阅读说明：本技术 一种基于心磁信号的心肌缺血评估方法和装置 (Myocardial ischemia assessment method and device based on magnetocardiogram signals ) 是由 许琳 封燮 黄燕飞 刘素霞 王睿奇 汤苏晋 于 2021-06-08 设计创作，主要内容包括：本发明公开了一种基于心磁信号的心肌缺血评估方法和装置。其中,所述方法包括：通过心磁图仪获取心脏的磁场图；将所述磁场图转换为对应的电流密度矢量图；对电流密度矢量图的QRS除极阶段和STT复极阶段进行分析,根据分析结果对心肌缺血情况进行评估。本发明实施例的技术方案,通过将磁场图转换为电流密度矢量图可以将心磁图的判读与医生熟知的电生理结合起来,使判读流程简便化、自动化和准确化,进而优化了心肌缺血的评估方法。(The invention discloses a myocardial ischemia assessment method and device based on magnetocardiogram signals. Wherein the method comprises the following steps: acquiring a magnetic field map of the heart through a magnetocardiogram instrument; converting the magnetic field map into a corresponding current density vector map; and analyzing the QRS depolarization stage and the STT repolarization stage of the current density vector diagram, and evaluating the myocardial ischemia condition according to the analysis result. According to the technical scheme of the embodiment of the invention, the interpretation of the magnetocardiogram can be combined with electrophysiology known by doctors by converting the magnetic field diagram into the current density vector diagram, so that the interpretation process is simple, convenient, automatic and accurate, and the myocardial ischemia assessment method is further optimized.)

1. A myocardial ischemia assessment method based on magnetocardiogram signals, the method comprising:

acquiring a magnetic field map of the heart through a magnetocardiogram instrument;

converting the magnetic field map into a corresponding current density vector map;

and analyzing the QRS depolarization stage and the STT repolarization stage of the current density vector diagram, and evaluating the myocardial ischemia condition according to the analysis result.

2. The method of claim 1, wherein analyzing the QRS depolarization phase and the STT repolarization phase of the current density vector map and assessing myocardial ischemia based on the analysis comprises:

dividing a current density vector diagram of a QRS depolarization stage into five regions;

respectively determining the blood vessel activity in the five regions according to the current vector density maps corresponding to the five regions;

wherein the five regions include the anterior wall, the left ventricular wall, the posterior wall, the interventricular septum, and the apex.

3. The method of claim 1, wherein analyzing the QRS depolarization phase and the STT repolarization phase of the current density vector map and assessing myocardial ischemia based on the analysis comprises:

comparing the current density vector diagram of the QRS depolarization stage with the current density vector diagram of the QRS depolarization stage of a normal person;

if there is a deviation, myocardial ischemia may occur.

4. The method of claim 1, wherein analyzing the QRS depolarization phase and the STT repolarization phase of the current density vector map and assessing myocardial ischemia based on the analysis comprises:

comparing the current density vector diagram of the STT repolarization stage with the current density vector diagram of the STT repolarization stage of a normal person;

if there is a deviation, myocardial ischemia may occur.

5. The method of claim 1, further comprising:

acquiring the ratio of a normal vector to an abnormal vector in a QRS depolarization stage, the ratio of a normal vector to an abnormal vector in an STT repolarization stage, the smoothness of data in the STT repolarization stage, the uniformity of the data in the STT repolarization stage, the ratio of R peak current to T peak current and the form of a magnetic field map;

adding the obtained values to determine a myocardial ischemia evaluation index;

the larger the myocardial ischemia assessment index value, the more normal the heart is.

6. A myocardial ischemia evaluation device based on magnetocardiogram signals, the device comprising:

the acquisition module acquires a magnetic field map of the heart through the magnetocardiogram instrument;

the conversion module is used for converting the magnetic field diagram into a corresponding current density vector diagram;

and the evaluation module is used for analyzing the QRS depolarization stage and the STT repolarization stage of the current density vector diagram and evaluating the myocardial ischemia condition according to the analysis result.

7. The apparatus of claim 6, wherein the evaluation module is specifically configured to:

dividing a current density vector diagram of a QRS depolarization stage into five regions;

respectively determining the blood vessel activity in the five regions according to the current vector density maps corresponding to the five regions;

wherein the five regions include the anterior wall, the left ventricular wall, the posterior wall, the interventricular septum, and the apex.

