X-ray mammography is the currently accepted standard for screening breast cancer. However, several other techniques have been developed as an adjunct to X-ray mammography to increase the sensitivity and specificity of the diagnosis. X-ray mammography provides high sensitivity but has a high rate of false-positives. Similarly/the sensitivity of breast MRI has been very high, but the specificity for the detection of abnormalities is variable. Besides the high rate of false positives, some of those techniques also fail to detect the breast cancer in certain cases, such as patients with dense breast tissue, which is common among younger patients. New imaging modalities that offer better specificity may have the potential to reduce the rate of false positives hence eliminate unnecessary biopsies. Several researchers have demonstrated that the electrical properties, specifically the impedance of malignant tissues is significantly different from those of normal and benign tissues. This property has been investigated using various impedance imaging systems. Magnetic Resonance Electrical Impedance Tomography (MREIT) is a new technique to obtain in vivo tissue conductivity images. Objective/Hypothesis: The following two hypotheses will be investigated in this project: 1) Spatial resolution of MREIT will be improved by using a priori information from high resolution MRI. 2) Increase in electrical conductivity in tumors is associated with increased extracellular volume and sodium ion content. Therefore, conductivity images obtained by MREIT method should be highly correlated with sodium-23 and diffusion tensor images obtained with MRI.
Specific Aims : 1) Develop and optimize 3D MREIT acquisition and image reconstruction: a) 3D MREIT acquisition; b) 3D FEM analysis; c) Iterative reconstruction to solve the nonlinear equation set; d) Improving MREIT resolution using high-resolution MRI images. 2) Characterization of spatial resolution and contrast of MREIT: Phantom experiments will be carried out to investigate resolution and contrast of MREIT. 3) Sodium and diffusion imaging: Sodium-23 and diffusion tensor images will be collected to investigate ion concentration and mobility and how they relate to conductivity. 4) In vivo imaging of tumors: MREIT, sodium and diffusion tensor imaging will be performed together with Contrast Enhanced-MRI to investigate the potential of these imaging techniques in cancer diagnosis. The MRI based impedance imaging method that we recently developed will be improved using 3D models. Phantom studies will be carried out to investigate image quality including spatial resolution and contrast. Sodium-23 imaging sequence and hardware will be developed and diffusion tensor imaging will be implemented at 4T to investigate ion concentration and mobility. Then, these imaging techniques will be tested on the same group of rats bearing malignant or benign tumors. Dynamic contract enhanced MRI will also be performed on the same animals to investigate tumor structure and how MREIT, sodium and diffusion images correlate with each other. Potential relationships and their complementary usage will be studied to improve quality and possible diagnostic efficacy of MREIT.
