A study of reconstruction in photoacoustic tomography with a focused transducer

So far most rigorous reconstruction algorithms for photoacoustic tomography (PAT), e.g., the modified back-projection algorithm, have been developed based on ideal point detectors. However, a flat unfocused transducer is commonly used in PAT, thus suffering from the finite aperture effect - tangential resolution deteriorates as the imaging point moves away from the scanning center. Based on a virtual-point-detector concept, we propose a PAT reconstruction with a focused transducer to improve the degraded tangential resolution. We treat the focal point of the focused transducer as a virtual-point detector, which means that delays applied in reconstruction are relative to the focal point. The geometric focus defines propagation path of photoacoustic signals. The simulation results show that compared with PAT with an unfocused transducer, PAT with a focused transducer having an f-number of 2.5 significantly improves tangential resolution by 29 microns up to 791 microns at the imaging positions of at least 4 mm away from the scanning center. The farther the imaging positions away from the scanning center, the larger the improvement. In the region of 4 mm away from the scanning center, PAT with a focused transducer slightly degrades the tangential resolution by up to 70 microns. The improvement in tangential resolution comes with a compromise of loss in radial resolution by 26 microns up to 79 microns depending on the distance from the scanning center. In terms of the significant improvement in tangential resolution, the loss in radial resolution is tolerable, especially for imaging of big objects, e.g., breast

Graphics processing unit accelerating compressed sensing photoacoustic computed tomography with total variation

Photoacoustic computed tomography with compressed sensing (CS-PACT) is a commonly used imaging strategy for sparse-sampling PACT. However, it is very time-consuming because of the iterative process involved in the image reconstruction. In this paper, we present a graphics processing unit (GPU)-based parallel computation framework for total-variation-based CS-PACT and adapted into a custom-made PACT system. Specifically, five compute-intensive operators are extracted from the iteration algorithm and are redesigned for parallel performance on a GPU. We achieved an image reconstruction speed 24–31 times faster than the CPU performance. We performed in vivo experiments on human hands to verify the feasibility of our developed method

Photoacoustic tomography with a virtual point detector

We devise and explore a ring-shaped acoustic detector associated with a virtual point detector concept for photoacoustic tomography. The center of the ring transducer scans a circle around the object to be imaged and then is treated as an omni-directional virtual point detector in photoacoustic image reconstruction. The virtual point detector introduces a space-invariant point spread function in photoacoustic image reconstruction and thus improves the tangential resolution, which is due to the finite aperture. Compared with a real point detector, the virtual point detector can provide similar spatial resolution but better SNR. Compared with a real finite-aperture detector, the virtual point detector can provide similar SNR but better spatial resolution. In addition, because of its virtual feature, the virtual point detector can be placed very close to and even inside of a tissue sample to locally scan a region of interest, which yields good SNR and spatial resolution

In vivo optical-resolution photoacoustic computed tomography with compressed sensing

Optical-resolution photoacoustic microscopy is becoming a powerful research tool for studying microcirculation in vivo. Moreover, ultrasonic-array-based optical-resolution photoacoustic computed tomography (OR-PACT), providing comparable resolution at an improved speed, has opened up new opportunities for studying microvascular dynamics. In this Letter, we have developed a compressed sensing with partially known support (CS-PKS) photoacoustic reconstruction strategy for OR-PACT. Compared with conventional backprojection reconstruction, the CS-PKS strategy was shown to produce high-quality in vivo OR-PACT images with threefold less measurement data, which can be leveraged to improve the data acquisition speed and costs of OR-PACT systems

Compressed-sensing photoacoustic computed tomography in vivo with partially known support

Compressed sensing (CS) can recover sparse signals from under-sampled measurements. In this work, we have developed an advanced CS framework for photoacoustic computed tomography (PACT). During the reconstruction, a small part of the nonzero signals’ locations in the transformed sparse domain is used as partially known support (PKS). PACT reconstructions have been performed with under-sampled in vivo image data of human hands and a rat. Compared to PACT with basic CS, PACT with CS-PKS can recover signals using fewer ultrasonic transducer elements and can improve convergence speed, which may ultimately enable high-speed, low-cost PACT for various biomedical applications

