SNR efficiency of combined bipolar gradient echoes: Comparison of three‐dimensional FLASH, MPRAGE, and multiparameter mapping with VFA‐FLASH and MP2RAGE

• SNR Efficiency in Bipolar Multiecho Gradient Echo

• Author(s) / Creator(s)

  • Jutras, Jean-David
  • Wachowicz, Keith
  • Gilbert, Guillaume
  • De Zanche, Nicola

• This is the peer reviewed version of the following article: Magn Reson Med 77:2186–2202, 2017, which has been published in final form at https://doi.org/10.1002/mrm.26306. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.

  Purpose
  High‐bandwidth bipolar multiecho gradient echo sequences are increasingly popular in structural brain imaging because of reduced water–fat shifts, lower susceptibility effects, and improved signal‐to‐noise ratio (SNR) efficiency. In this study, we investigated the performance of three three‐dimensional multiecho sequences (MPRAGE, MP2RAGE, and FLASH) with scan times < 9 min and 1‐mm isotropic resolution against their single‐echo, low‐bandwidth counterparts at 3T. We also compared the performance of multiparameter mapping (PD, T1, and T2*) with bipolar multiecho MP2RAGE versus the variable flip angle technique with multiecho FLASH (VFA‐FLASH).

  Methods
  Multiecho sequences were optimized to yield equivalent contrast and improved SNR compared with their single‐echo counterparts. Theoretical SNR gains were verified with measurements in a multilayered phantom. Robust image processing pipelines extracted PD, T1, and T2* maps from MP2RAGE or VFA‐FLASH, and the corresponding SNR was measured with varying SENSE accelerations (R = 1–5) and number of echoes (N = 1–12). All sequences were tested on four healthy volunteers.

  Results
  Multiecho sequences achieved SNR gains of 1.3–1.6 over single‐echo sequences. MP2RAGE yielded comparable T1‐to‐noise ratio to VFA‐FLASH, but significantly lower SNR (<50%) in PD and T2* maps. Measured SNR gains agreed with the theoretical predictions for SENSE accelerations ≤3.

  Conclusion
  Multiecho sequences achieve higher SNR efficiency over conventional single‐echo sequences, despite three‐fold higher sampling bandwidths. VFA‐FLASH surpasses MP2RAGE in its ability to map three parameters with high SNR and 1‐mm isotropic resolution in a clinically relevant scan time (∼8:30 min), whereas MP2RAGE yields lower intersubject variability in T1.

• Date created

  2016-07-15

• Subjects / Keywords

  • SNR efficiency; bipolar echoes; high resolution brain MRI; multiparameter mapping; T1 ; T2* ; proton density; FLASH; MPRAGE; MP2RAGE; Variable Flip Angle

• Type of Item

  Article (Published)

• DOI

  https://doi.org/10.7939/r3-bvrv-4k39

• License

  Attribution-NonCommercial-NoDerivatives 4.0 International