X-ray digital radiography and fluorescence dual-modality imaging system has become an important tool for in-vivo biomedical researches. However, current dual-modality imaging system generally employs two independent pixelated detectors, which is costly and bulky. Here we propose a novel approach to achieve dual-modality imaging system utilizing only one single-pixel detector. The prototype of the system is built based on a Fourier single-pixel imaging architecture. The spatial resolution of the X-ray digital radiography modality was measured to be 1.81mm, the sensitivity and the imaging depth of the fluorescence imaging modality was evaluated to be 1.48 nmol/ml and 4 mm, respectively. Compared with the conventional system, our system is cost affordable, with a more compact structure, and free of image registration from different modalities. In-vivo imaging results of a C57BL/6 female mouse bearing tumor targeted with mCherry demonstrates its capability for small animal researches.
Significance: The multimodality imaging system has become a powerful tool for in-vivo biomedical research. However, a conventional multimodality system generally employs two independent detectors, which is costly and bulky. Meanwhile, the geometric cocalibration and image registration between the imaging modalities are also complicated.Aim: To acquire the multimodality images for small animals with only one visible light sensed single-pixel detector.Approach: The system is built based on a structured detection Fourier single-pixel imaging architecture. A cesium iodide doped with thallium [CsI(Tl)] scintillator plate is placed behind the sample in x-ray imaging, so the x-ray images can be converted to be visible and sensed with the same single-pixel detector as applied in fluorescence imaging.Results: The spatial resolution of x-ray imaging was measured to be 1.81 mm, the sensitivity and the imaging depth of fluorescence imaging was evaluated to be ∼1.48 nmol / ml and 4 mm, respectively. In vivo multimodality imaging of a C57BL/6 female mouse bearing tumor targeted with mCherry was carried out.Conclusions: We proposed an x-ray and fluorescence multimodality imaging system for small animals via the structured detection FSI architecture. The system is low cost, with a more compact structure, and free of image registration from different modalities. In vivo multimodality imaging results of a mouse bearing tumor demonstrate its capability for small animal research.
Photoacoustic microscopy (PAM) is a promising biomedical imaging technique that relies on sequential excitation to generate three-dimensional images. It combines the high contrast of optical imaging with high penetration depth of ultrasound imaging. The normal respiration rate of mice is greater than 3 Hz, which leads to motion artifacts in most reported PAM for in-vivo imaging. Here, we introduce a prospective respiratory gating (PRG) method for photoacoustic microscopy to address this problem. We captured the mouse’s respiratory signal with a laser displacement sensor, when the detector detects a respiratory trough, the stage moves a certain number of positions and sends a corresponding number of pulses to trigger the laser light and the data acquisition. The stage will only move during the nadir of respiration, and the movement also must stop before the next respiration peak. We combined this method with our PAM to demonstrate its feasibility. A series of experiments were performed to verify the feasibility of this technology. The carbon fiber attached to the abdomen of mouse was visualized to quantify the performance of the PRG. The subcutaneous vascular imaging results of the mouse abdominal region with PRG are much better than those without any gating. Our experiments show that the proposed method can help to remove motion artifacts well.
KEYWORDS: Sensors, Photoacoustic microscopy, Visualization, Vascular imaging, Ultrasonography, Signal detection, Optical imaging, In vivo imaging, Data acquisition, Carbon
Photoacoustic microscopy with large depth of focus (DoF) is significant to the biomedical research. Here, we developed a virtual multi-focus optical-resolution photoacoustic microscope with extended depth of field by using block Discrete Cosine Transform (DCT) fusion. The source images from different focus is first 8 × 8 partitioned, and then DCT coefficients of each block can be calculated by using DCT transformation, and then the variance values of the corresponding blocks are calculated through DCT coefficients. The variance values are used as the activity level measures, blocks with large variances are selected. Finally, the fused image with virtual multi-focus is made up of blocks with the larger variances. Simulation and the in vivo imaging of zebra fish were performed to demonstrate that this method can extend the depth of field of PAM two times without the sacrifice of lateral resolution.
Photoacoustic microscopy with large depth of focus is significant to the biomedical research. Here, we developed a multifocus photoacoustic microscopy by using a tunable acoustic gradient (TAG) lens and optical delay pathways. We split a single laser pulse into three sub-pulses and introduce them into three multimode fibers with a length of 1 m, 26 m and 51 m, respectively. The sub-pulses out of the fibers were combined by a single-mode fiber thereafter. We then obtained a pulse train with a time interval of 120 ns. The output of the single-mode fiber is collimated by a fiber port, and then guided into homemade TAG lens vertically. A function generator generates a sinusoidal signal to drive the TAG lens at an eigenmode. The focusing power of the TAG lens will exhibit a sinusoidal oscillation at the frequency of the driving signal. By controlling the fire time of the pulse train and the driving signal of the TAG lens, the laser pulses out of three multimode fibers synchronize with three vibration states of the TAG lens. And we finally achieved three focal spots in one A line data acquisition using a single input laser pulse. The depth of focus (DoF) of the system was measured to be 360 μm, which is three times of that of single-focus system without the sacrifice of time resolution. A mouse cerebral vasculature were imaged in-vivo to demonstrate the feasibility of the extended DoF of our system.
