Abstract: A method for reducing distortion in magnetic resonance (MR) images of a subject employs distortion compensating MR pulses in a conventional MR imaging sequence. The distortion compensating pulses are determined by first creating a conventional MR image of a slice of a subject having inherent distortions; constructing a target slice which is distorted in a manner opposite the direction of distortions in the slice image; taking a multi-dimensional Fourier transformation of the target slice to obtain a k-space region; choosing a continuous trajectory which efficiently traverses the k-space region; applying principles of multidimensional selective-excitation design to create simultaneous RF pulses and magnetic field gradient waveforms from the trajectory; and simultaneously applying the RF pulses and gradient waveforms in place of a traditional slice-select pulse in conventional MR imaging sequences to obtain images having reduced distortion as compared with conventional images.

Abstract: In a nuclear magnetic resonance tomography apparatus, having a high-frequency excitation and measuring coil connected with a capacitor to form a resonant circuit, the capacitor being tuned to a desired operating frequency, a circuit is provided for limiting the voltage of the resonant capacitor in a transmission mode. Avoidance of impermissible peak amplitudes is thereby achieved without the necessity of over-dimensioning the components of the resonant circuit.

Abstract: A method and an apparatus are disclosed serving to localize proton-poor objects situated in aqueous surroundings, in particular to localize submarines or sea mines in an ocean or an inland water. By using a nuclear magnetic proton resonance technique, a magnetic disturbance caused by the proton-poor object in relation to its proton-rich aqueous surroundings is detected. The apparatus comprises at least one transmission coil for exciting the nuclear resonance by means of an alternating electromagnetic field and comprises detection means for detecting nuclear magnetic resonance signals. The transmission coil generates conditions in the aqueous surroundings in which water proton nuclear magnetic resonance occurs in a volume region of more than 50 cubic meters, preferably considerably more than 1000 cubic meters of water. The volume region is monitored for the presence of nuclear magnetic resonance signals and a predetermined decrease in such resonance signals is detected.

Abstract: A magnetic resonance imaging receiving coil having an improved signal-to-noise ratio comprising two or more separate quadrature volume coils, each intercepting the two quadrature components of the magnetic resonance signal within its own sensitive volume, and the two or more quadrature coils being magnetically isolated from each other by overlap geometry along the axis normal to the plane of the magnetic resonance rotating field. The coils are connected to independent image processing channels of a data acquisition system, the outputs of the processing channels being combined to form an overall image.

Abstract: An apparatus for microscopic imaging employing nuclear magnetic resonance is constructed from a cryogenic probe which is situated in a conventional magnetic resonance imaging system. The cryogenic probe employs a number of chambers and cryogenic liquids which cool a superconductor resonator to very low temperatures. A sample tube for containing a small specimen is heated to a temperature above its freezing point by flowing nitrogen gas over the specimen. A secondary resonant circuit is inductively coupled to the superconducting resonator. A transceiver passes RF signals to be transmitted into the specimen through the secondary resonant circuit causing the superconducting resonator to transmit the RF signal into the specimen. The resonator then acts as a receive coil and receives a signal from the specimen which is inductively passed to the secondary resonator circuit from which an image is generated.

Abstract: There is disclosed a gradient magnetic field coil for use in a magnetic resonance imaging system for imaging an imaginary or virtual cross-section of a desired portion of a subject to be inspected, utilizing a magnetic resonance phenomenon. The gradient magnetic field coil includes a coil bobbin and coil windings fixedly mounted on the coil bobbin. The coil bobbin includes a tubular body portion of a honeycomb construction having a number of vacancies formed in a wall of the tubular body portion, a sheet-like outer peripheral portion of a constrained damping structure fixedly secured to an outer peripheral surface of the body portion to reinforce the body portion, and a sheet-like inner peripheral portion fixedly having at least one layer and secured to an inner peripheral surface of the body portion to reinforce the body portion. The generation and continuation of vibrations in the coil bobbin are controlled or suppressed directly by the coil bobbin itself, thereby minimizing the generation of noise.

