Ryo Haraguchi

Gap junctions in cardiac myocytes are required to the excitation propagation in a heart. However, the existence of the gap junctions is insufficient to reproduce the transmural dispersion of repolarization which forms T wave of the electrocardiogram. In this study, we focus on a hypothesis of propagation mechanism "cleft potential mechanism" (so-called electric field mechanism) where the narrow cleft space between the cardiac myocytes brings the electrical coupling. Our results show that this mechanism can simultaneously reproduce both the large conduction velocity and the large transmural dispersion of repolarization.

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.

Congenital heart diseases include wide variations about the heart and great vessels. There are some difficulties in understanding the morphology and physiology of these conditions. In actual clinical circumstances, two-dimensional illustrations or schemas are used for education or undestanding. However, three-dimensional recognition of the morphology is mandatory to understand the complicated operative procedure. In this study, we have developed an operative procedure explanation system for Senning operation (atrial switch operation) for the therapy of corrected transposition of great arteries using three-dimensional computer graphics. For the evaluation of the developed system, a questionnaire survey has been performed for medical doctors and nursing staff. As a result, the survey revealed the system is useful for explaining and understanding the Senning operation procedure.

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.

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 developed an experimental system of Cardiac Arrhythmia Risk Evaluation (CARE) based on electrophysiological computer simulation. The system can evaluate a risk of tachyarrhythmia by the electrophysiological simulation with premature stimulation to many sites in the ventricular model, and users can browse the results on the web page with the visualized data. The system is expected to be useful to assist the prevention and treatment for tachyarrhythmia.

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.