JPH02201253A - Scanning for radiation ct apparatus - Google Patents

Abstract

PURPOSE:To prevent a streak artifact by performing translating actions more than one times for one rotating action a relative position between a radiation source and a detector to allow the sampling of a data in a direction between detectors. CONSTITUTION:In the case of a detector in which detectors each with an effective width of P/2 are arranged at a pitch P, in a first translating operation, a translating is performed with both of a radiation source and the detector left at specified positions. In a second translating operation, a translating operation is performed once the detector is shifted by P/2. By such operations, a data can be sampled by a method corresponding to a gas liable to be of oversight of detectors unable to be measured originally thereby enabling the prevention of a streak artifact.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a radiation CT apparatus that irradiates radiation such as X-rays and T-rays at a fan beam angle. The present invention relates to a scanning method suitable for reconstructing a tomographic image of a subject by sequentially repeating a translation operation in which the subject is moved in parallel and a rotation operation in which the subject is rotated around the subject.

[Conventional technology]

The conventional technology of radiation CT apparatus is shown in FIGS. 5 and 6.

As shown in FIG. 5, this prior art includes an X-ray source 1 as a radiation source, a detector 2, and a translation mechanism 3.
and a rotation mechanism 4. The X-ray source 1 is installed on a movable frame 6 provided on a rotating body 5, and is configured to irradiate the subject 100 at a fan beam angle (approximately 5 to 10 degrees) α as shown in FIG. There is. The movable frame 6 is mounted on a guide rail 7 fixed to the rotating body 5 and is configured to move along the guide rail 7.

The detector 2 is installed in the movable frame 6 at a position facing the X-ray tA1 so as to sandwich the subject 100, and its detection elements are arranged at equal intervals along the width direction of the X-ray fan beam angle. The X-ray dose at each corresponding angle within the X-ray fan beam angle α is measured. The translation mechanism 3 consists of a rack 3a provided on the moving frame 6, a pinion 3b for moving the rack, and a motor for driving the pinion 3b, and the moving frame 6 moves together with the rack 3a by rotation of the pinion 3b. Accordingly, the X-ray source 1 and the detector 2 are moved in parallel, thus performing a translation operation.

The rotation mechanism 4 includes a rotating motor 4a, a sprocket 1-4b attached to its rotating shaft, and a chain 4c wound between the sprocket 4b and the rotating body 5.
The rotating body 5 is driven by the sprocket 4b.
By sequentially rotating at an angle corresponding to the X-ray fan beam angle α, the X-ray source 1 and the detector 2 are rotated around the subject 100, thus performing a rotation operation.

Then, as shown in FIG. 6, the translation mechanism 3 moves the X-ray source 1 and the detector 2 relatively in one direction over the entire area of the subject 100 to perform a translation operation. , then each detection element of the detector 2 has an X-ray fan beam angle α at each point during the movement of the X-ray source l.
The data of X-rays transmitted through the subject 100 at corresponding angles is measured. That is, X-ray transmission data in the direction corresponding to each detection element within the fan beam angle α is measured for each point in the entire area of the subject 100.

Next, the rotation mechanism 4 rotates the X-ray source 1 and the detector 2 relative to each other by an angle corresponding to the fan beam angle α, and at this time, each detection element of the detector 2 detects X-rays. At each point during the rotation of the source 1, transmission data of the X-ray through the subject 100 is measured in the same manner as described above.

Thereafter, the translation mechanism 3 moves the X-ray source 1 and the detector 2 in the opposite direction to the first translation operation to perform a second translation operation, thereby measuring the X-ray transmission data. As shown in FIG. 7, by repeating the translation operation and the rotation operation several times sequentially and measuring the transmission data in the 360 degree direction for each point on the object 100, the object 100 can be
It is possible to reconstruct tomographic images of

[Problem to be solved by the invention]

By the way, in general, in a radiation CT apparatus, it is desired that the density of each angle measured by the detector is high, and for this reason, each detection element of the detector is made as small as possible and a large number are provided so as to be closely spaced. It is preferable. On the other hand, as the dimensions of each detection element become smaller, the amount of radiation incident on each of these detection elements decreases, making measurement difficult. Also, since each detection element measures data at each angle in the radiation fan beam, In order to prevent radiation from entering at angles other than the desired angle, each detection element must be partitioned with a septa as a radiation shielding member made of tungsten or the like.

In the conventional technology shown above, medical X-ray C
In the case of the T device, for example, the X-ray tube voltage is used at about 120 V, so there is no problem, but in particular, materials with a higher radiation absorption coefficient than the human body, such as iron.