We present a decoupled fluorescence Monte Carlo (dfMC) model for the direct computation of the fluorescence in turbid media. By decoupling the excitation-to-emission conversion and transport process of the fluorescence from the path probability density function and associating the corresponding parameters involving the fluorescence process with the weight function, the dfMC model employs the path histories of the excitation photons and the corresponding new weight function to directly calculate the fluorescence. We verify the model’s accuracy using phantom experiments and compare it with that of the perturbation fluorescence Monte Carlo model. The results indicate that the model is accurate for the direct fluorescence calculation and, thus, has great potential for application in fluorescence-based in vivo tomography.
Vasoactive drugs are normally utilized to elevate mean artery pressure and maintain adequate organ perfusion in clinical treatment. During the injection, morphological changes and the subsequent oxygen supply alteration in the brain, e.g., possible hypoxia, are prone to introduce serious damage and even dysfunction to the brain. Therefore, multiparameter monitoring of cerebral microvasculature is necessary during drug injection. An optical-resolution photoacoustic microscopy was used to assess the effects of norepinephrine on microvasculature in the brain cortex of mice. In our experiments, the diameter, total hemoglobin (HbT) and oxygen saturation (SO 2 ) of single cerebral microvessels during tail vein injection of norepinephrine were analyzed. Following the injection, vasoconstriction was observed, and HbT and SO 2 were decreased in turn. The vessel diameter and HbT recovered back to the base value without further injection, while the SO 2 remained low throughout the observation period. Arterioles showed more acute constriction but a smaller decline in HbT during the injection compared with venules, while SO 2 in arterioles increased slightly without further drug injection but not in venules. Our results suggested that photoacoustic microscopy may become a new method for early and comprehensive evaluation of the effect of drugs on microvasculature in brain.
The study of dual-modality technology which combines microcomputed tomography (micro-CT) and fluorescence molecular tomography (FMT) has become one of the main focuses in FMT. However, because of the diversity of the optical properties and irregular geometry for small animals, a reconstruction method that can effectively utilize the high-resolution structural information of micro-CT for tissue with arbitrary optical properties is still one of the most challenging problems in FMT. We develop a micro-CT-guided non-equal voxel Monte Carlo method for FMT reconstruction. With the guidance of micro-CT, precise voxel binning can be conducted on the irregular boundary or region of interest. A modified Laplacian regularization method is also proposed to accurately reconstruct the distribution of the fluorescent yield for non-equal space voxels. Simulations and phantom experiments show that this method not only effectively reduces the loss of high-resolution structural information of micro-CT in irregular boundaries and increases the accuracy of the FMT algorithm in both forward and inverse problems, but the method also has a small Jacobian matrix and a short reconstruction time. At last, we performed small animal imaging to validate our method.
Stroke is a devastating disease. The changes in cerebral hemodynamics and oxygen metabolism associated with stroke play an important role in pathophysiology study. But the changes were difficult to describe with a single imaging modality. Here the changes in cerebral blood flow (CBF), cerebral blood volume (CBV), and oxygen saturation (SO2) were yielded with laser speckle imaging (LSI) and photoacoustic microscopy (PAM) during and after 3-h acute focal ischemic rats. These hemodynamic measures were further synthesized to deduce the changes in oxygen extraction fraction (OEF). The results indicate that all the hemodynamics except CBV had rapid declines within 40-min occlusion of middle cerebral artery (MCAO). CBV in arteries and veins first increased to the maximum value of 112.42±36.69% and 130.58±31.01% by 15 min MCAO; then all the hemodynamics had a persistent reduction with small fluctuations during the ischemic. When ischemia lasted for 3 h, CBF in arteries, veins decreased to 17±14.65%, 24.52±20.66%, respectively, CBV dropped to 62±18.56% and 59±18.48%. And the absolute SO2 decreased by 40.52±22.42% and 54.24±11.77%. After 180-min MCAO, the changes in hemodynamics and oxygen metabolism were also quantified. The study suggested that combining LSI and PAM provides an attractive approach for stroke detection in small animal studies.
Because cerebral hypoperfusion brings damage to the brain, prevention of cerebrovascular diseases correlative to hypoperfusion by studying animal models makes great sense. Since complicated cerebrovascular adaptive changes in hypoperfusion could not be revealed only by cerebral blood flow (CBF) velocity imaging, we performed multi-parameter imaging by combining laser speckle imaging and functional photoacoustic microscopy. The changes in CBF, hemoglobin oxygen saturation (SO2), and total hemoglobin concentration (HbT) in single blood vessels of ipsilateral cortex were observed during transient cerebral hypoperfusion by ligating the unilateral common carotid artery in rats. CBF, SO2, and HbT, respectively, decreased to 37±3%, 71±7.5%, and 92±1.3% of baseline in 6 s immediately after occlusion, and then recovered to 77±4.8%, 84±8%, and 96±2% of baseline in 60 s. These parameters presented the decrease with different degree and the following recovery over time after ligation, the recovery of SO2 lagged behind those of CBF and HbT, which had the similar response. The results demonstrated that complete monitoring of both cerebral hemodynamic response and oxygen metabolic changes occurred at the earliest period of cerebral hypoperfusion was possible by using the two image modalities with high temporal and spatial resolution.
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