Lung disease is the third leading cause of death in the western world. Lung air volume measurements are
thought to be early indicators of lung disease and markers in pharmaceutical research. The purpose of this work
is to develop a lung phantom for assessing and comparing the quantitative accuracy of hyperpolarized xenon
129 magnetic resonance imaging (HP 129Xe MRI), conventional computed tomography (HRCT), and highresolution
small-animal CT (μCT) in measuring lung gas volumes. We developed a lung phantom consisting of
solid cellulose acetate spheres (1, 2, 3, 4 and 5 mm diameter) uniformly packed in circulated air or HP 129Xe gas.
Air volume is estimated based on simple thresholding algorithm. Truth is calculated from the sphere diameters
and validated using μCT. While this phantom is not anthropomorphic, it enables us to directly measure air
space volume and compare these imaging methods as a function of sphere diameter for the first time. HP 129Xe
MRI requires partial volume analysis to distinguish regions with and without 129Xe gas and results are within
%5 of truth but settling of the heavy 129Xe gas complicates this analysis. Conventional CT demonstrated
partial-volume artifacts for the 1mm spheres. μCT gives the most accurate air-volume results. Conventional
CT and HP 129Xe MRI give similar results although non-uniform densities of 129Xe require more sophisticated
algorithms than simple thresholding. The threshold required to give the true air volume in both HRCT and
μCT, varies with sphere diameters calling into question the validity of thresholding method.