WO2011018744A1 - Method and device for measuring conductivity of an object - Google Patents

Method and device for measuring conductivity of an object Download PDF

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Publication number
WO2011018744A1
WO2011018744A1 PCT/IB2010/053581 IB2010053581W WO2011018744A1 WO 2011018744 A1 WO2011018744 A1 WO 2011018744A1 IB 2010053581 W IB2010053581 W IB 2010053581W WO 2011018744 A1 WO2011018744 A1 WO 2011018744A1
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WIPO (PCT)
Prior art keywords
voltage
measuring
measuring unit
magnetic field
unit
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Application number
PCT/IB2010/053581
Other languages
French (fr)
Inventor
Ming Yan
Dayu Chen
Hui Li
Hua Jin
Original Assignee
Koninklijke Philips Electronics N.V.
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Publication of WO2011018744A1 publication Critical patent/WO2011018744A1/en

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/053—Measuring electrical impedance or conductance of a portion of the body
    • A61B5/0536—Impedance imaging, e.g. by tomography
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/0522—Magnetic induction tomography

Definitions

  • the invention relates to a method and device for measuring the conductivity of an object, in particular, a method and device for measuring the conductivity of an object, based on magnetic induction tomography technology.
  • Magnetic induction tomography is a non-invasive and contactless imaging technique with applications in industry and medical fields.
  • WO2007/072343 discloses an MIT device for studying the conductivity of an object.
  • the device comprises one or more generator coils adapted for generating a primary magnetic field, said primary magnetic field inducing an eddy current in an object to be measured, one or more sensor coils adapted for sensing a secondary magnetic field, said secondary magnetic field being generated as a result of said eddy current, and means for providing a relative movement between one or more generator coils and/or one or more sensor coils on the one hand and the object to be measured on the other hand.
  • the temperature of the MIT device and/or of the environment of the MIT device may change, and the temperature change may cause thermal drift of the measurement result. Said thermal drift of the measurement result may cause large artefacts in the (?) image reconstruction of the object. Thermal drift may be reduced by refining the design of the generator circuit and receiver circuit. However, refining the design of the generator circuit and receiver circuit will increase the cost of the MIT device.
  • the device for measuring the conductivity of an object comprises: a measuring unit for measuring a first voltage when the object is not placed in the measuring unit, for measuring the voltage of the object when the object is placed in the measuring unit after measuring the first voltage, and for measuring a second voltage when the object is moved away from the measuring unit after measuring the voltage of the object; a calculating unit for calculating the difference between the first voltage and the second voltage; and an adjusting unit for adjusting the voltage of the object, based on the difference, to generate an adjusted voltage of the object.
  • the invention also provides a method of measuring the conductivity of an object and a computer program used in the method of measuring the conductivity of an object.
  • Fig.l schematically depicts a device for measuring the conductivity of an object in accordance with an embodiment of the invention
  • Fig. 2 schematically depicts a device for measuring the conductivity of an object in accordance with a further embodiment of the invention
  • Fig. 3 A shows a picture reconstructed at a time ti
  • Fig. 3B shows a picture reconstructed at a time t 2 ;
  • Fig. 3C shows a picture of the object reconstructed at time t 2 after adjusting
  • Fig. 4 is a flowchart for illustrating a method of measuring the conductivity of an object in accordance with an embodiment of the invention
  • Fig. 5 is a flowchart for illustrating a method of measuring the conductivity of an object in accordance with a further embodiment of the invention.
  • Fig. 1 schematically shows a device for measuring the conductivity of an object according to an embodiment of the invention.
  • the device 10 is used for measuring the conductivity of an object 20.
  • the device 10 is used for measuring the conductivity of an object 20.
  • 10 comprises a measuring unit 11, a calculating unit 12, and an adjusting unit 13.
  • the measuring unit 11 is used for measuring a first voltage when the object 20 is not placed in the measuring unit 11.
  • the measuring unit 11 is also used for measuring the voltage of the object 20 when the object 20 is placed in the measuring unit 11 after measuring the first voltage.
  • the measuring unit 11 is further used for measuring a second voltage when the object 20 is moved away from the measuring unit 11 after measuring the voltage of the object 20.
  • the first voltage and the second voltage are measured when the object 20 is not placed in the measuring unit 11, so both of them are voltages of the measuring unit 11 itself.
  • Moving the object 20 away from the measuring unit 11 is a relative movement, which can be a movement consisting of moving the measuring unit 11 away from the object 20 or a movement consisting of moving the object 20 away from the measuring unit 11.
  • the calculating unit 12 is used for calculating the difference between the first voltage and the second voltage
  • the adjusting unit 13 is used for adjusting the voltage of the object 20, based on the difference, to generate an adjusted voltage of the object 20.
  • the measuring unit 11 comprises a generator 111, a receiver 112, and an acquiring element 113.
  • the generator 111 may comprise a coil or a set of coils excited by an alternating current for generating a primary magnetic field. If the measuring unit 11 is used for measuring the voltages of the object 20, the primary magnetic field induces an eddy current in the object 20.
