First assessment of thermoacoustic tomography for in vivo detection of rheumatoid arthritis in the finger joints detection of rheumatoid arthritis in the finger joints.

BACKGROUND: The diagnosis of rheumatoid arthritis (RA) is complicated because of the complexity of symptoms and joint structures. Current clinical imaging techniques for the diagnosis of RA have strengths and weaknesses. Emerging imaging techniques need to be developed for the diagnosis or auxiliary diagnosis of RA. PURPOSE: This study aimed to demonstrate the potential of thermoacoustic tomography (TAT) for in vivo detection of RA in the finger joints. METHODS: Finger joints were imaged by a TAT system using three different microwave illumination methods including pyramidal horn antenna, and parallel in-phase and anti-phase microwave illuminations. Both diseased and healthy joints were imaged and compared when the three microwave illumination methods were used. Magnetic resonance imaging (MRI) of all the joints was performed to validate the TAT findings. In addition, two diseased joints were imaged at two time points by the pyramidal horn antenna-based TAT to track/monitor the progression of RA during a time period of 16 months. Three-dimensional (3-D) TAT images of the joints were also obtained. RESULTS: The TAT images of the diseased joints displayed abnormalities in bone and soft tissues compared to the healthy ones. The TAT images by pyramidal horn antenna and in-phase microwave illumination showed high similarity in image appearance, while the anti-phase-based TAT images provided different information about the disease. We found that the TAT findings matched well with the MRI images. The 3-D TAT images effectively displayed the stereoscopic effect of joint lesions. Finally, it was evident that TAT could detect the development of the lesions in 16 months. CONCLUSION: TAT can noninvasively visualize bone lesions and soft tissue abnormalities in the joints with RA. This first in vivo assessment of TAT provides a foundation for its clinical application to the diagnosis and monitoring of RA in the finger joints.

Technical Note: Compact thermoacoustic imaging system based on a low-cost and miniaturized microwave generator for in vivo biomedical imaging.

PURPOSE: Most of existing thermoacoustic imaging (TAI) studies generally utilized a linear modulator-based high peak power magnetron generator (MG) for efficient TA signal excitation. However, a linear modulator-based MG is bulky and expensive. Here we present a low-cost and compact thermoacoustic imaging (TAI) system based on a miniaturized MG. METHODS: The MG is based on solid-state modulator and operates at 3.05 ± 0.025 GHz, with a peak power of up to 60 kW and adjustable pulse duration from 70 to 600 ns. The dimensions and weight of this MG are 350 × 210 × 70 mm3 (Width × Length × Height) and 7.5 kg, respectively. RESULTS: The spatial resolution of the miniaturized MG-based TAI system is determined to be from 0.3 to 1.4 mm using controlled phantom experiments. The system is further evaluated using in vivo experiments where the finger joints and vasculature in the forearm and opisthenar of human participants are successfully imaged. CONCLUSIONS: This study suggests that the miniaturized MG based TAI systems can be used for in vivo joint and vascular imaging with multiscale resolutions (0.3-1.4 mm).

Assessment of liver function reserve by photoacoustic tomography: a feasibility study.

Assessment of liver function reserve (LFR) is essential to determine liver resection scope and predict prognosis for patients with liver disease. Indocyanine green (ICG) concentration change is a classic marker to reflect liver function reserve as ICG is selectively taken up and eliminated by liver. Here we proposed a noninvasive approach for LFR assessment based on a real-time photoacoustic tomography (PAT) system. This feasibility study was to detect ICG concentration change by PAT in phantom and in vivo using both normal and partial hepatectomy (PH) rabbits. A linear relationship between photoacoustic signal intensity of ICG and ICG concentration was found in vitro. In vivo ICG concentration change over time after ICG injection was observed by PAT in normal rabbits, which was consistent with the findings measured by invasive spectrophotometry. Finally, clear difference in ICG clearance between the control and PH models was identified by PAT. Taken together, our study indicated the clinical potential of PAT to in vivo evaluate LFR noninvasively.

Photoacoustic assessment of hemodynamic changes in foot vessels.

Monitoring the blood supply in the lower extremities is critical for individuals who are vulnerable to vascular dysfunction. Current clinical approaches are ineffective in observing hemodynamic changes in peripheral vessels. In this paper, we investigate the potential of photoacoustic tomography (PAT) as an alternative way to in vivo monitor hemodynamic changes in foot vessels. High spatial and temporal resolution maps of hemoglobin in major arteries and veins are shown. Results from twelve human subjects are presented here to visualize vascular perfusion of healthy volunteers in two age groups (young vs aged). Significant differences between the two groups are observed and verify the declining in vascular function with aging, highlighting the potential of PAT as a new tool to evaluate vascular function in the lower extremities.

