Abstract: This invention relates to a technique for compensating for the inhomogeneity of the field generated by the RF coil (B1) in a nuclear magnetic resonance experiment. Current techniques for achieving accurate flip angles with non-uniform B1 transmit fields, are based upon modulation of the RF waveform. Inherent disadvantages of any RF-based compensation is an increased pulse length and/or increased RF power. Moreover, for some important applications, e.g. multi-slice excitation, no suitable pulses are known. We present an alternative strategy involving a Bz field whose spatial variation is correlated with that of the B1 field. This spatial correlation between the fields allows Bz-based compensation for the effects of B1 inhomogeneity. Successful operation over a wide bandwidth and range of B1 intensities may be achieved without any modification of the RF pulses. An alternative approach for compensating for B1 inhomogeneity is to apply a rapid oscillatory phase-modulation to an existing RF pulse waveform.

Abstract: This invention relates to a technique for compensating for the inhomogeneity of the field generated by the RF coil (B1) in a nuclear magnetic resonance experiment. Current techniques for achieving accurate flip angles with non-uniform B1 transmit fields, are based upon modulation of the RF waveform. Inherent disadvantages of any RF-based compensation is an increased pulse length and/or increased RF power. Moreover, for some important applications, e.g. multi-slice excitation, no suitable pulses are known. We present an alternative strategy involving a Bz field whose spatial variation is correlated with that of the B1 field. This spatial correlation between the fields allows Bz-based compensation for the effects of B1 inhomogeneity. Successful operation over a wide bandwidth and range of B1 intensities may be achieved without any modification of the RF pulses. An alternative approach for compensating for B1 inhomogeneity is to apply a rapid oscillatory phase-modulation to an existing RF pulse waveform.

Abstract: In nuclear magnetic resonance spectroscopy spatial localization of the output signal is achieved by using gradient magnetic fields and radio-frequency inversion pulses to define slices through a sample from which a signal is obtained. The use of intersecting slices allows the field of view to be reduced to the region of intersection to study a localized volume of interest in the sample. Conventionally, three orthogonal gradient magnetic fields can be defined by energizing successively three gradient magnetic field coils. With the present invention combinations of the gradient magnetic field coils are energized simultaneously to allow the field of view to be more closely conformed to a described volume of interest. This simultaneous energization allows the field of view to be rotated relative to the axes of the coils and/or allows non-orthogonal intersecting slices to be defined to alter the shape of the field of view at the intersection of the slices.

Abstract: In magnetic resonance spectroscopy or imaging, e.g. n.m.r. or e.s.r., a method of localizing the region of a sample from which a resonance signal is obtained by modulating the component M.sub.z of magnetization in the B.sub.o direction according to position in the sample. This is achieved by flipping the spins away from the B.sub.o direction, applying a gradient magnetic field so that they lose or gain phase according to their position, refocussing the effects of any resonance offsets including chemical shifts and subsequently returning them to the B.sub.o direction whereupon M.sub.z depends on the phase lost or gained and thus the position. This may be repeated, possibly with different gradient fields or different phase pulses, to further localize the region before a resonance signal is finally detected. The contribution to the resonance signal varies with M.sub.z and so is localized to regions of greater M.sub.z.