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Radiation therapy has long been known to be a very effective form of therapy in relieving symptoms and prolonging the life of patients with brain metastases. Novel developments in this field have allowed oncologists to improve on older forms of radiation therapy; these recent advances in radiotherapeutic techniques (stereotactic radiosurgery and hippocampal-avoidant whole brain radiation therapy) allow sparing of the healthy brain from receiving unnecessary radiation while delivering effective treatment to the metastases, thus improving the quality of life for surviving patients. Furthermore, multiple clinical trials have documented the increased loco-regional control in the brain when radiosurgery is interdigitated with immune check point inhibitors for treatment of melanoma brain metastases. Mild hyperthermia has been used for decades as an adjuvant to radiotherapy in the treatment of radiation resistant cancers; lately, however, thermal therapies, such as hyperthermia, cryoablation, radiofrequency ablation and high intensity focused ultrasound are being investigated to provide a new ablative approach to cancer while thermoacoustic imaging and thermometry have recently been proposed as new techniques for monitoring tissue temperature in the breast during ablation treatment. In addition, other hybrid techniques have emerged that combine ultrasounds with other forms of energy such as light to provide a more accurate diagnosis and enhance the efficacy of therapy for early and late stage cancers.

In recent years, there has been a progressive trend towards less invasive technologies for detecting metastatic cancer and guiding therapy with the goal of lower morbidity, better outcomes, and superior cosmetic appearance than traditional methods. This mini-review examines three emerging noninvasive hybrid technologies for detecting primary cancer, metastasis and guiding thermal therapy. Real-time thermoacoustic imaging and thermometry potentially provides valuable and critical feedback for guiding focused microwave ablation therapy. Label-free photoacoustic monitoring of cancer cells is a promising clinical diagnostic and theranostic tool for detecting metastatic disease and monitoring the response to therapy. Finally, immunologically targeted gold nanoparticles combined with photoacoustic imaging is able to detect lymph node micrometastasis in mouse models of breast cancer. These emerging techniques have the potential to improve the decision to biopsy, provide more accurate prognosis, and enhance the efficacy of therapy for early and late stage cancers.

Noninvasive thermal therapies for the treatment of breast cancer depend on accurate monitoring of tissue temperature to optimize treatment and ensure safety. This work describes a real-time system for 3-D thermoacoustic imaging and thermometry (TAI-TAT) for tracking temperature in tissue samples during heating. The study combines a 2.7-GHz microwave pulse generator with a custom 1.5-D 0.6 MHz ultrasound array for generating and detecting TA signals. The system is tested and validated on slabs of biological tissue and saline gel during heating. Calibration curves for relating the TA signal to temperature were calculated in saline gel (3.40%/°C), muscle (1.73%/°C), and fat (1.15%/°C), respectively. The calibrations were used to produce real-time, volumetric temperature maps at ~3-s intervals with a spatial resolution of approximately 3 mm. TAT temperature changes within a region of interest were compared to adjacent thermocouples with a mean error of 17.3%, 13.2%, and 20.4% for muscle, gel, and fat, respectively. The TAT algorithm was also able to simultaneously track temperatures in different tissues. With further development, noninvasive TAI-TAT may prove to be a valuable method for accurate and real-time feedback during breast cancer ablation therapy.

Aim: To determine whether differences in joint and tendon stiffness as measured by ultrasound shear wave elastography are present in breast cancer patients with aromatase inhibitor- associated arthralgias compared to age-comparable healthy control women. Methods: Postmenopausal women with stage I–III breast cancer who were taking adjuvant aromatase inhibitors and complained of joint pain were enrolled (n = 6). Postmenopausal women with no history of breast cancer, hormone treatment, or joint pain served as controls (n = 7). All subjects had bilateral hands and wrists evaluated by gray-scale and power Doppler ultrasound, and shear wave elastography ultrasound. Results: Patients with AI-associated arthralgias had significantly stiffer tendons than controls in the 1st extensor compartment (long axis; p = 0.001), 4th extensor compartment (long axis; p = 0.014), 3rd metacarpophalangeal joint (p = 0.002), the pooled values of the extensor compartments, both long (p = 0.044) and short axes (p = 0.035), and the pooled values for the metacarpophalangeal joints (p = 0.002). On ultrasound, the patients (but not controls) presented with hyperemia and increased tenosynovial fluid in the flexor and extensor tendon sheaths, and the median nerves were symptomatic and bifid; however, these differences were not statistically significant. Conclusions: This is the first study to identify increased tendon stiffness as a putative physiological characteristic of aromatase inhibitor–associated arthralgias. Future studies should determine whether increased tendon stiffness is a risk factor for the development of aromatase inhibitor–associated arthralgias, or a result of aromatase inhibitor treatment.

