JP4080738B2 - X-ray computed tomography system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a data acquisition system for amplifying a signal detected by an X-ray detector and converting it into a digital signal, and an X-ray computed tomography apparatus equipped with the data acquisition system.
[0002]
[Prior art]
As is well known, in an X-ray computed tomography apparatus, a signal transmitted through an object from an X-ray tube and detected by a detector is transferred to a computer apparatus responsible for reconstruction processing and the like through a data acquisition system (DAS). .
[0003]
A data acquisition system typically converts an output current from a detection element of a detector into a voltage signal by an amplifier, integrates the output for a certain period of time by a sample-and-hold type integrator, and converts the output to a successive approximation type. An analog-digital converter (ADC) has a function of converting to a digital signal.
[0004]
Due to the recent increase in resolution, reduction in scan time, and the increase in the number of channels associated with multi-slice, a data acquisition system is required to have a very high processing capability, particularly high speed. In order to answer this increase in speed, the number of channels has increased significantly. As the number of channels increases, variations in gain and offset between the channels increase, and correction is required.
[0005]
Usually, DAS boards equipped with 96 channels of amplifiers, integrators, and analog-digital converters are mounted by inserting them into dozens of connectors, thereby easily dealing with channel failures by replacing the DAS boards. This is realized.
[0006]
On the other hand, every time the DAS board is replaced, it is necessary to measure the gain and offset characteristics of each channel and feed back them to the correction unit. For this reason, an increase in cost due to an extended downtime and an increase in service man-hours due to replacement of the DAS board is inevitable.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to realize downtime reduction and service man-hour reduction by exchanging DAS boards.
[0008]
[Means for Solving the Problems]
The present invention relates to an amplifier for amplifying the output of the X-ray detector and an analog-to-digital conversion for digitization in a data acquisition system for processing a signal detected by the X-ray detector and transferring it to the X-ray computed tomography apparatus main body. Connected to the plurality of DAS boards via the plurality of connectors, a plurality of DAS boards equipped with a signal processing circuit including a multi-channel device, a plurality of connectors for detachably connecting the plurality of DAS boards A correction unit that corrects the output of the signal processing circuit, and each of the plurality of DAS boards corresponds to input / output characteristics of the plurality of signal processing circuits provided in each DAS board. A memory unit for storing data is provided, and the correction unit outputs the signal processing circuit based on the data stored in the memory unit. Correction.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of a data acquisition system according to the present invention and an X-ray computed tomography apparatus equipped with the data acquisition system will be described below with reference to the drawings.
[0010]
In the computed tomography apparatus, an X-ray tube and an X-ray detector are combined as a single body, and a number of detection elements arranged in a rotating / rotating type and ring shape are fixed. There are various types such as a fixed / rotating type in which only the tube rotates around the subject, and the present invention can be applied to any type. Here, the rotation / rotation type that currently occupies the mainstream will be described.
[0011]
In addition, in order to reconstruct one tomographic image, one set of projection data for about 360 degrees around the subject and one projection data for about 210 degrees to 240 degrees by the half scan method. A set is needed. The present invention can be applied to any method. Here, a description will be given assuming that one tomographic image is reconstructed from the general projection data set of about 360 degrees.
[0012]
In addition, the mechanism for converting incident X-rays into electric charge includes an indirect conversion type in which X-rays are converted into light by a phosphor such as a scintillator and the light is converted into electric charge by a photoelectric conversion element such as a photodiode, and a specific semiconductor The mainstream is the generation of electron-hole pairs in semiconductors by the X-rays and the transfer to the electrodes, that is, the direct conversion type utilizing the photoconductive phenomenon. Any of these methods may be employed as the X-ray detection element, but here, the former indirect conversion type will be described.
[0013]
FIG. 1 is a block diagram showing the configuration of an X-ray computed tomography apparatus (X-ray CT) according to this embodiment. The gantry 1 has an X-ray tube 3 and a multi-channel X-ray detector 5. The X-ray tube 3 is mounted together with the multi-channel X-ray detector 5 in a positional relationship facing the rotating ring. The X-ray tube 3 receives X-rays upon receiving application of tube voltage and supply of filament current from the high voltage generator 4. This X-ray is irradiated to the subject P. X-rays transmitted through the subject are detected by each channel of the X-ray detector 5.
