JP3463002B2 - Radiation tomography equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation tomography apparatus, and more particularly to radiation for correcting radiation transmission data (data) of an object to be imaged by radiation, and generating an image based on the corrected data. The present invention relates to a tomography apparatus.

[0002]

2. Description of the Related Art An example of a radiation tomography apparatus is, for example, an X-ray CT (computed tomograph).
y) There is a device. In the X-ray CT apparatus, X-rays are used as radiation. An X-ray tube is used for X-ray generation. An X-ray irradiating device including an X-ray tube irradiates an X-ray beam (beam) having a width including an imaging range and having a predetermined thickness in a direction perpendicular to the width. The thickness of the X-ray beam can be changed by adjusting the opening of the X-ray passage aperture of the collimator, and thereby the slice thickness of imaging is adjusted. The X-ray detector is
Many in the width direction of the X-ray beam (for example, about 1000)
The X-rays are detected by a multi-channel X-ray detector in which the X-ray detection elements are arranged in an array.

The X-ray irradiation / detection system is rotated (scan) around the object to be imaged,
X-ray transmission data of the imaging target is collected in each of a plurality of view directions around the imaging target. The data collected by the data collection device is transferred to the data processing device. The data processing device generates (reconstructs) a tomographic image based on the transferred X-ray transmission data.

Before image reconstruction, offset correction is performed on the X-ray transmission data. The data used for the offset correction is obtained from the measurement data of the X-ray detector measured without the X-ray irradiation, that is, the offset data. The data acquisition device measures offset data over multiple views prior to each scan and transfers the offset data to the data processing device. The data processing device obtains the average value of the transferred offset data for each channel to obtain the correction data. Then, offset correction is performed by subtracting this correction data from the X-ray transmission data.

[0005]

In the above-mentioned offset correction, the average value, that is, the accuracy of the correction data, improves as the number of measurement views of the offset data increases, but the data transfer rate and the storage in the data processing device side are improved. Due to the limitation imposed by the writing speed of the device, there is a problem that it is not always possible to send offset data with a sufficient number of views, and accurate offset correction cannot be performed.

The present invention has been made to solve the above problems, and an object thereof is to realize a radiation tomography apparatus for performing highly accurate offset correction.

[0007]

(1) A first aspect of the invention for solving the above-mentioned problems is to provide a data collecting means for collecting radiation transmission data and offset data of an object to be imaged by radiation for each of a plurality of views. A radiation tomography apparatus comprising: a correction unit that corrects the radiation transmission data with an average value of the offset data of the plurality of views; and an image generation unit that generates an image based on the corrected data. The collecting means is a radiation tomography apparatus characterized by totalizing the offset data for each predetermined number of views and supplying the sum to the correcting means.

(2) The invention in a second aspect for solving the above-mentioned problems is obtained by dividing the dynamic range of the radiation transmission data by the expected maximum value of the offset data as the predetermined number of views. The radiation tomography apparatus according to (1) is characterized in that a value equal to or smaller than a predetermined value is used.

(3) According to a third aspect of the invention for solving the above-mentioned problems, data collection means for collecting radiation transmission data and offset data of a radiographic object for each of a plurality of views, and the radiation transmission data are provided. A radiation tomography apparatus comprising: a correction unit that corrects with an average value of offset data of the plurality of views; and an image generation unit that generates an image based on the corrected data. The radiation tomography apparatus is characterized in that an average value of view offset data is obtained and supplied to the correction means.

(4) The invention according to a fourth aspect for solving the above-mentioned problems, characterized in that X-rays are used as the radiation, according to any one of (1) and (3). It is a radiation tomography apparatus.

(Operation) In the present invention, the offset data for each predetermined number of views is summed, or the offset data for a plurality of views is averaged in advance to compress the data volume transferred from the data collecting means. As a result, the number of offset data samples can be increased and the accuracy of offset correction can be improved.

[0012]

BEST MODE FOR CARRYING OUT 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 the radiation tomography apparatus. This device is an example of an embodiment of the present invention. The configuration of this device shows an example of an embodiment relating to the device of the present invention.

As shown in FIG. 1, the present apparatus includes a scanning gantry 2 and a photographing table 4.
And an operation console 6. The scanning gantry 2 is an example of an embodiment of the data collecting means in the present invention. The scanning gantry 2 has an X-ray tube 20 as a radiation source. The X-ray (not shown) emitted from the X-ray tube 20 is, for example, a fan-shaped X-ray beam, that is, a fan beam, by the collimator 22.
m), and irradiates the detector array 24. The detector array 24 has a plurality of X-ray detection elements arranged in an array in the width direction of the fan-shaped X-ray beam. The configuration of the detector array 24 will be described later.

