JPH01135332A - Data collector of x-ray computer tomographic apparatus - Google Patents

Abstract

PURPOSE:To obtain a good CT image having no artifact, by storing the error of the CT image data generated in the gain change-over of an automatic gain amplifier and correcting the CT image data on the basis of said error. CONSTITUTION:The input from an X-ray detector 3 enters a CPU 11 through an automatic gain amplifier 6 for automatically selecting a gain corresponding to the level of said input, an A/D converter 7 and a buffer memory 10. The CPU calculates CT image data to supply the same to a display 13 and a RAM 15 stores the error of the CT image data at the gain change-over point of the automatic gain amplifier 6 and the CPU 11 corrects the CT image data using said error as correction data.

Description

[Detailed description of the invention]

A. Field of Industrial Application This invention relates to a data collection bag FW (D AS ) for an X-ray computed tomography system (XMCT). B. Prior Art As shown in FIG. 9(A), X-rays emitted from an X-ray tube 1 pass through an object 2 and enter an X-ray detector 3. The X-ray detector 3 includes a large number (usually about several hundred) of X-ray detectors 3. ~3. It consists of an array of Each X-ray detector3. ~3. is sequentially converted to X by appropriate scanning.
Output line detection data. As shown in FIG. 8, each X-ray detector 31-3. The output from the is first amplified by a preamplifier 4, integrated by an integrator 5, amplified by an auto gain amplifier 6 with a gain corresponding to its input level, and then converted into a j-bit digital signal by an A/D converter 7. Certain A/D conversion data A
Converted to Doot. FIG. 9(B) shows the X-ray detector 3. ~3. The X-ray intensity distribution is shown with the horizontal axis representing the position of and the vertical axis representing the intensity of the X-rays emitted from the X-ray tube 1. As shown in this figure, since the X-ray intensity has a wide dynamic range, if A/D conversion is performed without the auto gain amplifier 6, an A/D converter 7 with a sufficient number of bits is required. This results in a significant increase in costs. Therefore, in order to allow the A/D converter 7 to have a relatively small number of bits, the auto gain amplifier 6 is used. The auto gain amplifier 6 includes a first amplifier Amp that doubles the output of the integrator 5 by 2, and a second amplifier A11ll! that further doubles the output of the first amplifier All1pl! , a first comparator Col1+1 + that compares the output of the first amplifier Amp with a reference voltage vth, and a second amplifier Ampz.
a second comparator Comp which compares the output of the first . a second comparator Comp,
, Co+nρ2, and gain selection signal NG (0) = (OO). NG(1) = (01) or N, (2) = (1
0), a logic circuit 8 that outputs a 2-bit signal, and an integrator 5.
, the output of the first amplifier Aspl, the output of the second amplifier Amp
The multiplexer 9 inputs the outputs of 1 and outputs one of them to the A/D converter 7 according to the gain selection signal Nc. The buffer memory 10 converts the 2-bit gain selection signal N0 from the logic circuit 8 and the j-bit A/D conversion data ADout from the A/D converter 7 into the gain selection signal N0.
This is a large-capacity memory that stores primary image data Y0 with r, as the upper focus and A/D conversion data ADouy as the lower bit. The CP Ull of the microcomputer controls the A/D converter 7 via the DAS control unit 12, reads the primary image data Y0 from the buffer memo January 0, and calculates the CT image data Y through predetermined arithmetic processing. , a tomographic image is displayed on the display 13 based on that. 14 is ROM, 15 is l'? AM, 16 is a keyboard. ■“22 to double mode” X-ray detectors 31 to 3. The output of the first X-ray detector 3 in the array is sent to a preamplifier 4. The integrated output amplified and integrated by the integrator 5 is transmitted to the V(, sth (ski)) X-ray detector 3.
Assuming that the integral output obtained by similarly amplifying and integrating the output of is vs,
V, X2gk=V, and X2=Vth. X-ray detector 3. ~31 and 3w~3. For the minimum range integral output for 1. second comparator C
ot! 191, Co1Ill's output is [00
]. The logic circuit 8 is

Input [00] to select gain selection signal N,
(2) = (10) is output to the multiplexer 9. As a result, the ×2z'' terminal of the multiplexer 9 is automatically selected, and the multiplexer 9 multiplies the minimum range integral output by 2zm by the first and second amplifiers Al111+ and Ampl and outputs it to the A/D converter 7. In this case, the analog output from the multiplexer 9 is the output AG, , AG corresponding to 31 to 3. and 3w to 3° in (C) of FIG.
