Comparison of air space measurement imaged by CT, small-animal CT and Hyperpolarized Xe MRI

摘要

Lung disease is the third leading cause of death in the western world. Lung air volume measurements arethought to be early indicators of lung disease and markers in pharmaceutical research. The purpose of this workis to develop a lung phantom for assessing and comparing the quantitative accuracy of hyperpolarized xenon129 magnetic resonance imaging (HP 129Xe MRI), conventional computed tomography (HRCT), and highresolutionsmall-animal CT (μCT) in measuring lung gas volumes. We developed a lung phantom consisting ofsolid 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 diametersand validated using μCT. While this phantom is not anthropomorphic, it enables us to directly measure airspace volume and compare these imaging methods as a function of sphere diameter for the first time. HP 129XeMRI 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 demonstratedpartial-volume artifacts for the 1mm spheres. μCT gives the most accurate air-volume results. ConventionalCT and HP 129Xe MRI give similar results although non-uniform densities of 129Xe require more sophisticatedalgorithms than simple thresholding.The threshold required to give the true air volume in both HRCT andμCT, varies with sphere diameters calling into question the validity of thresholding method.