Purpose:To characterize the effect of diffusion time on short-range hyperpolarized 3 He magnetic resonance imaging (MRI) diffusion measurements across a wide range of emphysema severity.
Materials and Methods:3 He diffusion MRI was performed on 19 lungs or lobes resected from 18 subjects with varying degrees of emphysema using three diffusion times (1.6 msec, 5 msec, and 10 msec) at constant b value. Emphysema severity was quantified as the mean apparent diffusion coefficient (ADC) and as the percentage of pixels with ADC higher than multiple thresholds from 0.30 -0.55 cm 2 /sec (ADC index). Quantitative histology (mean linear intercept) was obtained in 10 of the lung specimens from 10 of the subjects.
HYPERPOLARIZED3 He magnetic resonance imaging (MRI) depicts inhaled gas within the lungs. By applying diffusion-sensitizing gradients and measuring resultant changes in 3 He signal intensity, the restricted diffusion of 3 He within the airspaces of the lung can be quantified within each pixel as an apparent diffusion coefficient (ADC). Measuring the ADC over short diffusion times (milliseconds) has been used as a means of quantifying the increase in the size of lung airspaces, which defines emphysema. The 3 He ADC distinguishes individuals with and without emphysema (1,2), and is increased in many smokers with normal pulmonary function, suggesting that it is sensitive to the early stages of emphysema (3). Studies demonstrating that the ADC correlates with computed tomography (CT) measurements of lung attenuation (4,5) and with quantitative histologic measurements of airspace size (6 -8) further support its validity for quantifying emphysema. 3 He ADC measurements also appear to have good reproducibility (9 -11). Consequently, the 3 He ADC has