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Purpose: The delay alternating with nutation for tailored excitation (DANTE)–sampling perfection with application‐optimized contrasts (SPACE) sequence facilitates 3D intracranial vessel wall imaging with simultaneous suppression of blood and CSF. However, the achieved image contrast depends closely on the selected sequence parameters, and the clinical use of the sequence is limited in vivo by observed signal variations in the vessel wall, CSF, and blood. This paper introduces a comprehensive DANTE‐SPACE simulation framework, with the aim of providing a better understanding of the underlying contrast mechanisms and facilitating improved parameter selection and contrast optimization. Methods: An extended phase graph formalism was developed for efficient spin ensemble simulation of the DANTE‐SPACE sequence. Physiological processes such as pulsatile flow velocity variation, varying flow directions, intravoxel velocity variation, diffusion, and B1+$$ {\mathrm{B}}_1^{+} $$ effects were included in the framework to represent the mechanisms behind the achieved signal levels accurately. Results: Intravoxel velocity variation improved temporal stability and robustness against small velocity changes. Time‐varying pulsatile velocity variation affected CSF simulations, introducing periods of near‐zero velocity and partial rephasing. Inclusion of diffusion effects was found to substantially reduce the CSF signal. Blood flow trajectory variations had minor effects, but B1+$$ {\mathrm{B}}_1^{+} $$ differences along the trajectory reduced DANTE efficiency in low‐B1+$$ {\mathrm{B}}_1^{+} $$ areas. Introducing low‐velocity pulsatility of both CSF and vessel wall helped explain the in vivo observed signal heterogeneity in both tissue types. Conclusion: The presented simulation framework facilitates a more comprehensive optimization of DANTE‐SPACE sequence parameters. Furthermore, the simulation framework helps to explain observed contrasts in acquired data. [ABSTRACT FROM AUTHOR]

Purpose: Neurovascular MRI suffers from a rapid drop in B1+ into the neck when using transmit head coils at 7 T. One solution to improving B1+ magnitude in the major feeding arteries in the neck is to use custom RF shims on parallel‐transmit head coils. However, calculating such shims requires robust multichannel B1+ maps in both the head and the neck, which is challenging due to low RF penetration into the neck, limited dynamic range of multichannel B1+ mapping techniques, and B0 sensitivity. We therefore sought a robust, large‐dynamic‐range, parallel‐transmit field mapping protocol and tested whether RF shimming can improve carotid artery B1+ magnitude in practice. Methods: A pipeline is presented that combines B1+ mapping data acquired using circularly polarized (CP) and CP2‐mode RF shims at multiple voltages. The pipeline was evaluated by comparing the predicted and measured B1+ for multiple random transmit shims, and by assessing the ability of RF shimming to increase B1+ in the carotid arteries. Results: The proposed method achieved good agreement between predicted and measured B1+ in both the head and the neck. The B1+ magnitude in the carotid arteries can be increased by 43% using tailored RF shims or by 37% using universal RF shims, while also improving the RF homogeneity compared with CP mode. Conclusion: B1+ in the neck can be increased using RF shims calculated from multichannel B1+ maps in both the head and the neck. This can be achieved using universal phase‐only RF shims, facilitating easy implementation in existing sequences. [ABSTRACT FROM AUTHOR]

Purpose: Neurovascular MRI suffers from a rapid drop in B 1 into the neck when using transmit head coils at 7 T. One solution to improving B + into the neck when using transmit head coils at 7 T. One solution to improving B 1 + magnitude in the major feeding arteries in the neck is to use custom RF shims on parallel-transmit head coils. However, calculating such shims requires robust multichannel B 1 + maps in both the head and the neck, which is challenging due to low RF penetration into the neck, limited dynamic range of multichannel B 1 + mapping techniques, and B 0 sensitivity. We therefore sought a robust, large-dynamic-range, parallel-transmit field mapping protocol and tested whether RF shimming can improve carotid artery B 1 + magnitude in practice., Methods: A pipeline is presented that combines B 1 + mapping data acquired using circularly polarized (CP) and CP2-mode RF shims at multiple voltages. The pipeline was evaluated by comparing the predicted and measured B 1 + for multiple random transmit shims, and by assessing the ability of RF shimming to increase B 1 + in the carotid arteries., Results: The proposed method achieved good agreement between predicted and measured B 1 + in both the head and the neck. The B 1 + magnitude in the carotid arteries can be increased by 43% using tailored RF shims or by 37% using universal RF shims, while also improving the RF homogeneity compared with CP mode., Conclusion: B 1 + in the neck can be increased using RF shims calculated from multichannel B 1 + maps in both the head and the neck. This can be achieved using universal phase-only RF shims, facilitating easy implementation in existing sequences., (© 2023 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)