JP4915322B2 - Nuclear medicine equipment - Google Patents

Description

  The present invention provides a photon detection means comprising a scintillator and a photomultiplier tube in a gantry for inserting / removing a subject, and is generated from a radioactive source such as a radiopharmaceutical containing a radioisotope administered to the subject. A nuclear medicine device configured to detect and convert photons, such as gamma rays, into electrical signals, detect photons based on the electrical signals, determine the position of the radioactive source in the subject, and perform imaging processing About.

As this kind of nuclear medicine device, there was the following.
That is, a dual camera head is provided, and the camera head is provided with a scintillator that flashes when receiving gamma rays, and a photomultiplier tube is arranged behind the scintillator. When a signal is output from the camera head, the energy of the incident gamma ray is calculated and output to a two-channel window circuit.
In the window circuit, the energy window is set according to the photoelectric peak of the gamma ray emitted from the radioactive source, and when the energy signal from the energy calculator is within the energy window, one pulse is output to the counter circuit. It is configured as follows.
The concentration distribution of the radioisotope in the cross section of the subject is reconstructed based on the calculated value in the counter circuit (see Patent Document 1).

A scintillator block is formed by bundling a plurality of layers of scintillators having two or more different decay times in the depth direction, and the scintillator block is coupled to the position-sensitive optical sensor. There is also a PET detector configured to obtain position information in the Y direction (see Patent Document 2).
JP-A-11-352233 JP 2000-56023 A

However, the above-described conventional example has the following problems.
For example, in the positron emission tomograph (PET), 511 keV pair annihilation photons are detected, so the energy window is set to 400 keV to 700 keV with respect to the energy output from the photon detection means. A common value is set for the photon detection means.

However, in the photon detection means having self-radiation, even if the setting is optimized in the common energy window as described above, it contains more unnecessary components (scattered rays and noise components). Unnecessary coincidence count becomes incorrect position information, and there is a disadvantage that the image quality of the obtained image is lowered.
On the other hand, if the energy window is set narrow with respect to the photon detection means having a low resolution, the true count is lowered, and in this case, there is a disadvantage that the image quality of the obtained image is lowered. .

  The present invention has been made in view of the circumstances as described above, and is obtained by individually setting the energy window for each photon detection means, performing counting with as high accuracy as possible, and collecting position information. It is an object to improve the image quality of a recorded image.

The invention according to claim 1 has the following configuration in order to achieve the above-described object.
That is, a photon detection means arranged in a ring shape so as to surround the subject in the gantry, detects photons generated from the radioactive ray source, emits light, and converts the emitted light energy into an electric signal, and the photon detection means An energy window setting means for setting an energy window for an electrical signal of the image, a data collection circuit section for collecting data passed through the energy window setting means, and image reconstruction based on data collected by the data collection circuit section A nuclear medicine apparatus comprising an image processing unit for creating image data,
The energy window setting means, for each photon detection means, based on the half-value width of the energy spectrum based on the light emission amount or / and the light emission characteristics, from the peak center energy to the high energy side width from the peak center energy. It is characterized in that the energy window is set by setting an upper limit and a lower limit so as to be wider than the width on the low energy side.

(Action / Effect)
According to the configuration of the nuclear medicine apparatus of the first aspect of the present invention, an energy window is set for each photon detection means, and information from each photon detection means is set corresponding to the difference in resolution of each photon detection means. Based on this, it is possible to perform appropriate counting and collect appropriate position information.
Accordingly, since the energy window is individually set for each photon detection means based on the light emission amount or / and the light emission characteristics, counting with the highest possible accuracy is performed regardless of the difference in resolution between the photon detection means. In addition, it is possible to improve the image quality of the image obtained by collecting the position information with high accuracy.
In addition, according to the configuration of the nuclear medicine apparatus of the above-described invention, paying attention to the half-value width of the energy spectrum as a criterion for the difference in resolution of the photon detection means, and setting the energy window based on the half-value width of the energy spectrum, It is possible to perform counting with the highest possible accuracy and improve the image quality of images obtained by collecting positional information with high accuracy.
Further, according to the configuration of the nuclear medicine apparatus of the above-described invention, in addition to the half-value width of the energy spectrum as a criterion for the difference in resolution of the photon detection means, attention is paid to the upper and lower limits, and the center of the half-value width is not set to the peak value. In addition, the widths on the upper limit side and the lower limit side can be appropriately set to desired values from the peak value.
Therefore, for example, when the full width at half maximum is large, the center of the full width at half maximum is set to the side larger than the peak value, and the ratio of the width on the lower limit side that tends to contain a lot of noise components (scattered rays and noise) is set as the upper limit. It is possible to effectively cope with the difference in resolution of each photon detection means, such as reducing the noise component effectively by making it smaller than the width of the side, so that more accurate counting and position information can be performed with high accuracy. The quality of the image obtained by collecting can be improved.

The invention according to claim 2
The nuclear medicine apparatus according to claim 1,
The energy window setting means is configured to set an energy window for each photon detection means based on the detection sensitivity of the pair annihilation photons.

