Calibration‐free regional RF shims for MRS

Abstract

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Unsupervised deep learning with convolutional neural networks for static parallel transmit design: A retrospective study

“…In this study, we proposed an unsupervised DL method with CNNs for multi‐channel pTx design. We demonstrated its feasibility through static $$$ {B}_1^{+} $$$ shimming at 7T, employing a slice‐by‐slice shimming technique, 28,29 which offered an additional degree of freedom compared to regional approaches 30 . Our method enhanced the uniformity of flip angle profiles quantitatively, displaying favorable results compared to the unregularized MLS technique in terms of RMSE and CoV metrics while maintaining a comparable energy consumption level.…”

Calibration‐free parallel transmission of the cervical, thoracic, and lumbar spinal cord at 7T

“…Calibration‐free pTx employing universal RF pulses effectively alleviates the challenges associated with lengthy and error‐prone tailored pTx approaches and has been successfully implemented in various body regions, including the brain, heart, and C‐spine 16,19,21,25 . However, only a few studies have explored the use of universal RF shims for specific applications, such as localized spectroscopy 17 or a simulation study that focused on combined brain‐neck imaging, 18 with the latter work limited to simulations, despite their inherent advantages in terms of ease of design and application. Moreover, this shortage of applications is striking given that the temporal $$$ {B}_1^{+} $$$ efficiency of dynamic pulses, such as kT‐point pulses, is compromised by the additional RF dead time during gradient blips.…”

“…UPs are generated by optimizing across a library of $$$ {B}_1^{+} $$$ maps from multiple subjects and can be applied to novel subjects without additional calibration, eliminating the need for time‐consuming calibration procedures. Their effectiveness has inspired adaptations in other areas, such as the development of universal RF shims for spectroscopy in the head, 17 brain and C‐spine, 18 or dynamic UPs in the heart 19,20 and C‐spine 21 . Other calibration‐free approaches have been proposed for brain imaging, including machine‐learned slice‐by‐slice RF shims at 7T 22 and dynamic SmartPulses for liver imaging at 3T 23 or the combination of universal and tailored pulses for the brain at 7T 24,25 …”

Ultra-high field MRI: parallel-transmit arrays and RF pulse design

“…gradient echo, MPRAGE (Mugler and Brookeman 1990), MP2RAGE (Marques et al 2010), FLAWS (Beaumont et al 2020), SPACE (Mugler 2014)) in the PASTeUR package (Massire et al 2022) and have been refined to overcome high B 0 field off-resonance (Van Damme et al 2020) using the GRAPE algorithm (Khaneja et al 2005). They have been extended to 2D and 3D rFOV excitations (Geldschläger et al 2021) and the concept has been also been used to generate calibrationaless small region shims for single-voxel spectroscopy (Berrington et al 2021) Another further advancement are Fast-Online Customized or FOCUS pulses (Herrler et al 2021a), which leverage both universal and tailored pulse designs. In the FOCUS method, a tailored pTx pulse is designed rapidly, initializing the pulse with a UP.…”