Improved diffusion measurement in heterogeneous systems using the magic asymmetric gradient stimulated echo (MAGSTE) technique

Abstract

A magic asymmetric gradient stimulated echo (MAGSTE) sequence was recently proposed to improve molecular diffusion measurements in the presence of spatially varying background gradients. Its effectiveness has been demonstrated previously with simulated background gradients and in phantoms that contain bulk susceptibility differences. In this study, we investigated the MAGSTE technique in microscopically heterogeneous systems, and compared it with the conventional bipolar pulsed gradient stimulated echo (bPGSTE) sequence. We demonstrated that the MASGTE measurements, compared to the bPGSTE method, varied significantly less when the diffusion encoding/decoding interval (δ) was changed. In addition, the MAGSTE technique provided good characterization of the surface area-to-volume ratio for heterogeneous systems investigated in this study. In sum, this study showed that the MAGSTE technique provided diffusion measurements superior to those of the bPGSTE sequence, especially in the presence of severe heterogeneous background gradients.

The dependence on magnetic field strength of correlated internal gradient relaxation time distributions in heterogeneous materials

“…de Swiet et al [14] have tried to overcome this using magic angle spinning while Seland et al [15] used diffusion attenuation. Cotts et al [16], Sorland et al [17,19], and Sun [18] have developed bipolar gradient sequences to compensate for interactions between the applied and internal gradients in diffusion experiments.…”

Improved diffusion-weighting efficiency of pulsed gradient stimulated echo MR measurements with background gradient cross-term suppression

“…This was achieved by using different amplitudes, with a so-called ''magic" ratio, for the two gradients around each refocussing RF pulse [11,12]. The cross-term compensation capability of this magic asymmetric gradient stimulated echo (MAGSTE) sequence and the improvements achieved with it for the investigation of heterogeneous samples have been demonstrated recently [13,14]. But because the amplitude ratio required implicates that the two gradients around the refocussing RF have the same polarity, this solution is at a pronounced expense of the diffusion-weighting efficiency.…”

Cross-term-compensated pulsed-gradient stimulated echo MR with asymmetric gradient pulse lengths

“…The technique was termed ''magic asymmetric gradient stimulated echo" (MAGSTE) because the compensation is realized by using different amplitudes for the gradients applied in each interval with a certain, so-called ''magic", ratio [11][12][13][14]. More recently, an extension of MAGSTE has been proposed that involves a third gradient lobe within each interval and delivers an improved diffusion weighting efficiency without sacrificing the cross-term compensation [15].…”