(Action / Effect)
According to the configuration of the nuclear medicine apparatus of the invention of claim 2 , focusing on the detection sensitivity of the pair annihilation photon as a criterion for the difference in resolution of the photon detection means, the energy window is set based on the detection sensitivity of the pair annihilation photon Therefore, it is possible to improve the image quality of an image obtained by performing counting with as high accuracy as possible and collecting position information with high accuracy.

The invention according to claim 3
In the nuclear medicine apparatus according to claim 1 or 2 ,
The photon detection means is constructed by laminating a plurality of scintillators in the depth direction, and includes an energy window setting means corresponding to each scintillator in the depth direction.

(Action / Effect)
According to the configuration of the nuclear medicine apparatus of the invention according to claim 3 , when using the photon detection means configured by stacking a plurality of scintillators in the depth direction, the scintillator having different positions in the depth direction and the light emission energy therefrom There is a difference in the optical path length to the photomultiplier tube that converts the signal into an electric signal, which causes a difference in resolution. Paying attention to this, the energy window is set for each scintillator, so that it is possible to improve the image quality of the image obtained by accurately collecting the position information and collecting the position information, and stacking multiple scintillators in the depth direction. This is more useful when applied to the case where photon detection means configured as described above is used.

As described above, according to the configuration of the nuclear medicine apparatus according to the first aspect of the present invention, an energy window is set for each photon detection means, and each photon is matched with a difference in resolution of each photon detection means. Based on the information from the detection means, it is possible to perform appropriate counting and collect appropriate position information.
Accordingly, since the energy window is individually set for each photon detection means based on the light emission amount or / and the light emission characteristics, counting with the highest possible accuracy is performed regardless of the difference in resolution between the photon detection means. In addition, it is possible to improve the image quality of the image obtained by collecting the position information with high accuracy.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a partially cutaway side view of an embodiment of a nuclear medicine apparatus according to the present invention, and FIG. 2 is an enlarged cross-sectional view of a main part. A subject H is mounted on a support base 1 so as to be movable in the horizontal direction. And a gantry 3 for inserting / removing the subject H mounted on the bed 2 is provided, and the photon detection means 4 is arranged in a ring shape so as to surround the subject H in the gantry 3. ing. In the figure, reference numeral 5 denotes a console for operating the apparatus.

  The photon detection means 4 includes a scintillator 6 that emits light by detecting photons generated from a radioactive ray source, and a photomultiplier tube 7 that converts light emission energy of the scintillator 6 into an electric signal. Two layers of scintillators 6 are stacked in the depth direction, and photomultiplier tubes 7 are provided corresponding to the respective scintillators 6.

  As shown in the block diagram of the image processing configuration in FIG. 3, an energy window setting unit 8 is connected to each photomultiplier tube 7, and each energy window setting unit 8 is connected to a coincidence circuit unit 9. A data collection circuit unit 10 is connected to the coincidence circuit unit 9, an image processing unit 11 is connected to the data collection circuit unit 10, and a monitor 12 is connected to the image processing unit 11.

The energy window setting means 8 is configured to set an energy window for the electric signal from the photomultiplier tube 7. The setting method will be described later.
The coincidence circuit unit 9 is configured to extract data obtained within a so-called coincidence time window as coincidence count data based on the electric signal passed through the energy window setting means 8.
The data collection circuit unit 10 is configured to collect and store the coincidence count data extracted by the coincidence circuit unit 9.
The image processing unit 11 is configured to generate image data by performing image reconstruction based on the coincidence data collected by the data collection circuit unit 10, and output the created image data to the monitor 12 for display. ing.

Next, how to set the energy window by the energy window setting means 8 will be described.
As shown by the graph showing the relationship between the energy spectrum and the half-value width of FIG. 4 (the vertical axis is COUNT, which is the number of events, and the horizontal axis is energy: unit keV), each scintillator 6 is connected to a photomultiplier tube. Focusing on the peak value h of the energy spectrum formed by accumulating the electrical signal output through 7, the energy width ΔE at half height h / 2 of the peak value h is obtained as the half-value width.

As an example, as shown in the graph of the energy spectrum in FIG. 5 (the vertical axis is COUNT, which is the number of events, and the horizontal axis is energy: unit keV), the half-value width ΔE is 82 ch. The full width at half maximum ΔE is about 10 ch, and the resolution is determined to be 12% (≈10 ch ÷ 82 ch × 100). By making this resolution correspond to 511 keV radiation, ΔE = (511 keV × 12 ÷ 100) 61.32 keV is obtained. The full width at half maximum ΔE is recorded.
Next, based on the recorded half width ΔE, for example, the lower limit is set to 1.5 × ΔE, the upper limit is set to 2 × ΔE, and the energy window is set to 418 keV to 635 keV (511 keV−1.5 × ΔE to 511 keV + 2 × ΔE ) And set. It should be noted that 99% of the normal distribution of count data is included in an area having a width three times the half-value width ΔE (418 keV to 604 keV when the resolution is 12%).

