Are TrueFISP images T2/T1‐weighted?

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Abstract
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. Magn Reson Med 48:684–688, 2002.