Sci-Fri AM: Imaging - 02: Regional Ventilation Mapping of the Rat Lung Using Hyperpolarized 3 He Magnetic Resonance Imaging

Abstract

With the addition of inhaled contrast agents, namely hyperpolarized 3He and 129Xe, Magnetic Resonance (MR) imaging has the ability to measure anatomical and functional changes associated with disease progression in the rodent lung. Hyperpolarized 3He MR imaging has been used to measure regional ventilation in the normal rat lung using the dynamic gas signal from inside the lungs. This method employs a variable flip angle approach (FAVOR) to mitigate the effects of RF pulses and relaxation both in the ventilator system and in the rat lung. Theoretical models are used to fit signal enhancement curves to generate two-dimensional maps of the ventilation parameter, r, which is defined as the percent refreshment of gas per unit volume per breath. Healthy Sprague-Dawley rats (∼525 g) were anesthetized and ventilated with hyperpolarized 3He using a custom ventilator system. Imaging experiments were performed at 3.0 T and 2D projection images were acquired. The average r value obtained for the whole lung (r = 0.30 ± 0.02) agreed with expected values based on geometrical calculations. The ventilation gradient calculated in the anterior/posterior direction agreed with previously published xenon-enhanced CT results; however, there is no significant precedent for known ventilation gradients in the superior/inferior direction. In the future, these imaging techniques will be extended to measure ventilation gradients in all three dimensions using hyperpolarized 129Xe. The development of imaging tools to regionally quantify ventilation is expected to improve our understanding of breathing physiology in both normal rat lungs as well as rat models of asthma.