JPH0479258B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention uses an X-ray detector having a correction channel in addition to a large number of measurement channels, charges a capacitor with the output current of each channel, and Collect charging voltage as measurement data for each channel,
The present invention relates to an X-ray CT data acquisition device that corrects measurement data obtained from the measurement channel using measurement data obtained from the correction channel.

(Prior art) X-ray CT is a device that irradiates a subject with X-rays over the entire circumference, detects the X-rays that have passed through the subject, and reconstructs the image to take a tomogram. . There are various methods for acquiring data around the entire circumference of the subject, but there is a device called the R-R method in which the X-ray source and detector go around the subject once. Let's consider.

FIG. 3 is a diagram showing a conventional R-R type detector and its signal processing circuit. In the figure, 1 is an X-ray source that emits X-rays to irradiate the subject 2;
The X-rays that have passed through the subject 2 are incident on the X-ray detector 3. The detector 3 has a measurement channel 3A for detecting the X-rays that have passed through the subject 2 and creating a tomographic image, and a measurement channel 3A that detects the X-rays that are directly incident from the X-ray source 1 that do not pass through the subject 2. Correction channels 3B are provided on both sides of the measurement channel 3A to measure variations in the radiation source and correct the output data of the measurement channel 3A.
It is composed of 3C. Measurement channel 3A consists of, for example, 300 to 500 channels, and connecting preamplifiers to all channels for data processing would require an enormous amount of equipment, so measurements are divided into blocks of, for example, 8 to 10 channels. There is.

1C ₁ , 1C ₂ ,..., 1C _n is a group of capacitors connected between the output terminals of m channels belonging to the first block of n blocks of measurement channel 3A and the ground, and the output current of each channel is is integrated and output as a voltage. The output voltage v is as shown in the following equation.

v=(1/C)∫idt 1S ₁ , 1S ₂ ,..., 1S _n is a group of switches connected to each channel, and switch 1 is activated by the activation trigger.
When _S1 is activated, it is automatically switched sequentially and outputs the output signal of each channel as a continuous signal to the preamplifier 4a. nC ₁ , nC ₂ ,..., nC _n and
_nS1 , _{nS2 ,} . _{XC 1 , _ _ _ _ _}
. _. , XS _n and YS ₁ , YS ₂ , . The output of each preamplifier is switched by switches 5a, 5b, ..., 5n, 5X, 5Y, and is input to a programmable gain amplifier (hereinafter referred to as PGA) and amplified.
The signal is converted into a digital signal by the AD converter 7, and is input to the computer 8 for arithmetic processing.

(Problem to be solved by the invention) In the above X-ray CT, preamplifiers 4a to 4
Assume that sampling of a group of measurement channels 3A connected to n is started by each activation trigger, and if we try to accurately compensate for the effects of X-ray fluctuations due to the X-ray source 1, trigger cycle fluctuations, etc., each preamplifier Since the number of correction channels 4a to 4n is required, there is a problem in that the size of the detector and data acquisition device increases. Conventionally, the average value of multiple correction channels was measured without increasing the number of correction channels, and if an X-ray fluctuation occurred that affected only one of the activation triggers,
In some cases, even the data of normal effective channels was adversely affected.

The present invention has been made in view of the above points, and its purpose is to
The object of the present invention is to realize an X-ray CT data acquisition device that can accurately correct the influence of fluctuations in the integration time of a capacitor based on fluctuations in the intensity of irradiated X-rays and periodic fluctuations in the trigger.

(Means for Solving the Problems) The present invention for solving the above problems uses an X-ray detector having a correction channel in addition to a large number of measurement channels, charges a capacitor with the output current of each channel, and charges each capacitor with the output current of each channel. In an X-ray CT data collection device, the charging voltage of each channel is collected as measurement data of each channel, and the measurement data obtained from the measurement channel is corrected using the measurement data obtained from the correction channel. The measurement channel is divided into n blocks consisting of a plurality of measurement channels, and each block includes a first preamplifier provided for each block, a second preamplifier that receives measurement data from the correction channel of the detector, and the n blocks. a measurement channel data readout means for sequentially selecting a measurement channel and outputting measurement data to the first preamplifier and discharging the charge in the capacitor for each measurement channel for all measurement channels in the selected block; a correction channel data reset means for discharging the charge in the capacitor connected to the correction channel each time the measurement channel data reading means selects each of the blocks; Adding means for obtaining measurement data of the correction channel through the second preamplifier immediately before discharge, cumulatively adding and outputting the latest n measurement data among the obtained measurement data, and the adding means The present invention is characterized by comprising means for correcting the measurement data of the measurement channel output from the first preamplifier using the addition data output from the first preamplifier.