  • the receiver 112 comprises a coil or a set of coils for receiving the primary magnetic field and a secondary magnetic field being generated as a result of the eddy current, and the acquiring element 113 is used for acquiring voltages of the measuring unit 11 itself and voltages of the object 20 according to the primary magnetic field and the secondary magnetic field.
  • the frequency of the alternating current for generating the primary magnetic field to measure the first voltage, the second voltage, and the voltage of the object 20 is constant in value.
  • the generator 111 When the measuring unit 11 measures the first voltage and the second voltage, if the object 20 is not placed in the measuring unit 11: the generator 111 generates a primary magnetic field (shown as PMF in Fig. 1) in the measuring unit 11, the receiver 112 receives the primary magnetic field, and the acquiring element 113 acquires the first voltage and the second voltage, based on the primary magnetic field.
  • PMF primary magnetic field
  • the measuring unit 11 measures the voltage of the object 20 which is placed in the measuring unit 11 : the generator 111 generates the primary magnetic field and applies it (?) to the object 20 and the primary magnetic field induces an eddy current in the object 20, the receiver 112 receives the primary magnetic field and a secondary magnetic field (shown as SMF in Fig. 1) being generated as a result of the eddy current, and the acquiring element 113 acquires the voltage of the object 20 according to the primary magnetic field and the secondary magnetic field.
  • the measuring unit 11 may comprise a reconstructing element 114 for reconstructing an image for the object 20, based on the adjusted voltage of the object 20, and the image is shown in a picture (shown as P in Fig. 1).
  • the reconstructing element 114 may be further intended to reconstruct an initial image for the object 20, based on the voltage of the object 20.
  • Fig. 2 schematically shows a device for measuring the conductivity of an object in accordance with another embodiment of the invention.
  • the device 10 of Fig. 2 comprises two new units: a detecting unit 14 and a controlling unit 15.
  • the detecting unit 14 is used for detecting whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, and for generating an indication signal (shown as IS in Fig. 2).
  • the controlling unit 15 is used for controlling the measuring unit 11 so as to move away from the object 20 according to the indication signal.
  • the detecting unit 14 may be used for detecting whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, and for generating an alert to a user.
  • the controlling unit 15 serves for controlling the measuring unit 11 so as to cause it to move away from the object 20 according to an indication signal, the indication signal being inputted by the user according to the alert.
  • the alert can be a light, text, voice etc. For example, if a user notices the alert, he/she inputs an indication signal to the controlling unit 15 for controlling the measuring unit 11 so as to cause it to move away from the object 20.
  • the detecting unit 14 is not necessary for the device 10, and the controlling unit 15 is used for controlling the measuring unit 11 so as to cause it to move away from the object 20 according to an indication signal, the indication signal being inputted by a user according to the quality of the initial image of the object 20.
  • the controlling unit 15 inputs an indication signal to the controlling unit 15 for controlling the measuring unit 11 so as to cause it to move away from the object 20.
  • the controlling unit 15 may also be used to control the measuring unit 11, causing it to measure the second voltage after controlling it so as to cause it to move away from the object
  • the controlling unit 15 may be further intended to control the measuring unit 11 so as to cause it to move close to the object 20 after the reconstructing element 114 has reconstructed the image of the object 20.
  • the controlling unit 15 is not necessary for the device 10, and the detecting unit 14 is used for detecting whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, and for generating an alert to a user. The user moves the object 20 away from the measuring unit 11 according to the alert.
  • the object 20 may be moved away from the measuring unit 11 by a user according to the quality of the initial image of the object 20, and the object 20 is moved into the measuring unit 11 by the user after the reconstructing element 114 has reconstructed the image of the object (20).
  • the difference between the first voltage and the second voltage is caused by thermal drift generated when the device 10 measures the object 20.
  • the thermal drift may be caused by the change in temperature during measuring the object 20; for example, when the device 10 measures the object 20 in a monitoring mode for a long time, the temperature of the device 10 or of the environment around the device 10 may be changed.
  • the device 10 can also work in spot-shot mode (the device 10 is not continually measuring (monitoring) the object 20), in which case the temperature of the device 10 or the environment around the device 10 may also change.
  • the difference between the first voltage and the second voltage also reflects the thermal drift of the voltage of the object 20, so the difference is used to compensate the voltage of the object 20. In the following, an analysis procedure is given for supporting the invention.
  • Voltage ⁇ i-* is a combination voltage of the measuring unit 11 and the object 20 at time tl
  • v w / is a combination voltage of the measuring unit 11 and the object 20 at time 2 .
  • a voltage difference ⁇ V j s defined in equation (1): ⁇ V V(I 1 ) -V(t 2 ) (1)
  • the ⁇ V j s a voltage difference caused by a voltage change of the object 20 and a thermal drift.
  • the thermal drift will cause artefacts in the reconstruction image for the object 20.
  • Voltages e ⁇ l ' and e ⁇ 2 ' are voltages on the coil/coils of the receiver 112 of the measuring unit 11 and are measured at time ti and time t 2 respectively.
