Abstract
OBJECTIVE: The lung magnetic resonance longitudinal relaxation rate R1 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 R1 accounting for field strength B0 , acquisition method, and disease. MATERIALS AND METHODS: A systematic literature search was performed to identify studies quantifying R1 or its reciprocal T1 . The relationship between field strength and observed R(1) was analysed in all healthy subject data. Data were fit to the heuristic equation R1 = B ∗ (B0A) . The variances between-study bs , within-study-between-subject wsbs , and within-study-within-subject wsws , in HS were assessed. Linear correlation between observed R(1) and TE was also investigated. RESULTS: Fifty-nine papers were selected, 50 quantifying R(1) in HS and 20 in disease, representing 1559 human and non-human subjects, with B0 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 R(1) at B0 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 R1 and TE was confirmed. DISCUSSION: We provide reference values for lung R1 across all commonly used field strengths. The variation in HS lung observed R1 reported in different studies in different centres likely reflects methodological differences. Investigators wishing to compare lung R1 values with previous reports should take account of this irreproducibility, and multicentre projects should standardise to minimise between-centre variance.