Fat suppressed MRI of articular cartilage with a spatial-spectral excitation pulse

We developed a three-dimensional, gradient-recalled-echo imaging technique that incorporates a short-duration spatial-spectral excitation pulse from t he family of binomial pulses. Binomial pulses of different orders were test ed on phantoms and on normal volunteers to find the composite pulse that pr oduced in the shortest duration the most reliable fat suppression. Composit e pulses employing unipolar slice-selective gradients with explicit rewinde r gradients between each radio-frequency (RF) pulse were compared with comp osite RF pulses employing alternating-polarity, slice-select gradients. The advantage of the sequences using the unipolar gradients is improved fat su ppression. Images of the knees of volunteers produced with the composite RF pulse have contrast between fat and articular cartilage equivalent to that on images created by the gradient-recalled-echo imaging technique employin g a conventional chemsat pulse. The optimum RF pulse consisted of three amp litude- and phase-modulated pulses combined with unipolar slice-select grad ients.