[0014]
A data acquisition system 6, generally called a DAS (data acquisition system), is connected to the X-ray detector 5 via a slip ring 7. The data acquisition system 6 is a system that amplifies the signal detected by the X-ray detector 5, digitizes it, and passes it to the X-ray computed tomography apparatus main body (computer apparatus) 2. It is. Details of the data collection system 6 will be described later.
[0015]
The X-ray computed tomography apparatus main body 2 includes a preprocessing unit 15, a data storage unit 10, a reconstruction unit 11, a display processor 12, and a display 13 with a main controller 9 as a center. In the preprocessing unit 15, the signal (the data at this stage is generally referred to as raw data) sent from the data collection system 6 is used as the data (the data at this stage is generally referred to as raw data). In this process, typically, the reference detector detects fluctuations in the X-ray intensity associated with fluctuations in the tube voltage and tube current of the X-ray tube 3. Then, a so-called reference correction process that normalizes the raw data according to the detected value and corrects the variation in X-ray intensity, a wedge filter by subtracting the raw data of the water phantom collected in advance from the raw data of the subject P Water correction processing for canceling X-ray absorption and sensitivity differences between detector channels, beam hardening correction processing, body motion correction processing, etc. That.
[0016]
Projection data from the preprocessing unit 15 is temporarily stored in the data storage unit 10. Then, it is read from the data storage unit 10 as appropriate, and the tomographic image data is reconstructed by the reconstruction processor 11 based on the projection data. This tomographic image data is displayed on the display 13 via the display processor 12.
[0017]
In addition, the X-ray computed tomography apparatus main body 2 includes rotation of a rotating ring, generation of a high voltage pulse from the high voltage generator 4, processing of the data acquisition system 6 synchronized with the high voltage pulse, and bed operation. It has a scan controller that supervises control related to scanning.
[0018]
FIG. 2 schematically shows the configuration of the data collection system 6. FIG. 3 is a block diagram showing the configuration of the data collection system 6. The data collection system 6 has a plurality of DAS boards 16. Each of the plurality of DAS boards 16 includes an amplifier 19 that converts an output current from the detection element 26 of the X-ray detector 5 into a voltage signal, a sample-and-hold type integrator 20 that forms a signal processing circuit together with the amplifier 19, and The successive approximation type analog-digital converter 21 is equipped with a plurality of, for example, 96 channels. The data collection system 6 is equipped with a plurality of connectors 18 for detachably connecting a plurality of DAS boards 16, and can be replaced in units of boards in the event of a failure or the like.
[0019]
The plurality of DAS boards 16 have variations in input / output characteristics between signal processing circuits (channels) including an amplifier 19, an integrator 20, and an analog-digital converter 21 via a plurality of connectors 18 and a multiplexer 22. Here, a gain correction circuit 23 and an offset correction circuit 24 are connected as a correction circuit (mounted by a digital processing circuit or a ROM) for reducing and substantially uniformizing. The gain correction circuit 23 multiplies the output of the signal processing circuit by a correction multiplier corresponding to the gain characteristic of each signal processing circuit, and the offset correction circuit 24 calculates the DC of each signal processing circuit from the output of the signal processing circuit. Subtract noise (mainly consisting of drift components and solid noise).
[0020]
In order to correct variations between signal processing circuits regarding input / output characteristics such as gain correction and offset correction, data regarding input / output characteristics unique to each signal processing circuit is required.
[0021]
In the present embodiment, the data relating to the input / output characteristics unique to each signal processing circuit, or correction data (for example, the multiplication coefficient, the subtraction value itself) derived from the difference between the data and the reference input / output characteristic data are stored in the DAS board 16. It is measured at the manufacturing stage, calculated, and stored in the flash memory 17 mounted on the DAS board 16. That is, each DAS board 16 is equipped with a flash memory 17, and data corresponding to input / output characteristics of a plurality of signal processing circuits mounted on the DAS board 16 is stored in the flash memory 17. . In other words, each DAS board 16 has data corresponding to input / output characteristics of a plurality of signal processing circuits provided in its own board in the flash memory 17 also provided in its own board.
[0022]
By performing correction based on data corresponding to the input / output characteristics of a plurality of signal processing circuits stored in the flash memory 17, a plurality of DAS substrates 16 as well as between different DAS substrates 16 can be used. It is possible to substantially uniform the input / output characteristics of the signal processing circuit.
