X-ray Computer Tomography

Principles

Marcel Meinders

Outline

X-ray Tomography

● Principles of operation

● Comparison with other techniques

● Phoenix v[tome]x m

● Technical possibilities

● Computational facilities

X-ray tomography (XRT)

micro/nano computed tomography (μCT/nCT)

Non-invasively measurement of the 3D structure of objects at spatial resolution below 1 μm

2D shadow images Pixel: X-ray transmission

3D volumetric data : Voxel local density

X-ray tomography (XRT)

micro computer tomography (μCT)

Synchrotron polychromatic or monochromatic beam, parallel beam, resolution <0.5 μm, measurement time ~ 1 min

Lab scale, resolution <1 μm, measurement time > 15 min

● source/detector rotates (medical scanners)

● sample rotates

X-Ray Tomography: principle of operation

X-ray beam polychromatic

X-ray tube

Detector projection images cross sections

Tomographic reconstruction

3D model

sample rotation

Principles tomographic reconstruction

projection

Principles X-ray absorption

X-ray spectrum

V

Material parameter

Lambert Beer law

Filament

electrons

X-ray source

Anode

Bremsstrahlung

Comparison with other (3D) imaging techniques

XRT: a missing complementary technique

Technique Contrast Moisture Complexity Chemical specificity

MRI proton spin high High Moderate

XRT atomic density low Low Low

CLSM fluorescence markers high High High

TEM electron scatter dry High Low

available in Wageningen

1px=0.7m (228x228px2=0.16x0.16mm2)

1px=0.22m (727x727px2=0.16x0.16mm2) ESEM XRT (ESRF)

Electron microscopy bread like system

Gerard van Dalen, Unilever.

CSLM images model bread crusts

Red = protein Green = starch

CSLM CSLM XRT

Fluorescent probes that bind

specifically to a certain element

time: 3.1 13.4hrs

Spin Echo

~ 4 cm

~ 3 cm

Single Point Imaging

Magnetic Resonance Imaging

Experimental parameters: matrix 64x64x10; FOV 40x40 mm; TR 10ms; TD = 0.125 ms; 8 averages;

resolution 0.625 mm; total scan time:54m36s800ms

WUR X-ray tomography facility

CAT-AgroFood microCT centre operational since April 2013

● XRT Phoenix v[tome]x m GE

● Two X-ray sources

High Resolution (≥ 0.8 μm)

Large Sample Size (40cm/50kg)

Broad range of applications

● structure-function relations

● Foods, bio-based materials

● soil, roots,

● plants, seeds,

● insects , ….

Technical characteristics lab scale scanner

Spatial resolution / magnification (below 1 μm)

Low acquisition time (down to minute scale)

Good contrast and signal to noise ratio

Broad sample size/material range (from 1 mm up to 40 cm and 50 kg

Cone beam

X-ray sources

Two X-ray sources

● Reflection target (200kV/200W)

● high flux, small spot size

● strongly absorbing materials

● large sample size

● Transmission target (100kV/10W)

● low flux, tiny spot size

● soft materials

● small sample size

● Easy changeable

Resolution v[tome]x m

microfocus head / reflection target (5 and 3-4 μm)

(depends on direction due to elipsoidal shape source/target)

nanofocus head / transmission target (0.8 μm)

Computing facilities

• Dedicated high performance

workstations with maximal graphic

power and memory

• Fast tomography reconstruction

software with special correction

algorithms.

• State of the art software for

visualisation, image analysis,

meshing, and modeling.

Applications….