原口 亮

心筋組織の興奮伝播はギャップ結合によるものであるが,ギャップ結合による細胞間の電気的結合は,T波形成に必要な貫壁性心室較差を十分説明できない.本研究では,細胞間クレフトの電位変化が隣の細胞を刺激する新たな機構「クレフト電位機構」を検証した.その結果,クレフト電位機構によって貫壁方向の興奮伝播が成立すると同時に,貫壁性心室較差が再現可能であることがわかった.

インタラクティブな 3 次元コンピュータグラフィクスを用いた肝臓病に関する患者説明ツールについて紹介する。現在、肝臓病に関する、患者に対しての病状および治療方針の説明には、主に 2 次元の図が使われている。しかし、これらの方法では、 3 次元的な概要を捕らえることが困難である。本システムでは、肝臓の 3 次元的な形状がディプレイ上に表示されるので、それを自由な角度から閲覧することで 3 次元的な形状把握が可能となる。さらに、簡単なジェスチャーインタフェースで、自由な場所に病変を記入したり病変の切除を行ったりすることができる。さらに任意の場所に薬剤の注射する様子を 3 次元的に見せることも可能となっている。このシステムを利用することにより、インフォームドコンセントにおける患者説明をより充実させることが期待できる。This paper introduces a tool using interactive 3D computer graphics for explaining liver disease to patients. Medical doctors currently use 2D illustrations to describe the condition and treatment of a liver disease, but it is difficult to communicate 3D information in 2D format. This system shows the geometry of a liver as a 3D model and allows the user to browse it from arbitrary view point. In addition, the doctor can add tumors and remove them using simple gestural interface. It is also possible to show the process of drag injection as an animation. This system is expected to improve the quality of informed consent in liver disease treatment.

先天性心疾患は，生まれつき心臓および心臓周辺の血管構造の形態的異常を有する病気であり，非常に多くの種類が存在する．それらの疾患の中には，形態的に理解しやすいものもあれば，理解しにくいものもある．臨床では，それらの疾患の理解あるいは説明をするときに2次元のイラストやシェーマが用いられることが多い．しかし，複雑な先天性心疾患の手術を理解するためには，心臓構造を立体的に把握することが必要である．本研究では，先天性心疾患の手術において，特に心臓の立体的な把握が必要な修正大血管転位症に対するSenning手術（心房内血流転換術）を対象とし，3次元のコンピュータグラフィックスを用いた手術過程説明用システムを開発した．試作したシステムが有用かどうかを評価するため，医師および看護師を対象としたアンケート調査を実施した．その結果，アンケートの各項目において高い評価が得られ，本研究で開発したシステムは，Senning手術の手術過程の説明と理解のために有用であることが示唆された．

We propose a sketch-based interface for modeling the myocardial fiber orientation required in the electrophysiological simulation of the heart, especially the ventricles. The user can create a volumetric vector field that represents the myocardial fiber orientation in two steps. First, a depth field over the three-dimensional (3D) ventricular model is defined to create layers of myocardium. The user can then peel these layers and draw strokes on them to specify the myocardial fiber orientation in each layer. We represent the 3D ventricular model as a tetrahedral mesh and perform Laplacian smoothing over the mesh vertices to interpolate the vector field defined by the user-drawn strokes. Our method also allows the user to perform deformations on volumetric models of myocardial fiber orientation, which is very important for studying heart disease associated with morphological abnormalities. We created several examples of myocardial fiber orientation and applied them to a simplified simulator to demonstrate the effectiveness of our method.

