Real-Time Volume Rendering of Medical Data for a Virtual Environment - PowerPoint PPT Presentation

Real-Time Volume Rendering of Medical Data for a Virtual Environment Philippe Cattin Mathias Griessen and Benedikt Bitterli

Motivation

Thousands of years ago [Prof. Alt, Uni Basel]

Some history New stone age (10’000 B.C.) Middle age Today

Why Laser?

Functional cuts

Bone cut with a saw

Bone cut with our laser

Why still spend hours/days to segment data sets?

Solution?

Volume Rendering Basics

Volume Rendering: Why? Pros Cons • High quality images • Computationally complex • No manual input • In VR difficult • Difficult scene renderer to embed polygonal objects

Classes of Volume Rendering Algorithms Ray casting method Plane Composing (Object order algorithms) (Image order algorithms) • Basic ray-casting • Basic slicing with 2D textures • Using octrees • Shear-warp factorization • Translucent textures with image- aligned 3D textures

Basic Forward Ray-Casting

Transferfunction • Transparency • Color • Emissivity

Challenges • 1 Million Triangles • Is considered a big mesh • 1 Million Voxels • Is considered small (100x100x100) • Typical size 512x512x500

Design Choices • Interpolation method • Trilinear • Sampling method • Less in the peripheri • Step size along the ray • Adaptive using distance map • Early stopping

Difficult Cases

• Fluffy objects • Lots of air

Distance Map • Precalculated on GPU • Size of map ¼ x ¼ x ¼ • Closest pixel (according to the transferfunction) spherically

Shadows

Occlusion map • Pre-calculated on GPU • Size of map 1/4x1/4x1/4 • 32 different directions • Environmap either • Static HDR image • Dynamic lamp (Gaussian) • Time for each image on GPU [3ms] • Special case when volume is rotated/scaled

Fusion with Mesh Objects

Example Video

Video

Conclusion • Volume Rendering for VR is possible • Mainly thanks to • Modern GPU hardware • Modern VR glasses • Clever programming Soon demo app: https://www.diffuse.ch