WO2001006907A2 - Verfahren und vorrichtung zur messung biomagnetischer, insbesondere kardiomagnetischer felder - Google Patents
Verfahren und vorrichtung zur messung biomagnetischer, insbesondere kardiomagnetischer felder Download PDFInfo
- Publication number
- WO2001006907A2 WO2001006907A2 PCT/DE2000/002472 DE0002472W WO0106907A2 WO 2001006907 A2 WO2001006907 A2 WO 2001006907A2 DE 0002472 W DE0002472 W DE 0002472W WO 0106907 A2 WO0106907 A2 WO 0106907A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- coil
- squid
- pick
- fields
- antenna
- Prior art date
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/035—Measuring direction or magnitude of magnetic fields or magnetic flux using superconductive devices
- G01R33/0354—SQUIDS
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/242—Detecting biomagnetic fields, e.g. magnetic fields produced by bioelectric currents
- A61B5/243—Detecting biomagnetic fields, e.g. magnetic fields produced by bioelectric currents specially adapted for magnetocardiographic [MCG] signals
Definitions
- the invention relates to a method and a device for measuring biomagnetic, in particular cardiomagnetic, fields by means of at least one superconducting quantum interferometer (SQUID - superconducting quantum interference device).
- SQUID superconducting quantum interferometer
- the antenna usually have at least one antenna made of superconducting material, the antenna comprising at least a first coil for inductive detection of a magnetic field and a second coil and is usually inductively coupled to the SQUID ,
- the term “antenna” is understood to mean a conductor loop which is generally bent from a wire and has at least two coils each made up of one or more windings, one in one of the coils (the so-called pick-up coil) by a magnetic field a current is induced, which can then be inductively impressed on a superconducting quantum interferometer by means of the second coil (the so-called input coil), which leads to measurable physical processes.
- This type of measurement of magnetic fields essentially exploits the Josephson effect (Cooper pairs can tunnel a non-superconducting thin connection area (so-called Josephson junction) between two superconducting areas) and the fact that the magnetic flux through superconducting coils is quantized.
- MFM Magnetic Field Map
- the magnetic fields can be measured completely without contact, so that the patient, who is often psychologically stricken by his illness anyway, does not have to be "wired" to a device that is possibly uncanny to him.
- Another great advantage of measuring biomagnetic fields lies in the fact that the magnetic permeability of almost all substances is approximately equal to 1, so that e.g. the magnetic fields generated during cardiac activity can pass through bones, soft tissues and air to the corresponding sensors in an unadulterated and practically loss-free manner.
- the electrical conductivity varies relatively widely. It is therefore relatively difficult to interpret the currents that can be measured in the EKG and that always move along the path of the path to the measuring electrodes on those conduction paths that have the maximum conductivity and thus the lowest electrical resistance with respect to their place of origin.
- the magnetometers commonly used are based on direct current SQUIDs (DC SQUIDs) with a ring with two Josephson junctions and a direct current bias, these SQUIDSs having a hysteresis-free current-voltage characteristic. This requires a so-called shunting of the Josephson junctions with high capacitance, which in turn requires relatively slow analog electronics that work with signals in the microvoit range and require complex shielding and filtering, in particular when measuring fields of low frequency.
- DC SQUIDs direct current SQUIDs
- the object of the invention is a method and a
- Specify device of the type mentioned which allow the measurement of biomagnetic signals with particularly simple means, especially in unshielded rooms and thus inexpensively.
- the SQUID being a SQUID with a hysteretic current-voltage characteristic and means being provided for operating the SQUID in the relaxation-oscillation mode (RO mode).
- Magnetic field produced by a cordless screwdriver at a distance of 5 m still has a strength of at least 10 "9 to 10 " 10 Tesla (see, for example, J. Vrba: “SQUID Gradiometers in Real Environments", in: H. Weinstock (ed.): “SQUID Sensors - Fundamentals, Fabrication and Applications ", Kluwer Academic Publishers, 1996).
- the device is suitable for measuring a wide variety of magnetic fields, in particular for magnetocardiography, but also for a wide variety of other biomagnetic examinations, e.g. Magnetic susceptibility measurements of the liver.
- An advantage of operating in RO mode is that the essential information about the magnetic flux picked up by the antenna now no longer contains the noise-sensitive amplitude of the voltage signals tapped at the SQUID in a manner known per se, but rather the frequency of these signals and is therefore essential can be obtained more easily and quickly with greater insensitivity to ambient noise.