The D conversion data ADout is the gain (X2”) in Figure 10.
The output A D + corresponds to the range of . 2-bit gain selection signal N6 (2) from logic circuit 8
-(10) and the j-bit A/D conversion data ADout from the A/D converter 7 are the gain selection signal N, (2)
is recorded in the buffer memory 10 as (j+2)-bit primary image data Y0 with ADouv as the upper bit and A/D conversion data ADouv as the lower bit. Note that the A/D converter 7 for the X-ray detectors 3t and 3w
The output AD, is the full scale of j focus [11...
・11]. ■“Double mode” X-ray detector 3. °~3. and for the intermediate range integral output for 3u to 3w, the output of vJl, the second comparator Compl, Go+l1pz is
becomes. The logic circuit 8 inputs [O1] and outputs the gain selection signal Nc.
(1)=(01) is output to the multiplexer 9. As a result, the X2'' terminal of the multiplexer 9 is automatically selected, and the multiplexer 9 outputs the integrated output of the intermediate range multiplied by 2 by the first amplifier Ampl to the A/D converter 7. The analog outputs from A/D converter 7 are outputs AGz and AGJ corresponding to 3. to 3. and 3. to 3° in (C) of FIG.
/D conversion data ADouy is the gain (X2” in Fig. 10)
) is the output AD corresponding to the range. 2-bit gain selection signal Na(1) from logic circuit 8
= (1 where 011 is the upper bit and j-bit A/D converted data ADout from the A/D converter 7 is the lower bit)
Next image data Yo is recorded in the buffer memory 10. Note that the X-ray detector 3. ．． 3. A/D converter 7 for
The output AD□ is the full scale of j focus (11...
・11). ■“1x mode” X-ray detector 3. For the maximum range integral output for ~3u, the first. Second comparator CoIIIp1°C
The output of ompz is (11), and the logic circuit 8 is C1
1), the gain selection signal N, (0) = [0
0] is output to the multiplexer 9. As a result, the ×1 terminal of multiplexer 9 is selected, and multiplexer 9 directly outputs the integrated output of the maximum range without amplifying it.
Output to D converter 7. In this case, the analog output from the multiplexer 9 is 3s to 3. , and the A/D converted data ADoot from the A/D converter 7 is
is the output AD corresponding to the gain (×1) range in Figure 10.
It becomes i. 2-bit gain selection signal N0 (0) from logic circuit 8
Primary image data Yo is recorded in the buffer memory 10, with =(00) as the E-order bit and j-bit A/D converted data ADouy from the A/D converter 7 as the lower bit. All X-ray detectors 3. ~3. The X-ray detection data from the individual X-ray detectors 3. Every 3 degrees, it is recorded in the buffer memo January 0 as (j+2) bit primary image data Y0. CP Ull connects the buffer memory 10 to the X-ray detector 3
1-3. Sequentially reads (j+2) bits of primary image data Y0 for each of
From the conversion data ADout and the gain selection signal N of the upper 2 bits, the final OCT image data Y is obtained by the calculation: Y=ADout The CT image data Y for each is stored in the RAM 15.
2T: Since there is, Yzz* = ADout
Reduce the gain to 1/1 and return to the same gain as the 1x mode. When in 2x mode, N = (01)z = 1, so Yzh = A DouTX (2') -', which means that what was multiplied by 2 by auto gain amplifier 6 is divided by 2.
to return to the same gain as 1x mode. In the 1x mode, N = [00) and = O, so Y+ = ADouy
If yX(2')-' is expressed on the vertical axis,
It becomes as shown by the dotted line in the figure. As shown in FIG. 11, CT image data Y generally becomes discontinuous at a gain switching point. The display 13 is based on the CT image data Y having such discontinuous points.
When a tomographic image is displayed, an artifact (false image) occurs in the 1tlr layer image. The causes of discontinuity in CT image data Y are mainly caused by the following.
