Are trueFISP images T₂/T₁-weighted?

Images acquired using the TrueFISP technique (true fast imaging with steady-state precession) are generally believed to exhibit T₂/T₁-weighting. In this study, it is demonstrated that with the widely used half-flip-angle preparation scheme, approaching the steady state requires a time length comparable to the scan time such that the transient-state response may dominate the TrueFISP image contrast. Two-dimensional images of the human brain were obtained using various phase-encoding matrices to investigate the transient-state signal behavior. Contrast between gray and white matter was found to change significantly from proton-density- to T₂/T₁-weighted as the phase-encoding matrix size increased, which was in good agreement with theoretical predictions. It is concluded that TrueFISP images in general exhibit T₂/T₁-contrast, but should be more appropriately regarded as exhibiting a transient-state combination of proton-density and T₂/T₁ contrast under particular imaging conditions. Interpretation of tissue characteristics from TrueFISP images in clinical practice thus needs to be exercised with caution.