8. The apparatus of claim 6, wherein the evaluation module is further specifically configured to:

comparing the current density vector diagram of the QRS depolarization stage with the current density vector diagram of the QRS depolarization stage of a normal person;

if there is a deviation, myocardial ischemia may occur.

9. The apparatus of claim 6, wherein the evaluation module is further specifically configured to:

comparing the current density vector diagram of the STT repolarization stage with the current density vector diagram of the STT repolarization stage of a normal person;

if there is a deviation, myocardial ischemia may occur.

10. The apparatus according to claim 6, further comprising an evaluation index determination module, specifically configured to:

acquiring the ratio of a normal vector to an abnormal vector in a QRS depolarization stage, the ratio of a normal vector to an abnormal vector in an STT repolarization stage, the smoothness of data in the STT repolarization stage, the uniformity of the data in the STT repolarization stage, the ratio of R peak current to T peak current and the form of a magnetic field map;

adding the obtained values to determine a myocardial ischemia evaluation index;

the larger the myocardial ischemia assessment index value, the more normal the heart is.

Technical Field

The embodiment of the invention relates to the technical field of data analysis, in particular to a myocardial ischemia assessment method and device based on magnetocardiogram signals.

Background

Coronary heart disease is a common cardiovascular disease, and the prevalence rate is in a continuous rising stage in recent years. Coronary heart disease is often accompanied by myocardial ischemia, and the judgment of myocardial ischemia of patients plays an important role in the links of understanding the disease condition, making a treatment scheme and the like. At present, the condition of myocardial ischemia of a patient is detected by adopting an electrocardiogram, but the accuracy rate of the electrocardiogram is only 30-40 percent generally at present, so that a recessive heart disease patient cannot be screened out, and the disease is found to belong to a late stage or a disease onset stage. The heart magnetic map can obtain abundant heart electromagnetic activity information, and finds the heart disease patients with normal electrocardiogram.

The magnetocardiogram instrument is simple, fast, accurate and cheap examination equipment aiming at myocardial ischemia, adopts the SQUID detector with ultrahigh sensitivity, can completely capture the magnetic field generated by cardiac current, avoids attenuation and distortion of electrocardiosignals caused by the conduction of the conventional electrocardiogram from the sinoatrial node to the body surface electrode, and can accurately and reliably judge the myocardial ischemia condition accompanying coronary heart disease.

However, although the magnetocardiograph can accurately record the cardiac magnetic signals, the diagnosis of the magnetocardiograph needs to rely on manual interpretation of the magnetic field map, but many doctors do not know the magnetic field map, so that accurate interpretation cannot be performed, and certain application blind areas exist.

Disclosure of Invention

The invention provides a myocardial ischemia evaluation method and device for magnetocardiogram signals, so that the interpretation process is simple, convenient, automatic and accurate, and the myocardial ischemia evaluation method is optimized.

In a first aspect, an embodiment of the present invention provides a myocardial ischemia assessment method based on magnetocardiogram signals, where the method includes:

acquiring a magnetic field map of the heart through a magnetocardiogram instrument;

converting the magnetic field map into a corresponding current density vector map;

and analyzing the QRS depolarization stage and the STT repolarization stage of the current density vector diagram, and evaluating the myocardial ischemia condition according to the analysis result.

In a second aspect, an embodiment of the present invention further provides a myocardial ischemia evaluation apparatus based on magnetocardiogram signals, the apparatus including:

the acquisition module acquires a magnetic field map of the heart through the magnetocardiogram instrument;

the conversion module is used for converting the magnetic field diagram into a corresponding current density vector diagram;

an evaluation module: and analyzing the QRS depolarization stage and the STT repolarization stage of the current density vector diagram, and evaluating the myocardial ischemia condition according to the analysis result.

The invention firstly obtains the magnetic field diagram of the heart through the magnetocardiogram instrument, converts the obtained magnetic field diagram into the corresponding current density vector diagram, evaluates the myocardial ischemia condition through analyzing the current density vector diagram of the heart at different stages, combines the interpretation of the magnetocardiogram with the electrophysiology known by doctors through converting the magnetic field diagram into the current density vector diagram, simplifies, automates and accuracies the interpretation process, and further optimizes the myocardial ischemia evaluation method.

