JPH1099319A - X-ray ct system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent X-ray beams from being deviated from parallelism and to prevent the accumulation of deviation as well. SOLUTION: When the value of an (n) counter 6 becomes '1', a decoder 7 simultaneously outputs sampling timing signals to respective A/D converters AD01; AD02...AD-n. When the sampling timing signals are applied to the A/D converters AD01, AD02...AD-n themselves, they start A/D conversion but the sampling timing signals are simultaneously applied, the A/D conversion is started at the same time. Thus, the exact data of a group of parallel beams can be acquired.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT (Compo
More specifically, the present invention relates to an X-ray CT apparatus for acquiring data of a parallel beam from a fan beam type X-ray tube and a detector by controlling the timing of data acquisition.

[0002]

2. Description of the Related Art In an X-ray CT apparatus, an image is reconstructed from projection data by an image reconstruction operation. To perform this image reconstruction operation at a high speed, a group of parallel beams for different view angles is used. Data is needed. However, in an X-ray CT apparatus having a fan beam type X-ray tube and a detector, the X-ray beams incident on the respective detector channels are not parallel. For this reason, a method of collecting data while rotating an X-ray tube and a detector in an X-ray CT apparatus having a fan-beam type X-ray tube and a detector (R-
In an X-ray CT apparatus of the (R method), as one of methods for performing high-speed image reconstruction, data of a group of parallel beams for different view angles is acquired by controlling the timing of data acquisition.

FIGS. 3 to 5 are explanatory views of the principle of acquiring data of a group of parallel beams by controlling the timing of data acquisition in an RR type X-ray CT apparatus. As shown in FIG. 3A, 1/2 of the fan angle of the fan beam (the angle formed by the X-ray beams incident on the detector channels at both ends of the detector 2) is φ, and the detector angle pitch (adjacent) Ψ), the angle of the X-ray tube 1 is 0 °,
When the detector channel numbers are assigned from “1” to “D” in the direction opposite to the rotation direction of the X-ray tube 1 and the detector 2, the X-ray beam incident on the detector channel “1” has the 0 ° axis A. The angle formed is φ and X incident on the detector channel “2”
The angle that the line beam makes with the 0 ° axis A is (φ−ψ).
Next, as shown in FIG. 3 (b), when the X-ray tube 1 and the detector 2 are rotated by the detector angle pitch ψ, the X-ray beam incident on the detector channel “2” becomes the 0 ° axis. The angle formed with A is φ, and X incident on the detector channel “3” is
The angle that the line beam makes with the 0 ° axis A is (φ−ψ).
3 (a) and 3 (b), the X-ray beam incident on the first detector channel at the first X-ray tube angle and rotated by the detector angle pitch か ら from the first X-ray tube angle. The X-ray beam incident on the second detector channel adjacent to the first detector channel at the second X-ray tube angle in the direction opposite to the rotation direction of the X-ray tube and the detector at the second X-ray tube angle becomes a parallel beam. You can see that. That is, as shown in FIG. 4, every time the X-ray tube 1 and the detector 2 are rotated by the detector angular pitch ψ, the parallel X-ray beam is adjacent to the X-ray tube and the detector in the opposite direction. To each detector channel in turn. Therefore, as shown in FIG. 5, every time the X-ray tube 1 and the detector 2 rotate by the detector angular pitch ψ,
If data is acquired in the order of the number of the detector channel, data of a group of parallel beams can be acquired.

FIG. 6 is a configuration diagram of a main part of an example of a conventional X-ray CT apparatus (only a part related to the present invention).
In the X-ray CT apparatus 600, the X-ray tube 1 and the detector 2 rotate around the isocenter IC in the direction of the arrow in the figure. The number of channels of the detector 2 is mn
(= D in FIG. 3).

Each of the detector channels of the detector 2 includes m channel selectors cs01, cs02,
, Cs_n are connected to the input terminals. These channel selectors cs01, cs02, ..., cs_
n output terminals are n AD converters AD0
, AD02,..., AD_n. The AD converters AD01, AD02,.
Each output terminal of AD_n is connected to an input terminal of the AD selector 3. Further, the output terminal of the AD selector 3 is connected to the data buffer 4.

The data read controller 5 outputs a reset signal RST for initializing the n counter 6 and an LUT (Look Up Table) 8, and outputs a pulse signal CUP including a pulse counted by the n counter 6. The n counter 6 outputs "1" when initialized by the reset signal RST. Further, the pulses of the pulse signal CUP are counted, and the value is cyclically changed from “1” to “n”. Further, when the value is returned from "n" to "1", carry signal CRY is output.

