JP4064541B2 - Reference signal generating method and apparatus, and radiation tomography apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reference signal generation method and apparatus and a radiation tomography apparatus, and more particularly to a method and apparatus for generating a reference signal for correcting a detection signal of a radiation detector, and a reference signal generation apparatus. The present invention relates to a radiation tomography apparatus.
[0002]
[Prior art]
An example of a radiation tomography apparatus is an X-ray CT (computed tomography) apparatus. In the X-ray CT apparatus, X-rays are used as radiation. An X-ray tube or a linear accelerator is used for X-ray generation. Then, the radiation irradiation / detection device, that is, the X-ray irradiation / detection device is rotated (scanned) around the subject, and the X-rays of the subject are respectively observed in a plurality of view directions around the subject. Projection data (data) is measured, and a tomographic image is generated (reconstructed) based on the projection data.
[0003]
The X-ray irradiation apparatus irradiates an X-ray beam (beam) having a width including the imaging range and a predetermined thickness in a direction perpendicular thereto. The X-ray detection apparatus detects X-rays by a multi-channel X-ray detector in which a number of X-ray detection elements are arranged in an array in a direction perpendicular to the traveling direction of the X-ray beam.
[0004]
Several X-ray detection elements at both ends of the X-ray detector are arranged so as to be outside the range in which the subject is projected, and are directly irradiated with the X-ray beam. These X-ray detection elements are called a reference channel. The detection signal of the reference channel is used for X-ray intensity correction of measurement data as a reference signal representing the intensity of the X-ray beam. For the X-ray intensity correction, an average value of reference signals detected at both ends of the X-ray detector is used.
[0005]
[Problems to be solved by the invention]
In the above case, only one of the reference channels at both ends is blocked by the subject, the reference signal becomes inaccurate, an error occurs in the X-ray intensity correction of the measurement data, and the reconstructed image has an artifact. There was a problem of causing this.
[0006]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a reference signal generation method and apparatus for correctly generating a reference signal, and a radiation tomography apparatus including such a reference signal generation apparatus. Is to realize.
[0007]
[Means for Solving the Problems]
(1) A first invention for solving the above-described problem is to detect radiation irradiated from a radiation source with a radiation detection element array in which a plurality of radiation detection elements are arranged in an array, and both ends of the radiation detection element array A reference signal generation method for generating a reference signal based on detection signals of radiation detection elements positioned at each of the radiation detection elements, wherein at least one end of the radiation detection elements positioned at both ends of the radiation detection element array When the value of the detection signal of the detection element is equal to or greater than a specified value and the ratio of the detection signal values of the radiation detection elements located at both ends of the radiation detection element array is substantially 1, the radiation detection An average value of detection signals of the radiation detection elements positioned at both ends of the element array is used as a reference signal, and the radiation Of the radiation detection elements positioned at both ends of the detection element array, the radiation detection elements at least at one end have a detection signal value equal to or greater than a specified value, and the radiations positioned at both ends of the radiation detection element array, respectively. When the ratio of the detection signal values of the detection elements is not substantially 1, the larger one of the detection signals of the radiation detection elements located at both ends of the radiation detection element array is used as a reference signal. This is a characteristic reference signal generation method.
[0008]
(2) A second invention for solving the above-described problem is to detect radiation irradiated from a radiation source with a radiation detection element array in which a plurality of radiation detection elements are arranged in an array, and both ends of the radiation detection element array. A reference signal generation device for generating a reference signal based on detection signals of radiation detection elements located at each of the radiation detection elements, wherein at least one radiation of the radiation detection elements located at both ends of the radiation detection element array A ratio between the first determination means for determining whether or not the value of the detection signal of the detection element is equal to or greater than a specified value and the value of the detection signal of the radiation detection element located at each end of the radiation detection element array is Both the second determination means for determining whether or not it is substantially 1 and the determination results of the first determination means and the second determination means are “true”. In this case, the average value of the detection signals of the radiation detection elements located at both ends of the radiation detection element array is used as a reference signal, the determination result of the first determination means is “true”, and the second A reference signal generating means that uses a larger value of detection signals of the radiation detection elements located at both ends of the radiation detection element array as a reference signal when the determination result of the determination means is “false”; It is a reference signal generating device characterized by comprising.
