JP6179894B2 - Implant communication terminal position detection apparatus and position estimation method - Google Patents
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- 238000004891 communication Methods 0.000 title claims description 30
- 239000007943 implant Substances 0.000 title claims description 27
- 238000001514 detection method Methods 0.000 title claims description 19
- 230000005540 biological transmission Effects 0.000 claims description 23
- 230000005684 electric field Effects 0.000 claims description 8
- 239000002775 capsule Substances 0.000 description 24
- 238000004088 simulation Methods 0.000 description 21
- 238000012795 verification Methods 0.000 description 10
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- 238000013178 mathematical model Methods 0.000 description 4
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- 238000007796 conventional method Methods 0.000 description 3
- 238000003384 imaging method Methods 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000001727 in vivo Methods 0.000 description 2
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- 230000000747 cardiac effect Effects 0.000 description 1
- 238000002591 computed tomography Methods 0.000 description 1
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- 238000011156 evaluation Methods 0.000 description 1
- 210000001035 gastrointestinal tract Anatomy 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
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- 230000002572 peristaltic effect Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000001902 propagating effect Effects 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 210000000813 small intestine Anatomy 0.000 description 1
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Description
本発明は、カプセル型内視鏡等のインプラント通信機器の端末位置検出に関するものである。 The present invention relates to terminal position detection of an implant communication device such as a capsule endoscope.
近年、内視鏡分野では、撮影機能や無線通信機能等を内蔵したカプセル型内視鏡が消化管等の被検体内部を移動し、被検体内部を順次撮影して画像データを生成し、この画像データを順次無線送信し、被検体外部の受信装置が受信するシステムが普及してきた。受信した画像データは受信装置に内蔵されたメモリに記憶され、さらに検査後には画像データが画像表示装置に取り込まれて被検体の診断が行われる。 In recent years, in the field of endoscopes, capsule endoscopes with built-in imaging functions, wireless communication functions, etc. move inside the subject, such as the digestive tract, and sequentially image the inside of the subject to generate image data. A system in which image data is sequentially transmitted wirelessly and received by a receiving device outside the subject has become widespread. The received image data is stored in a memory built in the receiving device, and after the examination, the image data is taken into the image display device and the subject is diagnosed.
このカプセル型内視鏡は、外部からの制御ではなく蠕動運動により体腔内を移動するため、カプセル型内視鏡により送信された画像データが、体腔内のどの位置でされたか正しく認識することが必要となる。また、カプセル型内視鏡以外に心臓ペースメーカー等のインプラント機器の位置を取得するニーズが高くなり、種々提案されている。例えば、被検体を磁場中におき、カプセル型内視鏡に内蔵された磁場センサによりその磁場を検出してカプセル型内視鏡の位置を特定する方式がある。しかし、位置検出用の磁場以外に電子機器に起因するノイズ磁場を検出することとなり、位置検出精度が低下しやすい。そこで、例えば、このノイズ磁場と検出すべき磁場との比較判定手段を有する技術が特許文献１に開示されているが、磁場検出のための専用デバイスを内視鏡内に付加する必要があること、また高い検出精度を得るためには事前のキャリブレーションが必要となるという欠点がある。 Since this capsule endoscope moves in the body cavity by a peristaltic motion instead of external control, it is possible to correctly recognize where the image data transmitted by the capsule endoscope was in the body cavity. Necessary. In addition to capsule endoscopes, the need for acquiring the position of implant devices such as cardiac pacemakers has increased, and various proposals have been made. For example, there is a method in which a subject is placed in a magnetic field, and the position of the capsule endoscope is specified by detecting the magnetic field with a magnetic field sensor built in the capsule endoscope. However, a noise magnetic field caused by an electronic device other than the position detection magnetic field is detected, and the position detection accuracy is likely to be lowered. Therefore, for example, Patent Document 1 discloses a technique having a means for comparing and determining the noise magnetic field and the magnetic field to be detected, but it is necessary to add a dedicated device for detecting the magnetic field to the endoscope. In addition, there is a drawback in that prior calibration is required to obtain high detection accuracy.