  • ⁇ V new j s a voltage difference of the object 20 from time ti to t 2 during a measurement. Compared with ⁇ V ; a voltage difference e ⁇ 1 ⁇ e ⁇ 2 ⁇ of the measuring unit 11 from time tl to t2 is subtracted from new .
  • the real magnetic field r generated by the coil/coils of the generator 111 is shown in equation (3).
  • the s is a pure sine wave magnetic field
  • d is a magnetic field caused by thermal drift
  • n is the magnetic field caused by noise
  • V f Induc ⁇ on (B r ) +V nr +V dr
  • nr is a voltage caused by noise on the coil/coils of the receiver 112
  • dr is caused by thermal drift generated on the coil/coils of the receiver 112
  • V ' phantom + ⁇ V v dr
  • the thermal drift of measuring unit 11 and object 20 comprises Inductlon( - d ' induction * , ed > drp i>e ⁇ j j ⁇ ⁇ . secon( jary field generated by eddy currents induced by d . 1 ⁇ is much smaller than d , so induction ⁇ ed / j s a j so muc h smaller than
  • drp and dr are very small and can be ignored.
  • the thermal drift of the measuring unit 11 and the thermal drift of the 20 measuring unit 11 together with the object 20 are substantially equal.
  • the combined thermal drift of the measuring unit 11 and the object 20 is deemed to be equal to the thermal drift of measuring unit 11 itself, which is empty, i.e. does not include the object 20.
  • the difference e ⁇ e ⁇ 2 ' between the first voltage (measured at time ti) and the second voltage (measured at time t 2 ) is used to adjust the voltage of the object 20, so as to reduce the thermal drift caused during measuring the object 20.
  • the advantage is that the thermal drift caused by measuring the object 20 is largely reduced after adjusting the voltage of the object, and the corresponding reconstructed image of the object gets much clearer.
  • Fig. 3 A shows a picture reconstructed at a time ti (e.g. 0 hour) by the device 10, and the image of the object 20 is clear in the picture.
  • Fig. 3B shows a picture reconstructed at a time t 2 (e.g. 1 hour later) by the device
  • the image of the object 20 is affected by thermal drift and is obscured in the picture.
  • Fig. 3C shows a picture reconstructed at time t 2 by the device 10 after adjusting the voltage of the object.
  • the image of the object 20 measured at time t 2 is clear again in the picture.
  • Fig. 4 is a flowchart for illustrating a method of measuring a conductivity of an object in accordance with an embodiment of the invention. The method comprises the following steps. The method is intended to measure the conductivity of an object 20. The method comprises the following steps.
  • a step 41 is carried out to measure a first voltage when the object 20 is not placed in a measuring unit 11.
  • the first voltage is measured by generating a primary magnetic field, receiving the primary magnetic field, and acquiring the first voltage based on the primary magnetic field.
  • a step 42 is carried out to measure the voltage of the object 20 when the object 20 is placed in the measuring unit 11 after measuring the first voltage.
  • the voltage of the object 20 is measured by generating the primary magnetic field and applying it(?) to the object 20, which primary magnetic field induces an eddy current in the object 20, and receiving the primary magnetic field and a secondary magnetic field being generated as a result of the eddy current, and acquiring the voltage of the object 20 according to the primary magnetic field and the secondary magnetic field.
  • a step 43 is carried out to measure a second voltage when the object 20 is moved away from the measuring unit 11 after measuring the voltage of the object 20.
  • the second voltage is measured by generating a primary magnetic field, receiving the primary magnetic field, and acquiring the second voltage based on the primary magnetic field.
  • a step 44 is carried out to calculate the difference between the first voltage and the second voltage.
  • a step 45 is carried out to adjust the voltage of the object 20, based on the difference, to generate an adjusted voltage of the object 20.
  • the method further comprises a step of reconstructing 46 an image for the object 20 based on the adjusted voltage of the object 20.
  • the reconstructing step 46 is further intended to reconstruct an initial image for the object 20 based on the voltage of the object 20.
  • Fig. 5 is a flowchart illustrating a method of measuring the conductivity of an object in accordance with another embodiment of the invention.
  • the method of Fig. 5 comprises two new steps: - detecting 51 whether the voltage of the object 20 is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, to generate an indication signal, and
  • the method comprises the steps of:
  • the measuring unit 11 controls 52 the measuring unit 11 so as to cause it to move away from the object 20 according to an indication signal, the indication signal being inputted by the user according to the alert.
  • the method comprises a step of controlling 52 the measuring unit 11 so as to cause it to move away from the object 20 according to an indication signal, the indication signal being inputted by the user according to a quality of the initial image of the object 20.
  • the detecting step 51 is not necessary.
  • the controlling step 52 may be further intended to control the measuring unit 11 so as to cause it to move close to the object 20 after reconstructing the image of the object 20.
  • the controlling step 52 is not necessary for the method
  • the detecting step 51 is intended to detect whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, and to generate an alert to a user. The user moves the object 20 away from the measuring unit 11 according to the alert.