Abstract: To derive NMR imaging information an object is subjected to a static magnetic field on which is superimposed a sinusoidally time varying magnetic gradient field. A sequence of narrow 90.degree. rf pulses are applied around the instants when the gradient field has a zero value. The rf pulses have relative phase quadrature such that excited nuclei precess with accumulated phase in each sequence.

Abstract: To derive NMR imaging information, an object is subjected to a static magnetic field and a sinusoidally time-varying magnetic gradient field G. A 90.degree. rf selective pulse P is applied around the time the gradient field G is zero and the subsequent free induction echoes E are detected and decoded. Additional non-selective pulses may be inserted at the times of echo peaks to refresh the echo signals. Additionally, to obtain two-dimensional information, the gradient direction of the magnetic gradient field may be changed in successive cycles of the sinusoidal field.

Abstract: Apparati and methods for magnetic resonance imaging a selected interrogation volume in a tissue of a human or animal body, to provide increased signal-to-noise ratios for fixed data acquisition times. The method involves excitation of magnetic resonance in a selected interrogation volume that may be as small as 500-3,000 cm.sup.3, through controllable focusing or steering of a rotating magnetic field signal used to induce magnetic resonance. The response signals issued by the excited volume element are then collected by focusing of these response signals, using a phased array of antennae for this purpose. Use of the invention with well known nuclear magnetic resonance excitation procedures, such as spin echo, echo planar, gradient recalled and backprojection, are discussed.

Abstract: A method of nuclear magnetic resonance investigation of a repeated electromagnetic event in a sample comprises modulation of the nuclear spin polarization achieved during the recovery period between the final magnetic resonance signal detection period of one cycle and the initial signal generation RF pulse of the next cycle. This modulation is performed by giving the sample a different exposure to RF radiation in the different periods, for example by exposure to a different number of 180.degree. pulses in each period or by exposure to a frequency modulated continuous wave RF signal.

Abstract: A gated amplifier drives a gradient coil when the gate signal is applied and the gate signal also controls an FET switch to disconnect a shim power supply from shim coils and connects the shim power supply instead to a dummy load. When the gate signal is removed, the shim coil is restored to operation from the shim power supply.

Abstract: A method for suppressing fat in a magnetic resonance image of a target organ, wherein fat is present in the vicinity of the target organ involves subjecting the target organ to electromagnetic energy so as to cause an organ signal response and a fat signal response related to the magnetization of the organ and the fat, respectively. The subjecting to electromagnetic energy involves subjecting the target organ to a saturation preamble and thereafter subjecting the target organ to an offsetting spin-echo sequence. The organ and fat responses are detected and image information based on the responses is generated. The saturation preamble, selectively excites and then dephases a particular substance, such as fat, in the vicinity of the target organ. Preferably exciting and then dephasing involves subjecting the target organ to a Hore 1-3-3-1 signal.

Abstract: A high T.sub.c superconductive electromagnet winding is advantageously employed as part of an MRI magnet structure having a pair of magnetically permeable poles opposingly disposed about the patient imaging volume. The magnetic circuit is otherwise completed by a magnetically permeable yoke structure having plural open apertures for easy access to the patient imaging volume. Still further advantage can be had by asymmetrically disposing a single superconductive electromagnet winding with respect to the patient image volume thereby eliminating the need for more than one cryostat. When high T.sub.c superconductive electromagnetic windings are utilized, a non-conductive composite cryostat may also be used to further reduce spurious eddy current fields. When an asymmetric single high T.sub.

Abstract: Disclosed is a method of detecting NMR signals indicative of a short T.sub.2 species in the presence of a long T.sub.2 species by utilizing magnetization transfer between species without requiring an auxiliary RF amplifier and with reduced power deposition (SAR). One or more zero degree RF pulses are applied to a body containing the short T.sub.2 species and the long T.sub.2 species with the pulses being at the resonant frequency. The RF pulses provides selective magnetization saturation of the short T.sub.2 species, and the RF pulses are spaced in time to allow magnetization transfer from the short T.sub.2 species to the long T.sub.2 species. Gradients can then be applied to the body for signal localization with signals detected from the long T.sub.2 species due to magnetization transfer from the short T.sub.2 species being indicative of the presence of the short T.sub.2 species. The signals are indicative also of the magnetization transfer between species.

