CEST imaging at 9.4 T using adjusted adiabatic spin‐lock pulses for on‐ and off‐resonant T1⍴‐dominated Z‐spectrum acquisition

Abstract

By adapting a pulse shape for low-power SL experiments, we were able to acquire robust on- and off-resonant adiabatic SL prepared images in vivo at 9.4 T. This development leads directly to SL Z-spectrum acquisition, beneficial for chemical-exchange-weighted MRI.

T1ρ‐based dynamic glucose‐enhanced (DGEρ) MRI at 3 T: method development and early clinical experience in the human brain

“…The optimal method studied herein is off‐resonant SL, yet off‐resonant SL and CEST are very similar as shown previously . We think that SL has several advantages over a CEST experiment, especially in experiments close to the water resonance using high B 1 power where CEST is tricky and prone to instabilities, even with shaped pulses.…”

“…As shown previously, SL pulses have a higher exchange weighting than classical saturation pulses, such as Gaussian or rectangular‐shaped pulses, especially in the intermediate to fast exchange regime . Recently published adiabatic prepared SL pulses allow for stable saturation at off‐resonant frequencies with low direct water saturation. Because they were previously optimized for B 0 = 9.4 T, this optimization was repeated for B 0 = 3 T. The adiabatic pulses are defined by the adiabatic parameter µ, the bandwidth ∆f, the Hamming window size t window and duration t adia .…”

“…To overcome the obstacles at 3 T, we combined several recent developments: (1) The DGE effect strength was recently optimized based on quantitative CEST experiments . These optimal parameters were used and implemented with (2) a novel adiabatic pulse shape designed for off‐resonant spin‐lock (SL) experiments, which is favorable given that it has lower direct water saturation and high CEST labeling efficiency. (3) A 3D gradient‐echo snapshot readout was used for imaging of the CEST prepared signal to limit motion artifacts and to be able to perform volume registration of the acquired dynamic scans retrospectively.…”

Quantification of hydroxyl exchange of D‐Glucose at physiological conditions for optimization of glucoCEST MRI at 3, 7 and 9.4 Tesla

“…Shaped pulses will have strong flip‐angle‐like oscillations close to water, yet even at 3 T for offsets at 1 ppm these oscillations are minor and the pulses behave adiabatically (Figure B). Recently proposed matched adiabatic SL pulses can be used both on‐ and off‐resonant and are shown to perform well under the optimized conditions (Figure C). Thus, shaped off‐resonant pulses or adiabatic matched SL pulses can both realize the proposed optimal parameters.…”

“…T 1 and T 2 values were taken from the multi-field study of Zhu et al 24 MT parameters (pool C) were adapted from Stanisz et al 25 ; f C = 0.05, T 2c = 9.1 μs, k CA = 40 Hz, δ C = 0; Super-Lorentzian lineshape After acquisition of scout images, a T 2 -weighted anatomical reference image was acquired using a fast spin echo (FSE) sequence and the same geometry was used for the CESL experiments. Briefly, CESL Z-spectra were acquired by using an adiabatic SL pulse, as reported by Herz et al, 30 before and after the glucose injection with several saturation power levels (range: 0.6-5.0 μT) and irradiation times (range: 0.1-5.0 s). A singleshot FSE-centric encoding readout was used with the following parameters: TR = 6 s, TE = 3.5 ms, FOV = 3 x 3 cm, slice thickness = 2 mm, matrix size = 64 x 64.…”