Method and system for dual-band active thermal imaging using multi-frequency currents

Abstract

A hybrid system is developed using thermal and electrical impedance imaging methods together. The innovation of the approach relies on the frequency dependence of the tissue's electrical impedance which facilitates the acquisition of multiple thermal images with currents at different frequencies injected to the region of the body under inspection. Proposed method without current application (in passive mode of operation) provides images which are obtained by standard thermal imagers. On the other hand, the application of the electrical current (in active mode of operation) increases the temperature contrast on the body surface depending on the electrical property of tissue. Therefore, the technique while increasing the thermal contrast provides frequency dependent conductivity distribution data which can be used as a basis for the detection of the breast carcinoma. The sensitivity of the technique is increased by an infrared camera with dual band (MWIR/LWIR) imaging capability.

Claims

1. A medical electro-thermal imaging method, comprising the steps of: a. preparing a patient and the imaging room according to a thermal imaging standards; b. recording of a passive thermal image of the tissue in two different windows (MWIR and LWIR) using a dual band thermal camera; c. placing a plurality of non-invasive electrodes to the specified locations on the surface of the breast tissue; d. selecting frequency of an electric current that is inserted to the breast tissue using the control unit; e. applying the electric current to the targeted breast tissue for predetermined time period; f. recording an active thermal image of the stimulated area in, heating period (in both windows (MWIR and LWIR)); g. recording the active thermal image of the stimulated area in cooling period (in both windows (MWIR and LWIR)) until the temperature of the breast tissue becomes stable; h. going to the item c and repeating the same procedure for different frequency values of the applied electric current; i. eliminating the position differences of the active thermal image and the passive thermal image and matching the active thermal image and the passive thermal image (image registration); j. obtaining the absolute temperature value of the breast and cancerous tissue for any screening time period using the dual band property of the thermal camera; k. comparing and determining the ratio/difference of the active thermal image and the passive thermal image (in single band and dual band imaging modes) obtained under different frequencies using the image processing algorithm which is embedded in the control unit to detect the cancerous tissue (tumor tissue); l. if the active thermal image is not enough to make a healthy diagnosis for the presence of the tumor after changing the frequency of the electric current or the positions of the electrodes; carrying out the previous d, e, f, g, h, i, j, k and l steps until a healthy diagnosis or detection is made; wherein the decision in this sense is made with the help of the algorithm embedded in the control unit; and wherein the patients disrobe to the waist and let the surface of the breasts cool to room temperature of 18-22 C. for 10-15 minutes.

2. A medical electro-thermal imaging system configured to perform the method of claim 1, which uses the electric current as an external heat source to improve the temperature contrast, comprising: an imaging room configured to satisfy the thermal imaging standards; a dual-band infrared camera configured to sense temperature emission and emissivity of the focused area to record a passive and an active thermal image of the tissue in two different windows (MWIR and LWIR); a plurality of non-invasive electrodes are configured to insert the specified locations on the surface of the breast tissue deliver the electric current to the breast tissue; a voltage controlled current source configured to provide the electric current that is injected to the breast tissue; a control unit configured to regulate the alternating electric current that is provided by the current source to record image by the data provided by infrared camera to make image registration by eliminating the position differences of the active and passive thermal image and match the active thermal image and the passive thermal image, to obtain the absolute temperature value of the breast and cancerous tissue for any screening time period using the dual band property of the thermal camera, and to make comparison and determination of the ratio/difference of the active and passive thermal image (in single band and dual band imaging modes) obtained at different frequencies using the image and signal processing algorithms which are embedded in the control unit to detect the cancerous tissue (tumor tissue).

3. The medical electro-thermal imaging system of claim 2, wherein the current source is the multi-frequency voltage controlled alternating current source which injects controlled alternating currents in the frequency range of 0-1 MHz.

4. The medical electro-thermal imaging system of claim 2, wherein the control unit is configured to regulate the electric current that is provided by the current source to record image by the data provided by infrared camera and to make registration and comparison between the passive thermal image and active thermal image.

5. The medical electro-thermal imaging method of claim 1, wherein the analysis of the images is implemented by taking the electrical properties of tissue at operation frequency (electrical conductivity, electrical permittivity, and possibly magnetic permeability) into account.

6. The medical electro-thermal imaging method of claim 1, wherein the analysis of the images is made by collecting dual or multi-frequency data.

7. The medical electro-thermal imaging method of claim 1, wherein the positions and the number of electrodes are optimized so as to increase temperature and image contrast.

8. The medical electro-thermal imaging system of claim 2, wherein a dual-band (MWIR/LWIR) thermal camera in active mode of operation is used.

9. The medical electro-thermal imaging method of claim 1, wherein transient image analysis with more data is also implemented in addition to the steady-state imaging analysis.

Description

DESCRIPTIONS OF FIGURES

(1) The names of the drawings presented for better understanding of medical electro-thermal imaging method and the system thereof are listed as follows:

(2) FIG. 1. Schematic view of the medical electro-thermal imaging system

(3) FIG. 2. Application of the medical electro-thermal imaging method using the medical electro-thermal imaging system.