  • the object 20 may be moved away from the measuring unit 11 by a user according to the quality of the initial image of the object 20, and the object 20 is moved into the measuring unit 11 by the user after the reconstructing element 114 has reconstructed the image of the object 20.
  • a computer program is used in the method of measuring the conductivity of an object 20, and the method comprises the steps of:

Abstract

The invention provides a device (10) for measuring the conductivity of an object (20), and the device (10) comprises: a measuring unit (11) for measuring a first voltage when the object (20) is not placed in the measuring unit (11), for measuring the voltage of the object (20) when the object (20) is placed in the measuring unit (11) after measuring the first voltage, and for measuring a second voltage when the object (20) is moved away from the measuring unit (11) after measuring the voltage of the object (20); a calculating unit (12) for calculating the difference between the first voltage and the second voltage; and an adjusting unit (13) for adjusting the voltage of the object (20), based on said difference, to generate an adjusted voltage of the object (20).

Description

METHOD AND DEVICE FOR MEASURING CONDUCTIVITY OF AN OBJECT
FIELD OF THE INVENTION
The invention relates to a method and device for measuring the conductivity of an object, in particular, a method and device for measuring the conductivity of an object, based on magnetic induction tomography technology.
BACKGROUND OF THE INVENTION
Magnetic induction tomography (MIT) is a non-invasive and contactless imaging technique with applications in industry and medical fields.
WO2007/072343 discloses an MIT device for studying the conductivity of an object. The device comprises one or more generator coils adapted for generating a primary magnetic field, said primary magnetic field inducing an eddy current in an object to be measured, one or more sensor coils adapted for sensing a secondary magnetic field, said secondary magnetic field being generated as a result of said eddy current, and means for providing a relative movement between one or more generator coils and/or one or more sensor coils on the one hand and the object to be measured on the other hand.
During measuring the conductivity of an object, the temperature of the MIT device and/or of the environment of the MIT device may change, and the temperature change may cause thermal drift of the measurement result. Said thermal drift of the measurement result may cause large artefacts in the (?) image reconstruction of the object. Thermal drift may be reduced by refining the design of the generator circuit and receiver circuit. However, refining the design of the generator circuit and receiver circuit will increase the cost of the MIT device.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved device for measuring the conductivity of an object.
The device for measuring the conductivity of an object comprises: a measuring unit for measuring a first voltage when the object is not placed in the measuring unit, for measuring the voltage of the object when the object is placed in the measuring unit after measuring the first voltage, and for measuring a second voltage when the object is moved away from the measuring unit after measuring the voltage of the object; a calculating unit for calculating the difference between the first voltage and the second voltage; and an adjusting unit for adjusting the voltage of the object, based on the difference, to generate an adjusted voltage of the object. The advantage is that the thermal drift generated during measuring the conductivity of an object is largely reduced.
According to another object, the invention also provides a method of measuring the conductivity of an object and a computer program used in the method of measuring the conductivity of an object.
Detailed explanations and other aspects of the invention will be given below. DESCRIPTION OF THE DRAWINGS
The above and other objects and features of the present invention will become more apparent from the following detailed description considered in connection with the accompanying drawings, in which:
Fig.l schematically depicts a device for measuring the conductivity of an object in accordance with an embodiment of the invention; Fig. 2 schematically depicts a device for measuring the conductivity of an object in accordance with a further embodiment of the invention;
Fig. 3 A shows a picture reconstructed at a time ti; Fig. 3B shows a picture reconstructed at a time t2;
Fig. 3C shows a picture of the object reconstructed at time t2 after adjusting;
Fig. 4 is a flowchart for illustrating a method of measuring the conductivity of an object in accordance with an embodiment of the invention;
Fig. 5 is a flowchart for illustrating a method of measuring the conductivity of an object in accordance with a further embodiment of the invention.
The same reference numerals are used to denote similar parts throughout the Figures.
DETAILED DESCRIPTION Fig. 1 schematically shows a device for measuring the conductivity of an object according to an embodiment of the invention. The device 10 is used for measuring the conductivity of an object 20. The device
10 comprises a measuring unit 11, a calculating unit 12, and an adjusting unit 13.
The measuring unit 11 is used for measuring a first voltage when the object 20 is not placed in the measuring unit 11. The measuring unit 11 is also used for measuring the voltage of the object 20 when the object 20 is placed in the measuring unit 11 after measuring the first voltage. The measuring unit 11 is further used for measuring a second voltage when the object 20 is moved away from the measuring unit 11 after measuring the voltage of the object 20.
The first voltage and the second voltage are measured when the object 20 is not placed in the measuring unit 11, so both of them are voltages of the measuring unit 11 itself.
When measuring the voltage of the object 20, the voltage of the measuring unit
11 itself is also measured together with the voltage of the object 20. The voltage of the object 20 and the voltage of the measuring unit 11 are distinguishable. During reconstructing images for an object, based on a magnetic induction tomography device, it is well known that the voltage of the object and the voltage of a measuring unit of the magnetic induction tomography device are distinguishable.
