WO2009138934A1 - Method and system for detecting a fluid distribution in an object of interest - Google Patents

Method and system for detecting a fluid distribution in an object of interest Download PDF

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Publication number
WO2009138934A1
WO2009138934A1 PCT/IB2009/051908 IB2009051908W WO2009138934A1 WO 2009138934 A1 WO2009138934 A1 WO 2009138934A1 IB 2009051908 W IB2009051908 W IB 2009051908W WO 2009138934 A1 WO2009138934 A1 WO 2009138934A1
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WIPO (PCT)
Prior art keywords
interest
parameters
contrast agent
tissue
measurement data
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Application number
PCT/IB2009/051908
Other languages
French (fr)
Inventor
Claudia Hannelore Igney
Gerd Lanfermann
Matthias Hamsch
Marko Johannes Vauhkonen
Original Assignee
Koninklijke Philips Electronics N.V.
Philips Intellectual Property & Standards Gmbh
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Application filed by Koninklijke Philips Electronics N.V., Philips Intellectual Property & Standards Gmbh filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2009138934A1 publication Critical patent/WO2009138934A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/10—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils
    • G01V3/104—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils using several coupled or uncoupled coils
    • 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 
    • 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
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/40—Detecting, measuring or recording for evaluating the nervous system
    • A61B5/4076—Diagnosing or monitoring particular conditions of the nervous system

Definitions

  • the invention relates to magnetic induction tomography, particularly to a method and system for detecting a fluid distribution in an object of interest by using a magnetic induction tomography scanner.
  • Magnetic induction tomography is a noninvasive imaging technique with applications in industry and medical imaging. In contrast to other electrical imaging techniques, MIT does not require direct contact of the sensors with the imaged object. MIT applies a magnetic field from one or more generator coils (also called excitation coils) to induce eddy currents in the material/object of interest to be studied. In other words, the scanning region of the object of interest is excited with a time-varying magnetic field. The presence of conductive and/or permeable material distorts the energizing field within. The perturbation of said primary magnetic field, i.e. the secondary magnetic field resulting from the eddy currents, is detected by a number of sensor coils (also called measurement coils, detection coils or receiving coils).
  • sensor coils also called measurement coils, detection coils or receiving coils.
  • MIT is sensitive to all three passive electromagnetic properties: electrical conductivity, permittivity and magnetic permeability. As a result, for example, the conductivity contribution in a target object can be reconstructed. In particular MIT is suitable for examination of biological tissue, because of the magnetic permeability value of such tissue ⁇ R «1.
  • Prior art patent application WO2007072343 discloses a magnetic induction tomography system for studying the electromagnetic properties of an object.
  • the system comprises one or more generator coils adapted for generating a primary magnetic field, said primary magnetic field inducing an eddy current in the object. It also comprises 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 studied, on the other hand.
  • An object of this invention is to provide a method that enables a fluid distribution in an object of interest to be detected with a higher resolution.
  • This invention achieves this object by providing a method of detecting a fluid distribution in an object of interest, the method comprising the steps of:
  • the method further comprises a step of repeating steps (c) and (d) to identify said set of parameters, said set of parameters representing a maximum concentration of the contrast agent infused in the fluid.
  • the method further comprises a step of reconstructing an image, based on the set of parameters, to visualize the change of the conductivity of the fluid distribution.
  • this method further improves the detection resolution by identifying the maximum change of conductivity of the fluid distribution reflected by the maximum concentration of the contrast agent infused in the fluid.
  • the method further comprises a step of identifying characteristics reflecting hemorrhagic tissue, ischemic tissue or healthy tissue in the object of interest, based on the set of parameters.
  • the identifying step can be also based on the reconstructed image.
  • this method can classify the type of stroke as hemorrhagic or ischemic and thus provide reliable support for effective and safe treatment.
  • Another object of this invention is to provide a system that enables a fluid distribution in an object of interest to be detected with a higher resolution than static image reconstruction.
  • This invention achieves this object by providing a system for detecting a fluid distribution in an object of interest by using a magnetic induction tomography scanner, the system comprising:
  • a measurement unit for measuring magnetic induction signals associated with the object of interest to obtain a first and second set of measurement data; - introducing means for introducing a conductive contrast agent into the object of interest; and
  • a processor for calculating a set of parameters based on the first and second sets of measurement data, the set of parameters reflecting a change of conductivity of the fluid distribution in the object of interest, wherein the second set of measurement data is obtained after introducing the contrast agent into the object of interest.
  • Fig.l depicts a flowchart of a method in accordance with the invention
  • Figs.2 (a), (b) and (c) depict schematic diagrams of the signal strength for different tissue classes with and without contrast agent
  • Figs.3 (a) and (b) depict reconstructed images for a hemorrhagic stroke without contrast agent and with contrast agent, respectively, and Fig.3 (c) depicts a reconstructed difference image for a hemorrhagic stroke;
  • Figs.4 (a) and (b) depict reconstructed images for an ischemic stroke without contrast agent and with contrast agent, respectively, and
  • Fig.4 (c) depicts a reconstructed difference image for an ischemic stroke;
  • Fig.5 depicts an exemplary embodiment of the system in accordance with the invention.
