Multibreath Hyperpolarized 3He Imaging Scheme to Measure Alveolar Oxygen Tension and Apparent Diffusion Coefficient

Rationale and Objectives In this study, we compared a newly developed multibreath simultaneous alveolar oxygen tension and apparent diffusion coefficient (PAO2-ADC) imaging sequence to a single-breath acquisition, with the aim of mitigating the compromising effects of intervoxel flow and slow-filling regions on single-breath measurements, especially in chronic obstructive pulmonary disease (COPD) subjects. Materials and Methods Both single-breath and multibreath simultaneous PAO2-ADC imaging schemes were performed on a total of 10 human subjects (five asymptomatic smokers and five COPD subjects). Estimated PAO2 and ADC values derived from the different sequences were compared both globally and regionally. The distribution of voxels with nonphysiological values was also compared between the two schemes. Results The multibreath protocol decreased the ventilation defect volumes by an average of 12.9 ± 6.6%. The multibreath sequence generated nonphysiological PAO2 values in 11.0 ± 8.5% fewer voxels than the single-breath sequence. Single-breath PAO2 maps also showed more regions with gas-flow artifacts and general signal heterogeneity. On average, the standard deviation of the PAO2 distribution was 16.5 ± 7.0% lower using multibreath PAO2-ADC imaging, suggesting a more homogeneous gas distribution. Both mean and standard deviation of the ADC increased significantly from single- to multibreath imaging (p = 0.048 and p = 0.070, respectively), suggesting more emphysematous regions in the slow-filling lung. Conclusion Multibreath PAO2-ADC imaging provides superior accuracy and efficiency compared to previous imaging protocols. PAO2 and ADC maps generated by multibreath imaging allowed for the qualification of various regions as emphysematous or obstructed, which single-breath PAO2 maps can only identify as defects. The simultaneous PAO2 and ADC measurements generated by the presented multibreath method were also more physiologically realistic, and allowed for more detailed analysis of the slow-filling regions characteristic of COPD subjects.