JP3995612B2 - Ultrasonic receiving apparatus and ultrasonic receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve SN ratio, and the like, of a detecting signal while suppressing the enlargement of a device and the increase in the cost in an optical detection type ultrasonic receiver. <P>SOLUTION: The ultrasonic receiver is provided with a light source 11 producing a broad-band light, an ultrasonic detecting element 20 including an ultrasonic sensitive part which is extended/contracted according to the received ultrasonic wave, allows an optical reflectance to fluctuate according to the extension/contraction, and modulates the intensity of the light produced by the light source, a spectral diffraction element 15 spectrally diffracting the light whose intensity is modulated by the ultrasonic detecting element, a photodetector 16 having a plurality of photoelectric transducers detecting the light spectrally diffracted by the spectral diffraction element for every plurality of wavelength components and producing, at least, a first detecting signal obtained by detecting a first wavelength component and a second detecting signal obtained by detecting a second wavelength component, and an arithmetic processing part 56 arithmetically processing using the first and second detecting signals and finding information on the ultrasonic wave received by the ultrasonic detecting element. <P>COPYRIGHT: (C)2004,JPO

Description

となる。このように、１つの画素信号として、検出信号Ｓ_Aや検出信号Ｓ_Bを単独で用いる場合には、ＳＮ比はＳ_A／Ｎ_Aであるが、複数の信号を用いて演算処理を行うことにより、ＳＮ比は２^1/2倍に上昇する。また、演算処理によって得られた信号においては、加算した信号振幅は常に一定なので、温度変化等によって反射特性の初期位相がシフトした場合でも、温度変化等によるレベル変動や波形歪みの影響を受け難いというメリットがある。
【００６０】
（２）異なる光反射率を有する複数の波長を選択する場合
図１０の（ａ）に示すように、異なる光反射率（例えば、２５％及び５０％）を有する波長を動作波長として設定する。波長λ_Xに対して同じ側にある波長λ_C及びλ_Dを動作波長として選択すると、超音波を受信することによって図１０の（ａ）〜（ｃ）に示すように反射特性が変化した結果、図１１の（ａ）及び（ｂ）に示すように、同位相の検出信号Ｓ_C及びＳ_Dが得られる。この場合には、図１１の（ｃ）に示すように、検出信号Ｓ_Cと検出信号Ｓ_Dとを単純に加算して１つの画素信号とすれば良い。
【００６１】
なお、本実施形態においては、１つの光線に含まれる２つの波長成分から得られる２つの検出信号を演算処理することにより、１つの画素信号を取得しているが、３つ以上の波長成分から得られる３つ以上の検出信号を用いて同様の演算処理を行っても良い。
【００６２】
次に、本発明の第２の実施形態に係る超音波受信装置について、図１２を参照しながら説明する。図１２は、本実施形態に係る超音波受信装置を適用した超音波撮像装置を示すブロック図である。
図１２に示すように、この超音波撮像装置は、第１の実施形態における信号処理部２の替わりに、信号処理部４を有している。本実施形態に係る超音波受信装置は、超音波受信部１と、信号処理部４と、タイミングコントロール部３とを含んでおり、第１の実施形態とは、信号処理における動作が異なっている。その他の構成については、第１の実施形態と同様である。
【００６３】
信号処理部４は、反転回路７１と、加算回路７２と、ＴＧＣ増幅器７３と、Ａ／Ｄ変換器７４と、１次記憶部７５と、位相整合部７６と、動作波長制御部７７と、選択回路７８とを有している。
選択回路７８は、動作波長制御部７７の制御の下で、光検出器１６の複数の光電変換素子から出力される複数の検出信号の中から、２組の検出信号を選択する。反転回路７１は、選択回路７８が選択した第１組の検出信号を反転して出力する。加算回路７２は、反転回路７１によって反転された第１組の検出信号を、光電変換素子から入力された第２組の検出信号にそれぞれ加算して出力する。これらの回路は、例えば、オペアンプ等によって構成することができる。
【００６４】
ＴＧＣ増幅器７３は、加算回路７２から出力された信号を、検出時間に応じて利得を変化させながら増幅することにより、被検体内における超音波の減衰を調整する。Ａ／Ｄ変換器７４は、ＴＧＣ増幅器７３によって増幅された信号をディジタル信号に変換する。１次記憶部７５は、Ａ／Ｄ変換器７４から出力された信号を時系列に記憶し、位相整合部７６は、１次記憶部７５に記憶された信号に基づいて演算処理を行うことにより位相を整合する。動作波長制御部７７は、光検出器１６に含まれる列ごとに、動作波長成分が入射する複数の光電変換素子を選択すると共に、選択された光電変換素子から出力される検出信号が加算回路７２又は反転回路７１に入力されるように、光検出器１６又は信号処理部３を制御する。
【００６５】
次に、本実施形態に係る超音波受信装置の動作について、図１２〜図１４を参照しながら説明する。図１３は、本実施形態に係る超音波受信装置を含む超音波撮像装置の動作を示すフローチャートである。
本実施形態においては、第１の実施形態におけるステップＳ１〜Ｓ３と同様にキャリブレーションを行い、ステップＳ４〜Ｓ６と同様に超音波を受信し、選択された複数の光電変換素子からの検出信号を取得する。ここでは、図８の（ａ）〜（ｃ）に示す波長λ_A及びλ_Bを動作波長として設定する。
【００６６】
ステップＳ２１において、反転回路７１は、所定の光電変換素子から出力された第１組の検出信号を入力して反転する。次に、ステップＳ２２において、加算回路７２は、反転回路７１によって反転された第１組の検出信号と、別の所定の光電変換素子から出力された第２組の検出信号とを入力し、第１組の検出信号と第２組の検出信号とをそれぞれ加算して出力する。ここで、図１４の（ａ）は、波長成分λ_Aに対応する検出信号Ｓ_Aの波形を示している。また、図１４の（ｂ）は、波長成分λ_Bに対応する検出信号Ｓ_Bの波形を示し、図１４の（ｂ）における破線は、反転信号Ｓ_Bバーの波形を示している。さらに、図１４の（ｃ）は、検出信号Ｓ_Aと反転信号Ｓ_Bバーとを加算した信号の波形を示している。
【００６７】
ステップＳ２３において、加算回路７２から出力された信号は、ＴＧＣ増幅器７３及びＡ／Ｄ変換器７４による信号処理を経て、１次記憶部７５に時系列に記憶される。さらに、１次記憶部７５に記憶された信号は、位相整合部７６によって位相整合される。
さらに、第１の実施形態と同様に、位相整合された信号は、画像メモリ６１にフレームごとに記憶され、さらに、画像処理部６２において２次元又は３次元データとして再構成され、補間、レスポンス変調処理、階調処理等の画像処理を施された後に、画像表示部６３に表示される（ステップＳ１０）。
【００６８】
本実施形態によれば、アナログ信号を加算するので、図１４の（ｃ）に示すように、信号に含まれるＡＣ成分が増幅されると共に、ＤＣ成分がゼロに近くなる。このため、アンプやＡＤＣ等の信号処理系におけるダイナミックレンジが小さくて済む。
【００６９】
本発明の第１又は第２の実施形態は、次のように変形することができる。この変形例について、図１５を参照しながら説明する。この例は、図２における超音波検出素子２０の替わりに、図１５に示す超音波検出素子（エタロンセンサ）３０を用いている。その他の構成については、図１又は図１２を用いて説明したのと同様である。
図１５に示すように、基板３１は、超音波によって変形する膜状の基板である。基板３１に対向して、基板３２が配置されており、これらはエタロンと同様の構造を形成している。
【００７０】
基板３１及び３２の光反射率をＲ、これらの基板の間隔をｄとし、入射光の波長をλとすると、エタロンの透過率は次のように表される。ただし、ｎは任意の整数である。
Ｔ＝｛１＋４Ｒ／（１−Ｒ）²・ｓｉｎ²（φ／２）｝^-1 …（３）
φ＝２π／λ・２ｎｄ・ｃｏｓθ …（４）
ここで、θは出射面の垂線から測った出射角であり、θ＝０とすると次の式のようになる。