- the entire measuring electronics can be simplified compared to the known devices that operate the SQUIDs in analog mode and can therefore be constructed more cost-effectively.
- Another advantage of operating in RO mode is that simply by looking at the periodic current-flow characteristic (with feedback switched off) after the device has been installed, important information about the noise present at the installation site, in particular information about the causes of the noise, is obtained can be because certain noise sources have the characteristic in typical
- Characteristics are recognized whether it has a certain high-frequency noise external causes or whether the SQUID may be defective or of poor quality.
- the SQUID is preferably an internally unshunted direct current SQUID (DC-SQUID) with at least two Josephson junctions
- the means for operating the SQUID in the relaxation-oscillation mode preferably have a resistance R and one in series with the
- Resistor R switched inductance L, via which the two superconducting regions are connected to one another in addition to the Josephson junctions.
- the SQUID is preferably a low-temperature SQUID, that is to say a SQUID, the superconducting properties of which only occur at very low temperatures, for example the temperature of liquid helium.
- a low-temperature SQUID that is to say a SQUID
- the superconducting properties of which only occur at very low temperatures for example the temperature of liquid helium.
- the slightly higher operating costs of low-temperature SQUIDs are more than offset by the measurement advantages, in particular the simpler signal filtering.
- SQUIDs of different spatial designs can be used. However, it has proven to be advantageous if the area enclosed by the two superconducting regions of the SQUID is between 1200 and 2000 ⁇ m 2 , preferably around 1600 ⁇ m 2 . SQUIDs of the so-called washer type (see, for example, FIG. 5) have proven particularly useful, in particular those in which the larger of the two superconducting regions has an edge length between 1.5 and 2.5 mm, preferably about 2 mm.
- the device delivers very good results when the antenna forms a simple magnetometer together with the SQUID.
- the results can be improved even more in environments with strong magnetic noise if the antenna forms a gradiometer together with the SQUID, the design as a symmetrical axial gradiometer of the second order in particular having proven to be very advantageous.
- the sensitivity to magnetic fields drops with the fifth power of the distance between the sources of the fields to the pick-up coil, if this distance is significantly larger than the so-called baseline (the distance between the pick-up coil and the first bucking coil (i.e. the first differentiation coil wound in the opposite direction to the pick-up coil) of the gradiometer.
- the baseiine is between 5 and 7 cm, preferably about 6 cm, the diameter of the pick-up coil being both a magnetometer and a gradiometer and the like
- the diameter of the bucking coil or coils present in a gradiometer is between 1.5 and 2.9 cm, preferably about 2.2 cm.
- Niobium or niobium nitrate wire with a diameter between approximately 30 and 60 ⁇ m has proven itself as the material for producing the antenna.
- the pick-up coil and any bucking coils that may be present can each comprise several windings. However, they each preferably have only one winding, so that the inductance is low and the input coil must have only a few, for example 20 to 40 windings in order to inductively transmit the current to the SQUID in the desired manner.
- a gradiometer is advantageously used instead of a magnetometer, it must be adjusted due to the always present deviations from the ideal state (coils of the same size, uniform, exactly parallel), the deviations being largely compensated for.
- Various methods are known for compensating. Because of the simplicity, however, means for mechanically compensating the gradiometer, in particular a mechanism for precisely positioning one or more superconducting objects in the vicinity of the pick-up and bucking coils, have proven particularly useful.
- the device can also be used in unshielded rooms.
- a magnetic shield with the exception of an area below the pick-up coil, for example lining it with aluminum foil.
- a magnetically shielded housing in particular lined with aluminum foil, comprising the electronics and the essential sensitive parts of electronics necessary for operating the SQUID, an opening for the area of the Dewar containing the pick-up coil.
- the known devices in particular for recording cardiomagnetic fields, usually have a large number (generally between 35 and up to 60) of antennas and SQUIDs coupled to them. Also in the literature (see e.g. W. Andrä & H. Nowak (ed.):
- the device in particular for recording cardiomagnetic fields, it is provided that the device has only one or a few, preferably between four to nine antennas, each with a SQUID. This has a number of advantages.
- the measurement and evaluation electronics are significantly simpler than the known devices, and the Dewar vessel can be kept much smaller than in the known devices.
- the Dewar vessel in the device according to the invention can be dimensioned such that it only has a coolant capacity in the range a few liters, especially between 2.5 and 10 l.
