Relayed nuclear Overhauser enhancement imaging with magnetization transfer contrast suppression at 3 T

Abstract

Purpose: To develop a pulsed CEST magnetization-transfer method for rapidly acquiring relayed nuclear Overhauser enhancement (rNOE)-weighted images with magnetic transfer contrast (MTC) suppression at clinical field strength (3 T). Methods: Using a pulsed CEST magnetization-transfer method with low saturation powers (B 1) and long mixing time (t mix) to suppress contributions due to strong MTC from solid-like macromolecules, a low B 1 also minimized direct water saturation. These MTC contributions were further reduced by subtracting the Z-spectral signals at two or three offsets by assuming that the residual MTC is a linear function between −3.5 ppm and −12.5 ppm. Results: Phantom studies of a lactic acid (Lac) solution mixed with cross-linked bovine serum albumin show that strong MTC interference has a significant impact on the optimum B 1 for detecting rNOEs, due to lactate binding. The MTC could be effectively suppressed using a pulse train with a B 1 of 0.8 μT, a pulse duration (t p) of 40 ms, a t mix of 60 ms, and a pulse number (N) of 30, while rNOE signal was well maintained. As a proof of concept, we applied the method in mouse brain with injected hydrogel and a cell-hydrogel phantom. Results showed that rNOE-weighted images could provide good contrast between brain/cell and hydrogel. Conclusion: The developed pulsed CEST magnetization-transfer method can achieve MTC suppression while preserving most of the rNOE signal at 3 T, which indicates the potential for translation of this technique to clinical applications related to mobile proteins/lipids change.

Whole‐brain amide CEST imaging at 3T with a steady‐state radial MRI acquisition

“…With fixed TR, the number of lines per blade determines the mixing time between saturation pulses, following . Previous pulsed CEST optimization has already demonstrated that 1 pulse width larger than 40 ms would achieve enough frequency selectivity at 3T 49 . Hence, the pulse width of the sinc‐gauss saturation pulses was set to 50 ms. For the human brain study, images were acquired at 5 × 3 × 3 mm 3 resolution using 15 slices and a FOV of 220 × 220 mm 2 .…”

“…Previous pulsed CEST optimization has already demonstrated that 1 pulse width larger than 40 ms would achieve enough frequency selectivity at 3T. 49 Hence, the pulse width of the sinc-gauss saturation pulses was set to 50 ms. For the human brain study, images were acquired at 5 × 3 × 3 mm 3 resolution using 15 slices and a FOV of 220 × 220 mm 2 . The image matrix was resized to 96 × 96 during reconstruction.…”

Relayed nuclear Overhauser effect weighted (rNOEw) imaging identifies multiple sclerosis

“…Pulsed-CEST sequence was set up for rNOE imaging by modifying the turbo spin echo (TSE) sequence. The saturation parameters optimized in previous study on a preclinical 3T MRI scanner were applied here ( Huang et al, 2021a ). Briefly, the saturation module contained a pulse train with a saturation power (B 1 ) of 0.8 μT, a pulse duration (t p ) of 40 ms, a mixing time (t mix ) of 60 ms and a pulse number (N) of 10.…”

“…rNOE imaging has high specificity towards mobile proteins and lipids and thus holds the potential to detect myelin change in MS brain, as myelin consists of abundant lipids and proteins ( Baumann and Pham-Dinh, 2001 ). MT contrast and direct water saturation (DS) are two major contaminations in rNOE contrast especially at clinical field strengths (such as 3T) ( Huang et al, 2021a , Xu et al, 2016 ). Recently, we developed a rNOE imaging scheme with MT suppression using an optimized pulsed-CEST sequence, i.e.…”

“…Recently, we developed a rNOE imaging scheme with MT suppression using an optimized pulsed-CEST sequence, i.e. variable delay multi-pulse (VDMP) sequence ( Xu et al, 2014 ), to sensitively detect changes of mobile proteins and lipids in mouse brain at a preclinical 3T MRI scanner ( Huang et al, 2021a , Xu et al, 2016 ). In addition to high sensitivity for detecting mobile proteins and lipids, this rNOE imaging scheme has the advantages of easy implementation and rapid postprocessing, making it readily to be translated to clinical MRI.…”