φ＝４πｎｄ／λ …（５）
エタロンは、波長λの光を透過率Ｔで透過し、光反射率Ｒ＝（１−Ｔ）で反射する。
【００７１】
超音波検出素子３０に超音波を伝搬させると、基板３１が歪み、受信面の各位置において基板３１及び３２の間隔ｄが変化するので、波長λの光の反射率が変化する。そこで、図６を用いて説明したのと同様に、事前検出を行い、光検出器において、光反射率の変化の大きい領域に中心波長を有する光が入射する光電変換素子を選択し、ブロードバンド光を入射させながら基板３１に超音波を印加する。これにより、受信面の各位置における超音波の強さに応じた反射光において、波長成分ごとの強度変化を観測できる。この波長成分を示す検出信号について演算処理を施すことにより、超音波の強度を２次元的に計測することができる。
【００７２】
本発明の第１又は第２の実施形態における別の変形例について、図１６を参照しながら説明する。この変形例は、図２に示す超音波検出素子２０、光伝送路１３、及び、コリメート部１４の替わりに、図１６の（ａ）に示すように、超音波有感部を有するバンドルファイバ４０を用いている。その他の構成については、図１又は図１２を用いて説明したのと同様である。
【００７３】
図１６の（ｂ）に、バンドルファイバ４０に含まれる複数のファイバ４０ａの構成を示す。複数のファイバ４０ａの各々は、光ファイバ４１とコリメートレンズ４２とを含んでいる。本実施形態においては、第１の実施形態におけるものと同様に、コリメートレンズ４２として、０．２５Ｌの長さを有するセルフォックレンズを用いている。また、両者は、融着又はエポキシ系を含む樹脂系接着剤によって接続されている。
【００７４】
コリメートレンズ４２の一端には、２種類の材料層が交互に積層された多層膜４３が形成されている。この多層膜４３が、ブラッググレーティング構造を構成し、超音波有感部として働く。多層膜４３の材料としては、例えば、ＳｉＯ₂と酸化チタン（Ｔｉ₂Ｏ₃）との組み合わせや、ＳｉＯ₂と酸化タンタル（Ｔａ₂Ｏ₅）との組み合わせ等が用いられる。このような材料層は、コリメートレンズ４２上に、真空蒸着やスパッタリング等の方法によって形成されている。
【００７５】
ファイバ４０ａは、ファイバ４０ａの一端に伝搬した超音波が他端において反射する前に、超音波が減衰してしまうように、粘度の低い部材（被覆材４４）によって覆われている。さらに、図１６の（ｂ）に示すように、被覆材４４がコリメートレンズ４２まで覆うようにしても良い。これにより、ファイバ４０ａに伝搬した超音波のエネルギー損失を大きくすることができるので、超音波を早く減衰させてバッキング部としての効果を上げることができる。
このような複数のファイバ４０ａを、エポキシ系を含む樹脂系接着剤を用いて多数束ねることにより、超音波有感部を有するバンドルファイバ４０が作製される。
【００７６】
【発明の効果】
以上述べたように、本発明によれば、超音波検出素子の各々の検出領域において変調された光の複数の波長成分を検出して得られた複数の検出信号を用いて演算処理を施すので、検出信号のＳＮ比を向上させることができる。これらの検出信号は、キャリブレーションにより超音波検出素子の反射特性を求め、その反射特性に基づいて超音波の検出に用いる光電変換素子を選択することにより得られるので、温度や湿度等の環境によって反射特性が変化しても、検出感度の変動を低減することができ、超音波検出素子の構造的な歪みによる微小領域ごとの感度のバラツキを抑えて高い検出感度を維持することができる。さらに、ブロードバンド光を用い、その分光光の中から超音波の検出に用いる波長を選択するので、環境や検出領域に応じて光の波長を制御する必要がなく、また、検出領域ごとの反射特性を変える必要もない。これより、超音波受信装置の構成を簡単にして小型化することができる。従って、超音波受信装置の製造が容易になり、コストを削減することが可能である。
【図面の簡単な説明】
【図１】本発明の第１の実施形態に係る超音波受信装置を適用した超音波撮像装置の構成を示すブロック図である。
【図２】図１に示す超音波受信部の構成を示す模式図である。
【図３】ＡＷＧ分光素子の構成を示す図である。
【図４】図２に示す超音波検出素子の超音波検出原理を説明するための図である。
【図５】図２に示す超音波検出素子、コリメート部、及び、光伝送路の接続部分を拡大して示す断面図である。
【図６】本発明の第１の実施形態に係る超音波受信装置を含む超音波撮像装置の動作を示すフローチャートである。
【図７】本発明の第１の実施形態に係る超音波受信装置の動作を説明するための図である。
【図８】超音波検出素子における光の反射特性の変化を示す図である。
【図９】本発明の第１の実施形態に係る超音波受信装置の動作における信号処理方法を説明するための図である。
【図１０】超音波検出素子における光の反射特性の変化を示す図である。
【図１１】本発明の第１の実施形態に係る超音波受信装置の動作における別の信号処理方法を説明するための図である。
【図１２】本発明の第２の実施形態に係る超音波受信装置を適用した超音波撮像装置の構成を示すブロック図である。
【図１３】本発明の第２の実施形態に係る超音波受信装置を含む超音波撮像装置の動作を示すフローチャートである。
【図１４】本発明の第２の実施形態に係る超音波受信装置の動作における信号処理方法を説明するための図である。
【図１５】本発明の第１又は第２の実施形態に係る超音波受信装置の変形例を説明するための図である。
【図１６】本発明の第１又は第２の実施形態に係る超音波受信装置の別の変形例を説明するための図である。
【符号の説明】
１ 超音波受信部 ２、４ 信号処理部
３ タイミングコントロール部 １１ 光源
１２ 分波器 １３ 光伝送路
１４ コリメート部
１４ａ、１７、１８ コリメートレンズ
１５ 分光素子 １６ 光検出器
２０、３０ 超音波検出素子 ２０ａ 受信面
２１、３１、３２ 基板 ２２、４３ 多層膜
２３、４４ 被覆材 ２５ 接着剤
４０ 超音波有感部を有するバンドルファイバ
４０ａ ファイバ ４１、ＯＦ₁〜ＯＦ_M 光ファイバ
４２ コリメートレンズ ５１、７３ ＴＧＣ増幅器
５２、７４ Ａ／Ｄ変換器 ５３、７５ １次記憶部
５４、７６ 位相整合部 ５５、７７ 動作波長制御部
５６ 演算処理部 ６１ 画像メモリ（２次記憶部）
６２ 画像処理部 ６３ 画像表示部
７１ 反転回路 ７２ 加算回路
７８ 選択回路 ８０ 超音波送信部
８１ 駆動信号発生回路 ９１ 入力導波路
９２ 入力側スラブ導波路 ９３ａ、９３ｂ、… 出力導波路
９４ 出力側スラブ導波路 ９５ａ、９５ｂ、… アレイ導波路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic receiving apparatus and an ultrasonic receiving method used for obtaining an ultrasonic image by receiving ultrasonic waves.
[0002]
[Prior art]
Conventionally, in an ultrasonic imaging apparatus, a piezoelectric ceramic represented by PZT (lead zirconate titanate) or PVDF (polyfluoride) is used as an element (vibrator) for transmitting and receiving ultrasonic waves. One-dimensional sensor arrays using piezoelectric elements including polymer piezoelectric elements such as polyvinyl difluoride are common. While moving such a one-dimensional sensor array mechanically, a two-dimensional image at a plurality of cross-sections of a subject is acquired, and a three-dimensional image is obtained by combining the two-dimensional images.
[0003]
However, according to this method, since there is a time lag in the moving direction of the one-dimensional sensor array, cross-sectional images at different times are synthesized, so that the synthesized image becomes blurred. Therefore, it is not suitable for a subject that is intended for a living body as in the case where ultrasonic echo observation or the like is performed using an ultrasonic imaging apparatus.
[0004]
In order to acquire a high-quality three-dimensional image using ultrasonic waves, a two-dimensional sensor that can acquire a two-dimensional image without moving the sensor array is necessary.
