Date of Degree
PhD (Doctor of Philosophy)
Eric A. Hoffman
Edwin J. R. vanBeek
Hyperpolarized 3Helium (HP 3He) magnetic resonance imaging (MRI) has provided considerable insights into the anatomical structures and localized physiological phenomenon involved in pulmonary ventilation. The increasing mortality rates of pulmonary diseases such as COPD, gives rise to the need for sensitive and regional assessments of early disease conditions in attempts to decrease mortality and improve lifestyles. Evaluation of the HP 3He MRI diffusion weighted measurements of lung microstructure, demonstrated a statistically significant relationship between microstructure expansion and degree of lung inflation at the time of imaging. The ability of HP 3He MRI to assess regional ventilation was validated against air volume change estimates of ventilation attainable via conventional MDCT in a cohort of 8 normal never smokers. Great correlations and slope were observed between the functional estimates, with similar gravitationally dependent-nondependent gradients throughout. A small but significant preferential helium distribution was observed in the nondependent regions, most likely due to gas density differences between air and helium. Further validation of HP 3He MRI's ability to assess regional ventilation, was carried via quantitative and qualitative assessments against xenon-enhanced MDCT (normal = 4, COPD = 2). The MRI based estimates were found to be insensitive to slow and fast ventilating regions, while superior in exhibiting ventilation defects. Similar gravitationally dependent - nondependent gradients were observed throughout, along with a homogenous distribution of the exogenous contrast agents. Coefficient of variation (COV) values followed similar trends in the normal subjects, while only one COPD subject demonstrated an increase from the normal population baseline. Acquisition differences including single vs. multi-breath and z-axis coverage could attribute to the quantitative differences observed. Evaluation of the density dependent distribution patterns of helium in a normal airway model via dynamic HP 3He MRI and computational fluid dynamics, demonstrated an increased preferential distribution in the nondependent airways, in agreement with the ventilation discrepancies previously observed. In combination with the developmental aspects of the presented research, we have validated the ability of HP 3He MRI to assess regional ventilation, via multiple quantitative assessments against conventional based and exogenously enhanced MDCT techniques and extracted the lung inflation level dependencies. Complimented with dynamic imaging and CFD simulations of helium distribution, these results provide insight into future considerations critical to the establishment of the technique as a surrogate to the ionizing radiation based modalities.
Copyright 2011 Ahmed Fathi Halaweish