Diffraction Enhanced Imaging at the UK Synchrotron Radiation

Source

M.Ibison, K.C.Cheung, K.Siu, C.J.Hall, R.A.Lewis, A. Hufton, S.J.Wilkinson, K.D.Rogers, A.Round

Principal Objectives of DEI Development Activities at the SRS

reduce the proportion of available time spent on alignment, in preparation for useful imaging

increase reliability and stability in mechanics and software, to improve image quality

approach a ‘turn-key’ facility for DEI users without need for expertise in the detailed method.

Also:- obtain useful experience for designing 2nd generation DEI on higher-energy SRS station.

DEI System – Station 7.6• High precision optics required• 2-crystal monochromator and 2-crystal analyser• Si 311 crystals give sharper x-ray extinction• Higher contrast, higher resolution images.

X-Ray Optics Alignment Laser

• red beam ( = 623nm), <1 mW output

• compact (2.5cm x 1cm), power source = 2 x 1.5V batteries

• micrometer adjustments, Vertical & Horizontal angle & displacement

• spot of 2mm x 1mm at working range of 2m

Monochromator and 4-Crystal Alignment using Laser Assistance

Monochromator Alignment Analyser Alignment

NOTE: Vertical Spacing between crystals exaggerated for clarity.

Laser Method for Determination of Motor Drive Calibration Factors

Laser laser

Monochromator crystal cage scale

rotation

deflection

Tangent Arm

Motor Drive

Laser Method for Determination of Motor Drive Calibration Factors

Laser laser

Monochromator crystal cage scale

rotation

deflection

Tangent Arm

Motor Drive

Ionisation Chamber for X-Ray Beam Location

• polymer window (5cm x 1cm)

• thickness = 70m• atmospheric pressure

Silicon p.i.n. PhotoDiodefor DEI Alignment

• Sensitive Area: 3.5mm x 3.5mm

• Thickness (effective): 250m

• Window: 10m Al foil (for 14keV X-rays)

Medical Applications of DEI: Mouse Feet Study

Refraction Images

Normal Diseased

• vertical view• through sole of foot

Absorption Images

Normal Diseased

Mouse Feet Study (2)

Normal Diseased

Refraction

Images

• horizontal view• through side of foot

Absorption Images

Normal Diseased

DEI Insect Studies

Refraction

Image

Absorption

Image

Beetle Earwig

Computerised Tomography – Principles

Examples of CT Reconstruction

Input to Reconstruction = Set of Projections (Sinogram)

Results of Reconstruction = Cross-Section (Slice)

Effect of Filtering on Reconstructed Image

Unfiltered

Filtered

Volume Visualisation

• 3-D Rendering of a Mouse Liver, based on CT dataset (ELETTRA)• Uses Volume/Surface modelling features of software packages

Second-Generation DEI System:Some Design Considerations

higher energy and greater flux (on wiggler Station) - better penetration, lower subject dose

channel-cut crystals - facilitate alignment, reduce drift rigidity and anti-vibration built into support structure mountings optimize use of existing framework - station

sharing remains feasible vacuum enclosure of the monochromator - avoids

convection currents and ozone damage risk cooling provision for the 1st crystal - highest heat loading

from ‘white’ beam.

Acknowledgements

The authors would like to thank:-

Medical Research Council- for funding this research programme

Giuseppe Salvini and Janet Groves (CLRC Daresbury)- design and construction of the p.i.n. diode device

Greg Johnson (CLRC Rutherford Appleton Laboratory)- design and implementation of DSP reconstruction system

Andrew Mather (Liverpool University)- Java implementation of the FBP reconstruction software.