A computer-implemented method for calculating a fitted T1 value for a magnetic resonance, MR, acquisition, the method comprising: obtaining MR data from the acquisition, the acquisition including application of an MR pulse sequence that includes two or more inversion groupings, each inversion grouping including a plurality of steady-state free precession, SSFP, readouts following an inversion pulse in the MR pulse sequence; wherein the acquisition is designed to result in incomplete tissue magnetization recovery between at least two inversion groupings; applying a model in which fit parameters are variable dependent on each inversion grouping; calculating, for each inversion grouping, a respective T1 value using the fit parameters calculated using the model; wherein the model has the equation: S i A , B 1 , ... , B i , T 1 ∗ ; TI ≡ A − B i e − TI T 1 ∗ ; i = 1 , ... , n ; where S i is the signal behavior of inversion group i, n is the number of inversion groupings, T 1 ∗ is an apparent longitudinal relaxation rate, A is the steady state magnetization, and B i is defined as: B i = M 0 i + M 0 i ∗ ; where M0 i is the magnitude of magnetization immediately prior to each inversion pulse, and M 0 i * is the steady state magnetization for each inversion grouping; and wherein the respective T1 value for each inversion grouping is calculated using the equation: T 1 i = T 1 ∗ ⋅ B i A − 1 / δ i ; where T 1i is the respective T1 value calculated for the i th inversion grouping, where δ i is the fraction of magnetization prior to the i th inversion pulse, and wherein δ i is equal to one for when i is equal to one; and using the respective T1 value calculated for at least one inversion grouping as the fitted T1 value for the MR acquisition. obtaining MR data from the acquisition, the acquisition including application of an MR pulse sequence that includes two or more inversion groupings, each inversion grouping including a plurality of steady-state free precession, SSFP, readouts following an inversion pulse in the MR pulse sequence; wherein the acquisition is designed to result in incomplete tissue magnetization recovery between at least two inversion groupings; applying a model in which fit parameters are variable dependent on each inversion grouping; calculating, for each inversion grouping, a respective T1 value using the fit parameters calculated using the model; wherein the model has the equation: S i A , B 1 , ... , B i , T 1 ∗ ; TI ≡ A − B i e − TI T 1 ∗ ; i = 1 , ... , n ; where S i is the signal behavior of inversion group i, n is the number of inversion groupings, T 1 ∗ is an apparent longitudinal relaxation rate, A is the steady state magnetization, and B i is defined as: B i = M 0 i + M 0 i ∗ ; where M0 i is the magnitude of magnetization immediately prior to each inversion pulse, and M 0 i * is the steady state magnetization for each inversion grouping; and wherein the respective T1 value for each inversion grouping is calculated using the equation: T 1 i = T 1 ∗ ⋅ B i A − 1 / δ i ; where T 1i is the respective T1 value calculated for the i th inversion grouping, where δ i is the fraction of magnetization prior to the i th inversion pulse, and wherein δ i is equal to one for when i is equal to one; and using the respective T1 value calculated for at least one inversion grouping as the fitted T1 value for the MR acquisition. <EOS>