JP2002143147A - X-ray ct system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the side effect of correction for removing the influence of the error of an irradiation position. SOLUTION: The error of a primary irradiation position is calculated (113) to be compared with an allowable value (115) and a correction part 109 is controlled by a correction control part 117 based on this result. Thus, correction is not performed when the error of the irradiation position is within the allowable value and correction is performed when the error of the irradiation position exceeds the allowable value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an X-ray CT (Xr
More specifically, the present invention relates to an X-ray CT apparatus using a detector having a plurality of rows of X-ray detection elements.

[0002]

2. Description of the Related Art In an X-ray CT apparatus, transmission X-ray signals of a plurality of views are acquired for an object to be imaged by an X-ray irradiation / detection apparatus, and a tomographic image of the object is obtained by an image generation apparatus based on the transmission X-ray signals. Generate an image.

[0003] The X-ray irradiator irradiates a cone-shaped X-ray beam emitted from a focal point of an X-ray tube into a fan-shaped X-ray beam by a collimator and irradiates the X-ray beam to an imaging space.

The X-ray detecting device is a multi-channel device in which a large number of X-ray detecting elements are arranged in an array along a fan-shaped spread of an X-ray beam. ) Is detected by the X-ray detector.
Such an X-ray irradiation / detection device is rotated (scanned) around an object to acquire transmission X-ray signals of a plurality of views.

As one type of a multi-channel X-ray detector,
There is a type in which a plurality of detection element arrays are arranged in the direction of the thickness of a fan-shaped X-ray beam, and the X-ray beams are simultaneously received by a plurality of rows of detection element arrays. In such an X-ray detector, an X-ray detection signal for a plurality of slices can be obtained at once by a single scan.
It is used as an X-ray detector for efficiently performing lti-slice scan).

Some X-ray detectors have an array of X-ray detection elements in two rows so that projection data for two slices can be obtained at one time. There, two rows of arrays are arranged adjacent to and parallel to each other, and the X-ray beam is uniformly distributed in the thickness direction and irradiated. The thickness of the X-ray beam applied to each of the two rows of arrays at the target isocenter determines the slice thickness of the tomographic image.

In the X-ray tube, the focus of the X-ray moves due to thermal expansion or the like due to a rise in temperature during use, and this shift appears as a displacement in the thickness direction of the X-ray beam through an aperture of the collimator. When the X-ray beam is displaced in the thickness direction, the distribution ratio of the thickness of the X-ray beam in the two-row array changes, and the slice thickness of the target projected on the two arrays is not uniform. The ratio of the X-ray count of the irradiation position detection channel provided is monitored, and since the ratio is no longer 1, the deviation of the X-ray irradiation position is recognized, and the position of the collimator is adjusted to determine the X-ray irradiation position. It is controlled to be at the position. This control is a feedback (feed bac)
k) Controlled.

Further, as part of the irradiation position control, a change in the position of the X-ray focal point due to a decrease in the temperature of the X-ray tube is predicted according to the length of the stop time of the X-ray irradiation, and the collimator position is correspondingly adjusted. Adjustment is performed so that the correct position can be irradiated from the beginning at the next irradiation. This control is performed by feed forward control.

The irradiation position control by the feedback control is started at the same time as X-ray irradiation, that is, the start of scanning. The initial position of the control is a position adjusted by the feedforward control. When this position is different from the home position, the position is corrected by the feedback control.
It takes some time for the line irradiation position to reach the fixed position. During that time, normal data cannot be obtained,
Since the quality of the image obtained first is inferior, the transmitted X-ray signal obtained at the beginning of the scan is corrected to remove the influence of the irradiation position error.

[0010]

When the feedforward control is properly performed and the irradiation position is at the fixed position from the beginning, the image quality of the tomographic image is reduced as a side effect of the above correction.

An object of the present invention is to realize an X-ray CT apparatus which does not cause a side effect of correction for removing the influence of an irradiation position error.

