JPH08215187A - X-ray ct device and its data processing method - Google Patents

Abstract

PURPOSE: To obtain an image giving a CT value excellent in uniformity and the like, which is less adversely affected by archifact due to scattered light even if slicing is made thick in width by employing a split type detector which is made up of a detecting part divided into a plurality of numbers in the channel direction and the slicing direction. CONSTITUTION: A X-ray bulb 1 and a detector in a circular arc external shape provided with a plurality of detecting channels are mutually disposed face-to-face while a testee 7 is being held at the center, and X-ray beams 8 are irradiated onto the testee 7 from the X-ray bulb 1 while the bulb is being rotated around the testee 7, and measurement is simultaneously performed. A plurality of the channels consisting of the detector 4 in a circular arc shape are divided into a plurality of detecting sections (surface) 41 every each channel (ch) in the slicing direction. The output of the detector 4 is connected to a detecting circuit 5 in such a way that the respective detecting sections are independently connected to the circuit, after analogue signals have been converted into digital signals, measurement data is formed into the measurement data which is less in division number than that of the detector in the splicing direction by each divided data or through the addition process of mutually adjacent divided data by an image reconstruction processing means 6, and a measurement image is thereby reconstructed thereafter.

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 apparatus for obtaining a tomographic image of a human body or the like by X-rays. The present invention relates to a data processing method for obtaining various tomographic images.

[0002]

2. Description of the Related Art An X-ray CT apparatus is widely used as a means for obtaining a tomographic image of a subject including a human body in order to obtain internal information of lesions of the human body such as a patient. However, in such an X-ray CT apparatus, due to the influence of scattered X-rays generated from the subject, a band-shaped artifact (false image) on the CT image.
Appears or the CT value uniformity is deteriorated. Therefore, conventionally, various quality hardening corrections, scattered radiation corrections, and the like have been performed as measures against these factors of image deterioration. However, in these corrections, the higher the correction content, the longer the image processing time, and the partial volume effect deteriorates the correction effect when the measurement slice thickness is thick (wide). The problem of doing it remained.

In order to reduce the influence of such image deterioration factors, basically, the measurement slice thickness is made thin (narrow) and a large amount of measurement data is obtained. That is, the adverse effect of the scattered X-rays described above decreases as the measurement slice thickness becomes narrower, and therefore,
To simply reduce the influence of scattered radiation, it is better to perform measurement in a narrow slice, and the scattered radiation correction effect will be improved.

[0004]

However, in the above-mentioned conventional technique, image noise increases due to thin (narrow) slice measurement, and therefore, it is of diagnostic value to observe a lesion with a small contrast difference. In addition to the decrease, the inspection time, the calculation time, and the X-ray exposure amount of the subject increase, which is a big problem in the inspection by the X-ray CT apparatus.

Therefore, in the present invention, in view of the above-mentioned problems in the prior art, even when the slice width is thick (wide), the artifacts due to scattered rays are small, and an image with good CT value uniformity can be obtained. It is an object of the present invention to provide a line CT apparatus and a data processing method for obtaining a good tomographic image. That is, in the measurement of the X-ray CT apparatus, an artifact that interferes with the diagnosis caused by scattered radiation generated from the subject is reduced, and a tomographic image that is suitable for the diagnosis is provided at high speed.

[0006]

In order to achieve the above object, the present invention proposes that an X-ray from an X-ray source is first radiated in a channel (ch) direction with a predetermined slice width, An X-ray CT apparatus for detecting the X-ray transmitted through a subject by a detector arranged in the ch direction, and forming a tomographic image of the subject by the detection signal detected by the detector. , A detection unit divided into a plurality of ch directions, and a detection unit divided into a plurality of ch directions is further formed from a detection unit divided into a plurality of slice directions. The aggregate of detectors has a detector structure that constitutes a 1ch minimum unit detector, and is capable of performing slice measurement of a plurality of widths by one measurement, and further, the 1ch minimum unit detector. Make up A detection circuit which performs data correction processing from the detection unit divided into the number of slice direction, the correction data processed by the detection circuit, the 1ch
X-ray CT apparatus provided with an image reconstruction processing apparatus for reconstructing a slice image having a slice width equal to or thicker than the slice width measured by each of the plurality of divided detection units constituting the minimum unit detector. .

Further, according to the present invention, in order to achieve the above-mentioned object, the detector is divided into a plurality of sections in the channel direction, and each of the detector sections is further provided in the slice direction. The detector unit is divided into a plurality of detector units, and an aggregate of the detector units divided into a plurality of slice directions has a detector structure that constitutes a minimum unit detector of 1 ch. A slice width is radiated in the ch direction, and the X-ray transmitted through the subject is detected by a detector arranged in the ch direction to form a tomographic image of the subject, and slice measurement of a plurality of widths is performed once. A method for processing the detection data in an X-ray CT apparatus capable of performing the correction processing, wherein the correction processing is performed on the data from the detection units divided in a plurality of slice directions forming the minimum unit detector of the 1ch, and the correction is performed. processing Data processing method for an X-ray CT apparatus for reconstructing a slice image having a slice width equal to or thicker than the slice width measured by each of the plurality of divided detectors constituting the minimum unit detector of 1ch Is proposed.

Further, according to the present invention, the X-ray correction method is provided which corrects the measured value of the divided data at the end portion in the slice direction where the direct X-ray beam does not hit during the narrow slice measurement as the scattered dose to the measured data. A data processing method for a line CT apparatus has also been proposed.

