Abstract
Within an advisable measurement time, the signal-to-noise ratio (SNR) is a major limitation of nuclear magnetic resonance (NMR) microscopy at the spatial resolution of micrometers level. The ‘‘Diffusion Enhancement of Signal and Resolution’’ (DESIRE) scheme provides potential signal enhancement about 1-3 order of magnitude enhancement. In the previous report, the calculations of external magnetic fields and diffusion propagation are simulated by iterative numerical optimization methods and finite-differential (FD) method of Bloch-Torrey equation, respectively. The disadvantage of these processes is time-consuming. In this work, the simulation of external magnetic fields is accelerated by Shinnar-LeRoux (SLR) algorithm and diffusion propagation is accelerated by convolution-based on diffusion simulation method. Thus, the time-cost of simulation can be saved, reducing especially for 2D DESIRE simulations. We can use the saturation magnetization profile with the pulse duration of zero to instead that of non-zero within acceptable error range. The 1D simulation results reveal the optimal parameters setting of restricted condition and predict the effective resolution and the enhancement of different parameters for experiments. The simulated results indicate the pulse waveform of Sinc3 has the both sufficient spatial resolution as well as enhancement in this study. As the total diffusion time is constant of 1 s, the optimal enhancement can be achieved using the pulse number of Sinc3 pulse of 100, namely a RF pulse interval of 10 ms. We also present the 1D saturation profiles and DESIRE images of experiments, and the enhancements of that have high degree agreement with simulated values. For saturating a cylinder volume of 2D DESIRE technique, the gradient system requirements are suggested using spiral gradient method. The simulated results reveal that the requirement of gradient slew rate is also a critical factor as the gradient strength.