General Electric Company

Felix W Wehrli

James R MacFall

Ann Shimakawa

A time-of-flight magnetic resonance pulse sequence is used to detect arterial flow in an image of a slice of tissue. By timing the pulse sequence with the cardiac cycle and by holding the interpulse interval T.sub.I within time limits which ensure enhancement without significant change in flow velocity, arterial flow can be imaged. By triggering the pulse sequence from the QRS complex representative of the beginning of a body's cardiac cycle and delaying both excitation and detection pulses in the sequence by a time T.sub.A to ensure the pulses occur while flow is slow, MR signal data is generated which results in an image showing enhancement in the areas of arterial flow. In an extension of the foregoing, a second set of MR signal data is generated by adjusting the acquisition delay T.sub.A such that the excitation and detection pulses of a second sequence occur while arterial flow is fast. In the image formed from this second set of data, the increased arterial flow velocity decreases the enhanced image of the arteries. The images generated from the MR signals of the first and second sequences may be subtracted in order to give a single high contrast image showing only arterial flow.

Method for measuring and imaging fluid flow

A method for rapid acquisition of NMR data utilizes excitation pulses which rotate the longitudinal magnetization through an angle smaller than 90.degree. to create a relatively large transverse magnetization component. A first 180.degree. RF pulse is then applied to create a spin-echo signal, while a second 180.degree. RF pulse is used to rapidly return to equilibrium the residual longitudinal magnetization inverted by the first pulse. The combination of the excitation and the second 180.degree. pulses permits the sequence repetition time to be shortened, thereby reducing the total data collection time. The method is applicable to, for example, two- and three-dimensional embodiments of Fourier transform and multiple-angle projection reconstruction NMR imaging methods.

Method for rapid acquisition of NMR data

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 for measuring (direction and magnitude) and imaging fluid flow in an NMR sample. Nuclei in an imaging slice, transaxial, for example, to a direction of fluid flow, are first tagged (saturated or inverted) and then excited to produce a first NMR signal. This signal originates from tagged nuclei in the imaging slice and untagged nuclei which have partially or wholly replaced nuclei flowing out of the slice. Thereafter, nuclei are tagged in a second thicker sample region which includes the imaging slice and extends therefrom in a direction opposite to the fluid flow. The nuclei are again excited in the imaging slice. The NMR signal detected is again from the entire imaging slice but is due entirely to tagged nuclei (if the second slice is selected to have the appropriate thickness) and, therefore, has a smaller magnitude than the first signal. These signals are useful in measuring the fluid flow velocity. The method is also useful, for example, with multiple-angle projection reconstruction and two-dimensional Fourier transform (2DFT) techniques to reconstruct NMR images exhibiting flowing nuclei only.

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Shorewood, WI, United States of America

Felix W Wehrli