In the case of industrial CT equipment that targets copper, etc., the voltage is several hundred KV.
In some cases, a high-voltage X-ray tube is used, or an isotope that generates high-energy T-rays is used as a radiation source, so the thickness of the septa that separates each detection element of the detector must be increased. Therefore, the distance between each detection element becomes wide.

As a result, when the distance between each detection element becomes wider, the range of angles that are not measured within the fan beam angle becomes larger, and the measurement angle becomes coarser, so when the image is reconstructed, radial noise, That is, there is a problem in that noise called streak artifact occurs.

SUMMARY OF THE INVENTION In view of the problems of the prior art, an object of the present invention is to provide a scanning method for a radiation CT apparatus that can reliably prevent streak artifacts from occurring even if the distance between each detection element of a detector is wide. It is in.

[Means for Solving the Problems] In the scanning method of the present invention, (a) during the rotation operation, both the radiation source and the detector are simultaneously translated a number of times;
(k is an integer of 2 or more), (b) during the corresponding number of translation operations, the first translation operation is performed with both the radiation source and the detector remaining in the predetermined positions, (c) the second translation operation (P is the pitch between each detection element of the detector) (P is the pitch between each detection element of the detector) d) Thereafter, k times of translation operations and rotation operations are sequentially and repeatedly executed until k times of translation operations are repeated N times (provided that a radiation source is provided).

[Effect]

In the method of the present invention, as described above, (a) during the rotation operation, both the radiation source and the detector are translated a number of times, and (b) during the number of translation operations, the first translation is performed. The rate operation is performed with both the radiation source and the detector remaining in the predetermined position, and (c) the second to third translation operations are performed each time with only one of the radiation source and the detector. (D) Hereafter, the translation operation k times and the rotation operation are performed repeatedly in sequence until the translation operation k times is repeated N times. Therefore, by performing the translation operation k times, it is possible to reliably measure radiation from the direction between the detection elements that cannot be measured during each translation operation, and the density of the measurement angle can be increased accordingly.

As a result, even if the distance between each detection element increases, the measurement angle does not become coarser, and the density of the measurement angle is increased.
When reconstructing an image, noise such as streak artifacts can be prevented from occurring.

[Example] Hereinafter, an example of the method of the present invention will be described with reference to FIGS. 1 to 4. FIG. 1 is an explanatory time chart showing a first embodiment of the method of the present invention, FIG. 2 is an explanatory diagram of a detector, and FIG. 3 is an X-ray CT apparatus to which the method of the present invention is applied.

In the first embodiment of the method of the present invention, both the X-ray source 1 and the detector 2 are translated by a translation mechanism 3 a plurality of times, for example, twice.

As shown in FIGS. 1 and 3, the translation mechanism 3 that performs two translation operations operates the Xfi source 1.2 by driving the pinion 3a. The detector 2 is moved to the right to perform the first translation operation TI, and then the pinion 3a is driven in reverse, and both 1 and 2 are moved to the left to perform the second translation operation T2. do.

Furthermore, during the first translation operation TI, the detector 2 is left in the predetermined position as shown in FIG.
At the time of the second translation operation T2, only the detector 2 is shifted by half the pitch P between the detection elements 2I to 2n, as shown in FIG.

As shown in FIG. 3, the fine adjustment movement mechanism moves the detector 2
A rack 9a formed in the amplifier section 8 integrally provided with
, a pinion 9b that meshes with the rack 9a, and a motor (not shown) that drives the pinion 9b. When the translation mechanism 3 performs the second translation operation T2, in other words, when the first translation operation T2 is performed, the pinion 9b
By driving the rack 9a of the amplifier unit 8, the detection elements 21 to 2n are shifted to the right by an interval of 1/2P, as shown in FIG. As shown in Figure (C), each of the detection elements 21 to 2 during the first translation operation T1. It is possible to measure X-ray transmission data from mutual directions. Therefore, the valley detection element 2. ~21. Figure 2 (a), ■)
As shown in , even if the width dimension P/2 is half of the pitch P between each detection element and it is moved (shifted) by the fine adjustment movement mechanism 9, the fan beam angle α will naturally change.
is set to fall within the range of

Translate operation TI is performed twice as described above.

After execution of T2, the fine adjustment movement mechanism 9 returns each detection element 21 to 27 of the detector 2 to its original predetermined position, and then the iterotate mechanism 4 moves the X-ray source 1. The detector 2 is rotated once.

Then, two translation operations T1 and one rotation operation are sequentially and repeatedly performed so that the two translation operations are repeated N times up to an angular position of 180°.

It is established.

In FIG. 3, components other than the fine adjustment movement mechanism 9 are designated by the same reference numerals as in FIG. 5, so their explanation will be omitted.