[0009]
(3) A third invention for solving the above-mentioned problem has a radiation irradiation means for irradiating a radiation beam and a radiation detection element array in which a plurality of radiation detection elements are arranged in an array, and is irradiated from the radiation irradiation means. Whether the value of the detection signal of the radiation detection element at least one end of the radiation detection means for detecting the radiation and the radiation detection element located at both ends of the radiation detection element array is equal to or greater than a specified value And a second determination for determining whether or not the ratio of detection signal values of the radiation detection elements located at both ends of the radiation detection element array is substantially 1, respectively. And when the determination results of the first determination means and the second determination means are both “true”, the radiation detection elements respectively located at both ends of the radiation detection element array When the determination result of the first determination means is “true” and the determination result of the second determination means is “false”, both ends of the radiation detection element array are used as reference signals. A reference signal generation unit that uses a larger value of detection signals of the radiation detection elements located in the respective sections as a reference signal, and a detection signal of the radiation detection unit based on the reference signal generated by the reference signal generation unit And a tomographic image generating unit for generating a tomographic image of the radiation beam passage region based on the radiation detection signals of the plurality of views of the radiation detecting unit corrected by the correcting unit. This is a radiation tomography apparatus.
[0010]
In the third invention, it is preferable that the radiation beam is a fan beam from the viewpoint of efficiently collecting view data.
(Function)
In the present invention, when there is no abnormality in the signals of the reference channels at both ends of the radiation detection element array, the average value thereof is used as a reference signal, and when either one is abnormal, the normal one is automatically selected.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiment. FIG. 1 shows a block diagram of an X-ray CT apparatus. This apparatus is an example of an embodiment of the radiation tomography apparatus of the present invention. An example of an embodiment relating to the apparatus of the present invention is shown by the configuration of the apparatus. An example of an embodiment related to the method of the present invention is shown by the operation of the apparatus.
[0012]
As shown in FIG. 1, the apparatus includes a scanning gantry 2, an imaging table 4, and an operation console 6. The scanning gantry 2 has an X-ray tube 20 as a radiation source. The X-ray tube 20 is an example of an embodiment of a radiation source in the present invention. X-rays (not shown) radiated from the X-ray tube 20 are shaped by the collimator 22 into, for example, a fan-shaped X-ray beam, that is, a fan beam, and are irradiated to the detector array 24. The X-ray tube 20 and the collimator 22 are an example of an embodiment of radiation irradiating means in the present invention.
[0013]
The detector array 24 is an example of an embodiment of the radiation detection element array in the present invention. Moreover, it is an example of embodiment of the radiation detection means in this invention. The detector array 24 has a plurality of X-ray detection elements arranged in an array in the direction of the width of the fan-shaped X-ray beam. The configuration of the detector array 24 will be described later.
[0014]
The X-ray tube 20, the collimator 22, and the detector array 24 constitute an X-ray irradiation / detection device. The configuration of the X-ray irradiation / detection apparatus will be described later. A data collection unit 26 is connected to the detector array 24. The data collecting unit 26 collects detection data of individual X-ray detection elements of the detector array 24.
[0015]
X-ray irradiation from the X-ray tube 20 is controlled by an X-ray controller 28. The connection relationship between the X-ray tube 20 and the X-ray controller 28 is not shown. The collimator 22 is controlled by a collimator controller 30. The connection relationship between the collimator 22 and the collimator controller 30 is not shown.
[0016]
The X-ray tube 20 to the collimator controller 30 described above are mounted on the rotating unit 32 of the scanning gantry 2. The rotation of the rotating unit 32 is controlled by the rotation controller 34. The connection relationship between the rotating unit 32 and the rotation controller 34 is not shown.
[0017]
The imaging table 4 carries a subject (not shown) into and out of the X-ray irradiation space of the scanning gantry 2. The relationship between the subject and the X-ray irradiation space will be described later.
[0018]
The operation console 6 has a central processing unit 60. The central processing unit 60 is an example of an embodiment of the first determination means in the present invention. Moreover, it is an example of embodiment of the 2nd determination means in this invention. Moreover, it is an example of embodiment of the reference signal production | generation means in this invention. Moreover, it is an example of embodiment of the correction | amendment means in this invention. Moreover, it is an example of embodiment of the tomographic image generation means in this invention.
