Völzke Y, Akbey S, Löwen D, Pracht ED, Stirnberg R, Gras V, Boulant N, Zaiß M, Stöcker T (2025)
Publication Type: Journal article
Publication year: 2025
Book Volume: 93
Pages Range: 630-642
Journal Issue: 2
DOI: 10.1002/mrm.30305
PURPOSE: Chemical exchange saturation transfer (CEST) measurements at ultra-high field (UHF) suffer from strong saturation inhomogeneity. Retrospective correction of this inhomogeneity is possible to some extent, but requires a time-consuming repetition of the measurement. Here, we propose a calibration-free parallel transmit (pTx)-based saturation scheme that homogenizes the saturation over the imaging volume, which we call PUlse design for Saturation Homogeneity utilizing Universal Pulses (PUSHUP). THEORY: Magnetization transfer effects depend on the saturation B 1 rms $$ {\mathrm{B}}_1^{\mathrm{rms}} $$ . PUSHUP homogenizes the saturation B 1 rms $$ {\mathrm{B}}_1^{\mathrm{rms}} $$ by using multiple saturation pulses with alternating B 1 $$ {\mathrm{B}}_1 $$ -shims. Using a database of B 1 $$ {\mathrm{B}}_1 $$ maps, universal pulses are calculated that remove the necessity of time-consuming, subject-based pulse calculation during the measurement. METHODS: PUSHUP was combined with a whole-brain three-dimensional-echo planar imaging (3D-EPI) readout. Two PUSHUP saturation modules were calculated by either applying whole-brain or cerebellum masks to the database maps. The saturation homogeneity and the group mean CEST amplitudes were calculated for different B 1 $$ {\mathrm{B}}_1 $$ -correction methods and were compared to circular polarized (CP) saturation in five healthy volunteers using an eight-channel transmit coil at 7 Tesla. RESULTS: In contrast to CP saturation, where accurate CEST maps were impossible to obtain in the cerebellum, even with extensive B 1 $$ {\mathrm{B}}_1 $$ -correction, PUSHUP CEST maps were artifact-free throughout the whole brain. A 1-point retrospective B 1 $$ {\mathrm{B}}_1 $$ -correction, that does not need repeated measurements, sufficiently removed the effect of residual saturation inhomogeneity. CONCLUSION: The presented method allows for homogeneous whole-brain CEST imaging at 7 Tesla without the need of a repetition-based B 1 $$ {\mathrm{B}}_1 $$ -correction or online pulse calculation. With the fast 3D-EPI readout, whole-brain CEST imaging with 45 saturation offsets is possible at 1.6 mm resolution in under 4 min.
APA:
Völzke, Y., Akbey, S., Löwen, D., Pracht, E.D., Stirnberg, R., Gras, V.,... Stöcker, T. (2025). Calibration-free whole-brain CEST imaging at 7T with parallel transmit pulse design for saturation homogeneity utilizing universal pulses (PUSHUP). Magnetic Resonance in Medicine, 93(2), 630-642. https://doi.org/10.1002/mrm.30305
MLA:
Völzke, Yannik, et al. "Calibration-free whole-brain CEST imaging at 7T with parallel transmit pulse design for saturation homogeneity utilizing universal pulses (PUSHUP)." Magnetic Resonance in Medicine 93.2 (2025): 630-642.
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