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

Abstract

Rationale and objectives: 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.

Materials and methods: 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.

Results: 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.

Conclusion: 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.

Keywords: ADC; COPD; Hyper-polarized Helium-3; Hyper-polarized MRI; Imaging; Multi-breath; P(A)O(2).