JPS6363854B2 - - Google Patents
Info
- Publication number
- JPS6363854B2 JPS6363854B2 JP53120409A JP12040978A JPS6363854B2 JP S6363854 B2 JPS6363854 B2 JP S6363854B2 JP 53120409 A JP53120409 A JP 53120409A JP 12040978 A JP12040978 A JP 12040978A JP S6363854 B2 JPS6363854 B2 JP S6363854B2
- Authority
- JP
- Japan
- Prior art keywords
- ray
- wedge filter
- water
- absorption coefficient
- ratio
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000000463 material Substances 0.000 claims description 28
- 238000010521 absorption reaction Methods 0.000 claims description 25
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 17
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 11
- 229910052782 aluminium Inorganic materials 0.000 claims description 11
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 7
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- 238000010586 diagram Methods 0.000 description 7
- 230000005855 radiation Effects 0.000 description 7
- 239000003575 carbonaceous material Substances 0.000 description 6
- 238000001514 detection method Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000002591 computed tomography Methods 0.000 description 1
- 230000008094 contradictory effect Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000003325 tomography Methods 0.000 description 1
Landscapes
- Measurement Of Radiation (AREA)
- Apparatus For Radiation Diagnosis (AREA)
- Nuclear Medicine (AREA)
- Analysing Materials By The Use Of Radiation (AREA)
Description
【発明の詳細な説明】
本発明は、被検体の同一断層面上における多方
向からの放射線投影データを得、それに価いて前
記被検体の断層像を再構成するコンピユーテツ
ド・トモグラフイ装置（Computed
Tomography装置 以下「CT装置」と称する）
に用いられるウエツジフイルタに関するものであ
る。DETAILED DESCRIPTION OF THE INVENTION The present invention provides a computed tomography apparatus that obtains radiation projection data from multiple directions on the same tomographic plane of a subject and reconstructs a tomographic image of the subject based on the data.
Tomography device (hereinafter referred to as “CT device”)
The invention relates to wedge filters used in
CT装置は、原理的には被検体について多方面
からの放射線（例えばＸ線）の透過吸収に関する
情報を得、コンピユータ等を用いた演算処理によ
り前記情報に基いて被検体の断層像を再構成する
ものである。 In principle, a CT device obtains information about the transmission and absorption of radiation (e.g. It is something to do.
この場合、例えばＸ線ビームとして非常に細く
かつビーム拡がり角のほとんどない単一のペンシ
ルビーム、或いは扇状を呈するフアンビームのい
ずれを用いた場合でも、第１図に示すようにＸ線
源１からＸ線検出器２の検出面までの各Ｘ線パス
Po、Pa等について、被検体３に対する通過位置
の相違により被検体３における通過パス長（lo、
la等）がそれぞれ異なることになる。こため、各
Ｘ線パスにおけるＸ線の強度が同一であれば、当
然Ｘ線検出器２に入射するフオトンの数は各Ｘ線
パスによつて相違することとなつて、量子ノイズ
に対するSN比が各Ｘ線パスにより異なり、各Ｘ
線パスにおける検出信号のSN比がそれぞれ相違
する。又、この場合Ｘ線検出器２のダイナミツク
レンジにも大きな値が要求されることになる。そ
こで、このような問題に対しては、従来Ｘ線源１
とＸ線検出器２との間の被検体３における通過パ
ス長（lo、la等）の相違に応じて該通過パス長が
短かくなるに従つてフイルタ厚さが厚くなる形状
をなすウエツジフイルタと称するフイルタ４を挿
入し、前記パス長の相違による影響を補正するよ
うにしている。 In this case, for example, regardless of whether the X-ray beam is a single pencil beam that is very thin and has almost no beam divergence, or a fan beam that has a fan shape, the Each X-ray path to the detection surface of X-ray detector 2
Regarding Po, Pa, etc., the passing path length (lo,
la, etc.) will be different for each. Therefore, if the intensity of X-rays in each X-ray pass is the same, the number of photons incident on the X-ray detector 2 will naturally differ depending on each X-ray pass, and the SN ratio with respect to quantum noise will decrease. differs depending on each X-ray pass, and each
The SN ratio of the detection signal in each line path is different. Furthermore, in this case, the dynamic range of the X-ray detector 2 is also required to have a large value. Therefore, to solve such problems, conventional X-ray sources 1
and a wedge filter having a shape in which the filter thickness becomes thicker as the passing path length becomes shorter depending on the difference in passing path length (lo, la, etc.) in the subject 3 between the X-ray detector 2 and the A filter 4 called the above is inserted to correct the influence of the difference in path length.
