Advanced Nmr Systems, Inc.

Avideh Zakhor

Richard R Rzedzian

A method of cancelling ghosts from NMR images. The method involves estimating a phase difference function .DELTA. (n.sub.1, n.sub.2) and using that function to solve a linear system of equations to find the magnitudes of the true object densities at the true image and ghost locations x(n.sub.1,n.sub.2) and x(n.sub.1,n.sub.2 +N/2), respectively, where the image has dimensions N.times.N.sub.s. Experimental values of .DELTA. (n.sub.1, n.sub.2) for a variety of objects indicate that its variation along n.sub.1 is considerably larger than along n.sub.2. Thus, for each column n.sub.1, the phase difference function .DELTA. (n.sub.1, n.sub.2) can be modelled as a one-dimensional function of n.sub.2 with two parameters .alpha. (n.sub.1) and .beta. (n.sub.1), which are estimated from the pixels in the 2-D FFT processed reconstructed image Y(n.sub.1,n.sub.2). These parameters are then used to estimate .DELTA. (n.sub.1, n.sub.2), which is ultimately used to de-ghost the image.

Method of cancelling ghosts from NMR images

A method to recover MRI signals resulting from the application of time varying gradients. The raw MRI signal is demodulated, low pass filtered, and digitized using an A/D converter sampling linearly at the Nyquist rate. The samples from the A/D converter are compiled into a vector, which is multiplied by a least squares estimator matrix (H*H).sup.- H*, where H is a matrix whose mkth element, in the case of a sinusoidal gradient, is given by ##EQU1## This multiplication is repeated for each vector of samples from the A/D converter, and the vectors resulting from the multiplication are accumulated to form the columns of a matrix, the rows of which are Fourier transformed to obtain the MRI image.

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Encino, CA, United States of America

Avideh Zakhor