  In the above setting, in order to deal with a case where the resolution is extremely poor, it is desirable to set 400 keV to 700 keV as the limit range of the energy window in advance. This is because there is almost no count data with a normal distribution outside this range. In this way, the photon detection means 4 with a low resolution (for example, 18% resolution) can be set to 400 keV to 695 keV, and the photon detection means 4 with a high resolution (for example, 10% resolution) can be set narrowly to 435 keV to 588 keV. Become.

  Further, in the case of the photon detection means 4 of the type in which two layers of the scintillator 6 are laminated as described above, on the side far from the photomultiplier tube 7 (side near the subject H), the side near the photomultiplier tube 7 (the subject) Considering that the resolution is lower than that on the side away from the specimen H), for example, on the side away from the photomultiplier tube 7, the lower limit is 1.5 × ΔE, and the upper limit is 2 × ΔE (restricted range 400 keV to 700 keV). ), And on the side closer to the photomultiplier tube 7 (the side away from the subject H), the lower limit is 1.5 × ΔE, the upper limit is 1.7 × ΔE (restricted range 420 keV to 680 keV), and so on. The energy window may be set differently for each layer together with the limit range. Thereby, the energy window corresponding to the resolution can be set.

The energy window setting means 8 is configured to set an energy window for each photon detection means 4 based on the detection sensitivity of the pair annihilation photons.
That is, the number of events output from each photon detection means 4 and input to the coincidence circuit unit 9 within a set time is measured, an average value of the number of input events is obtained, and the photon detection means 4 larger than the average value is obtained. Then, the number of events input to the coincidence counting circuit unit 9 within a unit time is reduced by 1 or the like, while the photon detection means 4 having a number smaller than the average value is input to the coincidence counting circuit unit 9 within a unit time. It is configured to increase the number of events to be increased by one.

That is, the energy window setting means 8 adjusts the number of events that pass within a unit time, and the energy window is substantially narrowed for the highly sensitive photon detection means 4 so that unnecessary components (scattered rays and noises) are reduced. Component) is effectively removed, and the image quality of the obtained image is improved.
On the other hand, for the low-sensitivity photon detection means 4, the energy window is substantially widened to avoid reducing the true count as much as possible and improve the image quality of the obtained image.

  In the above embodiment, a nuclear medicine apparatus in which two scintillators 6 are stacked in a direction away from the subject H is shown. However, as the present invention, only one is arranged in the circumferential direction, or three or more. The present invention can also be applied when laminating.

  In addition, the present invention is not limited to the case where the initial setting of the energy window for each of the photon detection means 4 is initially set. For example, during normal operation, the photon detection means 4 is input to the coincidence counting circuit unit 9. Electric signals are accumulated, the half-value width of the energy spectrum is obtained every predetermined time, and upper and lower limit calculation formulas given to each photon detection means 4 in advance based on the half-value width (1.5ΔE, 2ΔE, etc. described above) ), And may be configured to make fine adjustment during operation, such as automatically changing the setting of the energy window in the energy window setting means 8 appropriately.

BRIEF DESCRIPTION OF THE DRAWINGS It is a partially broken whole side view of Example 1 of the nuclear medicine apparatus which concerns on this invention. It is an expanded horizontal sectional view of the principal part. It is a block diagram which shows an image processing structure. It is a graph which shows the relationship between an energy spectrum and a half value width. It is a graph which shows an example of an energy spectrum.

Explanation of symbols

3 ... Gantry 4 ... Photon detection means 6 ... Scintillator (photon detection means)
7. Photomultiplier tube (photon detection means)
8 ... Energy window setting means 10 ... Data collection circuit unit 11 ... Image processing unit H ... Subject

Claims (3)

A photon detector arranged in a ring shape so as to surround the subject in the gantry, detecting photons generated from the radioactive radiation source and emitting light, and converting the emitted light energy into an electric signal; and an electric from the photon detector Energy window setting means for setting an energy window for a signal, a data collection circuit section for collecting data that has passed through the energy window setting means, and image data that is reconstructed based on data collected by the data collection circuit section A nuclear medicine apparatus comprising an image processing unit for creating
The energy window setting means, for each photon detection means, based on the half-value width of the energy spectrum based on the light emission amount or / and the light emission characteristics, from the peak center energy to the high energy side width from the peak center energy. A nuclear medicine apparatus, wherein an energy window is set by setting an upper limit and a lower limit so as to be wider than a width on a low energy side. The nuclear medicine apparatus according to claim 1 ,
A nuclear medicine apparatus in which the energy window setting means sets an energy window for each photon detection means based on the detection sensitivity of pair annihilation photons. In nuclear medicine apparatus according to claim 1 or請 Motomeko 2,
A nuclear medicine apparatus comprising a plurality of scintillators arranged in the depth direction as photon detection means, and an energy window setting means corresponding to each scintillator in the depth direction.

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