Acoustoelectric Imaging (AEI) is a disruptive technology that exploits an ultrasound (US) beam to transiently interact with physiologic or artificial currents, producing a radiofrequency signature detected by one or more surface electrodes. By rapidly sweeping the US beam and simultaneously detecting the acoustoelectric modulations, 4D current density images are generated at high spatial resolution determined by the ultrasound beam focus. The principle has been used for in vivo mapping of currents in the swine heart during the cardiac activation wave. When applied to the brain, transcranial acoustoelectric imaging (tABI) overcomes limitations with electroencephalography (EEG), which suffers from poor spatial resolution and inaccuracies due to blurring of electrical signals as they pass through the brain and skull, and, unlike fMRI and PET that measure slow metabolic or hemodynamic signals, tABI directly maps fast time-varying current within a defined brain volume at the mm and ms scales. This invited presentation will describe the underlying physics and mathematics of tABI, recent progress and challenges using numerical simulations and bench-top models, and its potential impact as a cutting-edge noninvasive modality for fast and accurate electrical brain mapping in humans.

Acoustoelectric (AE) effect is a basic physical interaction that focused ultrasound that alters the resistivity at the focal spot. Exploiting the AE effect, noninvasive AE imaging (nAEI) of resistivity distribution is investigated based on lead field theory. According to lead field theory, measured AE signal is of good spatial position property, which is sifted by focused ultrasound. Therefore, nAEI can form images directly without resorting to the inverse algorithm. A uniform phantom, 15% NaCl solution, and a nonuniform phantom, composed of 15% NaCl solution and fat, are imaged and discussed. In the experiment, both stimulating and recording electrodes are noninvasive, fixed on the boundary of the imaging chamber. A 1-MHz focused ultrasound transducer scans across the imaging chamber to make spatial sifting. For the uniform phantom with the fixed focal spot, the linear relationship between measured AE signal envelope and injected current signal is tested. In addition, taking resistivity distribution into consideration, the $yz$ -section images of uniform and nonuniform phantoms are presented. Compared to that of the uniform phantom, the resistivity distribution interface of nonuniform phantom can be obviously imaged and distinguished, which is verified by ultrasound pulse-echo imaging. Also, the 3-D slice images confirm that, even taking injected current into consideration, nAEI is potential for resistivity distribution. Finally, the experiment results are discussed and the reason is analyzed from the aspect of enhanced ultrasound pressure and current density induced by resistivity distribution. Both experimental and simulation results validate the feasibility of nAEI of resistivity distribution, and this paper potentially enhances the application of nAEI for cancer detection.

As a major application focus of vascular ultrasonography, the carotid artery has long been the subject of phantom design and procedure focus. It is therefore important to devise procedures that are minimally invasive and informative, initially using a physiologically accurate anthropomorphic phantom to validate the methodology. In this article, a novel phantom design protocol is presented that enables the efficient production of a pulsatile ultrasound phantom consisting of soft and vascular tissue mimics, as well as a blood surrogate fluid. These components when combined give the phantom high acoustic compatibility and lifelike mechanical properties. The phantom was developed using "at-home" purchasable components and 3D printing technology. The phantom was subsequently used to develop a 4D reconstruction algorithm of the pulsing vessel in MATLAB. In pattern with recent developments in medical imaging, the 4D reconstruction enables clinicians to view vessel wall motion in a 3D space without the need for manual intervention. The reconstruction algorithm also produces measured inner luminal areas and vessel wall thickness, providing further information relating to structural properties and stenosis, as well as elastic properties such as arterial stiffness, which could provide helpful markers for disease diagnosis. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Constructing a pulsatile ultrasound phantom model Support Protocol: Creating a vascular mimic mold Basic Protocol 2: Creating a 4D reconstruction from ultrasound frames.