[0012]

According to the present invention, there is provided an X-ray tube for generating X-rays diverging from a focal point, a collimator for shaping the X-rays into a fan-shaped beam,
A detection element array in which a plurality of X-ray detection elements are arranged in the direction of the fan-shaped beam in a direction in which the fan-shaped beam spreads; An irradiation position detecting means for detecting an irradiation position of the fan-shaped beam in the arrangement direction of the detection element array; and an irradiation position of the fan-shaped beam being a preset irradiation position based on the detected irradiation position. Irradiation position control means for controlling the collimator so as to predict the position of the focal point at the start of X-ray irradiation, so that the irradiation position of the fan-shaped beam becomes the predetermined irradiation position. Second irradiation position control means for controlling the X-ray tube, the collimator, and the X-ray irradiation / detection system including the detection element array around an axis parallel to the direction of the thickness of the fan-shaped beam. Signal acquisition means for acquiring an X-ray detection signal of a plurality of views by inverting, and correction means for performing a correction for removing the influence of inaccuracy of an irradiation position at the start of X-ray irradiation on the acquired X-ray detection signal; Error calculating means for calculating an error between an irradiation position at the start of X-ray irradiation and the predetermined irradiation position; comparing means for comparing the error with a predetermined allowable value; Within the range, the correction is not performed, and the correction control means for performing the correction when the error exceeds the predetermined allowable value; and the fan-shaped beam based on the X-ray detection signal given through the correction means. And a tomographic image generating means for generating a tomographic image of a slice passed by the X-ray CT apparatus.

In the present invention, the correction is not performed when the irradiation position error is within a predetermined allowable value, and the correction is performed when the irradiation position error exceeds the predetermined allowable value. There are no side effects associated with the correction.

The correction reduces the weight of the X-ray detection signal of the view at the initial stage of the rotation with respect to the X-ray detection signals of the plurality of views, and reduces the X-ray detection signal of the opposite view.
By increasing the weight of the line detection signal,
This is preferable in that the influence of the inaccuracy of the irradiation position at the beginning of rotation is removed.

In this case, the X-ray detection signals of a plurality of predetermined views based on the first view are given weights varying from 0 to 1 in ascending order of the view numbers, and the X-ray detection signals of the opposing views are assigned. It is preferable to assign a weight that changes from 2 to 1 in ascending order of view numbers in order to more appropriately reduce the influence of the inaccuracy of the irradiation position in the initial stage of rotation.

In addition, X-ray detection signals of a plurality of predetermined views with reference to the central view are given weights varying from 2 to 1 in descending order of view numbers, and X-ray detection of the opposing views is performed. 0 in descending order of view number to signal
It is preferable to assign a weight that varies from to 1 in order to alleviate a sudden change in the weight.

Further, the irradiation position error is determined by detecting X-rays detected by X-ray detection elements adjacent to each other in the direction in which the detection element rows are arranged.
The determination based on the ratio of the difference to the sum of the line detection signals is preferable in that an error measurement value independent of the magnitude of the X-ray detection signal is obtained.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiment. FIG. 1 shows a block diagram of the X-ray CT apparatus. This device is an example of an embodiment of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention.

As shown in FIG. 1, this apparatus includes a scanning gantry 2 and a photographing table 4.
And an operation console (console) 6. The scanning gantry 2 is an example of an embodiment of a signal acquisition unit according to the present invention. The scanning gantry 2 is an X-ray tube 20
Having. The X-ray tube 20 is an example of an embodiment of the X-ray tube in the present invention. An X-ray (not shown) emitted from the X-ray tube 20 is shaped into, for example, a fan-shaped X-ray beam, that is, a fan beam by a collimator 22, and is applied to a detector array 24. The collimator 22 is an example of an embodiment of the collimator according to the present invention.

The detector array 24 has a plurality of X-ray detecting elements arranged in an array in the direction in which the fan-shaped X-ray beam spreads. The detector array 24 is an example of an embodiment of the detection element array in the present invention.
The configuration of the detector array 24 will be described later. The X-ray tube 20, collimator 22, and detector array 24 constitute an X-ray irradiation / detection device. The X-ray irradiation / detection device will be described later.

A data collection unit 26 is connected to the detector array 24. The data collection unit 26 includes the detector array 24
The detection data of the individual X-ray detection elements are collected. The irradiation of X-rays from the X-ray tube 20 is performed by an X-ray controller (cont.
(controller) 28. The illustration of the connection relationship between the X-ray tube 20 and the X-ray controller 28 is omitted. The collimator 22 is controlled by a collimator controller 30. The illustration of the connection relationship between the collimator 22 and the collimator controller 30 is omitted.

The components from the X-ray tube 20 to the collimator controller 30 are mounted on the rotating unit 34 of the scanning gantry 2. The rotation of the rotation unit 34 is controlled by a rotation controller 36. The illustration of the connection relationship between the rotation unit 34 and the rotation controller 36 is omitted.

