Tailored spiral in‐out spectral‐spatial water suppression pulses for magnetic resonance spectroscopic imaging

• Published in: Magnetic resonance in medicine Vol. 79; no. 1; pp. 31 - 40
• Main Authors: Ma, Jun, Wismans, Carrie, Cao, Zhipeng, Klomp, Dennis W. J., Wijnen, Jannie P., Grissom, William A.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.01.2018
• Subjects: Algorithms; Brain; Brain - diagnostic imaging; Brain Mapping - methods; Computer Simulation; High resolution; Humans; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Image Processing, Computer-Assisted; Image resolution; Inhomogeneity; Magnetic resonance imaging; Magnetic resonance spectroscopy; Magnetic Resonance Spectroscopy - methods; Neuroimaging; optimization; Phantoms, Imaging; Radio Waves; Reproducibility of Results; RF pulse design; RF pulses; selective excitation; Sensitivity and Specificity; Signal-To-Noise Ratio; Spatial discrimination; Spatial resolution; Spectra; spectroscopy; ultra‐high field MRI; Water - chemistry; RF pulses; RF pulse design; optimization; spectroscopy; ultra-high field MRI; selective excitation
• ISSN: 0740-3194; 1522-2594; 1522-2594
• DOI: 10.1002/mrm.26683

Purpose To develop short water suppression sequences for 7 T magnetic resonance spectroscopic imaging, with mitigation of subject‐specific transmit RF field ( B1+) inhomogeneity. Methods Patient‐tailored spiral in‐out spectral‐spatial saturation pulses were designed for a three‐pulse WET water suppression sequence. The pulses’ identical spatial subpulses were designed using patient‐specific B1+ maps and a spiral in‐out excitation k‐space trajectory. The subpulse train was weighted by a spectral envelope that was root‐flipped to minimize peak RF demand. The pulses were validated in in vivo experiments that acquired high resolution magnetic resonance spectroscopic imaging data, using a crusher coil for fast lipid suppression. Residual water signals and MR spectra were compared between the proposed tailored sequence and a conventional WET sequence. Results Replacing conventional spectrally‐selective pulses with tailored spiral in‐out spectral‐spatial pulses reduced mean water residual from 5.88 to 2.52% (57% improvement). Pulse design time was less then 0.4 s. The pulses’ specific absorption rate were compatible with magnetic resonance spectroscopic imaging TRs under 300 ms, which enabled spectra of fine in plane spatial resolution (5 mm) with good quality to be measured in 7.5 min. Conclusion Tailored spiral in‐out spectral‐spatial water suppression enables efficient high resolution magnetic resonance spectroscopic imaging in the brain. Magn Reson Med 79:31–40, 2018. © 2017 International Society for Magnetic Resonance in Medicine.