Cardiac arrhythmias are caused by irregular activation in the heart. When pharmaceutical therapy fails, severe arrythmias are often treated with radiofrequency ablation. Existing methods to map electrical activation in the heart have poor spatial resolution or are invasive. We proposed Acoustoelectric Cardiac Imaging (ACI) to achieve non-invasive mapping of cardiac electrical activities with mm resolution. In this study, we used simulations to develop a reconstruction method for generating current density map from multi-channel ACI signals, and applied it to in-vivo ACI data from a swine heart with a resolution less than 5mm. With 5 leads at SNR from 55 to 80, the five differential signals could be combined in simulation to reconstruct the source current density map, with a correlation coefficient ≈ 0.74 for the x-component. For in-vivo data, we find that singular values decomposition provides a criterion for reconstruction.

Lipids play a vital role in brain function; Alzheimer's disease and aging are both associated with changes in lipid composition. Current methods for imaging and monitoring lipid deposits within the brain have poor spatial resolution, sensitivity, and/or penetration depth. Photoacoustic imaging (PA/PAI) allows for deep (>5mm) mapping of optical absorption_properties of biological tissue.; however, water and lipid have relatively weak optical absorption properties in the typical near-infrared window used for PAI (700-1000nm). This study investigates PAI in the short-wave infrared (SWIR) range (>1200nm) as a method to dramatically enhance lipid and water contrast. Due to multiple strong absorption peaks within this optical window, a three wavelength unmixing technique labeled Tri-λ Concentration Mapping (CM) is shown to have the ability to quantify lipid and water content several millimeters into tissue. Values of lipid and water concentration are calculated at voxels within sections of marbled bovine muscular tissue. Investigated regions of muscular meat show a bimodal distribution about 75% and 50% predicted water concentration. Calculated lipid regions at depths of ~5mm display a more precise distribution centered around a lipid concentration of 57.25%. This technique demonstrates the ability of SWIR PAI and Tri-λ CM to identify and characterize lipid content within tissue at depths greater than 5mm. The results of this study show promise of the technique for use in more advanced studies, such as tracking Alzheimer's disease progression within mice.

Transcranial Acoustoelectric Brain Imaging (tABI) combines ultrasound (US) with radiofrequency detection to map electrical currents in the brain at the mm and ms scales. To optimize tABI and ensure safe exposure, a feedback system is required to monitor and track the US beam through the skull. This study proposes combining a real-time neuronavigation system with acoustic modeling and MRI-based skull segmentation to optimize transcranial US delivery. We developed a testbed to estimate targeting accuracy and algorithms to optimally steer and focus US through the human skull for tABI and other applications that require US delivery to the brain. The optimized system is modeled to deliver focused US to brain targets through the skull with a FWHM of 3.88mm at the focus with steering at sub-mm accuracy, enabling safe and accurate guidance of tABI. The integrated system allows for a prediction of the US beam trajectory through the human skull with registration to clinical images for guidance and improving accuracy of real-time tABI.

As a real-time high resolution imaging modality, pulse echo ultrasound (US) is a common screening tool for breast, thyroid, and other types of cancer. However, US has low specificity for detecting cancer due to poor contrast in soft tissue. Hybrid US techniques like photoacoustic (PA) and thermoacoustic (TA) imaging provide additional sources of contrast for cancer detection but are still mostly independent research tools not readily available in the clinic. The goal of this study was to develop and demonstrate advantages of a real-time trimodal imaging system that combines US, PA, and TA integrated into a commercial US system. Our trimodal system provided real-time feedback on near-infrared absorbing contrast agents, water content, and acoustic backscatter for structure, all important contrast features for accurate diagnostics and feedback during thermal therapy. Real-time video of the pumped Methylene Blue (MB, 0.025% in diH2O) was captured at a velocity resolution of 280 mm/s. Spectrally probed MB resulted in unique PA spectral responses, as well as qualitative images in false colors. Thermometry revealed a correlation between the PA and TA signal responses and MB temperature each with $\mathrm{R}^{2}=0.99$ . By combining all three modalities, the system is capable of detecting different sources of contrast, including acoustic backscatter (US), optical (PA) and microwave (TA) absorption, and changes in temperature (PA and TA).

