A Short-Breath-Hold Technique For Lung Po(2) Mapping With He-3 Mri

A pulse-sequence strategy was developed for generating regional maps of alveolar oxygen partial pressure (pO(2)) in a single 6-sec breath hold, for use in human subjects with impaired lung function. Like previously described methods, pO(2) values are obtained by measuring the oxygen-induced T-1 relaxation of inhaled hyperpolarized He-3. Unlike other methods, only two He-3 images are acquired: one with reverse-centric and the other with centric phase-encoding order. This phase-encoding arrangement minimizes the effects of regional flip-angle variations, so that an accurate map of instantaneous pO(2) can be calculated from two images acquired a few seconds apart. By combining this phase-encoding strategy with variable flip angles, the vast majority of the hyperpolarized magnetization goes directly into the T-1 measurement, minimizing noise in the resulting pO(2) map. The short-breath-hold pulse sequence was tested in phantoms containing known O-2 concentrations. The mean difference between measured and prepared pO(2) values was 1 mm Hg. The method was also tested in four healthy volunteers and three lung-transplant patients. Maps of healthy subjects were largely uniform, whereas focal regions of abnormal pO(2) were observed in diseased subjects. Mean pO(2) values varied with inhaled O-2 concentration. Mean pO(2) was consistent with normal steady-state values in subjects who inhaled He-3 diluted only with room air. Magn Reson Med 63:127-136, 2010. (C) 2009 Wiley-Liss, Inc.