Drawings

Fig. 1 is a flowchart of a myocardial ischemia assessment method based on magnetocardiogram signals according to an embodiment of the present invention;

FIG. 2 is an analog schematic diagram of a cardiac dipole according to an embodiment of the present invention;

FIG. 3 is a schematic diagram showing the direction of current flow during the depolarization and repolarization phases of the heart;

FIG. 4 is a flowchart illustrating a myocardial ischemia assessment method based on magnetocardiogram signals according to an embodiment of the present invention;

FIG. 5 is a graph illustrating the activity values of the patient in five regions;

FIG. 6 is a vector diagram of current density of normal person in QRS depolarization stage;

FIG. 7 is a comparison of current density vector diagrams for normal and coronary heart disease patients;

fig. 8 is a myocardial ischemia evaluation apparatus based on magnetocardiogram signals according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.

Examples

Fig. 1 is a flowchart of a myocardial ischemia assessment method based on magnetocardiogram signals according to an embodiment of the present invention, which is applicable to the assessment of myocardial ischemia condition, and can be executed by a myocardial ischemia assessment apparatus based on magnetocardiogram signals, and the apparatus can be implemented by software and/or hardware.

For the purpose of describing the subsequent embodiments of the present invention, the principle of the magnetic field generated by the heart will be described first.

When the heart chamber contracts, depolarization spreads through the heart, with the extracellular fluid surrounding the heart muscle being more negatively charged and the rest of the heart being positively charged. This creates a potential difference between the different regions that can be detected by the electrocardiographic electrodes. A heart dipole is a vector having both a direction (from the most negative region of the heart to the most positive region) and an amplitude (voltage). During cardiac depolarization, i.e., when cardiac action potentials diffuse from their source, the atria to the most distal corners of the ventricles, due to positively charged ions (Na)⁺And Ca²⁺) Entering the cardiomyocytes, the extracellular fluid surrounding the myocardium becomes more negative. Because the propagation of depolarization waves is not instantaneous, uniform, and because the masses of the myocardial walls are not equal, the minimum and the most depolarized myocardial masses vary with time. This is somewhat like a rotating battery with positive and negative ends that rotate in three dimensions as the depolarization wave propagates through the heart chamber. The dipole is a vector. That is, it has a direction and magnitude, just like wind. You can imagine a heart dipole as an arrow pointing from the most depolarized region of the heart to the most polarized region. Arrow headThe location of the two ends depends on how the depolarization wave spreads through the heart and how many myocardial cells are depolarized or repolarized. The even pole is at a particular time from the maximum mass of depolarized myocardium to the maximum mass of repolarized myocardium. A convenient analogy to cardiac dipoles is a vane that displays the direction of the wind, which has the disadvantage that vectors like cardiac dipoles have both a direction and a magnitude, whereas a vane only displays the direction of the wind. With specific reference to A, B, C and D in FIG. 2, this figure best describes what happens when the vector changes direction when viewed from a fixed perspective. The specific explanation is as follows:

A. the wind vane points in the direction of the wind because the tail of the vane has the greatest resistance to the wind and blows parallel to the wind.

B. Imagine you are looking at a vane from east to west. If the wind is blowing from north or south, the wind vane will appear as a straight long arrow.

C. If the wind blows more westward or eastward without you changing your position, the length of the wind vane will shorten as it rotates. From a fixed location, you do not know whether the wind is blowing east or west.

D. The wind vane will effectively disappear if the wind blows directly east or west.

This is the spread of depolarization across a pair of electrodes in a particular direction of the heart as the wave moves and the dipole changes direction. The action potential of muscle cells near the surface of the heart is shorter than the action potential of muscle cells located deep in the myocardium. This is because the cardiomyocytes near the surface of the heart (sub-epicardial cardiomyocytes) have more potassium channels, resulting in faster repolarization of the action potential. Because of this, repolarization of the ventricle begins under the outer pericardium, and you may think it begins at the septum and spreads out, just like depolarization. As a result, the positive and negative charges are similarly distributed when the ventricles depolarize and repolarize, and thus both deflect in the same direction on the electrocardiogram.

