Kiyoshi Matsumiya

A Variational Method for Geometric Regularization of Vascular Segmentation in Medical Images

In this paper, a level-set-based geometric regularization method is proposed which has the ability to estimate the local orientation of the evolving front and utilize it as shape induced information for anisotropic propagation. We show that preserving anisotropic fronts can improve elongations of the extracted structures, while minimizing the risk of leakage. To that end, for an evolving front using its shape-offset level-set representation, a novel energy functional is defined. It is shown that constrained optimization of this functional results in an anisotropic expansion flow which is useful for vessel segmentation. We have validated our method using synthetic data sets, 2-D retinal angiogram images and magnetic resonance angiography volumetric data sets. A comparison has been made with two state-of-the-art vessel segmentation methods. Quantitative results, as well as qualitative comparisons of segmentations, indicate that our regularization method is a promising tool to improve the efficiency of both techniques.

Adaptive 4D MR imaging using navigator-based respiratory signal for MRI-guided therapy.

For real‐time 3D visualization of respiratory organ motion for MRI‐guided therapy, a new adaptive 4D MR imaging method based on navigator echo and multiple gating windows was developed. This method was designed to acquire a time series of volumetric 3D images of a cyclically moving organ, enabling therapy to be guided by synchronizing the 4D image with the actual organ motion in real time. The proposed method was implemented in an open‐configuration 0.5T clinical MR scanner. To evaluate the feasibility and determine optimal imaging conditions, studies were conducted with a phantom, volunteers, and a patient. In the phantom study the root mean square (RMS) position error in the 4D image of the cyclically moving phantom was 1.9 mm and the imaging time was ≈10 min when the 4D image had six frames. In the patient study, 4D images were successfully acquired under clinical conditions and a liver tumor was discriminated in the series of frames. The image quality was affected by the relations among the encoding direction, the slice orientation, and the direction of motion of the target organ. In conclusion, this study has shown that the proposed method is feasible and capable of providing a real‐time dynamic 3D atlas for surgical navigation with sufficient accuracy and image quality. Magn Reson Med 59:1051–1061, 2008.

Miniature bending manipulator for fetoscopic intrauterine laser therapy to treat twin-to-twin transfusion syndrome

BackgroundRecent typical therapy for twin-to-twin transfusion syndrome (TTTS) is selective laser photocoagulation of anastomotic communicating vessels on the placenta using the fetoscopic approach. The difficulty of a conventional laser device approach for this procedure depends significantly on the placental location, so a new robotized device is required to bend the direction of laser irradiation flexibly within the narrow uterus.MethodsThe authors designed a miniature bending mechanism impelled by a wire-guided linkage driving method that provides a stable procedure for bending laser irradiation from −90° to 90°. Using this bending mechanism, the authors developed a bending manipulator with a diameter of 3.5 mm and a hollow central channel with a diameter of 0.8 mm for passing a glass fiber for neodymium:yttrium–aluminum-garnet (Nd:YAG) laser photocoagulation. The bending mechanism is motorized by an electrical actuator and controlled by a grip-type interface with a small joystick. The robotized tip’s part and the actuator’s part are easily separable for cleaning and sterilization.ResultsIn performance evaluations of the manipulator, the bending characteristics with a glass fiber were examined. The bending range was −52.6° to 80°, with a very small hysteresis error, and the bending repeatability error was 0.5° ± 0.2°, which corresponds with the high accuracy of 0.2 ± 0.1-mm positioning error at the glass fiber’s tip. In the evaluation of Nd:YAG laser photocoagulation, the study confirmed that the manipulator performed effective laser photocoagulation of the placental phantom surface (underwater chicken liver). The large bending range, reaching 80°, enabled a flexible approach from various directions with a high irradiation efficiency of no less than 96.6%.ConclusionsThe authors’ original miniature bending manipulator can change the laser irradiating direction with highly repeatable positioning accuracy for speedy, safe, and effective vessel occlusion in clinical practice.

Rigid-Flexible outer sheath model using slider linkage locking mechanism and air pressure for endoscopic surgery

The objective of this paper is to develop an outer sheath for flexible endoscopic manipulators. This sheath can switch two states including flexible and rigid, and make a rigid curved path for inserting manipulators. The flexible mode can be curved into a required shape. The rigid mode can hold the shape of the sheath, and then keep the path for instruments. Through the managed path, the flexible manipulators become easy to reach the target. We proposed a serial multi joint model to realize the flexible mechanism. This model is composed of a set of frame units which are connected serially. Each unit can be rotated to a given angle around the center of the joint. We developed a slider-link mechanism and a gear stopper controlled by air pressure for rigid mode. We designed and fabricated the prototype with a diameter of 16 mm and length of 290 mm. The experiment showed that the device could be switched from the flexible mode to the rigid mode when the air pressure was over 150 kPa, and each joint could hold its angle against the maximum 400 mNm. The phantom experiment showed that the flexible devices are possible to transmit the wire tension to the endpoint of the manipulator without changing the curving shape with by the developed outer sheath device.