The photographing table 4 carries a photographing object (not shown) into and out of the X-ray irradiation space of the scanning gantry 2. The relationship between the object and the X-ray irradiation space will be described later.

The operation console 6 has a data processing device 60. The data processing device 60 is constituted by, for example, a computer. The data processing device 60 includes a control interface (interfa).
ce) 62 is connected. Control interface 62
Is connected to the scanning gantry 2 and the imaging table 4. The data processing device 60 controls the scanning gantry 2 and the imaging table 4 through the control interface 62.

The data collection unit 26 in the scanning gantry 2, X
The line controller 28, collimator controller 30, and rotation controller 36 are controlled through a control interface 62. It should be noted that illustration of individual connections between these units and the control interface 62 is omitted.

A data collection buffer 64 is connected to the data processing device 60. The data collection buffer 26 is connected to the data collection unit 26 of the scanning gantry 2. The data collected by the data collection unit 26 is input to the data processing device 60 via the data collection buffer 64.

The data processing device 60 performs image reconstruction using the transmission X-ray signals of a plurality of views collected through the data collection buffer 64. Image reconstruction includes, for example, filtered back projection (filtered back projection).
A back projection method or the like is used.
The data processing device 60 is an example of an embodiment of a tomographic image generation unit according to the present invention.

A storage device 66 is connected to the data processing device 60. The storage device 66 stores various data, reconstructed images, programs for realizing the functions of the present device, and the like.

A display device 68 and an operation device 70 are connected to the data processing device 60, respectively. The display device 68 displays the reconstructed image output from the data processing device 60 and other information. The operation device 70 is operated by a user and inputs various instructions and information to the data processing device 60. The user uses the display device 68 and the operation device 70 to interactively operate (interact).
ive).

FIG. 2 shows a schematic configuration of the detector array 24. As shown in the figure, the detector array 24 is a multi-channel X-ray detector in which a plurality of X-ray detection elements 24 (ik) are arranged in an array.

The plurality of X-ray detecting elements 24 (ik) form an X-ray incident surface curved in a cylindrical concave shape as a whole.
i is a channel number, for example, i = 1 to 1000. k is a column number, for example, k = 1, 2. The X-ray detection elements 24 (ik) have the same column number k and constitute a detection element row. Note that the detector array 24
Is not limited to two rows, but may be three or more rows. Hereinafter, an example in which the detector array 24 has two columns will be described.
The same applies to the case of three or more rows.

A predetermined number of channels at both ends of the detector array 24 are reference channels 25 in each column. The reference channel 25 is outside the range in which the target is projected during shooting.

The X-ray detecting element 24 (ik) is composed of, for example, a combination of a scintillator and a photodiode. The present invention is not limited to this, and may be, for example, a semiconductor X-ray detection element using cadmium tellurium (CdTe) or the like, or an ionization box type X-ray detection element using Xe gas (gas).

FIG. 3 shows the interrelationship between the X-ray tube 20, the collimator 22, and the detector array 24 in the X-ray irradiation / detection device. FIG. 3A is a diagram illustrating a state of the scanning gantry 2 viewed from the front, and FIG. 3B is a diagram illustrating a state of the scanning gantry 2 viewed from the side. As shown in the figure, the X-ray radiated from the X-ray tube 20 is converted into a fan-shaped X-ray beam 40 by a collimator 22.
It is shaped so as to be zero, and is irradiated on the detector array 24.

FIG. 3A shows a fan-shaped X-ray beam 40.
Indicates a spread of 0. The spreading direction of the X-ray beam 400 is
It matches the arrangement direction of the channels in the detector array 24. (B) shows the thickness of the X-ray beam 400. The thickness direction of the X-ray beam 400 matches the direction in which the columns are arranged in the detector array 24 (k direction).

With the body axis intersecting the fan surface of the X-ray beam 400, for example, as shown in FIG. 4, the object 8 placed on the imaging table 4 is carried into the X-ray irradiation space. The scanning gantry 2 has a cylindrical structure including an X-ray irradiation / detection device inside.

The X-ray irradiation space is formed inside the cylindrical structure of the scanning gantry 2. An image of the object 8 sliced by the X-ray beam 400 is projected on the detector array 24. The detector array 24 detects X-rays transmitted through the subject 8. The thickness th of the X-ray beam 400 irradiating the target 8 is adjusted by the aperture of the collimator 22.

