Abstract
PURPOSE: To introduce a simple analytical formula for estimating T(2) from a single Double-Echo in Steady-State (DESS) scan. METHODS: Extended Phase Graph (EPG) modeling was used to develop a straightforward linear approximation of the relationship between the two DESS signals, enabling accurate T(2) estimation from one DESS scan. Simulations were performed to demonstrate cancellation of different echo pathways to validate this simple model. The resulting analytic formula was compared to previous methods for T(2) estimation using DESS and fast spin-echo scans in agar phantoms and knee cartilage in three volunteers and three patients. The DESS approach allows 3D (256×256×44) T(2)-mapping with fat suppression in scan times of 3-4min. RESULTS: The simulations demonstrated that the model approximates the true signal very well. If the T(1) is within 20% of the assumed T(1), the T(2) estimation error was shown to be less than 5% for typical scans. The inherent residual error in the model was demonstrated to be small both due to signal decay and opposing signal contributions. The estimated T(2) from the linear relationship agrees well with reference scans, both for the phantoms and in vivo. The method resulted in less underestimation of T(2) than previous single-scan approaches, with processing times 60 times faster than using a numerical fit. CONCLUSION: A simplified relationship between the two DESS signals allows for rapid 3D T(2) quantification with DESS that is accurate, yet also simple. The simplicity of the method allows for immediate T(2) estimation in cartilage during the MRI examination.