[0009]

According to the X-ray CT apparatus and the data processing method thereof according to the present invention, as described above, the channel (ch)
With the split-type detector that is composed of a plurality of detectors that are also divided into slice directions along with the direction, measurement data equivalent to thin slice width measurement is obtained, which suppresses artifacts due to partial volume, and Since the angle of the object to be inspected on the detector surface becomes small, the detection disturbance dose mixed in the measurement data can be reduced, and more precise scattered ray correction and X-ray quality correction can be performed, and a good image can be obtained. .

Further, according to the data processing method of the X-ray CT apparatus provided with the scattered radiation correction method according to the present invention, measurement data equivalent to thin slice width measurement can be obtained by the division type detector, and thus, It suppresses the artifacts caused by partial volume, and because the angle of the object to be inspected on the detector surface becomes smaller, the detected scattered dose mixed in the measurement data can be reduced, and not only a better image can be obtained, but also Since the measurement value of the divided data at the end of the slice direction where the direct X-ray beam does not hit during narrow slice measurement is corrected as the scattered dose to the measured data, highly accurate scattered ray measurement is possible for each slice measurement. As a result, it becomes possible to satisfactorily correct scattered radiation.

In addition, according to the present invention, the details of which will be described below, the processing of adding the data of the plurality of divided data is as small as the scattered radiation correction and the X-ray quality correction processing similar to the measurement data having a large slice thickness. By providing the image with the number of times,
The processing load on the device itself can be reduced. Further, the connection change between the split type detector and the detection hooves or the change process of the number of measurement data processing is naturally performed when the slice width is narrowed because the X-ray beam width on the detector entrance surface is narrowed. It is possible to reduce the number of detection units in the slice direction of the split detector, which can reduce the processing time of the device.

[0012]

The details of the embodiments of the present invention will be described below.
Description will be given with reference to the accompanying drawings. FIG. 1 shows a schematic structure of an X-ray CT apparatus according to an embodiment of the present invention. First, although not shown in FIG. 1A, the X-ray CT apparatus is placed in the scanner when the scanner direction is viewed from the bed side on which the subject 7 such as a patient is placed. The front view of the measurement-related device is shown in FIG.
Shows a side view of this measurement-related device.

In these figures, an X-ray tube 1 which is a source of X-rays, and an external arc-shaped detector 4 having a plurality of detection channels are arranged relative to each other with a subject 7 in the center. It is arranged in a positional relationship facing each other, and by such a layout relationship,
While rotating around the subject 7, irradiation and measurement of the X-ray beam 8 from the X-ray tube 1 to the subject 7 are performed. In addition,
Here, as the embodiment, the third generation CT apparatus in which the irradiation and measurement of the X-ray beam are performed while rotating around the subject 7 is shown, however, the present invention is not limited to this. Without any other generation X-ray CT
It is needless to say that the same can be applied to the apparatus or, for example, a continuous rotation type X-ray CT apparatus that performs spiral measurement on the subject.

First, the beam width of the X-ray beam 8 generated from the X-ray tube 1 is limited by the collimator 3 composed of a metal body or the like which blocks X-rays. Although not shown, the collimator 3 is mounted in the collimator device 2 shown by a broken line in the drawing together with an X-ray compensator or the like for adjusting the attenuation amount of the X-ray beam 8.

In the measurement by the CT device having such a configuration, as shown in FIG.
As shown in (b), by changing the slit width of the collimator 3 built in the above collimator device 2, X
Measurement is performed by changing the line beam width. That is, in the illustrated embodiment, the X-ray beam width can be varied as indicated by the broken line in the figure by appropriately adjusting the distance between the two metal plates forming the collimator 3 as indicated by the arrow in the figure. The structure is such that measurement is performed.

Further, according to the present invention, as a characteristic point, a plurality of channels forming the arc-shaped detector 4 are detected in a slice direction for each channel (hereinafter referred to as "CH"). It is divided into parts (faces) 41, 41 ... In this embodiment, an example in which each channel is divided into three will be described. Further, reference numeral 5 in the figure indicates a detection circuit, and the detection circuit 5 will be described in detail later, but the outputs of the detectors divided in the slice direction on each channel are connected independently. Further, reference numeral 6 is an image reconstruction processing device for performing an image reconstruction process using a signal obtained by converting the analog signal into the digital signal by the detection circuit 5.

That is, according to the present invention, as described above, the outputs of the detectors divided in the slice direction for each channel are independently connected to the detection circuit 5, where analog signals are converted to digital signals. After the conversion into the image reconstruction processing device 6, the image reconstruction processing device 6 performs a series of processing procedures described in detail later.
Measurement data smaller than the number of divisions of the detector in the slice direction is obtained by the addition processing of each divided data or each adjacent divided data. After that, the detailed contents thereof have been already proposed, for example, by the radiation quality correction as already proposed by Japanese Patent Application No. 6-1269, or by Japanese Patent Application Nos. 5-274171 and 6-7831. After the correction processing such as so-called scattered radiation correction is performed, the measurement image is reconstructed by the image reconstruction calculation method generally performed in the X-ray CT apparatus.

Next, more detailed contents of the X-ray CT apparatus according to the present invention, the outline of which is described above, will be described.
First, the detailed structure of the detector divided into a plurality of slices in each channel as described above will be described with reference to the attached FIG. This FIG. 3A shows a split-type X-ray CT.
A typical example of a solid-state detector for
Is a 1-ch type (1 ch) photosensor for X-ray CT (detection surface) in which a plurality of channels constituting the above are constituted by respective sensors. Its size is, for example, about 1 to 2 mm in the ch direction and about 20 to 30 mm in the slice direction. In this example, the light receiving portion on the surface is divided into three in the slice direction by the dead zone portion 40, each of which is an independent photo sensor 41 that receives light and generates a current signal. 41 ... These three independent photo sensors 41, 41 ...
As will be described later in detail, it has a structure in which one group constitutes one channel of the detector 4.