Since the scanning method of the embodiment has the above-mentioned configuration, its operation will be described next.

First, X! Execute the first translation operation to the right while leaving both IIA source I and detector 2 in the predetermined positions,
Next, only the detector 2 has P between its detection elements 21 to 2fi.
Execute the second translation operation to the left at a position shifted by /2.

Thereafter, the rotation mechanism 4 rotates both the X-ray source 1 and the detector 2 at an angle corresponding to the fan beam angle α to perform a rotation operation. Note that during rotational movement by the rotation mechanism 4, each detection element 2 of the detector 2 is rotated by the fine adjustment movement mechanism 9 being driven in reverse.
．． ~2. ．． Return it to its original position (.

Hereinafter, the above two translation operations and rotation operations are sequentially repeated around the subject 100, and the subject 100 is
A tomographic image is reconstructed by measuring X-ray transmission data in 3600 directions for each point in the entire area.

Therefore, during the backward movement of the translation operation, the detector 2 is shifted by a distance of half the pitch between each detection element 21 to 2fi by the fine adjustment movement mechanism 9, and between the detection elements 2+-2- that could not be measured during the forward movement. Since the X-ray transmission data is measured from the direction of However, the density of the X-ray measurement angle can be increased.

As a result, even if the distance between each detection element increases due to the use of radiation sources such as high-voltage or high-energy radiation, the measurement angle does not become rougher and the density of the measurement angle can be increased. Therefore, when an image is reconstructed, noise such as streak artifacts can be prevented from occurring.

In addition, since the density of the measurement angle can be increased, if both the X-ray source 1 and the detector 2 rotate 180 degrees around the subject 100 by repeating the transleft operation and rotation operation, the X-ray source 1 and detector 2 are further measured in the angular direction from 180' to 360'', and the data is on the measurement line in the same direction.
Measurement data for angles exceeding .degree. is no longer required, and the scanning time for both 1 and 2 can be shortened accordingly.

In the illustrated embodiment, the fine adjustment movement mechanism 9 moves each detection element 2. We have shown an example in which 27 is shifted by 1/2 pitch during the return movement of 1 translation operation, but for example,
Of course, it is possible to obtain the same effect as described above even if each detection element is shifted during the forward movement of one translation operation, but it is also possible to obtain the same effect as described above by leaving each detection element in the same position and moving the radiation source, which is an X-ray source. A similar effect can be obtained by shifting using a fine adjustment movement mechanism.

In addition, during the rotation operation, both the radiation source and the detector are translated three times at the same time, and the first translation operation is performed when both the radiation source and the detector are at the predetermined position. 2.
For each translation operation from the 3rd time to the 3rd time, only one of the radiation source and the detector performs P/3 according to each time.
(P is the pitch between each detection element of the detector), and hereafter, three batch translation operations and a rotation operation are performed. The same effect can be obtained even if the translation operation is repeated sequentially until it is repeated N times, and the more the number of batch translation operations increases, the more precise data of the angular direction between the detector elements can be measured. becomes possible.

FIG. 4 is an explanatory diagram showing another embodiment of the method of the present invention.

In this case, (a) radiation source fan beam angle α=360
°/2N, while collectively setting the first to Nth translation operations to m times, and collectively setting each translation operation from N+1st to second to -m times. (where N, m is an integer, and k)m); (b) Of the m number of translation operations, perform the first translation operation on the radiation source and detector. (c) During each translation operation from the second to the mth translation operation, only one of the radiation source and the detector remains shifted by P/ according to each translation operation. (P is the pitch between each detection element of the detector, k
is an integer greater than m), (d) Hereinafter, repeat the m number of translation operations and the mouth-tate operation in sequence until the m number of translation operations are repeated N times, and (e) perform the m number of translation operations. After executing the translation operation N times, each translation operation from the N+1st to the 2Nth time is executed k −m times, and (to) the first translation among the -m translation operations The operation is performed at a position where only one of the radiation source and the detector is deviated from the predetermined position by P / k Only one side is executed at a position sequentially shifted by P/ according to each time. It is designed to be executed repeatedly in sequence until it is executed.

Specifically, when m=1 and k=2, from the first angle to the Nth angle, that is, up to 180 degrees, the translate operation and rotate operation are repeated once each as in the conventional example. During the rotation operation from N+1 to 2N times, the fine adjustment movement mechanism 9 shifts each of the detection elements 21 to 2n of the detector 2 by 1/2 pitch for measurement.

According to this embodiment, since the angle data in the direction shifted by a minute angle corresponding to 1/2 pitch is measured from the opposite direction with respect to the angle from the first to the Nth angle, it is possible to measure the angle data from the opposite direction. Compared to measuring data twice, data can be measured at twice the angular density even with the same number of measurements, and the density of the measured angles can be increased accordingly.

