JP3775577B2 - Radiographic imaging method and apparatus - Google Patents

Description

但し、Ｔ（ｘ，ｙ）：透過率関数
Ａ（ｘ，ｙ）：透過率強度関数
ψ（ｘ，ｙ）：位相シフト量関数
（ｘ，ｙ）：検出パネル上の位置を表す座標値
【００３３】
ここで、透過率強度が無視できるような薄い物体（すなわちＡ（ｘ，ｙ）が１に近い）である場合、下記の式（２）に示すように、被写体２１と検出パネル３１，３２，３３との距離ｄｎ（ｎ＝１〜Ｎ）において撮影された画像Ｉ_dn（ｘ，ｙ）をフーリエ変換することにより得られた空間周波数成分Ｉ_dn（ｆｘ，ｆｙ）用いて、位相シフト量の空間周波数成分が算出される。
【００３４】
ここで、検出パネル３１，３２，３３に照射されるＸ線量と、画像データＳｎにより表される画像の各画素値との関係は予め検出することができる。したがって、この関係から画像データＳｎにより表される画像の画素値をＸ線量に変換する変換テーブルを作成しておき、この変換テーブルを参照することにより、距離ｄｎにおいて取得された画像データＳｎにより表される画像の位置（ｘ，ｙ）における画素値から画像Ｉ_dn（ｘ，ｙ）を求めることができる。
【数２】

但し、Ｎ：画像データＳｎの数
ｆ：空間周波数
ψ（ｆｘ，ｆｙ≠０）：周波数が０でないときの位相シフト量の空間周波数成分
Ｉ_dn（ｆｘ，ｆｙ）：Ｉ_dn（ｘ，ｙ）の空間周波数成分
【００３５】
そして、位相シフト量の空間周波数成分を逆フーリエ変換することにより、位相シフト量すなわち位相差ψ（ｘ，ｙ）を算出することができる。ここで、位相差ψ（ｘ，ｙ）は０〜２πの範囲の値を採るため、算出された位相差ψ（ｘ，ｙ）を例えば８ビットの値に割り当てることにより、位相コントラスト画像を表す画像データＳｐを得ることができる。
【００３６】
なお、ここでは透過率強度が無視できるＡ（ｘ，ｙ）が１に近い場合を想定しているが、厚い物体についても同様のアルゴリズムを用いて位相シフト量を算出することができるものである。
【００３７】
次いで、第１の実施形態の動作について説明する。図３は第１の実施形態の動作を示すフローチャートである。まず、線源１１を駆動してシンクロトロン放射光を結晶１３において反射させることにより、Ｘ線源１０から単色のＸ線１２を出射して、被写体２１にＸ線１２を照射する（ステップＳ１）。そして、複数の撮影位置において読出手段３４，３５，３６により検出パネル３１，３２，３３を構成する複数の検出素子の電気信号を読み出して、各撮影位置における画像データＳｎを取得する（ステップＳ２）。
【００３８】
取得された画像データＳｎは演算部４０に入力され、ここで拡大縮小処理が施され、さらに上述したように位相コントラスト画像を表す画像データＳｐが生成され（ステップＳ３）、処理を終了する。なお、画像データＳｐはモニタによる再生、あるいはプリンタによるプリント出力に供される。
【００３９】
このように、第１の実施形態においては、被写体２１から離れた撮影位置ほど感度が高い検出パネルを用いてＸ線画像を取得するようにしたため、被写体２１から離れた撮影位置における検出パネル３３においても、被写体２１に近い撮影位置にある検出パネル３１と同様に、精度よくＸ線１２を検出することができる。したがって、複数のＸ線画像の濃度を略等しくすることができ、これにより、位相コントラスト画像を表す画像データＳｐを精度よく生成することができる。また、検出パネル３１，３２，３３のゲインを調整したり、得られるＸ線画像の濃度を調整する必要もないため、精度よく位相コントラスト画像を得るためのＸ線画像を効率よく検出することができる。
【００４０】
次いで、本発明の第２の実施形態について説明する。図４は本発明の第２の実施形態による放射線画像撮影装置を適用した位相コントラスト撮影装置の構成を示す概略ブロック図である。なお、第２の実施形態において、第１の実施形態とは記録部の構成が異なるのみであるため、第１の実施形態と同一の構成については同一の参照番号を付し、詳細な説明は省略する。
【００４１】
第２の実施形態における記録部１３０は、第１および第２の撮影ユニット１３０Ａ，１３０Ｂを備える。
【００４２】
第１および第２の撮影ユニット１３０Ａ，１３０Ｂは、蛍光体および２次元状に配列された複数の検出素子からなる検出パネル１３１Ａ，１３１Ｂと、被写体２１を透過したＸ線１２の進行方向に対して平行な方向に検出パネル１３１Ａ，１３１Ｂを移動させる移動手段１３２Ａ，１３２Ｂと、検出パネル１３１Ａ，１３１Ｂの移動経路上に予め設定された複数の撮影位置において、検出パネル１３１Ａ，１３１Ｂを構成する複数の検出素子から電気信号を読み出して各撮影位置における画像データＳｎａ，Ｓｎｂを得る読出手段１３３Ａ，１３３Ｂとを備える。
【００４３】
なお、移動手段１３２Ａ，１３２Ｂは、検出パネル１３１Ａ，１３１Ｂを支持する、雌ネジ部が形成された支持部１３５Ａ，１３５Ｂと、Ｘ線１２の進行方向と平行な方向に延在するとともに支持部１３５Ａ，１３５Ｂの雌ネジ部に螺合する雄ネジ部１３６Ａ，１３６Ｂと、雄ネジ部１３６Ａ，１３６ＢをＸ線１２の進行方向に伸びる回転軸を中心として回転させるモータ１３７Ａ，１３７Ｂと、モータ１３７Ａ、１３７Ｂの駆動および停止を制御する制御部１３８Ａ，１３８Ｂとを備える。そして、制御部１３８Ａ，１３８Ｂによりモータ１３７Ａ，１３７Ｂを駆動することにより雄ネジ部１３６Ａ，１３６Ｂが回転され、その回転方向に応じて支持部１３５Ａ，１３５Ｂすなわち検出パネル１３１Ａ，１３１Ｂが被写体２１に近づく方向および被写体２１から離れる方向に移動する。
【００４４】
