Patent Application
20160184027
The invention relates to a magnetic excitation system and a method for operating the magnetic excitation system.
Currently, magnetic thermal ablation has been widely utilized for treating tumor. Specifically, an alternating magnetic field is generated to pass through a target (e.g., parts of a human body that contain tumor tissues), while a magnetic induction needle is punctured into the target. The magnetic induction needle is affected by the alternating magnetic field and produces a resulting eddy current. In turn, the magnetic induction needle is heated by thermal energy produced by the eddy current, and is able to provide the heat necessary for thermal ablation or other operations such as cauterization.
However, during the process of thermal ablation, it is critical, yet difficult, to determine a temperature and an effective ablating range after the magnetic induction needle has been punctured into the target, especially when thermal ablation needs to be operated strictly within a certain range (e.g., the tumor tissue has a small size and is surrounded by normal tissues). At present, an operator has to determine when to stop the operation based on no more than his/her past experience.
Therefore, the object of this invention is to provide a magnetic excitation system that is able to address the aforementioned drawbacks of the prior art.
Accordingly, a magnetic excitation system of this invention may include a magnetic excitation apparatus and an analyzing device.
The magnetic excitation apparatus is capable of generating a magnetic field.
The analyzing device includes at least one detecting unit configured to detect magnetic flux of the magnetic field passing therethrough, and a processing unit coupled communicatively to the at least one detecting unit.
The processing unit is configured to perform a simulation process for determining a magnetic flux distribution associated with a target, which is located within the magnetic field at a position corresponding to the at least one detecting unit, according to the magnetic flux detected by the at least one detecting unit before a magnetic induction needle is punctured into the target. The processing unit is configured to perform the simulation process further for generating, according to the magnetic flux distribution, a simulated magnetic field distribution associated with the target that would result from the magnetic induction needle being punctured into the target.
The processing unit is further configured to perform a real-time analysis process for calculating, in real time, a real-time magnetic field distribution associated with the target, and temperature and ablating range associated with the target based on the magnetic flux detected by the at least one detecting unit when the magnetic induction needle is punctured into the target.
Another object of this invention is to provide a method for operating the aforementioned magnetic excitation system.
Accordingly, a method of this invention may include the steps of:
positioning the detecting unit beside a target;
placing the electromagnetic excitation apparatus at a position corresponding to the target;
generating, by the electromagnetic excitation apparatus, a magnetic field that passes through the target and the detecting unit;
detecting, by the detecting unit, magnetic flux of the magnetic field passing therethrough; and
performing, by the processing unit, a simulation process for determining a magnetic flux distribution associated with the target according to the magnetic flux detected by the at least one detecting unit before a magnetic induct ion needle is punctured into the target, and for generating, according to the magnetic flux distribution, a simulated magnetic field distribution associated with the target that would result from the magnetic induction needle being punctured into the target.
Other features and advantages of the present invention will become apparent in the following detailed description of the embodiment with reference to the accompanying drawings, of which:
The magnetic excitation apparatus 1 includes a power supply 11, and a pair of induction coils 12 coupled to the power supply 11 for generating a magnetic field.
The analyzing device 2 includes at least one detecting unit 21, a processing unit 22 that is coupled communicatively to the detecting unit 21, and a marking device 23. The processing unit 22 is embodied as a computer in this embodiment for illustrative purposes, but should not be limited thereto in other embodiments of this invention.
Further referring to
Each of the fluxmeters 212 may be embodied using a magnetometer, an antenna or the like. The fluxmeters 212 are configured to detect magnetic flux of the magnetic field passing therethrough. The marking device 23 is coupled to and controlled by the processing unit 22, and includes alight source capable of illuminating a point.
In a preparation process 31, the two induction coils 12 are placed coaxially on vertically opposite sides of the bed (A) at respective positions corresponding to a target (C) of the patient (B), such that the two induction coils 12 are also placed on vertically opposite sides of the lying patient (B) (i.e., the front and back sides). Specifically, the induction coils 12 are aligned with the target (C). The detecting unit 21 is mounted horizontally to the bed (A) and is positioned between the two induction coils 12, such that the frame 211 of the detecting unit 21 is beside the target (C). It is noted that, in other embodiments, the detecting unit 21 may be attached directly to the patient (B).