Gain design values of the second amplifier Amρ, , Ampz (
This is due to the error in the resistance values of the feedback resistors R+ and Rt). Therefore, conventionally, in order to prevent artifacts, the feedback resistors R+ and Rz are adjusted to obtain the final CT.
An attempt was made to eliminate discontinuities in the image data Y. C1 Problems to be Solved by the Invention However, the adjustment work requires a lot of time and effort, and requires a device to input a predetermined voltage to the auto gain amplifier 6 in addition to the X-ray detector. The problem was that a programmable power supply was required to provide a very accurate measurement of the output voltage of the input device. That is, in order to adjust between the 1x mode and the 2x mode, the voltage input device is connected to the auto gain amplifier 6 to the X-ray detector 3. The input voltage V corresponds to the integral output of . Input the amplifier output in double mode (IVAzi+
seek. Next, switch to 1x mode and find the amplifier output value VAI, ■,! Compare /2 and vA1. If Vazv / 2'> VAI, the first amplifier A
Adjust the feedback resistor R+ so that the gain of III 91 decreases, and if vA□/2”<VAI,
The feedback resistor R is adjusted so that the gain of the first amplifier Amp increases. Then, switch between 21x mode and 1x mode again and do the same thing as above, Vain / 2' = VAI
Repeat many times until . Then double mode and 2! In order to make adjustments with the double mode, the voltage input device is connected to the auto gain amplifier 6 to the X-ray detector 3. Input the input voltage v2 corresponding to the integral output of 2! Find the amplifier output (iV^tZk) in the double mode. Next, switch to the double carp mode and calculate the amplifier output value V, □
Find vA! Compare □/2 wrinkles and V Ark. If V Azz*/2'> V azm, adjust the feedback resistor R2 so that the gain of the second amplifier A mp @ decreases, vA,! /2k<vA,
If so, the feedback resistor R2 is adjusted so that the gain of the second amplifier A ra p z increases. And 2 again! Switch between double mode and double mode and do the same thing as above with V azzh/'2 ' =
Repeat this many times until it reaches V atm. However, since the adjustment of the feedback resistance R,,R, is delicate and needs to be repeated many times,
Adjustment work is very troublesome and requires a lot of time. Additionally, voltage input devices with dedicated programmable power supplies are expensive. Furthermore, since this gain adjustment work is performed by the auto gain amplifier alone, when it is actually incorporated into the data acquisition device of an X-ray computed tomography system, there is a risk that errors may still occur due to differences in environmental conditions such as temperature. . This invention has been made in view of the above circumstances, and is aimed at preventing discontinuities (steps) in the final OCT image data Y caused by gain errors of the auto gain amplifier.
It is an object of the present invention to automatically correct this when an auto-gain amplifier is incorporated into a data acquisition device of an actual X-ray computed tomography apparatus. Means for Solving the D0 Problem In order to achieve the above object, the present invention has the following configuration. That is, the present invention provides an auto-gain amplifier that automatically selects a gain according to the input level from an X-ray detector, and an A/D converter that converts the output of the auto-gain amplifier into A/D.
An X-ray computed tomography apparatus comprising a D converter and a calculation means for calculating 07 image data from A/D conversion output data from the A/D converter and a gain selection signal obtained in the auto gain amplifier. The data acquisition device further comprises a storage means for storing an error in the 07 image data at the gain switching point of the auto gain amplifier, and a correction means for correcting the 07 image data by the calculation means using this error as correction data. This is a characteristic feature. Snake 0 Effect The effects of the configuration of this invention are as follows. The error stored in the storage means is not an error in the output of the auto gain amplifier, but an error in the 07 image data to be finally obtained. Since this error is used as correction data to correct the 07 image data by the calculation means,
The discontinuity at the gain switching point is always eliminated in the final OCT image data Y, regardless of changes in environmental conditions such as temperature. In addition, the manual work required for correction is the work to find the error in the final 07 image data as described above, and the gain is artificially set instead of auto gain operation. After setting the gain, all you need to do is create a program to automatically perform everything from X-ray irradiation to error calculation and storage.In other words, the necessary work is much easier than in the conventional case. And also,
There is no need for special equipment such as a voltage input device with a programmable power supply. F. Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings. FIG. 1 is a block diagram of a data acquisition device for an X-ray computed tomography apparatus according to a first embodiment of the present invention. In FIG. 1, the same reference numerals as those shown in FIG. 8 according to the conventional example refer to the same parts as those indicated by the reference numerals in this embodiment. The configurations of this embodiment that differ from the conventional example are as follows. Selector 1 is connected to the gain mode selection terminal of multiplexer 9.