FIG. 3B shows an example of a solid-state detector for X-ray CT by integrating a plurality of the above-mentioned 1-ch type solid-state detectors, and usually one sensor for about 8 to 32 channels is provided. It is converted into one sensor. Structurally, the light receiving portion on the surface is also divided into a plurality of parts by the dead zone portion 40 formed in a lattice shape, so that the photosensors 41, 41 ... Are independently configured. And these photosensor groups are fixed on the substrate 44. As is clear from the figure, a plurality of photosensors 41, 41 ... Constituting these photosensor groups are provided in the 1ch width on the substrate 44 (three photosensors 41 in this embodiment, 41 ...) are divided and formed so as to be arranged in series. Further, the respective photosensors 41, 41 ... Are electrically connected to respective signal terminals 42, 42 ... Formed in series in the ch direction on the side in the slice direction (right side in the drawing). In addition, the photo sensor board 44
A pattern made of a conductive metal is provided inside each of the signal terminals 42, so that the signal output ports 43, 4 formed at the end portions of the substrate are formed in the same manner as the signal terminals 42, 42 ...
3 ... is connected. Although not shown here, these signal output ports 43, 43, ... Are connected to an external detection circuit 5 (see FIG. 1B), and the signal of the detector is amplified by the detection circuit. , Where it is converted to a digital signal.

Next, FIG. 4 also shows the basic structural shape of the solid-state detector as in FIG. 3, and more specifically, the photosensor substrate 44 shown in FIG.
Instead of the above-mentioned photosensor, a scintillator 45 for converting X-rays into an optical signal is attached to the above. This scintillator includes, for example, single crystal type NaI, CdWo4, or the like, or may be a powder scintillator obtained by solidifying powdery single crystals into a single body.
In these scintillators, in order to maintain the independence of each channel, as shown in FIG. 4A, a slit 46 is provided on the dead zone 40 for each channel, or as shown in FIG. The slits 46 are also inserted at the division points in the slice direction. As a result, there is little crosstalk between each channel, and the independence of each channel is high.
It shows good results.

Next, FIGS. 5A and 5B show the side and top structures of the signal electrode plate in the ionization chamber type detector which is another detector. This signal electrode plate is, for example, a conductor metal plate (a plate made of molybdenum, tungsten, stainless steel, iron, copper, etc.) having a thickness of about 0.1 to 0.2 mm.
A thin insulating layer 401 of polyimide or the like having a thickness of about 0.02 to 0.05 mm is attached to both surfaces of 400, and further,
A copper foil layer 4 having a thickness of about 0.02 to 0.04 mm on its side surface
By laminating 10 together, it is possible to produce a signal electrode plate having a five-layer structure. Further, the copper foil layers 410 arranged on both surfaces of such a signal electrode plate may be formed by a pattern etching process as a method other than the above-mentioned bonding. It is also possible to divide into. In this embodiment, the electrode surface of the signal electrode plate is divided into three parts on each side, and the signal extraction terminals 420, 420 ... Are provided on each electrode surface to detect the individual signal electrode surface from each terminal. The signal may be connected by soldering an electric wire or the like, and thus may be connected to an external detection circuit 5 (not shown) (see FIG. 1B). Then, in the ionization chamber type detector having such a configuration, if the same processing is performed on both surfaces thereof, one signal electrode plate 400 will have six divided electrode layers.

In FIG. 6, the above-mentioned signal electrode 400 is composed of a simple conductor metal plate and is applied with a high voltage electrode 430 to which a high voltage is applied, or with another signal electrode 400 having a five-layer structure electrode structure. The state where the electrode blocks are configured by alternately arranging between the insulating plates 440 and 400 and fixing them with an adhesive or the like is shown. Although not shown in the figure, the electrode block configured in this way is arranged in a detector case filled with xenon gas, and thereby operates as an ionization chamber type detector. The details of the ionization chamber type detector structure adopting such a five-layer structure double-sided electrode plate are described in, for example, Japanese Patent Application No. 6-1269. Also, regarding the method of sticking the polyimide, JP-A-57-63254 and JP-A-62-62354 are used.
It is described in detail in Japanese Patent Publication No. 53827 and can be easily manufactured by the method shown therein.

Next, a detection circuit connected to the split type detector described in detail above will be described with reference to FIG. 7 showing an embodiment including the configuration thereof. The embodiment shown in FIG. 7 shows an example of the case where the solid-state detector shown in FIG. 3 is used as the split type detector 4, and in this figure, the detector shown in FIG. 4 and the detection circuit 5 are shown by a broken line in the figure as the detector 4 and the detection circuit 5 for one channel, respectively.

In FIG. 7, each photosensor 41 constituting the split type detector 4 has an independent output terminal and is simultaneously connected to a common ground point. The output of each photosensor 41 is connected to an independent amplifier circuit 51 in the detection circuit 5, whereby a current signal from each photosensor is converted into a voltage signal. (Also, when the ionization chamber type detectors shown in FIGS. 5 and 6 are used as the detectors, the outputs from the detectors also become current signals.) As the amplifier circuit 51 here For example, many circuit configuration methods such as Miller integrator, current-voltage converter, or various low-pass filters can be adopted.

Subsequently, the voltage signals from these amplifiers 51 are sequentially connected to the signal bus 53 by the adder (SUM-AMP) 52. Although not shown here, the voltage signal output to the signal bus 53 is sent to an A / D converter, where it is sequentially converted from an analog voltage signal to a digital signal. Here, the adder 52 is composed of, for example, a commercially available multiplexer or various analog switches. Further, in the circuit diagram of this embodiment, the signals from the independent divided electrodes of the detector 4 are described as being added on the side of the image reconstruction processing device 6 (see FIG. 1B above), Instead of this, for example, an adder is arranged inside the signal switching unit 52 so that the divided signals can be added to arbitrary divided data on the detection circuit 5 side, and the divided signals are summed up to 1
It should be added that a method of sending out as a ch signal or sending the digital output signal from the A / D converter to the image processing device 6 after being processed by the adder may be adopted.