However, when producing a two-dimensional sensor array using the above-mentioned PZT or PVDF, fine processing of elements and wiring to a large number of fine elements are necessary, and miniaturization and element integration beyond the current level are difficult. . Even if they are solved, there is a problem that crosstalk between elements increases, an SN ratio is deteriorated due to an increase in electrical impedance due to fine wiring, and an electrode portion of the fine element is easily broken. Therefore, it is difficult to realize a two-dimensional sensor array using PZT or PVDF.
[0005]
On the other hand, there is also known a sensor that detects a received ultrasonic signal by converting it into an optical signal. As such an optical detection type ultrasonic sensor, one using a fiber Bragg grating (abbreviated as FBG) (see Non-Patent Document 1) or one using a Fabry-Perot resonator (abbreviated as FPR) structure (Non-Patent Document 2). Have been reported). When a two-dimensional sensor array is manufactured using such an ultrasonic sensor, there is an advantage that electrical wiring to a large number of fine elements is unnecessary and good sensitivity can be obtained.
[0006]
An optical detection type ultrasonic sensor having a two-dimensional detection surface is also known. For example, Non-Patent Document 3 describes that a polymer film having a Fabry-Perot structure is used for ultrasonic detection. Such a film-like ultrasonic sensor does not require processing on a large number of microelements, and thus can reduce costs. A photodetection type ultrasonic sensor uses an ultrasonic detection element that changes the reflection characteristics of light when receiving an ultrasonic wave. Here, the reflection characteristic indicates the relationship of the reflection intensity with respect to the wavelength of light.
[0007]
However, such an ultrasonic detection element has a large variation in detection sensitivity because the light reflection characteristics change due to changes in temperature and humidity. In addition, in an ultrasonic detection element having a two-dimensional detection surface, the light reflection characteristics differ depending on the position of the detection surface, resulting in variations in detection sensitivity. As described above, in an ultrasonic receiving apparatus using a light detection method, it is a big practical problem to control a change or variation in detection sensitivity due to environmental factors such as temperature and structural factors. For this purpose, for example, the wavelength of the light emitted from the light source may be adjusted to a point where the sensitivity of the ultrasonic detection element is increased. However, the wavelength of the light source light is adjusted to a very steep reflection characteristic. It is difficult to install. On the other hand, a method of making broadband light incident on an ultrasonic detection element having different reflection characteristics depending on the position and filtering the reflected light may be considered, but in this case, the configuration of the ultrasonic detection element becomes complicated. There is a problem that the cost becomes high. Furthermore, a method of changing the reflection characteristics for each detection region of the ultrasonic detection element is also conceivable, but in this case also, the configuration of the ultrasonic detection element becomes complicated and the cost is increased.
[0008]
Further, in order to increase the detection sensitivity in such an ultrasonic receiving device, for example, the inclination of the light reflectance in the light reflection characteristics of the ultrasonic detecting element is increased, or the ultrasonic wave when receiving the ultrasonic wave is used. It is conceivable to increase the amount of distortion of the sensor. However, if the slope of the light reflectance in the reflection characteristics is increased, the accuracy of adjusting the wavelength of the light used for detection also becomes severe. In addition, in order to increase the distortion amount of the ultrasonic sensor, a soft member may be used on the ultrasonic receiving surface of the ultrasonic sensor, but this also increases the temperature dependence of the reflection characteristics of the ultrasonic sensor, and the detection. Operation becomes unstable.
[0009]
[Non-Patent Document 1]
TAKAHASHI and two others, “Underwater Acoustic Sensor with Fiber Bragg Grating”, OPTICAL REVIEW, Vol. 4, No. 6 (1997), P. 691-694
[Non-Patent Document 2]
Uno (UNO) and one other, "Fabrication and Performance of a Fiber Optic Micro-Probe for Megahertz Ultrasonic Field Measurement", Electronics (T IEE Japan), Vol. 118-E, No. 11 (1998), P. 487-492
[Non-Patent Document 3]
Beard and two others, “Transduction Mechanisms of the Fabry-Perot Polymer Film Sensing Concept for Wideband Ultrasound Detection”・ Ei Newsletter (IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL), VOL. 46, NO. 6 (NOVEMBER 1999), P.1575-1582
[0010]
[Problems to be solved by the invention]
Therefore, in view of the above points, the present invention is to improve the S / N ratio of a detection signal and the like while suppressing the increase in size and cost of the device in the photodetection type ultrasonic reception device and the ultrasonic reception method. Objective.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the ultrasonic receiver according to the present invention expands and contracts according to the light source that generates broadband light and the received ultrasonic waves, and the light reflectance varies according to the expansion and contraction. An ultrasonic detection element including an ultrasonic sensitive unit that modulates the intensity of light generated by the light source, a spectral unit that splits the light whose intensity is modulated by the ultrasonic detection element, and a plurality of lights dispersed by the spectral unit By detecting each wavelength component, at least a first detection signal obtained by detecting the first wavelength component and a second detection signal obtained by detecting the second wavelength component are generated. Arithmetic processing for obtaining information related to the ultrasonic wave received by the ultrasonic detecting element by performing arithmetic processing using the light detection means having a plurality of photoelectric conversion elements and the first detection signal and the second detection signal. Means .
[0012]
Here, the spectroscopic unit may simultaneously split a plurality of light beams guided from a plurality of detection areas of the ultrasonic detection element, respectively, and the light detection unit may respectively split the plurality of light beams separated by the spectroscopic unit. You may detect for every wavelength.
[0013]
In addition, the ultrasonic receiving method according to the present invention is an ultrasonic detecting element that modulates the intensity of light generated by a light source by expanding and contracting according to received ultrasonic waves and changing light reflectance according to expansion and contraction. Light is incident, and the intensity-modulated light is dispersed by receiving the ultrasonic wave at the ultrasonic detection element, and detected for each of a plurality of wavelength components using a light detection means having a plurality of photoelectric conversion elements. A first detection signal obtained by detecting the first wavelength component and a second detection signal obtained by detecting the second wavelength component for each of the plurality of detection areas of the ultrasonic detection element; At least in step (a), and by performing arithmetic processing using the first detection signal and the second detection signal, the ultrasonic wave received in each of the plurality of detection areas of the ultrasonic detection element Step for obtaining information (b Comprising the door.
[0014]
Here, step (b) may include adding the first detection signal and the second detection signal after inverting one of the phases.
According to the present invention, arithmetic processing is performed using a plurality of detection signals obtained by detecting a plurality of wavelength components of light modulated by the ultrasonic detection element, so that the SN ratio of the detection signal is improved. Can do.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a block diagram showing an ultrasonic imaging apparatus to which the ultrasonic receiving apparatus according to the first embodiment of the present invention is applied. The ultrasonic receiving apparatus includes an ultrasonic receiving unit 1 that receives ultrasonic waves and outputs detection signals, a signal processing unit 2 that processes detection signals output from the ultrasonic receiving unit 1, a timing control unit 3, have. The ultrasonic imaging apparatus further includes an image memory (secondary storage unit) 61, an image processing unit 62, an image display unit 63, an ultrasonic transmission unit 80, and a drive signal generation circuit 81. .
[0016]
The ultrasonic receiving unit 1 includes a light source 11, a duplexer 12, an ultrasonic detection element 20, a spectroscopic element 15, and a photodetector 16, and converts the received ultrasonic signal into an optical signal. Then, the signal is transmitted and further converted into a detection signal which is an electric signal and output. The photodetector 16 includes a plurality of photoelectric conversion elements for detecting a plurality of wavelength components that are dispersed in correspondence with the respective detection regions of the ultrasonic detection element 20. The configuration of the ultrasonic receiver 1 will be described in detail later.
[0017]
The signal processing unit 2 includes a TGC (time gain compensation) amplifier 51, an A / D converter 52, a primary storage unit 53, a phase matching unit 54, an operating wavelength control unit 55, and an arithmetic processing unit 56. And processing the detection signal output from the ultrasonic receiver 1 to generate a signal representing information such as the intensity of ultrasonic waves in a plurality of detection regions of the ultrasonic receiver 1.
