Fast online spectral-spatial pulse design for subject-specific fat saturation in cervical spine and foot imaging at 1.5 T

• Published in: Magma (New York, N.Y.) Vol. 37; no. 2; pp. 257 - 272
• Main Authors: Eisen, Christian Karl, Liebig, Patrick, Herrler, Jürgen, Ritter, Dieter, Lévy, Simon, Uder, Michael, Nagel, Armin Michael, Grodzki, David
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.04.2024
• Subjects: Basic Science - Contrast mechanisms; Biomedical Engineering and Bioengineering; Computer Appl. in Life Sciences; Health Informatics; Imaging; Medicine; Medicine & Public Health; Radiology; Research Article; Solid State Physics; 1.5 T MRI; Dynamic RF pulses; Fat saturation; Dynamic transmission; Pulse design
• ISSN: 1352-8661; 1352-8661
• DOI: 10.1007/s10334-024-01149-8

Objective To compensate subject-specific field inhomogeneities and enhance fat pre-saturation with a fast online individual spectral-spatial (SPSP) single-channel pulse design. Methods The RF shape is calculated online using subject-specific field maps and a predefined excitation k-space trajectory. Calculation acceleration options are explored to increase clinical viability. Four optimization configurations are compared to a standard Gaussian spectral selective pre-saturation pulse and to a Dixon acquisition using phantom and volunteer ( N  = 5) data at 1.5 T with a turbo spin echo (TSE) sequence. Measurements and simulations are conducted across various body parts and image orientations. Results Phantom measurements demonstrate up to a 3.5-fold reduction in residual fat signal compared to Gaussian fat saturation. In vivo evaluations show improvements up to sixfold for dorsal subcutaneous fat in sagittal cervical spine acquisitions. The versatility of the tailored trajectory is confirmed through sagittal foot/ankle, coronal, and transversal cervical spine experiments. Additional measurements indicate that excitation field (B1) information can be disregarded at 1.5 T. Acceleration methods reduce computation time to a few seconds. Discussion An individual pulse design that primarily compensates for main field (B0) inhomogeneities in fat pre-saturation is successfully implemented within an online "push-button" workflow. Both fat saturation homogeneity and the level of suppression are improved.