Objective
The lung magnetic resonance longitudinal relaxation rate \({R}_{1}\) varies with disease but reported values in healthy subjects (HS) also differ markedly between studies.
Objective
To evaluate the reported values and variances of observed \({R}_{1}\) accounting for field strength \({B}_{0}\) , acquisition method, and disease.
Materials and methods
A systematic literature search was performed to identify studies quantifying \({R}_{1}\) or its reciprocal \({T}_{1}\) . The relationship between field strength and observed R1 was analysed in all healthy subject data. Data were fit to the heuristic equation \({R}_{1}=B* {(B}_{0 }^A)\) . The variances between-study \(bs\) , within-study-between-subject \(wsbs\) , and within-study-within-subject \(wsws\) , in HS were assessed. Linear correlation between observed R1 and TE was also investigated.
Results
Fifty-nine papers were selected, 50 quantifying R1 in HS and 20 in disease, representing 1559 human and non-human subjects, with \({B}_{0}\) ranging from 0.2 T to 9.4 T. In HS, the result of the fit on all healthy subjects was A = -0.227 ± 0.020 s−1 T−1, B = 0.923 ± 0.014 s−1 with variance components \(bs>wsbs>wsws\) . The reference values for R1 at \({B}_{0}\) between 0.55 T and 7 T were derived. For inversion recovery with gradient echo readout at 1.5 T, a previously observed negative relationship between \({R}_{1}\) and TE was confirmed.
Discussion
We provide reference values for lung \({R}_{1}\) across all commonly used field strengths. The variation in HS lung observed \({R}_{1}\) reported in different studies in different centres likely reflects methodological differences. Investigators wishing to compare lung \({R}_{1}\) values with previous reports should take account of this irreproducibility, and multicentre projects should standardise to minimise between-centre variance.
