Abstract:
Apparatus (10) for making biomagnetic measurements includes a biomagnetometer (18) for measuring magnetic fields produced by the body and an electromagnetic location measurement and recording system (20 and 30) for automatically determining the location of the portion of the body (12) from which the magnetic signals are being gathered. The electromagnetic location recording system permits establishing a real time body frame of reference with respect to the biomagnetometer, so that biomagnetic signals can be correlated directly with body location and structure. The electromagnetic location recording system may be operated continuously at radiation wavelengths which do not interfere with the taking of data, or intermittently with the taking of biomagnetic data, to avoid interference with the measured values of the biomagnetic data. The elements of the electromagnetic location recording system have substantially no residual magnetism when the location recording system is not operating, as the biomagnetic signals are typically so small that even normal residual magnetism might be erroneously recorded as a biomagnetic signal.
Abstract:
A biomagnetometer includes a magnetic field sensor including a magnetic field pickup coil (210) and a detector (211) of small electrical currents flowing within the pickup coil. A vacuum-tight enclosure (212) surrounds the sensor. The enclosure has a concavely upwardly curved first wall, with the magnetic field pickup coil located adjacent to the first wall. A vented reservoir (220) of liquefied gas is located within the enclosure, and a solid thermal conductor (218) extends from the sensor. There is a vacuum-tight thermal feedthrough by which the solid thermal conductor passes between the interior and the exterior of the enclosure. Electronic circuitry for filtering and amplifying the signals of the detector is also provided. Such a biomagnetometer is placed below the body of a reclining subject, and a second portion of the biomagnetometer can be placed above the body. In one form, the enclosures are shaped to form a cavity that receives the head of the subject therein, to achieve full head coverage of the pickup coils in the biomagnetometer.
Abstract:
A biomagnetometer (10) has a magnetic pickup coil (12) positioned remotely from a detector (30). The detector (30) is made form a low-temperature superconductor, while in one approach the pickup coil (12) and an electrical connector (56) between the detector (30) and the pickup coil (12) are made of a high-temperature superconductor. In another approach, an inductive coupler (116') connects the detector (30') and the pickup coil (12'). Although the detector (12) is maintained in a dewar (32) at a sufficiently low temperature to reduce electronic noise, the pickup coil (12) and the connection means need only be maintained at a temperature at which they are superconducting. The resulting biomagnetometer (10) permits the pickup coil (12) to be moved and positioned easily, and to be changed readily.
Abstract:
Apparatus (12) for performing sensitive magnetic measurements using cryogenically cooled instrumentation (72), wherein the instrumentation (72) is separated from the bubbles present in a cryogenic cooling fluid. In one embodiment, the magnetic measurement instrumentation (72) is placed in a tail piece (31) joined by heat conducting bolts (64) to a dewar (30) containing a cryogenic fluid, and heat from the instrumentation is conducted to the cryogenic fluid heat sink by metallic strips (70) reaching to the bolts (64). The cryogenic fluid does not contact the instrumentation (72) directly, resulting in a significantly reduced level of noise in the instrumentation (72). The tail piece (31) may also be evacuated to avoid pressure and temperature variations that may cause noise and affect the magnetic instrumentation (72).
Abstract:
A measured magnetocardiography signal has a relatively small heart signal mixed with a large noise signal. To produce a heart signal having a reduced noise content, the times of occurrence of a time series of isoelectric intervals (54) of the measured signal is first determined (42) and a time series isoelectric artifact curve is formed from the measurements made at those times of occurrence (44). A time series non-isoelectric artifact curve for other times is determined from this information. The time series isoelectric and non-isoelectric artifact curve is subtracted from the measured cardiography time series signal (46) to yield a time series heart amplitude signal having reduced noise and undistorted form.
Abstract:
A dewar (20) includes an inner dewar (22) and a dewar thermal shield (24). The dewar thermal shield (24) has a thermal shield body (32) formed of a layer of radiative insulation, an inner layer of fiberglass cloth (102) overlying the layer of radiative insulation (100), a metallic screen (104) overlying the inner layer (102), and an outer layer (106) of fiberglass cloth overlying the metallic screen (104). The dewar thermal shield (24) also has a thermal shield tail cap (34) attached to the thermal shield body (32). The tail cap (34) is formed of a layer of radiative insulation (50), a layer of fiberglass cloth (51) overlying the layer of radiative insulation (50), a layer of thermal foil (52) overlying the layer of fiberglass cloth (51), the thermal foil (52) being formed of thermal conductors embedded in a film adhesive matrix with the thermal conductors extending to the body (32), and a top layer of fiberglass cloth (54) overlying the layer of thermal foil (52).
Abstract:
A magnetometer (20) is prepared by depositing three thin-film SQUID magnetic field detectors (26, 28, 30) upon a substrate (24). Two of the detectors incorporate stripline SQUID detectors (26, 28) deposited at right angles to each other, to measure the orthogonal components of a magnetic field that lie in the plane of the substrate. The third detector uses a planar loop SQUID detector (30) that measures the component of the magnetic field that is perpendicular to the substrate. The stripline SQUID detectors have thin-film base (42) and counter (46) electrodes separated by an insulating layer (50) which is at least about 1 micrometer thick, and a pair of Josephson junctions (52) extending between the electrodes through the insulating layer.
Abstract:
An apparatus and process for making biomagnetic measurements of a biological organism permits the internal sources of the activity to be identified. An array of dipole sources is identified by providing a plurality of biomagnetic sensors disposed at locations external to the biological organism, measuring a measured biomagnetic response at each of the sensors, and amplifiying and filtering the measured biomagnetic response. A solution of dipole sources within the biological organism is determined by forward calculating a computed biomagnetic response at each of the sensors resulting from the biomagnetic activity of a plurality of dipole sources, each of which dipole sources contributes a normalized total signal strength at the sensors, and solving for the strengths of each of the dipole sources by a minimum norm estimation procedure. Convergence on the solution is aided by iteratively removing from the determination those apparent sources that contribute only a small portion of the signal strength, and then resolving the resulting relationship.
Abstract:
A magnetometer includes a support having two support surfaces that intersect each other along an intersection line that is perpendicular to a reference axis of the magnetometer. The support surfaces are preferably perpendicular to each other and are each inclined at an angle of 45 degrees to the reference axis. A planar sensor/detector array is mounted on each support surface. Each array includes at least two pairs of magnetic field sensors and associated SQUID detectors arranged such that the magnetic field sensors lie on a line that is parallel to the intersection line of the two support surfaces. The magnetometer can be used adjacent to a surface to measure components and spatial variation of the magnetic field near the surface, with the measured components resolved into the magnetic field vectors parallel to and perpendicular to the surface.