一方、カプセル型内視鏡と被検体外部の受信装置では映像信号の送受が行われており、映像信号と同時に位置信号を無線通信で送受することにより、カプセル型内視鏡の位置を特定する方式が行われている。例えば、特許文献２はこの無線信号による位置検出方法を開示しており、より具体的には受信電界強度（または受信電力）を測定して位置検出を行う方法である。しかし、受信電界強度による位置検出の精度は十分ではなく、より精度が高い方式として、無線通信信号の到達時間を測定して位置を特定する方式（ＴＯＡ方式）が知られている。 On the other hand, a video signal is transmitted and received between the capsule endoscope and a receiving device outside the subject, and the position of the capsule endoscope is specified by transmitting and receiving a position signal by wireless communication simultaneously with the video signal. The scheme is done. For example, Patent Document 2 discloses a position detection method using this radio signal, and more specifically, a method for detecting a position by measuring a received electric field strength (or received power). However, the accuracy of position detection based on the received electric field strength is not sufficient, and a method of measuring the arrival time of a wireless communication signal and specifying the position (TOA method) is known as a method with higher accuracy.
カプセル型内視鏡等のインプラント機器が送信された無線通信信号は人体内を伝搬するため、人体による波長短縮効果の影響を受ける。一般的な無線通信端末の位置検出では、無線通信信号は空気中を伝搬するため伝搬速度は光速として取り扱うことが可能であるが（伝搬速度は既知で一定）、インプラント機器の無線通信信号は波長が短縮される影響があり、伝搬速度は光速で一定とは限らない。従って、インプラント機器において信号到来時間によって位置検出を行うためには、信号到来時間だけでなく信号伝搬速度の推定も必要となる。ところが、体腔内の各臓器によって誘電率が異なるため、信号伝搬速度は無線信号の伝搬経路によって異なり、事前に信号伝搬速度を把握することはできない。 A wireless communication signal transmitted from an implant device such as a capsule endoscope propagates through the human body and is therefore affected by the wavelength shortening effect of the human body. In the position detection of a general wireless communication terminal, since the wireless communication signal propagates in the air, the propagation speed can be treated as the speed of light (the propagation speed is known and constant), but the wireless communication signal of the implant device has a wavelength The propagation speed is not always constant at the speed of light. Therefore, in order to perform position detection based on the signal arrival time in the implant device, it is necessary to estimate not only the signal arrival time but also the signal propagation speed. However, since the dielectric constant varies depending on each organ in the body cavity, the signal propagation speed varies depending on the propagation path of the radio signal, and the signal propagation speed cannot be grasped in advance.
ＴＯＡ方式の非特許文献１では、ＣＴスキャン等によって取得した誘電率のマップを用いて信号伝搬速度の推定を行っている。しかしながら、カプセル型内視鏡を想定した場合では、事前に誘電率マップを取得することは実用上適しておらず、他のインプラント機器においても、事前に誘電率マップを取得することが困難な状況が想定される。他の手段として、人体の平均的な誘電率を利用する方法が考えられるが、高精度に位置検出を行う上で誘電率の差異がもたらす影響が懸念される。 In the non-patent document 1 of the TOA method, the signal propagation speed is estimated using a permittivity map acquired by CT scan or the like. However, when a capsule endoscope is assumed, it is not practically appropriate to obtain a dielectric constant map in advance, and it is difficult to obtain a dielectric constant map in advance for other implant devices. Is assumed. As another means, a method of using the average dielectric constant of the human body can be considered, but there is a concern about the influence caused by the difference in dielectric constant when performing position detection with high accuracy.
そこで、従来のＴＯＡ方式の課題を解決すべく、被検体の比誘電率を予め測定することなく、比誘電率を受信信号強度（ＲＳＳＩ）と信号到来時間とによって推定し、推定された比誘電率をもとに信号伝搬速度を求め、信号伝搬速度と信号到来時間をもとにインプラント機器の位置を推定すること、およびその実証を課題とした。 Therefore, in order to solve the problem of the conventional TOA method, the relative dielectric constant is estimated from the received signal strength (RSSI) and the signal arrival time without measuring the relative dielectric constant of the subject in advance, and the estimated relative dielectric constant The problem was to obtain the signal propagation speed based on the rate, to estimate the position of the implant device based on the signal propagation speed and the signal arrival time, and to demonstrate it.