The X-ray irradiating / detecting device including the X-ray tube 20, the collimator 22, and the detector array 24 rotates (scans) around the body axis of the object 8 while maintaining their mutual relationship. A plurality (for example, 100
The projection data of the view (about 0) is collected. The collection of projection data is performed by a system including the detector array 24, the data collection unit 26, and the data collection buffer 64.

Based on the projection data of two slices collected in the data collection buffer 64, the data processing device 60
Thus, generation of a tomographic image for two slices, that is, image reconstruction is performed. Image reconstruction is performed, for example, by using projection data of, for example, 1000 views obtained by one rotation scan, for example, using filtered back projection (filteredb
The processing is performed by, for example, an ack-projection method.

X-ray beam 40 for detector array 24
FIGS. 5 and 6 show more detailed schematic diagrams of the 0 irradiation state. As shown in FIG. 5, the slice thickness th of the projected images on the X-ray detectors 242 and 244 is reduced by displacing the collimator pieces 220 and 222 in the collimator 22 in a direction to narrow the aperture.

Further, as shown in FIG.
By moving 0,222 in the direction in which the aperture is widened, the slice thickness th of the projected image is increased. Such slice thickness adjustment is performed by the collimator controller 30 under the control of the data processing device 60.

Further, by simultaneously moving the collimator pieces 220 and 222 with the slice thickness th set in the k direction while maintaining the relative positional relationship, the irradiation position in the k direction on the detector array 24 is adjusted. by this,
The change of the irradiation position accompanying the movement of the focus of the X-ray is corrected, and the automatic control is performed so that the X-ray beam 400 is always irradiated to the fixed position.

The adjustment of the irradiation position in the k direction is performed by displacing the detector array 24 relative to the collimator 22 in the k direction, as indicated by a dashed arrow, instead of moving the collimator pieces 220 and 222. You may do it.
In this way, two separate systems for adjusting the slice thickness and controlling the irradiation position in the thickness direction can be provided.
Multilateral control becomes possible.

On the other hand, if all the operations are performed by the collimator 22 as described above, the control system can be unified into one system, and it is possible to meet the demand for simplifying the configuration. It is needless to say that the irradiation position may be adjusted by combining these two means. Hereinafter, the automatic control function of the irradiation position is also referred to as an auto collimator.

FIG. 7 is a block diagram of the present apparatus from the viewpoint of focusing on the autocollimator. As shown in FIG.
The irradiation position of the line beam 400 in the k direction is the irradiation position detection unit 1
01 is detected. The irradiation position detection unit 101 detects the irradiation position based on the ratio of the outputs of the two rows of reference channels 25 in the detector array 24.

When the ratio is 1, the irradiation position is at the fixed position and the irradiation position error is 0. At this time, the X-ray beam 400
Irradiation is performed so that the slice thickness is equal on the two detector rows. When there is an error in the irradiation position, the slice thickness becomes uneven and the ratio does not become one. Therefore, the deviation of the ratio from 1 indicates the irradiation position error. The function of the irradiation position detection unit 101 is realized by the data processing device 60. The irradiation position detection unit 101 is an example of an embodiment of an irradiation position detection unit in the present invention.

The irradiation position detection signal is input to the first control unit 103. The first control unit 103 performs feedback control of the collimator 22 based on the input signal, and
Is adjusted so that the irradiation position becomes the fixed position. The function of the first control unit 103 is realized by the data processing device 60 and the collimator controller 30. First control unit 10
3 is an example of an embodiment of the first irradiation position control means in the present invention.

With such an autocollimator, the X-ray irradiation position on the detector array 24 is kept constant even if the X-ray focal point moves due to self-heating of the X-ray tube 20 during scanning. When the scan is completed, the collimator 22 remains at the control position immediately before the end of the scan. This position corresponds to the X-ray focal position immediately before the end of the scan.

This position is the collimator 2 at the time of the next scan.
The initial position is 2, but if time elapses before the next scan, a change in the position of the X-ray focal point due to a decrease in the temperature of the X-ray tube 20 increases, and the initial position of the collimator 22 does not conform to that.

Therefore, the second control unit 105 predicts a change in the position of the X-ray focal point caused by a decrease in the temperature of the X-ray tube 20 during the scan stop period, and sets the collimator 22 to an appropriate initial position corresponding thereto. That is, feedforward control of the initial position of X-ray irradiation in the next scan is performed.

