Haptics for Surgical Simulation CPSC 599.86 / 601.86 Sonny Chan - - PowerPoint PPT Presentation

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Haptics for Surgical Simulation CPSC 599.86 / 601.86 Sonny Chan - - PowerPoint PPT Presentation

Mar 04, 2023 382 likes •735 views

Haptics for Surgical Simulation CPSC 599.86 / 601.86 Sonny Chan University of Calgary A few announcements CPSC Showcase / final project deliverables submit one-page project abstract by 9:00 AM , Tuesday April 10 - pick up Novint Falcon

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SLIDE 1

Haptics for Surgical Simulation

CPSC 599.86 / 601.86 Sonny Chan University of Calgary

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SLIDE 2

A few announcements

  • CPSC Showcase / final project deliverables
  • submit one-page project abstract by 9:00 AM, Tuesday April 10
  • pick up Novint Falcon devices in MS145 / MS156 at 12:30 PM before showcase
  • return devices and ball grip at 4:00 PM, after the event
  • End of semester logistics
  • last class is Monday, April 9
  • CPSC 599.86 final exam is Wednesday, April 25, 12:00 PM
  • CPSC 601.86 survey paper due Friday, April 20
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SLIDE 3

Motivation

  • I taught you all this great,

futuristic stuff this semester…

  • but where would I ever use it?
  • Few applications can support

the high cost of haptic devices

  • Luckily for us (me), the medical

community is well funded

  • surgery is a high-risk endeavour with

very, very costly mistakes!

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SLIDE 4

ACCEPTED

NeuroTouch (NRC Canada) and LAP Mentor (Simbionix)

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SLIDE 5
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SLIDE 6

neuroArm project, University of Calgary

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SLIDE 7

Opportunities for Surgical Simulation

What one is the simulator?

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SLIDE 8

My Research Mission

Virtual Surgical Environment Operating Room

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SLIDE 9

Volumetric Isosurfaces

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SLIDE 10

Volume Rendering

  • Implicit representations are now

uncommon, but...

  • 3D medical imaging (CT, MRI,

etc.) has resulted in an abundance of volume data

  • Can be rendered with (almost)

the same algorithm for implicit surfaces!

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SLIDE 11

Sampled Volume Data

  • Image values sampled on rectilinear grid
  • CT scans measure radiodensity in Hounsfield Units
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SLIDE 12

Interpolation

What is the value here?

(0,0) (1,1) 0.3 0.6 0.7 0.9 F(x, y) = (1 x + bxc)(1 y + byc) I(bxc, byc) + (x bxc)(1 y + byc) I(dxe, byc) + (1 x + bxc)(y byc) I(bxc, dye) + (x bxc)(y byc) I(dxe, dye) for x, y, z 2 R

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SLIDE 13

Isocontours & Isosurfaces

Choose a threshold value, T, to determine the surface function

S(x, y, z) = T − F(x, y, z)

T = -600 HU T = 300 HU

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SLIDE 14

Isosurfaces in 3D

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SLIDE 15

Rendering Algorithm

  • Our implicit surface rendering

algorithm has two specific requirements:

  • Inside-outside function for S(p)
  • The gradient of S(p)

S(x, y, z) = T − F(x, y, z) rS(x, y, z) = ???

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SLIDE 16

Gradient Estimation

  • Estimate gradient using central

difference:

  • What’s the best choice for the δ

value?

rS(x, y) = ∂S

∂x ∂S ∂y

! ⇡ @

S(x+δ,y)−S(x−δ,y) 2δ S(x,y+δ)−S(x,y−δ) 2δ

1 A

∂S/∂x ∂S/∂y

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SLIDE 17

Isosurface Rendering

  • The full rendering algorithm:
  • Detect initial contact when S(p) < 0
  • Find surface point with initial seed
  • Update surface point as the device

moves by using tangent plane

  • Contact breaks when device is

moved outside the constraint plane

  • Repeat from start…
  • Any issues?
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SLIDE 18

Demo?

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SLIDE 19

Deformable Tissue Simulation

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SLIDE 20

Continuum Mechanics

  • Governs the stress/strain

behaviour of materials

  • Includes Young’s modulus

(elasticity) and Poisson ratio (incompressibility)

  • Think of it as an “advanced”

version of mass-spring systems

[from continuummechanics.org]

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SLIDE 21

Finite Element Simulation

  • Partitions an object into small, discrete elements
  • Computes continuum mechanics on solid element mesh
x x ) ( x x − ) ( 1 x x R − − e x R 1 − e e R ) ( 1 x x R K R − − e e e ) ( 1 x x R K − − e e plastic

f

total

f

elastic

f

plastic
  • f
  • riginal state
plastic rest state deformed state

[from M. Müller & M. Gross, Proc. Graphics Interface, 2004]

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SLIDE 22

Data Representation

isosurface CT tetrahedral mesh

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SLIDE 23

Data Processing

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SLIDE 24

Deformation Simulation

  • Co-rotational linear elastic FEM
  • Computes nodal displacements

from external forces

  • Implementation from VEGA FEM

library (Jernej Barbič, USC)

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SLIDE 25

Haptic Rendering

  • Extension of original isosurface

rendering algorithm:

  • sampling deformed volume
  • force transfer
  • moving the proxy
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SLIDE 26

Sampling the Deformed Volume

  • How do we find the image intensity value

at a given location in deformed space, x?

p0

deformed tetrahedron

rest vertices barycentric coordinates  xm 1

  • =

 r0 r1 r2 r3 1 1 1 1  p0 p1 p2 p3 1 1 1 1 −1  x 1

  • r2

r1 r0 xm

x

p1 p2

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SLIDE 27

Force Transfer

  • Virtual coupling force is applied to mesh nodes with barycentric weighting

xp x

Fc F1 F2 F0

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SLIDE 28

Moving the Proxy

  • To avoid interpenetration, we must keep the proxy outside the isosurface, even

when the deformable mesh elements themselves move!

  • If a tetrahedron’s vertices move,
  • we displace the proxy’s with the tetrahedron:

x0

p

1

  • =

 q0 q1 q2 q3 1 1 1 1  p0 p1 p2 p3 1 1 1 1 1  xp 1

  • pi → qi
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SLIDE 29

Architecture

Haptic Rendering Deformation Simulation Visual Rendering

forces displacements displacements

1000 Hz ~10-100 Hz 60 Hz

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SLIDE 30

Results

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SLIDE 31

Results

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SLIDE 32

Summary

  • Surgical simulation is a popular

and promising application of high-fidelity computer haptics

  • can tolerate cost of hardware
  • Sampled volumetric images

(medical image data) can be described as implicit surfaces

  • adapt the implicit surface rendering

algorithm to compute forces