[0019]
The central processing unit 60 is configured by, for example, a computer. A control interface 62 is connected to the central processing unit 60. The control gantry 2 and the imaging table 4 are connected to the control interface 62.
[0020]
The central processing unit 60 controls the scanning gantry 2 and the imaging table 4 through the control interface 62. The data collection unit 26, the X-ray controller 28, the collimator controller 30 and the rotation controller 34 in the scanning gantry 2 are controlled through the control interface 62. Note that illustration of individual connections between these units and the control interface 62 is omitted.
[0021]
A data collection buffer 64 is also connected to the central processing unit 60. A data collection unit 26 of the scanning gantry 2 is connected to the data collection buffer 64. Data collected by the data collection unit 26 is input to the data collection buffer 64. The data collection buffer 64 temporarily stores input data. A storage device 66 is also connected to the central processing unit 60. The storage device 66 stores various data, reconstructed images, programs, and the like.
[0022]
Further, a display device 68 and an operation device 70 are connected to the central processing unit 60, respectively. The display device 68 displays a reconstructed image and other information output from the central processing unit 60. The operation device 70 is operated by an operator and inputs various instructions and information to the central processing device 60.
[0023]
FIG. 2 shows a schematic configuration of the detector array 24. The detector array 24 forms a multi-channel X-ray detector in which a large number (for example, 1000) of X-ray detection elements 24 (i) are arranged in an arc shape. i is a channel number, for example, i = 1 to 1000. The X-ray detection element 24 (i) is an example of an embodiment of the radiation detection element in the present invention. At both ends of the detector array 24, a plurality of reference X-ray detection elements, that is, reference channels 14, are provided.
[0024]
FIG. 3 shows the interrelationship among the X-ray tube 20, the collimator 22, and the detector array 24 in the X-ray irradiation / detection apparatus. 3A is a front view, and FIG. 3B is a side view. As shown in the figure, the X-rays radiated from the X-ray tube 20 are shaped by the collimator 22 into a fan-shaped X-ray beam 40 and irradiated to the detector array 24. FIG. 3A shows the spread of the fan-shaped X-ray beam 40, that is, the width of the X-ray beam 40. In FIG. 3B, the thickness of the X-ray beam 40 is shown.
[0025]
The body axis is crossed over the fan surface of the X-ray beam 40, and the subject 8 placed on the imaging table 4 is carried into the X-ray irradiation space, for example, as shown in FIG. A projection image of the subject 8 sliced by the X-ray beam 40 is projected onto the detector array 24. The thickness of the X-ray beam 40 at the isocenter of the subject 8 gives the slice thickness th of the subject 8. The slice thickness th is determined by the aperture of the collimator 22.
[0026]
The operation of this apparatus will be described. FIG. 5 shows a flow diagram of the operation of the apparatus. As shown in the figure, in step 502, the operator sets shooting conditions through the operation device 70.
[0027]
Next, in step 504, scanning is performed based on an instruction from the operator. That is, under the control of the central processing unit 60, the X-ray irradiation / detection device comprising the X-ray tube 20, the collimator 22 and the detector array 24 is around the body axis of the subject 8 while maintaining their mutual relationship. Is rotated (scanned), and projection data of the subject is collected at a plurality of (for example, 1000) view angles per one rotation of the scan. The projection data is collected by the system of detector array 24 -data collection unit 26 -data collection buffer 64.
[0028]
Next, in step 506, the central processing unit 60 preprocesses the collected projection data. Preprocessing includes logarithmic conversion, X-ray intensity correction of measurement data based on the detection signal of the reference channel 14, and other predetermined corrections such as offset correction and sensitivity correction. The details of the X-ray intensity correction will be described later.
[0029]
Next, in step 508, the central processing unit 60 performs tomographic image generation, that is, image reconstruction. The image reconstruction is performed by processing, for example, 1000 views of projection data obtained by one rotation scan by, for example, a filtered back projection method. The reconstructed image is stored in the storage device 66 and displayed as a visible image on the display device 68 in step 510.
[0030]
A detailed flowchart of the preprocessing in step 506 is shown in FIG. As shown in the figure, in step 602, any one of the reference signals REFa and REFb respectively obtained from the reference channels 14 at both ends of the detector array 24 is equal to or greater than a predetermined reference value REF. Determine whether or not. The value of the reference value REF is, for example, 90% of the value of the reference signal obtained when the intensity of the X-ray beam 40 and the sensitivity of the reference channel 14 are normal.