また、第１および第２の撮影ユニット１３０Ａ，１３０Ｂにおける各撮影位置には、移動手段１３２Ａ，１３２Ｂにより移動される検出パネル１３１Ａ，１３１Ｂが各撮影位置に到達したことを検出する位置センサ５１Ａ，５２Ａ，５１Ｂ，５２Ｂがそれぞれ配設されている。位置センサ５１Ａ，５２Ａ，５１Ｂ，５２Ｂは、検出パネル１３１Ａ，１３１Ｂが撮影位置に到達した際に検出信号を出力し、これが読出手段１３３Ａ，１３３Ｂに入力される。読出手段１３３Ａ，１３３Ｂは、検出信号が入力されると、検出パネル１３１Ａ，１３１Ｂを構成する複数の検出素子から電気信号を読み出してその撮影位置における画像データＳｎａ，Ｓｎｂを得る。
【００４５】
なお、第２の実施形態においては、第１および第２の撮影ユニット１３０Ａ，１３０Ｂにおいて、それぞれ２箇所に位置センサ５１Ａ，５２Ａおよび５１Ｂ，５２Ｂが配設されているため、４箇所の撮影位置において４つの画像データＳｎ（Ｓ１〜Ｓ４）が得られることとなる。
【００４６】
ここで、第２の実施形態においては、被写体２１から離れた側の撮影ユニット１３０Ｂを構成する検出パネル１３１Ｂの感度が、被写体２１に近い側の撮影ユニット１３０Ａを構成する検出パネル１３１Ａの感度よりも高くなっている。具体的には、検出パネル１３１Ｂの蛍光体を検出パネル１３１Ａの蛍光体よりも厚くして、後者の蛍光体の含有量を前者の蛍光体の含有量よりも大きくしている。これにより、被写体２１から離れた位置にあっても、Ｘ線１２を精度よく検出することができ、さらには回折像も精度よく検出できることとなる。
【００４７】
演算部４０は、第１の実施形態と同様に、画像データＳｎにより表されるＸ線画像のサイズが、被写体２１に最も近い撮影位置において得られる画像データＳ１により表されるＸ線画像のサイズと同一となるように、画像データＳｎにより表されるＸ線画像に対して縮小処理を施すとともに、位相コントラスト画像を表す画像データＳｐを得る。
【００４８】
次いで、第２の実施形態の動作について説明する。図５は第２の実施形態の動作を示すフローチャートである。まず、線源１１を駆動してシンクロトロン放射光を結晶１３において反射させることにより、Ｘ線源１０から単色のＸ線１２を出射して、被写体２１にＸ線１２を照射する（ステップＳ１１）。これと同時に、まず、第１の撮影ユニット１３０Ａにおいて撮影を行う。すなわち、制御部１３８Ａによりモータ１３７Ａを駆動して、検出パネル１３１Ａを被写体２１に最も近い初期位置から離れる方向に移動させる（ステップＳ１２）。そして、移動に応じて位置センサ５１Ａ，５２Ａからの検出信号が入力されるタイミングで、読出手段１３３Ａにより検出パネル１３１Ａを構成する複数の検出素子の電気信号を読み出して、各撮影位置における画像データＳｎａを取得する（ステップＳ１３）。
【００４９】
第１の撮影ユニット１３０Ａにおいて、被写体２１から最も離れた撮影位置における撮影に続いて、第２の撮影ユニット１３０Ｂにおいて撮影を行う。すなわち、制御部１３８Ｂによりモータ１３７Ｂを駆動して、検出パネル１３１Ｂを被写体２１に最も近い初期位置から離れる方向に移動させる（ステップＳ１４）。そして、移動に応じて位置センサ５１Ｂ，５２Ｂからの検出信号が入力されるタイミングで、読出手段１３３Ｂにより検出パネル１３１Ｂを構成する複数の検出素子の電気信号を読み出して、各撮影位置における画像データＳｎｂを取得する（ステップＳ１５）。
【００５０】
取得された画像データＳｎａ，Ｓｎｂは演算部４０に入力され、ここで第１の実施形態と同様に位相コントラスト画像を表す画像データＳｐが生成され（ステップＳ１６）、処理を終了する。なお、画像データＳｐはモニタによる再生、あるいはプリンタによるプリント出力に供される。
【００５１】
なお、上記第２の実施形態においては、第１の撮影ユニット１３０Ａにおいて撮影を行った後に、第２の撮影ユニット１３０Ｂにおいて撮影を行っているが、第１および第２の撮影ユニット１３０Ａ，１３０Ｂにおいて同時に撮影を行ってもよい。
【００５２】
また、上記第２の実施形態においては、撮影ユニットを２つ用いているが、３以上の撮影ユニットを用いるようにしてもよい。この場合、後段の撮影ユニットに用いられる検出パネルほど、感度が高いものが用いられる。
【００５３】
また、上記第１および第２の実施形態においては、被写体２１から離れた撮影位置ほど検出パネルの感度を高いものとしているが、さらに前段にある検出パネルの枚数にも応じて検出パネルの感度を設定してもよい。
【００５４】
また、上記第１の実施形態においては、検出パネル３１，３２，３３によりＸ線画像を取得しているが、検出パネル３１，３２，３３に代えて、図６に示す第３の実施形態のように、複数（ここでは３枚）の蓄積性蛍光体シート６１，６２，６３を使用してもよい。この場合、被写体２１から離れた撮影位置に配設される蓄積性蛍光体シートほど蛍光体が厚く、感度が高いものを用いればよい。
【００５５】
なお、蓄積性蛍光体シート６１，６２，６３にＸ線画像を蓄積記録した場合には、各シート６１，６２，６３に励起光を照射して輝尽発光光を発生させ、この輝尽発光光を光電的に読み取る読取部７０において、Ｘ線画像を表す複数の画像データＳｎが得られる。得られた複数の画像データＳｎは、上記第１の実施形態と同様に演算部４０に入力され、位相コントラスト画像を表す画像データＳｐが生成される。
【００５６】
また、上記各実施形態においては、線源１１としてシンクロトロン放射光を発するものを用いているが、これに限定されるものではない。また、被写体２１に照射するＸ線１２として単色Ｘ線を用いているが、単色Ｘ線に限定されるものではない。
【００５７】
また、上記各実施形態においては、被写体２１にＸ線１２を照射しているが、Ｘ線以外の他の放射線（α線，β線，γ線，電子線，紫外線等）を用いてもよい。
【図面の簡単な説明】