すなわち、本発明者は、鋭意検討の結果、上記推定のフローが実証できること、すなわち上記課題が解決しうることを見出した。すなわち、本発明によれば、以下のインプラント通信端末の位置検出装置および位置推定方法が提供される。 That is, as a result of intensive studies, the present inventor has found that the above estimation flow can be verified, that is, the above problem can be solved. That is, according to the present invention, the following implant communication terminal position detection apparatus and position estimation method are provided.
［１］被検体内のインプラント通信機器端末から送信された信号を複数の受信装置にて受信して前記インプラント通信機器端末の位置を検出する位置検出装置であって、前記受信装置が受信する受信電界強度と信号到来時間により被検体の比誘電率を推定する手段と、推定された比誘電率をもとに信号伝搬速度を推定する手段と、推定された信号伝搬速度と前記信号到来時間をもとに前記インプラント通信機器端末の位置を決定する手段と、を有する位置検出装置。 [1] A position detection device that receives a signal transmitted from an implant communication device terminal in a subject by a plurality of reception devices and detects a position of the implant communication device terminal , and the reception device receives means and, means for estimating the signal propagation speed based on the estimated relative dielectric constant, the estimated signal propagation speed and the previous SL signal arrival time of estimating the relative permittivity of the object by the electric field strength and signal arrival time position detection device including means, the determining the position of the implant communication equipment terminal based on.
［２］被検体内のインプラント通信機器端末から送信された信号を複数の受信装置にて受信して前記インプラント通信機器端末の位置を検出する位置推定方法であって、前記受信装置が受信する受信電界強度と信号到来時間により被検体の比誘電率を推定するステップと、推定された比誘電率をもとに信号伝搬速度を推定するステップと、推定された信号伝搬速度と前記信号到来時間をもとに前記インプラント通信機器端末の位置を決定するステップと、を有する位置推定方法。 [2] A position estimation method for detecting a position of the implant communication device terminal by receiving signals transmitted from the implant communication device terminal in the subject by a plurality of reception devices, the reception received by the reception device steps and, the steps of estimating a signal propagation speed based on the estimated relative dielectric constant, the estimated signal propagation speed and the previous SL signal arrival time of estimating the relative permittivity of the object by the electric field strength and signal arrival time position estimating method comprising the steps of: determining the position of the implant communication equipment terminal based on.
［３］前記比誘電率を推定するステップが、数式（１）および数式（２）で表される前記［２］に記載の位置推定方法。
（数式（１）および（２）において、Ｅ０は送信電界強度［Ｖ／ｍ］、Ｅは受信電界強度［Ｖ／ｍ］、ｄはインプラント通信機器端末と受信装置の距離［ｍ］、α(εｒ）は比誘電率εｒの関数である減衰係数、ωは角周波数［ｒａｄ／ｓ］（２π×送受信信号周波数）、σは導電率［Ｓ／ｍ］、Ｉｍは括弧内の虚数部である。)
[3] The position estimation method according to [2], wherein the step of estimating the relative dielectric constant is represented by Expression (1) and Expression (2).
(In Equations (1) and (2), E0 is the transmission field strength [V / m], E is the reception field strength [V / m], d is the distance [m] between the implant communication device terminal and the reception device, α ( εr) is an attenuation coefficient that is a function of relative permittivity εr, ω is angular frequency [rad / s] (2π × transmission / reception signal frequency), σ is conductivity [S / m], and Im is an imaginary part in parentheses. .)
