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High sensitivity imagers for functional imaging

Laser speckle imaging is a technique for imaging flow based functional vascular structures. The flow acts as a virtual contrast agent and increases the contrast-to-noise ratios and the amount of vascular structure that can be visualized. Speckles are interference patterns that move if the scattering particles move. This results in a blur when speckle patterns are imaged over an exposure time. Statistical arguments can be used to map the blur to velocity. Within blood vessels, RBCs act as the scattering particles leading to images where blood velocity is mapped to intensity.

vascular images in white, green, speckle and fluorescent
Cortical surface vascular images using (a) speckle, (b) white light, (b) green light and (d) rhodamine fluorescent imaging.

We are looking at the cortical surface vasculature in anesthetized and stereotactically restrained rodents. The imaging system constitutes of a red laser illuminating the region of interest at 632 nm and a cooled CCD camera acquiring a time stack of images for offline processing. We are designing a highly sensitive and low noise CMOS imager to develop a system for head-mounted functional imaging in awake and behaving animal models. We are investigating photodiode structures and novel pixel designs to come up with an optimum system.


References

  1. K. Murari, N. Li, A. Rege, X. Jia, A. All and N. Thakor, “Contrast-enhanced imaging of cerebral vasculature with laser speckle,“ Appl. Opt., 46, 5340-5346 (2007).