(4) FIG. 3. Flow chart of the medical electro-thermal imaging method.

(5) FIG. 4. Electromagnetic model of the tissue exposed to the electric current.

(6) FIG. 5. Thermal model of the tissue.

(7) FIG. 6. Temperature distribution of the healthy and the tumor tissue (realistic breast phantom) taken in passive mode.

(8) FIG. 7. Ratio of thermal images taken in active and passive mode.

(9) FIG. 8. Image showing the difference of healthy tissue and tumor in active mode of operation.

(10) The numerals referred to in the following description correspond to the following, 1. Infrared camera, 2. Electrodes, 3. Cancerous tissue (tumor), 4. Breast tissue, 5. Control unit, 6. Current source, 7. Surface of the breast tissue, 8. Thermal image.

DETAILED DESCRIPTION OF THE INVENTION

(11) Theory

(12) We present below the theoretical analysis of thermal contrast enhancement with current injection. Electromagnetic problem of the method is modeled and the schematic of the electromagnetic problem is shown in FIG. 4. The electrical model of the body is represented using permeability =.sub.0, electrical conductivity and permittivity . Sinusoidal currents are applied using two electrodes attached on the body surface at points A and B. Applied currents generate an electric field in the conductive body. The steady-state electric field {right arrow over (E)}=jw{right arrow over (A)} can be calculated using the following coupled partial differential equations,
.sup.2{right arrow over (A)}jw(+jw){right arrow over (A)}(+jw)=0
.[(+jw)]+(+jw).jw{right arrow over (A)}=0

(13) and boundary conditions

(14) $\frac{}{n}=\{\begin{array}{c}I\mathrm{on}A\\ -I\mathrm{on}B\\ 0\mathrm{otherwise}\end{array}$

(15) where {right arrow over (A)} is the magnetic vector potential, is the scalar potential, and I is the current applied from the surface.

(16) Thermal problem is also modeled to obtain the temperature distribution inside the tissue. Schematic of the Bio-Heat problem (including an external heat source due to current application) is shown in FIG. 5. Pennes Bio Heat Equation is used to describe the effects of metabolic generation and blood perfusion over the energy balance. It explains the thermal interaction between tissues and perfused blood in detail:

(17) $C_h\frac{T}{t}+.Math.\left(-kT\right)=Q_b+Q_{\mathrm{met}}$

(18) where, is the density (kg/m.sup.3), C.sub.h is the specific heat (J/kgK), T is the absolute temperature (K), k is thermal conductivity (W/mK), Q.sub.b is the heat source due to blood perfusion and Q.sub.met is the metabolic heat generation (W/m.sup.3).

(19) The first term on the right hand side is the source due to blood perfusion which can be expressed as
Q.sub.b=.sub.bC.sub.hbW.sub.b(T.sub.bT)

(20) where, .sub.b is blood mass density (kg/m.sup.3), C.sub.hb is the blood specific heat rate (J/kgK), W.sub.b is the blood perfusion rate (1/s), and T.sub.b is the blood temperature (K) which is approximated to the core temperature of the body, and the temperature of the venous blood is approximated to T which is the unknown temperature value (local tissue temperature (K)).

(21) Law of conservation of energy states that the heat lost from the skin surface is in a constant equilibrium with the heat supplied by the vascular flow to the skin in the steady state. Thus, heat transfer from the front skin surface (by both convection and radiation to the surrounding air and surfaces at specified temperatures) should be considered as the boundary conditions:
Q.sub.conv=h.sub.hA.sub.s(T.sub.ST.sub.)
Q.sub.rad=eA.sub.s(T.sub.s.sup.4T.sub.sur.sup.4)

(22) where, h.sub.h is the convection heat transfer coefficient (W/m.sup.2.K), A.sub.s is the surface area through which the convection heat transfer takes place, T.sub.s is the surface temperature, T.sub. is the temperature of the air, e is the emissivity of a skin (0.95), is the Stefan-Boltzmann constant (W/m.sup.2. K.sup.4), and T.sub.sur is the temperature of the walls, ceiling and floor. In this study, T.sub.sur is assumed to be equal to the air temperature (T.sub.sur=T.sub.).

(23) Note that, the boundary condition at the front skin surface can also be written as:
kT=h.sub.h(TT.sub.)

(24) Here, h.sub.h (W/m.sup.2K) represents the overall heat transfer coefficient due to the combined effect of radiation and convection.

(25) To set the boundary condition at the rear surface of the breast, the temperature of the thoracic wall can be assumed to be the core temperature of the body (i.e., 310 K).