- a Dewar vessel with a capacity of 6 l is provided, from which about 1.2 l evaporate daily, which, in view of the considerable costs of liquid helium, leads to significantly reduced maintenance costs.
- the pick-up coils have diameters between 0.5 and 1.0 cm, while according to the invention the coil diameter is preferably between 1.5 and 2.9 cm, in particular approximately 2.2 cm.
- a movable table for positioning an object to be examined relative to the pick-up coil (s). It has been shown that the noise at one and the same place in the room is relatively uniform over the typical measuring times, while a few centimeters next to it is a noise that is equally uniform but has a significantly different structure. If the measurements are carried out only at one or at a few points, the filter settings can be adopted for different points of the examined object measured successively at the respective location. For example
- CORRECTED SHEET (RULE 91) ISA / EP a rectangular grid, for example, with a distance of 4 cm to the neighboring points, for example. If one measured at these 36 points with a single-channel system (with only one antenna and one SQUID) and moved the antenna instead of the object to be examined, the recorded 36 measurement series would have to be filtered with individually new settings. Instead, move the thing to be examined
- the table is preferably made of non-magnetic and non-conductive materials such as wood and / or plastics.
- the table can be moved by hand, for which purpose a locking and guiding mechanism can be provided for moving the table along predetermined paths and fixing the table in certain positions. With greater effort, it is also possible to automatically position the table relative to the pick-up coil (s), although care must be taken to ensure that the corresponding mechanisms and drives do not
- the above-mentioned object is achieved by a method for measuring biomagnetic, in particular cardiomagnetic fields by means of at least one antenna made of superconducting material, preferably arranged in a Dewar vessel, the antenna having at least one first coil for inductive detection of a magnetic field and a second coil , and a SQUID inductively coupled to the antenna via the input coil, the SQUID being operated in the relaxation-oscillation mode.
- the procedure is preferably such that an internally unshunted SQUID with a hysteresis current-voltage characteristic and two planar superconducting regions connected to one another via two Josephson junctions (tunnel connections), which are connected externally via a resistor R and one in series with the resistor R switched inductance L are connected to each other, used and a
- Bias is applied to the SQUID in such a way that the relaxation-oscillation mode is established.
- FIG. 1 is a schematic diagram of a magnetograph for performing biomagnetic measurements on patients
- FIG. 3 shows a basic circuit diagram of a second-order gradiometer according to the invention with a SQUID that can be operated in RO mode
- Fig. 4 is a schematic diagram of measuring electronics for operating the
- FIG. 5 shows a top view of a washer-type SQUID
- FIG. 6 shows a basic circuit diagram of the antenna and a further second order gradiometer according to the invention with a SQUID which can be operated in RO mode and which is inductively coupled to the antenna,
- Fig. 7 is a schematic diagram of the magnetically shielded
- Fig. 10 shows the RO frequency dependence on the magnetic flux MF, with line 1 the course without and line 2 the
- the magnetograph which comprises a Dewar vessel 1 in which the actual measuring device is located and which is suspended from a gantry 2.
- the magnetograph further comprises a frame 3 with a movable support 4, by means of which the patient 5 to be examined can be positioned under the measuring device, a comparison EKG 6, a control unit 7, a personal computer 8 and a
- Connection cable 9 which connects the measuring device arranged in the vessel 1 to the control unit 7.
- Frames are made of non-magnetic materials such as Made of wood or textolite.
- the cryogenic magnetometer shown in section in FIG. 2 comprises a magnetically transparent Dewar vessel 2, which serves to cool the superconducting components to the necessary temperature and is filled with liquid helium 4.
- the vessel is made of glass fiber and has a capacity of approximately five liters.
- An antenna 5 is arranged in the end region 7 of the vessel facing the magnetic field to be measured, a signal processing unit 3 in the opposite region forming the head of the vessel and the SQUID 1 in the middle region of the vessel.
- the antenna 5 With its windings 8, 9 and 10, the antenna 5 forms a second-order gradiometer which detects the component d2B / dz2, that is to say the diagonal component of the magnetic gradient sensor.
- the gradiometer consists of a
- CORRECTED SHEET (RULE 91) ISA / EP is wound, the baseline being 60 mm.
- the reference winding 8 and the pick-up winding 10 each consist of a single winding, while the middle reference winding 9 has two windings.