［４］前記［３］に記載された数式（１）と数式（２）を用いる比誘電率を推定するステップと、推定された比誘電率情報に基づいた信号到来時間による位置を推定するステップとを交互に繰り返すアルゴリズムによる、前記［３］に記載の位置推定方法。
[4] A step of estimating a relative permittivity using Equations (1) and (2) described in [3], and a step of estimating a position based on a signal arrival time based on the estimated relative permittivity information The position estimation method according to [3], wherein the algorithm is alternately repeated.
以下、図面を参照しつつ本発明の実施の形態について説明する。本発明は、以下の実施形態に限定されるものではなく、発明の範囲を逸脱しない限りにおいて、変更、修正、改良を加え得るものである。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.
以下、インプラント通信機器端末の例として、カプセル型内視鏡を例にとって本発明の装置構成の概要を説明する。本発明に係る装置構成は従来の装置と同じであるが、本発明の特徴を述べる前に装置構成を簡単に説明する。 Hereinafter, as an example of an implant communication device terminal, an outline of a device configuration of the present invention will be described taking a capsule endoscope as an example. The apparatus configuration according to the present invention is the same as that of the conventional apparatus, but the apparatus configuration will be briefly described before describing the features of the present invention.
カプセル型内視鏡システムは、被検体内の体内画像を撮像するカプセル型内視鏡と、カプセル型内視鏡によって撮像された体内画像がカプセル型内視鏡から無線送信され、受信アンテナを介して受信し、画像表示装置へ転送する位置検出装置、および画像表示装置を含む構成からなる。カプセル型内視鏡は、透明で円筒状胴体とその両端に半球状のキャップが組み合わされた形状であり、照明部、レンズ、撮像部、撮像信号から画像信号を生成する回路基板、送受信回路、および電源部とからなる。位置検出装置は少なくとも４つの受信アンテナを含み、さらに画像記憶装置を含む受信装置からなる。そして、位置検出装置には、比誘電率を推定し、推定された比誘電率をもとに信号伝搬速度を推定し、推定された信号伝搬速度と測定された信号到達時間とからカプセル型内視鏡の位置を検出する演算処理部を含む。 A capsule endoscope system is a capsule endoscope that captures an in-vivo image in a subject, and an in-vivo image captured by the capsule endoscope is wirelessly transmitted from the capsule endoscope, via a receiving antenna. And a position detection device that receives the data and transfers it to the image display device, and an image display device. The capsule endoscope is a transparent cylindrical body with a hemispherical cap at both ends, a lighting unit, a lens, an imaging unit, a circuit board that generates an image signal from the imaging signal, a transmission / reception circuit, And a power supply unit. The position detection device includes at least four reception antennas and further includes a reception device including an image storage device. The position detection device estimates the relative permittivity, estimates the signal propagation speed based on the estimated relative permittivity, and uses the estimated signal propagation speed and the measured signal arrival time in the capsule type. An arithmetic processing unit for detecting the position of the endoscope is included.
位置検出装置において推定演算される比誘電率と測定する受信信号強度について、以下のモデルを提案する。そして、このモデルの有効性を後に検証する。ここで、比誘電率を推定するステップを、数式（１）および数式（２）で表す。
数式（１）および（２）において、Ｅ０は送信電界強度［Ｖ／ｍ］、Ｅは受信電界強度［Ｖ／ｍ］、ｄはインプラント通信機器端末（送信装置）と受信装置の距離［ｍ］、α(εｒ）は比誘電率εｒの関数である減衰係数、ｗは角周波数［ｒａｄ／ｓ］（２π×送受信信号周波数）、σは導電率［Ｓ／ｍ］、Ｉｍは括弧内の虚数部である。
数式（１）は、送信源を点波源として家庭した場合に距離ｄ離れた点の受信電界強度を表現したモデルであり、数式（２）は、比誘電率εｒと導電率σの物質中を伝搬した際の減衰係数を表現したモデルである。なお、送受信間距離（ｄ）は信号到来時間（τ）と光速（ｃ）の積を比誘電率（εｒ）の平方根で除したものである。
The following models are proposed for the relative permittivity estimated by the position detection device and the received signal strength to be measured. The effectiveness of this model will be verified later. Here, the step of estimating the relative permittivity is expressed by Equation (1) and Equation (2).