It is precisely these electrical activities of the heart that a large magnetic field is generated, so that the magnetocardiograph can collect and analyze the magnetic signals of the heart.

With continued reference to fig. 3, fig. 3 is a schematic view of the direction of current flow during the depolarization and repolarization phases of the heart. The direction of the current density vector diagram at the bottom coincides with the direction of the current at the top.

Further, the myocardial ischemia assessment method based on magnetocardiogram signals provided by the embodiment of the present invention specifically includes the following steps:

and S110, acquiring a magnetic field map of the heart through a magnetocardiogram instrument.

In this embodiment, in order to improve the accuracy of magnetic field map interpretation, the acquired magnetic field map needs to be detected. If the signals in the magnetic field map appear in many unsmooth places, preprocessing operations such as denoising and filtering need to be performed on the magnetic field signals to obtain a smooth magnetic field signal map. If the smooth magnetic field signal diagram cannot be obtained through the preprocessing mode, retesting needs to be carried out through the magnetocardiograph to obtain the smooth magnetocardiograph signal, so that the reliability of the signal is ensured, a reliable data source is provided for subsequent interpretation, and the accuracy of the interpretation is improved.

And S120, converting the magnetic field diagram into a corresponding current density vector diagram.

Specifically, in the current density reconstruction inverse algorithm for magnetocardiogram signals in this embodiment, a guidance field concept is first utilized to establish a relational expression between magnetic flux and current density, then a cardiac magnetic field differential equation (divergence and rotation) under a quasi-static condition is converted into a convolution component summation equation of a fourier space through double fourier transform, a green function and a wave plane method are then introduced to obtain a fourier space equation solution, and finally inverse fourier transform is applied to obtain spatial distribution of cardiac current sources, so as to obtain a current density vector diagram corresponding to a magnetic field diagram.

And S130, analyzing a QRS depolarization stage and an STT repolarization stage of the current density vector diagram, and evaluating the myocardial ischemia condition according to the analysis result.

In the embodiment, the magnetic field diagram is reversely developed into the current density vector diagram, so that the judgment of the magnetocardiogram instrument is combined with the electrophysiology known by doctors, and the myocardial ischemia condition of the patient can be rapidly and accurately determined by analyzing the difference between the current density vector diagram of the patient and the current density vector diagram of a normal person. Compared with the method of manually interpreting the magnetic field in the prior art, the method has the advantages that the interpretation process is simple, convenient, automatic and accurate.

In the present embodiment, by performing an omnidirectional analysis on the current density vector diagrams of the two phases, various means and approaches are provided for the assessment of myocardial ischemia.

With further reference to fig. 4, fig. 4 is a flowchart of another myocardial ischemia assessment method based on magnetocardiogram signals according to an embodiment of the present invention, and the present embodiment provides a specific magnetocardiogram interpretation method based on the above embodiment.

The method specifically comprises the following steps:

step 1, checking the detection signal of the magnetocardiogram instrument.

If the acquired magnetocardiogram signal is smooth, the signal is a normal signal; if the signal appears in many uneven places, representing noise interference, it needs to be preprocessed or retested.

And 2, judging the myocardial viability in 4 stages by QRS depolarization.

The 4 phases correspond to the ventricular septal depolarization phase, the precordial and sidewall depolarization phases, the ventricular complete depolarization phase, and the ventricular repolarization phase of fig. 2. Whether the patient has suffered myocardial infarction can be judged by comparing the heart activity corresponding to the four stages of the patient with the heart activity of a normal person.

And 3, dividing QRS into 5 regions to judge the conditions of three major blood vessels.

Specifically, a current density vector diagram of a QRS depolarization stage is divided into five regions;

respectively determining the blood vessel activity in the five regions according to the current vector density maps corresponding to the five regions;

wherein the five regions include the anterior wall, the left ventricular wall, the posterior wall, the interventricular septum, and the apex.

In this embodiment, the current density vector diagram may reflect the blood vessel activity of different regions of the heart, and the comparison result between the current density vector diagram corresponding to the different regions and the normal current density vector diagram may be output in the form of an image through application software, specifically, see fig. 5, where fig. 5 represents a curve diagram of activity values corresponding to five regions of a patient, each region corresponds to three activity value ranges, and if the curve is in the uppermost activity value range, it indicates that the blood vessel activity of the region is higher; if the curve is in the middle activity value range, the activity value of the area is normal; if the curve is in the range of the lowest activity value, the activity value of the area is lower. For example, the second half of the curve corresponding to the 1 region is in the lowest activity value range, so that the activity of the front wall is low.

