Multispectral Photoacoustic Tomography (MSPAT) is capable of visualizing the concentration distribution of various chromophores in biological tissues, where the unmixing process is usually performed with the spectral fitting method that requires the absorption spectral signatures of all chromophores in the tissue to be known. However, due to the changes of spectral signatures of some exogenous contrast agents in vitro and in vivo, the conventional fitting method will be hindered. Although the blind unmixing algorithms do not require the exact absorption spectrum of each chromophore in advance, it is often sensitive to noise, which may lead to low quantitative results. Considering that the non-negativity of concentration distribution and absorption spectra of the chromophores as well as the sparsity of concentration image of exogenous contrast agent in the gradient domain, we herein propose a modified MSPAT implementation that utilizes a non-negative matrix factorization iterative reconstruction framework with the support of a priori information of spectral signature of oxy-/deoxy-hemoglobin and valid sparsity regularization during the iteration. Consequently, the spectral signature of the exogenous contrast agent and the concentration distribution of each chromophore can be recovered simultaneously. The proposed approach has been validated by simulation and in vivo experiments, exhibiting promising performances in image fidelity even when the multi-wavelength photoacoustic tomographic images used for spectral unmixing are affected by noise or reconstruction artifacts.
Near infrared diffuse optical tomography (DOT) is a significant potential means of detecting breast cancer. Compared with other system structures, the parallel-plate scanning mode has such advantages like adapting to different breast size, as well as increasing the transmission of light by compressing. Traditional parallel-plate DOT systems utilized the fibers for photon transmission and photomultiplier tube (PMT) or CCD for photon detection, which resulted in the high complexity and cost. In this study, we propose a fiber-free parallel-plate continuous-wave DOT system for breast cancer detection based on Silicon photomultiplier (SiPM) and multi-wavelength light emitting diode (LED). 50 three-wavelength (660 nm, 750nm and 840nm) LEDs are arranged in a printed circuit board (PCB) array as the source plate. Parallel to this plate, the other plate with 56 silicon photomultipliers (SiPM) arranged is designed as the detection plate. The control of the light source excitation and the detection of the SiPMs output are implemented by a module based on a data acquisition card. The structure of proposed system is very simple, and the acquisition time is no more than 5 minutes. The feasibility of the system was verified by polyoxymethylene and agar phantom experiments, which indicated that the parallel-plate system can accurately reconstruct optical parameters.
Frequency domain diffuse optical tomography (FD-DOT) has been considered as a reliable method to quantify the absolute optical properties of tissues. In the conventional FD-DOT, PMTs coupled with optical fiber bundles were used as the detectors. Thus, the imaging system was expensive and complex in system structure. In this study, we propose to utilize the silicon photomultiplier (SiPM) to replace the PMT as the detectors in the FD-DOT system. SiPM can provide the similar level of gain as PMT. Meanwhile its price is much lower than PMT, and the use of optical fiber bundles can be avoided, which makes it possible to build a simple structure system. The feasibility of the SiPM based FD-DOT was studied in the experiment. A 660nm laser diode was utilized as the source to irradiate the phantom, and it was modulated from 10MHz to 40MHz with the step size 10MHz. The SiPM detectors with 1 mm2 detection area were used to collect the photons emitted from the phantom. We measured in several different source-detector distances for each modulation frequency, during which the bias voltage of SiPM remained constant. The results showed that we could restore the linear relationship between the phase lag and the transmission distance. We also obtained the expected linear curve of the logarithm of the product of the amplitude and distance versus transmission distance. In addition, the absorption and scattering coefficients of the phantom were calculated by the slope of the fitting curve, which showed a good consistency at different modulation frequencies. The experiments results illuminated that it is feasible to build a FD-DOT based on SiPM.
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