A Prototype for a Palm-sized Photoacoustic Sensing Unit

Photoacoustic sensing and imaging techniques have experienced tremendous research progress, ranging from fundamental physics and methodologies to various biomedical and clinical applications in recent years. However, the state-of-art photoacoustic systems still suffer from high cost and bulky size, which hinders their potential applications for low-cost and portable diagnostics. In this paper, we propose the design for a palm-size photoacoustic sensor prototype. The design’s lower cost and smaller size would allow it to be used for portable photoacoustic sensing applications like oxygen saturation and temperature. By converting the high-frequency photoacoustic pulse signal to low-frequency photoacoustic DC signal through a rectifier circuit, the proposed photoacoustic receiver could potentially reduce the cost and device size efficiently, compared with the conventional highspeed data acquisition card interfaced with computer solutions. Preliminary testing is demonstrated to show its feasibility for photoacoustic sensing applications.

Piezoelectric Micromachined Ultrasonic Transducers for Photoacoustic Imaging: Modeling and Simulation of Structural Parameters on Receive Performance

Introduction: Although many piezoelectric micromachined ultrasonic transducers (pMUTs) with different structures have been presented and fabricated for photoacoustic imaging (PAI), most of them are lack of systemic analysis and optimizations of design parameters. It is of important to explore the internal physical mechanisms and corresponding cause-effect relationships of the receive performance of pMUTs with different structures. The purpose of this study is to present a novel numerical method for an efficient design of the AlN-based pMUT for application in PAI system. Methods: A planar and two curved (dome-shaped and concave) structures of pMUTs based on aluminum nitride (AlN) were modeled numerically in this study. For each pMUT, the performance of receive sensitivity was simulated systemically using the finite elements analysis (FEA). Moreover, the physical parameters of three structureswere analyzed in detail, such as the radius of curvature, the height of SiO2, the height of AlN and the height of polyimide. Results: The obtained results show that the receive performance of three structures in water or air could be ordered as: the dome-shaped > the concave > the planar. Further, several valuable findings of this study would be used to design pMUTs so as to achieve better receive performance, such as: (a) for an optimum radius of curvature almost exists for any curved pMUT, (b) a thinner supporting layer means a better receive performance, (c) the piezoelectric layer in three structures have an optimum thickness, and (d) the height of polyimide affects little the receive performance in all structures. Conclusions: For a pMUT-based ultrasound sensor in photoacoustic imaging (PAI), the dome-shaped pMUT has a better receive sensitivity than that of the planar structure and the concave structure, whose physical parameters combining the work frequency could be optimized efficiently with a numerical method.

Imaging of myocardial infarction with thermoacoustic tomography: An ex vivo study

In the present study, we evaluated the feasibility of thermoacoustic tomography (TAT) for imaging of ex vivo mouse hearts with myocardial infarction. A circular scanning TAT system with an unfocused transducer was used to recover the dielectric property distribution of normal andmyocardial infarcted mouse heart tissues. The applicability of this myocardial infarction imaging system was validated using a model of myocardial infarction in two Sprague-Dawley rats and verified through comparison with magnetic resonance imaging (MRI). TAT results not only indicated the location and ischemia and the extent of myocardial ischemia (MI), but also showed good imaging contrast between infarcted and normal myocardium without the use of contrast agent. The experimental results suggest that TAT may provide a unique opportunity to enable real-time precision imaging to determine the site of injury intraoperatively

Thermoacoustic imaging of human finger joints and bones

In this study, we explore a new application of thermoacoustic tomography (TAT) for imaging human finger joints and bones. Three volunteers’ finger joints and bones were visualized with satisfying image contrast and spatial resolution by a TAT scanner. The recovered TAT images revealed apparent microwave absorption differences between the joint cavity and bone. Beyond the full single finger imaging, a volunteer’s four fingers were clearly and concurrently imaged. To confirm our observations, MRI images of two volunteers’ fingers were performed, and the TAT recovered shape/size of the fingers were consistent with the MRI findings. To further assess the feasibility of TAT for finger joint and bone imaging, we quantitatively calculated the conductivity of a case. This initial study suggests that TAT may be a good candidate for screening, diagnosing, and monitoring treatment of joint and bone diseases.

Detection of Ultrasound and Photoacoustic Imaging with Fiber Bragg Gratings

In this paper, we explore a simple and effective fiber Bragg grating demodulation setup to detect ultrasound. Different frequency ultrasound from hundreds of kHz to several MHz were detected successfully. For the first time, we combine ultrasound from a PZT transducer with a photoacoustic imaging systemto obtain a clear photoacoustic image of our pencil lead sample. With the advantage of small size and all-optical features, this method has the potential to be applied to medical endoscopic examination in an electromagnetic environment. This preliminary study suggests that the ultrasound detection with fiber Bragg grating is both meaningful and feasible.

