Abstract
Radiology, University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland Figure 1 Performance of the tailored pulses. a) Example characteristics of the HS1-derived TR-FOCI pulse. Note that the optimized pulse is broad compared to the standard HS1 (dotted line). b) Slice-excitation profile of the same HS1-derived TR-FOCI pulse. Above a low pulse power of gB1≈200 Hz, the profile has a very sharp transition. c) On-resonance inversion power requirements of the standard and TR-FOCI pulses. Once the HS1 pulse is optimized as a TR-FOCI pulse, it requires power similar to the standard HS8 pulse. d) Robustness of the same pulses to B0 variability at pulse power gB1 = 500 Hz. While the poor original profile of the HS8 pulse is improved after optimization, it is especially the optimized HS1 that has improved robustness. van Heeswijk et al. Journal of Cardiovascular Magnetic Resonance 2014, 16(Suppl 1):P41 http://www.jcmr-online.com/content/16/S1/P41
Highlights
Cardiac magnetic resonance imaging (CMR) has been shown to benefit from the higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) available at higher magnetic field strengths; in practice, CMR remains limited by the need for higher radiofrequency (RF) pulse power, which is in turn limited by the maximum specific absorption rate (SAR)
The design of T2Prep adiabatic inversion pulses requires a compromise between pulse performance and the energy deposition. To overcome this SAR limitation on T2Prep, we numerically optimized two hyperbolic secant (HSn; Silver et al JMagnReson1984) RF pulses and tested their performance for T2Prep refocusing in CMR at 3T
The Time-Resampled Frequency-Offset-Corrected Inversion (TR-FOCI) pulses required 54% less power than the HS1 pulse to achieve artifact-free images and stable CNR (Figure 2), while images obtained with an HS8 pulse were never artifact-free
Summary
Cardiac magnetic resonance imaging (CMR) has been shown to benefit from the higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) available at higher magnetic field strengths; in practice, CMR remains limited by the need for higher radiofrequency (RF) pulse power, which is in turn limited by the maximum specific absorption rate (SAR). 3T, an adiabatic (robust to RF inhomogeneity ΔB1) T2 preparation (T2Prep, Nezafat et al, MagnResonMed2006) can usually only be combined with balanced steady-state free precession (bSSFP) acquisitions with low nutation angles, or is played out only once every several heartbeats. The design of T2Prep adiabatic inversion pulses requires a compromise between pulse performance and the energy deposition. To overcome this SAR limitation on T2Prep, we numerically optimized two hyperbolic secant (HSn; Silver et al JMagnReson1984) RF pulses and tested their performance for T2Prep refocusing in CMR at 3T
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