ところで、従来のウエツジフイルタ４は第２図
に示すように一方の面（例えばＸ線源側の面）４
ａを平面状、他方の面（例えば被検体側の面）４
ｂを断面がほぼ円弧状の凹曲面として形成されて
おり、Ｘ線源１−被検体３間及び被検体３−Ｘ線
検出器２間の一方もしくは両方に配置して用いら
れる。すなわち、被検体３におけるＸ線のパス長
が短かくなるに従つてウエツジフイルタ４におけ
る通過パス長が長くなるようにして、Ｘ線パスの
相違によるＸ線検出器２の出力レベルの差を小さ
くするようにしている。 By the way, the conventional wedge filter 4 has one surface (for example, the surface on the X-ray source side) 4 as shown in FIG.
a is a plane, the other surface (for example, the surface on the subject side) 4
b is formed as a concave curved surface having a substantially arcuate cross section, and is used by being placed at one or both of the space between the X-ray source 1 and the subject 3 and between the subject 3 and the X-ray detector 2. That is, as the path length of the X-rays in the object 3 becomes shorter, the path length through the wedge filter 4 becomes longer, thereby reducing the difference in the output level of the X-ray detector 2 due to the difference in the X-ray paths. That's what I do.
ところで、このような機能を有するウエツジフ
イルタの材料を選択する場合、被測定物質（例え
ば人体）と同等のＸ線吸収特性を有するものが要
求される。即ち、人体のＸ線吸収特性は、ほぼ水
のそれに等しいので、これと同等のＸ線吸収特性
を有するものが要求されるわけである。このよう
な要求に応えるものとして従来は、Ｃ（カーボン）
又はAl（アルミニウム）等を選択し、これらを用
いてカーボン製又はアルミニウム製のウエツジフ
イルタを形成していた。しかしながら、これらの
材料はＸ線エネルギーに対して必ずしも均一な特
性を示すものでないことは、一般にもよく知られ
た事実である。 By the way, when selecting a material for a wedge filter having such a function, a material having X-ray absorption characteristics equivalent to that of the substance to be measured (for example, a human body) is required. That is, since the X-ray absorption characteristics of the human body are approximately equal to those of water, a material having X-ray absorption characteristics equivalent to that of water is required. Conventionally, C (carbon) has been used to meet these demands.
Or Al (aluminum), etc. were selected and used to form a wedge filter made of carbon or aluminum. However, it is a well-known fact that these materials do not necessarily exhibit uniform characteristics with respect to X-ray energy.
第５図は、横軸にＸ線エネルギーＥをとり、縦
軸には各材料の線吸収係数と水のそれとの比（Ｘ
線エネルギーが80KeVのときのその値で正規化
したもの）をとつた特性図である。ここでは各材
料の密度はアルミニウム、カーボンそれぞれ2.70
ｇ／cm3、1.73ｇ／cm3としている。この特性図から
明らかなように、Alの線吸収係数の水のそれに
対する比はＸ線エネルギーが80KeV以上ではほ
ぼ一定になるが、20KeV近辺では５倍前後とな
り、他方Ｃの線吸収係数の水のそれに対する比
は、Ｘ線エネルギーが80KeV以上ではほぼ一定
ではあるが20KeV近辺では逆に半分程度の値と
なる。このため前記ウエツジフイルタを使用した
場合には測定誤差が生ずるという欠点を有する。 In Figure 5, the horizontal axis shows the X-ray energy E, and the vertical axis shows the ratio of the linear absorption coefficient of each material to that of water (X
This is a characteristic diagram (normalized by the value when the line energy is 80 KeV). Here, the density of each material is 2.70 for aluminum and carbon respectively.
