KR100859740B1 - Apparatus for improvement in the image resolution of a compton camera and its principle - Google Patents

Abstract

An apparatus for improving the image resolution of a compton camera and a method for improving the resolution of images by using the apparatus are provided to estimate and determine the reaction depth of photons detected from the inside of an absorber and enhance the image resolution of a compton camera by using the reaction depth. An apparatus for improving the image resolution of a compton camera includes a source(100) emitting photons, a scatter(200), an absorber(300), and an image collector(400). The scatter is located at a distance from the source and compton-disperses the photons emitted from the source. The absorber is located at a distance from the scatter and determines a reaction depth of the photons according to the energy of the dispersed photons. The image collector acquires an image of the photon according to the determined reaction depth.

Description

Image Resolution Enhancement Device for Compton Camera and Method of Improving Image Resolution Using It {APPARATUS FOR IMPROVEMENT IN THE IMAGE RESOLUTION OF A COMPTON CAMERA AND ITS PRINCIPLE}

1 is a perspective view showing an image resolution improving apparatus for a Compton camera of the present invention.

Figure 2 is a graph showing the reaction depth according to the energy delivered to the absorber detector for the 364.5 keV dotted line according to the present invention.

3 is a graph showing the reaction depth according to the energy delivered to the absorber detector for the 511 keV dotted line according to the present invention.

FIG. 4A is a diagram showing an image of a 364.5 keV dotted circle obtained using a conventional Compton camera. FIG.

4B is a view showing an image of a 364.5 keV dotted circle obtained using the image resolution enhancing apparatus for a Compton camera of the present invention.

FIG. 5A illustrates an image of a 511 keV dotted line obtained using a conventional Compton camera. FIG.

FIG. 5B is a view showing an image of a 511 keV dotted circle obtained using the image resolution enhancing apparatus for a Compton camera of the present invention.

6 is a flowchart illustrating a method of improving resolution of an image using the image resolution enhancing apparatus for a Compton camera of the present invention.

** Description of symbols for the main parts of the drawing **

100: source 200: scattering detector (Scatterer)

300: Absorber 400: Image collector

The present invention relates to an image resolution improving device for a Compton camera and a method for improving the resolution of an image using the same, and more particularly, a correlation between energy and reaction depth when photons scattered in a scattering unit are absorbed in an absorbing unit. The present invention relates to a resolution enhancing apparatus for a Compton camera that can improve the resolution of an image of a Compton camera and a method of improving the resolution of an image using the same.

In general, Compton cameras are attracting attention as next generation gamma ray imaging devices because they can provide very high image sensitivity and image resolution at the same time, including the multi-tracer function. In Korea, the Compton camera, which consists of a double-sided silicon strip detector (50 mm x 50 mm x 1.5 mm, Micron Semiconductor, UK) and a split-electrode germanium detector (50 mm x 50 mm x 20 mm, Eurisys-Canberra, France), Currently, research is underway to achieve the high image resolution required in the field of nuclear medical imaging through the principle verification stage.

The principle of the Compton camera was proposed in 1974 by R.W.Todd et al., Which uses a process in which gamma rays enter the detector and scatter the Compton only once and stop completely by the photoelectric effect.

More specifically, the trajectory of photons emitted from an X-ray source or a gamma ray source has information about the location of the gamma ray source. Therefore, in order to calculate this information, the three-dimensional position where the Compton scattering occurred and the quantum conversion energy of the photons are first measured inside the detector called a scatterer, and the second Compton scattered photon absorber is measured. In the detector called an absorber, a gamma ray trajectory measurement technique that measures the three-dimensional position and the photon's quantum conversion energy that is finally lost to energy by the photoelectric effect is essential.

That is, the three-dimensional position or distribution of the gamma ray source is measured based on the Compton scattering equation by measuring the four detection elements for the trajectory of incident gamma rays (or X-rays) quantized by one Compton scattering and one photoelectric effect. Can be determined by applying an electrical connection.

Since the accuracy of the position of the gamma ray source is absolutely dependent on the four detection elements measured above, the gamma ray trajectory measurement technique is an important core technology of the Compton camera.

This can be achieved only by using a position sensitive gamma ray detector that can determine the three-dimensional reaction position of the photon of the scattering and absorbing detectors.

In conventional Compton cameras, it is assumed that when photons scattered at the scatter detector are absorbed at the absorber detector, the reaction occurs at the intermediate depth of each absorber detector. In the case of the scattering detector, the thickness thereof is very thin (= 1.5 mm), so even with this simple method, the reaction position in the depth direction can be accurately determined within an error range of ± 0.75 mm, which is not a big problem.