[0018]
The TGC amplifier 51 adjusts the attenuation of the ultrasonic wave in the subject by amplifying the detection signal output from the photodetector 16 while changing the gain according to the detection time. The A / D converter 52 converts the detection signal into a digital signal (data), and the primary storage unit 53 stores these signals in time series. The phase matching unit 54 adjusts the phase by performing arithmetic processing based on the data stored in the primary storage unit 53.
[0019]
When the calibration is performed before receiving the ultrasonic wave, the operating wavelength control unit 55 uses a plurality of photoelectric elements corresponding to each detection region of the ultrasonic detection element 20 based on the signal output from the photodetector 16. It is determined which photoelectric conversion element of the conversion elements is selected for ultrasonic detection. According to the present invention, a plurality of detection signals are used corresponding to one detection region, but in the present embodiment, the first detection signal and the second detection signal correspond to one detection region. In order to obtain the above, two photoelectric conversion elements are selected. Accordingly, a plurality of first photoelectric conversion elements and a plurality of second photoelectric conversion elements, that is, two sets of photoelectric conversion elements are selected corresponding to the plurality of detection regions. In addition, the operating wavelength control unit 55 receives the ultrasonic wave so that the detection signals output from the two selected photoelectric conversion elements are stored in the primary storage unit 53 when receiving the ultrasonic waves. The signal processing unit 2 is controlled.
[0020]
Further, the arithmetic processing unit 56 obtains ultrasonic intensity and the like by performing arithmetic processing using two sets of detection signals (data) stored in the primary storage unit 53.
The image memory (secondary storage unit) 61 stores a plurality of pieces of plane data based on the phase-matched data. The image processing unit 62 reconstructs two-dimensional data or three-dimensional data based on the data, and performs processing such as interpolation, response modulation processing, and gradation processing. The image display unit 63 is a display device such as a CRT or LCD, for example, and displays an image based on the image data subjected to these processes.
[0021]
The drive signal generation circuit 81 generates a drive signal for transmitting ultrasonic waves. The ultrasonic transmission unit 80 transmits ultrasonic waves based on the drive signal generated from the drive signal generation circuit 81. The ultrasonic transmission unit 80 is configured by a vibrator in which an electrode is formed on a piezoelectric element, for example. The piezoelectric element has a piezoelectric property represented by a piezoelectric ceramic represented by PZT (Pb (lead) zirconate titanate) and a polymer piezoelectric element represented by PVDF (polyvinyl difluoride). Contains materials. When a voltage is applied to the electrodes of the vibrator by sending a pulsed electric signal or a continuous wave electric signal from the drive signal generating circuit 81, the piezoelectric element expands and contracts due to the piezoelectric effect. Thereby, an ultrasonic pulse or a continuous wave ultrasonic wave is generated from the vibrator.
[0022]
The timing control unit 3 controls the drive signal generation circuit 81 so as to generate a drive signal at a predetermined timing, and also captures a detection signal output from the photodetector 16 after a predetermined time has elapsed from the transmission time. The processing unit 2 is controlled. The ultrasonic detection element 20 and the ultrasonic transmission unit 80 may be provided separately as shown in FIG. 1, or by combining the ultrasonic detection element 20 and the ultrasonic transmission unit 80, A probe may be formed.
[0023]
FIG. 2 is a schematic diagram showing a configuration of the ultrasonic wave receiver 1 shown in FIG. The ultrasonic receiver 1 includes a collimator lens 17 that converts the light emitted from the light source 11 into parallel light and guides it to the duplexer, and a collimator lens that converts the light reflected from the ultrasonic detection element 20 into parallel light and guides it to the duplexer. 18. Further, in order to guide light between the collimating lens 18 and the ultrasonic detection element 20, an optical transmission path 13 and a collimating unit 14 are provided.
Hereinafter, the relationship between the wavelength of light and the reflection intensity in the ultrasonic detection element 20 is referred to as reflection characteristics.
[0024]
As the light source 11, it is desirable to use a light source having a bandwidth that can cover a range equal to or greater than the slope band of the reflection characteristics. As a light source that generates such broadband light (broadband) light, for example, an LED (light emitting diode), an SLD (super luminescent diode), an ASE (Amplified Spontaneous Emission) light source, or an LD (with a relatively large line width) A light source such as a laser diode is used.
[0025]
The duplexer 12 is configured by a half mirror, an optical circulator, a polarization beam splitter, or the like, and allows incident light incident from the first direction to pass in the second direction and return from the second direction. Is reflected in a third direction different from the first direction. In the present embodiment, a half mirror is used as the duplexer 12. The half mirror transmits incident light in a direction opposite to the incident direction, and reflects light returning from the opposite direction of the incident direction in a direction that is approximately 90 ° with respect to the incident direction.
[0026]
The optical transmission path 13 guides the light that has passed through the duplexer 12 to the ultrasonic detection element 20. As the optical transmission line 13, a bundle fiber in which a large number (for example, 1024) of optical fibers are bundled is used. FIG. 2 shows an optical fiber OF arranged on one line.₁~ OF_MIt is shown. As shown in FIG. 2, a large number of optical fibers are bundled in accordance with the shape of the receiving surface (for example, a circle) on the ultrasonic detection element side (left side in the figure), and the duplexer 12 side (right side in the figure). ) Are arranged on one line. Alternatively, optical fibers arranged on one line may be stacked in a plurality of stages.
[0027]
The tip of the optical transmission line 13 is connected to the ultrasonic detection element 20 through the collimator 14 with the optical axis aligned. The collimating unit 14 includes, for example, a collimating lens array in which collimating lenses are arrayed. The configurations of the optical transmission line 13 and the collimator unit 14 will be described in detail later.
[0028]
The ultrasonic detection element 20 includes a two-dimensional reception surface 20a that is distorted by propagating ultrasonic waves, and an ultrasonic sensitive part that expands and contracts in accordance with the ultrasonic waves received on the reception surface 20a. Since the light reflectance of the ultrasonic sensitive part varies according to the expansion and contraction, the light incident on the ultrasonic detection element 20 through the optical transmission path 13 and the collimating part 14 is reflected after being subjected to intensity modulation.
[0029]
The spectroscopic element 15 is configured by, for example, a diffraction grating, a prism, or the like, and emits incident light in different directions depending on the wavelength. That is, the spectroscopic element 15 is an optical fiber OF.₁~ OF_MRays L emitted in parallel from₁~ L_MAnd a plurality of the separated light beams are guided to the photodetector 16.
[0030]
Alternatively, an AWG (arrayed waveguide grating) spectroscopic element may be used as the spectroscopic element 15. FIG. 3 shows the configuration of the AWG spectroscopic element.
As an AWG spectroscopic element, an arrayed waveguide grating included in a planar lightwave circuit (PLC) is generally used. As shown in FIG. 3, the arrayed waveguide grating includes an input-side slab waveguide 92 to which one input waveguide 91 is connected, and an output-side slab to which a plurality of output waveguides 93a, 93b,. A plurality of arrayed waveguides 95a, 95b,... Having a certain waveguide length difference are connected to the waveguide 94.
[0031]
The input-side slab waveguide 92 has a sector shape with the end of the input waveguide 91 as the center of curvature. The output-side slab waveguide 94 has a sector shape with the ends of the plurality of output waveguides 93a, 93b,. The plurality of arrayed waveguides 95a, 95b,... Are arranged radially so that their optical axes pass through the centers of curvature of both the input-side slab waveguide 92 and the output-side slab waveguide 94. Thereby, the input-side slab waveguide 92 and the output-side slab waveguide 94 realize a function equivalent to that of the lens.
[0032]
Different wavelengths λ₁~ Λ_NIs incident on the input waveguide 91 and guided to the plurality of arrayed waveguides 95a, 95b,... By the lens action of the input-side slab waveguide 92. The plurality of wavelength components included in the incident light are excited in the arrayed waveguides 95a, 95b,... And guided to the plurality of output waveguides 93a, 93b,.
[0033]
Referring again to FIG. 2, the photodetector 16 detects a plurality of wavelength components separated by the spectroscopic element 15. As the photodetector 16, a two-dimensional photoelectric converter is used in which a plurality of photoelectric conversion elements are two-dimensionally arranged and incident light can be divided and detected for each position. For example, a PDA (photodiode array), a MOS type sensor, or the like can be used. Alternatively, a programmable two-dimensional sensor such as a CCD (charge coupled device) may be used.
