Optical pacing (OP) has been proved to be a feasible noninvasive alternative to electrical pacing in recent years. IR lasers can be utilized for this purpose because of the absorption rate of infrared light, particularly wavelengths of 1450 nm, in biological tissue. As a result, the goal of this research is to look at the thermal effects of infrared radiation on cardiac pacemaker cells. To begin, we investigate the heat generation and temperature increases caused by IR pulses in biological tissues as a function of pulse length and radiant exposure depth. The toad heart is then treated with a pulsed infrared laser in an experiment (wavelength of 1450 nm). By measuring the toad's heart rhythm, the temperature effect of IR radiation on its cardiac pacemaker cells is examined. The findings reveal that the thermal effect of IR pulses can alter cardiac pacemaker cells based on variations in the T wave amplitude in the toad heart rhythm. In conclusion, this work shows that non-invasive IR pulses may successfully stimulate cardiac pacemaker cells.
Photoacoustic imaging is going to play an important role in clinical imaging methods by recent progress in illumination and detection techniques. Combining good contrast optical imaging with the high spatial resolution of ultrasound imaging converts this imaging to be an indispensable imaging method for skin tissue. Here, we study the abilities of this method for imaging the variation of depth of blood vessel in the skin. In order to do it, we simulate the generation and propagation of photoacoustic signals inside the skin using a hybrid model based on the Monte Carlo method and acoustic wave equation. The effects of depth of vessel on simulated photoacoustic signal are studied. In addition the axial and lateral resolution of this method is assessed. Finally the frequency dependence of spatial resolution in the spectrum of 5- 75 MHz is also estimated. These results show that photoacoustic imaging method can be applied to study the skin diseases such as hemangioma and Port-wine stain.
Determining cutaneous carotenoid plays an important role in the human health and nutrition studies. Recently, compression optical clearing (OC) was applied to detect dermal carotenoid using reflection spectroscopy. This study aims to improve compression OC to detect the absorption spectrum of beta-carotene inside the human dermal skin. We utilize a combination of experimental (including compression-immersion OC) and computational OC to enhance the ability of reflectance spectroscopy to detect the beta-carotene inside palm of hand. The presented OC techniques can be applied for determining chromophores, such as melanin and bilirubin that have good abilities for nutrition and oncology researches.
Considering the considerable use of sedative drugs like methadone as a frequent substitution for additive drugs, we have investigated their effect on the cell activity via highly-resolved optical sensing method. Using plasmonic ellipsometry technique, a conspicuous shift in plasmonic resonance wavelength of the cultured chips was observed due to methadone presence during the cell culture of mesenchymal stem cells. This highly-sensitive platform can open new avenues towards the detection of drug effect on human cells and in large scale, on human organs.
Infrared neurostimulation (INS) is a new approach for modulation or control of neuronal pulses. Recently, different studies have been presented to investigate the origin of generation of the action potentials during INS, and it seems that the photothermal mechanism has an important role during INS. So, spatial and temporal temperature changes are important parameters, because the heating of neural tissue can excite or block the activity of neurons and an excess deposit of thermal energy could damage the neural tissues. We aim to explore the effects of heat diffusion during INS. We model the generation of action potential using the photothermal mechanism to study the changes of electrical properties of the membrane of neural cell in the earthworm (as a simple neuronal network) during INS. The variation of electrical properties of the membrane causes the changes in the concentration of ions such as K + and Na + inside the cells, which can originate the action potentials. This study includes three sections: (1) exploring the effect of laser light properties (wavelength of 1450 and 1550 nm, repetition rate and energy per pulse) on the measurement of temperature rise inside a phantom similar to neuronal tissue, (2) theoretical modeling to predict the generation of action potentials induced by the local temperature rise inside the neuronal network of earthworm, and (3) detecting the variation of voltage of peripheral nervous system of the earthworm during INS. This modeling can help us to better understanding the mechanism of the blocking and controlling the action potentials for in-vivo applications in the brain cognitive studies and treatment of some neuron system diseases.
A co-planar, simultaneous, photoacoustic tomography guided, diffused optical tomography (CS-PAT-DOT) methodology has been presented in this paper. We detect the absorption of sub-regions with different absorption characteristics in deep tissue with a high spatial resolution. To this aim, we initially utilize compressed sensing (CS), time reversal (TR) and back projection (BP) reconstruction algorithms to reconstruct a priori information inside a heterogeneous phantom. Then the reconstructed images are used in DOT image reconstruction through the total variation method. Improvements obtained from such hybrid methodology are measured by comparing DOT and CS-PAT-DOT images. It will also show that each of the reconstructions based on the proposed method has a unique capability to accurately detect heterogeneities in the tissue at different depths; significantly improving spatial resolution in DOT images. The focus of this study is directed towards quantifying the concentrations of endogenous chromophores, e.g., oxyhemoglobin, deoxyhemoglobin and cytochrome-c-oxidase etc., which are significant indices in detecting tissue abnormalities.
Recently, compression optical clearing (OC) was applied to detect dermal carotenoid using reflection spectroscopy. To enhance the precision and accuracy of reflection spectroscopy to better detect the spectral absorption of beta-carotene inside biological phantom, here, we simultaneously use compression and immersion OC using dimethyl sulfoxide. In addition, we analytically extract the absorption coefficient of beta-carotene using diffuse reflectance spectroscopy (as an analytical OC). Our results show that the presented analytical OC can be applied alone as a noninvasive method to measure cutaneous chromophores at deep tissues. Finally, we also improve the ability of the analytical clearing method mediated with experimental OC. Our result demonstrates that the combination of analytical and experimental clearing methods enhance the ability of diffuse reflection spectroscopy for extracting the absorption coefficient of beta-carotene as one of the chromospheres inside biological phantom.
