A simple analytic method for estimating T2 in the knee from DESS.

PURPOSE

To introduce a simple analytical formula for estimating T 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 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 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-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 is within 20% of the assumed T, the T 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 from the linear relationship agrees well with reference scans, both for the phantoms and in vivo. The method resulted in less underestimation of T 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 quantification with DESS that is accurate, yet also simple. The simplicity of the method allows for immediate T estimation in cartilage during the MRI examination.