Abstract: A prescan for an MRI system (FIG. 1) automatically sets the rf power level to produce an excitation field that nutates spins in the image plane the amount prescribed by the scan. Nutation angle is measured with a pulse sequence comprised of three slice selective excitation pulses that produce a set of frequency encoded NMR echo signals (E.sub.1, S.sub.1, E.sub.2, E.sub.23, E.sub.13). Nutation angle is calculated at locations in the image slice from the Fourier transformation of these signals and the maximum nutation angle is employed to calculate the final rf power level setting for the scan.

Abstract: An NMR system acquires a series of spin-echo signals during a scan and these are used to reconstruct an image. The spin-echo signals are partially acquired by locating the data acquisition window asymmetrically with respect to the echo peak. A homodyne reconstruction is employed to fill in the missing data during the image reconstruction.