However, since the absorber detector has a thickness of 20 mm, the resolution of the reaction position in the depth direction is very low.

Therefore, in the case of using the above-described method, there is a problem that the image resolution of the Compton camera is drastically deteriorated since it is impossible to accurately determine the reaction position in the depth direction.

In addition, the conventional technique for accurately measuring the reaction position of the photon in the conventional position-sensitive radiation detector is a signal waveform analysis method. This is a technique that uses the correlation between the rise time of the signal and the depth of response in the detector when the signal is generated by the radiation.

However, this is a technique for revealing the correlation between the rise time of the signal and the reaction depth in the detector when the signal is generated through the repetitive experiment, there is a problem that the analysis time due to the repetitive experiment is increased.

Accordingly, the present invention has been made to solve the above problems, and the first object of the present invention is to predict and determine the reaction depth in the absorber detector from the energy of photons detected inside the absorber detector in advance. The present invention provides an image resolution improving apparatus for a Compton camera capable of improving an image resolution of a Compton camera and a method of improving the resolution of an image using the same.

The second object of the present invention is to advance the reaction depth in the absorber detector from the energy of photons detected inside the absorber detector within a short time without using a signal waveform analysis method which experimentally detects the reaction depth in the absorber detector of the photons. An object of the present invention is to provide an image resolution improving apparatus for a Compton camera and a method for improving the resolution of an image using the same.

In order to achieve the above object, the image resolution improving apparatus for a Compton camera of the present invention is a source that emits photons and a scattering unit that is spaced apart from the source and scatters Compton scattered photons emitted from the source. A detector, an absorption part detector spaced apart from the scattering part detector by a predetermined distance, the absorption part detector for determining the reaction depth of the photon according to the scattered photon energy, and an image acquisition part acquiring an image of the photons according to the determined reaction depth. do.

Here, the source and the absorber detector may be arranged in parallel with each other with respect to the scattering detector and form the same separation distance from each other.

In addition, it is preferable to use a 364.5 keV point source in consideration of ¹³¹ I.

In addition, the absorber detector is stored a trend equation for determining the reaction depth of the photon,

When the trend equation is the 364.5 keV dotted circle,

ego,

The d is the reaction depth, E is preferably the energy absorbed by the absorption detector of the photon.

In addition, the crew by may use the 511 keV dotted circle in consideration of the ¹⁸ F.

In this case, the absorber detector stores a trend formula for determining the reaction depth of the photon.

When the trend equation is the 511 keV dotted line source,

ego,

The d is the reaction depth, E is preferably the energy absorbed by the absorption detector of the photon.

In order to achieve the above object, the image resolution enhancing apparatus for a Compton camera of the present invention and a method for improving the resolution of an image using the same include: emitting photons through a source and using the scattering detector; Pn scattering, determining the reaction depth according to the energy of the photons absorbed by the absorber using the absorber detector, and acquiring an image of the photon according to the determined reaction depth through the image acquisition unit It includes.

In this case, it is preferable that a trend equation along a dotted line having different energy levels is set in the absorber detector, and the reaction depth of the photons is determined according to the trend equation.

In the case of using a 364.5 keV point source in consideration of ¹³¹ I as the source,

The above trend is

ego,

The d is the reaction depth, E is preferably the energy absorbed by the absorption detector of the photon.

In addition, in the case of using a 511 keV dotted line in consideration of ¹⁸ F as the source,

The above trend is

ego,

The d is the reaction depth, E is preferably the energy absorbed by the absorption detector of the photon.

In addition, the scattering unit detector and the absorbing unit detector are preferably spaced apart from each other by 6 cm, and arranged to be parallel to each other.

Hereinafter, with reference to the accompanying drawings, it will be described an image resolution improving apparatus for a Compton camera of the present invention and a method of improving the resolution of the image using the same.

First, an image resolution improving apparatus for a Compton camera of the present invention will be described.

1 is a perspective view showing an image resolution improving apparatus for a Compton camera of the present invention.

Referring to FIG. 1, an apparatus for improving image resolution of a Compton camera according to the present invention includes a source 100 emitting photons and a source spaced apart from the source 100 by a predetermined distance to scatter the emitted photons. The scattering detector 200 and the scattering detector 200 are spaced apart from the scattering detector 200 to determine the depth of response of the photons according to the energy of the scattered photons (see Equation 1 and 2 below). And a sub detector 300 and an image acquisition unit 400 for acquiring an image of a photon according to the determined reaction depth d. At this time, the front surface of the absorber detector 300 is a time point for determining the reaction depth, and the rear surface is an end point for determining the reaction depth.