The decoder 7 outputs a sampling timing signal to each of the AD converters AD01, AD02,..., AD_n when the value of the n counter 6 becomes "1", "2",. Output in order. When the value of the n counter 6 becomes "1", "2",..., "N", the AD converters AD01, AD02,.
A sampling timing signal for selecting each output value of _n is given to the AD selector 3. The AD
The converters AD01, AD02,..., AD_n start the AD conversion when the sampling timing signal is given to themselves. When a sampling timing signal for selecting the output value of each of the AD converters AD01, AD02,..., AD_n is given, the AD selector 3 receives the sampling timing signal after the time required for AD conversion has elapsed. The output value of the corresponding AD converter is written in the data buffer 4.

The LUT 8 is provided with the reset signal RST.
, The channel selection instruction signal is given to the channel selectors cs01, cs02,..., Cs_n, and the channel selectors cs01, cs02,.
Data of the detector channel connected to a predetermined one of the m input terminals of cs_n is input to corresponding AD converters AD01, AD02,..., AD_n. The carry signal C is output from the n counter 6.
Each time RY is input, a channel selection instruction signal is given to the channel selectors cs01, cs02,..., Cs_n, and the channel selectors cs01, cs02,.
One of the m input terminals of cs_n is selected in a predetermined order, and the data of the detector channel connected to the input terminal is converted to the corresponding AD converter AD01, AD02,
.., AD_n. The order of selection is written in the LUT 8 in advance.

FIG. 7 shows the channel selector cs01,
, cs_n and the order of selection of the detector channels and the AD converters AD01, AD02,..., AD_n
5 is a chart showing an example of the timing of AD conversion in FIG. It is assumed that m = 16 and n = 32. In the initial state, the channel selectors cs01, cs02,.
2, detector channels "1", "17", ..., "497"
Select Then, sampling is started by the AD converter AD01, and the data of the AD-converted detector channel "1" is written to the data buffer 4. Next, after time τ, sampling is started by the AD converter AD02, and A
The D-converted data of the detector channel “17” is written in the data buffer 4. Next, after time τ, sampling is started by the AD converter AD03, and the AD-converted data of the detector channel “33” is written to the data buffer 4. Thereafter, the sampling is started by the next AD converter at every τ time, and the AD converted data of the detector channel is written into the data buffer 4. When the block B01 ends, the channel selectors cs01, cs02,..., Cs
At 32, the detector channels “12”, “28”,.
8 ". Then, sampling is started by the AD converter AD01, and the AD-converted detector channel" 1 "is selected.
2 ”data is written into the data buffer 4. Hereafter, τ
Every time, sampling starts with the next AD converter,
The AD-converted data of the detector channel is written into the data buffer 4. When the block B16 ends, the process returns to the block B01. Then, the above processing is repeated.

Here, if the time τ is set to be equal to the time during which the X-ray tube 1 and the detector 2 rotate by ψ / 96, the data of the detector channel “1” is acquired and then the X-ray tube 1 is obtained. Each time the detector 2 rotates by the detector angular pitch ψ, the data of the detector channels “2”, “3”, “4”,. 4 and 5
As described with reference to, data of a group of parallel beams can be obtained.

The reason why the order is complicated as shown in FIG. 7 is to collect as much data as possible in a short time (that is, thereby shortening the scan time and reducing the burden on the patient). Do).

[0012]

In the above-mentioned conventional X-ray CT apparatus 600, the detector channel "16" is assigned to the AD converter AD01, but the detector channel "1" is assigned to it.
7 ”is assigned to the AD converter AD02.Therefore, the time from the timing of acquiring the data of the detector channel“ 16 ”to the timing of acquiring the data of the detector channel“ 17 ”is as shown in FIG. Is the time obtained by adding the time τ to the time required for the X-ray tube 1 and the detector 2 to rotate by the detector angle pitch ψ, but the time required for the X-ray tube 1 and the detector 2 to rotate by the detector angle pitch ψ Than τ
The longer the time, the more the X-ray beam deviates from the parallel. Further, there is a problem that the deviation from the parallel state is accumulated every time the AD converters respectively serving the adjacent detector channels change. The X-ray tube 1 and the detector 2 set the τ time at 16 ° / (16 · 96).
If it is set to be equal to the rotation time by +1), the problem that the deviation from parallel is accumulated is eliminated, but another problem that the parallelism between adjacent detector channels, which is covered by the same AD converter, deteriorates. Produces a point. SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray CT apparatus which can solve the above-mentioned problems and can acquire accurate data of a group of parallel beams.

