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

In this study, we compared a newly developed multibreath simultaneous alveolar oxygen tension and apparent diffusion coefficient (P_AO₂-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.

Both single-breath and multibreath simultaneous P_AO₂-ADC imaging schemes were performed on a total of 10 human subjects (five asymptomatic smokers and five COPD subjects). Estimated P_AO₂ 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.

The multibreath protocol decreased the ventilation defect volumes by an average of 12.9 ± 6.6%. The multibreath sequence generated nonphysiological P_AO₂ values in 11.0 ± 8.5% fewer voxels than the single-breath sequence. Single-breath P_AO₂ maps also showed more regions with gas-flow artifacts and general signal heterogeneity. On average, the standard deviation of the P_AO₂ distribution was 16.5 ± 7.0% lower using multibreath P_AO₂-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.

Multibreath P_AO₂-ADC imaging provides superior accuracy and efficiency compared to previous imaging protocols. P_AO₂ and ADC maps generated by multibreath imaging allowed for the qualification of various regions as emphysematous or obstructed, which single-breath P_AO₂ maps can only identify as defects. The simultaneous P_AO₂ 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.