【図１】 本発明の第１の実施形態による放射線画像撮影装置を適用した位相コントラスト撮影装置の構成を示す概略ブロック図
【図２】 検出パネルの厚さを説明するための図
【図３】 第１の実施形態の動作を示すフローチャート
【図４】 本発明の第２の実施形態による放射線画像撮影装置を適用した位相コントラスト撮影装置の構成を示す概略ブロック図
【図５】 第２の実施形態の動作を示すフローチャート
【図６】 本発明の第３の実施形態による放射線画像撮影装置を適用した位相コントラスト撮影装置の構成を示す概略ブロック図
【符号の説明】
１０ Ｘ線源
１１ 線源
１２ Ｘ線
１３ 結晶
２０ 被写体支持部
２１ 被写体
３０，１３０ 記録部
３１，３２，３３，１３１Ａ，１３１Ｂ 検出パネル
３３，１３３Ａ，１３３Ｂ 読出手段
４０ 演算部
５１Ａ，５１Ｂ，５２Ａ，５２Ｂ 位置センサ
６１，６２，６３ 蓄積性蛍光体シート
７０ 読取部
１３０Ａ，１３０Ｂ 撮影ユニット
１３２Ａ，１３２Ｂ 移動手段[0001]
BACKGROUND OF THE INVENTION
The present invention is suitable for detecting a radiation applied to a subject at a plurality of imaging positions at different distances from the subject to obtain a plurality of radiation images and generating a phase contrast image using the plurality of radiation images. The present invention relates to a radiographic imaging method and apparatus.
[0002]
[Prior art]
Conventionally, radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) is radiated on the subject, and the radiation that has passed through the subject is stored in a two-dimensional form. Are detected by a two-dimensional detector such as a radiation detection panel, and image data representing a radiographic image of a subject is obtained. The image data is subjected to various image processing and then used for reproduction. .
[0003]
Here, in the method using the stimulable phosphor sheet, a part of the radiation energy that has passed through the subject is accumulated, and then when the excitation light is irradiated, the stimulable fluorescence that emits the amount of stimulated emission light corresponding to the accumulated energy is emitted. Using the body (stimulable phosphor), the radiographic image information of the subject is recorded on a sheet-like storage phosphor (that is, the storage phosphor sheet), and this storage phosphor sheet is excited by laser light or the like. This is a method in which stimulated emission light is generated by scanning with light, and the generated stimulated emission light is photoelectrically read to obtain image data representing a radiographic image of a subject. In addition, the method using the radiation detection panel uses a radiation detection panel in which a plurality of detection elements are arranged in a two-dimensional manner, and generates an electrical signal corresponding to the amount of radiation irradiated to each of the detection elements, This is a method for obtaining image data representing a radiographic image of a subject based on the electrical signal.