  • the same reference numerals are used to denote similar parts throughout the
  • Fig.l depicts a flowchart of a method in accordance with the invention.
  • the method comprises a step 102 of measuring magnetic induction signals associated with the object of interest to obtain a first set of measurement data.
  • the measuring step 102 comprises the sub-steps of: generating a primary magnetic field by providing an excitation signal, the primary magnetic field inducing an eddy current in the object of interest; and sensing a secondary magnetic field to generate the corresponding set of measurement data, the secondary magnetic field being generated as a result of the eddy current and represented by a set of measurement data, for example, a vector of measured voltages.
  • the method further comprises a step 104 of introducing a conductive contrast agent into the object of interest.
  • the contrast agent is MIT-active, e.g. conductive.
  • the contrast agent can be a saline solution in an appropriate concentration.
  • the step of introducing a contrast agent into the object of interest can be performed in many ways, depending on the nature of the object of interest. For example, for a patient, this can be performed by delivering a bolus of a contrast agent or by a shot of a solution infused with conductive contrast agent.
  • the method further comprises a step 106 of measuring magnetic induction signals associated with the object of interest to obtain a second set of measurement data.
  • the measuring step 106 is similar to the measuring step 102, and the main difference is that the step 106 is performed after the step 104 of introducing a conductive contrast agent.
  • the fluid in the object of interest may be perfused with contrast agent, which may lead to a change of the conductivity of the fluid.
  • the method further comprises a step 108 of calculating a set of parameters based on the first and second sets of measurement data, the set of parameters reflecting a change of the conductivity of the fluid distribution in the object of interest.
  • the calculation of the step 108 follows the image reconstruction theory, for example, the method of conductivity calculations and image reconstruction that are described in the prior art document "Image reconstruction approaches for Philips magnetic induction tomograph", M. Vauhkonen, M. Hamsch and CH. Igney, ICEBI 2007, IFMBE Proceedings 17, pp. 468-471, 2007.
  • the set of parameters can be calculated according to the following equation, e.g., equation (8) in the mentioned prior art:
  • ⁇ (J T W T WJ + all Ly 1 (J 7 W 7 W (V -V 0 ))
  • " is a weighting matrix
  • a is a regularization parameter and ⁇ is a regularization matrix
  • J is the imaginary part of the complex Jacobian matrix
  • ° and V respectively, are the first and second sets of measurement data that are obtained by measuring step 102 without contrast agent and measuring step 106 with contrast agent.
  • the calculation can be advantageously implemented by means of a computer program. Generally, for a given object of interest, there is no natural change of conductivity when a series of measurement data are taken.
  • the method can reconstruct difference images based on two sets of static measurement data with and without contrast agent. Since, by using differential imaging, most of the artifacts and modeling errors are cancelled, the resolution of detecting a fluid distribution in the object of interest and the corresponding imaging are thus improved remarkably.
  • the method further comprises a step 110 of repeating the step 106 of measuring and the step 108 of calculating to identify said set of parameters, said set of parameters representing a maximum concentration of the contrast agent infused in the fluid.
  • the repetition in step 110 can be performed at regular intervals. Through the multiple sets of parameters, the arrival time and the decay of the contrast agent can be observed and compared to reveal the change of conductivity of the fluid distribution.
  • the method further comprises a step 112 of reconstructing an image based on the set of parameters, that visualizes the change of the conductivity of the fluid distribution in the object of interest.
  • the reconstructed image depicts the spatial change of the conductivity of the fluid distribution in the object of interest.
  • the method of detecting a fluid in an object can be applied in different clinical applications, for example, for classifying strokes into hemorrhagic type and ischemic type, based on the nature of these two types of strokes.
  • Figs.2 (a), (b) and (c) depict schematic diagrams of the signal strength for different tissue classes with and without contrast agent.
  • the object of interest in this application is the brain of a human being.
  • the line (Ll) on the left indicates the sensed, e.g., measured, signal strength when a magnetic induction signal is induced by a primary magnetic field on healthy tissue without a contrast agent and Ac indicates an average value of the measured signal strength, for example, an induced voltage, for healthy tissue.
  • the average value of the measured signal strength reflects the conductivity of the healthy tissue.
  • the lines (L2, L3) on the right indicate the sensed, e.g., measured, signal strength with a change of AS when a magnetic induction signal is induced by a primary magnetic field on healthy tissue after a contrast agent has been introduced into the brain.
  • the measured signal strength change AS reflects the change of conductivity of the healthy tissue.
  • the line (L4) on the left indicates the sensed, e.g., measured, signal strength when a magnetic induction signal is induced by a primary magnetic field on hemorrhagic tissue without a contrast agent.
  • the lines on the right indicate the sensed, e.g., measured, signal strength when a magnetic induction signal is induced by a primary magnetic field on hemorrhagic tissue after a contrast agent has been introduced into the brain.
  • the measured signal strength change AS reflects the change of conductivity of the hemorrhagic tissue.
  • the line on the left (L7) indicates the sensed, e.g., measured, signal strength when a magnetic induction signal is induced by a primary magnetic field on ischemic tissue without a contrast agent.