The X-ray tube 20, collimator 22 and detector array 24 constitute an X-ray irradiation / detection device. The X-ray irradiation / detection device will be described later again. A data collection unit 26 is connected to the detector array 24.
The data collection unit 26 collects detection data of individual X-ray detection elements of the detector array 24. The data collecting unit 26 will be described later.

The irradiation of X-rays 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 omitted in the figure. The collimator 22 is
It is controlled by the collimator controller 30. The connection relationship between the collimator 22 and the collimator controller 30 is not shown.

The components from the X-ray tube 20 to the collimator controller 30 described above are mounted on the rotating portion 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 omitted in the figure.

The imaging table 4 is adapted to carry an unillustrated imaging object into and out of the X-ray irradiation space of the scanning gantry 2. The relationship between the object to be imaged and the X-ray irradiation space will be described later.

The operation console 6 has a central processing unit 60. The central processing unit 60 is, for example, a computer (c
computer) and the like. The central processing unit 60 is an example of the embodiment of the correction means in the present invention. It is also an example of an embodiment of the image generating means in the present invention.

A control interface 62 is connected to the central processing unit 60. The scanning gantry 2 and the imaging table 4 are connected to the control interface 62. The central processing unit 60 controls the scanning gantry 2 and the imaging table 4 through the control interface 62.

The data acquisition unit 26, X in the scanning gantry 2
The line controller 28, collimator controller 30 and rotation controller 34 are controlled through the control interface 62. It should be noted that illustration of individual connections between these respective units and the control interface 62 is omitted.

A data collection buffer 64 is also connected to the central processing unit 60. Data collection buffer 6
The data acquisition unit 26 of the scanning gantry 2 is connected to the scanning unit 4. The data collected by the data collection unit 26 is input to the data collection buffer 64. Data collection buffer 6
4 temporarily stores the input data.

The central processing unit 60 performs offset correction as described later on the X-ray transmission data of a plurality of views acquired through the data acquisition buffer 64, and reconstructs an image based on the corrected X-ray transmission data. The X-ray transmission data is an example of an embodiment of the radiation transmission data in the present invention. For image reconstruction, for example, a filtered back projection (filtered back projection) is used.
projection method or the like is used. A storage device 66 is also connected to the central processing unit 60. The storage device 66 stores various types of data, reconstructed images, programs, and the like.

The central processing unit 60 also includes a display unit 6
8 and the operating device 70 are connected to each other. The display device 68 displays the reconstructed image and other information output from the central processing unit 60. Operating device 7
0 is operated by the operator to input various instructions and information to the central processing unit 60.

FIG. 2 shows a schematic structure of the detector array 24. The detector array 24 includes a large number of X-ray detection elements 24.
It is a multi-channel X-ray detector in which (i) is arranged. The large number of X-ray detection elements 24 (i) are
An X-ray incident surface curved in a cylindrical concave shape is formed. i is a channel number, for example, i = 1 to 1000.

The X-ray detection element 24 (i) is composed of, for example, a combination of a scintillator and a photo diode. However, the present invention is not limited to this, and may be, for example, a semiconductor X-ray detection element using cadmium tellurium (CdTe) or an ionization chamber type X-ray detection element using xenon (Xe) gas.

FIG. 3 shows the mutual relationship among the X-ray tube 20, the collimator 22 and the detector array 24 in the X-ray irradiation / detection device. 3A is a diagram showing a state viewed from the front, and FIG. 3B is a diagram showing a state viewed from the side. As shown in the figure, the X-rays emitted from the X-ray tube 20 are shaped by the collimator 22 into a fan-shaped X-ray beam 40, and are irradiated onto the detector array 24.

In FIG. 3A, a fan-shaped X-ray beam 40 is formed.
Of the X-ray beam 40. The width direction of the X-ray beam 40 coincides with the arrangement direction of the channels in the detector array 24. In (b), the thickness of the X-ray beam 40 is shown.

By intersecting the body axis with the fan surface of the X-ray beam 40 as described above, for example, as shown in FIG.
The imaging target 8 placed on is loaded into the X-ray irradiation space.
The scanning gantry 2 has a cylindrical structure including an X-ray irradiation / detection device inside.

The X-ray irradiation space is formed in the inner space of the cylindrical structure of the scanning gantry 2. An image of the imaged object 8 sliced by the X-ray beam 40 is projected on the detector array 24. The detector array 24 provides a measurement of the projection of the imaged object 8. The thickness t of the X-ray beam 40 with which the imaging target 8 is irradiated is set by adjusting the aperture of the collimator 22.