Next, the operation of the scattered radiation correction in the X-ray CT apparatus according to the embodiment of the present invention having the above-mentioned detailed construction will be described in detail with reference to the processing procedure of the flowchart of FIG. . In this procedure, all the data from each of the divided detector planes are measured, a plurality of divided data are added for each channel, and then the scattered ray correction and the radiation quality correction are performed once, so that the image reconstruction is performed. Is a procedure for performing.

First, in Step 1, the measurement condition is set before the measurement is started, and the measurement slice width is also set at this time. Although not shown in the figure, this operation is generally performed by an operation console that controls the operation of the X-ray CT apparatus, and then the measurement is started.

In Step 2, the data of the detector 4 divided in the slice direction is sequentially detected by the detection circuit 5 during a series of measurements.
It is taken in by and is sequentially sent to the image processing device 6.

Step 3 is the first processing performed in the processing process of the image processing apparatus 6, and generally, offset correction of the detector system and LOG (logarithmic) conversion processing are followed by X processing.
Pre-processing for reference correction and various sensitivity corrections associated with line fluctuations is performed for each measurement data.

At Step 4, an addition process is performed for each of the plurality of measurement data divided in the slice direction, whereby the data is converted into one data for one channel corresponding to the measurement data of the conventional CT apparatus. At this time, if the lengths of the respective divided detector surfaces of the detector are equal, simple addition processing is sufficient. Unlike this, if the division ratios of the detection surfaces are different, this corresponds to this division ratio. Weight addition processing may be performed.

In Step 5, for example, Japanese Patent Application No. 6-126
Known radiation quality corrections, whose details are described in No. 9, etc.,
Alternatively, Japanese Patent Application No. 5-274171 and Japanese Patent Application No. 6-78
The known correction processing such as the scattered radiation correction described in No. 31 and the like is performed, and the correction processing for reducing the CT value uniformity and the dark band artifact of the final image is performed.

In Step 6, image reconstruction is performed on the data after the correction processing by using a generally known image reconstruction method, and a series of processing is completed.

This series of flow is shown as a method of adding various divided measurement data on the image processing side.
As described in the description of the embodiment of the detection circuit described above, if the method of adding the divided data on the detection circuit side and sending it to the image processing is adopted, the number of pre-processing in Step 3 is reduced, and the processing of Step 4 is performed. No longer needed. In addition, in this processing method, as shown in Step 4 above, addition processing was performed at the stage of measurement data.
The order of ep5 is changed and the correction processing of Step5 is performed for each divided data, and then the addition is performed, or the correction processing is performed for each divided data without Step4, and the image reconstruction is performed for each data (narrow. Needless to say, a method of finally adding a plurality of images to obtain one thick slice image is also possible. The procedure of these modification methods has a drawback that the final processing time is increased because the processing procedure increases as the latter becomes, but it can be applied to the method described later.

Here, in the above description of the embodiment,
Although an example of a detector of three-division type in the slice direction has been described, however, according to the present invention, the number of divisions of this detector is basically the above-mentioned three because of the use and purpose of the CT apparatus. Plural other than division (especially, odd number: 2n-1
(N: integer of 1 or more)) is also possible, and is not necessarily limited to three divisions. Despite this, especially, the three-division structure in the slice direction of this detector is the most CT
Suitable for equipment. Therefore, the reason will be described below with reference to FIG. 8 attached.

First, a normal X-ray CT apparatus can measure a plurality of slices, and generally, 10, 5, 3,
A plurality of (5 types) slice widths of 2 and 1 mm can be set. This is because the measurement slice thickness (slice width) is changed according to the size of the subject and the examination target site. That is, since the CT measurement method has a thickness in the slice direction, when measuring a smaller object, the contrast becomes smaller due to the partial volume effect, and the shape becomes blurred and looks larger. In addition, there are some artifacts that should not occur. Therefore, in order to eliminate such problems,
The measurement slice thickness can be changed according to the size of the subject and the target site.

Here, the above-mentioned slice thickness (slice width) indicates the measured thickness at the center position of the subject 7 (which represents the measurement center position of the CT apparatus), and therefore the gap width of the collimator 3 The length of the detector 4 in the slice direction is the distance from the X-ray focal position of the X-ray tube 1 to the measurement center position (SO
D) or the distance from the focal point to the detector entrance plane position (SI
D), and further determined by the positional relationship from the focus to the collimator 3. Basically, these slice widths are in a proportional relationship with various collimator widths and detector slice direction lengths, and the width of the X-ray beam 8 to be originally measured is geometrical as shown in FIG. Is calculated. Also, of course, the smaller the slice width, the less the partial volume effect, and the less the artifacts,
However, since the amount of incident X-rays is reduced by that amount, there are many noises in the measurement image, and the required number of measurements increases, which poses a problem in terms of measurement throughput.

Then, as a result of examination from the viewpoint of how much the slice thickness is good in the correction effect for the artifact caused by the partial volume effect, the present inventors have found that the slice image is 3 mm slice image or less (3 mm or less). It was obtained that the remarkable correction effect of scattered rays and the quality of radiation was not obtained in the slice width). From this, it was concluded that the minimum correction unit is 3 mm slices or more.