- the gradiometer inductance is just like the inductance of the SQUID input coil
- FIG. 3 schematically shows the core of the measuring device, which consists of a SQUID 3, an input coil 6, a feedback coil 7 and means for operating the SQUID in RO mode.
- the DC-SQUID is shunted by means of a resistor R 4 and an inductor L 5 connected in series therewith, so that an RO generator is formed.
- the device is surrounded by a superconducting shield 8, which prevents external magnetic interference from entering the SQUID-Sch.
- the device's Tamsformation factor is 10 MHz / ⁇ Q
- the dynamic range is 140 dB
- the flux resolution is 8 ⁇ r VHz
- Input energy sensitivity at ⁇ s 10 " 30 J / Hz, the sensitivity with regard to the magnetic field at 30 fT ⁇ / Hz and the maximum slew rate is 3-10 6 ⁇ r j / s.
- FIG. 4 shows a basic circuit diagram of the measuring electronics for operating the SQUID in RO mode.
- the core of the system is the RO-SQUID, which, as shown in FIG. 6, consists of a SQUID with two superconducting regions shunted via a resistor R and an inductor L, which are connected in series.
- the magnetic field to be measured (MAGNETIC FIELD) is detected by the antenna (ANTENNA), which is inductively coupled to the SQUID.
- the SQUID is connected to a bias voltage source (BIAS SOURCE) and an amplifier (PULSE AMPLIFIER).
- the magnetic flux causes measurable voltage pulses in the SQUID, the frequency of which depends on the strength of the magnetic flux and which are amplified in the amplifier before being compared to a comparison device
- PULSE COMPARATOR a former (PULSE FORMER) and an integrator (INTEGRATOR).
- the integrator is via a memory follower / RI IPPPR.P ⁇ I I n FR ) with pinpr Stmmversnr ⁇ un ⁇ s- and control unit (CONTROL
- RO pulses When the DC bias voltage is applied to the RO-SQUID, the generation of RO pulses begins, the frequency of which is determined by a measurable magnetic field.
- the RO pulses run through the pulse amplifier and come to the pulse comparator, cutting off the own amplitude noise at the pulse amplifier output and extending the pulse duration to a value sufficient for the next cascade. After the RO pulses have left the comparator, they go to the pulse former and from there to the integrator.
- the signal leaving the integrator runs through the buffer follower.
- This signal processing electronics is arranged in the unit denoted by 9 in FIG.
- NbN-NbN x O y -Nb Josephson junctions 26 and 28 is based on non-shunted NbN-NbN x O y -Nb Josephson junctions 26 and 28 and comprises two regions 32 and 34 made of superconducting material that pass over the Josephson Junctions 26 and 28 are connected.
- the larger area 34 of the two areas 32 and 34 has an edge length of approximately 2 mm.
- the two areas 32 and 34 enclose an area 40, which is not drawn to scale here, and which naturally measures approximately 40 ⁇ m ⁇ 40 ⁇ m.
- the characteristic data of this SQUID which is useful for the application case described here, are.
- V g 3.8 - 4.0 mV
- R n 15 - 40 ohms
- RR n 12 - 44
- l c 3 - 5 ⁇ A. Its current-voltage characteristic is shown schematically in FIG. 8.
- FIG. 6 shows a second order gradiometer which, on the one hand, consists of an antenna, designated in its entirety by 10, with a pick-up coil 12, three bucking coils 14, 16 and 18 and an input coil 20.
- the antenna is bent from a single niobium wire loop 22.
- the "baseline” b (the distance between the pick-up coil 12 and the first bucking coil 14) is approximately 6 cm.
- the gradiometer also consists of a so-called "unshunted" low-temperature SQUID 24 with two Josephson junctions 26 and 28 of high capacity C, the SQUID 24 with the antenna 10 is inductively coupled via the input coil 20.
- the SQUID is also coupled to a feedback coil 30 in a manner known per se.
- the two superconducting regions 32 and 34 (see FIG. 5) of the SQUID are externally connected to one another via a resistor 36 with the value R and a coil 38 with inductance L, the coil 38 and the resistor 36 in Series are connected.
- the SQUID is supplied with a bias current l b which satisfies the condition l c ⁇ l b ⁇ V p / R, where l c is the critical voltage of a Josephson junction, R the resistance of the resistor 36 and V p the plasma voltage is a Josephson junction that the
- T T 0 [1 + ( ⁇ / 2) (L c / L)] + (4 / ⁇ + ⁇ / 4) ⁇ n ,
- the magnetic field is firmly enclosed in the SQUID interferometer ring via a negative feedback conclusion, which leads to a fixation of the operating point below a specified RO frequency.