And 4, analyzing a current density vector diagram of the QRS stage.

Specifically, comparing the current density vector diagram of the QRS depolarization stage with the current density vector diagram of the QRS depolarization stage of a normal person; if there is a deviation, myocardial ischemia may occur.

With further reference to fig. 6, fig. 6 is a vector diagram of current density of a normal person during QRS depolarization phase. Specifically, four phases may be identified, namely, the interventricular depolarization phase, the precordial and lateral-wall depolarization phases, the ventricular full depolarization phase, and the ventricular repolarization phase of fig. 2.

Starting from the interventricular septum, it flows through the left and right bundle branches to the left and right ventricles, eventually covering the entire ventricle. The QRS has the main current at the left lower part in the first stage, the main current at the right lower part in the second and third stages and the current at the fourth stage upwards. If the current direction and position of the acquired current density vector diagram corresponding to fig. 6 are different, it can be determined that myocardial ischemia exists in the heart.

Similarly, the QRS depolarization stage and the STT repolarization stage of the current density vector diagram are analyzed, and the myocardial ischemia condition is evaluated according to the analysis result, which comprises the following steps: comparing the current density vector diagram of the STT repolarization stage with the current density vector diagram of the STT repolarization stage of a normal person; if there is a deviation, myocardial ischemia may occur.

And 5, determining the KI value. Here, the myocardial ischemia evaluation index is expressed as KI value. In the embodiment, the ratio AIQRSTotal of a normal vector and an abnormal vector in a QRS depolarization stage, the ratio AIST-Ttotal of the normal vector and the abnormal vector in an STT repolarization stage, the smoothness ADur of data in the STT repolarization stage, the uniformity Ccor of the data in the STT repolarization stage, the ratio R/Tcurrent of R peak current and T peak current and the form MAPTyp of a magnetic field map are obtained; adding the obtained values to determine a myocardial ischemia evaluation index; the larger the myocardial ischemia assessment index value, the more normal the heart is.

Specifically, the KI value is calculated by dividing the STT period into several parts, each part being 12ms apart, and analyzing the magnetic field map of the time period, mainly by the following data: the ratio AIQRSotal of the normal vector and the abnormal vector of the QRS, the ratio AIST-Ttotal of the normal vector and the abnormal vector of the STT section, the smoothness ADur of data of the STT section, the uniformity C cor of data of the ST section, the ratio R/Tcurrent of R peak current and T peak current and the form MAPTyp of a magnetic field diagram.

The KI value is a coefficient generated by the data together, and KI is AIQRSITotal + AIST-Ttotal + ADur + CsCor + R/Tcurrent + MAPTyp.

Since the larger the value corresponding to each datum in the above formula is, the more healthy the heart is, the larger the KI is, the more normal the heart is, and the smaller the KI is, the more serious the heart problem is.

And 6, analyzing a current density vector diagram of the STT stage.

Specifically, comparing the current density vector diagram of the STT repolarization stage with the current density vector diagram of the STT repolarization stage of a normal person; if there is a deviation, myocardial ischemia may occur.

In the STT phase, the main current direction is pointing to the lower right, and fig. 7 is a comparison of current density vector diagrams for normal and coronary CAD patients. The current density vector diagram of a normal person is characterized in that the main vector points to the lower right and has two vortexes; if abnormal current exists in the upper right corner of the magnetic field map, the phenomenon of ischemia of the left circumflex branch is represented, the phenomenon of ischemia of the left descending branch is represented if abnormal current exists in the lower right corner and the middle, and the phenomenon of ischemia of the right branch is represented if abnormal current exists in the right side.