From this fact, in particular, the detector 4 (maximum 10 m
By dividing the (m slice) into three equal parts, approximately 3 mm
In the measurement below the slice, the central detector plane 4 of the detector 4
It can be easily inferred that the correction effect is large by using only the data of 1a. Moreover, in the measurement of 3 mm slices or more,
All the detector surfaces 41a, 4a of the detector 4 divided into three equal parts
It suffices to use the data (3 pieces of data) from 1b and 41c. Further, as will be described later in detail using an example, for example, in the case of a 5 mm slice, X to be measured
By adopting a method of shifting the position of the line beam, it is possible to perform measurement on any two (41a and 41b or 41a and 41c) detector planes of the uniform three-divided detector 4, which results in partial volume measurement. The effect can be reduced and the measurement time can be shortened. 10 mm
In the slice measurement, naturally, the three detector surfaces 41a, 41b, 41c of the uniform three-divided detector 4 are used for measurement.
In the three equally-divided arrangement structure of the detector 4, the same amplifier may be used, and the addition processing of each divided data and the weighting for each data in the correction may be equal, so that the system is systematic. Can also be said to be a suitable arrangement.

Further, in the case of the five divisions shown in FIG. 8B, if the divisions are made unevenly, for example, 1: 1: 2: 1: 1, in the measurement of 3 mm slices or less, there is one at the center position. In the 5 mm slice measurement, the data of the detector surface 41 ′ a is further divided into three detector surfaces 41 ′ a, 41 ′ b at the center,
The data of 41'c is used for all detector surfaces 41'a, 41'b, 41'c, 41'd, 4 in 10 mm slice measurement.
It suffices to measure the measurement data of 1'e. Naturally, in this case, a detection circuit corresponding to each divided detector is required, and a method of arranging an amplifier for each detector output by the circuit method shown in FIG. 7 or a detection circuit for the output of each detector instead. An analog switch etc. is arranged in the first stage and one is added in the latter stage or the number of adders is smaller than the number of split detectors
A method of arranging P) 52 and capturing only the data necessary for measurement can also be applied.

As described above, the method of dividing a detector into a plurality of divided detector surfaces which are equal or proportional to each other in proportion to the slice thickness of the CT apparatus has been described.
The number of divisions and the length of each detector surface may be arbitrary and are not limited. Further, the addition processing of the measurement data and the weighting for the correction for each divided data are basically performed by the division length ratio in the slice direction, and the division ratio is 1: 2: 4: 8. Is an integer and has an exponential function ratio of 2, it is efficient from the viewpoint of processing in terms of correction parameters and hardware, and if it is strong, it is easy to shorten the processing time. It goes without saying that it is not limited.

Next, FIG. 9 shows an apparatus in which the correction effect is reduced by the processing procedure shown in FIG.
In a device having a large measurement slice thickness (slice width) and a large number of detector divisions, an improvement method for reducing the correction effect and the increase in calculation time as much as possible is disclosed.

In the figure, Step 11 to Step 13
Is the same as Step 1 to Step 3 shown in FIG. Further, the processing of Step 15 to Step 17 is basically the same as that of Step 14 to Step 16 in FIG. In this process, the points different from FIG.
In Step 14, addition processing is performed for each of a plurality of adjacent measurement divisions, thereby reducing the measurement data into a smaller number of measurement data than the number of divisions of the detector, and further dividing into S groups.
In step 15, the calculation time is shortened by performing correction for each group rather than setting it for each divided data.

That is, according to the above embodiment of the present invention,
For example, in 10 mm slice measurement, all the data of the above-mentioned three-division detector is required, and in particular, in the example of the processing method shown in the above-mentioned FIG. Correction processing is required. On the other hand, according to the method of FIG. 9 described above, when the grouping is made independent, it is necessary to correct each divided data, and therefore three corrections (scattered ray correction and radiation quality correction) are required. The required method, or the three split detectors on the right and center detection data,
And addition processing of the center and left detection data (in such a case, data weighting is performed, for example, right: center = 1: 1).
/ 2, center: left = 1/2: 1), and two corrections are made in two groups, at least two methods are possible.

In such a method, when 10 mm slice measurement is performed by the non-uniform 5-division detector 4 as shown in FIG. It can be divided into a plurality of correction times.

[Table 1] Also, other combinations and weights can be set freely. Further, for these final combinations, when the slice width is set in Step 11 of FIG. 9 described above, the operator sets the measurement slice and the final display image (at this time, the combination can be instructed), Table 1 above
Various combinations such as those shown in are possible, and
By seeing this information, it is easy to automatically perform the processing procedure after Step 14.

In the embodiment of the present invention described in detail above, basically, a method is adopted in which data of all the divided detector planes in the slice direction of the detector 4 is taken in at any slice measurement (slice width). It is a thing. However,
In particular, during so-called narrow slice measurement, where the measurement slice width is narrow, there are detector planes that are unnecessary for measurement, and if the data from these unnecessary detector planes is not taken in, less measurement data will be handled, and the detection circuit There are great advantages on both the and image processing sides. That is, at the time of narrow slice measurement, when narrow slice measurement is set in the processing procedure shown in FIG. 2 or FIG. 9, particularly in the measurement condition setting of Step 1 (FIG. 2) or Step 11 (FIG. 9) thereof. , Step 2 or Step 12 may be taken in only from the divided detector plane corresponding to the narrow slice measurement. That is, in the example of the three-division type detector, only data from the central detector surface needs to be handled in the case of 3 mm slice measurement or less, which is the control method of the adder (SUM-APM) 52 shown in FIG. It can be changed easily by simply switching. This merit is not limited to the fact that the data to be handled is reduced to 1/3, and since the data on the detector surfaces at both ends in the slice direction where the scattered rays are originally mixed is not used, an even better image can be obtained. It will also happen.

