NEW METHOD FOR MRI BASED ON DETECTION OF INTERMOLECULAR ZERO QUANTUM COHERENCES

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Contrast in MRI is largely based on variations in spin density or relaxation times, sometimes enhanced by injected contrast agents such as gadolinium compounds. The relationship between these parameters and tissue morphology is not always unique. Thus it is not surprising that in some applications no combination of these parameters gives sufficient useful contrast. Even with brain imaging, particularly in the rapidly expanding field of functional MRI, contrast is frequently the limiting factor. New methods for contrast enhancement could thus improve soft tissue characterization, particularly if they correlate with physiologically important characteristics. Here we demonstrate a new type of MRI based on detection of "impossible" intermolecular multiple-quantum coherences (iMQCs), specifically the zero-quantum coherences (iZQCs) which correspond to simultaneously flipping two water spins in opposite directions on molecules separated by 10mm to1 mm. The iZQC linewidth (hence the image contrast) is determined by local susceptibility variations. These variations are physiologically important (for example, they are affected by tissue oxygen gradients in vivo) but are not directly measured by other imaging methods. We have obtained phantom images and in the process of extending this work to human studies. We expect that contrast generated by iZQC might be useful in the detection of small tumor since susceptibility correlates with oxygen concentration.