Apparatus for measuring weak, location-dependent and time-dependent magnetic field

• US 5,265,611 A
• Filed: 07/06/1992
• Issued: 11/30/1993
• Est. Priority Date: 09/23/1988
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Schneider, Siegfried, Hoenig, Eckhardt, Reichenberger, Helmut
• Primary Examiner(s): Smith, Ruth S.
• Application Number:
  US07/909,316
• Time in Patent Office: 512 Days
• Field of Search: 128/653.1, 128/731, 128/732, 324/248, 324/262
• US Class Current: 600/409
• CPC Class Codes: A61B 5/0046 Arrangements of imaging apparatus in a room, e.g. room provided with shielding or for improved access to apparatus
• CPC Class Codes: A61B 5/242 Detecting biomagnetic fields, e.g. magnetic fields produced by bioelectric currents
• CPC Class Codes: G01R 33/00 Arrangements or instruments for measuring magnetic variables
• CPC Class Codes: G01R 33/0354 SQUIDS

Abstract

An apparatus for measuring weak, location-dependent and time-dependent magnetic fields emitted from a source situated in an examination subject includes a sensor arrangement having at least ten gradiometers of the first order, each gradiometer being inductively coupled to a DC-SQUID. The sensor arrangement and the examination subject are disposed in a room which shields the examination subject and the sensor arrangement from magnetic fields. The room has a shielding factor of at least 10 for magnetic alternating fields having a frequency of 0.5 Hz, the shielding factor increasing with increasing frequency. A method for operating the apparatus is also disclosed.

Claims

1. An apparatus for measuring weak, location-dependent and time-dependent magnetic fields emitted from a source situated in an examination subject, said apparatus comprising:

bearing means for supporting said examination subject;

a sensor arrangement including an array of at least ten identical axial gradiometers of the first order, each gradiometer having a field coil and a corresponding compensation coil, with the field coils of the gradiometers being disposed in a substantially circular sensor surface, an array of DC-SQUIDs corresponding in number to the number of said gradiometers, each gradiometer being inductively coupled to one of said DC-SQUIDs and each DC-SQUID having an analog output, and a vessel containing said gradiometers and said DC-SQUIDs having a temperature therein at which said gradiometers and said DC-SQUIDs are superconducting;

mounting means for mounting said sensor arrangement;

means for adjusting said sensor arrangement, disposed in said mounting means, for adjusting said bearing means and said sensor arrangement relative to each other so that said sensor arrangement can be positioned relative to a selected zone of said examination subject;

a room surrounding said bearing means and said sensor arrangement, said room including means for shielding an interior of said room from magnetic fields, said means for shielding having a shielding factor of at least 10 for magnetic alternating fields having a frequency of 0.5 Hz, a shielding factor of at least 100 for magnetic alternating fields having a frequency of 5 Hz, and a shielding factor of at least 1,000 for magnetic alternating fields having a frequency of 50 Hz and above, said means for shielding consisting of an inner shell of a low-retentivity material having a relative permeability greater than 10⁴ an outer shell consisting of mu-metal, and an intermediate shell consisting of aluminum; and

electronic means for evaluating signals from said gradiometers, said electronic means including amplifier means for amplifying signals from analog outputs of said DC-SQUIDs, said amplifier means having a plurality of amplifier channels corresponding in number to, and respectively connected to, outputs of said DC-SQUIDs, an analog-to-digital converter connected to an output of said amplifier means, digital data processing means for selectively processing the amplified and converted output signals from said DC-SQUIDs, and means for visually displaying a selected output image constructed by said data processing means.