Multi-element Linear Transducer Array Research Articles

Towards real-time assessment of anisotropic plate properties using elastic guided waves.

A method to recover the elastic properties, thickness, or orientation of the principal symmetry axes of anisotropic plates is presented. This method relies on the measurements of multimode guided waves, which are launched and detected in arbitrary directions along the plate using a multi-element linear transducer array driven by a programmable electronic device. A model-based inverse problem solution is proposed to optimally recover the properties of interest. The main contribution consists in defining an objective function built from the dispersion equation, which allows accounting for higher-order modes without the need to pair each experimental data point to a specific guided mode. This avoids the numerical calculation of the dispersion curves and errors in the mode identification. Compared to standard root-finding algorithms, the computational gain of the procedure is estimated to be on the order of 200. The objective function is optimized using genetic algorithms, which allow identifying from a single out-of-symmetry axis measurement the full set of anisotropic elastic coefficients and either the plate thickness or the propagation direction. The efficiency of the method is demonstrated using data measured on materials with different symmetry classes. Excellent agreement is found between the reported estimates and reference values from the literature.

Linear-array-based photoacoustic imaging of human microcirculation with a range of high frequency transducer probes.

Photoacoustic imaging (PAI) with a linear-array-based probe can provide a convenient means of imaging the human microcirculation within its native structural context and adds functional information. PAI using a multielement linear transducer array combined with multichannel collecting system was used for in vivo volumetric imaging of the blood microcirculation, the total concentration of hemoglobin (HbT), and the hemoglobin oxygen saturation (sO₂) within human tissue. Three-dimensional (3-D) PA and ultrasound (US) volumetric scans were acquired from the forearm skin by linearly translating the transducer with a stepper motor over a region of interest, while capturing two-dimensional images using 15, 21, and 40 MHz frequency transducer probes. For the microvasculature imaging, PA images were acquired at 800- and 1064-nm wavelengths. For the HbT and sO₂ estimates, PA images were collected at 750- and 850-nm wavelengths. 3-D microcirculation, HbT, and sO₂ maps of the forearm skin were obtained from normal subjects. The linear-array-based PAI has been found promising in terms of resolution, imaging depth, and imaging speed for in vivo microcirculation imaging within human skin. We believe that a reflection type probe, similar to existing clinical US probes, is most likely to succeed in real clinical applications. Its advantages include ease of use, speed, and familiarity for radiographers and clinicians.

Integrative System of Fast Photoacoustic Imaging

Abstract An integrative fast (Photoacoustic) PA imaging system based on multi-element linear ultrasonic transducer array was developed, which integrates laser delivery, photoacoustic excitation and photoacoustic detection into a portable system. It collects PA signals by a multi-element linear transducer array in a reflection mode. The PA images with high spatial resolution and high contrast were obtained. Compared to other existing PA imaging methods, the integrative PA imaging system is characterized by rapidness, convenience and high practicality. The integrative system is mobile and portable, and it is suitable for imaging samples in natural condition with various different shapes. It will provide a novel and effective PA imaging approach for clinic diagnosis of neoplasm and tissue functional imaging in vivo, and has potential to be developed into a practical apparatus used in the early non-invasive detection of breast-cancer.

Direction Study of Multi-element Linear Transducer Array Based on Photoacoustic Imaging

In order to approve the direction property of multi-element linear ultrasonic transducer array, the multi-element phase-controlled technique was adopted. Here we have explored the detected direction influence from dominant frequency, number of multi-element transducer and space between transducer on direction of multi-element linearultrasonic transducer array. These results show that large sub-array has good direction property when the main frequency of detector is low. However it is contrary for high frequency of ultrasonic detector. This will be significative in photoacoustic signal detection and image reconstruction.

Three-dimensional endoscopic photoacoustic imaging based on multielement linear transducer array

An implementation system of three-dimensional endoscopic photoacoustic imaging is presented. The developed endoscopic photoacoustic detector integrates a multielement linear transducer array, a reflective device, a Plexiglass tube, and ultrasonic coupling medium. To match with the acoustic impendence of Plexiglass tube, a glycerin solution with 45% volume percentage was used as the ultrasonic coupling medium. This ultrasonic coupling medium can decrease photoacoustic pressure transmission loss during the progress of photoacoustic signal propagation. The capability of the system for three-dimensional imaging was verified with chicken breast tissue. Furthermore, pig normal rectal tissue and mouse breast tumor tissue in an ex vivo cavity model were imaged by the system. The reconstructed three-dimensional photoacoustic image presented the structural information of normal and lesion tissue. The experimental results demonstrate the multielement-based endoscopic photoacoustic imaging system with inside-out laser exciting mode has the ability of reconstructing three-dimensional images of biology tissue.

Dextran-coated Fe3O4 magnetic nanoparticles as a contrast agent in thermoacoustic tomography for hepatocellular carcinoma detection

Microwave-induced thermoacoustic tomography can provide a novel imaging modality for clinical detection. Significant progress has been made in the past several years in microwave-induced thermoacoustic tomography. In this paper, we investigate the feasibility of using dextran-coated Fe3O4 magnetic nanoparticles as a contrast agent in thermoacoustic tomography for hepatocellular carcinoma detection. Dextran-coated Fe3O4 magnetic nanoparticles administered intravenously are phagocytosed by resident Kupffer cells in normal reticuloendothelial system (RES) within the liver, but are not retained in tumor tissue. Consequently, there are significant differences in thermoacoustic signal intensity between normal RES and tumors, which result in increased lesion conspicuity and detectability. This provides the improvement of lesion-to-liver contrast for thermoacoustic tomography. A fast thermoacoustic computed tomography system with a multielement linear transducer array was used to image cancerous liver tissue with circular scanning. The results show that the system can provide molecular imaging with functionalized contrast agents for high-contrast detecting hepatocellular carcinoma and has the potential to become a novel approach for clinical diagnosis in the future.

