Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-08-29
2003-12-16
Manuel, George (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C324S248000, C324S249000
Reexamination Certificate
active
06665552
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a SQUID (Superconducting Quantum Interference Device) integrating pickup coils which can highly sensitively detect a magnetic field generated from a subject under testing, and more particularly, to a magnetic field measurement system using the SQUID integrating pickup coils. More specifically, the present invention relates to a biomagnetometer which uses a multichannel SQUID integrating pickup coils for measuring a biomagentic field generated by neural activities of a human brain, myocardium activities of a human heart, and so on, and a magnetic field measurement system which uses a multichannel SQUID integrating pickup coils for conducting a non-destructive evaluation.
Generally, a SQUID gradiometer for measuring a biomagnetic field is comprised of axial pickup coils formed of superconducting wires, and a SQUID formed of a thin film which is superconductively connected to the pickup coils. To reduce environmental magnetic field noise, a gradiometer is often used as a pickup coil for detecting a field gradient in a direction of a detected magnetic field. When the detected magnetic field is oriented in the normal direction (z-direction), the gradiometer detects a z-gradient of a z-component (&Dgr;Bz/&Dgr;z) of the detected magnetic field (Prior Art 1: J. Clarke, Proceedings of the IEEE, Vol. 77, No. 8, pp. 1208-1223 (1989)).
Since a pickup coil formed of a super-conducting wire is limited in a reduction ratio of the environmental magnetic field noise, there has been proposed a method of forming a pickup coil of a thin film for detecting a field gradient in one direction perpendicular to a detected magnetic field. In this event, a gradiometer detects (&Dgr;Bz/&Dgr;x) or (&Dgr;Bz/&Dgr;y), where Bz is a detected magnetic field (Prior Art 2: M. B. Ketchen, J. Appl. Phys., Vol. 58, No. 11, pp. 4322-4325 (1985)).
Also, for preventing the SQUID itself from picking up the environmental magnetic field noise, a known gradiometer comprises a differential SQUID configuration by arranging holes of the SQUID in series or in parallel (Prior Art 2 and Prior Art 3: R. S. Ahmad et al. Jpn. J. Appl. Phys., Vol. 36, Part 1, No. 11, pp. 6737-6741 (1997)).
Another known gradiometer has one of pickup coils constituting the gradiometer connected to the foregoing differential SQUID (Prior Art 4: K. Tsukada et al, Rev. Sci. Instrum., Vol. 66, No. 10, pp. 5085-5091 (1995)).
A further known gradiometer has one of pickup coils constituting the gradiometer and the differential SQUID fabricated on the same substrate (Prior Art 5: M. Koyanagi et al, IEEE Transactions on Magnetics, Vol. 25, No. 2, pp. 1166-1169 (1989)).
The foregoing exemplary gradiometers are configured to detect a field gradient (&Dgr;Bz/&Dgr;x) or (&Dgr;Bz/&Dgr;y) in one direction of the field. For estimating a source (current source) in a biomagnetometer, it is necessary to measure both (&Dgr;Bz/&Dgr;x) and (&Dgr;Bz/&Dgr;y) at the same time. To meet this requirement, there has been reported an element which has two gradiometers,fabricated on a single substrate, which detect field gradients rectangular to each other (Prior Art 6:
4
D Neuroimaging, Product Document).
A gradiometer integrating pickup coils according to the present invention is fabricated of thin films on a substrate. In the following description, a rectangular coordinate system (x, y, z) is used, where a plane parallel with the surface of the substrate is defined as an xy-plane; and a direction perpendicular to the substrate as a z-axis. The gradiometer integrating pickup coils according to one embodiment of the present invention is configured to detect a gradient (&Dgr;Bz/&Dgr;x) of a magnetic field component (Bz) in the normal direction (z-direction) with respect to the x-direction and/or a gradient (&Dgr;Bz/&Dgr;y) with respect to the y-direction. First, terms used in the following description will be explained below.
“A pickup coil” refers to a planar pickup coil fabricated of a thin film on a substrate.
“A center of a pickup coil” refers to the center of the outer shape of the pickup coil. Here, the center of the pickup coil is defined as the center of gravity of an ideal plate having an outer shape equal to the outer shape of the pickup coil.
“An axial segment of a pickup coil” refers to a segment connecting the centers of two pickup coils, which form part of a gradiometer, projected perpendicularly onto the surface of the substrate.
“An axial segment of a pickup coil in an x-direction” refers to a segment connecting the centers of two pickup coils positioned in the x-direction in a gradiometer for the x-gradient, projected perpendicularly onto the surface of the substrate. The length of this axial segment is a baseline length of the gradiometer in the x-direction.
“An axial segment of a pickup coil in a y-direction” refers to a segment connecting the centers of two pickup coils positioned in the y-direction in a gradiometer for y-gradient, projected perpendicularly onto the surface of the substrate. The length of this axial segment is a baseline length of the gradiometer in the y-direction.
“The center of a pickup coil” refers to the midpoint on an axial segment of a pickup coil.
“The center of a pickup coil in the x-direction” refers to the midpoint on the axial segment of a pickup coil in the x-direction.
“The center of a pickup coil in the y-direction” refers to the midpoint on the axial segment of a pickup coil in the y-direction.
“A differential SQUID” is a planar SQUID fabricated of a thin film on a substrate, the holes of which are in series or parallel differential configuration.
“An axial segment of a differential SQUID” refers to a segment connecting the center of a first superconducting loop (SQUID hole), forming part of a differential SQUID, with the center of a second superconducting loop (SQUID hole), likewise forming part of the differential SQUID, projected perpendicularly onto the surface of the substrate.
“The center of a differential SQUID” refers to the midpoint on the axial segment of the differential SQUID.
“An axial segment of a differential SQUID in the x-direction” refers to the axial segment of the differential SQUID oriented in the x-direction, projected perpendicularly onto the surface of the substrate.
“An axial segment of a differential SQUID in the y-direction” refers to the axial segment of the differential SQUID oriented in the y-direction, projected perpendicularly onto the surface of the substrate.
“The center of a differential SQUID in the x-direction” refers to the midpoint on the axial segment of the differential SQUID in the x-direction.
“The center of a differential SQUID in the y-direction” refers to the midpoint on the axial segment of the differential SQUID in the y-direction.
“An axial segment of a pickup coil is in alignment with an axial segment of a differential SQUID” means that the axial segment of a pickup coil overlaps the axial segment of the differential SQUID.
“An axial segment of a pickup coil in the x-direction is in alignment with an axial segment of a differential SQUID in the x-direction” means that the axial segment of a pickup coil in the x-direction overlaps the axial segment of the differential SQUID in the x-direction.
“An axial segment of a pickup coil in the y-direction is in alignment with an axial segment of a differential SQUID in the y-direction” means that the axial segment of a pickup coil in the y-direction overlaps the axial segment of the differential SQUID in the y-direction.
“The center of a gradiometer integrating pickup coils” (1) refers to a point at which the center of the pickup coil in the x-direction matches the center of the differential SQUID in the x-direction; (2) refers to a point at which the center of the pickup coil in the y-direction matches the center of the differential SQUID in the y-direction; and (3) refers to a point at which the center of the pickup coil in the x-direction, the center of the differential SQUID in the x-direction, the center of the pickup coil in the y-direction, and the center of the differen
Kandori Akihiko
Miyashita Tsuyoshi
Suzuki Daisuke
Tsukada Keiji
Yokosawa Koichi
Hitachi , Ltd.
Manuel George
Shah Devaang
LandOfFree
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