Slice-selective adiabatic magnetization T2 -preparation (SAMPA) for efficient T2 -weighted imaging at ultrahigh field strengths

Magn Reson Med. 2016 Dec;76(6):1741-1749. doi: 10.1002/mrm.26067. Epub 2015 Dec 1.

Abstract

Purpose: At high field, T2 -weighted (T2 w) imaging is limited by transmit field inhomogeneity and increased radiofrequency power deposition. In this work, we introduce SAMPA (Slice-selective Adiabatic Magnetization T2 PrepAration) and demonstrate its use for efficient brain T2 w imaging at 7 Tesla (T).

Methods: SAMPA was designed by subsampling an optimized B1 insensitive rotation (BIR4) waveform with small tip angle linear subpulses. To perform T2 w imaging, SAMPA was inserted before a fast gradient echo acquisition. The off-resonance behavior, B1 robustness, and slice selectivity of the novel T2 preparation module were analyzed using Bloch simulations. The performance of SAMPA for T2 w imaging was demonstrated in phantom experiments as well as in the brains of healthy volunteers at 7T.

Results: Based on simulations, the proposed design operates at peak B1 of 15 μT and higher, within a 400 Hz bandwidth. T2 values were in strong agreement with spin echo-based T2 mapping in phantom experiments. Whole brain, interleaved multislab three-dimensional imaging could be acquired with 0.8 mm3 isotropic resolution in 5:36 min per T2 weighting.

Conclusion: Compared with previous adiabatic T2 preparation techniques, SAMPA allows for slice-selectivity, which can lead to efficient and robust acquisitions for T2 w imaging at high field. Magn Reson Med 76:1741-1749, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Keywords: 3D; 7 Tesla; 7T; FLASH; RF pulse; T2 mapping; T2 preparation; adiabatic; multislab; ultrahigh field.

Publication types

  • Evaluation Study

MeSH terms

  • Algorithms*
  • Brain / anatomy & histology*
  • Diffusion Magnetic Resonance Imaging / methods*
  • Humans
  • Image Enhancement / methods*
  • Image Interpretation, Computer-Assisted / methods*
  • Phantoms, Imaging
  • Radiation Dosage
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Signal Processing, Computer-Assisted*