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The radiation force balance (RFB) is a widely used method for measuring acoustic power output of ultrasonic transducers. The reflecting cone target is attractive due to its simplicity and long-term stability, at a reasonable cost. However, accurate measurements using this method depend on the alignment between the ultrasound beam and cone axes, especially for highly focused beams utilized in therapeutic applications. With the advent of Dual-Mode Ultrasound Arrays (DMUA) for imaging and therapy, image-guided measurements of acoustic output using the RFB method can be used to improve the measurement accuracy. In this paper, we describe an image-guided RFB measurement of focused DMUA beams using a widely used commercial instrument. DMUA imaging is used to optimize the alignment between the acoustic beam and reflecting cone axes. In addition to image-guided alignment, DMUA echo data is used to track the displacement of the cone, which provides auxiliary measurement of acoustic power. Experimental results using a DMUA prototype with f

Carotid bodies (CBs) are chemoreceptors that monitor and register changes in the blood, including the levels of oxygen, carbon dioxide, and pH, and regulate breathing. Enhanced activity of CBs was shown to correlate with a significant elevation in the blood pressure of patients with hypertension. CB removal or denervation were previously shown to reduce hypertension. Here we demonstrate the feasibility of a dual-mode ultrasound array (DMUA) system to safely ablate the CB in vivo in a spontaneously hypertensive rat (SHR) model of hypertension. DMUA imaging was used for guiding and monitoring focused ultrasound (FUS) energy delivered to the target region. In particular, 3D imaging was used to identify the carotid bifurcation for targeting the CBs. Intermittent, high frame rate imaging during image-guided FUS (IgFUS) delivery was used for monitoring the lesion formation. DMUA imaging provided feedback for closed-loop control (CLC) of the lesion formation process to avoid overexposure. The procedure was tolerated well in over 100 SHR and normotensive rats that received unilateral and bilateral treatments. The measured mean arterial pressure (MAP) exhibited measurable deviation from baseline 2–4 weeks post IgFUS treatment. The results suggest that the direct unilateral FUS treatment of the CB might be sufficient to reduce the blood pressure in hypertensive rats and justify further investigation in large animals and eventually in human patients.

Transcranial focused ultrasound (tFUS) is a promising approach for the treatment of neurological disorders. It has proven useful in several clinical applications, with promising outcomes reported in the recent literature. Furthermore, it is currently being investigated in a range of neuromodulation (NM) and ablative applications, including epilepsy. In this application, tFUS access through the temporal window is the key to optimizing the treatment safety and efficacy. Traditional approaches have utilized transducers with low operating frequencies for tFUS applications. Modern array transducers and driving systems allow for more intelligent use of the temporal window by exploiting the spatio-spectral transmission bandwidth to a specified target or targets within the brain. To demonstrate the feasibility of this approach, we have investigated the ultrasound reflection and transmission characteristics for different access points within the temporal window of human skull samples ex vivo. Different transmit-receive (Rx) configurations are used for characterization of the spatio-spectral variability in reflection and transmission through the temporal window. In this article, we show results from a dual-piston transducer set up in the frequency range of 2-7 MHz. Broadband pulses as well as synthesized orthogonal frequency division multiplexed (OFDM) waveforms were used. The latter was used to improve the magnitude and phase measurements in 100-kHz subbands within the 2-7 MHz spectral window. A temperature-controlled water bath was used to characterize the change in reflection and transmission characteristics with temperature in the 25°C-43°C range. The measured values of the complex reflection and transmission coefficients exhibited significant variations with space, frequency, and temperature. On the other hand, the measured transmission phase varied more with location and frequency, with smaller sensitivity to temperature. A measurement-based hybrid angular spectrum (HAS) simulation through the human temporal bone was used to demonstrate the dependence of focusing gain on the skull profile and spatial distribution of change of speed of sound (SOS) at different skull temperatures.

Tissue Harmonic Imaging (THI) is a well studied method that reconstructs images using second harmonic echo data. However, the use of a band-pass filter to extract harmonic components reduces the signal bandwidth and hence degrades the axial resolution. Pulse Inversion (PI) is a promising technique that overcomes the issue of bandwidth and preserves axial resolution, but introduction of image artifacts due to tissue motion makes this method somewhat undesirable for processing in vivo data. In order to address the above mentioned issues, we have proposed a data-driven quadratic Volterra filter capable of capturing specific nonlinear frequency interactions to selectively enhance image quality without losing spatial resolution. The kernel synthesis is a multi-step procedure which analyzes the individual SVD decomposed kernels, filters them with 2D Gaussian filters to retain the desired frequency interactions and finally sums up the kernels coherently to reclaim the bandwidth. An in vivo dataset with and without contrast agents is used to demonstrate image quality improvement with no loss of axial resolution. The reconstructed nonlinear images also report enhancement in specificity of the heterogeneous perfusion of the tumor. Additionally, the proposed method is observed to reject acoustic artifacts and improve lateral resolution.