(26) Due to the applied external current sources, a new term should be added to the right-hand side of the Pennes Bio Heat equation:

(27) $C\frac{T}{t}+.Math.\left(-kT\right)=Q_b+Q_{\mathrm{met}}+Q_{\mathrm{ext}}$

(28) The external heat term Q.sub.est is calculated using the following Joule Heat Equation:

(29) $Q_{\mathrm{ext}}=\frac{1}{}{.Math.J.Math.}^2$

(30) where J is the electrical current density and is the electrical conductivity of the tissue.

(31) Medical electro-thermal imaging method comprises the steps of,

(32) a. Preparation of the patient and the imaging room according to the thermal imaging standards,

(33) b. Recording the passive mode thermal image(s) of the body in two different windows (MWIR and LWIR) using dual band infrared camera (1),

(34) c. Selecting the frequency of electric current that is attached to the breast tissue (4) using control unit (5),

(35) d. Placing the electrodes to the previously specified locations on the surface of the breast tissue (4),

(36) e. Applying the electric current for predetermined time period to the targeted breast tissue (4),

(37) f. Recording the active thermal image (8) of the stimulated area (in both bands (MWIR and LWIR)) in the heating period,

(38) g. Recording the active thermal image (8) of the stimulated area (in both bands (MWIR and LWIR)) in the cooling period until the temperature of the breast tissue (4) becomes stable,

(39) h. Going to the item c and repeating the same procedure for different frequency values of the applied electric current,

(40) i. Eliminating position differences of the active (8) and passive thermal images and making necessary matching processes (image registration),

(41) j. Obtaining the absolute temperature value of the breast and cancerous tissue (3 & 4) using the dual band property of the thermal camera (1),

(42) k. Comparing and determining the ratio/difference of the active (8) and passive thermal images obtained under different frequencies using the image processing algorithm which is embedded to the control unit to detect the cancerous tissue (3),

(43) l. Carrying out steps c through k until a healthy diagnosis or detection is made.

(44) The proposed hybrid imaging method is denoted in FIG. 1. FIG. 2 shows the application of the system in practice. In this imaging method, electrical current within medical safety limits is applied to the breast tissue from the surface, by means of electrodes (2) placed on the fingers. The temperature distribution on the breast surface (4) is recorded in real time with an infrared camera (1). Due to the current application, the presence of tumor in the breast causes higher temperature contrast on the breast surface. This temperature difference is determined in the thermal image (8) obtained by the infrared camera (1). FIGS. 6, 7, and 8 are thermal images of the realistic breast phantoms which mimic the healthy and cancerous breast tissue. These thermal images were obtained using a QWIP single band (LWIR band) thermal infrared camera.

(45) The preparation of the room and patient according to thermal imaging standards is an essential part of the medical electro-thermal imaging method for making correct diagnosis about the breast tissue. Imaging should be implemented in a controlled manner. Patients disrobe to the waist and let the surface of the breasts to cool to room temperature (18-22 C.) for 10-15 minutes.

(46) After the preparation procedure is completed, passive thermal image of the tissue is recorded. In this passive mode, since there are no external sources, the camera displays the surface radiance distribution due to the internal sources (metabolic heat generation and blood fusion). The passive thermal image is used for the comparison with an active thermal image (8) which is obtained after the medical electro-thermal imaging method is applied. The passive thermal image of the target area is given in the FIG. 6.

(47) After placement of the electrodes, the current is injected to the breast tissue (4). Since electrodes (2) are non-invasive type, there is no need for the insertion of the electrodes into the tissue. Electric current is injected from the surface of the breast tissue (7). The electric current is applied to the tissue (4) until the temperature of the tissue (4) become stable or along predetermined period and then active thermal image (8) is recorded using an infrared camera (1).

(48) Dual band sensor usage yields to measure the absolute temperature. Thermal imaging performance is improved by processing the images which are obtained in two different thermal imaging bands (MWIR and LWIR bands).

(49) Different thermal images can be recorded for different electrode locations. If the places of electrodes (2) are changed with respect to the location of the tumor tissue (3) higher temperature contrasts may be achieved by moving the electrodes (2).

(50) The parameters that affect the temperature contrast are the tumor dimension, amplitude, duration and frequency of the stimulation current, and location (depth) of the tumor tissue. Increasing the strength of the applied current causes higher contrast in the thermal images. Tumor dimension is also another important parameter affecting the temperature contrast. As the size of the tumor increases, higher temperature contrasts are obtained, and consequently, they can be diagnosed from deeper regions of the breast. An example to the ratio of passive and active (8) thermal images in other words contrast of the active (8) and passive thermal images given m the FIG. 7, and ratio of the healthy (8) and the tumor tissue (8) which are taken in active mode of operation is given in the FIG. 8.

(51) Medical electro-thermal imaging system comprises;

(52) Infrared camera (1) which can display temperature distribution in the focused area,

(53) Electrodes (2) that drive electric current to the breast tissue (4),

(54) Control unit (5) that regulates the electric current provided by current source (6), that records image by the data provided by infrared camera (1) and makes comparison between the passive and active thermal images (8).

(55) Current source (6) which provides the electric current that is inserted to the breast tissue (4).