In this paper, we establish the mathematical framework of a novel imaging technique, namely Photo-magnetic Imaging (PMI). PMI uses laser to illuminate biological tissues and measure the induced temperature variations using magnetic resonance imaging (MRI). PMI overcomes the limitation of conventional optical imaging and allows imaging of optical contrast at MRI spatial resolution. The image reconstruction for PMI, using a finite element-based algorithm with iterative approach, is presented in this paper. The quantitative accuracy of PMI is investigated for various inclusion sizes, depths and absorption values. Then, a comparison between conventional Diffuse Optical Tomography (DOT) and PMI is carried out to illustrate the superior performance of PMI. An example is presented showing that two 2 mm diameter inclusions embedded 4.5 mm deep and located side by side in a 25 mm diameter circular geometry medium is recovered as a single 6 mm diameter object with DOT. However, these two objects are not only effectively resolved with PMI, but their true concentration are also recovered successfully.

Due to the strong scattering nature of biological tissue, optical imaging beyond the diffusion limit suffers from low spatial resolution. In this letter, we present an imaging technique, laser-induced photo-thermal magnetic imaging (PMI), which uses laser illumination to induce temperature increase in a medium and magnetic resonance imaging to map the spatially varying temperature, which is proportional to absorbed energy. This technique can provide high-resolution images of optical absorption and can potentially be used for small animal as well as breast cancer and lymph node imaging. First, we describe the theory of PMI, including the modeling of light propagation and heat transfer in tissue. We also present experimental data with corresponding predictions from theoretical models, which show excellent agreement. V C 2012 American Institute of Physics.

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Abstract. We present a magnetic resonance (MR)-guided near-infrared dynamic contrast enhanced diffuse optical tomography (DCE-DOT) system for characterization of tumors using an optical contrast agent (ICG) and a MR contrast agent [Gd-diethylenetriaminepentaacetic acid (DTPA)] in a rat model. Both ICG and Gd-DTPA are injected and monitored simultaneously using a combined MRI-DOT system, resulting in accurate co-registration between two imaging modalities. Fisher rats bearing R3230 breast tumor are imaged using this hybrid system. For the first time, enhancement kinetics of the exogenous contrast ICG is recovered from the DCE-DOT data using MR anatomical a priori information. As tumors grow, they undergo necrosis and the tissue transforms from viable to necrotic. The results show that the physiological changes between viable and necrotic tissue can be differentiated more accurately based on the ICG enhancement kinetics when MR anatomical information is utilized. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

In this paper we present first-of-its-kind spatially resolved enhancement kinetics of optical and magnetic resonance (MR) agents obtained by a combined MR and Diffuse Optical Tomography (MR-DOT) animal imaging system. A unique MR compatible fiber optic interface allows co-registration of MR and DOT data in space and time. High temporal resolution of the hybrid system permits acquisition of data in dynamic mode. Rats bearing a R3230 AC breast cancer tumor model are used for in vivo studies. Thirty-two optical and thirty MR images are acquired during a single imaging session that lasts nearly ten minutes. Both optical, indocyanine green (ICG), and MR contrast agents, gadolinium-DTPA (Gd-DTPA), are injected simultaneously after the acquisition of several baseline frames. Contrast enhancement time curves obtained by MR and DOT systems both indicate higher average enhancement in tumor regions, up to ten-fold for MRI and 3-fold for DOT, compared to close by non-tumor regions. This feasibility study is the first step towards clinical translation of this hybrid imaging platform. The ultimate aim is to use the enhancement kinetics of the optical agent ICG, which binds to plasma proteins, as complementary information to the kinetics of the MR agent Gd-DTPA, a small molecular agent that does not bind to plasma proteins, to better differentiate benign and malignant lesions.