MAPPING STRAIN EXERTED ON BLOOD-VESSEL WALLS USING DEUTERIUM DOUBLE-QUANTUM-FILTERED MRI

A technique is described for displaying distinct tissue layers of larg e blood vessel walls as web as measuring their mechanical strain. The technique is based on deuterium double-quantum-filtered (DQF) spectros copic imaging. The effectiveness of the double-quantum filtration in s uppressing the signal of bulk water is demonstrated on a phantom consi sting of rat tail tendon fibers. Only intrafibrillar water is displaye d, excluding all other signals of water molecules that reorient isotro pically. One-and two-dimensional spectroscopic imaging of bovine aorta and coronary arteries show the characteristic DQF spectrum of each of the tissue layers. This property is used to obtain separate images of the outer lager? the tunica adventitia, or the intermediate layer, th e tunica media, or both. To visualize the effect of elongation, the av erage residual quadrupole splitting <Delta nu(q)> is calculated for ea ch pixel. Two-dimensional deuterium quadrupolar splitting images are o btained for a fully relaxed and a 55% elongated sample of bovine coron ary artery. These images indicate that the strong effect of strain is associated with water molecules in the tunica adventitia whereas the D QF NMR signal of water in the tunica media is apparently strain-insens itive. After appropriate calibration, these average quadrupolar splitt ing images can be interpreted as strain maps.