  • the lines on the right indicate (L8, L9) the sensed, e.g., measured, signal strength when a magnetic induction signal is induced by a primary magnetic field on ischemic tissue after a contrast agent has been introduced into the brain.
  • the measured signal strength change AS reflects the change of conductivity of the ischemic tissue.
  • the method shown in Fig.l further comprises a step 116 of identifying characteristics reflecting hemorrhagic tissue, ischemic tissue or healthy tissue in the object of interest, based on the set of parameters.
  • the identifying classes of tissues can be also based on the image reconstructed from the set of parameters that visualizes the change of the conductivity of the fluid distributed in the object of interest.
  • the method further comprises a step 118 of localizing the hemorrhagic area when identifying a hemorrhagic tissue.
  • Figs.3 (a) and (b) depict reconstructed images for a hemorrhagic stroke without contrast agent and with contrast agent, respectively, and Fig.3 (c) depicts a reconstructed difference image for a hemorrhagic stroke.
  • Figs.4 (a) and (b) depict reconstructed images for an ischemic stroke without contrast agent and with contrast agent, respectively, and Fig.4 (c) depicts a reconstructed difference image for an ischemic stroke.
  • the object to be measured is the brain tissue 310 in a head 300 of a patient. Stroke tissue in the brain tissue 310 is indicated as 312 in Fig.3 and 412 in Fig.4.
  • the gray level in reconstructed images is indicative of the measured signal strengths, e.g., the degrees of conductivity of the measured tissues. From Figs. 3(a) and 3(b), it is observed that in the case of a hemorrhagic stroke, the measured signal strengths, for the hemorrhagic tissue 312 in the brain tissue and the normal brain tissue 310, increase when the contrast agent is infused in the brain tissue.
  • Figs. 3(a), 3(b), 4(a) and 4(b) are consistent with the observations from Figs.2 (a), (b) and (c).
  • the explanation lies in the fact that in the case of a hemorrhagic stroke, the blood distribution in the hemorrhagic tissue 312 increases because of a ruptured artery; in the case of an ischemic stroke, the blood distribution in the ischemic tissue 412 does not change or even decreases because of blocked vessels.
  • Fig.3(c) and Fig.4(c) show reconstructed difference images for a hemorrhagic stroke and an ischemic stroke, respectively. It is observed that the change of conductivity of the normal brain tissue 310 is the same for both, but the change of conductivity of hemorrhagic tissue
  • the observations are consistent with the observations from Fig.2 (a), (b) and (c).
  • the explanation lies in the fact that, in the case of a hemorrhagic stroke, the blood distribution in the hemorrhagic tissue increases because of a ruptured artery that leads to a big change of the conductivity of the hemorrhagic tissue when a contrast agent is infused in the tissue.
  • a hemorrhagic stroke based on the change of the conductivity, which is for example visualized by a difference in gray level in the reconstructed images, one can easily distinguish between a hemorrhagic stroke and an ischemic stroke, and further localize the hemorrhagic area when the stroke is identified as a hemorrhagic stroke with the steps described in Fig.l.
  • the above method as illustrated in Figs. 1 and 3 can be implemented with hardware, or a combination of hardware and software.
  • Fig.5 depicts an exemplary embodiment of the system in accordance with the invention.
  • the system 500 comprises a measurement unit 510 for measuring magnetic induction signals associated with an object of interest 501 intended to be placed in a measurement chamber of the system to obtain a first and second set of measurement data.
  • the first set of measurement data is obtained without a contrast agent and the second set of measurement data is obtained after the contrast agent has been infused into the object of interest.
  • the measurement unit 510 is intended to carry out the measuring steps 102 and 106.
  • the measurement unit 510 comprises one or more generator coils 502 arranged for generating a primary magnetic field by providing an excitation signal, the primary magnetic field inducing an eddy current in the object to be measured.
  • the generator coils 502 may be connected to a signal generator, which is not shown in Fig.6, for generating an alternative current signal for the generator coils.
  • the measurement unit 510 further comprises one or more sensor coils 504 placed in the field of the generator coils and arranged for sensing a secondary magnetic field to generate the corresponding set of measurement data, the secondary magnetic field being generated as a result of the eddy current and represented by a set of measurement data.
  • the sensor coils 504 may be connected to a pre-amplifier, which is not shown in Fig.5, for amplifying the measured signals.
  • the system 500 further comprises introducing means 520 for introducing a conductive contrast agent into the object of interest.
  • the contrast agent can be introduced by delivering a bolus to the patient to be measured or a shot so that the contrast agent will be infused in the brain tissue of the patient.
  • the contrast agent is conductive, for example, a conductive saline solution.
  • the introducing means is intended to carry out the introducing step 104.
  • the system 500 further comprises a processor 530 for calculating a set of parameters based on the first and second sets of measurement data, the set of parameters reflecting a change of the conductivity of the fluid distributed in the object of interest.
  • the processor 530 is intended to carry out the calculating step 108. It is advantageous that the measuring unit 510 and the processor 530 are arranged for repeatedly carrying out the step 106 of measuring and the step 108 of calculating to identify an optimal set of parameters that represents a maximum concentration of the contrast agent infused in the fluid between the arrival time and the decay of the contrast agent.