The estimation of cerebral hemodynamic signals has an important role for monitoring the stage of neurological diseases. Functional Near-Infrared Spectroscopy (fNIRS) can be used for monitoring of brain activities. fNIRS utilizes light in the near-infrared spectrum (650-1000 nm) to study the response of the brain vasculature to the changes in neural activities, called neurovascular coupling, within the cortex when cognitive activation occurs. The neurovascular coupling may be disrupted in the brain pathological condition. Therefore, we can also use fNIRS to diagnosis brain pathological conditions or to monitor the efficacy of related treatments. The Cold pressor test (CPT), followed by immersion of dominant hand or foot in the ice water, can induce cortical activities. The perception of pain induced by CPT can be related to cortical neurovascular coupling. Hence, the variation of cortical hemodynamic signals during CPT can be an indicator for studying neurovascular coupling. Here, we study the effect of pain induced by CPT on the temporal variation of concentration of oxyhemoglobin [HbO2] and deoxyhemoglobin [Hb] in the healthy brains. We use fNIRS data collected on forehead during a CPT from 11 healthy subjects, and the average data are compared with post-stimulus pain rating scores. The results show that the variation of [Hb] and [HbO2] are positively correlated with self-reported scores during the CPT. These results depict that fNIRS can be potentially applied to study the decoupling of neurovascular process in brain pathological conditions.
These days, the biological effects of electromagnetic (EM) radiations on the brain, especially in the frequency range of mobile communications, have caught the attention of many scientists. Therefore, in this paper, the propagation of mobile phone electromagnetic waves in the brain tissues is investigated analytically and numerically. The brain is modeled by three layers consisting of skull, grey and white matter. First, we have analytically calculated the microwave reflection, transmission, and absorption coefficients using signal flow graph technique. The effect of microwave frequency and variations in the thickness of layers on the propagation of microwave through brain are studied. Then, the penetration of microwave in the layers is numerically investigated by Monte Carlo method. It is shown that the analytical results are in good agreement with those obtained by Monte Carlo method. Our results indicate the absorbed microwave energy depends on microwave frequency and thickness of brain layers, and the absorption coefficient is optimized at a number of frequencies. These findings can be used for comparing the microwave absorbed energy in a child's and adult's brain.
Photoacoustic imaging (PAI) is an imaging modality for obtaining absorption coefficient at every location inside the tissue based on the detected photoacoustic signals. PA image reconstruction aims to determine the initial PA pressure everywhere inside the tissue. The pressure is proportional to both absorption coefficient and light fluence. Provided that fluence is homogenous, the reconstructed image will be an accurate mapping of the absorption coefficient of the tissue. Here we presented a method for obtaining uniform fluence inside the region of interest. We created a large dataset of fluence maps for different source locations, diameters and numerical apertures with Monte Carlo simulations, then used this dataset to solve an optimization problem for finding the source configuration which results in the best fluence distribution.
Photoacoustic imaging (PAI) has proved to be a promising non-invasive technique for diagnosis, prognosis and treatment monitoring of neurological disorders in small and large animals. The conventional illumination method for photoacoustic is a called top-illumination were diffused light hit the target from one side. However, this method is not suitable for all target shapes and body parts like breast. To overcome this problem we proposed a novel side-illumination scheme where light comes from a set of fibers all around the object. We showed that this method can improve the obtained images with phantom experiments and simulations. This method is particularly useful for in-plane imaging where the ring of fibers scan long objects.
The accurate quantification of lesions located in deep tissue is an important challenge in diffuse optical tomography (DOT), while photoacoustic tomography (PAT) as a non-invasive optical imaging provides high-resolution imaging of optical contrast in deep tissue that can be served as a complementary modality to improve the accuracy of DOT. Here, we coupled advantages of photoacoustic tomography (PAT) to diffuse optical tomography (DOT) for enhancing reconstructed DOT images. Using a priori information provided by PAT was used to reasonably regularize the DOT inversion procedure.. The results show that hybrid DOT-PAT can provide high-resolution image in deep tissue.
With the growing application of photoacoustic imaging (PAI) in medical fields, there is a need to make them more compact, portable, and affordable. Therefore, we designed very low-cost PAI systems by replacing the expensive and sophisticated laser with a very low-energy laser diode. We implemented photoacoustic (PA) microscopy, both reflection and transmission modes, as well as PA computed tomography systems. The images obtained from tissue-mimicking phantoms and biological samples determine the feasibility of using a very low-energy laser diode in these configurations.
The study of short-pulse propagation through biological tissues is important due to the medical applications of short-pulse lasers. Techniques used for numerical study of short pulses through human tissues include the Monte Carlo (MC) method, the finite-element method, and the finite-difference time-domain (FDTD), but these are often time consuming. Recently, the boundary integral method (BIM) was applied to overcome this problem. The literature shows that the BIM is faster than the other mentioned methods. We first investigate the precision of results obtained by the BIM by comparison with those results obtained by the MC and FDTD methods. Then we use the BIM to investigate the short-pulse penetration into biological tissues. We also study the effects of optical properties of tissues such as scattering, the absorption coefficient, the anisotropic factor on the penetrating pulse. We also, consider the propagation of pulses emitted from extended sources with different temporal evolutions.
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