[0004]
By the way, the radiographic image obtained in this way represents an intensity difference of transmitted radiation in the subject as an image. For example, when a subject including a bone and a soft part is photographed, the radiation that has passed through the bone part is greatly attenuated, so the amount of radiation that reaches the detector is reduced, but the radiation that has passed through the soft part is not attenuated so much. The amount of radiation that reaches the vessel is relatively high. Therefore, in the case of such a subject, a radiographic image having a large contrast difference in which the bone portion is expressed in white and the soft portion is expressed in black, that is, a large amount of information is obtained.
[0005]
However, when the subject is mainly composed only of soft parts as in breast cancer diagnosis, for example, the difference in radiation attenuation due to the tissue is not so large, so that only a radiographic image with a small contrast difference, that is, a small amount of information is obtained. I can't.
[0006]
For this reason, there has been proposed a phase contrast imaging method for visualizing the phase difference of radiation caused by passing through a subject. In this phase contrast imaging method, radiation is an electromagnetic wave like light, and a wave travels and propagates. Therefore, when radiation is irradiated to two different substances, due to the difference in how the radiation is transmitted in the substance, The subject is imaged based on the fact that the phase of the radiation wave is different before and after the transmission of the substance, resulting in a phase difference. Here, when the subject is a soft part, the phase difference of the radiation is larger than the difference in the amount of attenuation of the radiation. Therefore, imaging is performed by the phase contrast imaging method and the phase difference of the radiation is expressed as a phase contrast image. Thus, it is possible to visualize a subtle difference in the tissue included in the soft part. For phase contrast imaging methods, see “Peter Cloetens, et al.,“ Quantitative aspects of coherent hard X-ray imaging: Talbot image and holographic reconstruction ”, Proc, SPIE, Vol. 3154 (1977), 72-82 ( Reference 1) ”and“ Peter Cloetens, et al., “Hard x-ray phase imaging using simple propagation of a coherent synchrotron radiation beam”, J. Phys. D: Appl. Phys. 32 (1999), A145-A151 ( The details are described in “Literature 2)”. According to these documents, image data representing a plurality of radiation images is obtained by performing imaging using a two-dimensional detector such as a radiation detection panel at a plurality of imaging positions at different distances from the subject, and a plurality of image data A phase contrast image can be generated by performing an operation based on a predetermined algorithm using.
[0007]
On the other hand, when obtaining a radiation image, the radiation dose irradiated to the two-dimensional detector changes inversely proportional to the square of the distance between the radiation source and the two-dimensional detector. Further, since the radiation spreads from the radiation source and propagates, the larger the distance between the subject and the two-dimensional detector, the larger the size of the radiation image detected by the two-dimensional detector. For this reason, there has been proposed a radiographic imaging apparatus that adjusts the gain for reading a radiographic image or obtains the enlargement ratio of the radiographic image according to the distance between the subject and the two-dimensional detector (Japanese Patent Application Laid-Open No. 2005-318867). 2000-245721).
[0008]
There has also been proposed a method for obtaining a phase contrast image with high accuracy by performing enlargement / reduction processing and density conversion processing on radiation images obtained at a plurality of imaging positions (Japanese Patent Application No. 2001-146138).
[0009]
[Problems to be solved by the invention]
However, adjusting the reading gain or converting the density requires a long time for the operation, and the radiation image cannot be detected efficiently.
[0010]
The present invention has been made in view of the above circumstances, and an object thereof is to efficiently detect radiation and generate a phase contrast image with high accuracy.
[0011]
[Means for Solving the Problems]
The radiographic image capturing method according to the present invention is a radiographic image that acquires a plurality of radiographic images by irradiating a subject with radiation and detecting the radiation transmitted through the subject at a plurality of imaging positions having different distances from the subject. In the shooting method,
The radiographic image is acquired by a two-dimensional detector with higher sensitivity as the imaging position is farther from the subject.
[0012]
The sensitivity of the two-dimensional detector increases as the phosphor content increases. Therefore, in the present invention, the sensitivity of the two-dimensional detector can be increased as the position is farther from the subject by using a two-dimensional detector having a larger phosphor content at the photographing position farther from the subject.
[0013]
Moreover, the greater the phosphor content, the thicker the phosphor, and the lower the radiation transmittance. On the other hand, the two-dimensional detector located at the photographing position close to the subject can detect the radiation image with high accuracy even if the sensitivity is not so high. For this reason, it is preferable to use a two-dimensional detector having a fluorescent material that is thinner and has a higher radiation transmittance as the photographing position is closer to the subject.
[0014]
In the radiographic image capturing method according to the present invention, a phase contrast image may be generated based on the plurality of radiographic images.
