sub-therapeutic temperature changes due to high intensity focused ultrasound (HIFU) shots in the hind limb of the Copenhagen rats in vivo. In addition to the reconstruction filter, a motion compensation method is presented which takes advantage of the deformation field outside the region of interest to correct the motion errors during temperature tracking. The combination of the RESF model and motion compensation algorithm is shown to greatly enhance the accuracy of the in vivo temperature estimation using ultrasound echo shifts.

We present the results from an ultrasound-guided focused ultrasound platform designed to perform real-time monitoring and control of lesion formation. Real-time signal processing of echogenicity changes during lesion formation allows for identification of signature events indicative of tissue damage. The detection of these events triggers the cessation or the reduction of the exposure (intensity and/or time) to prevent overexposure. A dual mode ultrasound array (DMUA) is used for forming single- and multiple-focus patterns in a variety of tissues. The DMUA approach allows for inherent registration between the therapeutic and imaging coordinate systems providing instantaneous, spatially-accurate feedback on lesion formation dynamics. The beamformed RF data has been shown to have high sensitivity and specificity to tissue changes during lesion formation, including in vivo. In particular, the beamformed echo data from the DMUA is very sensitive to cavitation activity in response to HIFU in a variety of modes, e.g. boiling cavitation. This form of feedback is characterized by sudden increase in echogenicity that could occur within milliseconds of the application of HIFU (see http://youtu.be/No2wh-ceTLs for an example). The real-time beamforming and signal processing allowing the adaptive control of lesion formation is enabled by a high performance GPU platform (response time within 10 msec). We present results from a series of experiments in bovine cardiac tissue demonstrating the robustness and increased speed of volumetric lesion formation for a range of clinically-relevant exposures. Gross histology demonstrate clearly that adaptive lesion formation results in tissue damage consistent with the size of the focal spot and the raster scan in 3 dimensions. In contrast, uncontrolled volumetric lesions exhibit significant pre-focal buildup due to excessive exposure from multiple full-exposure HIFU shots. Stopping or reducing the HIFU exposure upon the detection of such an events has been shown to produce precisely controlled lesions with no evidence of overexposure even when fast raster scan of volumetric HIFU lesion is attempted. We also show that the DMUA beamformed echo data is capable of detecting underexposure condition at the target location, e.g. due to the obstruction of the HIFU beam resulting from cavitation activity in the path of the beam. The results clearly demonstrate the advantage of adaptive lesion formation in reducing the treatment time while confining the tissue damage to the target volume.

Atherosclerosis is a chronic vascular disease affecting large and medium sized arteries. Several treatment options are already available for treatment of this disease. Targeting atherosclerotic plaques by high intensity focused ultrasound (HIFU) using dual mode ultrasound arrays (DMUA) was recently introduced in literature. We present a finite difference time domain (FDTD) simulation modeling of the wave propagation in heterogeneous medium from the surface of a 3.5 MHz array prototype with 32-elements. After segmentation of the ultrasound image obtained for the treatment region in-vivo, we integrated this anatomical information into our simulation to account for different parameters that may be caused by these multi-region anatomical complexities. The simulation program showed that HIFU was able to induce damage in the prefocal region instead of the target area. The HIFU lesions, as predicted by our simulation, were well correlated with the actual damage detected in histology.

We present the system architecture of an integrated Ultrasound-guided High Intensity Focused Ultrasound (USgHIFU) system for image-guided surgery and temperature tracking in vivo. The system is capable of operating with multiple frontends. Current implementation has a SonixRP for imaging and a custom designed dual mode ultrasound array (DMUA) system (32Tx/32Rx) for imaging/therapy. The highlights of the system include a fully-programmable, multiple data stream capable data processing engine, and an arbitrarily programmable high power array driver that is able to synthesize complex beam patterns in space and time. The data processing engine features a pipeline-style design that can be programmed on-the-fly by re-arranging the pre-verified GPU-accelerated high performance pipeline blocks, which cover an extensive range from basic functions such as filtering to specialized processing like speckle tracking. Furthermore, the pipeline design also has the option of bringing in MATLAB (Mathworks, Natick, MA, US) ...

Objective of this study was to noninvasively extract quantitative estimates of heart tissue absorption before and after lesion formation. To extract tissue absorption, ultrasound temperature maps were reconstructed from single transmit focus (STF) images acquired with a 3.5MHz Dual-Mode Ultrasound Array (DMUA). Initial heating rate is estimated before and after therapeutic lesion formation through a delivery of a subtherapeutic intensity shot in ex vivo bovine heart tissue. Changes in heating rate are documented for a subset of five subtherapeutic shot intensities. Additionally, repeatability is demonstrated for before and after measurement of the initial heating rate. Careful gross examination of tissue was performed for every location where an absorption measurement was made.