Vanderbilt Addiction Center

Proton Relaxation and Contrast Mechanisms in MRI

This proposal aims to continue studies to better understand the factors that affect the NMR relaxation properties of protons in tissues and which determine contrast in MR images. We aim to better understand the factors that influence the fundamental processes involved in relaxation in tissues at the molecular and cellular level. In the next phase of this program we will continue to study processes that are likely to become more important with increasing field strength. We will continue to measure the absolute values of rates of magnetization transfer and' proton pool sizes of proton pools undergoing exchange using novel transient methods, and to distinguish MT effects due to chemically shifted labile protons from those due to intact water molecules. We aim to quantify the contributions of different chemical species to the increased rate of transverse relaxation at high fields. We also propose three new directions for better understanding relaxation in tissues and for developing new imaging methods based on novel contrast mechanisms. First, we will further develop and understand the information obtainable from the creation of intermolecular multiple quantum coherences (IMQC) in water in tissues, which has evolved as an important new imaging technique for characterizing tissue structure. We aim to elucidate the signal dependence in IMQC-MRI on tissue structure, relaxation times, diffusion, chemical shift heterogeneity, and pulse sequence timings. Second, we will implement T1 rho imaging and make measurements of T1 rho dispersion as a function of locking frequency in order to probe the importance of slow motions and slow exchange on relaxation. Third, we will investigate the correlation between spatial patterns of quantitative measurements of relaxation rates and other NMR parameters and the corresponding patterns of protein expression as measured using imaging mass spectrometry. We will develop multiparameter high resolution 3D MR imaging techniques at 9.4T in mice, and use imaging mass spectrometry (MALDI) to record the spatial distributions of different molecular weight species within corresponding tissue slices at comparable spatial resolution. We will then use multivariate correlational methods to explore whether specific patterns of protein expression within tissues correlate with specific tissue characteristics measured by quantitative MRI. We will study a selected group of tissues and biopolymers, in different conditions and of varied composition. Overall this project should provide many new insights into tissue relaxation phenomena to aid in the better understanding of the origin of contrast in NMR images and to motivate new approaches to tissue characterization.

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