Improvised explosive devices (IEDs) have always been a major threat to personnel safety with continuous evolutions and new variants. Traditional methods for detecting IEDs, such as X-ray, have some drawbacks, so safe and efficient new detection techniques are highly desired. Microwave-induced thermoacoustic imaging (MITAI), being widely investigated for biomedical applications, is a promising candidate for detecting explosives embedded in high-water content materials due to its intrinsic advantages of nonionizing radiation, high contrast, and easy imaging procedure. Proof-of-concept demonstration is theoretically and experimentally carried out by successful detection of an explosive surrogate sample immersed in water. Good accordance between the experimental and simulation results validates the effectiveness of this approach. A parametric study of some key parameters is then performed to investigate their impact on detection efficiency and to evaluate the performance of a practical MITAI system for explosive detection.

We describe a new application of acoustoelectric imaging for non-invasive mapping of the location, magnitude and polarity of current generated by a clinical deep brain stimulation (DBS) device. Ultrasound at 1MHz was focused near the DBS device as short current pulses were injected across different DBS leads. A recording electrode detected the high-frequency acoustoelectric interaction signal. Linear scans of the US beam produced time-varying images of the magnitude and polarity of the induced current, enabling precise localization of the DBS leads within 0.70mm, a detection threshold of 1.75mA at 1 MPa and a sensitivity of 0.52 ± 0.07 μV/(mA*MPa). Monopole and dipole configurations in saline were repeated through a human skullcap. Despite 13.8-dB ultrasound attenuation through bone, acoustoelectric imaging was still >10dB above background with a sensitivity of 0.56 ± 0.10 μV/(mA*MPa). This proof-of-concept study indicates that selective mapping of lead currents through a DBS device may be possible using non-invasive acoustoelectric imaging.

Radiation therapy has long been known to be a very effective form of therapy in relieving symptoms and prolonging the life of patients with brain metastases. Novel developments in this field have allowed oncologists to improve on older forms of radiation therapy; these recent advances in radiotherapeutic techniques (stereotactic radiosurgery and hippocampal-avoidant whole brain radiation therapy) allow sparing of the healthy brain from receiving unnecessary radiation while delivering effective treatment to the metastases, thus improving the quality of life for surviving patients. Furthermore, multiple clinical trials have documented the increased loco-regional control in the brain when radiosurgery is interdigitated with immune check point inhibitors for treatment of melanoma brain metastases. Mild hyperthermia has been used for decades as an adjuvant to radiotherapy in the treatment of radiation resistant cancers; lately, however, thermal therapies, such as hyperthermia, cryoablation, radiofrequency ablation and high intensity focused ultrasound are being investigated to provide a new ablative approach to cancer while thermoacoustic imaging and thermometry have recently been proposed as new techniques for monitoring tissue temperature in the breast during ablation treatment. In addition, other hybrid techniques have emerged that combine ultrasounds with other forms of energy such as light to provide a more accurate diagnosis and enhance the efficacy of therapy for early and late stage cancers.

Acoustoelectric cardiac imaging (ACI) is a hybrid modality that exploits the interaction of an ultrasonic pressure wave and the resistivity of tissue to map current densities in the heart. This study demonstrates for the first time in vivo ACI in a swine model. ACI measured beat-to-beat variability ( n = 20 ) of the peak of the cardiac activation wave at one location of the left ventricle as 5.32 ± 0.74 µ V , 3.26 ± 0.54 m m below the epicardial surface, and 2.67 ± 0.56 m s before the peak of the local electrogram. Cross-sectional ACI images exhibited propagation velocities of 0.192 ± 0.061 m / s along the epicardial–endocardial axis with an SNR of 24.9 dB. This study demonstrates beat-to-beat and multidimensional ACI, which might reveal important information to help guide electroanatomic mapping procedures during ablation therapy.

In recent years, there has been a progressive trend towards less invasive technologies for detecting metastatic cancer and guiding therapy with the goal of lower morbidity, better outcomes, and superior cosmetic appearance than traditional methods. This mini-review examines three emerging noninvasive hybrid technologies for detecting primary cancer, metastasis and guiding thermal therapy. Real-time thermoacoustic imaging and thermometry potentially provides valuable and critical feedback for guiding focused microwave ablation therapy. Label-free photoacoustic monitoring of cancer cells is a promising clinical diagnostic and theranostic tool for detecting metastatic disease and monitoring the response to therapy. Finally, immunologically targeted gold nanoparticles combined with photoacoustic imaging is able to detect lymph node micrometastasis in mouse models of breast cancer. These emerging techniques have the potential to improve the decision to biopsy, provide more accurate prognosis, and enhance the efficacy of therapy for early and late stage cancers.

