Effect of T1 relaxation on ventilation mapping using hyperpolarized 129Xe multiple breath wash-out imaging
Funding information: Natural Sciences and Engineering Research Council of Canada; The Hospital for Sick Children
Abstract
Purpose
To investigate the effect of incorporating T1 as a function of wash-out breath number (T1(n)) on estimation of fractional ventilation (r) using hyperpolarized 129Xe multiple breath wash-out (MBWO) imaging in rats.
Methods
MBWO imaging was performed in 8 healthy mechanically ventilated rats at several inter-image delay times (τ) and tidal volumes (TV). r maps were calculated from the imaging data using a model of T1(n) (assuming that the longitudinal relaxation rate of 129Xe in the lung is directly proportional to pAO2) and compared to r maps obtained by assuming a fixed T1 measured before wash-out breaths (r′).
Results
Fractional ventilation was overestimated by up to 19.3% when T1 was fixed. An inverse relationship between bias (Δr) and ventilation was observed at all τ and TV. Additionally, Δr significantly increased when TV was decreased (F statistic F(2,7) = 48.97, P < 10−4). Histograms from r′ maps were significantly more skewed toward lower values as compared to r histograms at all τ and TV (P < 0.05) except TV = Vdose – 1 mL.
Conclusion
Analysis of hyperpolarized 129Xe MBWO imaging using a model incorporating T1(n) corrects for an overestimating bias in the mapping of fractional ventilation in mechanically ventilated rats introduced by assuming a fixed T1.
