Measurement of Regional Lung Ventilation Using Hyperpolarized ³He MRI –Potential in Clinical Studies

Pulmonary ventilation is an important marker in lung physiology and sensitive to many obstructive and restrictive pulmonary diseases. Conventional techniques for measuring regional ventilation are based on delivery/clearance rates of radioactive gases, as well as xenon-contrast X-ray CT. These techniques, however, expose patients to radiation and preclude frequent screening necessary for monitoring progression of disease or response to therapy. Hyperpolarized (HP) (HP ³He MRI has emerged as a novel technique with unique capabilities in visualizing ventilated airspaces noninvasively. Deninger, et al. developed a technique for regional measurement of pulmonary ventilation which was based on HP ³He signal buildup in the lung following a sequence of helium breaths. This technique, however, is limited to use in small animals as it requires many HP 3He breaths (typically 30~50 breaths) and a relatively long acquisition time. This large number of
breaths requires very good accuracy in gas delivery to avoid image misregistration problems. Therefore, we have developed a new technique for measuring regional
ventilation that is acquirable over a much shorter period of time and requires a substantially fewer number of helium breaths. These properties allow the new technique
to be implemented in humans. Results of the new technique are closely comparable to that of Deninger’s method. It is also shown that measurements can be performed
with mixtures of helium and oxygen without sacrificing accuracy. This avoids perturbing the physiological state of the subject while measurements are being performed.

Dynamic ventilation sequence compared to n-th step of Deninger’s ventilation sequence.

Details of the breathing cycle for rats.