Thermoacoustic (TA) thermometry requires calibration to establish the relationship between the change in TA signal with the change in temperature. Previous studies have used a priori slopes values (i.e. TA signal vs temperature), typically determined experimentally from previously performed standard calibrations. However, standard calibration requires more than one test and is not robust to changing sample orientation or composition. The goal of this study is to compare a previously studied self-calibration method to the standard calibration method in estimating temperature using real-time 3D TA thermometry in bovine udder tissue kept in the same orientation for both methods. The self-calibration and standard methods estimated temperatures of the udder sample during localized heating with a normalized root mean square errors (NRMSE) of 7.1% and 8.4%, respectively. The predicted temperatures produced by the self-calibration method were less variable than the standard method. Overall, the qualitative and quantitative results comparing predicted change in temperature suggested that self-calibration is as accurate as standard calibration with less variability and less experimentation. These advantages point to self-calibration being a more preferred method to provide temperature predictions for feedback control in future breast cancer ablation therapy.

Cardiac ventricular arrhythmias - electrical activation abnormalities that can result in sudden cardiac death - are difficult to manage with ablative treatment as many have complex, non-sustained 4D (volume over time) activation patterns that cannot be fully captured by existing electroanatomic mapping systems. In this study, we describe the use of acoustoelectric cardiac imaging (ACI) for high resolution, beat-to-beat mapping of electrical dynamics in an in vivo swine model. Beat-to-beat variability was tracked in the swine; the variation in the peak magnitude, peak myocardial location, peak time, and SNR across 20 beats were measured as 5.27 ± 0.68 µV, 3.32 ± 0.41 mm from the epicardium, -2.73 ± 0.38 ms from the peak EGM, and 25.3 ± 8.1 dB, respectively. Additionally, propagation velocity was tracked across four pigs and was calculated as 0.153 ± 0.108 m/s along the endocardial-epicardial axis and 0.123 ± 0.098 m/s along the apicobasal axis. This study suggests that ACI has the potential to improve ablation treatment of arrhythmias through higher resolution, beat-to-beat pre-ablation mapping and characterization of ventricular arrhythmias.

Transcranial ultrasound (US) is impeded by attenuation and aberration of the pressure wave induced by the skull. One method for correcting for these errors is through time-reversal of the transmit US waveform. However, robust innate acoustic reflectors, which are typically necessary for time-reversal US, do not exist in the brain. Some methods exist to either create or embed reflectors or US emitters at target locations. However, these methods lack in either specificity, accuracy or are invasive. In this paper we explore the use of acoustoelectric imaging (AEI) in order to utilize an electrical current as a point for performing time-reversal aberration corrections. We modeled a section of human skull and brain in MatLab and used the k- Wave package to simulate transcranial US propagation. A monopole was modeled in the brain in order to simulate AEI for performing time-reversal and correct for focal aberrations. Our AEI TR results were compared to TR delays determined through direct detection of the pressure wave itself for validation. Both TR methods resulted in very similar pressure profiles at the target focal point and outperformed an uncorrected delay profile in lateral FWHM (1.17 vs 3.4), peak amplitude (0.41MPa vs 0.24MPa), and side lobe power (~-27dB vs ~17dB). Collectively, these results advocate the use of AEI for utilizing current sources in the brain, natural or implanted, as a source for performing TR-based aberration corrections and enhancing transcranial US focus.

Objective: New innovations in deep brain stimulation (DBS) enable directional current steering – allowing more precise electrical stimulation of the targeted brain structures for Parkinson's disease, essential tremor and other neurological disorders. While intra-operative navigation through MRI or CT approaches millimeter accuracy for placing the DBS leads, no existing modality provides feedback of the currents as they spread from the contacts through the brain tissue. In this study, we investigate transcranial acoustoelectric imaging (tAEI) as a new modality to non-invasively image and characterize current produced from a directional DBS lead. tAEI uses ultrasound (US) to modulate tissue resistivity to generate detectable voltage signals proportional to the local currents. Approach: An 8-channel directional DBS lead (Infinity 6172ANS, Abbott Inc) was inserted inside three adult human skulls submerged in 0.9% NaCl. A 2.5MHz linear array delivered US pulses through the transtemporal window and focused near the contacts on the lead, while a custom amplifier and acquisition system recorded the acoustoelectric (AE) interaction used to generate images. Main Results: tAEI detected monopolar current with stimulation pulses as short as 100 µs with an SNR ranging from 10 – 27 dB when using safe US pressure (mechanical indices