  • the processor 530 is further arranged to reconstruct an image, based on the set of parameters, that visualizes the change of the conductivity of the fluid distributed in the object of interest, e.g. carry out the reconstructing step 112 .
  • the processor 530 is further arranged to identify characteristics reflecting hemorrhagic tissue, ischemic tissue or healthy tissue in the object of interest, based on the set of parameters, e.g. carry out the identifying step 116 .
  • the processor 530 is further arranged to localize the hemorrhagic area when identifying hemorrhagic tissue, e.g. carry out the localizing step 118.
  • the method and the system provided by the invention can be further used in other clinical applications, such as identifying a lesion in normal tissue, breast cancer or a lung node, based on reconstructing a difference image without and with a conductive contrast agent, by using a MIT scanner.

Abstract

This invention relates to a method and device for detecting a fluid distribution in an object of interest. The method comprises the steps of: (a) measuring (102) magnetic induction signals associated with the object of interest to obtain a first set of measurement data; (b) introducing (104) a conductive contrast agent into the object of interest; (c) measuring (106) magnetic induction signals associated with the object of interest to obtain a second set of measurement data; and (d) calculating (108) a set of parameters based on the first and second sets of measurement data, the set of parameters reflecting a change of conductivity of the fluid distribution in the object of interest. In an embodiment, the method further comprises a step of identifying characteristics reflecting hemorrhagic tissue, ischemic tissue or healthy tissue in the object of interest, based on the set of parameters. (Fig.l)

Description

METHOD AND SYSTEM FOR DETECTING A FLUID DISTRIBUTION IN AN
OBJECT OF INTEREST
FIELD OF THE INVENTION
The invention relates to magnetic induction tomography, particularly to a method and system for detecting a fluid distribution in an object of interest by using a magnetic induction tomography scanner.
BACKGROUND OF THE INVENTION
Magnetic induction tomography (MIT) is a noninvasive imaging technique with applications in industry and medical imaging. In contrast to other electrical imaging techniques, MIT does not require direct contact of the sensors with the imaged object. MIT applies a magnetic field from one or more generator coils (also called excitation coils) to induce eddy currents in the material/object of interest to be studied. In other words, the scanning region of the object of interest is excited with a time-varying magnetic field. The presence of conductive and/or permeable material distorts the energizing field within. The perturbation of said primary magnetic field, i.e. the secondary magnetic field resulting from the eddy currents, is detected by a number of sensor coils (also called measurement coils, detection coils or receiving coils). Sets of measurements are taken and used to visualize changes over time of the electromagnetic properties of the object. MIT is sensitive to all three passive electromagnetic properties: electrical conductivity, permittivity and magnetic permeability. As a result, for example, the conductivity contribution in a target object can be reconstructed. In particular MIT is suitable for examination of biological tissue, because of the magnetic permeability value of such tissue μR «1.
Prior art patent application WO2007072343 discloses a magnetic induction tomography system for studying the electromagnetic properties of an object. The system comprises one or more generator coils adapted for generating a primary magnetic field, said primary magnetic field inducing an eddy current in the object. It also comprises 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 studied, on the other hand.
SUMMARY OF THE INVENTION
An object of this invention is to provide a method that enables a fluid distribution in an object of interest to be detected with a higher resolution.
This invention achieves this object by providing a method of detecting a fluid distribution in an object of interest, the method comprising the steps of:
(a) measuring magnetic induction signals associated with the object of interest to obtain a first set of measurement data;
(b) introducing a conductive contrast agent into the object of interest;
(c) measuring magnetic induction signals associated with the object of interest to obtain a second set of measurement data; and
(d) calculating a set of parameters based on the first and second sets of measurement data, the set of parameters reflecting a change of conductivity of the fluid distribution in the object of interest.
By calculating the change of the conductivity of the fluid distribution in the object of interest before and after introducing a conductive contrast agent, a difference image instead of a static image can be reconstructed, and thus the detection resolution of the fluid distribution can be improved remarkably.
In an embodiment, the method further comprises a step of repeating steps (c) and (d) to identify said set of parameters, said set of parameters representing a maximum concentration of the contrast agent infused in the fluid.
It is advantageous that the method further comprises a step of reconstructing an image, based on the set of parameters, to visualize the change of the conductivity of the fluid distribution. As the concentration of the contrast agent infused in the object of interest indicates the amount of the change of conductivity of the fluid distribution, this method further improves the detection resolution by identifying the maximum change of conductivity of the fluid distribution reflected by the maximum concentration of the contrast agent infused in the fluid.
In an embodiment, the method further comprises a step of identifying characteristics reflecting hemorrhagic tissue, ischemic tissue or healthy tissue in the object of interest, based on the set of parameters. Alternatively, the identifying step can be also based on the reconstructed image.
As the change of the conductivity of hemorrhagic tissue and ischemic tissue with and without agent is different, this method can classify the type of stroke as hemorrhagic or ischemic and thus provide reliable support for effective and safe treatment.