Moving the object 20 away from the measuring unit 11 is a relative movement, which can be a movement consisting of moving the measuring unit 11 away from the object 20 or a movement consisting of moving the object 20 away from the measuring unit 11.
The calculating unit 12 is used for calculating the difference between the first voltage and the second voltage, and the adjusting unit 13 is used for adjusting the voltage of the object 20, based on the difference, to generate an adjusted voltage of the object 20. The measuring unit 11 comprises a generator 111, a receiver 112, and an acquiring element 113. The generator 111 may comprise a coil or a set of coils excited by an alternating current for generating a primary magnetic field. If the measuring unit 11 is used for measuring the voltages of the object 20, the primary magnetic field induces an eddy current in the object 20. The receiver 112 comprises a coil or a set of coils for receiving the primary magnetic field and a secondary magnetic field being generated as a result of the eddy current, and the acquiring element 113 is used for acquiring voltages of the measuring unit 11 itself and voltages of the object 20 according to the primary magnetic field and the secondary magnetic field.
The frequency of the alternating current for generating the primary magnetic field to measure the first voltage, the second voltage, and the voltage of the object 20 is constant in value.
When the measuring unit 11 measures the first voltage and the second voltage, if the object 20 is not placed in the measuring unit 11: the generator 111 generates a primary magnetic field (shown as PMF in Fig. 1) in the measuring unit 11, the receiver 112 receives the primary magnetic field, and the acquiring element 113 acquires the first voltage and the second voltage, based on the primary magnetic field.
When the measuring unit 11 measures the voltage of the object 20 which is placed in the measuring unit 11 : the generator 111 generates the primary magnetic field and applies it (?) to the object 20 and the primary magnetic field induces an eddy current in the object 20, the receiver 112 receives the primary magnetic field and a secondary magnetic field (shown as SMF in Fig. 1) being generated as a result of the eddy current, and the acquiring element 113 acquires the voltage of the object 20 according to the primary magnetic field and the secondary magnetic field. The measuring unit 11 may comprise a reconstructing element 114 for reconstructing an image for the object 20, based on the adjusted voltage of the object 20, and the image is shown in a picture (shown as P in Fig. 1). The reconstructing element 114 may be further intended to reconstruct an initial image for the object 20, based on the voltage of the object 20.
Fig. 2 schematically shows a device for measuring the conductivity of an object in accordance with another embodiment of the invention. Compared to the device 10 of Fig. 1, the device 10 of Fig. 2 comprises two new units: a detecting unit 14 and a controlling unit 15. The detecting unit 14 is used for detecting whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, and for generating an indication signal (shown as IS in Fig. 2). The controlling unit 15 is used for controlling the measuring unit 11 so as to move away from the object 20 according to the indication signal.
Alternatively, the detecting unit 14 may be used for detecting whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, and for generating an alert to a user. The controlling unit 15 serves for controlling the measuring unit 11 so as to cause it to move away from the object 20 according to an indication signal, the indication signal being inputted by the user according to the alert. The alert can be a light, text, voice etc. For example, if a user notices the alert, he/she inputs an indication signal to the controlling unit 15 for controlling the measuring unit 11 so as to cause it to move away from the object 20.
Alternatively, the detecting unit 14 is not necessary for the device 10, and the controlling unit 15 is used for controlling the measuring unit 11 so as to cause it to move away from the object 20 according to an indication signal, the indication signal being inputted by a user according to the quality of the initial image of the object 20. For example, when a user notices that the initial image of the object 20 is not clear, he/she inputs an indication signal to the controlling unit 15 for controlling the measuring unit 11 so as to cause it to move away from the object 20.
The controlling unit 15 may also be used to control the measuring unit 11, causing it to measure the second voltage after controlling it so as to cause it to move away from the object
20.
The controlling unit 15 may be further intended to control the measuring unit 11 so as to cause it to move close to the object 20 after the reconstructing element 114 has reconstructed the image of the object 20.
Alternatively, the controlling unit 15 is not necessary for the device 10, and the detecting unit 14 is used for detecting whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, and for generating an alert to a user. The user moves the object 20 away from the measuring unit 11 according to the alert.
Alternatively, the object 20 may be moved away from the measuring unit 11 by a user according to the quality of the initial image of the object 20, and the object 20 is moved into the measuring unit 11 by the user after the reconstructing element 114 has reconstructed the image of the object (20).
The difference between the first voltage and the second voltage is caused by thermal drift generated when the device 10 measures the object 20. The thermal drift may be caused by the change in temperature during measuring the object 20; for example, when the device 10 measures the object 20 in a monitoring mode for a long time, the temperature of the device 10 or of the environment around the device 10 may be changed. The device 10 can also work in spot-shot mode (the device 10 is not continually measuring (monitoring) the object 20), in which case the temperature of the device 10 or the environment around the device 10 may also change. The difference between the first voltage and the second voltage also reflects the thermal drift of the voltage of the object 20, so the difference is used to compensate the voltage of the object 20. In the following, an analysis procedure is given for supporting the invention.