The source 100 and the absorber detector 300 are arranged to be spaced apart from each other by a predetermined distance, preferably 6 cm, with respect to the scattering detector 200 and arranged side by side.

In addition, in the present invention, the Doppler energy spreads, the energy resolution of the scattering detector 200 and the absorbing detector 300, the screening level, and the reaction position resolution by splitting the detectors 200 and 300. Compton cameras were computerized in consideration of the various detector factors influencing.

Here, the computer simulation uses a version 8.1 of the GEANT4 toolkit, which is a general Monte Carlo radiation transport code.

Trend formulas are preset in the absorber detector 300. The trend equations may be determined by the energy of the dotted line source.

In the present invention, 364.5 keV dotted lines and 511 keV dotted lines were computerized in consideration of the isotopes ¹³¹ I and ¹⁸ F that are used in the field of nuclear medicine imaging as the source 100.

First, a case in which a 364.5 keV point source is used in consideration of ¹³¹ I as the source 100 will be described.

In this case, the following [formula 1] applies.

..[식1]

[Equation 1]

Here, d is the reaction depth, and E is the energy in KeV units absorbed by the absorber detector 300 of the photon.

Next, a case in which 511 keV dotted line circles are used in consideration of ¹⁸ F as the source 100 will be described.

In this case, the following [formula 2] applies.

..[식2]

[Equation 2]

Here, d is the reaction depth, and E is the energy in KeV units absorbed by the absorber detector 300 of the photon.

Next, an image resolution improving apparatus for a Compton camera of the present invention and a method of improving the resolution of an image using the same will be described.

The present invention generates effective reactions by computing the Compton camera by Monte Carlo simulation method, and between the energy delivered to the absorber detector 300 and the reaction depth (d) at this time with respect to the generated effective reactions. Analyze the relationship. In addition, based on the analyzed data, the correlation is derived as a trend equation, and the derived trend equation is preset in the absorber detector 300.

That is, the present invention does not assume that the reaction depth d is simply 10 mm when the photon Compton scattered in the scatter detector 200 is absorbed by the absorber detector 300, the trend according to the present invention The image resolution can be improved by using the equation to make the most predictive decision.

 Then, in order to quantitatively evaluate how much the image resolution of the Compton camera is improved by applying this method, the image of the Compton camera with respect to the dotted circle and the corresponding profile are obtained, and then the image resolution is measured at the half width (FWHM). Compare.

6 is a flowchart illustrating a method of improving resolution of an image using the image resolution enhancing apparatus for a Compton camera of the present invention.

This will be explained in more detail.

1 and 6, the image resolution improving apparatus for a Compton camera of the present invention and a method for improving the resolution of an image using the same emit photons through the source 100 (S100). At this time, the trajectory of this photon has information about the position of the source 100.

The emitted photons are delivered to the scatter detector 200 to calculate information about the position. The scattering detector 200 causes the photons to be Compton scattered (S200). The scatterer detector 200 may measure the three-dimensional position where the scattering is generated and the quantum conversion energy of photons.

Subsequently, the scattered photons are transmitted to the absorber detector 300. The absorber detector 300 may measure the three-dimensional position and the quantum conversion energy of photons in which energy is lost by photoelectric effect.

Figure 2 is a graph showing the reaction depth according to the energy delivered to the absorber detector for the 364.5 keV dotted line according to the present invention. 3 is a graph showing the reaction depth according to the energy delivered to the absorber detector for the 511 keV dotted line according to the present invention.

2 and 3, at this time, the energy in keV units measured by the absorber detector 300 is substituted into a trend equation according to a dotted line, and the depth of reaction inside the absorber detector 300 of the photon is measured. (d) is calculated and determined (S300).

Here, in the present invention, since 364.5 keV dotted line and 511 keV dotted line are simulated in consideration of the isotopes ¹³¹ I and ¹⁸ F used in the field of nuclear medicine imaging as the source 100, there are two trend equations according to the present invention. Can be

First, in the case of using a 364.5 keV point source in consideration of ¹³¹ I as the source 100, the following equation is applied.

..[식1]

[Equation 1]

Second, when using a 511 keV dotted line in consideration of ¹⁸ F as the source 100, the following formula is applied to the trend equation.

..[식2]

[Equation 2]

Here, d is the reaction depth, and E is the energy in keV absorbed by the absorption detector of the photon.

