105 research outputs found
Time-domain reconstruction for thermoacoustic tomography in a spherical geometry
Reconstruction-based microwave-induced thermoacoustic tomography in a spherical configuration is presented. Thermoacoustic waves from biological tissue samples excited by microwave pulses are measured by a wide-band unfocused ultrasonic transducer, which is set on a spherical surface enclosing the sample. Sufficient data are acquired from different directions to reconstruct the microwave absorption distribution. An exact reconstruction solution is derived and approximated to a modified backprojection algorithm. Experiments demonstrate that the reconstructed images agree well with the original samples. The spatial resolution of the system reaches 0.5 mm
Time-domain reconstruction for thermoacoustic tomography in a spherical geometry
Reconstruction-based microwave-induced thermoacoustic tomography in a spherical configuration is presented. Thermoacoustic waves from biological tissue samples excited by microwave pulses are measured by a wide-band unfocused ultrasonic transducer, which is set on a spherical surface enclosing the sample. Sufficient data are acquired from different directions to reconstruct the microwave absorption distribution. An exact reconstruction solution is derived and approximated to a modified backprojection algorithm. Experiments demonstrate that the reconstructed images agree well with the original samples. The spatial resolution of the system reaches 0.5 mm
Deep penetrating photoacoustic tomography in biological tissues
Photoacoustic tomography (PAT) in a circular scanning configuration was developed to image the deeply embedded optical heterogeneity in biological tissues. Based on the intrinsic contrast between blood and chicken breast muscle, an embedded blood object that was 5 cm deep in the tissue was detected using pulsed laser light at a wavelength of 1064 nm. Compared with detectors for flat active surfaces, cylindrically focused ultrasonic transducers can reduce the interference generated from the off-plane photoacoustic sources and make the image in the scanning plane clearer. While the optical penetration was optimized with near-infrared laser pulses of 800 nm in wavelength, the optical contrast was enhanced by indocyanine green (ICG) whose absorption peak matched the laser wavelength. This optimized PAT was able to image fine objects embedded at a depth of up to 5.2-cm, which is 6.2 times the 1/e optical penetration depth, in chicken breast muscle, at a resolution of < ~750 microns with a sensitivity of <7 pmol of ICG in blood. The resolution was found to deteriorate slowly with increasing imaging depth
Photoacoustic Imaging using Combination of Eigenspace-Based Minimum Variance and Delay-Multiply-and-Sum Beamformers: Simulation Study
Delay and Sum (DAS), as the most common beamforming algorithm in
Photoacoustic Imaging (PAI), having a simple implementation, results in a
low-quality image. Delay Multiply and Sum (DMAS) was introduced to improve the
quality of the reconstructed images using DAS. However, the resolution
improvement is now well enough compared to high resolution adaptive
reconstruction methods such as Eigenspace- Based Minimum Variance (EIBMV). We
proposed to integrate the EIBMV inside the DMAS formula by replacing the
existing DAS algebra inside the expansion of DMAS, called EIBMV-DMAS. It is
shown that EIBMV-DMAS outperforms DMAS in the terms of levels of sidelobes and
width of mainlobe significantly. For instance, at the depth of 35 mm,
EIBMV-DMAS outperforms DMAS and EIBMV in the term of sidelobes for about 108
dB, 98 dB and 44 dB compared to DAS, DMAS, and EIBMV, respectively. The
quantitative comparison has been conducted using Full-Width-Half-Maximum (FWHM)
and Signal-to-Noise Ratio (SNR), and it was shown that EIBMV-DMAS reduces the
FWHM about 1.65 mm and improves the SNR about 15 dB, compared to DMAS.Comment: Submitted in 24th Iranian Conference on Biomedical Engineering (ICBME
2017
High-resolution spectroscopic photoacoustic tomography for non-invasive functional imaging of small-animal brains in vivo
Based on the multiwavelength laser-based photoacoustic tomography, noninvasive imaging of cerebral blood oxygenation and blood volume in small-animal brains in vivo was realized. The high sensitivity of this technique is based on the spectroscopic differences between oxy- and deoxy-hemoglobins whereas its spatial resolution is diffraction-limited by the photoacoustic signals. The point-by-point distributions of hemoglobin oxygen saturation and total concentration of hemoglobin in the cerebral cortical venous vessels, altered by systemic physiological modulations including hyperoxia and hypoxia, were visualized successfully through the intact skin and skull. This technique can potentially accelerate the progress in neuroscience and provide important new insights into cerebrovascular physiology and brain function
