XXVI New Patents

A system for decoupling the body coil of the magnetic resonance imaging system when sur- face coils are used, and especially when the sur- face coils are used only for receiving. Semi- conductor switches; i.e., diodes are used in the body coil to decouple the body coils. However, gradient generated transients often erroneously switch off the diodes which are then destroyed by a subsequent transmitted RF signal. The inven- tion provides fail safe circuitry for preventing RF transmission when the diode switches are in the non-conducting condition.

5258709

METHOD AND APPARATUS FOR LOCALIZING SUBMARINES

Gunther Laukien, Rheinstetten Forchheim, Federal Republic Of Germany

A method and an apparatus are disclosed ser- ving 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 detec- ted. The apparatus comprises at least one trans- mission coil for exciting the nuclear resonance by means of an alternating electromagnetic field and comprises detection means for detecting nuclear magnetic resonance signals. The trans- mission 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 con- siderably more than 1000 cubic meters of water. The volume region is monitored for the presence of nuclear magnetic resonance signals and a pre- determined decrease in such resonance signals is detected.

5258710

CRYOGENIC PROBE FOR NMR MICROSCOPY

Robert D Black, Peter B Roemer, Antonio A Mogro-Campero. Larry G Turner assigned to General Electric Company

An apparatus for microscopic imaging em- ploying nuclear magnetic resonance is con-

structed 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 tem- peratures. 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 induc- tively 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 gene- rated. The use of superconductors having low resistance and low temperatures causes noise to be significantly reduced, and the signal-to-noise ratio to be substantially increased.

5258711

NMR SELECTIVE EXCITATION OF BENT SLICES

Christopher Hardy assigned to General Electric Company

A method for reducing distortion in magnetic resonance (MR) images of a subject employs distortion compensating MR pulses in a conven- tional 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 op- posite the direction of distortions in the slice im-

age; 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 simul- taneous RF pulses and magnetic field gradient waveforms from the trajectory; and simul- taneously 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 com- pared with conventional images.