The Purkinje fibers are located in the ventricular walls of the heart, just beneath the endocardium and conduct excitation from the right and left bundle branches to the ventricular myocardium. Recently, anatomists succeeded in photographing the Purkinje fibers of a sheep, which clearly showed the mesh structure of the Purkinje fibers. In this study, we present a technique for modeling the mesh structure of Purkinje fibers semiautomatically using an extended L-system. The L-system is a formal grammar that defines the growth of a fractal structure by generating rules (or rewriting rules) and an initial structure. It was originally formulated to describe the growth of plant cells, and has subsequently been applied for various purposes in computer graphics such as modeling plants, buildings, streets, and ornaments. For our purpose, we extended the growth process of the L-system as follows: 1) each growing branch keeps away from existing branches as much as possible to create a uniform distribution, and 2) when branches collide, we connect the colliding branches to construct a closed mesh structure. We designed a generating rule based on observations of the photograph of Purkinje fibers and manually specified three terminal positions on a three-dimensional (3D) heart model: those of the right bundle branch, the anterior fascicle, and the left posterior fascicle of the left branch. Then, we grew fibers starting from each of the three positions based on the specified generating rule. We achieved to generate 3D models of Purkinje fibers of which physical appearances closely resembled the real photograph. The generation takes a few seconds. Variations of the Purkinje fibers could be constructed easily by modifying the generating rules and parameters.

Torsion movement of the left ventricle has significance in ventricle contraction and dilation. In this study, we propose methods of analyzing torsion movement of whole body and local region of left ventricle using three-dimensional images of MR Phase-contrast method. The method calculates torsion angle from average angular velocity of central axis by determining central axis from velocity field and torsion ratio from relative velocity of cross sections. In addition, we propose a method, which has no need for determining central axis, by calculating time variation of principal strain. Results showed maximum value of torsion ratio of endocardium between ventricular apex and base in the end of contraction. In addition, the result showed that torsion between cross images in the beginning of contraction and dilation is large and torsion within cross image is large in the end of contraction and dilation.

本論文では、心筋MR位相コントラスト法(以下、MR-PC法)により得られた心筋各部の速度をもとに、自動的に左室心筋の局所ひずみ速度を求め、その分布を可視化する手法を提案する。提案手法ではまず、心筋線維方向が短軸断面とほぼ平行になる左室心筋中層部を抽出するために、MR強度画像から大まかに心筋部分を分類し、画像間位置合せの後、心筋部分の距離画像を生成して左室心筋中層部分を定めた。その後、MR位相画像から断面内速度場を生成し、心室内外膜に平行な方向の圧縮ひずみと断面内ずりひずみを求めることで、局所心筋における短縮伸展速度とずりひずみ速度を求めた。提案した手法により、自動的に左室心筋の局所ひずみ速度が算出され可視化されること、収縮過程における圧縮ひずみとずりひずみの優位性の変化などが示された。任意断面において三次元的に速度を直接算出できるMR-PC法は、心筋収縮機能を評価する上でエコーや心筋タギング法等の他手法より有利であり、提案手法と開発したプログラムによる局所心筋ひずみ速度の算出とその可視化は、肥大心における心筋収縮機能の異常の程度を評価する際に有効であると考えられる。(著者抄録)

Ventricular fibrillation (VF) is the major cause of sudden cardiac death by lethal arrhythmia. Regional abnormalities such as myocardial infarction are regarded as the cause of VF; however, VF is clinically caused without the organic heart disease. Then we hypothesized that a human heart equips a protective mechanism against VF and thus the breakdown of the protective mechanism induces VF. We considered that the essence of the mechanism is the ventricular transmural gradient (electrophysiological heterogeneity). To confirm this hypothesis, we have developed a 3-D ventricular wall model and analyzed the dynamics of spiral wave reentry and filament (reentrant organizing center). It was found that the ventricular gradient forces an intramural filament to drift out a boundary and reduces the sustainment of VF. On the other hand, the pharmacological modifications of ventricular gradient to increase transmural dispersion of repolarization (TDR) break the protective mechanism and sustain VF.

Selecting a region of interest (ROI) within unsegmented volume data is one of the fundamental operations in volume data processing and analysis, yet it is difficult to perform the task efficiently. This paper proposes several simple and intuitive sketching user interface tools for the selection task, in which the user can directly click or draw a stroke on the volume-rendered object on the screen. The main contribution is that the user's input is pre-processed in 2D domain before applying the traditional 2D-to-3D stroke elevation algorithm (the Volume Catcher system [1]). We tested the system with real-world examples to verify the effectiveness of our approach.

