Chao Tao

Photoacoustic tomography of tissue subwavelength microstructure with a narrowband and low frequency system

Based on the analyzed relationship between the microstructure and the spectral parameters of photoacoustic signal, a tomography scheme with a narrowband and low frequency is designed to evaluate the subwavelength microstructure of tissues. Experiments show that this approach can differentiate the subwavelength microstructures of two melanomas-like samples, where their structure scales (49 and 199 μm) are much smaller than the working wavelength 0.3–1.5 mm of the imaging system. Since the microstructure is an effective indicator to tissue characteristics, the proposed imaging scheme could have the potential to classify different tissue types and achieve improved diagnosis in deep tissues.

Photoacoustic spectrum analysis for microstructure characterization in biological tissue: A feasibility study

This study investigates the feasibility of characterizing the microstructures within a biological tissue by analyzing the frequency spectrum of the photoacoustic signal from the tissue. Hypotheses are derived from theoretical analyses on the relationships between the dimensions/concentrations of the photoacoustic sources within the region-of-interest and the linear model fitted to the power spectra of photoacoustic signals. The hypotheses are validated, following the procedures of ultrasound spectrum analysis, by simulations and experiments with phantoms fabricated by embedding the polyethylene microspheres in porcine gelatin, indicating that photoacoustic spectrum analysis could be a potential tool for characterizing microstructures in biological samples.

Quantitative detection of stochastic microstructure in turbid media by photoacoustic spectral matching

Quantitative detection of stochastic microstructure in turbid media remains a challenge to both optical and acoustical observation. A method of photoacoustic spectral matching is proposed to solve this problem. This method allows us to quantitatively detect the characteristic dimension of stochastic microstructures using a long wavelength. Using a working wavelength of about 375 μm, we accurately measure the dimensions (49, 94.8, and 199 μm) of particles hidden in turbid phantoms. Since stochastic microstructures composed of particles commonly appear in tissue, this method might provide an insight into the physiological and pathological processes deep within organisms.

Evaluation of bladder microvasculature with high-resolution photoacoustic imaging

We explored the potential of an emerging laser-based technology, photoacoustic imaging (PAI), for bladder cancer diagnosis through high-resolution imaging of microvasculature in the bladder tissues. Imaging results from ex vivo canine bladders demonstrated the excellent ability of PAI in mapping three-dimensional microvasculature in optically scattering bladder tissues. By comparing the results from human bladder specimens affected by cancer to those from the normal control, the feasibility of PAI to differentiate malignant from benign bladder tissues was also explored. The distinctive morphometric characteristics of tumor microvasculature can be seen in the images from cancer samples, suggesting that PAI may allow in vivo assessment of neoangiogenesis that is closely associated with bladder cancer generation and progression. By presenting subsurface morphological and physiological information in bladder tissues, PAI, when performed in a similar way as in conventional endoscopy, provides an opportunity for improved diagnosis, staging, and treatment guidance of bladder cancer.

Reconstruction of high quality photoacoustic tomography with a limited-view scanning

The goal of this work is to resolve the limited-view problem of photoacoustic tomography (PAT). We report a two-loop iteration method to inverse the photoacoustic sources from the measured photoacoustic signals. PAT reconstruction with this method does not depend on the detection path. Therefore, the proposed method can provide recognizable image even when the detector only scans a small angle (about 20 degrees approximately 30 degrees). The comparison with the delay-and-sum method shows the advantage of the proposed method in reconstructing image from incomplete data.

Photoacoustic spectrum analysis for microstructure characterization in biological tissue: Analytical model

Photoacoustic spectrum (PA) analysis (PASA) has been found to have the ability to identify the microstructures in phantoms and biological tissues. PASA adopts the procedures in ultrasound spectrum analysis, although the signal generation mechanisms related to ultrasound backscatter and PA wave generation differ. The purpose of this study was to theoretically validate PASA. The analytical solution to the power spectrum of PA signals generated by identical microspheres following discrete uniform random distribution in space was derived. The simulation and experiment validation of the analytical solution include: (i) the power spectrum profile of a single microsphere with a diameter of 300 μm, and (ii) the PASA parameters of the PA signals generated by randomly distributed microspheres 100, 200, 300, 400 and 500 μm in diameter, at concentrations of 30, 60, 120, 240, 480 per 1.5(3) cm(3) in the observation range 0.5-13 MHz.