High-resolution photoacoustic tomography
Optical contrast is sensitive to physiological parameters, such as the oxygen saturation and total concentration of hemoglobin, in biological tissues. Photoacoustic tomography is based on the high optical contrast yet utilizing the high ultrasonic resolution. Our work in this emerging area of research will be summarized in this invited talk. In this technology, a diffraction-based inverse-source problem is solved in the image reconstruction, for which we developed the rigorous reconstruction theory. We implemented a prototype and accomplished non-invasive transdermal and transcranial functional imaging of small-animal brains in vivo. Changes in the cerebral blood oxygenation and blood volume of a rat, as a result of the alternation from hyperoxia to hypoxia, were imaged successfully
Image Enhancement and Noise Reduction Using Modified Delay-Multiply-and-Sum Beamformer: Application to Medical Photoacoustic Imaging
Photoacoustic imaging (PAI) is an emerging biomedical imaging modality
capable of providing both high contrast and high resolution of optical and
UltraSound (US) imaging. When a short duration laser pulse illuminates the
tissue as a target of imaging, tissue induces US waves and detected waves can
be used to reconstruct optical absorption distribution. Since receiving part of
PA consists of US waves, a large number of beamforming algorithms in US imaging
can be applied on PA imaging. Delay-and-Sum (DAS) is the most common
beamforming algorithm in US imaging. However, make use of DAS beamformer leads
to low resolution images and large scale of off-axis signals contribution. To
address these problems a new paradigm namely Delay-Multiply-and-Sum (DMAS),
which was used as a reconstruction algorithm in confocal microwave imaging for
breast cancer detection, was introduced for US imaging. Consequently, DMAS was
used in PA imaging systems and it was shown this algorithm results in
resolution enhancement and sidelobe degrading. However, in presence of high
level of noise the reconstructed image still suffers from high contribution of
noise. In this paper, a modified version of DMAS beamforming algorithm is
proposed based on DAS inside DMAS formula expansion. The quantitative and
qualitative results show that proposed method results in more noise reduction
and resolution enhancement in expense of contrast degrading. For the
simulation, two-point target, along with lateral variation in two depths of
imaging are employed and it is evaluated under high level of noise in imaging
medium. Proposed algorithm in compare to DMAS, results in reduction of lateral
valley for about 19 dB followed by more distinguished two-point target.
Moreover, levels of sidelobe are reduced for about 25 dB.Comment: This paper was accepted and presented at Iranian Conference on
Electrical Engineering (ICEE) 201
High-resolution functional photoacoustic tomography
All-optical imaging has high contrast but poor spatial resolution beyond the ballistic and quasiballistic regimes. All-ultrasonic imaging has high spatial resolution but poor contrast for early stage tumors. Photoacoustic tomography combines the high optical contrast and the high ultrasonic resolution. Our work in this emerging area of research will be summarized in this invited talk. In this technology, a diffraction-based inverse-source problem is solved in the image reconstruction, for which our group developed the rigorous reconstruction theory. We developed a prototype and accomplished noninvasive transdermal and transcranial functional imaging of small-animal brains in vivo
Photoacoustic tomography and molecular fluorescence imaging: dual modality imaging of small animal brains in vivo
We present a dual modality imaging technique by combining photoacoustic tomography (PAT) and near-infrared (NIR) fluorescence imaging for the study of animal model tumors. PAT provides high-resolution structural images of tumor angiogenesis, and fluorescence imaging offers high sensitivity to molecular probes for tumor detection. Coregistration of the PAT and fluorescence images was performed on nude mice with M21 human melanoma cell lines with αvβ3 integrin expression. An integrin αvβ3-targeted peptide-ICG conjugated NIR fluorescent contrast agent was used as the molecular probe for tumor detection. PAT was employed to noninvasively image the brain structures and the angiogenesis associated with tumors in nude mice. Coregistration of the PAT and fluorescence images was used in this study to visualize tumor location, angiogenesis, and brain structure simultaneously
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