7 is connected, and the input side of this selector 17 is connected to the output terminal of the logic circuit 8, the gain setting terminals T+, T* of the rod section 122 of the DAS III control section 12, and the output of the logic circuit 8 and the gain setting terminal T+, It is connected to a select terminal T0 in the DAS control unit 12 for determining which of the outputs of Tz to select. 1st. Signal output to the second gain setting terminals T+, T□ and select terminal T is performed via the CPU 11# and the DAS control unit 12 by operations on the keyboard 16. In addition to a program for collecting CT image data Y, the ROM 14 stores a program for determining errors in CT image data Y. The rest of the configuration is the same as the conventional example, so the explanation will be omitted. Next, the operation of this first embodiment will be explained. (a) Error Calculation/Storing Operation First, the operation of calculating the error at the gain switching point for the CT image data Y and storing it in the RAM 15 will be explained based on the flowchart of FIG. Initialization is performed in step Sl, and in step S2, the first . In order to determine the magnification of the auto gain amplifier 6 independently from the influence of the gain error of the second amplifiers Asp, , Al1, the select terminal T is set to "L" level, and the first... The output of the second gain setting terminals T, , T, is switched to be input to the selector 17. In step S3, the first gain setting terminal T1 is set to "0", and in step S4, the second gain setting terminal T is set to 1.
Select 2&x mode by setting m. This corresponds to collecting X-ray detection data according to the characteristics shown in FIG. 3(B). In step S5, Y=ADouy X (2”) −
"1" is stored in the register N which stores "N" in the X-ray detector 3.' in step S6. ~3. 1+1t+ is stored in register n that counts the number of . In step S7, the X-ray tube 1 is driven to start irradiating the X-ray detector 3 with X-rays. In step S8, the data from the n-th X-ray detector 37 (initially the first X-ray detector 3.) is input, and the auto-gain amplifier 6 inputs the data from the
The amplified signal is A/D converted by the A/D converter 7, and together with the A/D converted data ADoutn, the gain selection signal N, which is the content of the register N, (1) = (01) is converted into the first bit of the bit. It is stored in the buffer memory 10 as image data Y0. In step S9, the contents of register n are set to xl detector 3, -
3. It is determined whether the number m has been reached, and if it has not reached the number m, the process advances to step S10, where the content of the register n is increased by 1 (+1)L, and the process returns to step S8. All X-ray detectors 31-3. When the primary image data Y0 with the gain selection signal N and (1) is stored in the buffer memo In0, the determination in step S9 becomes YES, and the process proceeds to step 311 to stop the X-ray irradiation. In step 312, it is determined whether the flag F1 is set to 1''. Since the flag F1 is set to θ'' due to the initialization in step 31, step S14
Then, the gain selection signal NG (
1) Read out the primary image data Y0 and calculate the X-ray detector all near the output saturation point by a predetermined calculation. When in the 21x mode, the X-ray detector 3. is required (see Figure 3). In step S15, A D for X-ray detector 3II
ou! Multiply (3Il) by (2'')-H and store the result in register α.When in double mode, α=A
Douv (L) If it is the 2 carp double mode, it is determined as YES and the process proceeds to step S17, where it is determined whether the flag F is set to "1°°". The flag F3 is set to 0 by initialization in step Sl.