Wireless communications from an airborne device to an underwater receiver is challenging because the conductivity of water severely dampens the magnitude of electromagnetic waves in the spectrum commonly used for wireless applications. In this paper, microwave-induced thermoacoustic communications (TAC), a hybrid technique for wireless communications, is investigated and experimentally demonstrated to provide a potential solution to this deficiency. TAC is based on the thermoacoustic effect and directly converts electromagnetic energy in air into acoustic energy in water. Experimental demonstration of TAC is reported by successful wireless information transmission from a microwave antenna in air to an acoustic transducer in water. Bench-top TAC experiments are combined with an analytical model to study the influences of pivotal design parameters on the performance of TAC. The experiments and theoretical analysis suggest that TAC might lead to a new paradigm of air-to-underwater wireless communications.

In the past 2 decades, sonoelastography has been progressively used as a tool to help evaluate soft-tissue elasticity and add to information obtained with conventional gray-scale and Doppler ultrasonographic techniques. Recently introduced on clinical scanners, shear-wave elastography (SWE) is considered to be more objective, quantitative, and reproducible than compression sonoelastography with increasing applications to the musculoskeletal system. SWE uses an acoustic radiation force pulse sequence to generate shear waves, which propagate perpendicular to the ultrasound beam, causing transient displacements. The distribution of shear-wave velocities at each pixel is directly related to the shear modulus, an absolute measure of the tissue's elastic properties. Shear-wave images are automatically coregistered with standard B-mode images to provide quantitative color elastograms with anatomic specificity. Shear waves propagate faster through stiffer contracted tissue, as well as along the long axis of tendon and muscle. SWE has a promising role in determining the severity of disease and treatment follow-up of various musculoskeletal tissues including tendons, muscles, nerves, and ligaments. This article describes the basic ultrasound physics of SWE and its applications in the evaluation of various traumatic and pathologic conditions of the musculoskeletal system.

This study describes real-time thermoacoustic imaging (TAI) and thermometry (TAT) for feedback during thermal therapies. The system uses a linear ultrasound array and imaging system to noninvasively estimate temperature. The system was validated in gel phantoms, muscle and fat tissue samples. A mean error between 10 and 20% per degree was observed for estimating temperature. A TAT system using a single element ultrasound probe was also integrated with a focused microwave therapy (FMT) setup for generating local heating, leading to a mean error of 1.18±0.87 °C compared to thermocouples placed near the region of interest. The results support the long-term goal of developing a closed-loop platform for image-guided ablation therapy for breast cancer.

A broad spectrum of brain disorders—from epilepsy to depression – are characterized by abnormal electrical conduction. Often, electroencephalography (EEG) is incapable of recording the complex dynamics behind these disorders due to poor spatial resolution. We are proposing transcranial acoustoelectric brain imaging (tABI) to overcome these limitations. tABI may be able to accurately resolve deep neuronal currents with high spatial resolution ( 50 mm below the phantom surface with an axial resolution of ~3mm at 0.6 MHz. Current detection limits through the skull at biologically safe US intensities were

The efficacy of deep brain stimulation (DBS) for relieving motor symptoms from Parkinson’s disease or essential tremor is highly dependent on accurate placement of the electrode. New current-steering electrodes can reduce the burden of placement by directing the stimulating currents toward the target locations. However, no imaging modality exists in the clinic or operating room to provide feedback of the currents as they are delivered/steered from the contacts. In this study we investigate the prospects of high resolution, transcranial acoustoelectric imaging (AEI) as a method for non-invasively imaging DBS currents. A DBS electrode was inserted into a brain gel phantom inside a human skull and monopoles were generated at individual contacts. A linear array ultrasound (US) transducer was coupled to the temporal window and focused toward the DBS electrode to induce AE signals proportional to the time-varying current densities. The AE signals using an injected current of 11 mA and focal pressures of 2.04 MPa were detected with SNRs between 716 dB, mean accuracy along the length of the electrode of 0.35 mm, radial separation of segmented contacts in a ring-triplet of 1.21 mm, mean monopole FWHMs of 3.54 mm, and a sensitivity of 0.283 pVfmA/MPa. Our results advocate AEI as a promising tool for providing non-invasive, high resolution feedback of the spread of current from a directional DBS electrode with potential roles in enhancing placement of the electrode and chronically monitoring the integrity of the stimulation.

