Whole‐brain chemical exchange saturation transfer imaging with optimized turbo spin echo readout

Abstract

Purpose: To achieve fast whole-brain chemical exchange saturation transfer (CEST) imaging with negligible susceptibility artifact. Methods: An optimized turbo spin echo readout module, also known as sampling perfection with application optimized contrasts by using different flip angle evolutions (SPACE), was deployed in the CEST sequence. The SPACE-CEST sequence was tested in a phantom, 6 healthy volunteers, and 3 brain tumor patients on a 3T human scanner. A dual-echo gradient echo sequence was used for B 0 inhomogeneity mapping. In addition, the proposed SPACE-CEST sequence was compared with the widely used turbo spin echo-CEST sequence for amide proton transfer-weighted (APTw) images. Results: The SPACE-CEST sequence generated highly consistent APTw maps to those of the turbo spin echo-CEST sequence in the phantom. In healthy volunteers, the SPACE-CEST sequence yielded whole-brain 2.8-mm isotropic APTw source images within 5 minutes, with no discernible susceptibility artifact. As for the B 0 maps in the whole brain, its mean, median, and standard deviation B 0 offset values were 5.0 Hz, 5.6 Hz, and 16 Hz, respectively. Regarding the APTw map throughout the whole brain, its mean, median, and standard deviation values were 0.78%, 0.56%, and 1.74%, respectively. The SPACE-CEST sequence was also successfully applied to a postsurgery brain tumor patient, suggesting no disease progression. In addition, on the newly diagnosed brain tumor patients, the SPACE-CEST and turbo spin echo-CEST sequences yielded essentially identical APTw values. Conclusion: The proposed SPACE-CEST technique can rapidly generate wholebrain CEST source images with negligible susceptibility artifact. K E Y W O R D Samide proton transfer, chemical exchange saturation transfer, fast imaging, sampling perfection with application optimized contrasts by using different flip angle evolutions (SPACE), whole brain 1162 | ZHANG et Al.

Chemical exchange saturation transfer imaging for epilepsy secondary to tuberous sclerosis complex at 3 T: Optimization and analysis

“…The CEST sequence was performed with single‐shot TSE readout 28,29 using the following parameters: FOV = 212 mm × 185.5 mm; acquisition resolution = 1.0 mm × 1.0 mm; turbo factor = 208; slice thickness = 5 mm; TE = 8.1 ms; RF saturation duration = 400, 700 and 1000 ms with corresponding TR = 3, 4 and 5 s, respectively (with corresponding recovery times of ~ 2.6, ~ 3.3 and ~ 4.0 s, respectively); RF saturation power = 1, 2, 3 and 4 μT; and total number of saturation duration and power combinations = 12. Specifically, the CEST saturation was achieved with multiple 100 ms‐long Gaussian pulse elements with a gap of 5 ms in between 30 . Furthermore, 63 CEST frames were acquired including an unsaturated reference image, and saturated images at 0, ±0.25, ±0.5, ±0.75, ±1, ±1.25, ±1.5, ±1.75 (2), ±2 (2), ±2.25 (2), ±2.5 (2), ±2.75 (2), ±3 (2), ±3.25 (2), ±3.5 (2), ±3.75 (2), ±4 (2), ±4.5, ±5, ±5.5, ±6 and 15.6 ppm, where the number in the parentheses represents the number of averages.…”

Fast chemical exchange saturation transfer imaging based on PROPELLER acquisition and deep neural network reconstruction

“…Usually, CEST MRI sequences are composed of a long‐duration off‐resonance RF irradiation module and a fast image readout module such as fast spin echo (FSE) or echo planar imaging (EPI) 25‐28 . Compared with FSE, EPI can significantly reduce scan time, but it is vulnerable to field inhomogeneity and chemical shift effects, and generates signal voids or distortion at the tissue‐air interface, which might disturb the accuracy of the measured results 29 …”

“…[25][26][27][28] Compared with FSE, EPI can significantly reduce scan time, but it is vulnerable to field inhomogeneity and chemical shift effects, and generates signal voids or distortion at the tissue-air interface, which might disturb the accuracy of the measured results. 29 In this study, we introduce a sampling pattern based on periodically rotated overlapping parallel lines enhanced reconstruction (PROPELLER) 30 into CEST MRI to dramatically accelerate CEST imaging (dubbed as CEST-PROPELLER). Similar to the compressed sensing method in CEST imaging that can reduce the scan time by randomly undersampling k-space data, 31 the CEST-PROPELLER sampling scheme is used to acquire only several lines from the k-space center per saturated image.…”

Frequency‐stabilized chemical exchange saturation transfer imaging with real‐time free‐induction‐decay readout

“…[28][29][30] Importantly, these artifacts due to temporal B 0 drift cannot be corrected retrospectively by conventional methods for the correction of spatial B 0 inhomogeneity. [31][32][33] Thus, if CEST imaging is performed subject to temporal B 0 drift in practice, the validity of final CEST maps can be compromised. Recently, several studies have attempted to resolve artifacts caused by temporal B 0 drift in CEST imaging.…”

“…Furthermore, the temporal drift of CEST z‐spectra can distort MTR asym spectra, leading to abnormally high or low signal intensities on CEST maps 28‐30 . Importantly, these artifacts due to temporal B 0 drift cannot be corrected retrospectively by conventional methods for the correction of spatial B 0 inhomogeneity 31‐33 . Thus, if CEST imaging is performed subject to temporal B 0 drift in practice, the validity of final CEST maps can be compromised.…”