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
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