In Equations (1) and (2), E 0 is the transmission field strength [V / m], E is the reception field strength [V / m], and d is the distance between the implant communication device terminal (transmission device) and the reception device [m. ], Α (ε r ) is an attenuation coefficient that is a function of the relative permittivity ε r , w is an angular frequency [rad / s] (2π × transmission / reception signal frequency), σ is conductivity [S / m], and Im is a parenthesis Is the imaginary part.
Equation (1) is a model that expresses the received electric field strength at a point away from the distance d when the transmission source is a point wave source, and Equation (2) is a substance having a relative permittivity ε r and conductivity σ. It is a model expressing the attenuation coefficient when propagating through the. Note that the distance (d) between transmission and reception is the product of the signal arrival time (τ) and the speed of light (c) divided by the square root of the relative permittivity (ε r ).
上記の数式（１）および数式（２）で表されるモデルを時間領域差分法（ＦＤＴＤ法）によって検証を行った。主に筋肉から構成される直方体のモデル１と、解剖学的人体数値モデルを用いたモデル２を対象に検証を行った。モデル１は本発明で仮定している数式モデルに極力沿うように設計されており、一方、モデル２は実際の人体を模した解剖学的人体数値モデルを利用し、数式（１）と数式（２）で表現される数学モデルによって実際の人体でも推定が可能であるか検証するモデルとなっている。なお、人体の比誘電率と導電率は周波数によって変化する周波数依存性を有するが、モデル１では中心周波数４．１ＧＨｚでの比誘電率と導電率を用いた。一方、モデル２では実際の環境をよりよく表現するため、デバイ分散式によって比誘電率と導電率の周波数依存性も考慮した。 The models represented by the above formulas (1) and (2) were verified by the time domain difference method (FDTD method). Verification was performed for a rectangular parallelepiped model 1 mainly composed of muscles and a model 2 using an anatomical human body numerical model. The model 1 is designed to be as close as possible to the mathematical model assumed in the present invention. On the other hand, the model 2 uses an anatomical human body numerical model imitating an actual human body, and the mathematical expressions (1) and ( It is a model that verifies whether or not an actual human body can be estimated by the mathematical model expressed in 2). Although the relative permittivity and conductivity of the human body have frequency dependency that varies depending on the frequency, Model 1 uses the relative permittivity and conductivity at the center frequency of 4.1 GHz. On the other hand, in Model 2, in order to better represent the actual environment, the frequency dependence of the dielectric constant and conductivity was also taken into account by the Debye dispersion formula.
（シミュレーションモデル１による検証）
図１、図２および図３に示すように、人体を最も単純化して模した、２０ｃｍ（奥行方向／Ｙ軸方向）×３０ｃｍ（横方向／Ｘ軸方向）×４０ｃｍ（縦方向／Ｚ軸方向）の直方体を対象として、その表面から順に皮膚（２ｍｍ厚）、脂肪（４ｍｍ厚）、筋肉とした。この直方体内に発信点を１８点、立方体表面上に受信点を１０点取り、中心周波数４．１ＧＨｚ、周波数帯域１．４ＧＨｚのＵＷＢパルスを使用して、ＦＤＴＤ法によりシミュレーションを行った。送信アンテナはダイポールアンテナである。発信点の１８点は、直方体縦方向の中央に２ｃｍの差異を設けた上段と下段、上段と下段それぞれに、ＸＹ断面中央部に２ｃｍ間隔でずらした９点をとった。受信点の１０点は直方体Ｚ方向の中央に、対向する各横方向（Ｘ軸方向）に３点、同じく各奥行方向（Ｙ軸方向）に２点とった。なお、図２に、本シミュレーションで用いた皮膚、脂肪、および筋肉の比誘電率および導電率を示す。
(Verification by simulation model 1)
As shown in FIGS. 1, 2, and 3, 20 cm (depth direction / Y-axis direction) × 30 cm (lateral direction / X-axis direction) × 40 cm (longitudinal direction / Z-axis direction), which is the most simplified model of the human body ), The skin (2 mm thickness), the fat (4 mm thickness), and the muscles. A simulation was performed by the FDTD method using 18 transmission points in this rectangular parallelepiped and 10 reception points on the cube surface, and using a UWB pulse with a center frequency of 4.1 GHz and a frequency band of 1.4 GHz. The transmitting antenna is a dipole antenna. The 18 points of the transmission points were 9 points that were shifted at 2 cm intervals in the center of the XY cross section in each of the upper and lower stages, and the upper and lower stages with a difference of 2 cm in the center in the longitudinal direction of the rectangular parallelepiped. Ten reception points were set in the center of the rectangular parallelepiped Z direction, three points in each opposing lateral direction (X-axis direction), and two points in each depth direction (Y-axis direction). FIG. 2 shows the relative permittivity and conductivity of skin, fat, and muscle used in this simulation.