[0023]
The data collection system 6 is provided with a memory controller 14 that performs read control of the flash memory 17. Typically, the memory controller 14 is shared by a plurality of DAS boards 16 and is connected to a plurality of flash memories 17 of the plurality of DAS boards 16 via a connector 18 and a multiplexer 22.
[0024]
The memory controller 14 supplies data corresponding to the input / output characteristics of each signal processing circuit read from the flash memory 17 to the correction circuits 23 and 24, or corresponds to the input / output characteristics of each signal processing circuit read from the flash memory 17. The input / output characteristics of the signal processing circuit are made uniform by controlling the correction circuits 23 and 24 based on the data to be processed.
[0025]
In this way, by holding the input / output characteristic data of the signal processing circuit installed in the DAS board 16, when replacing the DAS board 16 due to a failure or the like, the new DAS board 16 can be replaced at the replacement site. It is not necessary to measure the input / output characteristic data of the signal processing circuit and reflect it in the correction process. Therefore, it is possible to realize downtime reduction and service man-hour reduction by replacing the DAS board.
[0026]
Raw data is generated by logarithmically converting the corrected data by the logarithmic conversion circuit 25. This logarithmic conversion is a process generally performed in CT, and may be performed in the preprocessing unit 15 of the main body 2. As is well known, X-rays are exponentially attenuated in the subject, while the detector 5 outputs a signal proportional to the transmitted dose of the X-rays attenuated exponentially in this way. In order to obtain projection data that is the sum of the X-ray absorption coefficients on the X-ray path, it is essential to subject the output of the detector 5 to logarithmic conversion.
[0027]
(Modification)
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Furthermore, the above embodiment includes various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, some constituent requirements may be deleted from all the constituent requirements shown in the embodiment.
[0028]
【The invention's effect】
According to the present invention, it is possible to reduce downtime and service man-hours by exchanging DAS boards.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an X-ray computed tomography apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of the data collection system of FIG.
3 is a block diagram of the data collection system of FIG.
[Explanation of symbols]
1 ... Gantry,
2 ... X-ray computed tomography main body (computer device),
3 ... X-ray tube,
4 ... High voltage generator,
5 ... X-ray detector,
6 ... Data collection device,
7 ... Slip ring,
9 ... Main controller,
10: Data storage unit,
11 ... Reconstruction unit,
12 ... display processor,
13 ... Display,
14 ... Memory controller,
15 ... Pretreatment unit,
16 ... DAS board,
17 ... Correction parameter flash memory,
18 ... DAS board connector,
19 ... Amplifier,
20 ... integrator,
21: Analog-digital converter.
22: Multiplexer,
23 ... Gain correction circuit,
24. Offset correction circuit,
25: Logarithmic amplifier,
26: Detection element.

Claims (5)

An X-ray tube that irradiates a subject with X-rays, an X-ray detector that detects X-rays transmitted through the subject, and an X-ray computed tomography apparatus that processes signals detected by the X-ray detector A data collection system delivered to the main body, and a reconstruction unit for reconstructing image data based on the output of the data collection system,
The data acquisition system includes a plurality of DAS boards equipped with a multi-channel signal processing circuit including an amplifier for amplifying the output of the X-ray detector and an analog-digital converter for digitization.
A plurality of connectors for detachably connecting the plurality of DAS boards;
A correction unit that is connected to the plurality of DAS boards via the plurality of connectors and corrects the output of the signal processing circuit;
Each of the plurality of DAS boards is equipped with a memory unit that stores data corresponding to input / output characteristics of a plurality of signal processing circuits provided in each DAS board, and the correction unit is stored in the memory unit. An X-ray computed tomography apparatus which corrects an output of the signal processing circuit based on stored data. The input-output characteristic, X-rays computed tomography system according to claim 1, characterized in that the gain and / or offset characteristic. The memory unit, X-rays computed tomography system according to claim 1, characterized in that it is a flash memory. The data, X-rays computed tomography system according to claim 1, characterized in that the correction data for equalizing the input and output characteristics of the signal processing circuit. The data corresponds to input / output characteristics of a plurality of signal processing circuits provided in each of the plurality of DAS boards, and is data measured in a manufacturing stage of each of the DAS boards. The X-ray computed tomography apparatus according to claim 1.

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