In a magnetic field generating process 32, the power supply 11 is turned on, enabling the two induction coils 12 to generate a magnetic field therebetween (i.e., passing through the detecting unit 21 and the target (C)). The fluxmeters 212 of the detecting unit 21 continuously detect the magnetic flux of the magnetic field passing through the detecting unit 21, and data regarding the magnetic flux is then transmitted to the processing unit 22.
In a simulation process 33 (i.e., before a magnetic induction needle (not shown) is actually punctured into the target (C)), the processing unit 22 determines a magnetic flux distribution associated with the target (C) according to the magnetic flux detected by the detecting unit 21 before the magnetic induction needle is punctured into the target (C). The operator is then allowed to select a location into which the magnetic induction needle is to be simulatively punctured.
In response to the selection of the location, the processing unit 22 generates a simulated magnetic field distribution associated with the target (C) that would result from a magnetic induction needle being punctured into the selected location of the target (C).
The operator may also input into the processing unit 22 other supportive data such as material of the magnetic induction needle, an intended depth to which the magnetic induction needle is to be punctured, information regarding the target (C), or a combination thereof, in order to assist the processing unit 22 to obtain better simulation results.
With the simulated magnetic field distribution available, the operator and/or the processing unit 22 may determine an optimal puncturing location that yields a desired result. After the optimal puncturing location is determined, the processing unit 22 is configured to control the marking unit 23 to mark the optimal puncturing location into which the magnetic induction needle should be punctured to reach the target (C) so as to assist the operator in accurately puncturing the magnetic induction needle.
In a real-time analysis process 34 (i.e., after the magnetic induction needle is actually punctured into the optimal puncturing location as marked by the marking unit 23), the detecting unit 21 continuously detects the magnetic flux and transmits the detected data to the processing unit 22. In the real-time analysis process 34, the processing unit 22 calculates, in real time, temperature and ablating range associated with the target (C) based on the magnetic flux detected by the detecting unit 21.
In particular, the calculation of the temperature associated with the target (C) as attributed to the magnetic field is described in the following.
By Faraday's law of induction, an electromotive force (EMF) attributed to change of the magnetic field can be calculated using
where E represents the EMF, N represents the turns of the induction coils 12, Φ represents the magnetic flux, and t represents time.
The magnetic flux Φ can be calculated using
Φ=∫Bds,
where B represents magnitude of the magnetic field (which can be detected by the detecting unit 21), and S represents an area of the surface on which the magnetic field passes.
In cases where the magnetic field cannot be directly detected (e.g., one that passes through the body of the patient (B)), with the current (I) available, the Biot-Savart Law can be used to approximate the magnetic field B(r):
where μ0 represents the magnetic constant, and (r-r′) represents the point where the magnetic field is computed.
Using the above data regarding the magnetic field, an approximated magnetic field on a particular height B(z) can be calculated using:
With the magnetic field data now available, an eddy current (I) flowing through the magnetic induction needle can be calculated using Ampere's Law:
where H represents the magnetic field measured in units of amperes per meter (A/m), and dl represents an infinitesimal element.
Due to the skin effect, when current flows through the magnetic induction needle, a current density is largest near a surface and decreases within the magnetic induction needle. This in turn effectively increases an equivalent resistance of the magnetic induction needle and power dissipation (in the form of heat). As a result, the heat (Q) thus generated can be calculated using
Q=0.24I2Rt,
where I represents an equivalent current flowing through the magnetic induction needle, R represents an equivalent resistance of the magnetic induct ion needle, and t represents time.
In this embodiment, the heat dissipated due to heat transfer (thermal conduction, thermal radiation and convection) will be taken into consideration.
Using the Fourier's law, an outflow of heat from thermal conduction (Qcond) can be calculated using:
where k represents thermal conductivity, A represents the heat transfer surface area, and dT/dX represents a temperature gradient.
Using the Newton's law of cooling, an outflow of heat from convection (Qconv) can be calculated using:
Q
conv.
=−hA(Ts−T∞),
where h represents the heat transfer coefficient, A represents the heat transfer surface area, Ts represents the temperature on the surface of the magnetic induction needle, and T∞ represents the temperature of the environment (i.e., a place that is far away from the magnetic induction needle).
Using the Stefen-Bolzmann law, an outflow of heat from thermal radiation (Qrad.) can be calculated using:
Q
rad.