FIG. 5 shows a block diagram of the data collection unit 26. As shown in the figure, the data collection unit 26 has a data collection circuit 262, an offset data compression circuit 264, and a data transfer circuit 266. Data collection circuit 262
Collects output data for each channel of the detector array 24. The output data of the detector array 24 is collected over multiple views.

The output data of a plurality of views forms a two-dimensional data space as shown in FIG. 6A, for example. In the data space, the channel number i is one coordinate axis and the view number j is the other coordinate axis. Hereinafter, data in this data space will be referred to as view channel data. View
The channel data consists of a combination of offset data and scan data.

The offset data is X-valued before the start of scanning.
Output data of detector array 24 collected over multiple views in the non-illuminated state. The number of collected views is 512, for example. The scan data is X-ray transmission data of a plurality of views of an imaging target collected by irradiating X-rays.
The number of views is 1024, for example.

The offset data compression circuit 264 compresses offset data for such view channel data. Data compression is performed by summing offset data for each channel for m views. m is 8, for example.

When the number of effective bits of data is 14, for example, the dynamic range (dyn) of 14-bit data is
The atomic range is 16384 when the minimum count is 1. On the other hand, for example, if the expected maximum value of the offset data can be estimated to be 2000 counts or less, the maximum value of the offset data is 16000 counts in total over 8 views. This count is included with a margin in the dynamic range of 14-bit data. Therefore, the eight offset data can be compressed into one data by summing the offset data for each eight views.

Such an offset data compression circuit 26
By the data compression by 4, the view channel data is compressed to 1 / m in the view direction, that is, 1/8, for example, in the view direction, as shown in FIG. 6B. By this, 51
The offset data of 2 views is compressed into a volume of 64 views, so to speak. Conversely speaking, offset data of 512 views can be packed in the offset data space of 64 views.

Generally, when the number of bits of data is k and the expected maximum count of offset data is K, m
Is given by As described above, m means the degree of compression of the volume of offset data, so m is an integer of 2 or more.

[0037]

[Equation 1]

Here, fix means integerization. The view channel data obtained by compressing the offset data portion is sent to the operation console 6 by the data transfer circuit 266.
To the data collection buffer 64 on the side
l) Transferred. A slip ring or the like for transmitting a signal between the rotating portion 32 and the non-rotating portion of the scanning gantry 2 is interposed in the middle of the data transfer path.

Since the volume of the entire transfer data is reduced by compressing the offset data, the time required for data transfer can be shortened. Conversely, by compressing the offset data, it is possible to increase the substantial volume of the offset data that can be transferred within the allowable time.

The central processing unit 60 obtains correction data for each channel from the compressed offset data. The correction data is obtained by summing the compressed offset data for each channel and dividing it by the total number of views (eg 512) of offset data measurements.
As a result, the correction data becomes the average value of the offset data measured for each channel. Since the number of measurement data, that is, the number of views is large, highly accurate correction data can be obtained by averaging them.

The central processing unit 60 subtracts this correction data from the scan data of each view of the corresponding channel to perform offset correction of the scan data of each view. Due to the high accuracy of the correction data, offset correction can be performed accurately.

The offset data compression circuit 264 calculates the offset data measurement value Fi, j of one view each time the offset data measurement value Fi, j is input, instead of calculating the sum for each m views as described above. You may do it.

[0043]

[Equation 2]

Here, i: channel number j: view number (2) is the offset data Fi, j of the new view.
Each time, the weighted addition is performed with the average value Gi, j−1 of the offset data up to that point to obtain a new average value Gi, j
It is a calculation formula for obtaining j. By performing such a calculation, it is possible to determine the average value of the data measured up to that point, depending on the measurement of new offset data. Therefore, when the offset data is measured for all the views, the average value is immediately established.

As a result, the number of offset data is one for each channel, so the volume of data is set to 1
It is possible to compress up to the volume corresponding to the view. Therefore, the time required for data transfer can be further shortened as compared with the above case, and conversely, the substantial volume of data that can be transferred within the allowable time can be further increased.

However, in order to maintain the accuracy of the average value including a decimal value or less, it is desirable to set the number of bits of data to, for example, 32 bits. And the high compression rate can still be maintained.

On the side of the central processing unit 60, it is not necessary to obtain an average value by receiving such offset data, and this can be immediately subtracted from the scan data to perform offset correction.

The operation of this apparatus will be described. FIG. 7 shows a flow chart of the operation of the present apparatus. As shown in the figure, in step 602, the operator inputs a scan plan through the operating device 70. The scan plan includes X-ray irradiation conditions, slice thickness, slice position, and the like. Hereinafter, the present apparatus operates under the operation of the operator and the control by the central processing unit 60 according to the input scan plan.