Therefore, the process proceeds to step 318 and stores the contents of register α in register C. That is, C=ADo
uv ('3.) Since R=1, the process advances to step S25. In step S25, it is determined whether the flag F1 is set to "1". Since it is 0", step S
In step 26, the flag F is set to "1", and in step 327, the second gain setting terminal T2 is set to "0" to select the 1x mode (the first gain setting terminal T1 is set to "1"). This corresponds to collecting X-ray detection data according to the characteristics shown in (A) in FIG. 3. In step 32B, register N is set to 1 Denotes mode °“
After storing 0°, the process returns to step S6. Hereinafter, the process advances from step S6 to step S7, and then,
After repeatedly executing steps S8→S9→SIO→S8, the process proceeds from step Sll to step S12. In this case, since the flag F was previously set to 1" in step S26, the process advances to step S13, and the flag F is set to 1" in step S26.
2 is set to "1". ”
0'', the process jumps to step 514 and proceeds to step S15, and calculates the result of multiplying the previously obtained A DoII?(3-) by (2')-' for the X-ray detector 3. Store in register α.In 1x mode, N
Since =0, α=ADout(L)X(2')'. Since N=0, Step 516 makes a NO decision and proceeds to Step 319. Imamaro makes a YES decision and proceeds to Step S20, where the contents of register α are stored in register D. In other words, D=ADauy (3s) Proceed to step S and determine whether flag F1 is set to "1".
26 is set to "1", so step 329
It is determined whether the flag F2 is set to "1". At this time, since it is “0”, step S
Proceeding to step 30, the flag F2 is set to "1". In step S31, the double mode is selected for 22 by setting the first gain setting terminal T to 1'' (the second
(The gain setting terminal T□ has already been set to 0'' in step S27), which corresponds to collecting X-ray detection data according to the characteristics shown in (C) of FIG. 3. In step $32, After storing "2" representing the 2zk times mode in the register N, the process returns to step S6. From step S6, the process proceeds to step S7, and then,
After repeatedly executing steps S8→S9→510→S8, the process proceeds from step 311 to step S12. In this case, since the flag F1 is set to "BI" in step S26 and the flag F2 is set to 1 in step S30, the process proceeds from steps S12 to S13 to S14, and the gain selection 13 is performed from the buffer memo view month O. No. N. The primary image data Y0 with (2) is read out, and the X-ray detector 3x near the output saturation point is determined by a predetermined calculation. is required (see Figure 3). In step S15, A Do regarding the X-ray detector 3X
Multiply Ili(3X) by (2k)-' and store the result in register α. 22. When in double mode, α=A
Dout (3t) X (2") -". 22, in the double mode, N=2, so the process proceeds from steps 316-319 to S21, and the contents of register α are stored in register A. That is, A=ADout (3t) The process then proceeds from step S29 to step S33, where the flag F is set to "0", and in step S34, the flag F is set to "1", and then the process returns to step S3. That is, in step S3 , the first gain setting terminal T+ is set to "0°", and the second gain setting terminal T is set to "1" in step S4, so that the gain is set to 2° again.
゛Select double mode. Then, in the same manner as last time, from step S5 to step S
It reaches 13. In step 333, since the flag Fz is set to 0'', the process jumps to step S14 and proceeds to step 315, where ADoav(3,) for the previously obtained X-ray detector triplex is converted to (2k)-' Multiply and store the result in register α.When in double mode,
Since N=1, α=ADout (3t) x (2'')'. Since N=1 and F=1, step S16 → S
17→S22, the contents of register α are stored in register B. That is, B=ADauv (3t) X (2')'. Next, in step S23, the contents of register R are added by 1 (+1)L, and in step S24, since n=4 at present, the process proceeds to step 335. In step S35, from the contents of register D, register C
Subtract the contents of and use the result as correction data 0ffSetc
It is stored in the RAM 15 as +. Correction data 0ffse
tct+ is 0ffsetcIl=D C=ADOIIT (L
) X (2') 'ADout (L)
2') -'. In step 336, the contents of register A are subtracted from the contents of register B, and the result is stored in the RAM 15 as correction data Offsetam. The correction data Offsetam is 0ffsetA1”B-A=ADoot (3+)
X (2”) −'-ADaat (3t) x
(2”) −”. Next, in step S37, the select terminal T0 is set to “Ho”.
“ level, the selector 17 is switched to a state where the output of the logic circuit 8 is input, and the series of sequence operations is completed. This corresponds to the error Δ, D between the value of Po and the value of point Pc, and the correction data is 0.
ffset411 is the error Δ between the value of point P3 and the value of point P.
