INTERACTIVE
VOLUME RENDERING FOR
VIRTUAL COLONOSCOPY
IEEE Proceedings of Visualization,
Phoenix, U.S.A.,
19-24 Oct. 1997, pp. 433 – 436
Presented by Ku-Yaw Chang
OUTLINE
Introduction
 System Overview
 Direct Volume Rendering
 Experimental Results
 Conclusions

INTRODUCTION (1/4)

Optical colonoscopy
Effective diagnostic and surgical tool in medical
clinics
 Examine the inner mucosal surface of the human
colon
 Problems

Patient discomfort
 High cost
 Sedation
 Risk of perforation
 A limited range of exploration

INTRODUCTION (2/4)

Virtual Colonoscopy

An alternative procedure for optical colonoscopy
3D volumetric image / reconstruction
 Colon region extraction


A virtual environment of the interior colon

User can navigate and probe interactively
INTRODUCTION (3/4)

Center for Visual Computing at SUNY Stony
Brook
http://www.cvc.sunysb.edu/
 A virtual colonoscopy system

Based on surface rendering techniques
 Improve rendering speed by a hardware-assisted visibility
algorithm
 Guided navigation avoiding collision with the surface

INTRODUCTION (4/4)

Problems

Diagnostic capability is limited


Only the interior surface is visible
In this paper

A novel feature of direct volume rendering is
proposed

Can visualize
 Detailed structure of the possible abnormality
 Tissues beneath the colon surface
OUTLINE
Introduction
 System Overview
 Direct Volume Rendering
 Experimental Results
 Conclusions

SYSTEM OVERVIEW (1/2)

3 stages of the VC procedure

Data acquisition


The colon must be cleansed and inflated with air
Pre-processing
A 3D volumetric data set is constructed
 The colonic surface is extracted
 Center-line(or skeleton)
 Potential-field


Navigation

Planned navigation


The view moves along the centerline
Interactive navigation

To manipulate the camera interactively
• Without colliding with the colon surface
SYSTEM OVERVIEW (2/2)
OUTLINE
Introduction
 System Overview
 Direct Volume Rendering
 Experimental Results
 Conclusions

DIRECT VOLUME RENDERING (1/3)

Motivation

A detailed study and analysis of the tissues under the
surface are necessary

Possible abnormalities are found
Directly map certain ranges of sample values of the
original data to different colors and opacities
 Perspective volume ray casting

Traverse and resample along the ray cast
 Assign color and opacity to each sampling point
 Composite along the ray to obtain the pixel color


Strategies to accelerate the VR rate
Surface-assistant ray casting
 Parallel processing

DIRECT VOLUME RENDERING (2/3)

Surface-Assisted Ray Casting
VR works along with SR(surface rendering)
 Simply perform sampling in the neighbor of the colon
surface



Skip over those empty spaces
Determine two bounds of the ray integral
The hither (front) bound
 Use depth information produced by the surface
navigation – hardware-assisted visibility
 The yon (back) bound
 Define a length



Sufficiently cover the region of interest
Stop when the accumulated opacity reaches unity or a
user-defined threshold – a front-to-back along each ray
DIRECT VOLUME RENDERING (3/3)

Parallelization

Skipped
OUTLINE
Introduction
 System Overview
 Direct Volume Rendering
 Experimental Results
 Conclusions

EXPERIMENTAL RESULTS (1/3)

Simulation data

A CT scan of a plastic pipe


Radius : 20 mm
Simulate colonic polyps

Attach three small rubber
objects
 7mm
 5mm
 3mm
EXPERIMENTAL RESULTS (2/3)

Patient data

358 slices of high-resolution(512*512) abdomen
images

GE HighSpeed CT in the helical mode
EXPERIMENTAL RESULTS (3/3)

Patient data
OUTLINE
Introduction
 System Overview
 Direct Volume Rendering
 Experimental Results
 Conclusions

CONCLUSIONS

Computerized virtual colonoscopy
An effective alternative for clinical diagnostics
 Advantages

Non-invasive
 Patient comfort
 Cost-effective


To remove guesswork


VR is adopted as a supplement to the interactive
surface navigation
To speed up

Surface-assistant techniques

Skip empty spaces inside the colon
THE END