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Keywords:

  • adiabatic turbo spin echo;
  • magnetic resonance imaging;
  • superadiabaticity;
  • 7 T

Abstract

Nonuniform B1 fields in ultrahigh-field MR imaging cause severe image artifacts, when conventional radiofrequency (RF) pulses are used. Particularly in MR sequences that encompass multiple RF pulses, e.g., turbo spin echo (TSE) sequences, complete signal loss may occur in certain areas. When using a surface coil for transmitting the RF pulses, these problems become even more challenging, as the spatial B1 field variance is substantial. As an alternative to conventional TSE sequences, adiabatic TSE sequences can be applied, which have the benefit that these sequences are insensitive to B1 nonuniformity. In this study, we investigate the potential of using adiabatic TSE at 7 T with surface coil transceivers in human applications. The adiabatic RF pulses were tuned to deal with the constraints in B1 strength and RF power deposition, but remained in the superadiabatic regime. As a consequence, the dynamic range in B1 is compromised, and signal modulation is obtained over the echo train. Multidimensional Bloch simulations over the echo train and phantom measurements were obtained to assess these limitations. Still, using proper k-space sampling, we demonstrate improved image quality of the adiabatic TSE versus conventional TSE in the brain, the neck (carotid artery) and in the pelvis (prostate) at 7 T. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.