Abstract
PurposeSimultaneous multi‐slice techniques are reliant on multiband RF pulses, for which conventional design strategies result in long pulse durations, lengthening echo‐times so lowering SNR for spin‐echo imaging, and lengthening repetition times for gradient echo sequences. Pulse durations can be reduced with advanced RF pulse design methods that use time‐variable selection gradients. However, the ability of gradient systems to reproduce fast switching pulses is often limited and can lead to image artifacts when ignored. We propose a time‐efficient pulse design method that inherently produces gradient waveforms with lower temporal bandwidth.MethodsEfficient multiband RF pulses with time‐variable gradients were designed using time‐optimal VERSE. Using VERSE directly on multiband pulses leads to gradient waveforms with high temporal bandwidth, whereas VERSE applied first to singleband RF pulses and then modulated to make them multiband, significantly reduces this. The relative performance of these approaches was compared using simulation and experimental measurements.ResultsApplying VERSE before multiband modulation was successful at removing out‐of‐band slice distortion. This effectively removes the need for high frequency modulation in the gradient waveform while preserving the benefit of time‐efficiency inherited from VERSE.ConclusionWe propose a time‐efficient RF pulse design that produces gradient pulses with lower temporal bandwidth, reducing image artifacts associated with finite temporal bandwidth of gradient systems.
Highlights
This method quickly reaches hardware limits on peak amplitudes as the number of slices increases, forcing pulse designers to either increase the pulse duration or reduce the flip angle, both of which are problematic for sequences such as spin‐echo diffusion imaging and turbo spin echo (TSE) where high signal and short echo times are important.[4,5,6]
|2 (SAR) constraints in MB SSFP applications force the use of sub‐peak amplitude MB RF pulses, which have long pulse durations and become difficult to fit within TR constraints.[7,8]
Application of VERSE leads to a compression of the RF waveforms with the MBv methods (Figures 3b, d) showing the smallest durations for this design, with little difference between linear and Figure 5 compares the slice profile errors inside and outside the imaging slice‐pack for various different N as predicted by both gradient impulse response function (GIRF) (h1 and h2)
Summary
We propose a time‐efficient pulse design method that inherently produces gradient waveforms with lower temporal bandwidth. Methods: Efficient multiband RF pulses with time‐variable gradients were designed using time‐optimal VERSE. Using VERSE directly on multiband pulses leads to gradient waveforms with high temporal bandwidth, whereas VERSE applied first to singleband RF pulses and modulated to make them multiband, significantly reduces this. Results: Applying VERSE before multiband modulation was successful at removing out‐of‐band slice distortion. This effectively removes the need for high frequency modulation in the gradient waveform while preserving the benefit of time‐efficiency inherited from VERSE. Conclusion: We propose a time‐efficient RF pulse design that produces gradient pulses with lower temporal bandwidth, reducing image artifacts associated with finite temporal bandwidth of gradient systems. KEYWORDS gradient frequency characterization, minimum duration, multiband, RF pulse design, time optimal, VERSE
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.