[0013]

According to a first aspect, the present invention comprises a fan-beam x-ray tube and a detector, and a plurality of A / D converters each serving a plurality of detector channels. In an X-ray CT apparatus which obtains data by sequentially AD converting data of each detector channel by a corresponding AD converter while rotating an X-ray tube and a detector, a first detector channel is provided at a first X-ray tube angle. First to AD convert the data of
And a second X-ray tube angle rotated from the first X-ray tube angle by a detector angle pitch ψ to the first detector channel in a direction opposite to the rotation direction of the X-ray tube and the detector. And the second AD converter for AD-converting the data of the second detector channel adjacent to is a separate AD converter,
An X-ray CT apparatus comprising: a sampling timing control unit for simultaneously setting sampling timings of both AD converters at the second X-ray tube angle. Attention is paid to a first X-ray tube angle and a second X-ray tube angle rotated from the first X-ray tube angle by a detector angle pitch ψ. In addition, attention is paid to the first detector channel and the second detector channel adjacent to the first detector channel in the direction opposite to the rotation direction of the X-ray tube and the detector. At this time,
In the X-ray CT apparatus according to the first aspect, data of a first detector channel is acquired at a first X-ray tube angle,
When acquiring data of the second detector channel at the second X-ray tube angle, sampling of the second AD converter that performs AD conversion of the data of the second detector channel at the second X-ray tube angle The timing is the same as the sampling timing of the first AD converter that performs AD conversion of the data of the first detector channel at the second X-ray tube angle. Conventionally, since the sampling timing of the first AD converter at the second X-ray tube angle and the sampling timing of the second AD converter are different, the sampling timing of the first AD converter is different. Is adjusted to the detector angular pitch ψ, a shift from parallel occurs each time an AD converter that serves an adjacent detector channel changes, and the shift is accumulated. Further, if the sampling timing of the second AD converter is adjusted to the detector angular pitch ψ,
Although the accumulation of the shift disappears, the parallelism between the adjacent detector channels, which is assigned to the same AD converter, is deteriorated. However, in the X-ray CT apparatus according to the first aspect, the sampling timing of the first AD converter and the sampling timing of the second AD converter at the second X-ray tube angle are set at the same time. If this sampling timing is adjusted to the detector angular pitch ψ, the deviation from the parallel state will not occur, and the accumulation of the deviation will also disappear. Therefore, it is possible to acquire accurate data of a group of parallel beams.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited by this.

FIG. 1 is a configuration diagram of a main part (only a part related to the present invention) of an X-ray CT apparatus according to an embodiment of the present invention. In the X-ray CT apparatus 100, the X-ray tube 1 and the detector 2 rotate around the isocenter IC in the direction of the arrow in the figure. The number of channels of the detector 2 is:
mn.

Each of the detector channels of the detector 2 includes m channel selectors cs01, cs02,
, Cs_n are connected to the input terminals. These channel selectors cs01, cs02, ..., cs_
n output terminals are n AD converters AD0
, AD02,..., AD_n. The AD converters AD01, AD02,.
Each output terminal of AD_n is connected to an input terminal of the AD selector 3. Further, the output terminal of the AD selector 3 is connected to the data buffer 4.

The data read controller 5 outputs a reset signal RST for initializing the n counter 6 and the LUT 8, and outputs a pulse signal CUP including a pulse counted by the n counter 6. The n counter 6 outputs "1" when initialized by the reset signal RST. Further, the pulses of the pulse signal CUP are counted, and the value is cyclically changed from “1” to “n”. Further, when the value is returned from "n" to "1", carry signal CRY is output. When the value of the n counter 6 becomes "1", the decoder 7 outputs the AD converters AD01 and AD01.
, AD_n are simultaneously output. When the value of the n counter 6 becomes “1”, “2”,.
A sampling timing signal for selecting the output value of each of the D converters AD01, AD02,.
This is given to the AD selector 3. The AD converter AD0
, AD_n start AD conversion when their own sampling timing signal is given.
Here, since the sampling timing signal is supplied at the same time, AD conversion is started at the same time. Further, the AD selector 3 is provided with the AD converter AD01,
When a sampling timing signal for selecting the output value of each of AD02,..., AD_n is given, the output value of the AD converter corresponding to the sampling timing signal is stored in the data buffer 4 after a lapse of time required for AD conversion. Write.

The LUT 8 receives the reset signal RST.
, The channel selection instruction signal is given to the channel selectors cs01, cs02,..., Cs_n, and the channel selectors cs01, cs02,.
Data of the detector channel connected to a predetermined one of the m input terminals of cs_n is input to corresponding AD converters AD01, AD02,..., AD_n. The carry signal C is output from the n counter 6.
Each time RY is input, a channel selection instruction signal is given to the channel selectors cs01, cs02,..., Cs_n, and the channel selectors cs01, cs02,.
One of the m input terminals of cs_n is selected in a predetermined order, and the data of the detector channel connected to the input terminal is converted to the corresponding AD converter AD01, AD02,
.., AD_n. The order of selection is written in the LUT 8 in advance.