[0034]
These optical elements are arranged so that a component having a predetermined wavelength included in a light beam reflected from a predetermined minute region of the ultrasonic detection element is incident on a predetermined photoelectric conversion element of the photodetector 16. . In the present embodiment, the optical fiber OF connected to different areas of the ultrasonic detection element.₁, OF₂,...₁, L₂,... Correspond to the first column, the second column,... Of the photoelectric conversion elements arranged two-dimensionally. In addition, the wavelength λ of the dispersed component₁, Λ₂Are made to correspond to the first row, the second row, ... of the photoelectric conversion elements, respectively. By arranging the optical system so as to obtain such correspondence, the signal output from the photoelectric conversion element located in the nth row and mth column of the photodetector 16 is converted into the optical fiber OF._mRay L emitted from_mWavelength λ included in_nIs identified as a component having
[0035]
Next, the structure of the ultrasonic detection element 20 and the principle of ultrasonic detection will be described in detail with reference to FIG. The ultrasonic detection element 20 is a multilayer film sensor including a substrate 21 and a multilayer film 22 laminated on the substrate.
The board | substrate 21 is a film | membrane-like board | substrate which produces distortion by receiving an ultrasonic wave, for example, has a circle | round | yen about 2 cm in diameter, or an area beyond it. A multilayer film 22 having a Bragg grating structure is formed on the substrate 21 by alternately laminating two kinds of material layers having different refractive indexes. In FIG. 4, the refractive index n₁A material layer A having a refractive index n₂And a material layer B having
[0036]
When the pitch (interval) of the periodic structure of the multilayer film 22 is d and the wavelength of incident light is λ, the Bragg reflection condition is expressed by the following equation. However, m is an arbitrary integer.
2d · sin θ = mλ (1)
Here, θ is an incident angle measured from the incident surface, and when θ = π / 2, the following equation is obtained.
2d = mλ (2)
The Bragg grating selectively reflects light of a specific wavelength that satisfies the Bragg reflection condition and transmits light of other wavelengths.
[0037]
When the ultrasonic wave is propagated to the ultrasonic wave detection element 20, the ultrasonic wave detection element 20 is distorted as the ultrasonic wave propagates, and the pitch d of the periodic structure changes at each position of the multilayer film 22. As a result, the wavelength λ of the selectively reflected light changes. In the reflection characteristic of the Bragg grating, there is an inclined band in which the light reflectance changes before and after the center wavelength having the highest light reflectance (low transmittance). When an ultrasonic wave is applied to the substrate 21 while light having a central wavelength in the range of the inclined band is incident on the multilayer film 22, reflected light (or transmitted light) corresponding to the intensity of the ultrasonic wave at each position on the receiving surface is obtained. Intensity change can be observed. By converting the change in the intensity of the light into the intensity of the ultrasonic wave, the two-dimensional intensity distribution information of the ultrasonic wave can be acquired.
[0038]
The material of the substrate 21 is quartz glass (SiO 2₂And optical glass such as BK7 (product of Schott). Moreover, as a substance used for the material layers A and B, a combination of substances whose refractive indexes are different from each other by 10% or more is desirable. This includes, for example, SiO₂And titanium oxide (Ti₂O_Three) And SiO₂And tantalum oxide (Ta₂O_Five) And the like. The material layers A and B are formed on the substrate 21 by a method such as vacuum deposition or sputtering.
[0039]
By the way, in order to suppress the multiple reflection of the ultrasonic wave, it is effective to increase the distance that the ultrasonic wave propagates. Ultrasonic waves are attenuated to a large extent when propagating, and the amount of attenuation increases as the propagation distance increases. Therefore, if a sufficient propagation distance is provided, the ultrasonic wave can be sufficiently attenuated while the ultrasonic wave propagated to one end is reflected and returned at the other end. For this reason, in the present embodiment, an optical fiber is used as the optical transmission path, and the received ultrasonic wave is propagated to the optical fiber. In other words, the optical transmission path is provided with a function as a backing part for attenuating ultrasonic waves as well as a function for transmitting light.
[0040]
FIG. 5 is an enlarged cross-sectional view showing a part of the optical transmission path 13, the collimator 14 and the ultrasonic detection element 20 shown in FIG. As shown in FIG. 5, the optical fiber OF included in the optical transmission line (bundle fiber) 13₁, OF₂,... Are connected to a plurality of collimating lenses 14a included in a collimating section (collimating lens array) 14 with their optical axes aligned, and are further two-dimensionally arranged and connected to the ultrasonic detection element 20. . Optical fiber OF₁, OF₂,... Are bundled using an adhesive 25.
[0041]
Optical fiber OF₁, OF₂,... Are, for example, single mode or multimode fibers having a length of about 2 m and are covered with a low-viscosity member (covering material 23) containing a resin-based material. In order to attenuate the ultrasonic wave while propagating through the optical fiber, a length of 2 m is effective. However, by covering the optical fiber with the above member, the propagation energy loss of the ultrasonic wave can be further increased. Ultrasonic attenuation can be accelerated.
[0042]
Here, optical fiber OF₁, OF₂,... The light transmitted through is diffracted when it is emitted from the optical fiber. For this reason, when the optical fiber 13a is directly connected to the ultrasonic detection element 20, light is diffused, and sufficient interference does not occur in the ultrasonic detection element. For this reason, the detection sensitivity of an ultrasonic detection element will deteriorate remarkably. To avoid this phenomenon, optical fiber OF₁, OF₂,... Are connected to a collimating lens 14a in order to prevent diffusion of emitted light. The plurality of collimating lenses 14 a included in the collimating lens array collimates the light guided by the respective optical fibers with respect to a plurality of positions on the ultrasonic receiving surface of the ultrasonic detection element 20.
[0043]
As the collimating lens 14a, a gradient index lens (hereinafter abbreviated as GRIN lens) is used. The GRIN lens is known, for example, under the product name of Selfoc (registered trademark of Nippon Sheet Glass Co., Ltd.) lens. The GRIN lens is a gradient index lens having a different refractive index depending on its position, and its optical characteristics change by changing its length. For example, when the GRIN lens has a length that is ¼ of the distance between the object image planes (the pitch at which the light erects), the incident light is emitted as parallel light.
[0044]
In this embodiment, a Selfoc lens array NA0.46 (product of Nippon Sheet Glass Co., Ltd.) in which a number of Selfoc lenses are arranged is used with a length of 0.25 L (L is the distance between object image planes). Each Selfoc lens is connected to an optical fiber as a collimating lens 14a.
As shown in FIG. 5, the collimating lens 14 a may be covered with a covering material 23. Optical fiber OF₁, OF₂This is because the ultrasonic waves are attenuated quickly in the same manner as in.
[0045]
The optical fiber and the collimating lens, or the collimating lens and the ultrasonic detection element are connected using fusion or an adhesive. When using an adhesive, it is desirable to use a resin adhesive including an epoxy resin. In such adhesives, the acoustic impedance is similar to that of optical fiber and collimating lens members and the substrate of the ultrasonic detection element, so that reflection of ultrasonic waves at the boundary of each member is suppressed when propagating. Because it can. In addition, it is desirable to use a resin adhesive including an epoxy as the adhesive 25 for bundling a plurality of optical fibers. This is because the ultrasonic wave is attenuated to prevent ultrasonic crosstalk between adjacent optical fibers and to maintain flexibility as a cable. In the present embodiment, STYCAST (product of Emerson & Cuming) is used as such an adhesive.
[0046]
Next, the operation of the ultrasonic receiving apparatus according to the present embodiment will be described with reference to FIG. 2, FIG. 6, and FIG. FIG. 6 is a flowchart showing the operation of the ultrasonic imaging apparatus including the ultrasonic receiving apparatus according to this embodiment.