The change in the position of the X-ray focal point is predicted on the basis of the X-ray irradiation conditions and the irradiation time immediately before the stop of the scan, the elapsed time after the stop of the scan, and the like. When the predicted position of the X-ray focus is obtained, the initial position of the collimator is determined by the X-ray tube 2.
0, based on the geometry of the collimator 22 and the detector array.

The function of the second control unit 105 is realized by the data processing device 60 and the collimator controller 30. The second control unit 105 is an example of an embodiment of the second irradiation position control unit in the present invention.

Since the initial position of the collimator 22 is determined based on the prediction of the X-ray focal position, an irradiation position error occurs when the predicted position is different from the actual position. When there is an irradiation position error, the adjustment for adjusting the X-ray irradiation position to the home position by the autocollimator starts at the start of scanning, but the state where the irradiation position error remains until the position is settled.

An irradiation position error Δz as shown, for example, in FIG. View data obtained during such a period in which there is an irradiation position error is data having a slice thickness different from the original slice thickness. As a result, data obtained by one scan partially includes data having different conditions, and thus the quality of an image reconstructed from such scan data is reduced.

Therefore, the scan data acquired by the signal acquisition unit 107 is corrected by the correction unit 109, and the tomographic image is reconstructed by the tomographic image generation unit 111 using the corrected scan data.

The signal acquisition unit 107 includes a data collection unit 26,
This is realized by the rotation controller 36 and the data collection buffer 64. The signal acquisition unit 107 is an example of an embodiment of a signal acquisition unit according to the present invention. Correction unit 10
9 is realized by the data processing device 60. Correction unit 1
Reference numeral 09 denotes an example of an embodiment of a correction unit according to the present invention. The tomographic image generation unit 111 is realized by the data processing device 60. The tomographic image generation unit 111 is an example of an embodiment of a tomographic image generating unit according to the present invention.

For example, as shown in (b), the correcting unit 109 adds the view numbers of a plurality of views obtained within a predetermined period of the initial scan to the view data in ascending order based on the settling time of the autocollimator known in advance. Are assigned weights that gradually increase from 0 to 1, and accordingly, weights that gradually decrease from 2 to 1 are assigned to the view data of the opposite view in ascending view number order. As a result, the contribution of inaccurate view data obtained during a period in which the X-ray irradiation position is not settled can be reduced, and quality degradation of the reconstructed image can be avoided.

As shown by the dashed line, the weight characteristic is such that the view data of a plurality of views before the opposite view is given a weight that gradually decreases from 2 to 1 in descending order of the view number, thereby avoiding a sudden change in the weight. It is preferred in that respect. In addition,
In this case, the view data of the opposite views are set to 0 in descending view number order, as indicated by the broken line.
From 1 to 1. Such weighting is performed by using a data table (data t
able).

When there is no error in the initial position of X-ray irradiation,
Such weighting of the view data is not necessary, and a higher quality reconstructed image can be obtained without weighting.

Therefore, the correction is not performed when the position error is within the allowable range, but is corrected only when the position error exceeds the allowable range. The initial position error of the X-ray irradiation is calculated by the initial error calculator 113. The initial error calculator 113 is realized by the data processing device 60. The initial error calculator 113 is an example of an embodiment of the error calculator according to the present invention.

The position error is calculated using the X-ray detection signals A and B of the two rows of reference channels immediately after the start of the irradiation of the X-ray beam 400.

[0062]

(Equation 1)

Is performed. Thus, an error measurement value independent of the magnitude of the X-ray detection signal can be obtained.
The error e is compared with the allowable value α by the comparator 115, and an output signal indicating the result of the comparison is input to the correction controller 117. The correction control section 117 controls the correction section 109 based on the comparison result. That is,

[0064]

(Equation 2)

In the case of, since the error is within the allowable range, the correction unit 109 does not perform the correction.

[0066]

(Equation 3)

If so, the error is beyond the allowable range, and the correction unit 109 is caused to make a correction. The comparison unit 115 is realized by the data processing device 60. The comparison unit 115 is an example of an embodiment of the comparison unit in the present invention. The correction control unit 117 is realized by the data processing device 60. The correction control unit 117 is an example of an embodiment of a correction control unit according to the present invention.

In this manner, the necessity of correction is discriminated according to the magnitude of the irradiation position error. When the irradiation position error is large, the correction is performed to prevent the image quality from deteriorating and the irradiation position error is small. In some cases, the side effects can be avoided without performing correction. That is, a high-quality tomographic image can be obtained regardless of the presence or absence of an irradiation position error.