FIG. 2 shows the channel selector cs01,
, cs_n and the order of selection of the detector channels and the AD converters AD01, AD02,..., AD_n
5 is a chart showing an example of the timing of AD conversion in FIG. It is assumed that m = 16 and n = 32. In the initial state, the channel selectors cs01, cs02,.
2, detector channels "1", "17", ..., "497"
Select Then, the AD converters AD01, AD02,
,..., AD32, sampling is started at the same time, and the data of the detector channel “1” that has been AD-converted by the AD converter AD01 is written to the data buffer 4. Next, after time τ, the data of the detector channel “17” that has been AD-converted by the AD converter AD02 is written to the data buffer 4. Next, after time τ, the data of the detector channel “33” that has been AD-converted by the AD converter AD03 is written to the data buffer 4. Thereafter, the data of the detector channel AD-converted by the next AD converter is written to the data buffer 4 every τ time. When the block B01 ends, the detector channels "12", "28", ..., "508" are selected by the channel selectors cs01, cs02, ..., cs32. Then, sampling is started simultaneously by the AD converters AD01, AD02,.
The D-converted data of the detector channel “12” is written in the data buffer 4. Thereafter, the data of the detector channel AD-converted by the next AD converter is written to the data buffer 4 every τ time. When the block B16 ends, the process returns to the block B01. Then, the above processing is repeated.

Here, if the τ time is set equal to the time during which the X-ray tube 1 and the detector 2 rotate by ψ / 96, the data of the detector channel “1” is acquired and then the X-ray tube 1 is obtained. Each time the detector 2 rotates by the detector angular pitch ψ, the data of the detector channels “2”, “3”, “4”,. 4 and 5
As described with reference to, data of a group of parallel beams can be obtained. Then, the detector channel “1”
The A / D converter AD01 that handles the “6” and the A / D converter AD02 that handles the detector channel “17” are different,
Since the timing at which the data of the detector channel "16" is A / D converted is the same as the timing at which the data of the detector channel "17" is A / D converted, the data of the detector channel "17" is also transmitted as shown in FIG. , X-ray tube 1 and detector 2 are obtained during the rotation of detector angle pitch ψ, and the corresponding X-ray beams are exactly parallel.

The reason why the order is complicated as shown in FIG. 2 is to collect as much data as possible in a short time (that is, thereby shortening the scan time and reducing the burden on the patient). Do).

According to the X-ray CT apparatus 100 described above, no deviation from parallelism occurs, and no accumulation of deviation occurs. Therefore, it is possible to acquire accurate data of a group of parallel beams.

[0023]

According to the X-ray CT apparatus of the present invention, no deviation from parallelism occurs, and no accumulation of deviation occurs. Therefore, it is possible to acquire accurate data of a group of parallel beams.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of an X-ray CT apparatus according to an embodiment of the present invention.

FIG. 2 is a table showing an example of a detector channel selection order in a channel selector and AD conversion timing in an AD converter.

FIG. 3 is an explanatory diagram showing a relationship between a rotation angle of an X-ray tube and a detector and a detector channel when an X-ray beam is parallel.

FIG. 4 is an explanatory diagram showing a relationship between a rotation angle of an X-ray tube and a detector which can acquire data of a group of parallel beams and a detector channel.

FIG. 5 is an explanatory diagram showing a relationship between a rotation angle of an X-ray tube and a detector capable of acquiring data of a group of parallel beams and a channel number of a detector to be sampled.

FIG. 6 is a main part configuration diagram of an example of a conventional X-ray CT apparatus.

FIG. 7 is a table showing a conventional example of a detector channel selection order in a channel selector and AD conversion timing in an AD converter.

[Explanation of symbols]

 100,600 X-ray CT apparatus 1 X-ray tube 2 detector 3 AD selector 4 data buffer 5 data read controller 6 n counter 7 decoder 8 LUT AD01 to AD_n AD converter cs01 to cs_n Channel selector φ 1/2 of fan angle Detector angle pitch

Claims (1)

[Claims] 1. An X-ray tube and a detector of a fan beam type, and a plurality of AD converters each of which has a plurality of detector channels, wherein each of the detector channels is rotated while rotating the X-ray tube and the detector. In the X-ray CT apparatus, which obtains the data of the first detector channel at the first X-ray tube angle in the X-ray CT apparatus,
A first AD converter for D-conversion and an X-ray tube and a detector connected to the first detector channel at a second X-ray tube angle rotated from the first X-ray tube angle by a detector angle pitch ψ When the second AD converter for AD-converting the data of the second detector channel adjacent in the direction opposite to the rotation direction is a separate AD converter, both ADs at the second X-ray tube angle are provided. X-ray CT having sampling timing control means for making the sampling timing of a converter simultaneous.
apparatus.