Another object of this invention is to provide a system that enables a fluid distribution in an object of interest to be detected with a higher resolution than static image reconstruction. This invention achieves this object by providing a system for detecting a fluid distribution in an object of interest by using a magnetic induction tomography scanner, the system comprising:
- a measurement unit for measuring magnetic induction signals associated with the object of interest to obtain a first and second set of measurement data; - introducing means for introducing a conductive contrast agent into the object of interest; and
- a processor for calculating a set of parameters based on the first and second sets of measurement data, the set of parameters reflecting a change of conductivity of the fluid distribution in the object of interest, wherein the second set of measurement data is obtained after introducing the contrast agent into the object of interest.
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 depicts a flowchart of a method in accordance with the invention; Figs.2 (a), (b) and (c) depict schematic diagrams of the signal strength for different tissue classes with and without contrast agent;
Figs.3 (a) and (b) depict reconstructed images for a hemorrhagic stroke without contrast agent and with contrast agent, respectively, and Fig.3 (c) depicts a reconstructed difference image for a hemorrhagic stroke; Figs.4 (a) and (b) depict reconstructed images for an ischemic stroke without contrast agent and with contrast agent, respectively, and Fig.4 (c) depicts a reconstructed difference image for an ischemic stroke; and
Fig.5 depicts an exemplary embodiment of the system in accordance with the invention. The same reference numerals are used to denote similar parts throughout the
Figures.
DETAILED DESCRIPTION
Fig.l depicts a flowchart of a method in accordance with the invention. According to the invention, the method comprises a step 102 of measuring magnetic induction signals associated with the object of interest to obtain a first set of measurement data.
In an application of using a magnetic induction tomography system for detecting a fluid distribution in an object of interest (e.g. a patient), the measuring step 102 comprises the sub-steps of: generating a primary magnetic field by providing an excitation signal, the primary magnetic field inducing an eddy current in the object of interest; and sensing a secondary magnetic field to generate the corresponding set of measurement data, the secondary magnetic field being generated as a result of the eddy current and represented by a set of measurement data, for example, a vector of measured voltages. The method further comprises a step 104 of introducing a conductive contrast agent into the object of interest. The contrast agent is MIT-active, e.g. conductive. For example, the contrast agent can be a saline solution in an appropriate concentration.
The step of introducing a contrast agent into the object of interest can be performed in many ways, depending on the nature of the object of interest. For example, for a patient, this can be performed by delivering a bolus of a contrast agent or by a shot of a solution infused with conductive contrast agent.
The method further comprises a step 106 of measuring magnetic induction signals associated with the object of interest to obtain a second set of measurement data. The measuring step 106 is similar to the measuring step 102, and the main difference is that the step 106 is performed after the step 104 of introducing a conductive contrast agent. When the measuring step 106 is performed, the fluid in the object of interest may be perfused with contrast agent, which may lead to a change of the conductivity of the fluid.
The method further comprises a step 108 of calculating a set of parameters based on the first and second sets of measurement data, the set of parameters reflecting a change of the conductivity of the fluid distribution in the object of interest.
The calculation of the step 108 follows the image reconstruction theory, for example, the method of conductivity calculations and image reconstruction that are described in the prior art document "Image reconstruction approaches for Philips magnetic induction tomograph", M. Vauhkonen, M. Hamsch and CH. Igney, ICEBI 2007, IFMBE Proceedings 17, pp. 468-471, 2007. The set of parameters can be calculated according to the following equation, e.g., equation (8) in the mentioned prior art:
Δσ = (JTWTWJ + all Ly1 (J7W7W (V -V0)) where " is a weighting matrix, a is a regularization parameter and ^ is a regularization matrix, J is the imaginary part of the complex Jacobian matrix and ° and V , respectively, are the first and second sets of measurement data that are obtained by measuring step 102 without contrast agent and measuring step 106 with contrast agent. The calculation can be advantageously implemented by means of a computer program. Generally, for a given object of interest, there is no natural change of conductivity when a series of measurement data are taken. By using a contrast agent to artificially create a change of fluid conductivity in the object of interest, the method can reconstruct difference images based on two sets of static measurement data with and without contrast agent. Since, by using differential imaging, most of the artifacts and modeling errors are cancelled, the resolution of detecting a fluid distribution in the object of interest and the corresponding imaging are thus improved remarkably.
Advantageously, the method further comprises a step 110 of repeating the step 106 of measuring and the step 108 of calculating to identify said set of parameters, said set of parameters representing a maximum concentration of the contrast agent infused in the fluid.
The repetition in step 110 can be performed at regular intervals. Through the multiple sets of parameters, the arrival time and the decay of the contrast agent can be observed and compared to reveal the change of conductivity of the fluid distribution.
In an embodiment, the method further comprises a step 112 of reconstructing an image based on the set of parameters, that visualizes the change of the conductivity of the fluid distribution in the object of interest. The reconstructed image depicts the spatial change of the conductivity of the fluid distribution in the object of interest.
The method of detecting a fluid in an object can be applied in different clinical applications, for example, for classifying strokes into hemorrhagic type and ischemic type, based on the nature of these two types of strokes.
Figs.2 (a), (b) and (c) depict schematic diagrams of the signal strength for different tissue classes with and without contrast agent.