Analysis of Forces during Robotic Needle Insertion to Human Vertebra

The purpose of this study is assessment of forces and torques required for robotic needle insertion to human vertebra. Axial forces during robotic insertion to human vertebrae fixed with formalin (water solution of formaldehyde(FA)) did not exceed 25 N when the feed rate was no more than 0.5 mm/s. There was relatively strong correlation between the axial force variation during insertion and the distribution of bone local CT-value along the needle path. This result shows the importance of preoperative X-ray CT image guidance for robotic needle insertion with safely small axial forces. There was no significant influence of FA-fixation on axial forces during robotic needle insertion to human femoral heads. The forces during robotic insertion to human femoral head were as small as less than 50% of those during manual insertion, and which indicates that the robot can contribute to the safe needle insertion to human vertebra in percutaneous vertebroplasty.

Effective statistical edge integration using a flux maximizing scheme for volumetric vascular segmentation in MRA

Evolutionary schemes based on the level set theory are effective tools for medical image segmentation. In this paper, a new variational technique for edge integration is presented. Region statistical measures and orientation information from ramp-like edges, are fused within an energy minimization scheme that is based on a new interpretation of edge concept. A region driven advection term simulating the edge strength effect is directly obtained from this minimization strategy. We have applied our method to several real Magnetic Resonance Angiography data sets and comparison has been made with a state-of-the-art vessel segmentation method. Presented results indicate that using this method a significant improvement is achievable and the method can be an effective tool to extract vessels in MRA intracranial images.

MRI-Compatible Rigid and Flexible Outer Sheath Device with Pneumatic Locking Mechanism for Minimally Invasive Surgery

To reduce the invasiveness of surgery, we developed an outer sheath device using a flexible toothed link and pneumatic locking mechanism that works with flexible devices used in minimally invasive surgery. The outer sheath can be switched between flexible and rigid modes, and the angle of its tip can be controlled by a nylon wire. All parts of this device are made of plastic and are MRI-compatible. We manufactured a sheath prototype, 300 mm long, with a 20-mm outer diameter, and an 8-mm inner diameter. Experiment results showed that the outer sheath can protect tissues from high insertion force and secure the path for flexible devices. It can follow a curved path with a reasonable radius.

Forces and torques during robotic needle insertion to human vertebra

Abstract The purpose of this study is assessment of forces and torques required for robotic needle insertion to human vertebra. Axial forces during robotic insertion to human vertebrae fixed with formalin (4% solution of formaldehyde (FA)) did not exceed 25 N when the feed rate was no more than 0.5 mm/s. There were no significant differences between mechanical properties of the bones conserved under FA-fixation and under freezing. The forces during robotic insertion to using human femoral head were as small as less than 50% of those in case of manual insertion, which indicates the safety of robotic needle insertion to human vertebra.

Wide FOV Wedge Prism Endoscope

We have developed a novel robotic endoscope system. It can be used to observe a wide field of view without moving or bending the whole endoscope system. It consists of a rigid endoscope and two wedge prisms at the distal tip. Rotating each wedge prism respectively, we can change the direction of view. Accordingly it becomes possible to observe a wide field of view even in a small space, and suited to clinical uses because it does not damage body tissues or internal organs. Wedge prisms are designed to avoid vignetting which is caused by the refraction or the reflection at prisms. The endoscope has 10 mm in diameter, and the drive unit is simply separable for the sterilization. In addition, since it has a simple and small drive unit, it does not obstruct surgeon or other surgery robots. The maximum movement of local field of view is 19deg, and global field of view is 93deg. In the evaluation experiment, we conformed that both of the image quality and the performance are acceptable

Real-Time Autostereoscopic Visualization of Registration-Generated 4D MR Image of Beating Heart

This paper presents a real-time autostereoscopic visualization system using the principle of Integral Videography(IV). We develop MIP and composite volume ray casting method for IV volume rendering, and implemented the algorithm on GPU to achieve real-time rendering. The system was used to visualize 4D MR image that was generated from registration of 3D MR image and 4D ultrasound image. The registration scheme consists of inter-modality rigid registration between 3D MR image and 3D ultrasound image and intra-modality non-rigid registration between 3D ultrasound images. Registration processes were also implemented on GPU. Evaluation of processing speed showed that GPU processing time was 48x, 13x, 21x faster than CPU processing time for IV volume rendering, rigid registration, and non-rigid registration respectively. We also enabled real-time user interactivity for IV visualization system. In the future, We plan to use this system to develop intra-operative surgery navigation system for intra-cardiac surgery on beating heart.