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Open Access Publications from the University of California

A TRUE MULTI-MODALITY SYSTEM FOR OPTICAL IMAGING WITH MR RESOLUTION: PHOTO-MAGNETIC IMAGING

  • Author(s): Luk, Alex T.
  • Advisor(s): Gulsen, Gultekin
  • et al.
Abstract

A major goal of in vivo imaging is to obtain individualized structural, functional, and molecular information to provide personalized medicine. In particular, optical imaging uses non-ionizing radiation to provide functional information such as hemoglobin concentration and also visualize exogenous contrast agents as well as molecular and functional markers. Indeed, in vivo optical imaging extends across a wide range of applications, from cellular to organ levels. At high end of the spectrum, diffuse optical tomography (DOT) can penetrate up to 10 centimeters but only offer low-resolution images (> 5mm) due to highly scattering nature of the tissue.

Significant effort has been spent on multi-modality imaging techniques to improve the resolution of DOT. While combining DOT with spatial information defined by a separate anatomical imaging modality is promising, there are many challenges and inaccuracies that arise with co-registration. However this can be overcome with a novel multi-modality imaging technique, Photo-Magnetic Imaging (PMI) which uses MRI as a detector to provide both high resolution anatomical and optical information. PMI takes advantage of the 3D measurement capabilities of MR thermometry (MRT) to non-invasively measure the temperature increase of the medium induced by a laser to acquire a temperature map of the entire volume. As DOT measures the photon flux only from the boundary, the major advantage of PMI is that high absorbing regions can be resolved directly from the high spatial resolution temperature map. These measurements can then be converted to obtain the optical absorption properties of the tissue using a reconstruction algorithm to model the light propagation and heat transfer in tissue.

This thesis will present the development of the first preclinical in vivo small animal PMI system prototype using the safety standards set by the American National Standard Institution. To optimize the system for in vivo studies, a fast PMI reconstruction method was also developed to accelerate the original PMI reconstruction method ~1000 times faster. These promising results validated the practicality of PMI for preclinical studies and showed the potential of PMI for clinical studies. This led to the development of the first human PMI prototype for clinical breast studies.

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