Corresponds to Al. (2) Correction operation of CT image data during actual measurement Next, the correction operation of CT image data during actual measurement will be explained based on the flowchart of FIG. In step #1, all registers and flags are initialized, in step #2, 1' is stored in register n, and in step #3, the primary image of the nth (j+2) bit from the buffer memory 1 O is stored. This primary image data Y, which reads data Yo, consists of the gain selection signal NG of the upper 2 bits and the A/D conversion data A D of the lower j bits.
It is a combination of o and u↑. In step #4, the gain selection signal N is set to [O1] (2'
(double mode). m X-ray detectors3. .about.31 are scanned in the order of their arrangement, so the first one is the gain selection signal Nc. is (00) (2" mode), it is determined as No and the process proceeds to step #5. In step #5, the gain selection signal N is set to [10] (2t
``'' double mode).The X-ray detectors 31 to 3 determine YES and proceed to step #11.Step #11 stores the corrected CT image data Y' in the RAM.
15, but in the double mode, the CTWI image data Y is written as is as corrected CT image data Y' in 21 (Y'-Y). In step #12, the contents of register n are
~3. It is determined whether the number m has been reached. If not, in step #13, the contents of register n are incremented by 1' (+1)L, and then the process returns to step #3. When n=1 to i, almost step #3 → #4
→ Repeat #5 → #11 → #12 → #13 → #3. When n=i+1, it corresponds to the double mode, and the judgment in step #4 becomes YES, and step #6
Step #7 reads the correction data Offsetam from the RAM 15, and in step #7, the corrected CT image data Y' is obtained by subtracting the correction data 0ffset□ from the CT image data Y. Y' = Y -0ffset, B - Next, proceed to step #11 and calculate CTjii after correction.
Write the i-image data Y' into the RAM 15, and return to step #3 from step #12→#13.
When n=i+1 to S, steps #3 → #4 → #6
→ Repeat #7 → #11 → #12 → #13 → #3. When n=s+1, it corresponds to the 1x mode, and the judgment in step #4 is No and the judgment in step #5 is also N.
0, proceed to step #8, read the correction data (lffsatam) from the RAM 15, and in step #9,
The correction data 0ffsetce is read from the RAM 15, and in step #10, correction data 0ffsetA and correction data 0ffsetc+ are read from the CT image data Y.
By subtracting +, the corrected CT image data Y'
get. Y'=Y-Offsetam-Offsetc. Next, the process proceeds to step #ll, where the corrected CT image data Y' is written into the RAM 15, hereinafter step #12.
→ Return to step #3 from #13, but n=s+
1 to m, step #3 → #5 → #8 → #9 →
Repeat #10 → #11 → #12 → #13 → #3. Then, when n=m, the series of sequence operations ends. As mentioned above, double king-do to 2, 2! By correcting for each double mode, instead of the conventional CT image data Y having discontinuity at the gain switching point, the final OCT image data Y' to be obtained is made continuous as shown by the solid line OQ in Figure 11. It can be calibrated to a certain value to prevent artifacts. First Example Next, a second embodiment will be explained based on FIGS. 5 and 6. In FIG. 5, the same reference numerals as those shown in FIG. 1 according to the first embodiment refer to the same parts as those indicated by the reference numerals in this embodiment as well. The configurations of this embodiment that are different from the first embodiment and the embodiment are as follows. 18 is A/D conversion data ADou from the A/D converter 7
The variable bit shifter, LUT, inputs t and changes the decimal point position of A/D conversion data ADOI+T according to the gain selection signal N from the selector 17 and outputs the correction obtained in the same manner as in the first embodiment. A lookup table 19 stores data and outputs correction data according to the gain selection signal N6, and an adder 19 adds the output data of the variable bit shifter 18 and the output data of the lookup table LUT. The rest of the configuration is the same as that of the first embodiment, so a description thereof will be omitted. Next, the operation of this second embodiment will be explained. As shown in the format of FIG. 6, the lookup table LUT outputs O when the gain selection signal N is [lO], and outputs -Offsetam when it is [O1].
is output, and when it is [OO], -(OffSetas+
0fflietcD). Variable bit shifter 18 operates as shown in FIG. The j-bit A/D conversion data ADout is expressed in binary as: aj-1・2'-' +a7-, ・2to2+...
