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Single-Acquisition Sequence for the Measurement of Regional Alveolar Oxygen Pressure and Oxygen Depletion Rate by 3 He MRI

M. C. Fischer, J. Yu, M. Ishii, Z. Z. Spector, K. Emami, M. Itkin, A. Jalali, R. R. Rizi Radiology, University of Pennsylvania, Philadelphia, PA, United States, Otolaryngology, Johns Hopkins University, Baltimore, MD, United States Introduction: Regional alveolar oxygen partial pressure (pO2) and regional oxygen depletion rate (ODR) are of great importance in the detection and evaluation of lung disorders. These parameters can be utilized to extract the regional pulmonary perfusion and the ventilation to perfusion ratio. Hyperpolarized (HP) He MRI has been successfully used to extract these parameters in normal and diseased lungs [1, 2]. In the presence of oxygen, the magnetization of initially polarized He will gradually decrease due to the interaction between the two gas species [3]. The depolarization rate is strongly dependent on the partial pressure of oxygen in the gas mixture. By measuring this depolarization rate the partial pressure of oxygen can be calculated. The time evolution of pO2, and therefore the ODR, can be obtained by extracting the evolution of the oxygen induced depolarization rate from a time series of images. In previous work, two series of pictures with different inter-scan times were analyzed, which allowed the separation of oxygen induced depolarization effects from the depolarization due to the applied imaging RF fields [1]. The method described here requires only one image series yielding similar accuracy for both pO2 and ODR. This approach not only uses half the amount of polarized He but also eliminates the necessity of preparing identical initial conditions two times. A previous attempt to use a single modified sequence had been undertaken but it did not yield the desired accuracy [4].