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 degrees to 90 degrees), 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 degrees) relative to axis of polarization of incident light.