[0069]

As described above in detail, according to the present invention, it is possible to realize an X-ray CT apparatus which does not cause the side effect of correction for eliminating the influence of the irradiation position error.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device according to an example of an embodiment of the present invention.

FIG. 2 is a schematic view of a detector array in the apparatus shown in FIG.

FIG. 3 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

FIG. 4 is a schematic view of an X-ray irradiation / detection device in the device shown in FIG.

FIG. 5 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

6 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

FIG. 7 is a block diagram of another example of the apparatus according to the embodiment of the present invention from another viewpoint.

FIG. 8 is a graph for explaining weighting of view data.

[Explanation of symbols]

 Reference Signs List 2 scanning gantry 4 imaging table 6 operation console 8 target 20 X-ray tube 22 collimator 24 detector array 26 data collection unit 28 X-ray controller 30 collimator controller 34 rotation unit 36 rotation controller 60 data processing device 62 control interface 64 data collection buffer 66 Storage device 68 Display device 70 Operation device 101 Irradiation position detection unit 103 First control unit 105 Second control unit 107 Signal acquisition unit 109 Correction unit 111 Tomographic image generation unit 113 Initial error calculation unit 115 Comparison unit 117 Correction control unit 400 X-ray beam

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masatake Nukai 127 7-4 Asahigaoka, Hino-shi, Tokyo F-term (reference) 4G093 AA22 CA05 CA13 EA02 EA14 EB18 EB28 FA16 FA43 FC22 FC27 FD12

Claims (5)

[Claims] An X-ray tube for generating X-rays diverging from a focal point; a collimator for shaping the X-rays into a fan-shaped beam; and a plurality of X-ray detection elements arranged in a direction in which the fan-shaped beam spreads. A detection element array in which a plurality of detection element arrays are arranged in the direction of the thickness of the fan-shaped beam, and the irradiation position of the fan-shaped beam in the arrangement direction of the detection element arrays in the detection element array. Irradiation position detection means for detecting; first irradiation position control means for controlling the collimator so that the irradiation position of the fan-shaped beam becomes a predetermined irradiation position based on the detected irradiation position; A second irradiation position control unit that predicts the position of the focal point at the start of irradiation and controls the collimator so that the irradiation position of the fan-shaped beam becomes the predetermined irradiation position; and the X-ray tube, Ko Signal acquisition means for acquiring an X-ray detection signal of a plurality of views by rotating an X-ray irradiation / detection system including a remeter and the detection element array around an axis parallel to the direction of the thickness of the fan-shaped beam; Correction means for correcting the effect of the inaccuracy of the irradiation position at the start of X-ray irradiation on the obtained X-ray detection signal; and correcting the error between the irradiation position at the start of X-ray irradiation and the preset irradiation position. Error calculating means to be obtained; comparing means for comparing the error with a predetermined allowable value; when the error is within the predetermined allowable value, the correction is not performed, and the error is the predetermined allowable value. Correction control means for performing the correction when the distance exceeds the limit, and a tomographic image generator for generating a tomographic image for a slice through which the fan-shaped beam has passed based on an X-ray detection signal provided through the correction means. X-ray CT apparatus characterized by comprising a means. 2. The correction means decreases the weight of the X-ray detection signal of the view at the initial stage of the rotation and increases the weight of the X-ray detection signal of the opposite view for the X-ray detection signals of the plurality of views. The X-ray CT apparatus according to claim 1, wherein: 3. The correction means assigns weights varying from 0 to 1 in ascending order of view numbers to X-ray detection signals of a plurality of predetermined views based on the first view,
3. The X-ray CT apparatus according to claim 2, wherein weights varying from 2 to 1 are assigned to the X-ray detection signals of the opposed views in ascending order of view numbers. 4. The correction means assigns weights that change from 2 to 1 in descending order of view numbers for X-ray detection signals of a plurality of predetermined views based on a center view,
4. The X-ray CT apparatus according to claim 3, wherein weights that change from 0 to 1 in descending order of view numbers are assigned to the X-ray detection signals of the opposing views. 5. An X-ray detector according to claim 1, wherein said error calculation means detects X-rays detected by X-ray detection elements adjacent to each other in a direction in which said detection element rows are arranged.
The X-ray CT apparatus according to any one of claims 1 to 4, wherein the error is obtained based on a ratio of a difference to a sum of the line detection signals.