Voltage ^ i-* is a combination voltage of the measuring unit 11 and the object 20 at time tl, and v w/ is a combination voltage of the measuring unit 11 and the object 20 at time 2 . A voltage difference ^V js defined in equation (1): ΔV = V(I1) -V(t2) (1)
From time ti to t2, the ΔV js a voltage difference caused by a voltage change of the object 20 and a thermal drift. The thermal drift will cause artefacts in the reconstruction image for the object 20.
Voltages e^ l' and e^ 2' are voltages on the coil/coils of the receiver 112 of the measuring unit 11 and are measured at time ti and time t2 respectively. The voltage difference of the object 20 from time ti to t2 during a measurement is shown in equation (2): ΔV new = [V(tl) -Ve(tl)] - [V(t2) -Ve(t2)] _ (2)
ΔV new js a voltage difference of the object 20 from time ti to t2 during a measurement. Compared with ^V ; a voltage difference e^ 1^ e ^ 2^ of the measuring unit 11 from time tl to t2 is subtracted from new . During measuring the object 20, the real magnetic field r generated by the coil/coils of the generator 111 is shown in equation (3). The s is a pure sine wave magnetic field,
TJ T)
d is a magnetic field caused by thermal drift, and n is the magnetic field caused by noise.
Br = Bs + Bd + Bn (3)
If the measuring unit 11 is empty, i.e. does not include the object 20, the measured voltage V induced by r is shown in equation (4):
V = fInducύon(Br ) +Vnr +Vdr
\ Q ~ I Induction^ -Ds / "*" * Induction^ "ά ) "*" * Induction^ -^n ) "*" *nr "*" *dr (Λ \
In the equation (4), nr is a voltage caused by noise on the coil/coils of the receiver 112, dr is caused by thermal drift generated on the coil/coils of the receiver 112, f (B ^
induction^ d > js (J16 voltage caused by thermal drift on the coil/coils of the generator 111,
15 fmduction(Bs) is the voltage caused by the pure sine wave magnetic field, and fmduction(Bn) is the voltage caused by noise. When the device 10 is empty, the thermal drift is reflected by
Figure imgf000011_0001
*dr _
If the object 20 is placed in the measuring unit 11, the whole magnetic field is
20 composed of R R rr aanndd tthhee sseeccoonnddaarryy mmaaggnneettiicc ffiieelldd BB ee ccaauusseedd bbyy eeddddyy ccuumrrents in the object 20 is based on Br. The measurement magnetic field Bm is shown in equation (5):
B = BL + B.
(5)
25 The secondary magnetic field is shown in equation (6): Be = feddy(Bs + Bd + Bn) = Bes + Bed + Ben
(6)
The voltage VPhantom of the measuring unit 11 and the object 20 (phantom) is shown in equation (7):
5
V ' phantom =
Figure imgf000012_0001
+ ~ V vdr
Figure imgf000012_0002
Inserting equation (5) into equation (7), the Vphantom is shown in equation (8):
" phantom ~~
Figure imgf000012_0003
~"~ "drp
= induction' "i > + induction' "ej + induction' "ei > + induction' "ej + V + *drp
γ Q
Figure imgf000012_0004
) + Iliiductioiil "es ) + Iliiductioii(-°ed ) + IliiductioiiΑJ + V
Figure imgf000012_0005
According to equation (8), the thermal drift of measuring unit 11 and object 20 comprises Inductlon(- d ' induction*, ed > drp i>e<j j§ ^. secon(jary field generated by eddy currents induced by d . 1^ is much smaller than d , so induction^ ed / js ajso much smaller than
15 induction^ d > an(j can J36 ignored. If the measurements for the device 10 and the object 20 are
V V
taken within a short time interval and the environment does not change, drp and dr are very small and can be ignored.
Thus, the thermal drift of the measuring unit 11, and the thermal drift of the 20 measuring unit 11 together with the object 20 are substantially equal.
In the embodiment of the invention, from time ti to t2, the combined thermal drift of the measuring unit 11 and the object 20 is deemed to be equal to the thermal drift of measuring unit 11 itself, which is empty, i.e. does not include the object 20.
25 The thermal drift of measuring unit 11 from time tl to t2 is shown in equation (9). ∞^ l' and ∞^ 2/ are ^j16 voltages induced by the measuring unit 11 without thermal drift and have constant values. et^ 1^ and et^ 2' are thermal drifts at time i and 2 of the measuring unit 11, respectively.
V0(^) -V0Ct2) = [vβc(t1)+v-(t1)] -[vβc(t2)+vβt(t12)] = V-^)-V-Ct2) (9)
The difference e^ e^ 2' between the first voltage (measured at time ti) and the second voltage (measured at time t2) is used to adjust the voltage of the object 20, so as to reduce the thermal drift caused during measuring the object 20.
Based on the difference between the first voltage and the second voltage, the advantage is that the thermal drift caused by measuring the object 20 is largely reduced after adjusting the voltage of the object, and the corresponding reconstructed image of the object gets much clearer.