g/cm 3 and 1.73 g/cm 3 . As is clear from this characteristic diagram, the ratio of the linear absorption coefficient of Al to that of water is almost constant when the X-ray energy is 80 KeV or higher, but it becomes around 5 times as large near 20 KeV. The ratio of X-ray energy to that is almost constant when the X-ray energy is 80 KeV or higher, but it becomes about half the value when the X-ray energy is around 20 KeV. For this reason, when the wedge filter is used, there is a drawback that measurement errors occur.
本発明は上記した点についてなされたもので、
Ｘ線エネルギーの高低に関係なく、水のＸ線吸収
係数とほぼ等しくなるウエツジフイルタを提供す
ることを目的とする。この目的を達成するために
本発明は所定のＸ線エネルギー範囲でＸ線吸収係
数が水のＸ線吸収係数よりも大きくなる第１の材
料と、前記所定のＸ線エネルギー範囲でＸ線吸収
係数が水のＸ線吸収係数よりも小さくなる第２の
材料とを含み、前記所定のＸ線エネルギー範囲に
おいて水に対するＸ線吸収係数比がほぼ均一に変
化するように前記第１の材料と前記第２の材料の
それぞれの厚みを調整して組み合せたことを特徴
とするものである。 The present invention has been made in view of the above points,
It is an object of the present invention to provide a wedge filter whose X-ray absorption coefficient is approximately equal to that of water, regardless of the level of X-ray energy. To achieve this object, the present invention provides a first material whose X-ray absorption coefficient is larger than that of water in a predetermined X-ray energy range; a second material whose X-ray absorption coefficient is smaller than an X-ray absorption coefficient of water; This material is characterized by combining the two materials by adjusting their respective thicknesses.
以下実施例により本発明を具体的に説明する。 The present invention will be specifically explained below using Examples.
第３図及び第４図は本発明ウエツジフイルタの
一実施例をそれぞれ示す断面図である。第３図に
示すウエツジフイルタ５は、一方の面（例えばＸ
線源側の面）を平面状とし、他方の面（例えば被
検体側の面）を断面がほぼ円弧状の凹曲面を為す
如く形成されたカーボン材料５ｂと、このカーボ
ン材料５ｂの凹曲面に沿つてほぼ均等の厚さで延
在する如く形成されたアルミニウム材料５ａとに
よつて構成されている。又、第４図に示すウエツ
ジフイルタ５は、前記第３図に示したものと同一
の形状を為すカーボン材料５ｂと、このカーボン
材料５ｂの周面に沿い、かつ、それを覆う如く形
成されたアルミニウム材料５ａとによつて構成さ
れている。そして、これらは共に、放射線（例え
ばＸ線）源からのＸ線通過パス方向の長さの比
（各材料の厚さの比と同じ）が全て一定となるよ
うに構成されている。 FIGS. 3 and 4 are sectional views showing one embodiment of the wedge filter of the present invention, respectively. The wedge filter 5 shown in FIG.
A carbon material 5b is formed so that the surface (on the radiation source side) is flat and the other surface (for example, the surface on the subject side) is a concave curved surface with a substantially arc-shaped cross section, and the concave curved surface of this carbon material 5b is The aluminum material 5a is formed so as to extend along the length with a substantially uniform thickness. The wedge filter 5 shown in FIG. 4 includes a carbon material 5b having the same shape as that shown in FIG. It is made of material 5a. Both of these materials are configured such that the length ratio (same as the thickness ratio of each material) in the direction of the X-ray path from the radiation (for example, X-ray) source is constant.
