Multimodality, multiscale imaging systems for investigating physiological random processes

This paper presents new imaging systems for the estimation of physiological random processes in medical imaging. In this work, a physiological random process is a sequence of biochemical interactions taking place inside a living organism. These interactions involve things such as proteins and enzymes, that behave differently in response to external stimuli (such as nutrients or administered drugs). Understanding how these physiological processes interact and evolve is critical in the development of effective therapeutic approaches. The general setup of our imaging systems includes a fast detector for the measurement of visible light from which to estimate various parameters about the radiation emitted by the physiological process(es) of interest. Our setup is applicable to imaging with different kinds of radiation, including gamma rays (SPECT and PET), and charged particles, such as alpha and beta particles. Parameters we are interested in estimating for these photons/particles go beyond the 2D or 3D position typically measured in medical imaging applications, and include the direction of propagation and photon/particle energy. Recent work has shown the advantage of measuring direction of propagation and photon/particle energy, in addition to just position. It has been shown that if these additional photon/particle parameters are taken into account during reconstruction, the null space of the imaging system is strongly reduced or eliminated. This reduction in null space is critical to adequately characterize complicated physiological processes.