・+a, ・2°. The gain selection signal N is

When [00], CT image data Y=ADout
"ADouv X (2') -'-ADout X
2°, the output data of the variable bit shifter 18 is (o, aj-1...ao). When the gain selection signal NG is [01], Yzh=AD
ot+tX(2')-'=ADot+tx2
-, the output data of the variable bit shifter 18 becomes (0, 0...0aj-+...ao).The decimal point position is shifted by (2'')-. '
= 2-''. When the gain selection signal N is [11], Yzt*
=ADoutX(2')-"=ADou
t X 2-'', variable bit shifter 1
The output data of 8 is [0, OO...'00 a, -+
...ao ]. Shifting the decimal point to 2 is (2&)-”=2-
This is because 2. By shifting the decimal point position in this way, it is possible to output from the variable bit shifter 18 in a state in which both the 2x mode and the 20x mode are converted to the 1x mode. The output from the adder 19 is Y' in the 2× mode.
=Y+O=Y, and when in 2x mode, Y'''' Y -Offsetam, and when in 1x mode, Y' = Y - (Offsetal + 0ffsetco
). Therefore, as in the case of the first embodiment, the final CT image data Y' to be obtained can be calibrated to be continuous as shown by the solid line OQ in FIG. 11, and artifacts can be prevented. Effects of G1 Invention According to this invention, the following effects are exhibited. The error stored in the storage means is not an error in the output of the auto gain amplifier, but is an error in the CTitt image data to be finally obtained, and the correction means uses this error as correction data to calculate the CT image by the calculation means. Since the data is corrected, discontinuities at the gain switching point can always be eliminated in the final CT image data without fluctuations in environmental conditions such as temperature, resulting in a good 01 image without artifacts. be able to. In addition, the only manual work required for correction is to manually set the gain instead of auto-gain operation to find the error in CTg image data, and the work to prevent artifacts is much easier compared to conventional methods. This method can be significantly simplified and can be implemented economically without requiring a voltage input device with a dedicated programmable power supply.

[Brief explanation of the drawing]

1 to 4 relate to a first embodiment of the present invention, in which FIG. 1 is a block diagram of a data acquisition device of an X-ray computed tomography apparatus, and FIG. 2 is a flowchart for explaining error calculation and storage operations. FIG. 3 is a characteristic diagram of A/D conversion in each magnification mode, and FIG. 4 is a flowchart for explaining the correction operation of CT image data during actual measurement. 5 to 7 relate to the second embodiment, and FIG. 5 is a block diagram of a data acquisition device of an X-ray computed tomography device;
Figure 6 shows the memory format of the lookup table.
FIG. 7 shows the format of the output data of the variable bit shifter. 8 to 11 relate to conventional examples, FIG. 8 is a block diagram of a data acquisition device of an X-ray computed tomography apparatus, and FIG. 9 (A) is a schematic diagram showing an X-ray tube and an X-ray detector. figure,(
B) is an X-ray intensity distribution diagram, (C) is an output characteristic diagram of the auto gain amplifier, Figure 1θ is a characteristic diagram of A/D conversion data with respect to integral output, and Figure 11 is a characteristic diagram of CT image data with respect to integral output. It is a diagram. 3...X-ray detection section' 31-3. ...X-ray detector 6...Auto gain amplifier 7...A/D converter A/D conversion data N6...Gain selection signal Y...CT image data 15... RAM (storage means) 11...cpu (including calculation means and correction means) Δ^
,,Δco...Error

Claims (1)

[Claims] (1) An auto-gain amplifier that automatically selects a gain according to the input level from the X-ray detector, an A/D converter that converts the output of this auto-gain amplifier into A/D, and this A/D conversion C from the A/D conversion output data by the device and the gain selection signal obtained in the auto gain amplifier.
A data acquisition device for an X-ray computed tomography apparatus, comprising: arithmetic means for calculating T image data; A data acquisition device for an X-ray computed tomography apparatus, comprising a correction means for correcting CT image data obtained by the calculation means.