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

Abstract

Purpose: To develop a steady-state saturation with radial readout chemical exchange saturation transfer (starCEST) for acquiring CEST images at 3 Tesla (T). The polynomial Lorentzian line-shape fitting approach was further developed for extracting amideCEST intensities at this field. Method: StarCEST MRI using periodically rotated overlapping parallel lines with enhanced reconstruction-based spatial sampling was implemented to acquire Zspectra that are robust to brain motion. Multi-linear singular value decomposition postprocessing was applied to enhance the CEST SNR. The egg white phantom studies were performed at 3T to reveal the contributions to the 3.5 ppm CEST signal.Based on the phantom validation, the amideCEST peak was quantified using the polynomial Lorentzian line-shape fitting, which exploits the inverse relationship between Z-spectral intensity and the longitudinal relaxation rate in the rotating frame.The 3D turbo spin echo CEST was also performed to compare with the starCEST method. Results: The amideCEST peak showed a negligible peak B 1 dependence between 1.2 µT and 2.4 µT. The amideCEST images acquired with starCEST showed much improved image quality, SNR, and motion robustness compared to the conventional 3D turbo spin echo CEST method with the same scan time. The amideCEST contrast extracted by the polynomial Lorentzian line-shape fitting method trended toward a stronger gray matter signal (1.32% ± 0.30%) than white matter (0.92% ± 0.08%; P = .02, n = 5). When calculating the magnetization transfer contrast and T 1 -corrected rotating frame relaxation rate maps, amideCEST again was not significantly different for white matter and gray matter.How to cite this article: Sui R, Chen L, Li Y, et al. Whole-brain amide CEST imaging at 3T with a steady-state radial MRI acquisition.

Early detection of Alzheimer's disease using creatine chemical exchange saturation transfer magnetic resonance imaging

“…Lower saturation power and longer saturation length will lead to a larger contribution from Guan proton to CEST signal at 2 ppm. On contrary to CrCEST in brain, GuanCEST contrast shows an opposite trend regarding pH reduction, which means lower pH yields higher GuanCEST contrast as evidenced by both eggwhite phantom ( Sui et al, 2021 ) and ischemic stroke studies ( Jin et al, 2017 ; Zhou et al, 2019 ). Therefore, in practice, appropriate saturation parameters should be chosen to ensure the CEST signal at 2 ppm is dominated by Cr.…”

“…For CrCEST study, the peak is much close to the water signal. In order to improve the fitting, an updated background function was introduced by including one Lorentzian function to account for the water direct saturation (DS) ( Sui et al, 2021 ): where the polynomial function ( C 2 + C 3 · Δω) was implemented to fit the background, consisting of magnetization transfer contrast (MTC) and exchanging protons such as amines and hydroxyls. We found that a linear function was sufficient to fit this combined background line shape between 1–3.5 ppm.…”

Mapping intracellular pH in tumors using amide and guanidyl CEST‐MRI at 9.4 T

“…A reliable extraction of the amide and guanidyl signals from the background of other magnetization transfer signals (i.e. pH-independent) was realized by a separate firstorder polynomial and Lorentzian-fit 14,24,61 (Equation 10). In order to assess the specificity of the pH-dependent signals extracted by the fit model, the resulting MTR Rex (pH) curves were investigated, which served as a kind of ground truth.…”

Molecular Imaging of Brain Tumors and Drug Delivery Using CEST MRI: Promises and Challenges

“…Since the quantification of Z-spectra is exquisitely sensitive to static magnetic field (B 0 ) inhomogeneity, which exists in most MRI scanners, B 0 correction is needed. Typically B 0 correction is performed in two steps: (i) Generate a B 0 map: the B 0 map can be obtained by estimating the minimum of interpolated/fitted Z-spectra [48,171,172], water saturation shift referencing (WASSR) [173], or other B 0 mapping methods [174][175][176].…”

“…After B 0 correction, it is sometimes suggested performing B 1 correction if the scanner has large B 1 inhomogeneity [35,176]. Similar to B 0 correction, B 1 correction includes two steps: (i) Generate B 1 map: the B 1 map can be acquired using flip-angle mapping [35,177], double angle method (DAM) [174,178], or other B 1 mapping methods [175,176]. (ii) Correct B 0 inhomogeneity for Z-spectra or CEST contrasts: the relative values on B 1 map are applied to correct the corresponding Z-spectra or CEST contrasts on a pixel-by-pixel basis.…”