Therefore, in the present invention, in addition to the above-described embodiment, another embodiment suitable for such narrow slice measurement will be described with reference to the processing procedure shown in FIG. First, in the embodiment shown in FIG.
At 21, the operator of the apparatus sets the measurement conditions before starting the measurement, and at this time, the narrow measurement slice width is set. This operation is generally performed by a console (not shown) that controls the operation of the X-ray CT apparatus, and then the measurement is started.

In Step 22, among a plurality of divided data from the detector 4, during the series of measurement, the data of the central detector surface and the data of the end detector surface necessary for the narrow slice measurement (either one is sufficient. ) Are sequentially captured by the detection circuit 5 and sequentially transmitted to the image processing device 6. That is, for example, in the uniform three-division detector shown in FIG.
In the case of mm slice measurement data, the center detector surface 41
Only a should be handled.

At Step 23, addition processing of each measurement data from a plurality of detector surfaces divided in the central portion is performed,
It is converted into one data for one channel corresponding to the conventional CT device measurement data. At this time, if the lengths of the divided detector surfaces are equal, a simple addition process may be performed, or if the division ratios are different, a weight addition process corresponding to this division ratio may be performed.

In Step 24, the scattered radiation correction processing is performed by multiplying the added measurement data by a certain weighting constant on the detector data of the end face portion, and subtracting the result, and thus the CT value of the final image is obtained. Performs scattered ray correction processing that reduces uniformity and dark band artifacts.

At Step 25, the processing that is first performed in the general CT apparatus in the processing process of the image processing apparatus 6, generally, the offset correction of the detector system and the LOG (logarithmic) conversion processing are followed by the X-ray fluctuation. Preprocessing for reference correction and various sensitivity corrections is performed on the measurement data.

Then, in Step 6, image reconstruction is performed on the data after the correction processing by using a generally known image reconstruction method, and a series of processing is completed.

As the flow of this series of processing, the method of adding various divided measurement data on the image processing side is shown, but as described in the description of the concrete embodiment of the detection circuit 5 of FIG. 7, as described above. If the detection circuit side adds the central portion divided data and then sends it to the image processing, the processing on the image processing side in Step 23 is not necessary. Further, in this processing, there is no problem even if the order of the steps from Step 23 to Step 25 is changed. Furthermore, a method is also possible in which scattered ray correction processing is performed for each divided data, image reconstruction is performed for each data (narrow slice image), and multiple images are finally added to obtain one thick slice image. Needless to say. In addition, in this processing, we narrowed down only the split detector data necessary to reduce the measurement data, but in order to operate the same as at the maximum measurement slice, the data from all split detector surfaces is Even if imported, there is no problem in terms of processing. It should be noted that the procedure of these modification methods can be applied to various methods described later. Therefore, in the following description, these modification methods will be omitted.

In the example shown in FIG. 10B, the correction effect is reduced in the example of FIG. 10A described above, the measurement slice thickness is large, and the correction is performed in an apparatus having a large number of detector divisions. This is a description of an improvement method for reducing the increase in the effect and the calculation time as much as possible. In the processing procedure of this embodiment, the procedure of Step 21 'to Step 22' is the same as the example of FIG. 10 (a). Step25 '
Basically, the processing of ~ Step 27 'is also as shown in FIG.
It is the same as Step 24 to Step 26 of (a),
At the different points, in particular, in Step 23 ′, addition processing is performed for each of a plurality of adjacent measurement divisions, the measurement data is reduced to a number smaller than the number of detector divisions and divided into groups, and in Step 25 ′, scattered ray correction is performed for each group. By doing so, it is a method in which the calculation time is shorter than that for each division. When this is performed, for example, in a 5 mm slice measurement and with a five-division detector as shown in FIG. 8B, the measurement requires three division detector data in the central portion, and this FIG. In the example of b), division into 2 or 3 groups is possible.

These final combinations are shown in FIG.
When the slice is set in Step 21 ′ of (b), the operator sets the measurement slice and the final table image (at this time, a combination instruction is possible) in advance, so that the specified combination is used in Step 23 ′ and later. It is easy to automatically perform the processing procedure of.

In the above description, it was assumed that the X-ray beam position in slice measurement was fixed. However, in the case of the above-mentioned uniform three-division detector, especially 5 mm
In the slice measurement, the effective detection area in the data on the detector surfaces at both ends is about half as in the X-ray beam 8 shown by the broken line in FIG. Therefore, it becomes impossible to obtain a good result as in the case of 3 mm slice measurement. Therefore, in such a case, the measurement X-ray beam is shifted to a position as shown by a wavy line 8'in the figure, and the number of divided detector planes to be measured for image reconstruction is set to three. The number can be reduced from two to two, and measurement similar to the above-described 3 mm slice measurement can be performed with little influence of scattered radiation.

Then, still another embodiment which enables such measurement is shown in FIGS. 12 to 14 attached. FIG. 12 shows a side view of an X-ray CT apparatus according to still another embodiment, and as is clear from this figure,
The structure is almost the same as the side view of the embodiment shown in FIG. 1B, except that the X-ray tube 1 and the collimator 3 are different.
Further, in order to move the positional relationship between the X-ray detector 4 and the X-ray detector 4 in the slice direction to enable measurement, an X-ray tube moving device 7, a collimator moving device 8, and a detector moving device 9 are further provided, and The point is that a control device 10 for controlling each of these moving devices is added. The control device 10 reads the measurement conditions set by the operator prior to the measurement, and thereby operates the moving devices so that the devices corresponding to the measurement conditions are moved.