シミュレーションモデル１の結果を図４に示す。横軸にｄ（送受信機間距離）、縦軸にｌｏｇ（ｄＥ／Ｅ０）として、前記１８点の送信点と１０点の受信点との組み合わせ（計１８０点）をプロットしたところ、ほぼ直線状に並ぶことが分かった。そこで、簡易的に、前記数式（２）に筋肉の比誘電率として５０．６９５を代入して得た、傾きα（εｒ）：８１．８０６と、これら多数のプロット点の最小二乗法による近似式の傾きとがほぼ一致することが分かった。 The result of the simulation model 1 is shown in FIG. When the horizontal axis is d (distance between transmitter and receiver) and the vertical axis is log (dE / E 0 ), the combinations of the 18 transmission points and the 10 reception points (180 points in total) are plotted. It turned out to be lined up in a shape. Therefore, the slope α (ε r ): 81.806 obtained by simply substituting 50.695 as the relative dielectric constant of muscle into the mathematical formula (2), and the least square method of these many plot points. It was found that the slope of the approximate expression almost coincided.
（シミュレーションモデル２による検証）
前記単一物質（実質的に筋肉のみ）から構成されるシミュレーションモデル１に加えて、解剖学人体数値モデルを用いたシミュレーションモデル２による検証を実施した。解剖学的人体数値モデルとして、情報通信研究機構が開発した人体モデルを用いた。このモデルは、身長１７３ｃｍ、体重６５ｋｇ、そして５１種類の生体組織から構成されている。ＦＤＴＤ法で用いるセルは１辺４ｍｍ角の立方体セルである。送信信号の周波数はモデル１同様に中心周波数４．１ＧＨｚ、周波数帯域１．４ＧＨｚとし、送信アンテナはダイポールアンテナを用いた。図５に示すように、受信点は腹部周り１０箇所に配置した。一方、送信点は小腸を中心に６点を配置し、各送信点から送信された信号に対する各受信点での受信電界強度をＦＤＴＤシミュレーションによって算出した。なお、デバイ分散式により、モデル２における各組織の比誘電率と導電率の周波数依存性を考慮している。
(Verification by simulation model 2)
In addition to the simulation model 1 composed of the single substance (substantially only muscles), verification by the simulation model 2 using an anatomical human body numerical model was performed. The human body model developed by the National Institute of Information and Communications Technology was used as the anatomical human body numerical model. This model is composed of 173 cm tall, 65 kg weight, and 51 types of biological tissues. A cell used in the FDTD method is a cubic cell having a side of 4 mm square. The frequency of the transmission signal was set to a center frequency of 4.1 GHz and a frequency band of 1.4 GHz as in the model 1, and a dipole antenna was used as the transmission antenna. As shown in FIG. 5, the receiving points were arranged at 10 locations around the abdomen. On the other hand, six transmission points are arranged around the small intestine, and the received electric field strength at each reception point with respect to the signal transmitted from each transmission point is calculated by FDTD simulation. Note that the frequency dependence of the relative dielectric constant and conductivity of each tissue in the model 2 is taken into account by the Debye dispersion formula.
