In vivo 19F NMR imaging of the cardiovascular system

A technique is described that permits the 19F nuclear magnetic resonance (NMR) imaging of the vascular system in animals that have been infused with certain perfluorocarbon blood substitutes. The essence of the technique is the selection for imaging of a narrow group of spectral lines from the fluorocarbon using a combination of selective excitation and selective spin echo. For perfluorotributylamine (FTBA), this uses 56% of the available fluorine signal. Both slice and whole body projection images were obtained. The method was studied on an experimental NMR imaging system based on a 1.4 T, 31 cm diameter magnet. Phantom tests showed that misregistration artifacts, due to the imaging of unwanted spectral lines, were negligible. The spatial resolution obtained in a scan time of 8.5 min was approximately 1 mm. The technique was tested with living rats in which 50% of the blood volume was replaced with an emulsion of FTBA. Short echo times, less than 15 ms, were essential to avoid losing signal from flow effects in the larger vessels. Structures identified included the heart, liver, spleen, lungs, kidneys, and major veins. A diffuse fluorine signal seen in most tissues is indicative of tissue perfusion. The problems and possibilities of potential clinical applications are discussed.