In this case, in particular, the way the X-ray beam spreads from the X-ray source 1 to each detection element 21 to 2o will be different, and the X-rays irradiated from 7ml of X-rays will In some cases, each detection element 2. even on the same measurement line. A slight difference in data occurs depending on the direction of incidence on ~2n, resulting in a slight difference in data on the same measurement line. Therefore, both the X-ray source 1 and the detector 2 are moved around the subject, It is suitable for improving the image quality of reconstructed images by measuring data from 360° directions.

〔Effect of the invention〕

As described above, according to claim 1 of the present invention, it is possible to measure radiation transmission data from directions between the detection elements that cannot be measured during movement in the translation operation, and to reliably increase the density of measurement angles accordingly. As a result, noise such as streak artifacts can be prevented from occurring.

According to claim 2, in addition to the effects similar to those described above, there is an effect that is particularly beneficial in the case of a subject with non-uniform radiation absorption distribution.

[Brief explanation of the drawing]

Figure 1 is an explanatory time chart showing the first embodiment of the method of the present invention, Figure 2 (a) is an explanatory diagram showing the position of the detector during the forward movement of the translation operation, Explanatory diagram showing the position of the detector during double movement, same figure (C)
3 is an explanatory diagram showing the detector position during forward movement and backward movement in the translation operation, 3rd is an explanatory diagram showing another embodiment of the method of the present invention, and 5 is a configuration of a conventional X-ray CT apparatus. FIG. 6 is a schematic diagram showing an example, FIG. 6 is an explanatory diagram showing a scanning method, and FIG. 7 is a time chart of conventional translation operation and rotation operation. DESCRIPTION OF SYMBOLS 1... X-ray source, 2... Detector, 21-2□... Detection element, 3... Translate mechanism, 4... Rotate mechanism, 9... Fine adjustment movement mechanism, P ...Pitch between detection elements. Patent Applicant Hitachi Medical Co., Ltd. Agent Patent Attorney Tadashi Akimoto 1 other person Diagram NIK = +80° Diagram (a) 1゛X-ray group 2 Nairokai 2~2n゛Utsuba f, -) P: h Pitch between pinching elements Diagram (b) 21-2n: Gauge Akako P: Wax island beak Cshi 14 bite diagram

Claims (1)

[Claims] 1. By sequentially repeating a translation operation in which a fan beam radiation source and a detector are moved in parallel, and a rotation operation in which the radiation source and detector are rotated at a fan beam angle, In a scanning method for a TR-type radiation CT apparatus that measures transmission data of a radiation source around a is an integer of 2 or more), (b) during the k number of translation operations, the first translation operation is performed with both the radiation source and the detector remaining in the predetermined positions, (c) the second to k During each translation operation up to the first translation operation, only one of the radiation source and the detection is executed at a position sequentially shifted by P/k depending on each time (P is the pitch between each detection element of the detector), ), the translation operation k times and the rotation operation are sequentially repeated until the translation operation k times is repeated N times (however, the radiation source fan beam angle α=180°/N (N is an integer). )) A scanning method in a radiation source CT apparatus, characterized in that: 2. By sequentially repeating a translation operation in which the fan beam radiation source and the detector are moved in parallel and a rotation operation in which the radiation source and the detector are rotated at the fan beam angle, the radiation source around the subject is In the scanning method of a TR-type radiation CT device that measures transmission data, (a) the radiation source fan beam angle α is set as 360°/2N, while each translation operation from the 1st to the Nth translation is performed at once; In addition, each translation operation from the N+1st to the 2Nth time is set to km times (however, N, k, and m are integers, and k>m (b) Perform the first translation operation of the m number of translation operations until both the radiation source and the detector reach the predetermined position, and (c) Perform each translation operation from the second to the m-th translation operation. During the rate operation, only one of the radiation source and the detector is operated with a sequential shift of P/k depending on each time (P is the pitch between each detection element of the detector, k is an integer larger than m), ( d) Hereafter, repeat the m number of translation operations and the rotate operation in sequence until the m number of translation operations are repeated N times, (e) After performing the m number of translation operations N times, (f) Perform each translation operation from the N+1st to the 2Nth time km times; Execute only at a position shifted by (P/k) x m from the predetermined position, and (g)
The second and subsequent translation operations are performed at positions where only one of the radiation source and the detector is sequentially shifted by P/k each time, and (h) the following translate operations and rotation are performed km times. A scanning method in a radiation CT apparatus, characterized in that the above operations are sequentially and repeatedly performed until the translation operation is repeated km times 2N times.