[0031]
The reference signals REFa and REFb are preferably average values of the detection signals of the reference channel 14 at both ends of the detector array 24, from the viewpoint of obtaining a reference signal with little influence of noise.
[0032]
If it is determined that neither of the reference signals REFa and REFb has reached the reference value REF, reference abnormality is displayed on the display device 68 in step 604, and the subsequent processing is continued.
[0033]
If it is determined that one of the reference signals REFa or REFb is greater than or equal to the reference value REF, that is, if the determination result is “true” (Yes), the ratio of the reference signals REFa and REFb is obtained in step 606. Then, it is determined whether or not the absolute value of the difference between this ratio and 1 is within a predetermined error e. The value of the predetermined error e is, for example, 0.1. Thus, it is determined whether or not the ratio of the reference signals REFa and REFb is substantially 1. Even if the reference value REF and the error e are not necessarily the above values, the effect of the present invention can be exhibited.
[0034]
When the ratio of the reference signals REFa and REFb is substantially 1, that is, when the determination result is “true” (Yes), the average value of the reference signals REFa and REFb is obtained in step 608 and obtained. Use the reference value. The ratio of the reference signals REFa and REFb becomes substantially 1 when, for example, the reference channel 14 at both ends of the detector array 24 is normally irradiated with the X-ray beam 40 as shown in FIG. Therefore, the reference signals REFa and REFb are both normal, and their average value may be used as the reference value. Of course, not only the average value but also the MOD (middleof data) value of REFa and REFb, that is, an intermediate value may be adopted. In this specification, in addition to the above-described addition average value, the MOD value and the multiplication average value are also included in the category of average values in a broad sense.
[0035]
When the ratio of the reference signals REFa and REFb is not substantially 1, that is, when the determination result is “false” (No), the larger one of the reference signals REFa and REFb is selected in step 610. This is the reference value. The ratio of the reference signals REFa and REFb is not substantially 1, for example, as shown in FIG. 8, the X-ray beam 40 is normally applied to the reference channel 14 at one end of the detector array 24 (the right end in the figure). However, the reference channel 14 is blocked by the subject 8 at the other end (left end in the figure). In such a case, an X-ray detection signal smaller than the reference value REF is generated when it is blocked by the subject 8. Therefore, by selecting the larger value, a normal reference signal can be obtained.
[0036]
In this way, a normal reference signal can be obtained as long as the X-ray beam is normally applied to at least one of the reference channels 14 at both ends of the detector array 24.
[0037]
Next, in step 612, X-ray intensity correction is performed on the measurement data using the reference signal obtained as described above. Since the reference signal is a normal signal, the X-ray intensity correction can be performed correctly, and the occurrence of artifacts in the reconstructed image can be eliminated. X-ray intensity correction is performed, for example, by subtracting measurement data from the reference signal after logarithmic conversion. Alternatively, before logarithmic conversion, the value of the reference signal is divided by the value of the measurement data.
[0038]
In the above, an example in which the radiation tomography apparatus is a medical X-ray CT apparatus has been described. However, the present invention is not limited to medical use. Needless to say. The X-ray CT apparatus in that case is not limited to the so-called third-generation X-ray CT apparatus of the above-described rotate-rotate system, but is a so-called second of the translate-rotate system. Of course, it may be a generation X-ray CT apparatus.
[0039]
Further, although an example using X-rays as radiation has been described, the radiation is not limited to X-rays, and may be other types of radiation such as γ-rays, for example. However, at the present time, X-rays are preferred in that they have the most practical means for their generation, detection and control.
[0040]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to realize a reference signal generation method and apparatus that correctly generates a reference signal, and a radiation tomography apparatus including such a reference signal generation apparatus.
[Brief description of the drawings]
FIG. 1 is a block diagram of an exemplary apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a detector array in an apparatus according to an example of an embodiment of the present invention.
FIG. 3 is a schematic configuration diagram of an X-ray irradiation / detection apparatus in an apparatus according to an example of an embodiment of the present invention.
FIG. 4 is a schematic configuration diagram of an X-ray irradiation / detection apparatus in an apparatus according to an example of an embodiment of the present invention.