Therefore, the present invention determines the reaction depth (d) of the absorber detector 300 by applying the above trend equation.

Subsequently, an image of the photon having the determined reaction depth d is acquired through the image acquisition unit 400.

In this way, the profile and the image resolution of the image acquired through the image acquisition unit 400 are compared with reference to FIGS. 4A to 5B.

FIG. 4A is a diagram showing an image of a 364.5 keV dotted circle obtained using a conventional Compton camera. FIG. 4B is a view showing an image of a 364.5 keV dotted circle obtained using the image resolution enhancing apparatus for a Compton camera of the present invention. FIG. 5A illustrates an image of a 511 keV dotted line obtained using a conventional Compton camera. FIG. FIG. 5B is a diagram showing an image of a 511 keV dotted circle obtained using the image resolution enhancing apparatus for a Compton camera of the present invention.

4A and 4B, in the case of a 364.5 keV dotted circle, the full width at half maximum (FWHM) was improved from 10.1 mm to 6.9 mm.

5A and 5B, in the case of a 511 keV dotted line, the full width at half maximum (FWHM) was improved from 9.4 mm to 8.1 mm.

In the case of the low energy source 100, the improvement of the image resolution is larger because the energy of the scattered photons entering the absorber detector 300 is lower than that of the high energy source 100. This is because the reaction depth d is not relatively deep.

Therefore, the distribution of the reaction depth (d) is formed in a relatively narrow range, it is determined by predicting to a closer value using the trend equations in the present invention.

In addition, as the scattered photons have a low energy, the probability of reacting at the front surface of the absorber detector 300 increases, and the distance from the center depth of the absorber detector 300 increases.

Accordingly, the present invention further improves the image resolution than assuming that the center depth of the absorber detector 300 is a reaction depth.

For this reason, the trend equations in the present invention can significantly improve the image resolution in the case of a lower energy source 100 than in the case of a high energy source 100 when applied.

As described above, the present invention has the effect of predicting and determining the reaction depth in the absorber detector from the energy of photons detected inside the absorber detector in advance, thereby improving the image resolution of the Compton camera. .

In addition, the present invention predicts the reaction depth in the absorber detector in advance from the energy of photons detected within the absorber detector in a short time without using a signal waveform analysis method for experimentally detecting the reaction depth in the absorber detector of the photon. It has an effect that can be determined.

Claims (11)

Sources that emit photons; A scattering detector which is spaced apart from the source and scatters the photons emitted from the source by Compton; An absorber detector spaced apart from the scattering detector by a predetermined distance and determining a reaction depth of the photon according to the energy of the scattered photons; And And an image acquiring unit for acquiring an image of a photon according to the determined reaction depth. The method of claim 1, And the source and the absorber detector are disposed in parallel with each other at the scattering detector and form the same separation distance from each other. The method of claim 1, And a 364.5 keV point source in consideration of ¹³¹ I as the source. The method of claim 3, The absorber detector is stored a trend equation for determining the reaction depth of the photon, When the trend equation is the 364.5 keV dotted circle,

This, And d is the reaction depth, and E is energy absorbed by the absorber detector of the photon. The method of claim 1, Compton camera image resolution enhancement apparatus which is characterized in that the crew is to use a 511 keV dotted circle in consideration of the ¹⁸ F. The method of claim 5, The absorber detector is stored a trend equation for determining the reaction depth of the photon, When the trend equation is the 511 keV dotted line source,

This, And d is the reaction depth, and E is energy absorbed by the absorber detector of the photon. Emitting photons through the source; Compton scattering the emitted photons using a scatter detector; Determining the reaction depth according to the energy of the photons absorbed by the absorber using an absorber detector; And And obtaining an image of a photon according to the determined reaction depth through an image acquisition unit. The method of claim 7, wherein The absorber detector is preset with a trend equation along dotted lines with different energy levels, and the depth of response of the photons is determined according to the trend equation. How to improve. The method of claim 8, In case of using a 364.5 keV point source considering ¹³¹ I as the source, The above trend is

ego, Wherein d is the reaction depth, E is the energy absorbed by the absorption detector of the photon, the resolution of the image using the image resolution improving device for a Compton camera. The method of claim 8, In the case of using a 511 keV dotted line in consideration of ¹⁸ F as the source, The above trend is

ego, Wherein d is the reaction depth, E is the energy absorbed by the absorption detector of the photon, the resolution of the image using the image resolution improving device for a Compton camera. The method of claim 7, wherein And the scattering detector and the absorbing detector are spaced apart from each other by 6 cm with respect to the source and arranged in parallel with each other.

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