Magnetic circuit system with opposite permanent magnets

Details Magnetic circuit system with opposite permanent magnets Magnetic circuit system with opposite permanent magnets

1997-04-11

1998-10-20

Arana, Louis M.

Electricity: measuring and testing

Particle precession resonance

Spectrometer components

324320, G01V 300

Patent

active

058251871

ABSTRACT:
The present invention provides is an improvement in a magnetic circuit system with a pair of opposite permanent magnets to construct an MRI instrument comprising a pair of upper and lower permanent magnets connected with yokes to form an air gap space therebetween, in which the patient under MRI inspection is kept lying, a pair of shimmed pole pieces each mounted on the permanent magnet to face the air gap and a pair of gradient coils each mounted on the shimmed pole piece to face the air gap. The improvement comprises mounting a cancellation magnetic plate, which is a thin plate of a magnetic material having a coercive force of 0.1 to 500 Oe, on the gradient coil to face the air gap with an object to cancel the residual magnetization of the shimmed pole piece by the gradient magnetic field. The cancellation magnetic plate has a thickness not exceeding 0.5 mm and has a base area which is 5 to 75% relative to the base area of the gradient coil.

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patent: 5555251 (1996-09-01), Kinanen
patent: 5631616 (1997-05-01), Ohta et al.

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