FIG. 5 is a flowchart of the operation of the apparatus according to the embodiment of the present invention.
FIG. 6 is a flowchart of the operation of the apparatus according to the embodiment of the present invention. .
FIG. 7 is a schematic diagram showing a reference signal detection state in an apparatus according to an example of an embodiment of the present invention.
FIG. 8 is a schematic diagram showing a reference signal detection state in an apparatus according to an example of an embodiment of the present invention.
[Explanation of symbols]
2 Scanning gantry 20 X-ray tube 22 Collimator 24 Detector array 24 (i) X-ray detection element 26 Data collection unit 28 X-ray controller 30 Collimator controller 32 Rotating unit 34 Rotating controller 4 Imaging table 6 Operation console 60 Central processing unit 62 Control Interface 64 Data acquisition buffer 14 Reference channel 40 X-ray beam 8 Subject

Claims (3)

A radiation detection element array in which a plurality of radiation detection elements are arranged in an array detects radiation irradiated from a radiation source, and a reference signal based on detection signals of radiation detection elements respectively positioned at both ends of the radiation detection element array A reference signal generation method for generating
The value of the detection signal of the radiation detection element at least at one end of the radiation detection elements positioned at both ends of the radiation detection element array is equal to or greater than a specified value, and is positioned at both ends of the radiation detection element array. When the ratio of detection signal values of the radiation detection elements is substantially 1 and both detection signals are determined to be normal, the detection signals of the radiation detection elements located at both ends of the radiation detection element array, respectively. The average value of is the reference signal,
The value of the detection signal of the radiation detection element at least at one end of the radiation detection elements positioned at both ends of the radiation detection element array is equal to or greater than a specified value, and is positioned at both ends of the radiation detection element array. When the ratio of the detection signal values of the radiation detection elements is substantially 1 , and only one of the detection signals is determined to be normal, the radiation detection elements of the radiation detection elements respectively positioned at both ends of the radiation detection element array The larger one of the detection signals is used as a reference signal.
A reference signal generation method characterized by the above. A radiation detection element array in which a plurality of radiation detection elements are arranged in an array detects radiation irradiated from a radiation source, and a reference signal based on detection signals of radiation detection elements respectively positioned at both ends of the radiation detection element array A reference signal generator for generating
First determination means for determining whether or not a value of a detection signal of a radiation detection element at least at one end of the radiation detection elements located at both ends of the radiation detection element array is equal to or greater than a specified value;
It is determined whether or not any detection signal is normal by determining whether or not the ratio of the detection signal values of the radiation detection elements located at both ends of the radiation detection element array is substantially 1, respectively. a second determination means for,
When both the determination results of the first determination unit and the second determination unit are “true”, the average value of the detection signals of the radiation detection elements located at both ends of the radiation detection element array is used as a reference signal. And when the determination result of the first determination means is “true” and the determination result of the second determination means is “false”, the radiation detection elements respectively positioned at both ends of the radiation detection element array A reference signal generating means that uses a larger value of the detection signals of the reference signal as a reference signal;
A reference signal generating device comprising: Radiation irradiating means for irradiating a radiation beam; radiation detecting means for detecting radiation irradiated from the radiation irradiating means having a radiation detecting element array in which a plurality of radiation detecting elements are arranged in an array;
Any detection signal is determined by determining whether or not the value of the detection signal of the radiation detection element at least one of the radiation detection elements located at both ends of the radiation detection element array is equal to or greater than a specified value. First judging means for judging whether or not normal ,
Second determination means for determining whether a ratio of detection signal values of the radiation detection elements located at both ends of the radiation detection element array is substantially 1, the first determination means; When both of the determination results of the second determination means are “true”, an average value of detection signals of the radiation detection elements located at both ends of the radiation detection element array is used as a reference signal, and the first determination is performed. When the determination result of the means is “true” and the determination result of the second determination means is “false”, the value of the detection signals of the radiation detection elements respectively located at both ends of the radiation detection element array is A reference signal generator that uses the larger one as a reference signal;
Correction means for correcting the detection signal of the radiation detection means based on the reference signal generated by the reference signal generation means;
A tomographic image generating means for generating a tomographic image of the radiation beam passing region based on the radiation detection signals of the plurality of views of the radiation detecting means corrected by the correcting means;
A radiation tomography apparatus comprising:

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