=−εσA(TS4−T∞4),
where ε represents the emissivity of the surface of the magnetic induction needle, and σ represents the Stefen-Bolzmann constant.
Moreover, internal heat (Qbio) (i.e., heat generated from the biological activities within human body) may be calculated using:
Q
bio=ρbCbωb(Tb−T)+Qmet,
Where ρb represents the density of blood, Cb and ωb are parameters regarding bloodflow, Tb represents a temperature on the target, and Qmet represents heat generated through metabolism. The above parameters regarding the human body may be obtained from prior experimental results and/or from performing an (MRI) procedure on the human body.
Afterward, the heat equation can be used to calculate the heat distribution
where ρ represents mass density, Cp represents heat capacity, k represents heat conductivity, ∇T represents the temperature gradient, Tu represents a heat transfer rate from convection.
On the other hand, the ablating range associated with the target (C) can be calculated using the following process.
In this embodiment, the target (C) is considered a concentric sphere with a body of normal tissues surrounding and enclosing the target (C) (i.e., the target (C) being a sphere with a radius R, the body being a sphere with an infinite radius, and tissues within the range of r where R≦r≦∞ are considered normal tissues).
It is assumed that a heat transfer equation regarding the body can be expressed as:
where i=1 represents tissues of the target (C), i=2 represents normal tissues, ρi represents a density of the tissues of type i, ci represents a heat capacity of the tissues of type i, ki represents a thermal conductivity of the tissues of type i, τq represents a relaxation time of thermal flux, and τT represents a relaxation time of temperature.
It is further assumed that at r=0, the temperature is a constant (dT1/dr=0), at r=R, the temperature and a thermal flux of the normal tissues and the tissues of the target (C) are identical (i.e., T1=T2, q1=q2), and the temperature in the normal tissues (T2, r=∞) is constant at 37° C. Using these assumptions as boundary conditions, the ablating range can be calculated.
One advantage of the real-time analysis process 34 is that since the temperature can be calculated, there is no need to attach an additional temperature sensor for measuring the temperature associated with the target (C) in real time.
In an alternative implementation (see
In this implementation, the magnetic flux can be detected from two different heights. Therefore, in the simulation process 33, the processing unit 22 may determine a three-dimensional magnetic flux distribution associated with the target (C) according to the magnetic flux detected by the two detecting units 21, and may generate a three-dimensional simulated magnetic field distribution associated with the target (C) that would result from the magnetic induction needle being punctured into the target (C).
It is noted that for achieving a more accurate simulation, additional detecting units 21 may be placed between the induction coils 12 for obtaining more magnetic flux data for simulation. In another embodiment where only one detecting unit 21 is employed, the detecting unit 21 may be driven to move along a direction of the magnetic field (i.e., a direction perpendicular to a surface of the frame 211 that confronts the patient (B)) for obtaining more magnetic flux data for simulation. Moreover, an ultrasonic scanning apparatus (not depicted in the drawings) may be employed to obtain information regarding the target (C) and to provide the information thus obtained to the processing unit 22.
Further, in the real-time analysis process 34, the processing unit 22 may calculate a three-dimensional temperature distribution and a three-dimensional ablating based on the magnetic flux detected by the detecting units 21 when the magnetic induction needle is punctured into the target (C).
To sum up, the magnetic excitation of this invention employs the detecting unit(s) 21 for detecting the magnetic flux passing therethrough, and enables the processing unit 22 to generate the simulated magnetic field distribution associated with the target (C) that would result from a magnetic induction needle being punctured into the target (C) before the magnetic induction needle is actually punctured. The simulated temperature and ablating range associated with the target (C) may enable the operator and/or the processing unit 22 to determine an optimal puncturing location for puncturing of the magnetic induction needle, and the marking unit 23 is controlled to mark the optimal puncturing location to facilitate accurate puncturing of the magnetic induction needle at the optical puncturing location.
Furthermore, as the thermal ablation is in progress, the temperature and ablating range associated with the target (C) may be continuously monitored by the real-time analysis process 34. As a result, the operator has now an analytic basis, instead of past experience, as a guidance to determining when to stop performing the thermal ablation.
While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.
| Number | Date | Country | |
|---|---|---|---|
| 62098095 | Dec 2014 | US |