Abstract: In particular with 3D tomography, it is necessary to acquire a large number of individual spectra. Therefore it is advisable to reduce the time needed for the acquisition of a single spectrum without loosing too much in signal-to-noise ratio. To a significant extent, this time is determined by the relaxation time of the spins. Prior to each excitation a significant quantity of these spins have to return into their equilibrium (z-direction of the homogeneous magnetic field) in order to create a usable signal with the next excitation. For spins with long relaxation times T.sub.2 this time can be reduced by a -90.degree. pulse 12 that coincides with the center of the last spin echo 9 with appropriate application of the gradient fields. This -90.degree. pulse returns the x-y magnetization that exists in the x-y plane into the z-direction. The diagnostic relevance can be significantly increased by such a procedure.

Abstract: An MRI signal processing apparatus is disclosed which provides a low noise output signal for use in a multi-coil MRI system, wherein each sensing coil provides an input signal to the MRI signal processing apparatus.

Abstract: A sequence acts--preferably several times--upon an examination region, which sequence comprises two frequency-selective high-frequency pulses not exciting the water component, between which a 180.degree. high-frequency pulse is present. Such a sequence can be more insensitive to imperfections of the 180.degree. pulse in that the second frequency-selective high-frequency pulse is followed by a further frequency-selective high-frequency pulse not exciting the water component and in that between the second frequency-selective high frequency pulse and the further high-frequency pulse as well as after the further high-frequency pulse a magnetic gradient field is switched on and off in such a manner that the time integrals across this gradient field before and after the further high-frequency pulse are equal to each other.

Abstract: A magnetic resonance imaging sequence (FIG. 2 ) is applied with a phase encode gradient (60) between an RF excitation pulse (50) and a refocusing pulse (54) such that out-of-slice artifacts are collapsed into a single line or column (64) in a resultant image display (38). A digital radio frequency transmitter (20) adds an adjustable RF phase component (70) to the excitation pulse and digital radio frequency receiver (26) adds the inverse or negative of the phase component (72) to a received magnetic resonance echo (56). The RF phase increment is adjusted such that the artifact line is displayed at the edge or other selected portion of the resultant image away from a region (74) of primary interest. An operator control (80) enables the field of view to be shifted in the phase encode direction to view different portions of the patient along the phase encode axis.

Abstract: A pair of serially-connected coils detect noise variations in an MRI background magnetic field. Although the coils are closely coupled to the primary background magnetic field generator of the MRI system, they are disposed so as to be substantially de-coupled from rapidly changing MRI gradient magnetic fields. The noise detecting loops drive a negative feedback loop including a low pass filter, amplifier and controlled current source driving a large correcting loop. The device attenuates background magnetic field noise during MRI data acquisition over a frequency band extending from a few millihertz to more than 100 Hz. It is preferably used with existing field stabilization software that otherwise compensates for fluctuations in an overlapping frequency band which starts at d.c. Thus, when used together, background magnetic field noise may be attenuated (or compensated for in subsequent MRI data processing) over a frequency band that extends from d.c. to more than 100 Hz.

Abstract: A new three-dimensional (3D) MR imaging pulse sequence can produce over 100 high-resolution, high-contrast images in as little as 6 minutes of imaging time. Without additional imaging time, this same image data can be post-processed to yield high-resolution, high-contrast images in any arbitrary orientation. Thus, this new pulse sequence technique provides detailed yet comprehensive coverage. The method of this invention relates to a preparation-acquisition-recovery sequence cycle. The first step is magnetization preparation (MP) period. The MP period can emply a series of RF pulses, gradient field pulses, and/or time delays to encode the desired contrast properties in the form of longitudinal magnetization. A data acquisition period includes at least two repetitions of a gradient echo sequence to acquire data for a fraction of k-space. A magnetization recovery period is provided which allows T1 and T2 relaxation before the start of the next sequence cycle.