First, before receiving ultrasonic waves, calibration is performed to set the wavelength of light used in ultrasonic detection, that is, the operating wavelength. Here, the calibration refers to an operation of measuring the reflection characteristics of the ultrasonic detection element and determining a wavelength component to be used as a detection signal. In the present embodiment, a pixel signal is generated using a first detection signal and a second detection signal obtained from two predetermined wavelength components from among a plurality of wavelength components included in broadband light. The ultrasonic detection element is very sensitive to the surrounding environment such as temperature and humidity, and the light reflection characteristics are likely to change. For example, the center wavelength of reflected light of an ultrasonic detection element using a Bragg grating changes at a rate of 0.01 nm / ° C. Further, in an ultrasonic detection element having a two-dimensional receiving surface, there is a structural variation for each minute region of the receiving surface. For this reason, before receiving an ultrasonic wave, two operating wavelengths are set for each minute region of the ultrasonic detection element.
This calibration may be performed at any time after the reception of ultrasonic waves is started.
[0047]
In step S1, the ultrasonic receiver is driven. Thereby, for example, broadband light having a spectral characteristic as shown in FIG. 7A is emitted from the light source 11. The light emitted from the light source passes through the collimating lens 17, the duplexer 12, and the collimating lens 18, and the optical fibers OF arranged on one line.₁~ OF_MIs incident on. The light transmitted through each optical fiber is incident on each minute region of the ultrasonic detection element 20, and the reflected light corresponding to the light reflectance of each minute region is emitted from the optical fiber. Optical fiber OF₁~ OF_MRay L emitted from₁~ L_MAgain passes through the collimating lens 18, is reflected by the duplexer 12, and enters the spectroscopic element 15. Ray L₁~ L_MAre spectrally separated by the spectroscopic element 15 and the respective wavelength components are incident on the plurality of photoelectric conversion elements included in the respective rows of the photodetectors 16 according to the wavelength.
[0048]
Thereby, in step S2, the light beam L₁~ L_MFrom each column of photodetectors 16 corresponding to₁~ Λ_NThe detection signal of the photoelectric conversion element corresponding to is obtained. Signals output from the respective photoelectric conversion elements are converted into data by the TGC amplifier 51 and the A / D converter 52 and stored in the primary storage unit 53. FIG. 7B is a graph obtained based on the signal output from the photoelectric conversion element included in the m-th column of the photodetector 16, and the optical fiber OF._m, And the light beam L reflected from the micro area of the ultrasonic detection element corresponding to this._mThe spectral distribution is shown. As shown in FIG._mIs the wavelength λ selectively reflected by Bragg reflection conditions_XHas the highest strength.
[0049]
Next, in step S3, two photoelectric conversion elements used for detection are selected for each column of the photodetectors 16. As shown in FIG. 7C, the operating wavelength control unit 55 obtains a light reflection characteristic for each minute region based on the signal obtained in step S2, and based on this, a plurality of wavelengths ( (Operation wavelength) is determined, and two photoelectric conversion elements on which those wavelength components are incident are selected. The method for determining the operating wavelength will be described in detail later.
[0050]
Similarly, optical fiber OF₁, OF₂,...₁, L₂The operating wavelength is set by selecting two sets of photoelectric conversion elements that acquire detection signals for a plurality of columns on which.
[0051]
Next, ultrasonic waves are received.
In step S4, the ultrasonic receiver is driven. Thereby, the broadband light emitted from the light source is converted into the optical fiber OF.₁~ OF_MThrough the microscopic region of the ultrasonic detection element 20. Rays L reflected from each minute region₁~ L_MIs split by the spectroscopic element 15 and enters the photodetector 16.
[0052]
Next, in step S5, an ultrasonic wave is transmitted from the ultrasonic wave transmission unit 80 included in the ultrasonic imaging apparatus, and an echo wave reflected from the subject is received. As a result, the pitch of the periodic structure changes in each minute region of the ultrasonic detection element 20 and the reflection characteristics of the Bragg grating change, so that the intensity of light incident on the photoelectric conversion element selected in step S3 also changes.
[0053]
Next, in step S6, detection signals output from at least two selected sets of photoelectric conversion elements are acquired. The photodetector 16 outputs a detection signal from the photoelectric conversion element selected in step S <b> 3 to the signal processing unit 2 under the control of the operating wavelength control unit 55.
The detection signal acquired in step S6 is processed in the TGC amplifier 51 and the A / D converter 52 and stored in the primary storage unit 53 in time series (step S7).
[0054]
Next, in step S <b> 8, the arithmetic processing unit 56 performs arithmetic processing using the detection signal stored in the primary storage unit 53. This arithmetic processing is performed using two selected sets of signals for one row of photoelectric conversion elements included in the photodetector, and a signal obtained as a result is a signal related to one pixel (pixel signal). To express. This calculation process will be described in detail later. This detection signal is again stored in the primary storage unit 53 in time series.
[0055]
In step S <b> 9, the phase matching unit 54 performs phase matching on the detection signal stored after the arithmetic processing.
Further, in step S10, the phase-matched signal is stored for each frame in the image memory 61, and further reconstructed as two-dimensional or three-dimensional data in the image processing unit 62 to perform interpolation, response modulation processing, gradation After image processing such as processing is performed, the image is displayed on the image display unit 63.
[0056]
Next, operation wavelength setting and detection signal calculation processing will be described in detail.
(C) in FIG._mRepresents the reflection characteristics of the Bragg grating in the minute region of the ultrasonic detection element corresponding to. As described above, in this reflection characteristic, the center wavelength λ having the highest light reflectivity is obtained._XBefore and after the slope band Δλ where the light reflectance changes_nAnd Δλ_mExists. This slope band Δλ_nAnd Δλ_mA wavelength component λ having a center wavelength at_nAnd λ_mThe intensity of is greatly changed by the geometric change of the ultrasonic detection element caused by receiving the ultrasonic wave. That is, the slope band Δλ_nAnd Δλ_mA large intensity change is observed in the spectral region. If this intensity change is converted into the intensity of the ultrasonic wave, the received ultrasonic information can be obtained, but if the intensity change is slight or there is a lot of noise, accurate measurement cannot be performed. For this reason, in this embodiment, in order to amplify the detection signal and increase the SN ratio, arithmetic processing is performed on the acquired signal. Hereinafter, this arithmetic processing will be specifically described.
[0057]
(1) When setting a plurality of wavelengths having equal light reflectance
As shown in FIG. 8A, the center wavelength λ having the highest light reflectivity is set as the operating wavelength._XWavelength components (λ having a predetermined light reflectance (for example, 25%) on both sides of_AAnd λ_B) As the operating wavelength. By receiving ultrasonic waves, this reflection characteristic is₀~ T_FourIn FIG. 8, it changes as shown in (a) to (c) of FIG. Accordingly, the wavelength component λ_AAnd λ_BThe intensity changes as shown in FIGS. 9A and 9B. Here, (a) in FIG. 9 shows the wavelength component λ._ASignal S indicating the intensity of_AFIG. 9B shows the wavelength component λ._BSignal S indicating the intensity of_BThe waveforms are shown respectively.
[0058]
Wavelength λ_XWavelength λ on both sides of_AAnd λ_BIs selected as the operating wavelength, as shown in FIGS. 9A and 9B, a signal having the same absolute value of amplitude and opposite phase can be obtained. Therefore, in this case, the phase of any signal is inverted and then added. For example, as shown in FIG._BInverted signal S_BAs shown in FIG. 9C, the detection signal S is obtained._AAnd inverted signal S_BAdd the bar. This added signal is defined as one pixel signal.
[0059]
Where signal S_AAnd S_BThe absolute value of the amplitude of each | S_A| And | S_B|, And each noise is N_A, N_BThen, the amplitude when added is | S_A| + | S_B|, Noise is (N_A ²+ N_B ²)^1/2It becomes. Therefore, the S / N ratio is expressed by the following equation.
S / N = (| S_A| + | S_B|) / (N_A ²+ N_B ²)^1/2
Here, since the absolute values of the amplitudes of both signals are equal,

It becomes. Thus, the detection signal S is used as one pixel signal._AAnd detection signal S_BIs used alone, the S / N ratio is S_A/ N_AHowever, the signal-to-noise ratio is 2 by performing arithmetic processing using a plurality of signals.^1/2Doubles. In addition, in the signal obtained by the arithmetic processing, since the added signal amplitude is always constant, even if the initial phase of the reflection characteristic is shifted due to a temperature change or the like, it is difficult to be affected by level fluctuations or waveform distortion due to a temperature change or the like. There is a merit.