It is assumed that the object of interest in this application is the brain of a human being. In Fig.2 (a), the line (Ll) on the left indicates the sensed, e.g., measured, signal strength when a magnetic induction signal is induced by a primary magnetic field on healthy tissue without a contrast agent and Ac indicates an average value of the measured signal strength, for example, an induced voltage, for healthy tissue. The average value of the measured signal strength reflects the conductivity of the healthy tissue.
The lines (L2, L3) on the right indicate the sensed, e.g., measured, signal strength with a change of AS when a magnetic induction signal is induced by a primary magnetic field on healthy tissue after a contrast agent has been introduced into the brain. For example, L2 is the measured signal strength change (AS =I) after the first bolus of contrast agent, while L3 is the measured signal strength change ( AS =2) after the second bolus of contrast agent. The measured signal strength change AS reflects the change of conductivity of the healthy tissue. In Fig.2 (b), the line (L4) on the left indicates the sensed, e.g., measured, signal strength when a magnetic induction signal is induced by a primary magnetic field on hemorrhagic tissue without a contrast agent.
The lines on the right (L5, L6) indicate the sensed, e.g., measured, signal strength when a magnetic induction signal is induced by a primary magnetic field on hemorrhagic tissue after a contrast agent has been introduced into the brain. For example, L5 is the measured signal strength change (AS =1.5) after the first bolus of contrast agent, while L6 is the measured signal strength change (Δ5 =2.5) after the second bolus of contrast agent. The measured signal strength change AS reflects the change of conductivity of the hemorrhagic tissue.
In Fig.2 (c), the line on the left (L7) indicates the sensed, e.g., measured, signal strength when a magnetic induction signal is induced by a primary magnetic field on ischemic tissue without a contrast agent.
The lines on the right indicate (L8, L9) the sensed, e.g., measured, signal strength when a magnetic induction signal is induced by a primary magnetic field on ischemic tissue after a contrast agent has been introduced into the brain. For example, L8 is the measured signal strength change ( AS =0) after the first bolus of contrast agent, while L9 is the measured signal strength change (Δ5 =0.5) after the second bolus of contrast agent. The measured signal strength change AS reflects the change of conductivity of the ischemic tissue.
From the lines (Ll, L4, L7) on the left of Figs.2 (a), (b) and (c), respectively, it is observed that the signal strength of healthy tissue is higher than that of ischemic tissue, but smaller than that of hemorrhagic tissue when no contrast agent is applied to the tissues. This is because more fluid, e.g. blood, is distributed in hemorrhagic tissue, e.g. a bleeding tissue, than in healthy tissue. The characteristics of tissue classes make it possible to distinguish a stroked tissue from a healthy tissue and to identify a stroke type as either hemorrhagic or ischemic, based on the measured signal strength in association with the conductivity of the blood distribution in the tissue. It is advantageous that the method shown in Fig.l further comprises a step 116 of identifying characteristics reflecting hemorrhagic tissue, ischemic tissue or healthy tissue in the object of interest, based on the set of parameters. Alternatively, the identifying classes of tissues can be also based on the image reconstructed from the set of parameters that visualizes the change of the conductivity of the fluid distributed in the object of interest.
The method further comprises a step 118 of localizing the hemorrhagic area when identifying a hemorrhagic tissue. The steps will be explained and become more apparent with reference to Fig.3 and Fig.4.
Figs.3 (a) and (b) depict reconstructed images for a hemorrhagic stroke without contrast agent and with contrast agent, respectively, and Fig.3 (c) depicts a reconstructed difference image for a hemorrhagic stroke.
Figs.4 (a) and (b) depict reconstructed images for an ischemic stroke without contrast agent and with contrast agent, respectively, and Fig.4 (c) depicts a reconstructed difference image for an ischemic stroke.
The object to be measured is the brain tissue 310 in a head 300 of a patient. Stroke tissue in the brain tissue 310 is indicated as 312 in Fig.3 and 412 in Fig.4. The gray level in reconstructed images is indicative of the measured signal strengths, e.g., the degrees of conductivity of the measured tissues. From Figs. 3(a) and 3(b), it is observed that in the case of a hemorrhagic stroke, the measured signal strengths, for the hemorrhagic tissue 312 in the brain tissue and the normal brain tissue 310, increase when the contrast agent is infused in the brain tissue.
From Figs.4 (a) and 4(b), it is observed that in the case of an ischemic stroke, the measured signal strengths for normal brain tissue 310 increase when the contrast agent is infused in the brain tissue, while the measured signal strength for the ischemic tissue 412 in the brain tissue does not show a clear increase with the contrast agent.
The observations from Figs. 3(a), 3(b), 4(a) and 4(b) are consistent with the observations from Figs.2 (a), (b) and (c). The explanation lies in the fact that in the case of a hemorrhagic stroke, the blood distribution in the hemorrhagic tissue 312 increases because of a ruptured artery; in the case of an ischemic stroke, the blood distribution in the ischemic tissue 412 does not change or even decreases because of blocked vessels.
Fig.3(c) and Fig.4(c) show reconstructed difference images for a hemorrhagic stroke and an ischemic stroke, respectively. It is observed that the change of conductivity of the normal brain tissue 310 is the same for both, but the change of conductivity of hemorrhagic tissue
312 is bigger than that of ischemic tissue 412.