Ring-based ultrasonic virtual point detector with applications to photoacoustic tomography

This is the published version. Copyright © 2007 American Institute of PhysicsAn ultrasonic virtual point detector is constructed using the center of a ring transducer. The virtual point detector provides ideal omnidirectional detection free of any aperture effect. Compared with a real point detector, the virtual one has lower thermal noise and can be scanned with its center inside a physically inaccessible medium. When applied to photoacoustictomography, the virtual point detector provides both high spatial resolution and high signal-to-noise ratio. It can also be potentially applied to other ultrasound-related technologies

A study of reconstruction in photoacoustic tomography with a focused transducer

So far most rigorous reconstruction algorithms for photoacoustic tomography (PAT), e.g., the modified back-projection algorithm, have been developed based on ideal point detectors. However, a flat unfocused transducer is commonly used in PAT, thus suffering from the finite aperture effect - tangential resolution deteriorates as the imaging point moves away from the scanning center. Based on a virtual-point-detector concept, we propose a PAT reconstruction with a focused transducer to improve the degraded tangential resolution. We treat the focal point of the focused transducer as a virtual-point detector, which means that delays applied in reconstruction are relative to the focal point. The geometric focus defines propagation path of photoacoustic signals. The simulation results show that compared with PAT with an unfocused transducer, PAT with a focused transducer having an f-number of 2.5 significantly improves tangential resolution by 29 microns up to 791 microns at the imaging positions of at least 4 mm away from the scanning center. The farther the imaging positions away from the scanning center, the larger the improvement. In the region of 4 mm away from the scanning center, PAT with a focused transducer slightly degrades the tangential resolution by up to 70 microns. The improvement in tangential resolution comes with a compromise of loss in radial resolution by 26 microns up to 79 microns depending on the distance from the scanning center. In terms of the significant improvement in tangential resolution, the loss in radial resolution is tolerable, especially for imaging of big objects, e.g., breast

Transplantation of Bone Marrow Mesenchymal Stem Cells Prevents Radiation-Induced Artery Injury by Suppressing Oxidative Stress and Inflammation

The present study aims to explore the protective effect of human bone marrow mesenchymal stem cells (hBMSCs) on radiation-induced aortic injury (RIAI). hBMSCs were isolated and cultured from human bone marrow. Male C57/BL mice were irradiated with a dose of 18-Gy 6MV X-ray and randomly treated with either vehicle or hBMSCs through tail vein injection with a dose of 103 or 104 cells/g of body weight (low or high dose of hBMSCs) within 24 h. Aortic inflammation, oxidative stress, and vascular remodeling were assessed by immunohistochemical staining at 3, 7, 14, 28, and 84 days after irradiation. The results revealed irradiation caused aortic cell apoptosis and fibrotic remodeling indicated by aortic thickening, collagen accumulation, and increased expression of profibrotic cytokines (CTGF and TGF-β). Further investigation showed that irradiation resulted in elevated expression of inflammation-related molecules (TNF-α and ICAM-1) and oxidative stress indicators (4-HNE and 3-NT). Both of the low and high doses of hBMSCs alleviated the above irradiation-induced pathological changes and elevated the antioxidant enzyme expression of HO-1 and catalase in the aorta. The high dose even showed a better protective effect. In conclusion, hBMSCs provide significant protection against RIAI possibly through inhibition of aortic oxidative stress and inflammation. Therefore, hBMSCs can be used as a potential therapy to treat RIAI

Imaging microvascular dynamics noninvasively with realtime photoacoustic microscopy

A realtime photoacoustic microscopy system consisting of a high-repetition rate pulsed laser, high-frequency (30 MHz) ultrasound array transducer, and realtime receiving system was used to visualize microvessels pulsations over a cardiac cycle. The system offers 100 μm lateral spatial resolution, 25 µm axial spatial resolution, and can image at a rate of 83 frames per second. The system shows promise for visualizing time-varying processes in the microvasculature