In step 604, scan positioning is performed. That is, the operator pushes a table feed switch (not shown) of the operation device 70 to move the photographing table 4,
The center of the imaged region (for example, abdomen) of the imaged object 8 is the center of rotation of the X-ray irradiation / detection device (isocenter: isoce
nter).

After performing such scan positioning, offset data is collected in step 606. The offset data acquisition is performed by measuring the output signal of the detector array 24 in the X-ray non-illuminated state over 512 views, for example, as described above. As described above, the collected offset data is transferred to the data collection buffer 64 after the data volume is compressed by addition of m views or sequential averaging operation.

Next, in step 608, scanning is performed.
That is, the X-ray irradiation / detection device is rotated around the imaging target 8 while irradiating X-rays, and for example, X-ray transmission data (scan data) of 1024 views is collected and transferred to the data collection buffer 64.

Next, in step 610, the offset correction as described above is performed. Since the accuracy of the correction data is high, the offset correction is performed with high accuracy, and particularly, the accuracy of scan data with low count can be improved.

Next, in step 612, the image data is reconstructed using the offset-corrected scan data, for example, by the filtered back projection method. Since the accuracy of low count scan data is improved by the offset correction described above, it is possible to accurately image even a portion having a large X-ray attenuation rate. The reconstructed tomographic image is displayed on the display device 68 in step 614. The displayed image also accurately shows the cross-sectional structure of a portion where the amount of X-ray transmission is small.

Although the example of using X-rays as the radiation has been described above, the radiation is not limited to X-rays and may be other types of radiation such as γ-rays. However,
At the present time, X-rays are preferable because they have the most practical means for generation, detection, control, and the like.

[0055]

As described in detail above, according to the present invention, it is possible to realize a radiation tomography apparatus for performing highly accurate offset correction.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus according to an example of an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a detector array in the apparatus shown in FIG.

FIG. 3 is a schematic configuration diagram of an X-ray irradiation / detection device in the device shown in FIG.

FIG. 4 is a schematic configuration diagram of an X-ray irradiation / detection device in the device shown in FIG.

5 is a block diagram of a data collection unit in the apparatus shown in FIG.

FIG. 6 is a diagram showing an operation of the data collection unit shown in FIG.

7 is a flow chart of the operation of the apparatus shown in FIG.

[Explanation of symbols]

2 scanning gantry 4 shooting table 6 Operation console 8 shooting target 20 X-ray tube 22 Collimator 24 detector array 26 Data Collection Department 28 X-ray controller 30 Collimator controller 32 rotating parts 34 Rotation controller 40 X-ray beam 60 Central processing unit 62 control interface 64 data collection buffer 66 storage 68 Display 70 Operating device 262 Data acquisition circuit H.264 offset data compression circuit 266 data transfer circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Bessho 127, 7-7 Asahigaoka, Hino-shi, Tokyo GE Yokogawa Medical Systems Co., Ltd. 127 GE Yokogawa Medical Systems Co., Ltd. (56) References JP-A-63-288139 (JP, A) JP-A-62-286447 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) (Name) A61B 6/00-6/14

Claims (4)

(57) [Claims] 1. Data collection means for respectively collecting radiation transmission data and offset data of a radiation imaging target for a plurality of views, and correction means for correcting the radiation transmission data with an average value of the offset data of the plurality of views, A radiation tomography apparatus comprising: an image generating unit that generates an image based on the corrected data, wherein the data collecting unit sums the offset data for each number m of views defined by the following formula. A radiation tomography apparatus, comprising: supplying to the correction means. Record Here, m is an integer of 2 or more, k is the number of bits of data, K is the expected maximum count of offset data, and fix is integerization. 2. The radiation tomography apparatus according to claim 1, wherein k = 14 bits and K = 2000 counts, and as a result, m = 8. 3. The radiation tomography apparatus according to claim 1, wherein the data acquisition unit is on the scanning gantry side and includes a detector array, a data acquisition circuit, an offset data compression circuit, and a data transfer circuit. And the data flows in this order, and the data collecting means is on the operation console side and has a data collecting buffer and a central processing unit. A radiation tomography apparatus characterized in that data flows. 4. The radiation tomography apparatus according to claim 3, wherein the correction unit totals the compressed offset data for each channel of the detector array, and totals the totaled value to measure the offset data. A radiation tomography apparatus characterized in that correction data is obtained by dividing by the number of views, and the correction data is subtracted from the scan data of each view of the corresponding channel to perform offset correction of the scan data of each view.