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Effect of T 1 relaxation on ventilation mapping using hyperpolarized 129 Xe multiple breath wash‐out imaging
Author(s) -
Morgado Felipe,
Couch Marcus J.,
Stirrat Elaine,
Santyr Giles
Publication year - 2018
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.27234
Subject(s) - ventilation (architecture) , nuclear medicine , lung ventilation , relaxation (psychology) , nuclear magnetic resonance , chemistry , inverse , physics , mathematics , lung , medicine , geometry , thermodynamics
Purpose To investigate the effect of incorporating T 1 as a function of wash‐out breath number (T 1 ( n )) on estimation of fractional ventilation ( r ) using hyperpolarized 129 Xe 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 T 1 ( n ) (assuming that the longitudinal relaxation rate of 129 Xe in the lung is directly proportional to p A O 2 ) and compared to r maps obtained by assuming a fixed T 1 measured before wash‐out breaths ( r ′). Results Fractional ventilation was overestimated by up to 19.3% when T 1 was fixed. An inverse relationship between bias (Δ r ) and ventilation was observed at all τ and TV . Additionally, Δ r 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 = V dose – 1 mL. Conclusion Analysis of hyperpolarized 129 Xe MBWO imaging using a model incorporating T 1 ( n ) corrects for an overestimating bias in the mapping of fractional ventilation in mechanically ventilated rats introduced by assuming a fixed T 1 .