これまで開発された手術シミュレータは腹腔鏡下手術の訓練を対象としたものが多い．本研究では，脳外科手術における微細血管吻合タスクを対象として，マスタ・スレーブ型手術ロボットの開発や評価だけでなく，ロボット手術の訓練に活用できるシミュレータを開発した．このようなシミュレータの開発にあたってはリアルタイム性や操作性，リアリティが重要となるが，リアリティを高めるためにモデルを複雑かつ詳細にすると計算負荷が増大し，リアルタイム性や操作性が損なわれる．本研究では，このトレードオフを考慮してシミュレータの開発を行った．ロボット術具のモデルでは，剛体間をバネとダンパの特性を有するジョイントで接続した．縫合糸は剛体を2自由度のジョイントで連結し，剛体の質量や慣性モーメント及びジョイントのバネ・ダンパの特性を調整することにより縫合糸の挙動を再現した．針は凸形状の組み合わせにより円弧状の剛体として近似し，縫合糸の端部に固定した．血管は多数の剛体を球ジョイントで接続することで再現した．これらのモデル化手法により，60Hzでのリアルタイムなシミュレーションが可能となった．更にリアリティを高めるため，3Dレンダリングやマスタでの力覚フィードバックを実装した．シミュレータは操作中の各物体の位置情報を記録して出力することができるため，自動手術手技評価への応用も検討している．

1. ロボット手術を対象とした微細
血管吻合シミュレータの開発
サウル・エレディア1)，中冨浩文1)，斉藤延人1)，森田明夫2)，
渡辺英寿3)，原田香奈子1,4)，○光石衛1)
1)東京大学，2)日本医科大学，3)自治医科大学，4) 科学技術振興機構

2. 2Introduction
Suture 0.02
mm
< 0.7 mm
[1] Mitsuishi, M., Morita, A., Sugita, N., Sora, S., Mochizuki, R., Tanimoto, K., ... & Harada, K. (2013). Master-slave robotic platform and its feasibility study for micro-
neurosurgery. The International Journal of Medical Robotics and Computer Assisted Surgery, 9(2), 180-189.
Master-slave robotic system
MM3 Robot
End-to-end anastomosis of micro vessel is task that
require high precision, a Master-Slave robotic
platform was developed to assist this procedure [1].
Neurosurgeons require hours of training using
artificial vessel to proficiency. VR simulation provides
a safe platform for repeatedly practice without
risking the robot.
Needle
diameter
0.070 mm
Video

3. 3Objective
[1] Perrenot, C., et al. (2012). The virtual reality simulator dV-Trainer® is a valid assessment tool for robotic surgical skills. Surgical endoscopy, 26(9), 2587-2593.
Existing VR simulators such a as the dV-
Trainer [1] for the da Vinci Surgical System
focus on laparoscopic surgery but there are
no micro anastomosis VR simulators.
To develop a VR simulator to imitate robot
assisted micro anastomosis.
Desired features:
• Real time (60 FPS)
• Physical accuracy
• Robustness
• Visual realism
Applications:
• Testing robot control algorithms
• Surgery training
• Data extraction for machine learning purposes
• Skills assessment

4. 4Thread modeling
The segments are connected by soft
constraints with stiffness and
damping properties
Each segment has mass and
moment of inertia properties
Cubic Hermite spline
Visualization
Rigid bodySpherical joint
Collision shape
(Capsule)
Simulation
Node
Link
Abstract
data
structure
Segment
length Center of
mass
reference
frame
Collision
radius
,m I
,k D
Rotational
spring
The thread is modeled as a chain of rigid elements of the
same length connected by 3 DOF rotational joints [1].
[1] Choi, K. S., Chan, S. H., & Pang, W. M. (2012). Virtual suturing simulation based on commodity physics engine for medical learning. Journal of medical systems,
36(3), 1781-1793.
100 elements/cm

5. 5Needle modeling
Simulated as a rigid body
connected to an end of the
thread by a fixed joint.
Fixed joint
3D modeling Collision model
(Convex decomposition)
Triangle
mesh
Reference picture
from microscope

6. 6Simulation of micro vessels
Nodes
(275 joints)
Mesh
(3046 vertices,
6092 triangles)
Linear
blend
skinning
Modified
clusters Deformed mesh
Clusters
(165 rigids)
,m I
,k D
Mass,
moment of
inertia
Stiffness,
damping
Soft body motion is modeled using a network of rigid bodies connected by soft constraints [1]
Real time interaction with
simulated vessels at 60 FPS
[1] Budsberg, J., Zafar, N. B., Aldén, M., & Animation, D. (2014, July). Elastic and plastic deformations with rigid body dynamics. In SIGGRAPH Talks (pp. 52-1).
Video
Ellipsoids
Triangles
Hexagons

7. 7Simulator parameters
Adjust rigid body
simulation parameters
to achieve same
behavior
Finite element simulation
Rigid-body based
deformation
RMS alignment error: 1.8×10-5 m
, ,E 
, , ,m k DI
Continuum elasticity
Rigid body dynamics
Basic idea
Given the material properties
(density, Young’s modulus,
Poisson ratio)

8. 8Needle and thread insertion
Penetration
If penetration>threshold
Equivalent virtual mechanism
Create a
“suture point”
constraint
Abstract needle
and thread
representation
Segment constrained
to a point on a plane
Stuck Slide
Offset >
threshold
Offset
Offset <
threshold
On right vessel
On left vessel
Piercing
Inserting Removing
Passed
through
Removed
Passing
thread

9. 9Virtual robotic tools
CAD Model
Collision geometry
(Convex decomposition)
Left tool Right tool
Bent tipStraight tip
Each part is modeled
as rigid elements, tips
are connect to the
shaft using hinge joint
with stiffness and
damping parameters to
simulate grasping.
Input
position
Tool proxy Ideal position
obtained after
simulation
Linear &
rotational
damped spring
Virtual coupling
x
ˆx
Haptic
device
VR
Simulation
PID
Controller
Operator
F
x
ˆxForce feedback
User interacts with the virtual
environment through haptic
interfaces

10. 10Simulator system
L R
Interleaved frames
120 Hz
3D monitor with
active glasses
Stereo monitor
Side-by-side
3D visualization
Gaming laptop
Phantom Premium
or Omni (Geomagic
Touch)
USB footswitch
User interface
Hapticdevices
Software implemented in C++ using
the NVIDIA PhysX [1] engine to
solve the rigid body dynamics
[1] https://www.geforce.com/hardware/technology/physx
or

11. 11Current state and future steps
VR Simulation running at 60 FPS
Needle grasping
Needle adjustment
Positioning (Right)
Insertion (Right)
Extraction
Looping
Thread grasping
Knot tying
Positioning (Left)
Insertion (Left)
Simulation
data
Skills assessment /
Surgical skills
Assistance /
Automation
Surgical activity segmentation
Video

12. 12Conclusion
• We developed a VR simulator for robot assisted end-
to-end micro anastomosis.
• By using rigid body dynamics simulation we achieve
real time execution (60 FPS).
• It is possible to adjust the simulator parameters to
achieve similar behavior as physical materials.
• The developed simulator has many potential
applications: surgical training, skills assessment, etc.