[0015]
The first radiographic image capturing apparatus according to the present invention is disposed at a plurality of imaging positions at different distances from a subject, and detects the radiation transmitted through the subject at the plurality of imaging positions, away from the subject. It has a plurality of two-dimensional detectors that are more sensitive to the position,
A plurality of radiation images are acquired by detecting radiation transmitted through the subject by the two-dimensional detector at the plurality of imaging positions.
[0016]
In the first radiographic imaging apparatus according to the present invention, the plurality of two-dimensional detectors may have a higher transmittance of the radiation as the imaging position is closer to the subject.
[0017]
The first radiographic imaging device according to the present invention may further include image generation means for generating a phase contrast image based on the plurality of radiographic images.
[0018]
A second radiographic imaging apparatus according to the present invention includes a two-dimensional detector that detects radiation transmitted through a subject, a moving unit that moves the two-dimensional detector in the optical axis direction of the radiation, and a movement path by the moving unit. A plurality of photographing units arranged sequentially in the optical axis direction, comprising a position sensor for detecting that the two-dimensional detector has reached a plurality of predetermined photographing positions above;
A reading means for reading a signal from the two-dimensional detector when the two-dimensional detector reaches each imaging position based on a detection result by the position sensor and acquiring a plurality of radiation images;
The two-dimensional detector of the photographing unit disposed away from the subject has higher sensitivity.
[0019]
In the second radiographic image capturing apparatus according to the present invention, the reading unit may be provided for each of the plurality of image capturing units. Thereby, acquisition of the radiographic image in each imaging | photography unit can be performed simultaneously, As a result, acquisition of the radiographic image in all the imaging positions can be performed efficiently.
[0020]
In the second radiographic image capturing apparatus according to the present invention, the radiation transmittance of the two-dimensional detector of the imaging unit disposed near the subject may be higher.
[0021]
Furthermore, the second radiographic image capturing apparatus according to the present invention may further include image generation means for generating a phase contrast image based on the plurality of radiographic images.
[0022]
【The invention's effect】
According to the present invention, since the radiographic image is acquired using the two-dimensional detector having a higher sensitivity as the photographing position is farther from the subject, the two-dimensional detector at the photographing position farther from the subject also takes a picture closer to the subject. As with the two-dimensional detector at the position, the radiation can be detected with high accuracy. Therefore, it is possible to make the densities of the plurality of obtained radiographic images substantially equal, thereby generating a phase contrast image with high accuracy. Further, since there is no need to adjust the gain of the two-dimensional detector or the density of the obtained radiographic image, it is possible to efficiently acquire the radiographic image from which the phase contrast image can be obtained with high accuracy.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram showing the configuration of a phase contrast imaging apparatus to which a radiographic imaging apparatus according to the first embodiment of the present invention is applied. As shown in FIG. 1, the phase contrast imaging apparatus detects an X-ray source 10 that irradiates a subject with X-rays, a subject support unit 20 that supports the subject 21, and X-rays that have passed through the subject 21 to detect the subject. A recording unit 30 that obtains image data Sn (n = 1 to N) representing a plurality of 21 X-ray images, and a calculation unit 40 that generates image data Sp representing a phase contrast image based on the plurality of image data Sn. Prepare.
[0024]
The X-ray source 10 includes a radiation source 11 that emits synchrotron radiation, and a crystal 13 such as silicon that monochromatizes synchrotron radiation into monochromatic X-rays (hereinafter simply referred to as X-rays) 12. The monochromatic X-ray 12 is obtained by reflecting the synchrotron radiation emitted from the light beam at the crystal 13.
[0025]
The subject support unit 20 includes a support base 24 that supports the subject 21.
[0026]
The recording unit 30 includes a phosphor and a plurality of detection elements and phosphors arranged two-dimensionally, and a plurality of (three in this embodiment) detections arranged at a plurality of preset photographing positions. Panels 31, 32, and 33 and reading means 34, 35, and 36 that read out electrical signals from a plurality of detection elements constituting the detection panels 31, 32, and 33 and obtain a plurality of image data Sn. Note that only one reading means may be provided, and electric signals may be sequentially read from the detection panels 31, 32, 33 by this reading means.
[0027]
Here, as in the first embodiment, when imaging is performed using the plurality of detection panels 31, 32, 33, the X-ray dose irradiated to the detection panel decreases as the imaging position increases from the subject 21. At the same time, diffraction increases. For this reason, in the first embodiment, the detection panel disposed at a photographing position away from the subject 21 has higher sensitivity. Specifically, as shown in FIG. 2, the thickness of the phosphor is increased so that the detection panel disposed at a photographing position away from the subject 21 increases the phosphor content. As a result, the X-ray 12 can be detected with high accuracy even at a position away from the subject 21, and further, the diffraction image can be detected with high accuracy.
[0028]
Note that the phosphor is thinner as the detection panel is located closer to the subject 21. For this reason, it is possible to reduce the attenuation amount of the X-ray 12 that reaches the detection panel located in the subsequent stage.
