Optical polarization technique—for enhancement of image quality—in speckle contrast-based perfusion imaging: A characterization study

Study of an optical polarization technique for enhancement of achievable image quality (contrast and imaging depth), in speckle contrast-based perfusion imaging modality, is reported. A linearly polarized optical beam is employed to interrogate tissue sample of interest. Light, which is diffusively reflected from tissue sub-surfaces, is selectively acquired while rejecting the specularly reflected light from tissue superficial surface. This selective detection of light is achieved by adoption of optical filtering technique where a linear optical polarizer is kept in front of optical detector (CCD-camera, in our case) at a particular configuration. Experiments were conducted in various samples including tissue-mimicking Agar-phantom and tissue sample (volunteer). Characterization studies of enhancement were carried out in various cases: (i) with variation in orientation of axis, covering entire range (0° to 90°), of polarizer (in the detection arm) with respect to polarization axis of incident (polarized) light and (ii) with blood vessel-mimicking targets being kept at various depths (0-4mm). Experimental results demonstrate that enhancement in image quality is characterized by orientation of axis of optical polarizer (with the best performance observed at 90°) relative to axis of polarization of incident light.