ここで、各材料の厚さの比の最適条件を求める
ための計算結果を第６図に示した特性図を参照し
て説明する。同図では横軸にＸ線エネルギーＥ
（単位KeV）をとり、縦軸に本発明に係るアルミ
ニウムとカーボンを組み合せたウエツジフイルタ
の複合線吸収係数の水の線吸収係数に対する比を
とつた場合の特性を示すものであり、アルミニウ
ムとカーボンの厚さの比（Al：Ｃ）をそれぞれ
１：14（図中□印）、１：15（図中×印）、１：16
（図中〇印）、１：17（図中△印）とした場合のそ
れぞれの軌跡を描いたものである。同図から明ら
かなように、いずれの場合もＸ線エネルギーの変
化に対して均一な線吸収係数を示しており、特に
アルミニウムとカーボンの厚さの比を１：16とし
たものが最も良好な均一性を表わしている。又、
これらは共に、水の線吸収係数に対して1.5倍以
上の高い線吸収係数を有している。したがつて、
本発明のウエツジフイルタの好適な構成例として
はアルミニウム材５ａとカーボン材５ｂとの厚さ
の比を１：16とすれば良いことが理解されよう。 Here, the calculation results for determining the optimum conditions for the thickness ratio of each material will be explained with reference to the characteristic diagram shown in FIG. In the same figure, the horizontal axis shows the X-ray energy E
(unit: KeV), and the vertical axis shows the characteristics when the ratio of the composite linear absorption coefficient of the wedge filter combining aluminum and carbon according to the present invention to the linear absorption coefficient of water is taken. The thickness ratio (Al:C) is 1:14 (□ mark in the figure), 1:15 (x mark in the figure), and 1:16, respectively.
(marked with ○ in the figure) and 1:17 (marked with △ in the figure), respectively. As is clear from the figure, all cases show uniform linear absorption coefficients with respect to changes in X-ray energy, and in particular, the one with an aluminum to carbon thickness ratio of 1:16 is the best. It represents uniformity. or,
Both of these have linear absorption coefficients that are 1.5 times or more higher than that of water. Therefore,
It will be understood that as a preferred example of the structure of the wedge filter of the present invention, the ratio of the thicknesses of the aluminum material 5a and the carbon material 5b may be 1:16.
以上のように本発明によれば、Ｘ線エネルギー
の高低にかかわらず、水のＸ線吸収特性とほぼ同
じ吸収特性を有するウエツジフイルタとなる。こ
のため、このウエツジフイルタを例えばCT装置
になどに適用した場合、水とほぼ同じＸ線吸収特
性なので、Ｘ線エネルギーの変化によつて測定値
が水のそれとなくずれることがない。 As described above, according to the present invention, a wedge filter can be obtained which has almost the same X-ray absorption characteristics as water, regardless of the level of X-ray energy. For this reason, when this wedge filter is applied to, for example, a CT device, the X-ray absorption characteristics are almost the same as those of water, so the measured values will not deviate from those of water due to changes in X-ray energy.
しかも、上記のようにアルミニウム材とカーボ
ン材を組み合せた場合、Ｘ線吸収特性は水とほぼ
同じであるが、Ｘ線吸収係数は水のそれよりも
1.5倍ほど大きくなるので、水の厚さよりも薄い
ウエツジフイルタとなる利点がある。 Moreover, when aluminum and carbon materials are combined as described above, the X-ray absorption characteristics are almost the same as water, but the X-ray absorption coefficient is higher than that of water.
Since it is about 1.5 times larger, it has the advantage of being a wedge filter that is thinner than the thickness of water.
尚、本発明は前記実施例に限定されず、放射線
エネルギーに対して線吸収係数特性が互いに相反
する（対称）ような材料を組み合せることにより
同一の効果を得ること、又は３種類以上の材料を
適宜に組み合せることによつて同一の効果を得る
ようにしてもよい。更に、数種類の材料を結合さ
せる方法に限らず、各材料を単に重ね合せて構成
してもよい。 It should be noted that the present invention is not limited to the above-mentioned embodiments, and the same effect can be obtained by combining materials whose linear absorption coefficient characteristics are mutually contradictory (symmetrical) with respect to radiation energy, or by combining three or more types of materials. The same effect may be obtained by appropriately combining them. Furthermore, the structure is not limited to the method of combining several types of materials, but may be constructed by simply overlapping each material.
