Echo-Spacing Optimization for the Simultaneous Measurement of Reversible (R2′) and Irreversible (R2) Transverse Relaxation Rates

摘要

Accurate measurement of reversible (R2′) and irreversible (R2) transverse relaxation rates plays a key role in various MRI research and applications. Although optimizing the echo spacing for a multi-echo pulse sequence measuring a single exponential decay has been investigated, optimization in sequences such as GESFIDE (Gradient-Echo Sampling of Free Induction Decay and Echo), in which two echo trains are simultaneously measured to obtain both R2 and R2′, has not been reported. In this work, optimum echo spacings for the GESFIDE sequence are determined to improve the accuracy of the measured relaxation parameters. Various relaxation rates and numbers of acquired echoes are considered, as well as whether or not the receiver bandwidth is kept fixed or varied with the echo spacing. In the case of constant receiver bandwidth, results show that the echo train length approximately equal to T2^* should be used for each echo train in GESFIDE to minimize the uncertainty in R2 or R2′. If the receiver bandwidth is allowed to change with echo spacing in order to maximize the image SNR, the optimum echo train length will vary, generally increasing with the number of echoes.