(Operation) In the present invention, n blocks are sequentially selected, and the charge in each capacitor is discharged for all measurement channels in the selected block. On the other hand, the charge in the capacitor connected to the correction channel is discharged every time each block is selected by the measurement channel data reading means. In addition, for both the measurement and correction channels, measurement data is obtained immediately before the discharge of the charge in each capacitor, and for the correction channel, the latest n measurement data among the measurement data obtained in this way are accumulated. to add. Then, the measurement data of the measurement channel is corrected using this added data.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. In the figure, parts equivalent to those in FIG. 3 are given the same reference numerals. In the figure, 9a, 9b,...,
9n is a switch inserted between each signal line and ground for discharging the charge charged in the integrating capacitor of each block, and 9X is a signal line for discharging the charge charged in the integrating capacitor of correction channel 3B. This is a switch inserted between ground. 10 and 11 operate simultaneously, AD converter 7
Two data selectors are provided on the input side and the output side of the adder 12 to select execution of addition calculation processing of the output signal of the adder 12. Also, data selector 10,1
1 is linked to the switch 5X, and when the switch 5X is turned on, the data selector 10,1
1 contacts A and A' turn on, and switch 5
When X becomes “off”, data selector 1
Contacts A and A' of 0 and 11 are turned "off", and contacts B and B' are turned "on". 13 is a computer that processes input data and reconstructs an image.
The control circuit 14 controls the operation of each switch as indicated by arrows in the figure.

Next, the operation of the device configured as described above is explained in a second manner.
This will be explained with reference to the time chart shown in the figure. In FIG. 2, each waveform is a waveform showing a pulse sequence with the horizontal axis as the time axis. 1T ₁ , 1T ₂ in the upper column,
..., IT _o is the number of each activation trigger, the first number 1 is the first measurement by all measurement channels, 2T ₁ ,
..., 2T _o , the first number 2 means the activation trigger for the second measurement, and the subscript is a number indicating the number of each block in the measurement channel 3A. At the bottom, each timing is written in 50 syllables, with katakana indicating the timing of the first measurement and hiragana indicating the timing of the second measurement.

Correction channel 3 by start trigger 1T ₁ in (a)
B and measurement channel 3A leading to preamplifier 4a
Data measurement of the first block is performed. First of all,
At _1T1 in (a), the switch 5X is turned on, and the data from the correction channel 3B is amplified by the PGA 6 via the preamplifier 4X and the switch 5X. The data is transferred to the AD converter 7 by the AD trigger in (a).
It is converted into a digital signal at Also, in (A), the contacts A and A' of the data selectors 10 and 11 that are linked to the switch 5X are turned on,
Send the data to adder 12. As will be explained later, the adder 12 cumulatively adds data a required number of times and sends the result to the computer 13 when the contacts A and A' of the data selectors 10 and 11 are "on".
Between (c) and (d), the switch 9X is turned on, the accumulated charge in the capacitor XC is discharged, and the data in the correction channel is reset. In (d), the switch 5X is turned "off" and the switch 5a is turned "on", and at the same time the data selectors 10 and 11
The contacts B and B' of the data selectors 10 and 11 become "on" and the paths of the contacts B and B' of the data selectors 10 and 11 become valid.
Also, in this (d), the switch 1S ₁ is turned on, and the AD trigger is also input to the AD converter 7, and the 1S
The signal of _C1 is AD converted, and the data selector 10,
It is sent to the computer 13 via contacts B and B' of 11.
Switch 9a is turned on during periods (e) to (f),
Since the switch _1S1 is in the "on" state, the charge on the capacitor _1C1 is discharged and the measured data is reset.

Similarly, in (f), switch 1S ₂ is turned on, switch 5a continues to be on, and in response to the AD trigger input, AD converter 7 performs AD conversion of the signal from capacitor 1C ₂ . conduct. (K)～(K)
During this period, the switch 9a turns "on" again and resets the data on the capacitor _1C2 . (ke) ~
In the period (sa), capacitor 1 is
After the C _n signal is measured and reset, the switch 5a is turned off and the measurement of the first block of the measurement channel 3A handled by the preamplifier 4a is completed.

Similarly, preamplifier 4b is activated by starting trigger 1T ₂ .
Measurement of the second block of the measurement channel 3A connected to is started. This is to measure the voltage signal due to the charge charged in capacitors 2C ₁ to 2C _n , and at the same time, the correction channel 3 by capacitor XC
B is measured. During this period, the paths of the contacts A and A' of the data selectors 10 and 11 are selected during the period when the switch 5X is turned on, and the data addition of the correction channel 3B and the data transfer to the computer 13 are performed. The switch 5b is turned on during the period (S) to (D), and the data selector 1 is turned on.
The path of contacts B and B' of contacts 0 and 11 is selected, and the data of the second block of measurement channel 3A is transferred to computer 1.
Sent to 3.

In this series of operations, starting trigger 1T _o causes measurement channel 3A connected to preamplifier 4n.
After measuring the signals of capacitors nC ₁ to nC _n of the n-th block, the _first
Returning to the measurement of the block, measurement is performed using the charged charge of the capacitor _1C1 .