第１図はパス方向の相違による被検体における
パス長の相違を説明するための図、第２図は従来
のウエツジフイルタの構成を示す斜視図、第３図
及び第４図は本発明のウエツジフイルタの一実施
例を示す断面図、第５図は従来のウエツジフイル
タに用いられた材料のＸ線吸収特性を示す特性
図、第６図は本発明のウエツジフイルタのＸ線吸
収特性を示す特性図である。
１，１′……放射線源、２，２′……放射線検出
器、３……被検体、４……ウエツジフイルタ、５
……ウエツジフイルタ、５ａ……アルミニウム
材、５ｂ……カーボン材。
FIG. 1 is a diagram for explaining the difference in path length in the specimen due to the difference in path direction, FIG. 2 is a perspective view showing the configuration of a conventional wedge filter, and FIGS. 3 and 4 are diagrams of the wedge filter of the present invention. FIG. 5 is a characteristic diagram showing the X-ray absorption characteristics of a material used in a conventional wedge filter, and FIG. 6 is a characteristic diagram showing the X-ray absorption characteristics of the wedge filter of the present invention. 1, 1'... Radiation source, 2, 2'... Radiation detector, 3... Subject, 4... Wedge filter, 5
...Wedge filter, 5a...aluminum material, 5b...carbon material.
Claims (1)
水のＸ線吸収係数よりも大きくなる第１の材料
と、前記所定のＸ線エネルギー範囲でＸ線吸収係
数が水のＸ線吸収係数よりも小さくなる第２の材
料とを含み、前記所定のＸ線エネルギー範囲にお
いて水に対するＸ線吸収係数比がほぼ均一に変化
するように前記第１の材料と前記第２の材料のそ
れぞれの厚みを調整して組み合せたことを特徴と
するウエツジフイルタ。 ２ 前記第１の材料をアルミニウム、前記第２の
材料をカーボンとしたことを特徴とする特許請求
の範囲第１項記載のウエツジフイルタ。 ３ 前記アルミニウムとカーボンとの厚さの比を
１：16としたことを特徴とする特許請求の範囲第
２項記載のウエツジフイルタ。[Scope of Claims] 1. A first material whose X-ray absorption coefficient is larger than that of water in a predetermined X-ray energy range; and a second material whose X-ray absorption coefficient is smaller than the X-ray absorption coefficient, and the first material and the second material are arranged such that the X-ray absorption coefficient ratio to water changes almost uniformly in the predetermined X-ray energy range. A wedge filter characterized by adjusting the thickness of each and combining them. 2. The wedge filter according to claim 1, wherein the first material is aluminum and the second material is carbon. 3. The wedge filter according to claim 2, wherein the ratio of the thicknesses of the aluminum and carbon is 1:16.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12040978A JPS5547467A (en) | 1978-10-02 | 1978-10-02 | Wedge filter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12040978A JPS5547467A (en) | 1978-10-02 | 1978-10-02 | Wedge filter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5547467A JPS5547467A (en) | 1980-04-03 |
| JPS6363854B2 true JPS6363854B2 (en) | 1988-12-08 |
Family
ID=14785497
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP12040978A Granted JPS5547467A (en) | 1978-10-02 | 1978-10-02 | Wedge filter |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5547467A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58165657U (en) * | 1982-04-15 | 1983-11-04 | 横河電機株式会社 | X-ray filter |
| JPS60174139A (en) * | 1984-02-20 | 1985-09-07 | 理学電機株式会社 | X-ray tomography apparatus |
| JP4585064B2 (en) * | 1999-11-01 | 2010-11-24 | 株式会社東芝 | Radiation diagnostic equipment |
| BR112014022541B1 (en) * | 2012-03-13 | 2022-03-08 | Mayekawa Mfg. Co., Ltd | DEVICE AND METHOD FOR CAPTURING X-RAY IMAGE OF BONE-IN MEAT |
-
1978
- 1978-10-02 JP JP12040978A patent/JPS5547467A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5547467A (en) | 1980-04-03 |
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