Here, a typical method of each of the above moving devices will be briefly described. First, in the X-ray tube moving device 7, when fixing the X-ray tube to the scanner rotating disc (rotating base for arranging the X-ray tube and the detector and the detection circuit), the fixing for fixing the tube is performed. Since it is general that the X-ray tube is fixed by sandwiching the X-ray tube with metal fittings or the like, this X-ray tube is not directly fixed to the scanner, but a linear guide that is movable in the slice direction (structurally Two metal plates are combined by bearing coupling and are accurately moved linearly in one direction), and the metal plate portion at one end thereof is mounted on the rotating disk. Furthermore, since the feed screw (ball screw) mechanism is attached to the metal plate on the X-ray tube side and the screw shaft is directly controlled to rotate by a torque motor or pulse motor, the rotation speed of the ball screw can be changed. The fixed linear guide can be moved. Therefore, the X-ray tube position can be moved accurately.

The collimator moving device 8 and the detector moving device 9 also have basically the same structure as the X-ray tube moving device, and a linear guide having the collimator 2 and the detector 4 attached thereto. The structure mount may be indirectly moved in the slice direction. Needless to say, all of the three moving devices shown here are not necessary to obtain the result as shown in FIG. 5, and any one of them may be installed. There are various other methods for moving in the slice direction, and the method and method are not limited to those shown in the present embodiment.

Next, the procedure in the X-ray CT apparatus capable of varying the X-ray beam position in such a slice direction is shown in FIG. 13 (a) or (b). In addition,
Here, as for the processing procedure for grouping the measurement data to be corrected, FIG. 13A is a method of fetching all data as in FIG. 2 above, and this is not performed.
In FIG. 13B, grouping is performed as in the case of FIG. However, since the details of the content have already been described above, they are omitted here.

However, in the procedure shown in FIG. 13A or 13B, the difference from the procedure in FIG. 2 or 9 is that Step 31 or S
In step 31 ', the operator sets measurement conditions. Further, in Step 32 or Step 32 ′, the X-ray CT apparatus moves the X-ray beam position corresponding to the measurement slice according to the set measurement conditions, as shown in FIG.
One of the moving devices shown in Fig. 1 or a plurality of moving devices is moved in the slice direction to start the measurement, and the data of the split detector surface corresponding to the position and width of the measurement beam and the detector of the end face portion are detected. All you have to do is capture the data.

Further, in FIG. 14 (a) or (b),
The X-ray beam position can be changed in the slice direction,
Furthermore, in an X-ray CT apparatus that measures a narrow slice width, measurement data of a substantially narrow slice width is measured at the same time, and good measurement data with a small partial volume effect is taken in, and finally the addition of each data is performed. A procedure is shown that can provide a good image with less image noise and artifacts in the process. Here again, regarding the processing procedure for grouping the measurement data to be corrected,
FIG. 14A shows a method for fetching all data similarly to FIG. 10A, while FIG. 14B shows the method shown in FIG.
Grouping is performed in the same manner as in (b). Since the details of the content have already been described above, they are omitted here.

However, the difference between these embodiments is that Step 41 in FIG. 14 (a) or (b) is different.
Alternatively, in Step 41 ′, the measurement condition is set by the operator, and before the actual measurement is started, the movement shown in FIG. 12 is performed according to the set condition so that the X-ray beam position corresponds to the measurement slice width. Any one of the devices or a plurality of moving devices is moved in the slice direction to start measurement. Then, in Step 42 or Step 42 ', the X-ray CT apparatus may take in the data of the split detector surface and the detector data of the end surface portion corresponding to the measurement beam position and width. In particular, in the example of the uniform three-division type detector,
As shown in FIG. 1, two pieces of divided data corresponding to the X-ray beam 8 ′ may be used for measuring the object transmitted X-ray, and the remaining one-divided detector data may be used for measuring the scattered radiation.

[0063]

As is apparent from the above detailed embodiments, according to the present invention, a split type detector composed of a plurality of detectors divided in the slice direction as well as the channel (ch) direction is provided. By measuring the X-ray beam that has passed through the subject, measurement data with a substantially narrow slice width is measured at the same time, and the image is reconstructed by performing a predetermined process on the measurement data. It is possible to obtain good tomographic images with little image noise and little artifacts by the addition processing of each data, by taking in good measurement data with less noise.

Further, the measurement data from each of the detection units of the split type detector is added by an addition process into measurement data smaller than the number of divisions of the split type detector in the slice direction, and the calculation time is calculated for each data. The scatter ray correction and the radiation quality correction are remarkable, and then these measurement data are combined into one to reconstruct the image, thereby reducing the increase in the calculation time in the X-ray CT apparatus, and In addition, it is possible to provide a high-quality image with a high correction effect. Furthermore, when performing narrow slice measurement, the number of calculation processes can be reduced by measuring only the split detector related to the actual measurement X-ray beam. As a result, it is possible to speed up the process.

Further, according to the present invention, in the narrow slice measurement, only the split detector related to the actual measurement X-ray beam is measured, and the measurement data of the remaining slice-direction end face is measured by the scattered radiation measurement detector for scattered radiation correction. Then, the measurement value of the divided data at the end of the slice direction where the direct X-ray beam does not hit during this narrow slice measurement is collected as the scattered dose, and in the subsequent narrow slice measurement, individual c
Since the scattered radiation correction is performed for each h, it is possible to perform the highly accurate scattered radiation measurement for each slice measurement, and thus the favorable scattered radiation correction can be performed.

[Brief description of drawings]

FIG. 1 is a front view and a side view of an X-ray CT apparatus equipped with a slice direction division type detector according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a measurement data processing procedure in the X-ray CT apparatus shown in FIG.

3 is a diagram showing an example of a photosensor for a split solid-state detector that constitutes the slice direction split type detector of the X-ray CT apparatus shown in FIG.

FIG. 4 is an external view of a detection element for divided solid-state detection that constitutes a slice direction division type detector of the X-ray CT apparatus.