The data of each measurement channel 3A measured during this time will be considered. Start trigger 2
Switch 1S ₁ and switch 5a are turned on by T ₁
The integration time of the charge on the capacitor 1C ₁ measured at the moment when the switch 1S ₁ and the switch 9a are turned off and charging of the capacitor 1C ₁ is started (f) is the same as that of the second measurement. For Switch 1S ₁
There is a period from when the switch 9a is turned on until (o) when the switch 9a is turned on, and for the capacitor _1C2 , it is a period from (h) to (ki). During this time, the data of correction channel 3B shows that the capacitor XC is reset by turning on the switch 9X in the starting trigger _1T1 and starts charging (E).
Measured data of the output voltage due to the charge charged in the capacitor XC during the period (ce) from 9X to the next time when the switch 9X is turned "on" and the charge on the capacitor XC is discharged, and similarly at the start trigger 1T ₂ This is data obtained by adding n pieces of data such as data for periods (X) to (X) and data for a period up to (F) at activation trigger 1T _o by an adder 12. The adder 12 outputs the result of cumulative addition of these n pieces of data, and when the data of the next period is inputted by the next activation pulse, the adder 12 erases the first data and always uses the latest n pieces of data. Add the data.

In this way, the data of the capacitor 1C1 inputted to the computer 13 through the contact points B and B' of the data selectors 10 and ₁₁ , and the data of the data selector 10,
Considering the charging time of both capacitors to obtain the data cumulatively added by the adder 12 through the path of contacts A and A' of 11, the capacitor XC
and 1C Since the time constant for discharging ₁ charge is small,
Since the "on" time of the switches 9X and 9a is short and can be ignored, it can be assumed that the time during which each capacitor, which is the source of both data, is charged is approximately equal. Therefore, the computer 13 corrects the data of the measurement channel 3A with the output data of the adder 12 and performs the necessary calculation processing to reconstruct the image while eliminating errors caused by fluctuations in X-ray intensity and fluctuations in the integration time of the capacitor. . In this configuration, the data obtained from capacitors 1C ₂ to 1C _n in the same block will be corrected using the same added data as in the case of capacitor 1C ₁ , but the integration time (time) of both The maximum deviation of the starting trigger is 1T ₁ , 1
The time between T ₂ is small and accurate correction can be made.
Note that since the addition data (data used for correction, ie, correction data) is obtained for each block, the difference in integration time (time) between the measurement data of the measurement channel and the correction data in each block is small.

As explained above, according to this embodiment, the measurement data of the correction channel is cumulatively added by a number n corresponding to the integration time of the measurement channel, and this is used as the data for correcting the measurement data of the measurement channel in the corresponding block. Since the correction data is used as correction data, data that is approximately equal in time to the measurement data of the measurement channel can be obtained, making it possible to perform correct correction.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, the correction channel is set to 1.
Although the explanation has been made assuming that only the correction channel is used, the correction channel may be provided on both sides of the measurement channel in consideration of the case where it is blocked by the subject.

(Effects of the Invention) As explained in detail above, according to the present invention,
Even with one correction channel, it is possible to obtain correction data that is approximately equal in time to the measurement data of the measurement channel, and it is possible to accurately account for the effects of fluctuations in X-ray intensity and capacitor integration time. This can now be corrected, which has a great practical effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention, FIG. 2 is a time chart of the operation of the apparatus according to the embodiment, and FIG. 3 is a diagram of a conventional apparatus. 1... X-ray source, 2... Subject, 3... Detector, 3A...
Measurement channel, 3B, 3C...Correction channel, 4
X, 4a, 4b,..., 4n...Preamplifier, 5a,
5b,..., 5n, 5X...switch, 6...PGA,
7...AD converter, 9a, 9b,..., 9n, 9X...
Switch, 10, 11...Data selector, 12...
Adder, 13... Computer, 14... Control circuit, 1C ₁ ,
1C ₂ ,..., 1C _n , nC ₁ , nC ₂ ,..., nC _n , XC... Capacitor, 1S ₁ , 1S ₂ ,..., 1S _n , 2S ₁ , 2S ₂ ,
..., 2S _n , nS ₁ , nS ₂ , ..., nS _n ... switch.

Claims (1)

[Claims] 1. Using an X-ray detector having a correction channel in addition to a large number of measurement channels, a capacitor is charged with the output current of each channel, and the charging voltage of each capacitor is collected as measurement data of each channel. , an X-ray CT that corrects the measurement data obtained from the measurement channel using the measurement data obtained from the correction channel;
In the data acquisition device, all measurement channels of the detector are divided into n blocks each consisting of a plurality of measurement channels, and a first preamplifier provided for each block receives measurement data from a correction channel of the detector. a second preamplifier, and sequentially selects the n blocks, and for all measurement channels in the selected block, outputs the measurement data to the first preamplifier and discharges the charge of the capacitor to the measurement channel. a correction channel data reset means for discharging the charge in the capacitor connected to the correction channel each time the measurement channel data reading means selects each block; Immediately before the channel data reset means discharges the charge in the capacitor, the second
an adding means that obtains measurement data of the correction channel through a preamplifier of the correction channel, and cumulatively adds and outputs the latest n measurement data among the obtained measurement data; 1
An X-ray CT data acquisition device, comprising: means for correcting the measurement data of the measurement channel output by the preamplifier.