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Keywords:

  • B1 mapping;
  • Bloch-Siegert shift;
  • CPMG;
  • multi-spin echo;
  • turbo-spin echo

Abstract

Bloch-Siegert (BS) based Bmath image mapping methods use off-resonant pulses to encode quantitative Bmath image information into the signal phase. It was recently shown that the principle behind BS-based Bmath image mapping can be expanded from spin echo (BS-SE) and gradient-echo (BS-FLASH) based BS Bmath image mapping to methods such as Carr, Purcell, Meiboom, Gill (CPMG)-based turbo-spin echo (BS-CPMG-TSE) and multi-spin echo (BS-CPMG-MSE) imaging. If CPMG conditions are preserved, BS-CPMG-TSE allows fast acquisition of the Bmath image information and BS-CPMG-MSE enables simultaneous mapping of Bmath image, M0, and T2. To date, however, two separate MRI experiments must be performed to enable the calculation of Bmath image maps. This study investigated a modified encoding strategy for CPMG BS-based methods to overcome this limitation. By applying a “bipolar” off-resonant BS pulse before the refocusing pulse train, the needed phase information was able to be encoded into different echo images of one echo train. Thus, this technique allowed simultaneous Bmath image and T2 mapping in a single BS-CPMG-MSE experiment. To allow single-shot Bmath image mapping, this method was also applied to turbo-spin echo imaging. Furthermore, the presented modification intrinsically minimizes phase-based image artifacts in BS-CPMG-TSE experiments. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.