[0029]
The calculation unit 40 has an X-ray image represented by the image data S1 obtained at the imaging position where the size of the X-ray image represented by the image data Sn obtained by the detection panels 31, 32, and 33 is closest to the subject 21. The X-ray image represented by the image data Sn is subjected to a reduction process so that the image data Sp represents a phase contrast image from the image data Sn subjected to the reduction process.
[0030]
Here, as in the first embodiment, when imaging is performed using the plurality of detection panels 31, 32, and 33, the X-ray image size increases as the imaging position increases from the subject 21. For this reason, the size of the X-ray image represented by the image data Sn is corrected according to the distance from the subject 21. Specifically, when the enlargement ratio at another photographing position with respect to the photographing position closest to the subject 21 is M (> 1), a reduction process is performed to reduce the size of the X-ray image to 1 / M times.
[0031]
In addition, when the size of the X-ray image is increased at the time of imaging, the dose of X-rays 12 irradiated per unit area of the detection panel is reduced. To correct this, 1 / M is applied to each pixel of the X-ray image. ² May be used to compensate for a decrease in the dose of X-rays 12 due to image enlargement.
[0032]
Then, based on the image data Sn that has been subjected to the reduction process, image data Sp representing a phase contrast image is obtained by the method described in Document 1 above. Hereinafter, the method described in Document 1 will be described. Assume that the transmittance of the subject 21 is expressed by the following equation (1).
[Expression 1]

Where T (x, y): transmittance function
A (x, y): Transmittance intensity function
ψ (x, y): phase shift amount function
(X, y): Coordinate value representing the position on the detection panel
[0033]
Here, in the case of a thin object whose transmittance intensity can be ignored (that is, A (x, y) is close to 1), as shown in the following equation (2), the subject 21 and the detection panels 31, 32, Image I taken at a distance dn (n = 1 to N) _dn Spatial frequency component I obtained by Fourier transform of (x, y) _dn Using (fx, fy), the spatial frequency component of the phase shift amount is calculated.
[0034]
Here, the relationship between the X-ray dose irradiated to the detection panels 31, 32, and 33 and each pixel value of the image represented by the image data Sn can be detected in advance. Therefore, a conversion table for converting the pixel value of the image represented by the image data Sn into an X-ray dose is created from this relationship, and the table is represented by the image data Sn acquired at the distance dn by referring to this conversion table. From the pixel value at the position (x, y) of the image to be processed _dn (X, y) can be obtained.
[Expression 2]

N: number of image data Sn
f: Spatial frequency
ψ (fx, fy ≠ 0): Spatial frequency component of the phase shift amount when the frequency is not 0
I _dn (Fx, fy): I _dn Spatial frequency component of (x, y)
[0035]
Then, the phase shift amount, that is, the phase difference ψ (x, y) can be calculated by performing inverse Fourier transform on the spatial frequency component of the phase shift amount. Here, since the phase difference ψ (x, y) takes a value in the range of 0 to 2π, a phase contrast image is represented by assigning the calculated phase difference ψ (x, y) to an 8-bit value, for example. Image data Sp can be obtained.
[0036]
Here, it is assumed that A (x, y) where the transmittance intensity is negligible is close to 1, but the phase shift amount can be calculated using a similar algorithm for a thick object. .
[0037]
Next, the operation of the first embodiment will be described. FIG. 3 is a flowchart showing the operation of the first embodiment. First, the radiation source 11 is driven to reflect synchrotron radiation at the crystal 13, thereby emitting a monochromatic X-ray 12 from the X-ray source 10 and irradiating the subject 21 with the X-ray 12 (step S1). . Then, electrical signals from a plurality of detection elements constituting the detection panels 31, 32, and 33 are read out by the reading means 34, 35, and 36 at a plurality of photographing positions, and image data Sn at each photographing position is acquired (step S2). .
[0038]
The acquired image data Sn is input to the calculation unit 40, where enlargement / reduction processing is performed, and as described above, the image data Sp representing the phase contrast image is generated (step S3), and the processing ends. The image data Sp is used for reproduction by a monitor or print output by a printer.
[0039]
As described above, in the first embodiment, since the X-ray image is acquired using the detection panel having a higher sensitivity as the shooting position is farther from the subject 21, the detection panel 33 at the shooting position farther from the subject 21 is used. In addition, the X-ray 12 can be detected with high accuracy in the same manner as the detection panel 31 at the photographing position close to the subject 21. Therefore, it is possible to make the densities of the plurality of X-ray images substantially equal, thereby generating the image data Sp representing the phase contrast image with high accuracy. In addition, since it is not necessary to adjust the gain of the detection panels 31, 32, and 33 or to adjust the density of the obtained X-ray image, it is possible to efficiently detect an X-ray image for obtaining a phase contrast image with high accuracy. it can.
[0040]
Next, a second embodiment of the present invention will be described. FIG. 4 is a schematic block diagram showing a configuration of a phase contrast imaging apparatus to which the radiographic imaging apparatus according to the second embodiment of the present invention is applied. In the second embodiment, the configuration of the recording unit is different from that of the first embodiment. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. Omitted.
