Physics and Astronomy Colloquium
Surgical Fluorescence Imaging with Computational Single Photon Cameras
Presented by Andreas Velten, U. Wisconsin, Madison
Our cameras usually measure light as an analog flux that varies as a function of space and time. This approximation ignores the quantum nature of light which is actually made of discrete photons each of which is collected at a sensor pixel at an instant in time. Single photon cameras have pixels that can detect photons and the timing of their arrival resulting in cameras with unprecedented capabilities. Concepts like motion blur, exposure time, and dynamic range that are essential to conventional cameras do not really apply to single photon sensors. In this presentation I will cover computational imaging capabilities enabled by single photon cameras and their application in surgical fluorescence imaging.
Extreme Dynamic Range: Conventional cameras attempt to estimate light flux by integrating the amount of light arriving at a pixel over a fixed exposure time. This leads to the problems of saturation and motion blur. Estimating flux based on the average duration between photons turns out to provide a flux estimate that does not saturate even for extreme flux values.
Motion Compensation: Because each photon detection event can be time-tagged with picosecond precision, single photon cameras have no inherent motion blur. If the motion is known, it can be compensated for in post processing with no loss in SNR. This allows us to implement improved burst photography methods based on single photon sensors.
These enhanced imaging capabilities are particularly interesting in applications with extreme demands, such as Fluorescence Guided Surgery (FGS). FGS methods make use of fluorescent markers that selectively attach to and label different anatomical structures in the human body to make them visible during surgery. Labels for vasculature, tumors, and nerves are under investigation. Imaging systems need to work with weak signals in moving scenes covered by bright ambient light. We are applying a series of computational imaging improvements to allow our cameras to produce image qualities during surgery that used to only be achievable in static scenes in a dark laboratory.
This high signal quality and the exceptional time resolution of our cameras may further enhance future FGS methods by capturing fluorescence lifetime. The nanosecond scale fluorescence lifetime of a fluorescent marker is related to the markers surroundings and molecular binding partners. By measuring lifetime we may better differentiate between marker molecules that are actually bound to the target site and those that are floating freely. It may even be possible to perform label free FGS by making use of fluorescent molecules that are naturally present in human cells.
Bio:
Andreas Velten is Assistant Professor at the Department of Biostatistics and Medical Informatics and the department of Electrical and Computer Engineering at the University of Wisconsin-Madison and directs the Computational Optics Group. He obtained his PhD with Prof. Jean-Claude Diels in Physics at the University of New Mexico in Albuquerque and was a postdoctoral associate of the Camera Culture Group at the MIT Media Lab. He has won numerous awards for his research, such as inclusion in the MIT TR35 list of the world's top innovators under the age of 35. He is co-Founder of Onlume, a company that develops imaging solutions for medical procedures, and Ubicept, a company developing single photon imaging solutions.
3:30 pm, Friday, November 19, 2021
PAIS-1100, PAIS
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