- FIG. 7 is a schematic diagram of a Dewar vessel 44 arranged in a magnetically shielded housing 42 along with that of antenna 10 and SQUID 24
- Housing 42 and Dewar 44 are on the inside for magnetic
- the Dewar vessel is designed such that the distance between the underside of the pick-up coil facing the vessel and the outside of the vessel is between about 3 and 10 mm and the vessel holds about 6 liters of coolant. If liquid helium is used for cooling, a typical loss rate is about 1.2 l of helium per
- a system for measuring biomagnetic fields can be set up, the system noise of which is below 30 fT ⁇ / Hz with a dynamic width of
- the data recorded with such a system can be evaluated in a wide variety of ways, in particular with regard to the strength and the location of the sources of the magnetic fields.
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- Heart & Thoracic Surgery (AREA)
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- Measurement And Recording Of Electrical Phenomena And Electrical Characteristics Of The Living Body (AREA)
- Measuring Magnetic Variables (AREA)
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU69815/00A AU6981500A (en) | 1999-07-27 | 2000-07-27 | Method and device for measuring biomagnetic and in particular cardiomagnetic fields |
CA002379800A CA2379800A1 (en) | 1999-07-27 | 2000-07-27 | Method and device for measuring biomagnetic and in particular cardiomagnetic fields |
EP00958181A EP1210010A2 (de) | 1999-07-27 | 2000-07-27 | Verfahren und vorrichtung zur messung biomagnetischer felder |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE19934476 | 1999-07-27 | ||
DE19934476.0 | 1999-07-27 |
Publications (2)
Publication Number | Publication Date |
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WO2001006907A2 true WO2001006907A2 (de) | 2001-02-01 |
WO2001006907A3 WO2001006907A3 (de) | 2001-08-23 |
Family
ID=7915729
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/DE2000/002472 WO2001006907A2 (de) | 1999-07-27 | 2000-07-27 | Verfahren und vorrichtung zur messung biomagnetischer, insbesondere kardiomagnetischer felder |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP1210010A2 (de) |
AU (1) | AU6981500A (de) |
CA (1) | CA2379800A1 (de) |
DE (1) | DE10037519A1 (de) |
WO (1) | WO2001006907A2 (de) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1818678A1 (de) * | 2006-02-10 | 2007-08-15 | Forschungszentrum Jülich Gmbh | Anordnung zur Messung magnetischer Signale |
US10235635B1 (en) | 2017-10-19 | 2019-03-19 | International Business Machines Corporation | Capacitively-shunted asymmetric DC-SQUID for qubit readout and reset |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE102005023937A1 (de) * | 2005-05-20 | 2006-11-23 | Ruprecht-Karls-Universität Heidelberg | Sensor zum Vermessen von Potentialfeldern und Verfahren zum Betreiben des Sensors |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH05323004A (ja) * | 1992-05-22 | 1993-12-07 | Chodendo Sensor Kenkyusho:Kk | Squid磁束計 |
-
2000
- 2000-07-27 WO PCT/DE2000/002472 patent/WO2001006907A2/de not_active Application Discontinuation
- 2000-07-27 AU AU69815/00A patent/AU6981500A/en not_active Abandoned
- 2000-07-27 EP EP00958181A patent/EP1210010A2/de not_active Withdrawn
- 2000-07-27 CA CA002379800A patent/CA2379800A1/en not_active Abandoned
- 2000-07-27 DE DE10037519A patent/DE10037519A1/de not_active Withdrawn
Non-Patent Citations (1)
Title |
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None |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1818678A1 (de) * | 2006-02-10 | 2007-08-15 | Forschungszentrum Jülich Gmbh | Anordnung zur Messung magnetischer Signale |
US10235635B1 (en) | 2017-10-19 | 2019-03-19 | International Business Machines Corporation | Capacitively-shunted asymmetric DC-SQUID for qubit readout and reset |
Also Published As
Publication number | Publication date |
---|---|
WO2001006907A3 (de) | 2001-08-23 |
CA2379800A1 (en) | 2001-02-01 |
EP1210010A2 (de) | 2002-06-05 |
AU6981500A (en) | 2001-02-13 |
DE10037519A1 (de) | 2001-03-01 |
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