3D T2-weighted imaging at 7T using dynamic kT-points on single-transmit MRI systems

Eggenschwiler, Florent, O'Brien, Kieran Robert, Gallichan, Daniel, Gruetter, Rolf and Marques, Jose Pedro (2016) 3D T2-weighted imaging at 7T using dynamic kT-points on single-transmit MRI systems. Magnetic Resonance Materials in Physics, Biology and Medicine, 29 3: 347-358. doi:10.1007/s10334-016-0545-4


Author Eggenschwiler, Florent
O'Brien, Kieran Robert
Gallichan, Daniel
Gruetter, Rolf
Marques, Jose Pedro
Title 3D T2-weighted imaging at 7T using dynamic kT-points on single-transmit MRI systems
Formatted title
3D T2-weighted imaging at 7T using dynamic kT-points on single-transmit MRI systems
Journal name Magnetic Resonance Materials in Physics, Biology and Medicine   Check publisher's open access policy
ISSN 0968-5243
1352-8661
Publication date 2016-04-08
Year available 2016
Sub-type Article (original research)
DOI 10.1007/s10334-016-0545-4
Open Access Status Not Open Access
Volume 29
Issue 3
Start page 347
End page 358
Total pages 12
Place of publication Heidelberg, Germany
Publisher Springer
Language eng
Subject 3614 Radiological and Ultrasound Technology
1304 Biophysics
2741 Radiology Nuclear Medicine and imaging
Abstract Objectives: For turbo spin echo (TSE) sequences to be useful at ultra-high field, they should ideally employ an RF pulse train compensated for the B inhomogeneity. Previously, it was shown that a single k-point pulse designed in the small tip-angle regime can replace all the pulses of the sequence (static k-points). This work demonstrates that the B dependence of T-weighted imaging can be further mitigated by designing a specific k-point pulse for each pulse of a 3D TSE sequence (dynamic k-points) even on single-channel transmit systems Materials and methods: By combining the spatially resolved extended phase graph formalism (which calculates the echo signals throughout the sequence) with a gradient descent algorithm, dynamic k-points were optimized such that the difference between the simulated signal and a target was minimized at each echo. Dynamic k-points were inserted into the TSE sequence to acquire in vivo images at 7T. Results: The improvement provided by the dynamic k-points over the static k-point design and conventional hard pulses was demonstrated via simulations. Images acquired with dynamic k-points showed systematic improvement of signal and contrast at 7T over regular TSE—especially in cerebellar and temporal lobe regions without the need of parallel transmission. Conclusion: Designing dynamic k-points for a 3D TSE sequence allows the acquisition of T-weighted brain images on a single-transmit system at ultra-high field with reduced dropout and only mild residual effects due to the B inhomogeneity.
Formatted abstract
Objectives: For turbo spin echo (TSE) sequences to be useful at ultra-high field, they should ideally employ an RF pulse train compensated for the B1+ inhomogeneity. Previously, it was shown that a single kT-point pulse designed in the small tip-angle regime can replace all the pulses of the sequence (static kT-points). This work demonstrates that the B1+ dependence of T2-weighted imaging can be further mitigated by designing a specific kT-point pulse for each pulse of a 3D TSE sequence (dynamic kT-points) even on single-channel transmit systems

Materials and methods: By combining the spatially resolved extended phase graph formalism (which calculates the echo signals throughout the sequence) with a gradient descent algorithm, dynamic kT-points were optimized such that the difference between the simulated signal and a target was minimized at each echo. Dynamic kT-points were inserted into the TSE sequence to acquire in vivo images at 7T.

Results: The improvement provided by the dynamic kT-points over the static kT-point design and conventional hard pulses was demonstrated via simulations. Images acquired with dynamic kT-points showed systematic improvement of signal and contrast at 7T over regular TSE—especially in cerebellar and temporal lobe regions without the need of parallel transmission.

Conclusion: Designing dynamic kT-points for a 3D TSE sequence allows the acquisition of T2-weighted brain images on a single-transmit system at ultra-high field with reduced dropout and only mild residual effects due to the B1+ inhomogeneity.
Keyword B1+inhomogeneity correction
Dynamic kT-points
Spatially resolved extended phase graph
T2-weighted imaging
TSE sequence
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: HERDC Pre-Audit
Centre for Advanced Imaging Publications
 
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