Fig. 3 A shows a picture reconstructed at a time ti (e.g. 0 hour) by the device 10, and the image of the object 20 is clear in the picture. Fig. 3B shows a picture reconstructed at a time t2 (e.g. 1 hour later) by the device
10. The image of the object 20 is affected by thermal drift and is obscured in the picture.
Fig. 3C shows a picture reconstructed at time t2 by the device 10 after adjusting the voltage of the object. The image of the object 20 measured at time t2 is clear again in the picture.
The pictures of Fig. 3A to Fig. 3C may be reconstructed by measuring a bottle of 50ml saline of conductivity 0.75S/m. Fig. 4 is a flowchart for illustrating a method of measuring a conductivity of an object in accordance with an embodiment of the invention. The method comprises the following steps. The method is intended to measure the conductivity of an object 20. The method comprises the following steps.
A step 41 is carried out to measure a first voltage when the object 20 is not placed in a measuring unit 11.
When the object 20 is not placed in the measuring unit 11, the first voltage is measured by generating a primary magnetic field, receiving the primary magnetic field, and acquiring the first voltage based on the primary magnetic field. A step 42 is carried out to measure the voltage of the object 20 when the object 20 is placed in the measuring unit 11 after measuring the first voltage.
When the object 20 is placed in the measuring unit 11, the voltage of the object 20 is measured by generating the primary magnetic field and applying it(?) to the object 20, which primary magnetic field induces an eddy current in the object 20, and receiving the primary magnetic field and a secondary magnetic field being generated as a result of the eddy current, and acquiring the voltage of the object 20 according to the primary magnetic field and the secondary magnetic field. A step 43 is carried out to measure a second voltage when the object 20 is moved away from the measuring unit 11 after measuring the voltage of the object 20.
The second voltage is measured by generating a primary magnetic field, receiving the primary magnetic field, and acquiring the second voltage based on the primary magnetic field. A step 44 is carried out to calculate the difference between the first voltage and the second voltage.
A step 45 is carried out to adjust the voltage of the object 20, based on the difference, to generate an adjusted voltage of the object 20.
The method further comprises a step of reconstructing 46 an image for the object 20 based on the adjusted voltage of the object 20. The reconstructing step 46 is further intended to reconstruct an initial image for the object 20 based on the voltage of the object 20.
Fig. 5 is a flowchart illustrating a method of measuring the conductivity of an object in accordance with another embodiment of the invention.
Compared to the method of Fig. 4, the method of Fig. 5 comprises two new steps: - detecting 51 whether the voltage of the object 20 is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, to generate an indication signal, and
- controlling 52 the measuring unit 11 so as to cause it to move away from the object 20 according to the indication signal.
Alternatively, the method comprises the steps of:
- detecting 51 whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, to generate an alert to a user,
- controlling 52 the measuring unit 11 so as to cause it to move away from the object 20 according to an indication signal, the indication signal being inputted by the user according to the alert.
Alternatively, the method comprises a step of controlling 52 the measuring unit 11 so as to cause it to move away from the object 20 according to an indication signal, the indication signal being inputted by the user according to a quality of the initial image of the object 20. In this condition, the detecting step 51 is not necessary.
The controlling step 52 may be further intended to control the measuring unit 11 so as to cause it to move close to the object 20 after reconstructing the image of the object 20.
Alternatively, the controlling step 52 is not necessary for the method, the detecting step 51 is intended to detect whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object 20 is lower than a pre-defined quality threshold, and to generate an alert to a user. The user moves the object 20 away from the measuring unit 11 according to the alert.
Alternatively, the object 20 may be moved away from the measuring unit 11 by a user according to the quality of the initial image of the object 20, and the object 20 is moved into the measuring unit 11 by the user after the reconstructing element 114 has reconstructed the image of the object 20.
A computer program is used in the method of measuring the conductivity of an object 20, and the method comprises the steps of:
- measuring 41 a first voltage when the object 20 is not placed in a measuring unit
11,
- measuring 42 the voltage of the object 20 when the object 20 is placed in the measuring unit 11 after measuring the first voltage,
- measuring 43 a second voltage when the object 20 is moved away from the measuring unit 11 after measuring the voltage of the object 20,
- calculating 44 the difference between the first voltage and the second voltage, and
- adjusting 45 the voltage of the object 20, based on said difference, to generate an adjusted voltage of the object 20. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim or in the description. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by a unit of hardware comprising several distinct elements and by a unit of a programmed computer. In the system claims enumerating several units, several of these units can be embodied by one and the same item of hardware or software.
The use of the words first, second and third, et cetera, does not indicate any ordering. These words are to be interpreted as names.

Claims

CLAIMS:
1. A device for measuring the conductivity of an object (20), the device (10) comprising:
- a measuring unit (11) for measuring a first voltage when the object (20) is not placed in the measuring unit (11), for measuring a voltage of the object (20) when the object (20) is placed in the measuring unit (11) after measuring the first voltage, and for measuring a second voltage when the object (20) is moved away from the measuring unit (11) after measuring the voltage of the object (20),
- a calculating unit (12) for calculating the difference between the first voltage and the second voltage, and
an adjusting unit (13) for adjusting the voltage of the object (20), based on said difference, to generate an adjusted voltage of the object (20).