[0041]
The recording unit 130 in the second embodiment includes first and second photographing units 130A and 130B.
[0042]
The first and second imaging units 130A and 130B have detection panels 131A and 131B each composed of a phosphor and a plurality of detection elements arranged in a two-dimensional manner, and the traveling direction of the X-ray 12 transmitted through the subject 21. Moving means 132A and 132B for moving the detection panels 131A and 131B in parallel directions and a plurality of detections constituting the detection panels 131A and 131B at a plurality of photographing positions set in advance on the movement path of the detection panels 131A and 131B Readout means 133A and 133B are provided for reading out electrical signals from the element and obtaining image data Sna and Snb at the respective photographing positions.
[0043]
The moving means 132A and 132B support the detection panels 131A and 131B, support portions 135A and 135B formed with female screw portions, and extend in a direction parallel to the traveling direction of the X-ray 12 and support portions 135A. , 135B, male screw portions 136A, 136B screwed into the female screw portions, motors 137A, 137B for rotating the male screw portions 136A, 136B around a rotation axis extending in the traveling direction of the X-ray 12, and motors 137A, 137B Control units 138A and 138B for controlling the driving and stopping. Then, when the motors 137A and 137B are driven by the control units 138A and 138B, the male screw portions 136A and 136B are rotated, and the support portions 135A and 135B, that is, the detection panels 131A and 131B approach the subject 21 according to the rotation direction. And move away from the subject 21.
[0044]
Also, position sensors 51A and 52A for detecting that the detection panels 131A and 131B moved by the moving means 132A and 132B reach the respective photographing positions at the respective photographing positions in the first and second photographing units 130A and 130B. , 51B, 52B are disposed. The position sensors 51A, 52A, 51B, and 52B output detection signals when the detection panels 131A and 131B reach the photographing position, and the detection signals are input to the reading units 133A and 133B. When the detection signals are input, the reading units 133A and 133B read the electrical signals from the plurality of detection elements constituting the detection panels 131A and 131B, and obtain the image data Sna and Snb at the shooting positions.
[0045]
In the second embodiment, since the position sensors 51A, 52A and 51B, 52B are arranged at two locations in the first and second photographing units 130A, 130B, respectively, at the four photographing positions. Four pieces of image data Sn (S1 to S4) are obtained.
[0046]
Here, in the second embodiment, the sensitivity of the detection panel 131B constituting the photographing unit 130B on the side away from the subject 21 is higher than the sensitivity of the detection panel 131A constituting the photographing unit 130A on the side closer to the subject 21. It is high. Specifically, the phosphor of the detection panel 131B is made thicker than the phosphor of the detection panel 131A, and the content of the latter phosphor is made larger than the content of the former phosphor. As a result, the X-ray 12 can be detected with high accuracy even at a position away from the subject 21, and further, a diffraction image can also be detected with high accuracy.
[0047]
Similar to the first embodiment, the calculation unit 40 has the size of the X-ray image represented by the image data S1 obtained at the imaging position where the size of the X-ray image represented by the image data Sn is closest to the subject 21. The X-ray image represented by the image data Sn is reduced so that the image data Sp representing the phase contrast image is obtained.
[0048]
Next, the operation of the second embodiment will be described. FIG. 5 is a flowchart showing the operation of the second embodiment. First, the radiation source 11 is driven to reflect the synchrotron radiation light at the crystal 13, thereby emitting the monochromatic X-ray 12 from the X-ray source 10 and irradiating the subject 21 with the X-ray 12 (step S11). . At the same time, first, shooting is performed in the first shooting unit 130A. That is, the controller 138A drives the motor 137A to move the detection panel 131A away from the initial position closest to the subject 21 (step S12). Then, at the timing when the detection signals from the position sensors 51A and 52A are input according to the movement, the readout means 133A reads out the electrical signals of the plurality of detection elements constituting the detection panel 131A, and the image data Sna at each photographing position. Is acquired (step S13).
[0049]
In the first photographing unit 130A, following the photographing at the photographing position farthest from the subject 21, photographing is performed in the second photographing unit 130B. That is, the control unit 138B drives the motor 137B to move the detection panel 131B in a direction away from the initial position closest to the subject 21 (step S14). Then, at the timing when the detection signals from the position sensors 51B and 52B are input according to the movement, the readout means 133B reads out the electrical signals of the plurality of detection elements constituting the detection panel 131B, and the image data Snb at each photographing position. Is acquired (step S15).
[0050]
The acquired image data Sna and Snb are input to the calculation unit 40, where image data Sp representing a phase contrast image is generated as in the first embodiment (step S16), and the process is terminated. The image data Sp is used for reproduction by a monitor or print output by a printer.
[0051]
In the second embodiment, the first photographing unit 130A performs photographing and then the second photographing unit 130B performs photographing. However, in the first and second photographing units 130A and 130B, the first photographing unit 130A performs photographing. Shooting may be performed at the same time.
[0052]
In the second embodiment, two photographing units are used, but three or more photographing units may be used. In this case, a detection panel having a higher sensitivity is used as the detection panel used in the subsequent photographing unit.
