The equivalence between off-resonance and on-resonance pulse sequences and its application to steady-state free precession with diffusion in inhomogeneous fields.
We show that the spin dynamics of any pulse sequence with off-resonant pulses is identical to that of a modified sequence with on-resonant pulses, including relaxation and diffusion effects. This equivalence applies to pulse sequences with arbitrary offset frequency deltaomega(0) which may exceed the RF field strength omega(1). Using this approach, we examine steady-state free precession (SSFP) in grossly inhomogeneous fields. We show explicitly that the magnitude of the magnetization for each mode at an offset frequency deltaomega(0) is equal to that for SSFP with on-resonance pulses of rescaled amplitude, with the same dependence on relaxation times and diffusion coefficient. The rescaling depends on offset frequency and RF field strength. The theoretical results have been tested experimentally and excellent agreement is found.
Freed
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Schlumberger-Doll Research, 36 Old Quarry Road, Ridgefield, CT 06877, USA. dfreed@ridgefield.oilfield.slb.com
Hürlimann
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Scheven
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