Creation of 3-D models


1. Types of data

1.1 Vibration measurements

1.2 Moiré

Moire: interference pattern

Decraemer and Dirckx in Antwerp can measure the precise 3-D shape of the eardrum using phase-shift moiré topography, a non-contacting optical method.

The method uses a grid of straight lines.

A light shone through the grid onto a curved surface causes curved shadows.

Looking at the shadows through the grid produces a moiré interference pattern.

The illusory lines of the interference pattern form contours of constant depth, defining the shape of the surface.

xkcd cartoon

xkcd.com/1814/


We obtain an image of the eardrum in which the grey level of each pixel is proportional to the z coördinate (modulo 2π times a constant).

The application of static pressures during the shape measurement allows us to


Special software allows us to transfer the z coördinates from the moiré image to a finite-element mesh.

1.3 High-resolution X-ray CT

Principle of tomography

Single microscopic X-ray image of human middle and inner ear.

Taken with SkyScan 1072 scanner.
Resolution down to 5 μm if specimen small enough.

Mainly bone.
Section with eardrum

μCT reconstructed slice (human) showing eardrum and manubrium.
Section with stapes

μCT reconstructed slice showing stapes and tip of incus.
Section with heads of malleus and incus

μCT reconstructed slice showing heads of malleus and incus.

3-D volume.

1.4 Magnetic-resonance microscopy

Soft tissues more clearly visible.

Resolutions down to 10’s of μm.

1.5 Histology

Great detail; problems with distortion and alignment

Expensive and time-consuming, especially for 1-µm sections

2. 3-D model creation

Gerbil MRM data

Image segmentation with stacks of images.
Threshold-based
segmentation of part of gerbil middle ear

Threshold-based segmentation

Fast but often unsatisfying.

Good for some applications.

Not so good for complex models.
Human MRM segmentation

Manual segmentation.

Semi-automatic segmentation with ‘snake’ algorithm


Triangulation across slices to form surface

Complex and irregular surfaces

Connections and shared surfaces

Volume meshes

Variety of algorithms


BMDE-501 Modelling middle-ear mechanics

R. Funnell
Last modified: 2017-04-09 09:13:43