[0060]
(2) When selecting a plurality of wavelengths having different light reflectivities
As shown in FIG. 10A, wavelengths having different light reflectances (for example, 25% and 50%) are set as operating wavelengths. Wavelength λ_XWavelength λ on the same side with respect to_CAnd λ_DIs selected as the operating wavelength, the reflection characteristics are changed as shown in FIGS. 10 (a) to 10 (c) by receiving ultrasonic waves, and as shown in FIGS. 11 (a) and 11 (b), In-phase detection signal S_CAnd S_DIs obtained. In this case, as shown in FIG._CAnd detection signal S_DAre simply added to form one pixel signal.
[0061]
In the present embodiment, one pixel signal is obtained by performing arithmetic processing on two detection signals obtained from two wavelength components included in one light beam, but from three or more wavelength components. Similar arithmetic processing may be performed using three or more detection signals obtained.
[0062]
Next, an ultrasonic receiving apparatus according to the second embodiment of the present invention will be described with reference to FIG. FIG. 12 is a block diagram showing an ultrasonic imaging apparatus to which the ultrasonic receiving apparatus according to this embodiment is applied.
As shown in FIG. 12, this ultrasonic imaging apparatus has a signal processing unit 4 instead of the signal processing unit 2 in the first embodiment. The ultrasonic receiving apparatus according to the present embodiment includes an ultrasonic receiving unit 1, a signal processing unit 4, and a timing control unit 3. Operation in signal processing is different from that of the first embodiment. . About another structure, it is the same as that of 1st Embodiment.
[0063]
The signal processing unit 4 includes an inverting circuit 71, an adding circuit 72, a TGC amplifier 73, an A / D converter 74, a primary storage unit 75, a phase matching unit 76, an operating wavelength control unit 77, a selection Circuit 78.
The selection circuit 78 selects two sets of detection signals from the plurality of detection signals output from the plurality of photoelectric conversion elements of the photodetector 16 under the control of the operating wavelength control unit 77. The inverting circuit 71 inverts and outputs the first set of detection signals selected by the selection circuit 78. The adder circuit 72 adds the first set of detection signals inverted by the inversion circuit 71 to the second set of detection signals input from the photoelectric conversion elements, and outputs the result. These circuits can be configured by, for example, an operational amplifier.
[0064]
The TGC amplifier 73 adjusts the attenuation of the ultrasonic wave in the subject by amplifying the signal output from the adder circuit 72 while changing the gain according to the detection time. The A / D converter 74 converts the signal amplified by the TGC amplifier 73 into a digital signal. The primary storage unit 75 stores the signal output from the A / D converter 74 in time series, and the phase matching unit 76 performs arithmetic processing based on the signal stored in the primary storage unit 75. Match the phase. The operating wavelength control unit 77 selects, for each column included in the photodetector 16, a plurality of photoelectric conversion elements on which the operating wavelength components are incident, and a detection signal output from the selected photoelectric conversion elements is added to the adder circuit 72. Alternatively, the photodetector 16 or the signal processing unit 3 is controlled so as to be input to the inverting circuit 71.
[0065]
Next, the operation of the ultrasonic receiving apparatus according to the present embodiment will be described with reference to FIGS. FIG. 13 is a flowchart showing the operation of the ultrasonic imaging apparatus including the ultrasonic receiving apparatus according to this embodiment.
In this embodiment, calibration is performed in the same manner as in steps S1 to S3 in the first embodiment, ultrasonic waves are received in the same manner as in steps S4 to S6, and detection signals from a plurality of selected photoelectric conversion elements are received. get. Here, the wavelength λ shown in (a) to (c) of FIG._AAnd λ_BIs set as the operating wavelength.
[0066]
In step S21, the inverting circuit 71 receives and inverts the first set of detection signals output from a predetermined photoelectric conversion element. Next, in step S22, the addition circuit 72 inputs the first set of detection signals inverted by the inverting circuit 71 and the second set of detection signals output from another predetermined photoelectric conversion element, One set of detection signals and the second set of detection signals are added and output. Here, FIG. 14A shows the wavelength component λ._ADetection signal S corresponding to_AThe waveform is shown. 14B shows the wavelength component λ._BDetection signal S corresponding to_BThe broken line in FIG. 14B indicates the inverted signal S._BThe waveform of the bar is shown. Further, FIG. 14C shows the detection signal S._AAnd inverted signal S_BThe waveform of the signal obtained by adding the bars is shown.
[0067]
In step S <b> 23, the signal output from the adder circuit 72 undergoes signal processing by the TGC amplifier 73 and the A / D converter 74 and is stored in the primary storage unit 75 in time series. Further, the signal stored in the primary storage unit 75 is phase-matched by the phase matching unit 76.
Further, as in the first embodiment, the phase-matched signal is stored in the image memory 61 for each frame, and further reconstructed as two-dimensional or three-dimensional data in the image processing unit 62 to perform interpolation and response modulation. After image processing such as processing and gradation processing is performed, the image is displayed on the image display unit 63 (step S10).
[0068]
According to the present embodiment, since analog signals are added, the AC component included in the signal is amplified and the DC component is close to zero, as shown in FIG. For this reason, the dynamic range in a signal processing system such as an amplifier or an ADC is small.
[0069]
The first or second embodiment of the present invention can be modified as follows. This modification will be described with reference to FIG. In this example, an ultrasonic detection element (etalon sensor) 30 shown in FIG. 15 is used instead of the ultrasonic detection element 20 in FIG. Other configurations are the same as those described with reference to FIG. 1 or FIG.
As shown in FIG. 15, the substrate 31 is a film-like substrate that is deformed by ultrasonic waves. Opposite the substrate 31, a substrate 32 is disposed, and these form a structure similar to that of an etalon.
[0070]
When the light reflectance of the substrates 31 and 32 is R, the distance between these substrates is d, and the wavelength of the incident light is λ, the transmittance of the etalon is expressed as follows. However, n is an arbitrary integer.
T = {1 + 4R / (1-R)²・ Sin²(Φ / 2)}^-1  ... (3)
φ = 2π / λ · 2nd · cos θ (4)
Here, θ is an emission angle measured from the normal of the emission surface, and when θ = 0, the following equation is obtained.
φ = 4πnd / λ (5)
The etalon transmits light of wavelength λ with a transmittance T and reflects it with a light reflectance R = (1−T).
[0071]
When ultrasonic waves are propagated to the ultrasonic detection element 30, the substrate 31 is distorted, and the distance d between the substrates 31 and 32 changes at each position on the receiving surface, so that the reflectance of light of wavelength λ changes. Therefore, in the same manner as described with reference to FIG. 6, prior detection is performed, and in the photodetector, a photoelectric conversion element in which light having a central wavelength is incident on a region having a large change in light reflectance is selected, and broadband light is selected. Applying ultrasonic waves to the substrate 31. Thereby, the intensity change for every wavelength component can be observed in the reflected light according to the intensity of the ultrasonic wave at each position on the receiving surface. By applying arithmetic processing to the detection signal indicating the wavelength component, the intensity of the ultrasonic wave can be measured two-dimensionally.
[0072]
Another modification of the first or second embodiment of the present invention will be described with reference to FIG. In this modification, instead of the ultrasonic detection element 20, the optical transmission line 13, and the collimating portion 14 shown in FIG. 2, a bundle fiber 40 having an ultrasonic sensitive portion as shown in FIG. Is used. Other configurations are the same as those described with reference to FIG. 1 or FIG.
[0073]
FIG. 16B shows a configuration of a plurality of fibers 40 a included in the bundle fiber 40. Each of the plurality of fibers 40 a includes an optical fiber 41 and a collimating lens 42. In the present embodiment, a selfoc lens having a length of 0.25 L is used as the collimating lens 42 as in the first embodiment. Moreover, both are connected by the resin-type adhesive agent containing melt | fusion or an epoxy type.