The observations are consistent with the observations from Fig.2 (a), (b) and (c). The explanation lies in the fact that, in the case of a hemorrhagic stroke, the blood distribution in the hemorrhagic tissue increases because of a ruptured artery that leads to a big change of the conductivity of the hemorrhagic tissue when a contrast agent is infused in the tissue.
Therefore, based on the change of the conductivity, which is for example visualized by a difference in gray level in the reconstructed images, one can easily distinguish between a hemorrhagic stroke and an ischemic stroke, and further localize the hemorrhagic area when the stroke is identified as a hemorrhagic stroke with the steps described in Fig.l. The above method as illustrated in Figs. 1 and 3 can be implemented with hardware, or a combination of hardware and software.
Fig.5 depicts an exemplary embodiment of the system in accordance with the invention. The system 500 comprises a measurement unit 510 for measuring magnetic induction signals associated with an object of interest 501 intended to be placed in a measurement chamber of the system to obtain a first and second set of measurement data. The first set of measurement data is obtained without a contrast agent and the second set of measurement data is obtained after the contrast agent has been infused into the object of interest. The measurement unit 510 is intended to carry out the measuring steps 102 and 106.
In an embodiment, the measurement unit 510 comprises one or more generator coils 502 arranged for generating a primary magnetic field by providing an excitation signal, the primary magnetic field inducing an eddy current in the object to be measured. The generator coils 502 may be connected to a signal generator, which is not shown in Fig.6, for generating an alternative current signal for the generator coils.
The measurement unit 510 further comprises one or more sensor coils 504 placed in the field of the generator coils and arranged for sensing a secondary magnetic field to generate the corresponding set of measurement data, the secondary magnetic field being generated as a result of the eddy current and represented by a set of measurement data. The sensor coils 504 may be connected to a pre-amplifier, which is not shown in Fig.5, for amplifying the measured signals. The system 500 further comprises introducing means 520 for introducing a conductive contrast agent into the object of interest. The contrast agent can be introduced by delivering a bolus to the patient to be measured or a shot so that the contrast agent will be infused in the brain tissue of the patient. As explained before, the contrast agent is conductive, for example, a conductive saline solution. The introducing means is intended to carry out the introducing step 104.
The system 500 further comprises a processor 530 for calculating a set of parameters based on the first and second sets of measurement data, the set of parameters reflecting a change of the conductivity of the fluid distributed in the object of interest. The processor 530 is intended to carry out the calculating step 108. It is advantageous that the measuring unit 510 and the processor 530 are arranged for repeatedly carrying out the step 106 of measuring and the step 108 of calculating to identify an optimal set of parameters that represents a maximum concentration of the contrast agent infused in the fluid between the arrival time and the decay of the contrast agent.
In an embodiment, the processor 530 is further arranged to reconstruct an image, based on the set of parameters, that visualizes the change of the conductivity of the fluid distributed in the object of interest, e.g. carry out the reconstructing step 112 .
It is advantageous that when the object of interest is a brain of a living human being, the processor 530 is further arranged to identify characteristics reflecting hemorrhagic tissue, ischemic tissue or healthy tissue in the object of interest, based on the set of parameters, e.g. carry out the identifying step 116 .
In an embodiment, the processor 530 is further arranged to localize the hemorrhagic area when identifying hemorrhagic tissue, e.g. carry out the localizing step 118.
It should be noted that the method and the system provided by the invention can be further used in other clinical applications, such as identifying a lesion in normal tissue, breast cancer or a lung node, based on reconstructing a difference image without and with a conductive contrast agent, by using a MIT scanner.
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 usage 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 method of detecting a fluid distribution in an object of interest, the method comprising the steps of: (a) measuring (102) magnetic induction signals associated with the object of interest to obtain a first set of measurement data;
(b) introducing (104) a conductive contrast agent into the object of interest;
(c) measuring (106) magnetic induction signals associated with the object of interest to obtain a second set of measurement data; and (d) calculating (108) a set of parameters based on the first and second sets of measurement data, the set of parameters reflecting a change of conductivity of the fluid distribution in the object of interest.
2. A method as claimed in claim 1, further comprising a step (110) of repeating steps (c) and (d) to identify said set of parameters, said set of parameters representing a maximum concentration of the contrast agent infused in the fluid.
3. A method as claimed in claim 1 or 2, further comprising a step (112) of reconstructing an image, based on the set of parameters, to visualize the change of conductivity of the fluid distribution in the object of interest.
4. A method as claimed in any one of the preceding claims 1 to 3, further comprising a step (116) of identifying characteristics reflecting hemorrhagic tissue, ischemic tissue or healthy tissue in the object of interest, based on the set of parameters.
5. A method as claimed in claim 4, further comprising a step (118) of localizing the hemorrhagic area in the object of interest when identifying hemorrhagic tissue.
6. A method as claimed in claim 1, wherein the step of introducing (104) a conductive contrast agent comprises introducing a conductive saline solution.
7. A system for detecting a fluid distribution in an object of interest, the system comprising:
- a measurement unit (510) for measuring magnetic induction signals associated with the object of interest to obtain a first and second set of measurement data;
- introducing means (520) for introducing a conductive contrast agent into the object of interest; and
- a processor (530) for calculating a set of parameters based on the first and second sets of measurement data, the set of parameters reflecting a change of conductivity of the fluid distribution in the object of interest, wherein the second set of measurement data is obtained after the contrast agent has been introduced into the object of interest.
