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Effect of skull thickness on quantitative brain imaging

Effect of skull thickness on quantitative brain imaging. Dr Nigel Williams Nuclear Medicine Department Walsgrave Hospital, Coventry. DaTSCAN: Quantification. Software to aid quantification has been developed. Accuracy depends on attenuation, scatter and septal penetration. Aim

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Effect of skull thickness on quantitative brain imaging

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  1. Effect of skull thickness on quantitative brain imaging Dr Nigel Williams Nuclear Medicine Department Walsgrave Hospital, Coventry

  2. DaTSCAN: Quantification Software to aid quantification has been developed Accuracy depends on attenuation, scatter and septal penetration Aim Impact of skull thickness on attenuation

  3. Attenuation • 140keV • Soft Tissue µ 0.11cm-1 HVL 4.5cm • Bone µ 0.24cm-1 HVL 2.9cm • Skull Thickness Variation 0.3 – 0.9cm

  4. A Suitable Phantom GE Healthcare Biosciences

  5. Walsgrave Phantom Mk I Perspex Cylinder Diameter 19cm ‘Skull’ Aluminium 1.5mm (x3) 15MBq Tc99m (10ml vial) 266MBq Tc99m (3l cylinder)

  6. Acquisitions (All Beacon) No Attenuation Water only 1.5mm Al 3.0mm Al 4.5mm Al

  7. Reconstruction • Same filter LP Order 6 / Cut off 0.6 cycles per pixel • TransaxialsNo correctionChang uniform attenuation correctionBeacon NUAC

  8. Results Phantom Mk I

  9. Walsgrave Phantom Mk II

  10. Construction Perspex cylinder Cylinder of dense foam with skull shape removed Grout layer for bone tissue Two conical chambers to simulate striata

  11. CT Numbers 1050 ± 36 979 ± 28

  12. Acquisitions Phantom with simulated skull (10mm) Phantom without simulated skull

  13. Reconstruction • Same filter LP Order 6 / Cut off 0.6 cycles per pixel • TransaxialsNo correctionChang uniform attenuation correctionBeacon NUAC

  14. Chang Uniform Attenuation Correction

  15. Results Phantom Mk II

  16. Conclusions For absolute quantification Variation in skull thickness will have to be considered The accuracy of uniform attenuation correction is influenced by region delineation Beacon type attenuation correction appears to offer a solution although system specific phantom acquisitions will be required.

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