A Three-Dimensional NMR Imaging Scheme Utilizing Doubly Resonant Gradient Coils

A 3DFT gradient-echo technique has been developed which, in conjunction with series-resonant gradient-coil circuits, can produce three-dimensional NMR images with an echo time of less than 100 μs. The method involves a read-gradient waveform composed of two sinusoids of different frequencies. This is an improvement on previous imaging sequences using a single sinusoid where only half ofkspace was sampled and where the second half was calculated using conjugate symmetry. The inaccuracies involved in the necessary “cut and paste” ofkspace inevitably lead to artifacts in the final image. The important features of the new method are that with suitable phase encoding all octants ofkspace are sampled, the RF pulse is applied when the gradients are all zero, and the echo forms when the gradient is essentially constant. This method will allow more extensive application of solid imaging techniques to biological samplesin vivo.