[0053]
In the first and second embodiments, the sensitivity of the detection panel is higher as the shooting position is farther from the subject 21, but the sensitivity of the detection panel is further increased according to the number of detection panels in the previous stage. It may be set.
[0054]
In the first embodiment, X-ray images are acquired by the detection panels 31, 32, and 33. Instead of the detection panels 31, 32, and 33, the X-ray image of the third embodiment shown in FIG. As described above, a plurality (three in this case) of stimulable phosphor sheets 61, 62, 63 may be used. In this case, the stimulable phosphor sheet disposed at the photographing position away from the subject 21 may be thicker and more sensitive.
[0055]
In addition, when X-ray images are accumulated and recorded on the stimulable phosphor sheets 61, 62, 63, the sheets 61, 62, 63 are irradiated with excitation light to generate stimulated emission light. In the reading unit 70 that photoelectrically reads light, a plurality of image data Sn representing an X-ray image is obtained. The obtained plurality of image data Sn is input to the calculation unit 40 as in the first embodiment, and image data Sp representing a phase contrast image is generated.
[0056]
In each of the above embodiments, the radiation source 11 that emits synchrotron radiation is used. However, the present invention is not limited to this. Further, although the monochromatic X-ray is used as the X-ray 12 irradiated to the subject 21, it is not limited to the monochromatic X-ray.
[0057]
In each of the above embodiments, the subject 21 is irradiated with the X-rays 12, but other radiation (α rays, β rays, γ rays, electron beams, ultraviolet rays, etc.) other than the X rays may be used. .
[Brief description of the drawings]
FIG. 1 is a schematic block diagram showing the configuration of a phase contrast imaging apparatus to which a radiographic imaging apparatus according to a first embodiment of the present invention is applied.
FIG. 2 is a diagram for explaining the thickness of a detection panel
FIG. 3 is a flowchart showing the operation of the first embodiment.
FIG. 4 is a schematic block diagram showing a configuration of a phase contrast imaging apparatus to which a radiographic imaging apparatus according to a second embodiment of the present invention is applied.
FIG. 5 is a flowchart showing the operation of the second embodiment.
FIG. 6 is a schematic block diagram showing the configuration of a phase contrast imaging apparatus to which a radiographic imaging apparatus according to a third embodiment of the present invention is applied.
[Explanation of symbols]
10 X-ray source
11 Radiation source
12 X-ray
13 Crystal
20 Subject support part
21 Subject
30,130 recording unit
31, 32, 33, 131A, 131B detection panel
33, 133A, 133B reading means
40 Calculation unit
51A, 51B, 52A, 52B Position sensor
61, 62, 63 Storage phosphor sheet
70 Reading unit
130A, 130B shooting unit
132A, 132B moving means

Claims (8)

In a radiographic imaging method of acquiring a plurality of radiographic images from radiation detected at a plurality of imaging positions irradiated to a subject, transmitted through the subject, and different from the subject,
The radiographic image is acquired by a two-dimensional detector with higher sensitivity as the imaging position is farther from the subject ,
A radiographic imaging method comprising generating a phase contrast image based on the plurality of radiographic images .   The radiographic image capturing method according to claim 1, wherein the two-dimensional detector has a higher transmittance of the radiation toward an imaging position closer to the subject. A plurality of two-dimensional detections, which are arranged at a plurality of photographing positions at different distances from the subject, detect radiation transmitted through the subject at the plurality of photographing positions, and have a higher sensitivity at a photographing position away from the subject. a vessel, by detect radiation transmitted through the object at the plurality of photographing positions, a plurality of 2-dimensional detector for obtaining a plurality of radiation images,
A radiographic imaging apparatus comprising: an image generation unit configured to generate a phase contrast image based on the plurality of radiographic images . The radiographic image capturing apparatus according to claim 3, wherein the plurality of two-dimensional detectors have a higher transmittance of the radiation toward an imaging position closer to the subject. A two-dimensional detector for detecting radiation transmitted through a subject, a moving means for moving the two-dimensional detector in the optical axis direction of the radiation, and a plurality of imaging positions predetermined on a movement path by the moving means. A plurality of imaging units, each comprising a position sensor for detecting that the two-dimensional detector has arrived, and sequentially disposed in the optical axis direction;
A reading means for reading a signal from the two-dimensional detector when the two-dimensional detector reaches each imaging position based on a detection result by the position sensor and acquiring a plurality of radiation images;
The radiographic image capturing apparatus according to claim 1, wherein the two-dimensional detector of the imaging unit disposed away from the subject has higher sensitivity. 6. The radiographic image capturing apparatus according to claim 5 , wherein the reading unit is provided for each of the plurality of imaging units. Radiographic imaging apparatus according to claim 5 or 6, wherein said those high the approximately two-dimensional detector transmittance of the radiation of the imaging unit which is disposed at a position closer to the subject. On the basis of the plurality of radiographic images, radiographic imaging device according to any one of claims 5, characterized in that further comprising image generating means for generating a phase contrast image 7.

Images