Recent Progress in Multimodal Photoacoustic Tomography

Since its first demonstration of functional imaging in small animals about a decade ago, photoacoustic tomography (PAT) has quickly become one of the fastest growing biomedical imaging modalities. Combining optical excitation with acoustic detection, PAT can provide detailed images of tissues deep in the body. While PAT technology continues to improve significantly, substantial efforts have also been made to develop multimodal PAT systems. These systems not only provide complementary information for more comprehensive characterization of tissue, they also generate data that can be used to further improve PAT reconstruction. This review will present current progress in multimodal PAT imaging, focusing on the technical aspects of integration and its applications in biomedicine.

Magnetoacoustic Tomography with Magnetic Induction (MAT-MI) Reconstruction Algorithm Based on Characteristics of Acoustic Transducer

A MAT-MI reconstruction algorithm was applied to general sound detection systems, and the influence of acoustic transducers on MAT-MI image reconstruction was investigated in this paper. The acoustic intensity measurement system was used to measure the acoustic field, and the data was then used to build the acoustic transducer model by a interpolation method. The model was applied to forward and inverse problems of MAT-MI based on Green’s function and discretization method. In order to verify the algorithm, a simulation was carried out using sphere scan schema and cylinder scan schema. A 3D phantom model was set up based on S-L model in CT, with the help of finite element analysis method and the distribution of the transient electromagnetic field and the eddy currentwere calculated. Simulation and reconstruction results through numerical calculation using MATLAB were obtained. Results show that the algorithm can reconstruct the distribution of acoustic source vector; the correlation coefficients are 98.49% and 94.96%, and can be applied to the general transducer. This study provided a basis for the experimental study of MAT-MI and a precise reconstruction of conductivity distribution.

Thermoacoustic tomography: A novel method for early breast tumor detection

This article presents a comprehensive review on a non-invasive, high resolution and high contrast imaging modality, called thermoacoustic tomography (TAT). Details about the principles, history and future directions of TAT are described.

Label-Free Photoacoustic Cell-Tracking In Real-Time

Cell-tracking method has an important role in detection of metastatic circulating tumor cells (CTCs) and cell-based therapies. Label-free imaging techniques are desirable for cell-tracking because they enable long time observations without photobleaching in living cells or tissues where labeling is not always possible. Photoacoustic microscopy is a label-free imaging technique that offers rich contrast based on nonfluorescent cellular optical absorption associated with intrinsic chromophores and pigments. We show here that photoacoustic imaging is feasible for detecting very low numbers (x 104) of melanoma cells without labeling because of the strong instinct optical absorption of melanin in near-infrared wavelength. Flowing melanoma cells are imaged with micrometerresolution (40 μm) and penetration depths of centimeters (13 mm) in real-time. Photoacoustic imaging as a new cell-tracking method provides a novel modality for cancer screening and offers insights into the underlying biological process of cancer growth and metastasis and cell therapy.

Trans-rectal thermo-acoustic computed tomography: An initial in silico study

Background: The purpose of this in silico study is to demonstrate thermo-acoustic computed tomography (CT) based reconstruction of frequency-dependent true electrical conductivity distribution in a trans-rectal axialimaging geometry. Since cancerous tissue is expected to exhibit different conductivity profile compared to normal tissue, reconstructing conductivity based on thermoacoustic CT in a trans-rectal geometry has a potential for prostate cancer detection.Methodology: A trans-rectal axial-imaging geometry is illuminated by an electromagnetic (EM) point source at a microwave frequency. The source is located on a transrectal EM applicator close to the rectal wall. The applicator also houses a convex-array of point acoustic receivers that capture the acoustic pressure generated within the geometry as a result of EM illumination. The finite element method (FEM) along with an absorbing boundary condition is applied for solving the electric field (E-field) distribution, the power loss density and the acoustic pressure. The Levenberg-Marquardt regularization scheme is applied to reconstruct the conductivity distribution by decoupling the E-field from the power loss density.Results: For an excitation frequency of 915 MHz, various 2-D reconstructed images based on a 2:1 conductivity ratio between the background and object in a trans-rectal geometry of 40 mm radius are shown. Both single and double objects of 3 mm radius positioned at 4, 7, 10 and 15 mm depth with respect to the acoustic receiver are considered. The quality of the reconstructed image is shown to be object-depth dependent. The effect of different levels of Gaussian noise on the reconstructed images is shown. The contrast-to-noise ratios (CNRs) of the reconstructed images for the objects of different sizes and depths are also computed.Conclusions: Feasibility of recovering heterogeneous conductivity distribution in a trans-rectal axial-imaging geometry by thermo-acoustic CT is demonstrated in silico. The results implicate an alternative imaging mechanism for prostate cancer detection.