Microwave‐induced thermoacoustic scanning CT for high‐contrast and noninvasive breast cancer imaging

A fast thermoacoustic computed tomography system with a multielement linear transducer array was developed to image biological tissues with circular scanning. The spatial resolution of the imaging system and the spectra of the thermoacoustic signals were analyzed. A modified integration backprojection algorithm using velocity potential was employed to recover the direct energy deposition distribution, signal processing methods, and reconstruction algorithms were validated by imaging a phantom. The differences of the microwave-frequency dielectric properties between malignant and normal adipose-dominated tissues in the breast are considerable, and the absorption contrast can reach as large as 6:1 at 1.2 GHz. An experiment of human breast tissue with a tumor was performed with this system; the thermoacoustic images reconstructed by a limited-field-filtered backprojection algorithm and a modified integration backprojection algorithm were also compared with a mammogram. Our results show that the system can provide a rapid and noninvasive approach for high-contrast breast cancer imaging.

Fast Photoacoustic System Based on an Acoustic Lens and the Peak Detection Technology

A fast photo-acoustic (PA) imaging system was developed and tested on phantom sample, which consists of an acoustic lens，a multi-element linear transducer array, and the peak detection circuit. The multi-element linear transducer array consists of 64 elements. By utilizing an acoustic lens, the PA signals generated from the sample are imaged and detected by a multi-element linear transducer array, which directly changes the PA signals into the homologous electronic signals. Thus we can map the image more rapidly, with the peak detection circuit, which was designed specially. Compared to other exiting technology and algorithm, the PA imaging system based on an acoustic lens and the peak detection technology was characterized with speediness and real-time. The images reconstructed in this experiment have high definition and resolution，and may have potential for developing an appliance for clinical diagnosis.

Detection of foreign body using fast thermoacoustic tomography with a multielement linear transducer array

Current imaging modalities face challenges in clinical applications due to limitations in resolution or contrast. Microwave-induced thermoacoustic imaging may provide a complementary modality for medical imaging, particularly for detecting foreign objects due to their different absorption of electromagnetic radiation at specific frequencies. A thermoacoustic tomography system with a multielement linear transducer array was developed and used to detect foreign objects in tissue. Radiography and thermoacoustic images of objects with different electromagnetic properties, including glass, sand, and iron, were compared. The authors' results demonstrate that thermoacoustic imaging has the potential to become a fast method for surgical localization of occult foreign objects.

Fast Microwave-Induced Thermoacoustic Tomography Based onMulti-Element Phase-Controlled Focus Technique

We develop a fast microwave-induced thermoacoustic tomography systembased on a 320-element phase-controlled focus linear transducer array.A 1.2-GHz microwave generator transmits microwave with a pulse width of0.5 μs and an incident energy density of 0.45 mJ/cm2, and themicrowave energy is delivered by a rectangular waveguide with a crosssection of (80.01±0.02)×10−4 m2. Compared to singletransducer collection, the system with the multi-element lineartransducer array can eliminate the mechanical rotation of thetransducer, hence can effectively reduce the image blurring and improvethe image resolution. Using a phase-controlled focus technique to collectthermoacoustic signals, the data need not be averaged because of a highsignal-to-noise ratio, resulting in a total data acquisition time ofless than 5 s. The system thus provides a rapid and reliable approachto thermoacoustic imaging, which can potentially be developed as apowerful diagnostic tool for early-stage breast caners.

Fast multielement phase-controlled photoacoustic imaging based on limited-field-filtered back-projection algorithm

In this paper, the multielement phase-controlled technique and the limited-field -filtered back-projection algorithm are used to investigate the two-dimensional fast noninvasive photoacoustic imaging. By the use of the former to collect photoacoustic signals, which are of high signal-to-noise ratio, one needs not to average the data and can acquire them in less than 5s. The later can greatly improve the lateral resolution of the multielement linear transducer array imaging system from 1.5mmto0.24mm. This method and system can provide a fast and reliable approach to photoacoustic imaging that could be applied to noninvasive imaging and clinic diagnosis.

Fast photoacoustic imaging system based on 320-element linear transducer array

A fast photoacoustic (PA) imaging system, based on a 320-transducer linear array, was developed and tested on a tissue phantom. To reconstruct a test tomographic image, 64 time-domain PA signals were acquired from a tissue phantom with embedded light-absorption targets. A signal acquisition was accomplished by utilizing 11 phase-controlled sub-arrays, each consisting of four transducers. The results show that the system can rapidly map the optical absorption of a tissue phantom and effectively detect the embedded light-absorbing target. By utilizing the multi-element linear transducer array and phase-controlled imaging algorithm, we thus can acquire PA tomography more efficiently, compared to other existing technology and algorithms. The methodology and equipment thus provide a rapid and reliable approach to PA imaging that may have potential applications in noninvasive imaging and clinic diagnosis.