AN ANALYSIS OF THE EFFECTS OF SHORT T2 VALUES ON THE HYPERBOLIC-SECANT PULSE

A computer simulation of the Bloch equations which takes account of the effects of T2 relaxation is used to simulate the effects of short T2 relaxation times on the inversion profiles obtained with the hyperbolic-secant pulse. The degradation of the slice profile is demonstrated, and it is shown that under these conditions the pulse loses its normal insensitivity to variations in B1. Systematic errors in the ISIS experiment arising from these effects are examined, and it is shown that the signal originating from within the selected slice is always reduced, but that spurious signal arises from outside the slice, which may, in a heterogenous medium, lead to an increase or a decrease in the signal measured. © 1991.