In vivo photoacoustic imaging of vasculature with a low-cost miniature light emitting diode excitation.

In this Letter, we present a photoacoustic imaging (PAI) system based on a low-cost high-power miniature light emitting diode (LED) that is capable of in vivo mapping vasculature networks in biological tissue. Overdriving with 200 ns pulses and operating at a repetition rate of 40 kHz, a 1.2 W 405 nm LED with a radiation area of 1000 µm×1000 µm and a size of 3.5 mm×3.5 mm was used to excite photoacoustic signals in tissue. Phantoms including black stripes, lead, and hair were used to validate the system in which a volumetric PAI image was obtained by scanning the transducer and the light beam in a two-dimensional x-y plane over the object. In vivo imaging of the vasculature of a mouse ear shows that LED-based PAI could have great potential for label-free biomedical imaging applications where the use of bulky and expensive pulsed lasers is impractical.

Two schemes for quantitative photoacoustic tomography based on Monte Carlo simulation.

PURPOSE: The aim of this study was to develop novel methods for photoacoustically determining the optical absorption coefficient of biological tissues using Monte Carlo (MC) simulation. METHODS: In this study, the authors propose two quantitative photoacoustic tomography (PAT) methods for mapping the optical absorption coefficient. The reconstruction methods combine conventional PAT with MC simulation in a novel way to determine the optical absorption coefficient of biological tissues or organs. Specifically, the authors' two schemes were theoretically and experimentally examined using simulations, tissue-mimicking phantoms, ex vivo, and in vivo tests. In particular, the authors explored these methods using several objects with different absorption contrasts embedded in turbid media and by using high-absorption media when the diffusion approximation was not effective at describing the photon transport. RESULTS: The simulations and experimental tests showed that the reconstructions were quantitatively accurate in terms of the locations, sizes, and optical properties of the targets. The positions of the recovered targets were accessed by the property profiles, where the authors discovered that the off center error was less than 0.1 mm for the circular target. Meanwhile, the sizes and quantitative optical properties of the targets were quantified by estimating the full width half maximum of the optical absorption property. Interestingly, for the reconstructed sizes, the authors discovered that the errors ranged from 0 for relatively small-size targets to 26% for relatively large-size targets whereas for the recovered optical properties, the errors ranged from 0% to 12.5% for different cases. CONCLUSIONS: The authors found that their methods can quantitatively reconstruct absorbing objects of different sizes and optical contrasts even when the diffusion approximation is unable to accurately describe the photon propagation in biological tissues. In particular, their methods are able to resolve the intrinsic difficulties that occur when quantitative PAT is conducted by combining conventional PAT with the diffusion approximation or with radiation transport modeling.

First assessment of three-dimensional quantitative photoacoustic tomography for in vivo detection of osteoarthritis in the finger joints.

PURPOSE: The purpose of this pilot clinical study is to assess three-dimensional (3-D) quantitative photoacoustic tomography (qPAT) for in vivo detection of osteoarthritis (OA) in the finger joints. METHODS: All subject data were handled in compliance with the rules and regulations concerning the privacy and security of protected health information under HIPAA. Seven female subjects (two OA patients and five healthy controls) entered the study and their distal interphalangeal (DIP) joints were examined by a 3-D photoacoustic scanner. 3-D optical absorption coefficient images of all the photoacoustically examined joints were recovered using a 3-D qPAT reconstruction algorithm. RESULTS: The recovered quantitative photoacoustic images revealed obvious difference in the optical absorption coefficient of the joint cavity (cartilage and synovial fluid) between the OA and healthy joints. Quantitative analysis of the joints also indicated an apparent difference in the recovered joint spacing between the OA and healthy subjects. CONCLUSION: This initial clinical evaluation suggests that it is feasible to detect osteoarthritis in the finger joints with our 3-D qPAT approach, which has paved the way to further statistically evaluate the diagnostic performance of the 3-D qPAT approach in comparison with radiography or magnetic resonance imaging (MRI) on a sample of hand osteoarthritis.

A higher order diffusion model for three-dimensional photon migration and image reconstruction in optical tomography.

In this work, we derived three-dimensional simplified spherical harmonics approximated higher order diffusion equations. We also solved the higher order diffusion equations using a finite element method and compared the solutions from the first-order diffusion equation and Monte Carlo simulations. We found that the conducted model is able to improve the first-order diffusion solution in a transport-like homogeneous or heterogeneous medium. Reconstructed images based on the higher order diffusion model are also presented. We conclude that the developed higher order diffusion model is able to accurately describe light propagation in biological tissues and to offer improved image reconstruction.