According to the embodiment of the invention, the magnetocardiograph interpretation can be combined with electrophysiology known by doctors by inverting the magnetic field diagram into the current density vector diagram, so that the interpretation process is simple, convenient, automatic and accurate. Meanwhile, a calculation method of a KI value is set, whether a testee has myocardial ischemia or not can be preliminarily obtained by visually observing the KI value, and the myocardial ischemia degree is determined by a QRS and STT section current density vector diagram and a QRS partition staged myocardial activity diagram. This semi-automated diagnostic procedure may help physicians diagnose more quickly and better, thereby eliminating the need for invasive testing to determine myocardial ischemia. The clinical verification scheme of the embodiment of the invention is designed as follows:

the subjects in the clinical trial were divided into three groups: one group of patients who were determined to be myocardial ischemia and to meet revascularization criteria by "gold criteria" (coronary angiography and coronary flow reserve fraction) was "case group 1"; the second group was patients who had confirmed myocardial ischemia by "gold standard" but had not yet reached the criteria for revascularization, and was "case group 2"; the third group is a negative control group which is a normal group confirmed by 'gold standard' examination without myocardial ischemia or clinical examination (resting electrocardiogram, load electrocardiogram and echocardiography).

The number of case groups 1 must not be less than 30% of the total number of samples.

Case group 1 enrollment requirements: if the coronary artery stenosis degree is more than or equal to 80 percent, the FFR examination is not needed; the coronary artery stenosis degree is more than or equal to 50 percent and less than 80 percent, and the coronary artery blood flow reserve fraction FFR is less than or equal to 0.8;

if one of the two items is satisfied, the patient can be selected as the case group 1.

Case group 2 enrollment requirements: the coronary artery stenosis degree is more than or equal to 50 percent and less than 80 percent, and the coronary artery blood flow reserve fraction FFR is more than 0.8;

negative control group selection requirement: the coronary artery stenosis degree is less than 50 percent; no history of cardiovascular disease, normal physical examination, no clinical abnormalities of resting electrocardiogram, loaded electrocardiogram and echocardiogram.

When the two items meet one of the two conditions, the negative control group can be selected.

After the interpretation is carried out by using the method, the clinical report of the judgment result is shown as the following table:

total rate of agreement	90.48％
		Sensitivity of the probe	93.75％
Specificity of	87.10％
		Positive predictive value	88.24％
Negative predictive value	93.10％
		Kappa number	80.93％

Therefore, the total coincidence rate of the detection result obtained by the magnetocardiogram instrument through interpretation by the method and the gold standard result reaches the preset target, and the consistency is good.

Fig. 8 is a myocardial ischemia evaluation apparatus based on magnetocardiogram signals, which includes:

an obtaining module 210, configured to obtain a magnetic field map of the heart through a magnetocardiogram apparatus;

a conversion module 220 for converting the magnetic field map into a corresponding current density vector map;

and the evaluation module 230 analyzes the QRS depolarization stage and the STT repolarization stage of the current density vector diagram and evaluates the myocardial ischemia condition according to the analysis result.

Wherein the evaluation module is specifically configured to:

dividing a current density vector diagram of a QRS depolarization stage into five regions;

respectively determining the blood vessel activity in the five regions according to the current vector density maps corresponding to the five regions;

wherein the five regions include the anterior wall, the left ventricular wall, the posterior wall, the interventricular septum, and the apex.

The evaluation module 210 is further specifically configured to:

comparing the current density vector diagram of the QRS depolarization stage with the current density vector diagram of the QRS depolarization stage of a normal person;

if there is a deviation, myocardial ischemia may occur.

The evaluation module 210 is further specifically configured to:

comparing the current density vector diagram of the STT repolarization stage with the current density vector diagram of the STT repolarization stage of a normal person;

if there is a deviation, myocardial ischemia may occur.

Further, the apparatus further comprises an evaluation index determination module, specifically configured to:

acquiring the ratio of a normal vector to an abnormal vector in a QRS depolarization stage, the ratio of a normal vector to an abnormal vector in an STT repolarization stage, the smoothness of data in the STT repolarization stage, the uniformity of the data in the STT repolarization stage, the ratio of R peak current to T peak current and the form of a magnetic field map;

adding the obtained values to determine a myocardial ischemia evaluation index;

the larger the myocardial ischemia assessment index value, the more normal the heart is.

The myocardial ischemia evaluation device for magnetocardiogram signals provided by the embodiment of the invention can execute the myocardial ischemia evaluation method for magnetocardiogram signals provided by any embodiment of the invention, and has corresponding functional modules and beneficial effects of the execution method.

It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.