On- and off-resonance T MRI in acute cerebral ischemia of the rat

Olli H.J. Gröhn, Heidi I. Mäkelä, Jouko A. Lukkarinen, Lance DelaBarre, Joseph Lin, Michael Garwood, Risto A. Kauppinen

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37 Scopus citations


The ability of on-resonance T (T) and off-resonance T (Toff) measurements to indicate acute cerebral ischemia in a rat model of transient middle cerebral artery (MCA) occlusion was investigated at 4.7 T. T was determined with B1 fields of 0.4, 0.8, and 1.6 G, and Toff with five offset frequencies (Δω) ranging from 0-7.5 kHz at B1 of 0.4 G, yielding effective B1 (Beff) from 0.4 to 1.8 G. Diffusion, T1, and T2 were also quantified. Both T and Toff acquired with Δo < 2.5 kHz showed positive contrast during the first hours of MCA occlusion in the ischemic tissue delineated by low diffusion. Interestingly, Toff contrast acquired with Δω > 2.5 kHz was clearly less sensitive to ischemic alterations, and developed with a delayed time course. This discrepancy is thought to be a consequence of the frequency dependency of cross-relaxation during irradiation with spin-lock pulses.

Original languageEnglish (US)
Pages (from-to)172-176
Number of pages5
JournalMagnetic resonance in medicine
Issue number1
StatePublished - Jan 1 2003


  • Brain
  • Ischemia
  • Relaxation
  • Spin-lock
  • T


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