Though atrial fibrillation (AF) is a growing public health problem, electrical characterization of the disease with electrocardiography (ECG) is inadequate due to poor spatial resolution. The goal of this study was to investigate propagation of the cardiac activation wave in a healthy swine model using acoustoelectric cardiac imaging (ACI), a noninvasive mapping technology that combines ultrasound with electrical recording to overcome limitations with standard ECG. Real-time 4D ACI with a custom 2D 0.6 MHz matrix US array demonstrated conduction velocities of 2.21 m/s, validated with standard epicardial recording. ACI FWHM at a single timepoint, a measure related to the resolution of ACI in imaging the volume of activation at peak ECG signal, was 7.31 mm, 7.63 mm, and 6.23 mm in the depth, lateral, and elevational directions, respectively. SNR of ACI was 21dB at peak activation. ACI signals tracked through a 4D volume demonstrated appropriate propagation of the signal from base to apex and from endocardium to epicardium. This study demonstrated the potential for this technology to noninvasively map arrhythmias, such as AF, at high resolution.

This paper reports studies on EM characterization, instrumentation development and proof of concept experimental evaluation of a novel system capable of focused microwave therapy (FMT) at 915 MHz integrated with thermoacoustic imaging (TAI). The combined TAI-FMT prototype assists accurate dielectric property mapping, precise temperature prediction and treatment monitoring through TA thermometry feedback for adaptive beamforming. A 32-element array prototype is simulated and focusing is evaluated through time reversal. Initial experimental results using a 4-element FMT system showed 2°C accuracy in temperature prediction.

Accurate 3-D mapping of multiple bioelectric sources in nerve fibers with high spatial resolution is challenging for the diagnosis and treatment of a variety of neural abnormalities. Ultrasound current source density imaging exploits the acoustoelectric (AE) effect, an interaction between electrical current and acoustic pressure waves propagating through a conducting material, and has distinct advantages over conventional electrophysiology (i.e., without ultrasound) for mapping electrical current flow in tissue. Ultrasound current source density imaging and two complementary Wheatstone bridge circuits were used to simultaneously detect two separate current flows induced in tissue phantoms. It has been found that the addition and subtraction of AE signals acquired by two circuits are independent components, regardless of whether the two sources are positioned at the same or different depths. In the ultrasound field, the AE signal from the bridge circuits is stronger, with a higher signal-to-noise ratio, than without a bridge circuit. Both experimental and simulated AE images depend on the magnitude and direction of the current, as well as the geometry (shape and thickness) and location of the current sources in the ultrasound field (2.25-MHz transducer). The experimental results are consistent with simulations consisting of multiple current sources. Real-time 3-D ultrasound current source density images of multiple current flows co-registered with convention pulse echo ultrasound potentially facilitate monitoring of neurologic disorders.

Objective. This study employs a human head model with real skull to demonstrate the feasibility of transcranial acoustoelectric brain imaging (tABI) as a new modality for electrical mapping of deep dipole sources during treatment of epilepsy with much better resolution and accuracy than conventional mapping methods. Approach. This technique exploits an interaction between a focused ultrasound (US) beam and tissue resistivity to localize current source densities as deep as 63 mm at high spatial resolution (1 to 4 mm) and resolve fast time-varying currents with sub-ms precision. Main results. Detection thresholds through a thick segment of the human skull at biologically safe US intensities was below 0.5 mA and within range of strong currents generated by the human brain. Significance. This work suggests that 4D tABI may emerge as a revolutionary modality for real-time high-resolution mapping of neuronal currents for the purpose of monitoring, staging, and guiding treatment of epilepsy and other brain disorders characterized by abnormal rhythms.

Thermoacoustic (TA) imaging is a modality where pulsed microwaves are used to generate ultrasound waves in tissue, which are highly correlated with temperature. This study uses a self-calibration approach to improve the estimation of temperature using 3D real-time TA thermometry in porcine tissue during localized heating. The self-calibration method estimated temperatures at eight embedded thermocouple locations with a normalized root-mean-square error of 3.25 ± 2.08 % . The results demonstrate that the method has the suitable accuracy and resolution to provide feedback control for breast cancer ablation therapy.