8. A system as claimed in claim 7, wherein the measurement unit (510) is further arranged for repeatedly measuring magnetic induction signals associated with the object of interest after the contrast agent has been introduced into the object of interest to obtain said second set of measurement data, and the processor (530) is further arranged for repeatedly calculating a set of parameters based on the first and said second set of measurement data to identify said set of parameters, said set of parameters representing a maximum concentration of the contrast agent infused in the fluid.
9. A system as claimed in claim 8, wherein the processor (530) is further arranged for reconstructing an image, based on the set of parameters, to visualize the change of the conductivity of the fluid distribution in the object of interest.
10. A system as claimed in any one of the preceding claims 7 to 9, wherein the processor (530) is further arranged for identifying characteristics reflecting hemorrhagic tissue, ischemic tissue or healthy tissue in the object of interest, based on the set of parameters.
1. A system as claimed in claim 10, wherein the processor (530) is further arrangedr localizing the hemorrhagic area in the object of interest when identifying hemorrhagic tissue.
PCT/IB2009/051908 2008-05-15 2009-05-08 Method and system for detecting a fluid distribution in an object of interest WO2009138934A1 (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012071103A1 (en) * 2010-11-24 2012-05-31 Chevron U.S.A. Inc. System and method for estimating fluid distribution in a subterranean reservoir
US9207197B2 (en) 2014-02-27 2015-12-08 Kimberly-Clark Worldwide, Inc. Coil for magnetic induction to tomography imaging
US9320451B2 (en) 2014-02-27 2016-04-26 Kimberly-Clark Worldwide, Inc. Methods for assessing health conditions using single coil magnetic induction tomography imaging
US9442088B2 (en) 2014-02-27 2016-09-13 Kimberly-Clark Worldwide, Inc. Single coil magnetic induction tomographic imaging

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5352979A (en) * 1992-08-07 1994-10-04 Conturo Thomas E Magnetic resonance imaging with contrast enhanced phase angle reconstruction
US20030055358A1 (en) * 2000-04-07 2003-03-20 Ko Harvey W. Apparatus for sensing human prostate tumor
WO2003051197A1 (en) * 2001-12-18 2003-06-26 Mri Devices Corporation Method and apparatus for noise tomography
US20050021019A1 (en) * 2003-07-24 2005-01-27 Dune Medical Devices Ltd. Method and apparatus for examining a substance, particularly tissue, to characterize its type
US20050177042A1 (en) * 2002-06-07 2005-08-11 Takayuki Abe Magnetic resonance imaging device
WO2008011649A1 (en) * 2006-07-24 2008-01-31 Technische Universität Graz Device and method for magnetic induction tomography

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5352979A (en) * 1992-08-07 1994-10-04 Conturo Thomas E Magnetic resonance imaging with contrast enhanced phase angle reconstruction
US20030055358A1 (en) * 2000-04-07 2003-03-20 Ko Harvey W. Apparatus for sensing human prostate tumor
WO2003051197A1 (en) * 2001-12-18 2003-06-26 Mri Devices Corporation Method and apparatus for noise tomography
US20050177042A1 (en) * 2002-06-07 2005-08-11 Takayuki Abe Magnetic resonance imaging device
US20050021019A1 (en) * 2003-07-24 2005-01-27 Dune Medical Devices Ltd. Method and apparatus for examining a substance, particularly tissue, to characterize its type
WO2008011649A1 (en) * 2006-07-24 2008-01-31 Technische Universität Graz Device and method for magnetic induction tomography

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CSAR A GONZALEZ ET AL: "In Vivo Inductive Phase Shift Measurements to Detect Intraperitoneal Fluid", IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, IEEE SERVICE CENTER, PISCATAWAY, NJ, US, vol. 54, no. 5, 1 May 2007 (2007-05-01), pages 953 - 956, XP011176943, ISSN: 0018-9294 *

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012071103A1 (en) * 2010-11-24 2012-05-31 Chevron U.S.A. Inc. System and method for estimating fluid distribution in a subterranean reservoir
AU2011332287B2 (en) * 2010-11-24 2013-10-17 Chevron U.S.A. Inc. System and method for estimating fluid distribution in a subterranean reservoir
US8645070B2 (en) 2010-11-24 2014-02-04 Chevron U.S.A. Inc. System and method for estimating fluid distribution in a subterranean reservoir
US9207197B2 (en) 2014-02-27 2015-12-08 Kimberly-Clark Worldwide, Inc. Coil for magnetic induction to tomography imaging
US9320451B2 (en) 2014-02-27 2016-04-26 Kimberly-Clark Worldwide, Inc. Methods for assessing health conditions using single coil magnetic induction tomography imaging
US9442088B2 (en) 2014-02-27 2016-09-13 Kimberly-Clark Worldwide, Inc. Single coil magnetic induction tomographic imaging
US10278609B2 (en) 2014-02-27 2019-05-07 Kimberly-Clark Worldwide, Inc. Methods for assessing health conditions using single coil magnetic induction tomography imaging

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