心房細動に対するアミオダロンの長期作用を明らかにするために、ヒト心房細動in silicoモデルを使用して実験し、電気的・構造的リモデリング及びアミオダロンの長期・短期作用による電気生理学的変化、心房細動誘発性と興奮伝播様式の変化について検討した。in silicoの心房細動モデルに電気的・構造的リモデリングを導入すると心房細動の持続性が高まることが確認された。また慢性心房細動モデルにおける興奮伝播解析によりアミオダロンによる心房細動停止はspiral wave旋回周期や興奮性波長の延長、meandering拡大によるspiral wave同士の衝突やspiral wave媒質端への衝突によるものであることが明白になった。更にアミオダロンによる慢性心房細動停止効果は短期作用よりも長期作用の方が高いと思われた。但し短期作用と長期作用による慢性心房細動停止効果は心房筋リモデリングのタイプにより異なることが示唆された。

Purpose: The aim of this study was to investigate whether bipolar electrode potentials (BEPs) reflect local myocardial repolarization dynamics, using computer simulation. Methods: Simulated action potential and BEP mapping of myocardial tissue during fibrillation was performed. The BEP was modified to make all the fluctuations have the same polarity. Then, the modified BEP (mBEP) was transformed to "dynamic relative amplitude" (DRA) designed to make all the fluctuations have the similar amplitude. Results: The repolarization end point corresponded to the end of the repolarization-related small fluctuation that clearly appeared in the DRA of mBEP. Using the DRA of mBEP, we could reproduce the repolarization dynamics in the myocardial tissue during fibrillation. Conclusions: The BEP may facilitate identifying the repolarization time. Furthermore, BEP mapping has the possibility that it would be available for evaluating repolarization behavior in myocardial tissue even during fibrillation. The accuracy of activation-recovery interval was also reconfirmed. (c) 2007 Elsevier Inc. All rights reserved.

Objectives: This paper introduces a pen-based interface for the graphical reporting of findings in cardiac catheterization. Methods: The user can interactively draw, erase, move, and deform coronary arteries as well as record stenoses on them. The location and degree of each stenosis is represented visually and the doctor can record various treatments such as bypasses and stents on the diagram. In addition, the system automatically extracts semantic information from the graphical representation and stores it in XML format. The system can also generate a table in the format specified by the American Heart Association. Results: Our current implementation is a research prototype and is not yet being used in clinical practice. However, we hove already demonstrated it to medical professionals and confirmed the following benefits. Conclusions: This system is useful not only as a tool for efficiently generating reports of findings but also as an effective explanation tool for patients.

We present an electrophysiological heart simulator equipped with sketchy 3-D modeling interface. It has been tedious and time-consuming to create the shape of heart for use it in the simulator. In this study, we developed a new simulator that is combined with a sketch-based 3-D modeling interface for the shape transformation. We also developed a semiautomatic method in order to save labor for pre-process of the simulation. The sketchy 3-D modeling interface increases the facility of computer simulation.

This article proposes a sketch-based interface for modeling muscle fiber orientation of a 3D virtual heart model. Our target was electrophysiological simulation of the heart and fiber orientation is one of the key elements to obtaining reliable simulation results. We designed the interface and algorithm based on the observation that fiber orientation is always parallel to the surface of the heart. The user specifies the fiber orientation by drawing a freeform stroke on the object surface. The system first builds a vector field on the surface by applying Laplacian smoothing to the mesh vertices and then builds a volumetric vector field by applying Laplacian smoothing to the voxels. We demonstrate the usefulness of the proposed method through a user study with a cardiologist.

We previously developed an electrophysiological heart simulator. However, it was tedious and time-consuming to create the heart models for the simulation. In this study, we newly developed the graphical interface for modeling an excitation map and setting up some physiological parameters. Utilizing our interface enables us to save the labor for repetitive simulation trials using the individual and modified ventricular models.