Noninvasive Assessment of Early Dental Lesion Using a Dual-Contrast Photoacoustic Tomography.

Dental hard tissue lesions, including caries, cracked-tooth, etc., are the most prevalent diseases of people worldwide. Dental lesions and correlative diseases greatly decrease the life quality of patients throughout their lifetime. It is still hard to noninvasively detect these dental lesions in their early stages. Photoacoustic imaging is an emerging hybrid technology combining the high spatial resolution of ultrasound in deep tissue with the rich optical contrasts. In this study, a dual-contrast photoacoustic tomography is applied to detect the early dental lesions. One contrast, named B-mode, is related to the optical absorption. It is good at providing the sharp image about the morphological and macro-structural features of the teeth. Another contrast, named S-mode, is associated with the micro-structural and mechanical properties of the hard tissue. It is sensitive to the change of tissue properties induced by the early dental lesions. Experiments show that the comprehensive analysis of dual-contrast information can provide reliable information of the early dental lesions. Moreover, the imaging parameter of S-mode is device-independent and it could measure tissue properties quantitatively. We expect that the proposed scheme could be beneficial for improving safety, accuracy and sensitivity of the clinical diagnosis of the dental lesion.

Limited-view photoacoustic tomography utilizing backscatterers as virtual transducers

In photoacoustic tomography, acoustic scattering is usually considered as a nuisance, because it distorts an incident wavefront and then induces artifacts and distortion. This work demonstrates that backscatterers could function as virtual transducers arranged behind the region of interest and are used to improve limited-view reconstruction. This idea is confirmed by both simulations and experiments. Our results suggest that enhanced photoacoustic tomography could be obtained by taking advantage of native scatterers in tissues or artificial ones injected around the region of interest.

High resolution Physio-chemical Tissue Analysis: Towards Non-invasive In Vivo Biopsy

Conventional gold standard histopathologic diagnosis requires information of both high resolution structural and chemical changes in tissue. Providing optical information at ultrasonic resolution, photoacoustic (PA) technique could provide highly sensitive and highly accurate tissue characterization noninvasively in the authentic in vivo environment, offering a replacement for histopathology. A two-dimensional (2D) physio-chemical spectrogram (PCS) combining micrometer to centimeter morphology and chemical composition simultaneously can be generated for each biological sample with PA measurements at multiple optical wavelengths. This spectrogram presents a unique 2D “physio-chemical signature” for any specific type of tissue. Comprehensive analysis of PCS, termed PA physio-chemical analysis (PAPCA), can lead to very rich diagnostic information, including the contents of all relevant molecular and chemical components along with their corresponding histological microfeatures, comparable to those accessible by conventional histology. PAPCA could contribute to the diagnosis of many diseases involving diffusive patterns such as fatty liver.

Theoretical and experimental study of spectral characteristics of the photoacoustic signal from stochastically distributed particles

Photoacoustic imaging is an emerging technique which inherits the merits of optical imaging and ultrasonic imaging. However, classical photoacoustic imaging mainly makes use of the time-domain parameters of signals. In contrast to previous studies, we theoretically investigate the spectral characteristics of the photoacoustic signal from stochastic distributed particles. The spectral slope is extracted and used for describing the spectral characteristics of the photoacoustic signal. Both Gaussian and spherical distributions of optical absorption in particles are considered. For both situations, the spectral slope is monotonically decreased with the increase of particle size. In addition, the quantitative relationship between the spectral slope and the imaging system factors, including the laser pulse envelope, directivity of ultrasound transducer, and signal bandwidth, are theoretically analyzed. Finally, an idealized phantom experiment is performed to validate the analyses and examine the instrument independent of the spectral slope. This work provides a theoretical framework and new experimental evidence for spectrum analysis of the photoacoustic signal. This could be helpful for quantitative tissue evaluation and imaging based on the spectral parameters of the photoacoustic signal.