シミュレーションモデル２における６箇所の発信点（Ｔｘ１〜Ｔｘ６）から送信された信号を受信する受信点の結果として、典型的な結果であった２箇所の受信点（Ｒｘ２，Ｒｘ３）での結果を、横軸にｄ（送受信機間距離）、縦軸にｌｏｇ（ｄＥ／Ｅ０）として、図６および図７にそれぞれ示す。数式（１）と（２）によって最小二乗法によるパラメータフィッティングを行った結果、モデル１同様に、直線的な関係が得られることが分かり、本発明の数学モデルによって比誘電率の推定が可能であることを示している。つまり、シミュレーションモデル１のほぼ筋肉から構成される単純モデルだけでなく、シミュレーションモデル２のような複数の組織から構成される人体においても、本発明の数学モデルが有効であることが確認された。 As a result of the reception points that receive signals transmitted from the six transmission points (Tx1 to Tx6) in the simulation model 2, the results at the two reception points (Rx2, Rx3), which are typical results, FIG. 6 and FIG. 7 show d (distance between transmitter and receiver) on the horizontal axis and log (dE / E 0 ) on the vertical axis. As a result of performing parameter fitting by the least square method using the mathematical formulas (1) and (2), it can be seen that a linear relationship is obtained as in the case of the model 1, and the dielectric constant can be estimated by the mathematical model of the present invention. It shows that there is. That is, it was confirmed that the mathematical model of the present invention is effective not only for the simple model composed of almost muscles of the simulation model 1 but also for a human body composed of a plurality of tissues such as the simulation model 2.
次に、カプセル型内視鏡等の対象物の位置を推定するため、上記の比誘電率推定モデルを用いた位置推定のアルゴリズムのフローチャートを図８に示す。本発明における位置推定方式は、初期化ステップ、位置推定ステップおよび比誘電率推定ステップにより行われ、また、繰り返し推定アルゴリズムにより、カプセル内視鏡位置と比誘電率パラメータは交互に繰り返して推定される。まず、初期化ステップでは推定する比誘電率パラメータεm r,nとイタレーション回数を表現するパラメータmの初期化を行う。ここで，nは受信点のインデックスであり、n=1,2,…Nの値を取る（Nは総受信点数を示す）。比誘電率パラメータの初期としては人体の平均パラメータ等を用いる。次に、位置推定ステップでは、最小二乗法により位置推定を行い、推定位置の更新を行う。推定ステップにおけるtはカプセル内視鏡位置の三次元位置[x,y,z]Tを示し，tmはm回目に更新された推定位置を表現している．そして，更新された推定位置を用いて比誘電率の更新を行う。さらに、比誘電率推定の原理としては，前記数式（１）と（２）を用いる。数式（１）ではカプセル内視鏡と受信点の距離が必要となるが，これは位置推定ステップで更新された推定位置を用いて算出する。比誘電率パラメータを更新した後，イタレーション数がmmaxに到達しているかを判定し、到達していなければイタレーション数mを１増加させ、位置推定ステップへ戻る。イタレーション数がmmaxに到達していれば位置推定アルゴリズムを終了する。
以上のように、本発明の位置推定方法は、前記数式（１）と数式（２）を用いる比誘電率を推定するステップと、推定された比誘電率情報に基づいたＴＯＡ（信号到達時間）による位置を推定するステップとを交互に繰り返すアルゴリズムに基づくものである。
Next, FIG. 8 shows a flowchart of a position estimation algorithm using the relative dielectric constant estimation model in order to estimate the position of an object such as a capsule endoscope. The position estimation method in the present invention is performed by an initialization step, a position estimation step, and a relative permittivity estimation step, and the capsule endoscope position and the relative permittivity parameter are alternately and repeatedly estimated by an iterative estimation algorithm. . First, in the initialization step, the estimated dielectric constant parameter ε m r, n and the parameter m expressing the number of iterations are initialized. Here, n is an index of reception points and takes values of n = 1, 2,... N (N indicates the total number of reception points). As the initial value of the relative dielectric constant parameter, an average parameter of the human body is used. Next, in the position estimation step, position estimation is performed by the least square method, and the estimated position is updated. In the estimation step, t represents the three-dimensional position [x, y, z] T of the capsule endoscope position, and t m represents the estimated position updated m times. Then, the dielectric constant is updated using the updated estimated position. Furthermore, the above formulas (1) and (2) are used as the principle of relative permittivity estimation. In Formula (1), the distance between the capsule endoscope and the reception point is required, and this is calculated using the estimated position updated in the position estimation step. After updating the dielectric constant parameter, it is determined whether the number of iterations has reached m max. If not, the number of iterations m is increased by 1, and the process returns to the position estimation step. If the number of iterations has reached m max , the position estimation algorithm is terminated.