5 is a side view and a top view of a signal electrode plate for a split ionization chamber detector that constitutes the slice direction split type detector of the X-ray CT apparatus shown in FIG.

6 is a diagram showing an example of the structure of a detection block of an ionization chamber detector using the signal electrode plate for the split ionization chamber detector of FIG.

7 is a circuit diagram showing an embodiment of a detection circuit for the split detector CT used in the X-ray CT apparatus shown in FIG.

FIG. 8 is an explanatory diagram for explaining a relationship between a measurement slice width and a division detector in the X-ray CT apparatus.

9 is a diagram illustrating an example of X in place of the measurement data processing procedure shown in FIG.
It is a flow chart which shows a processing procedure which divides measurement data in a line CT device.

10 is a flowchart showing a processing procedure when the processing procedure of measurement data in the X-ray CT apparatus shown in FIGS. 2 and 9 is applied to narrow slice width measurement.

FIG. 11 is an explanatory diagram illustrating a relationship between an X-ray beam position and a split detector in order to describe a problem in the above embodiment.

FIG. 12 is a side view of an X-ray CT apparatus showing the structure of still another embodiment of the present invention which is different from the above embodiment.

13 is a flowchart showing a processing procedure for grouping measurement data in the X-ray CT apparatus according to the embodiment of FIG.

14 is a flowchart showing a processing procedure in the X-ray CT apparatus according to the embodiment of FIG. 12 applied to narrow slice width measurement.

[Explanation of symbols]

 1 X-ray tube 2 Collimator device 3 Collimator 4 Detector 41 Detection part (surface) 5 Detection circuit 6 Image reconstruction processing device 7 Subject 8 X-ray beam

Claims (8)

[Claims] 1. An X-ray from an X-ray source is emitted in a channel (ch) direction with a predetermined slice width, and the X-ray transmitted through an object is detected by a detector arranged in the ch direction. An X-ray CT apparatus for forming a tomographic image of the subject by the detection signal detected in 1., wherein the detector is composed of a plurality of detectors divided in the ch direction, and the detectors in each ch direction are provided. Further has a detector structure that is composed of a plurality of detection units divided in the slice direction, and an aggregate of the detection units divided in the slice direction forms a minimum unit detector of 1ch, and A detection circuit capable of performing slice measurement of a plurality of widths by one measurement, and further performing a correction process on data from a detection unit divided in a plurality of slice directions which constitutes the minimum unit detector of 1ch. When, An image reconstruction for reconstructing a slice image having a slice width equal to or thicker than the slice width measured by each of the plurality of divided detectors forming the minimum unit detector of 1ch is corrected by the data corrected by the detection circuit. X-ray C characterized by comprising a configuration processing device
T device. 2. The X-ray CT apparatus according to claim 1,
The correction processing is performed for each data of the data from the plurality of divided detection units which the detection circuit constitutes the minimum unit detector of 1ch, or for each data obtained by adding a plurality of the data and grouping the data. An X-ray CT apparatus characterized by: 3. The X-ray CT apparatus according to claim 1,
The detector is divided into a plurality of slices in the slice direction, the X-ray focal point of the X-ray source, the collimator defining the slice width of the X-ray, and the X-ray incident surface of the detector. An X-ray CT apparatus characterized by being determined by a positional relationship between the two. 4. The X-ray CT apparatus according to claim 1, wherein:
A collimator for narrowing the X-ray from the X-ray source into a narrow slice width, and means for moving at least one of the X-ray source, the collimator, and the detector in the slice direction, In a device including a collimator that narrows the X-ray from the X-ray source into a narrow slice width, the image reconstruction processing apparatus corrects the narrow slice measurement data after the correction process is performed by the detection circuit. X is characterized by reconstructing an image with the narrow slice measurement data obtained, and further subjecting these narrow slice images to addition processing so as to reconstruct a slice image that is equal to or thicker than the narrow slice width. X-ray CT equipment. 5. The X-ray CT apparatus according to claim 1, wherein
Further, the detection circuit includes, for each 1-ch minimum unit detector of the detector, the minimum-unit detectors of the number of detection units constituting the 1-ch minimum-unit detector of the detector or less. And an adder that selectively adds the outputs from the detectors in the smallest unit.
apparatus. 6. The detector is composed of a plurality of detectors divided in the channel direction, and each detector further comprises:
It is composed of multiple detectors divided in the slice direction,
A group of detectors divided into a plurality of slice directions has a detector structure that constitutes a minimum unit detector of 1 ch, and emits X-rays from an X-ray source with a predetermined slice width in the ch direction. The detection in an X-ray CT apparatus capable of forming a tomographic image of the object by detecting the X-ray transmitted through the sample by a detector arranged in the ch direction and performing slice measurement of a plurality of widths with one measurement. A method of processing data, wherein correction processing is performed on data from a detection unit divided in a plurality of slice directions which constitutes the minimum unit detector of the 1ch, and the correction data is used to detect the minimum of the 1ch. A data processing method for an X-ray CT apparatus, which comprises reconstructing a slice image having a slice width equal to or thicker than a slice width measured by each of a plurality of divided detectors constituting a unit detector. 7. The data processing method for an X-ray CT apparatus according to claim 6, further comprising: a measurement value of data of a detector of the detector at an end in a slice direction where the X-ray beam does not directly impinge during narrow slice measurement. Is corrected as the scattered dose to the measurement data, and the data processing method of the X-ray CT apparatus is characterized. 8. The data processing method for an X-ray CT apparatus according to claim 6, wherein the detection is divided in a plurality of slice directions forming the minimum unit detector of 1ch according to a slice width to be measured. A data processing method for an X-ray CT apparatus, which is characterized in that the number of data from a unit is reduced.