Inversion recovery TrueFISP: Quantification of <i>T</i>₁, <i>T</i>₂, and spin density

A novel procedure is proposed to extract T(1), T(2), and relative spin density from the signal time course sampled with a series of TrueFISP images after spin inversion. Generally, the recovery of the magnetization during continuous TrueFISP imaging can be described in good approximation by a three parameter monoexponential function S(t) = S(stst)(1-INV exp(-t/T(*) (1)). This apparent relaxation time T(*) (1) <or= T(1) depends on the flip angle as well as on both T(1) and T(2). Here, it is shown that the ratio T(1)/T(2) can be directly extracted from the inversion factor INV, which describes the relation of the signal value extrapolated to t = 0 and the steady-state signal. Analytical expressions are given for the derivation of T(1), T(2), and relative spin density directly from the fit parameters. Phantom results show excellent agreement with single point reference measurements. In human volunteers T(1), T(2), and spin density maps in agreement with literature values were obtained.