T. Duczmal, J. Kubiak, H. Buckmaster
May 1, 1988
Journal of Magnetic Resonance
Abstract The well-known fast passage effect, known as the “wiggles” signal, is observed when the angular frequency ω is swept linearly and rapidly through the resonance frequency ω0. This paper establishes the functional relationships between the quantitative parameters describing the “wiggles” signal and the absolute and relative values of a B gradient. This was achieved by numerical simulation of the “wiggles” signal using approximations to the Fourier and convolution theorems. The “energy” parameter E = f−∞+∞ [R(w)″]2dw, where R(ω)″ is the absorption component of the complex “wiggles” signal [R(ω) = R(ω)′ + i(Rw)″], enables the absolute value of the B gradient to be determined provided that a spherical sample is used. The functional relationship between the B gradient and the “energy” parameter has been determined. The “area modulus” parameter |A| = f −∞ +∗ |R(ω)″|dω is the most suitable parameter for relative B-gradient determinations. Superposition of various instrumental effects such as high-pass filtering, AM noise, and detection phasing has a nonlinear effect on the calibration curves.