Retrospective correction for T1-weighting bias in T2 values obtained with various spectroscopic spin-echo acquisition schemes

Magn Reson Imaging. 2009 Dec;27(10):1410-9. doi: 10.1016/j.mri.2009.05.033. Epub 2009 Jun 25.

Abstract

Localized tissue transverse relaxation time (T(2)) is obtained by fitting a decaying exponential to the signals from several spin-echo experiments at different echo times (TE). Unfortunately, time constraints in magnetic resonance spectroscopy (MRS) often mandate in vivo acquisition schemes at short repetition times (TR), that is, comparable with the longitudinal relaxation constant (T(1)). This leads to different T(1)-weighting of the signals at each TE. Unaccounted for, this varying weighting causes systematic underestimation of the T(2)'s, sometimes by as mush as 30%. In this article, we (i) analyze the phenomenon for common MRS spin-echo T(2) acquisition schemes; (ii) propose a general post hoc T(1)-bias correction for any (TR, TE) combination; (iii) show that approximate knowledge of T(1) is sufficient, since a 20% uncertainty in T(1) leads to under 3% bias in T(2); and consequently, (iv) efficient, precision-optimized short TR spin-echo T(2) measurement protocols can be designed and used without risk of accuracy loss. Tables of correction for single-refocusing (conventional) spin-echo and double refocusing, such as, PRESS acquisitions, are provided.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Algorithms
  • Brain / pathology
  • Computer Simulation
  • Electron Spin Resonance Spectroscopy / methods
  • Humans
  • Image Processing, Computer-Assisted / methods
  • Magnetic Resonance Spectroscopy / methods*
  • Phantoms, Imaging
  • Reproducibility of Results
  • Retrospective Studies
  • Signal Processing, Computer-Assisted
  • Software
  • Time Factors