2. The device as claimed in claim 1, wherein the measuring unit (11) comprises a generator
(111), a receiver (112), and an acquiring element (113),
when the measuring unit (11) measures the first voltage and the second voltage, the generator (111) generates a primary magnetic field, the receiver (112) receives the primary magnetic field, and the acquiring element (113) acquires the first voltage and the second voltage based on the primary magnetic field, and
when the measuring unit (11) measures the voltage of the object (20) which is placed in the measuring unit (11), the generator (111) generates the primary magnetic field and applies it (?) to the object (20) and the primary magnetic field induces an eddy current in the object (20), the receiver (112) receives the primary magnetic field and a secondary magnetic field being generated as a result of the eddy current, and the acquiring element (113) acquires the voltage of the object (20) according to the primary magnetic field and the secondary magnetic field.
3. The device as claimed in claim 1, wherein the measuring unit (11) comprises a reconstructing element (114) for reconstructing an image for the object (20), based on the adjusted voltage of the object (20).
4. The device as claimed in claim 3, wherein the reconstructing element (114) is further intended to reconstruct an initial image for the object (20), based on the voltage of the object (20).
5. The device as claimed in claim 4, further comprising:
- a detecting unit (14) for detecting whether the voltage of the object is not in a predefined voltage range or the quality of the initial image of the object (20) is lower than a pre-defined quality threshold, and for generating an indication signal, and a controlling unit (15) for controlling the measuring unit (11) so as to cause it to move away from the object (20) according to the indication signal.
6. The device as claimed in claim 4, further comprising:
a detecting unit (14) for detecting whether the voltage of the object is not in a predefined voltage range or the quality of the initial image of the object (20) is lower than a pre-defined quality threshold, and for generating an alert to a user,
- a controlling unit (15) for controlling the measuring unit (11) so as to cause it to move away from the object (20) according to an indication signal, wherein the indication signal is inputted by the user according to the alert.
7. The device as claimed in claim 4, further comprising a controlling unit (15) for controlling the measuring unit (11) so as to cause it to move away from the object (20) according to an indication signal, wherein the indication signal is inputted by a user according to the quality of the initial image of the object (20).
8. A method of measuring the conductivity of an object (20), the method comprising the steps of: measuring (41) a first voltage when the object (20) is not placed in a measuring unit
(H),
measuring (42) the voltage of the object (20) when the object (20) is placed in the measuring unit (11) after measuring the first voltage,
- measuring (43) a second voltage when the object (20) is moved away from the measuring unit (11) after measuring the voltage of the object (20),
calculating (44) a difference between the first voltage and the second voltage, and adjusting (45) the voltage of the object (20), based on said difference, to generate an adjusted voltage of the object (20).
9. The method as claimed in claim 8, wherein
the first voltage and the second voltage are measured by generating a primary magnetic field, receiving the primary magnetic field, and acquiring the first voltage and the second voltage based on the primary magnetic field, and
- when the object (20) is placed in the measuring unit (11), the voltage of the object (20) is measured by generating the primary magnetic field and applying it (?) to the object (20), which primary magnetic field induces an eddy current in the object (20), and receiving the primary magnetic field and a secondary magnetic field being generated as a result of the eddy current, and acquiring the voltage of the object (20) according to the primary magnetic field and the secondary magnetic field.
10. The method as claimed in claim 8, further comprising a reconstructing (46) step for reconstructing an image for the object (20), based on the adjusted voltage of the object (20).
11. The method as claimed in claim 10, wherein the reconstructing step (46) is further intended to reconstruct an initial image for the object (20), based on the voltage of the object (20).
12. The method as claimed in claim 11, further comprising the steps of: detecting (51) whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object (20) is lower than a pre-defined quality threshold to generate an indication signal, and
controlling (52) the measuring unit (11) so as to cause it to move away from the object (20) according to the indication signal.
13. The device as claimed in claim 11, further comprising the steps of:
detecting (51) whether the voltage of the object is not in a pre-defined voltage range or the quality of the initial image of the object (20) is lower than a pre-defined quality threshold, to generate an alert to a user,
controlling (52) the measuring unit (11) so as to cause it to move away from the object (20) according to an indication signal, wherein the indication signal is inputted by the user according to the alert.
14. The method as claimed in claim 11, further comprising a step of controlling (52) the measuring unit (11) so as to cause it to move away from the object (20) according to an indication signal, wherein the indication signal is inputted by the user according to the quality of the initial image of the object (20).
15. A computer program is used in the method of measuring the conductivity of an object
(20), the method comprising the steps of:
measuring (41) a first voltage when the object (20) is not placed in a measuring unit
(H),
measuring (42) the voltage of the object (20) when the object (20) is placed in the measuring unit (11) after measuring the first voltage,
measuring (43) a second voltage when the object (20) is moved away from the measuring unit (11) after measuring the voltage of the object (20),
calculating (44) the difference between the first voltage and the second voltage, and adjusting (45) the voltage of the object (20), based on said difference, to generate an adjusted voltage of the object (20).
4
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