[0074]
At one end of the collimating lens 42, a multilayer film 43 in which two types of material layers are alternately laminated is formed. The multilayer film 43 constitutes a Bragg grating structure and functions as an ultrasonic sensitive part. As a material of the multilayer film 43, for example, SiO₂And titanium oxide (Ti₂O_Three) And SiO₂And tantalum oxide (Ta₂O_Five) And the like are used. Such a material layer is formed on the collimating lens 42 by a method such as vacuum deposition or sputtering.
[0075]
The fiber 40a is covered with a low-viscosity member (covering material 44) so that the ultrasonic wave propagated to one end of the fiber 40a is attenuated before the other end is reflected. Further, as shown in FIG. 16B, the covering material 44 may cover the collimating lens 42. Thereby, since the energy loss of the ultrasonic wave propagated to the fiber 40a can be increased, the ultrasonic wave can be attenuated quickly and the effect as a backing portion can be improved.
A bundle fiber 40 having an ultrasonic sensitive part is produced by bundling a plurality of such a plurality of fibers 40a using a resin adhesive containing an epoxy resin.
[0076]
【The invention's effect】
As described above, according to the present invention, arithmetic processing is performed using a plurality of detection signals obtained by detecting a plurality of wavelength components of light modulated in each detection region of the ultrasonic detection element. The SN ratio of the detection signal can be improved. These detection signals are obtained by obtaining the reflection characteristics of the ultrasonic detection element by calibration and selecting a photoelectric conversion element to be used for ultrasonic detection based on the reflection characteristics, so depending on the environment such as temperature and humidity. Even if the reflection characteristics change, fluctuations in detection sensitivity can be reduced, and high detection sensitivity can be maintained by suppressing variations in sensitivity for each minute region due to structural distortion of the ultrasonic detection element. Furthermore, since the wavelength used for ultrasonic detection is selected from the spectral light using broadband light, there is no need to control the wavelength of light according to the environment and detection area, and the reflection characteristics for each detection area There is no need to change. Thus, the configuration of the ultrasonic receiving apparatus can be simplified and reduced in size. Accordingly, the ultrasonic receiving device can be easily manufactured, and the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an ultrasonic imaging apparatus to which an ultrasonic receiving apparatus according to a first embodiment of the present invention is applied.
FIG. 2 is a schematic diagram illustrating a configuration of an ultrasonic receiving unit illustrated in FIG.
FIG. 3 is a diagram showing a configuration of an AWG spectroscopic element.
4 is a diagram for explaining the principle of ultrasonic detection of the ultrasonic detection element shown in FIG. 2; FIG.
5 is an enlarged cross-sectional view illustrating a connection portion of the ultrasonic detection element, the collimator unit, and the optical transmission path illustrated in FIG. 2;
FIG. 6 is a flowchart showing an operation of the ultrasonic imaging apparatus including the ultrasonic receiving apparatus according to the first embodiment of the present invention.
FIG. 7 is a diagram for explaining the operation of the ultrasonic receiving apparatus according to the first embodiment of the present invention.
FIG. 8 is a diagram showing a change in light reflection characteristics in the ultrasonic detection element.
FIG. 9 is a diagram for explaining a signal processing method in the operation of the ultrasonic receiving apparatus according to the first embodiment of the present invention.
FIG. 10 is a diagram showing a change in light reflection characteristics in the ultrasonic detection element.
FIG. 11 is a diagram for explaining another signal processing method in the operation of the ultrasonic receiving apparatus according to the first embodiment of the present invention.
FIG. 12 is a block diagram showing a configuration of an ultrasonic imaging apparatus to which an ultrasonic receiving apparatus according to a second embodiment of the present invention is applied.
FIG. 13 is a flowchart showing an operation of an ultrasonic imaging apparatus including an ultrasonic receiving apparatus according to the second embodiment of the present invention.
FIG. 14 is a diagram for explaining a signal processing method in the operation of the ultrasonic receiving apparatus according to the second embodiment of the present invention.
FIG. 15 is a diagram for explaining a modification of the ultrasonic receiving apparatus according to the first or second embodiment of the present invention.
FIG. 16 is a diagram for explaining another modified example of the ultrasonic receiving apparatus according to the first or second embodiment of the present invention.
[Explanation of symbols]
1 Ultrasonic receiver 2, 4 Signal processor
3 Timing control section 11 Light source
12 splitter 13 optical transmission line
14 Collimating section
14a, 17, 18 Collimating lens
15 Spectroscopic element 16 Photodetector
20, 30 Ultrasonic detection element 20a Reception surface
21, 31, 32 Substrate 22, 43 Multilayer film
23, 44 Covering material 25 Adhesive
40 Bundled fiber with ultrasonic sensitive part
40a Fiber 41, OF₁~ OF_M  Optical fiber
42 Collimating lens 51, 73 TGC amplifier
52, 74 A / D converter 53, 75 Primary storage unit
54, 76 Phase matching unit 55, 77 Operating wavelength control unit
56 arithmetic processing unit 61 image memory (secondary storage unit)
62 Image processing unit 63 Image display unit
71 Inversion circuit 72 Addition circuit
78 Selection circuit 80 Ultrasonic transmitter
81 Drive signal generation circuit 91 Input waveguide
92 Input side slab waveguide 93a, 93b, ... Output waveguide
94 Output-side slab waveguide 95a, 95b, ... Array waveguide

Claims (5)

A light source that generates broadband light;
An ultrasonic detecting element including an ultrasonic sensitive part that modulates the intensity of light generated by the light source by expanding and contracting according to the received ultrasonic wave, and the light reflectance varies according to the expansion and contraction;
A spectroscopic means for spectroscopically splitting the light whose intensity is modulated by the ultrasonic detection element;
By detecting the light separated by the spectroscopic means for each of the plurality of wavelength components, the first detection signal obtained by detecting the first wavelength component and the second wavelength component are obtained. Photodetecting means having a plurality of photoelectric conversion elements that generate at least a second detection signal;
An arithmetic processing means for obtaining information on the ultrasonic wave received by the ultrasonic detection element by performing an arithmetic process using the first detection signal and the second detection signal;
An ultrasonic receiving apparatus comprising: The ultrasonic receiving apparatus according to claim 1, wherein the arithmetic processing unit adds the first detection signal and the second detection signal after inverting one of the phases. Based on the detection result of the light detection means at the time of calibration, two sets of photoelectric conversion elements used for ultrasonic detection are selected from the plurality of photoelectric conversion elements of the light detection means, and the ultrasonic wave Control means for controlling the arithmetic processing means so as to perform arithmetic processing using the first detection signal and the second detection signal respectively output from the two selected sets of photoelectric conversion elements. The ultrasonic receiving apparatus according to claim 1, further comprising: The light is incident on an ultrasonic detecting element including an ultrasonic sensitive part that modulates the intensity of incident light by expanding and contracting according to the received ultrasonic wave, and the light reflectance varies according to the expansion and contraction. By dispersing the intensity-modulated light by receiving the ultrasonic wave in the sound wave detecting element, and detecting the dispersed light for each of a plurality of wavelength components using a light detecting means having a plurality of photoelectric conversion elements, For each of the plurality of detection areas of the ultrasonic detection element, a first detection signal obtained by detecting the first wavelength component and a second detection signal obtained by detecting the second wavelength component And (a) generating at least
A step (b) of obtaining information relating to ultrasonic waves received in each of the plurality of detection areas of the ultrasonic detection element by performing arithmetic processing using the first detection signal and the second detection signal;
An ultrasonic receiving method comprising: Prior to step (a), light is incident on the ultrasonic detection element, the light reflected by the ultrasonic detection element is dispersed, and the light detection means is used to detect each of a plurality of wavelength components. Further comprising the step (c) of selecting two sets of photoelectric conversion elements to be used for ultrasonic detection from among the plurality of photoelectric conversion elements of the light detection means,
Step (a) uses the two sets of photoelectric conversion elements selected in step (c) to generate a first detection signal and a second detection signal for each of the plurality of detection areas of the ultrasonic detection element. The ultrasonic receiving method according to claim 4, comprising generating.

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