Reproducibility and comparison of oxygen-enhanced T(1) quantification in COPD and asthma patients

T(1) maps have been shown to yield useful diagnostic information on lung function in patients with chronic obstructive pulmonary disease (COPD) and asthma, both for native T(1) and ΔT(1), the relative reduction while breathing pure oxygen. As parameter quantification is particularly interesting for longitudinal studies, the purpose of this work was both to examine the reproducibility of lung T(1) mapping and to compare T(1) found in COPD and asthma patients using IRSnapShotFLASH embedded in a full MRI protocol. 12 asthma and 12 COPD patients (site 1) and further 15 COPD patients (site 2) were examined on two consecutive days. In each patient, T(1) maps were acquired in 8 single breath-hold slices, breathing first room air, then pure oxygen. Maps were partitioned into 12 regions each to calculate average values. In asthma patients, the average T(1,RA) = 1206ms (room air) was reduced to T(1,O2) = 1141ms under oxygen conditions (ΔT(1) = 5.3%, p < 5⋅10(−4)), while in COPD patients both native T(1,RA) = 1125ms was significantly shorter (p < 10(−3)) and the relative reduction to T(1,O2) = 1081ms on average ΔT(1) = 4.2%(p < 10(−5)). On the second day, with T(1,RA) = 1186ms in asthma and T(1,RA) = 1097ms in COPD, observed values were slightly shorter on average in all patient groups. ΔT(1) reduction was the least repeatable parameter and varied from day to day by up to 23% in individual asthma and 30% in COPD patients. While for both patient groups T(1) was below the values reported for healthy subjects, the T(1) and ΔT(1) found in asthmatics lies between that of the COPD group and reported values for healthy subjects, suggesting a higher blood volume fraction and better ventilation. However, it could be demonstrated that lung T(1) quantification is subject to notable inter-examination variability, which here can be attributed both to remaining contrast agent from the previous day and the increased dependency of lung T(1) on perfusion and thus current lung state.