As described above, the position estimation method of the present invention includes the steps of estimating the relative permittivity using the formulas (1) and (2), and the TOA (signal arrival time) based on the estimated relative permittivity information. This is based on an algorithm that alternately repeats the step of estimating the position according to.
上記位置推定アルゴリズムを検証するために、シミュレーションモデル１において位置推定精度を評価した。その結果を図９に示す。比較として、比誘電率の推定を行わずに、筋肉の比誘電率を既知の情報として与える手法についても評価を行った（予め被検体の誘電率を測定する従来方式）。図９より、全送信点１８点において従来法とほぼ同精度が達成できていることが分かる。さらに、全送信点１８点に対する二乗平均平方根誤差（ＲＭＳＥ）を求めたところ、シミュレーションモデル１は０．０１４０ｍであり、一方、筋肉の比誘電率が既知の情報として与えられた従来方式は０．０１３７ｍと得られたので、二乗平均平方根誤差の観点でもほぼ同精度での位置推定結果となった。以上の結果より、本発明による位置推定方式を用いれば、予め被検体の比誘電率の測定を行わずに、カプセル型内視鏡等のインプラント通信端末の位置の確度高い推定が可能であることが示された。 In order to verify the position estimation algorithm, the position estimation accuracy was evaluated in the simulation model 1. The result is shown in FIG. As a comparison, a method of giving the relative dielectric constant of muscle as known information without estimating the relative dielectric constant was also evaluated (conventional method for measuring the dielectric constant of a subject in advance). FIG. 9 shows that almost the same accuracy as the conventional method can be achieved at all 18 transmission points. Further, when the root mean square error (RMSE) for all 18 transmission points is obtained, the simulation model 1 is 0.0140 m, while the conventional method in which the relative dielectric constant of the muscle is given as known information is 0. Since 0137m was obtained, the position estimation result was obtained with substantially the same accuracy from the viewpoint of root mean square error. From the above results, if the position estimation method according to the present invention is used, it is possible to estimate the position of the implant communication terminal such as a capsule endoscope with high accuracy without measuring the relative permittivity of the subject in advance. It has been shown.
本発明はカプセル型内視鏡等のインプラント通信端末の位置検出装置に利用できる。
The present invention can be used for a position detection device of an implant communication terminal such as a capsule endoscope.
Claims (4)
（数式（１）および（２）において、Ｅ０は送信電界強度［Ｖ／ｍ］、Ｅは受信電界強度［Ｖ／ｍ］、ｄはインプラント通信機器端末と受信装置の距離［ｍ］、α(εｒ）は比誘電率εｒの関数である減衰係数、ωは角周波数［ｒａｄ／ｓ］（２π×送受信信号周波数）、σは導電率［Ｓ／ｍ］、Ｉｍは括弧内の虚数部である。) The position estimating method according to claim 2, wherein the step of estimating the relative permittivity is expressed by mathematical formulas (1) and (2).
(In Equations (1) and (2), E0 is the transmission field strength [V / m], E is the reception field strength [V / m], d is the distance [m] between the implant communication device terminal and the reception device, α ( εr) is an attenuation coefficient that is a function of relative permittivity εr, ω is angular frequency [rad / s] (2π × transmission / reception signal frequency), σ is conductivity [S / m], and Im is an imaginary part in parentheses. .)
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