Purpose High-intensity focused ultrasound (HIFU) is a potential noninvasive thermal ablation method for the treatment of peripheral artery disease. Dual-mode ultrasound arrays (DMUA) offer the possibility of simultaneous imaging and treatment. In this study, safety and feasibility of femoral artery robot-assisted HIFU/DMUA therapy was assessed. Methods In 18 pigs (∼50kg), angiography and diagnostic ultrasound were used to visualize diameter and blood flow of the external femoral arteries (EFA). HIFU/DMUA-therapy was unilaterally applied to the EFA dorsal wall using a 3.5 MHz, 64-element transducer, closed-loop-control was used to automatically adjust energy delivery to control thermal lesion formation. A continuous lesion of at least 25 mm was created by delivering 6–8 HIFU shots per imaging plane perpendicular to the artery spaced 1 mm apart. Directly after HIFU/DMUA-therapy and after 0, 3 or 14 days follow up, diameter and blood flow were measured and the skin was macroscopically examined for thermal damage. The tissue was removed for histological analysis. Results No complications were observed. The most frequently observed treatment effect was formation of scar tissue, predominantly in the adventitia and the surrounding tissue. No damage to the endothelium or excessive damage of the surrounding tissue was observed. There was no significant decrease in the mean arterial diameter after HIFU/DMUA-therapy. Conclusion HIFU/DMUA therapy successfully targeted the vessel walls of healthy porcine arteries, without causing endothelial damage or other vascular complications. Therefore, this therapy can be safely applied to healthy arterial walls in animals. Future studies should focus on safety and dose-finding in atherosclerotic diseased arteries.

Background Transcranial focused ultrasound (tFUS) at low intensities has been reported to directly evoke responses and reversibly inhibit function in the central nervous system. While some doubt has been cast on the ability of ultrasound to directly evoke neuronal responses, spatially-restricted transcranial ultrasound has demonstrated consistent, inhibitory effects, but the underlying mechanism of reversible suppression in the central nervous system is not well understood. Objective/hypothesis In this study, we sought to characterize the effect of transcranial, low-intensity, focused ultrasound on the thalamus during somatosensory evoked potentials (SSEP) and investigate the mechanism by modulating the parameters of ultrasound. Methods TFUS was applied to the ventral posterolateral nucleus of the thalamus of a rodent while electrically stimulating the tibial nerve to induce an SSEP. Thermal changes were also induced through an optical fiber that was image-guided to the same target. Results Focused ultrasound reversibly suppressed SSEPs in a spatially and intensity-dependent manner while remaining independent of duty cycle, peak pressure, or modulation frequency. Suppression was highly correlated and temporally consistent with in vivo temperature changes while producing no pathological changes on histology. Furthermore, stereotactically-guided delivery of thermal energy through an optical fiber produced similar thermal effects and suppression. Conclusion We confirm that tFUS predominantly causes neuroinhibition and conclude that the most primary biophysical mechanism is the thermal effect of focused ultrasound.

This article describes the basic principles of ultrasound thermography (UST) and its real-time implementation using graphics processing unit (GPU)-enabled software architecture. In medicine, the term thermography is mostly associated with heat-sensing infrared cameras for recording surface temperature changes. In this article, we use this term to describe the qualitative noninvasive imaging of tissue temperature change using any imaging modality. Examples of these modalities include microwave radiometry, magnetic resonance imaging (MRI), US imaging, and photoacoustic tomography. Of these imaging methods, US and MR are the most widely investigated. Table S1 in "Real-Time Thermography in Medicine" lists some US- and MRbased methods for tissue thermography reported in recent literature.

Dual-mode ultrasound arrays (DMUAs) have been used for monitoring and delivery of transcranial focused ultrasound (tFUS) in small-animal models in vivo. Synthetic-aperture (SA) imaging can be used for stereotaxic guidance, while high frame rate imaging modes, such as single-transmit focus (STF) imaging, can provide feedback for thermal and mechanical closed-loop control of lesion formation and neuromodulation. The objective of this study is to demonstrate the feasibility of DMUA guidance and control of tFUS application in a realistic human head phantom. A DMUA was used to image through the temporal bone of the phantom in SA and STF modes. Results from the SA imaging mode demonstrates the ability to image fine targets such as vessels with aneurysms. Additionally, subaperture processing of SA data shows it is possible to reduce reverberation. Results from the STF imaging mode show the feasibility of speckle tracking using transranial echo data, both with and without subaperture processing. These results demonstrate the value of judicial design of subaperture beamforming for identifying tissue structure and improving speckle statistics for high fidelity thermography and elastography. Results from tFUS-monitoring experiments will be given.