General Electric Company

James R MacFall

Gary H Glover

Felix W Wehrli

Norbert Joseph Pelc

A method for reducing image artifacts due to signal variations in the course of examining a subject using nuclear magnetic resonance (NMR) techniques includes the acquisition of NMR data for imaging the object. The NMR data is composed of a number of views. The acquisition of each view includes the implementation of a pulse sequence to generate an NMR signal and application of a magnetic gradient along at least one dimensional axis of the object. A gating technique is used to define a window during a portion of each respiratory cycle and NMR data is acquired only during each window. A view ordering technique is employed during the data acquisition by altering the magnitude of a field gradient in a nonmonotonic manner.

Method for acquiring NMR data which is subject to periodic variations

A method is provided for enhancing image signal-to-noise ratio (SNR) by combining NMR acquired images of differing pulse sequence timing. In one embodiment, a plurality of multi-echo images acquired at different spin-echo times are used to compute values of spin-spin relaxation (T.sub.2) and pseudospin density (PD) for each pixel in the multi-echo images. These values are used to generate new images at a spin-echo time TE.sub.c for which actual measurements may not have been taken. In another embodiment, the calculated T.sub.2 images are used to extrapolate (by multiplying each pixel by an appropriate factor) each of the acquired images to some spin-echo time TE.sub.c. The extrapolated image can now be averaged to produce an image with improved SNR. In yet another embodiment, similar techniques are used to improve the SNR of images acquired by varying parameters, such as pulse sequence repetition time TR, which effect the spin-lattice (T.sub.1) dependence of the image.

Method of enhancing image signal-to-noise ratio by combining NMR images

A method for reducing baseline errors in NMR signals utilizes NMR signals produced by RF excitation pulses selected to be 180.degree. out of phase relative to one another to derive a baseline error signal. The baseline error signal is then used to compensate for baseline error component in other NMR signals. In the preferred embodiment, the method is useful in NMR imaging pulse sequences to not only achieve compensation of the baseline error, but also to shorten scan time.

Method for reducing baseline error components in NMR signals

A method for visualizing in-plane flow utilizing an NMR pulse sequence to produce a plurality of odd and even spin-echo signals occurring respectively at echo delay times, T.sub.E, of 2.tau., 6.tau., 10.tau., etc., and 4.tau., 8.tau., 12.tau., etc. In the preferred embodiment, a fictitious spin-echo amplitude is calculated from the odd and even spin-echo signals at an echo delay time T.sub.E =0, for example. The calculated values for the odd spin-echo signals are lower than those calculated for the even spin-echo signals due to incomplete rephasing of the odd spin-echo signals in the presence of a read-out magnetic field gradient and flow. Subtraction of the calculated image pixel value of the odd spin-echo signals from the calculated pixel values of the even spin-echo signals results in a difference image which highlights the flowing nuclear spins. The image pixels due to stationary nuclear spins experience exact cancellation.

Method for visualization of in-plane fluid flow by proton NMR imaging

A method is provided for accurate and rapid NMR imaging of computed T.sub.1 and M.sub.o (spin density) NMR images. The imaging data is acquired using a repetition of a sequence made up of RF and magnetic-field-gradient pulses. Each repetition of the sequence includes at least one step of reducing the net longitudinal magnetization in a predetermined region of the sample to zero. The longitudinal magnetization is allowed to at least partially recover prior to exciting nuclear spins in the predetermined region to produce at least one NMR spin-echo signal due primarily to the recovered magnetization. The spin-echo signal is sampled in the presence of a magnetic-field gradient for encoding spatial information.

Method of accurate and rapid NMR imaging of computed T.sub.1 and spin

A method is provided utilizing combined, interleaved pulse sequences for reducing motion artifacts in computed T.sub.1, T.sub.2, and M.sub.0 (spin density) NMR images. The imaging data is acquired using a repetition of a sequence made up of RF and magnetic-field-gradient pulses. Each repetition of the sequence includes at least two steps of exciting nuclear spins so as to produce a corresponding number of NMR signals. The NMR signals are sampled in the presence of a magnetic-field gradient for encoding spatial information into the NMR signals. Each repetition of the sequence includes at least two different sequence repetition times such that the NMR signals are sampled at approximately the same average time relative to any sample motion.

Growing community of inventors

Hartland, WI, United States of America

James R MacFall