We report a fiber-optic sensor that can be deployed through a standard 250-µm injection needle (25 gauge) for minimally invasive measurements of deep-tissue biomechanical properties in vivo. We have demonstrated the sensor’s ability to provide distinct readouts of muscle stiffness when the hind limb of a rat is relaxed and stretched. To ensure minimal tissue damage and distortion, we have integrated optical proximity sensing within the same fiber for real-time, precise control of the sensor position. To facilitate clinical translation, we have designed the sensor to be disposable and autoclavable and have developed a strategy for mass production.
KEYWORDS: Super resolution, Photoacoustic microscopy, Red blood cells, Signal detection, Ultrasonography, Laser soldering, Blood circulation, Biological imaging, 3D tracking, Two photon excitation microscopy
Exploiting the optical absorption of hemoglobin, photoacoustic microscopy (PAM) has achieved label-free imaging of the microvasculature in vivo and enabled simultaneous quantification of blood oxygenation and flow. However, the axial resolution of PAM is limited to the mesoscopic level due to the finite bandwidth of detected ultrasound signals. To address this limitation, we have developed a super-resolution functional PAM technique based on spatiotemporal tracking of red blood cells, which enables label-free functional microvascular imaging in 3D at the single-cell level. We have demonstrated the utility of this technique by imaging the mouse brain’s responses to a single-vessel stroke in 3D.
Interferometry is an optical measuring method with the character of non-destructive, high sensitivity and high accuracy. However, its measurement range is limited by the phase ambiguity. Hence the method with two separate different wavelengths light source is introduced to enlarge the measurement range.
As for the two-wavelength interferometry case, phase shifting is the traditional way to acquire the phase map, it needs to repeat the measurement twice, which means the measurement cannot be accomplished in real time. Hence to solve the problem, a temporal sequence interferometry has been used. This method can obtain the desired phase information in real time by using the Fourier transform methods of the interferogram recorded in a sequence while the object is being deformed. But, it is difficult to retrieve the phase information directly due to the multi extreme points in one period of the cosine function.
In this paper, an algorithm based on the wavelet ridge analysis is adopted to retrieve the two wavelength phase fluctuation caused by the displacement simultaneously.
The preliminary experiment is conducted and the results are compared with theoretical simulations to validate the proposed approach. The laser emits light with two wavelengths 532 nm and 473 nm, two separated interference patterns in time sequence are detected by the CCD camera in the same time. The overlapped interferograms of two colors are analyzed by this algorithm and the corresponding phase information are obtained. The maximum error value between the simulation and theory is 0.03 um and the relative error is 0.33%.
Digital shearing speckle pattern interferometry (DSSPI) is a powerful tool in the measurement of strain, residual stress and the non-destructive testing (NDT). It is widely used in the fields of wood testing, tire inspection and aerospace, etc. The DSSPI system based on the Wollaston prism is attractive because of its compact arrangement, high immunity to disturbance, and, most of all, the ability to measure strain directly. It could show the strain distribution of the measured object by producing fringe patterns. In conventional DSSPI systems, phase-shifting devices are commonly adopted to extract phase information from the fringe patterns, which means dynamical measurement cannot be realized. In this paper, the principle of a novel DSSPI system based on the temporal analysis is presented. Phase information is extracted with the Fourier Transform method instead of the phase-shifting devices in this system. In this way, dynamical measurement is realized. The measuring accuracy is mostly determined by the quality of the fringe patterns (the fringe width and the contrast ratio). There are several factors that influence the quality of the fringe patterns. Here we mainly discuss the influence of the shearing distance and the polarization state. The preliminary experiments with different shearing distances and polarization states are conducted. The ideal shearing distance and polarization state are suggested.
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