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

Abstract

Rationale and Objective: In this study, we compared a newly developed multi-breath simultaneous alveolar oxygen tension and apparent diffusion coefficient (P A O 2-ADC) imaging sequence to a single-breath acquisition, with the aim of mitigating the compromising effects of inter-voxel flow and slow-filling regions on single-breath measurements, especially in COPD subjects. Materials and Methods: Both single-breath and multi-breath simultaneous P A O 2-ADC imaging schemes were performed on a total of ten human subjects (five asymptomatic smokers and five COPD subjects). Estimated P A O 2 and ADC values derived from the different sequences were compared both globally and regionally. The distribution of voxels with non-physiological values was also compared between the two schemes. Results: The multi-breath protocol decreased the ventilation defect volumes by an average of 12.9±6.6%. The multi-breath sequence generated non-physiological P A O 2 values in 11.0±8.5% fewer voxels than the single-breath sequence. Single-breath P A O 2 maps also showed more regions with gas-flow artifacts and general signal heterogeneity. On average, the standard deviation of the P A O 2 distribution was 16.5±7.0% lower using multi-breath P A O 2-ADC imaging, suggesting a more homogeneous gas distribution. Both mean and standard deviation of the ADC increased significantly from single-to multi-breath imaging (P=0.048 and p=0.070, respectively), suggesting more emphysematous regions in the slow-filling lung. Conclusion: Multi-breath P A O 2-ADC imaging provides superior accuracy and efficiency compared to previous imaging protocols. P A O 2 and ADC maps generated by multi-breath imaging allowed for the qualification of various regions as emphysematous or obstructed which singlebreath P A O 2 maps can only identify as defects. The simultaneous P A O 2 and ADC measurements

Mapping Alveolar Oxygen Partial Pressure in COPD Using Hyperpolarized Helium-3: The Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study

“…These appear in three forms. As has been discussed previously [ 18 , 19 ], mixing from different regions can result in negative p A O 2 values. In addition, mixing can also create the opposite effect, namely that p A O 2 results with values greater than the oxygen partial pressure of air can be recorded.…”

“…In particular, 3 He gas flowing to neighboring voxels during the p A O 2 acquisition results in partial pressure measurements that are negative [ 18 ]. Subsequent studies using HP 3 He and more sophisticated multi-breath imaging techniques [ 19 ] partially alleviate this difficulty, but with some loss in the signal-to-noise ratio (SNR). In parallel to studies of p A O 2 from HP 3 He MRI, ADC measurements on COPD participants have reached a quite advanced stage of development and suffer less from systematic uncertainties and provide a metric complementary to CT data for characterizing emphysema subtypes.…”

Hyperpolarized 3helium MRI measured apparent diffusion coefficient and its correlations with pulmonary functions tests in patients with chronic obstructive pulmonary disease: A meta‐analysis

“…Moreover, many of the included studies also observed significant correlations between FEV1 and hyperpolarized 3 He MRI measured ventilation defect volume (r = À0.53; p = 0.04 21 ; r = À0.58; p = 0.007 29 ) or ventilation defect percentage (r = À0.42; p = 0.2 15 ; r = À0.55; p = 0.03 21 ; r = À0.84; p < 0.001 25 ). Also, significant correlations were observed between DLCO and hyperpolarized 3 He MRI measured ventilation defect percentage (r = À0.83; p = 0.0001 14 and r = À0.61; p = 0.04 25 ).…”

Simultaneous quantification of hyperpolarized xenon‐129 ventilation and gas exchange with multi‐breath xenon‐polarization transfer contrast (XTC) MRI

“…By reducing breath-hold lengths and more closely representing physiological breathing, multi-breath hyperpolarized (HP) gas imaging has been shown to reduce artifact-induced heterogeneity and reveal "slow-filling" regions, therefore, enabling a more comprehensive evaluation of lung ventilation. [26][27][28] Here, we present an expanded multi-breath approach that incorporates compartment-selective XTC methodology 29,30 to simultaneously capture gas exchange with the tissue membrane and red blood cells (RBCs) in addition to regional ventilation. A model of per-breath gas replacement is then derived to describe the observed HXe signal profile and extract the ventilation and gas exchange parameters.…”