effect of skull thickness on quantitative brain imaging
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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
AimImpact of skull thickness on attenuation
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
A Suitable Phantom
GE Healthcare Biosciences
Walsgrave Phantom Mk I
Perspex Cylinder Diameter 19cm
‘Skull’ Aluminium 1.5mm (x3)
15MBq Tc99m (10ml vial)
266MBq Tc99m (3l cylinder)
Acquisitions
(All Beacon)
No Attenuation
Water only
1.5mm Al
3.0mm Al
4.5mm Al
Reconstruction
• Same filter LP Order 6 / Cut off 0.6 cycles per pixel
• TransaxialsNo correctionChang uniform attenuation correctionBeacon NUAC
Results Phantom Mk INo
AttenuationWater Only 3mm 6mm 9mm
No Correction 179164 66524 63330 58894 54846
Chang 166283 156613 149433 145175
Beacon 278164 276124 265456 238434
No Correction 100% 37 35 33 31
Chang 93 87 83 81
Beacon 100 99 95 86
Walsgrave Phantom Mk II
Construction
Perspex cylinder
Cylinder of dense foam with skull shape removed
Grout layer for bone tissue
Two conical chambers to simulate striata
CT Numbers
979 ± 281050 ± 36
Acquisitions
Phantom with simulated skull (10mm)
Phantom without simulated skull
Reconstruction
• Same filter LP Order 6 / Cut off 0.6 cycles per pixel
• TransaxialsNo correctionChang uniform attenuation correctionBeacon NUAC
Chang Uniform Attenuation Correction
Right Left
No Corr Chang Beacon No Corr Chang Beacon
No Skull 419160 776836 1061549 346811 616050 852320
Skull 351924 633336 1040277 281961 489305 866383
% Difference -16.0 -18.5 -2.0 -18.7 -20.6 1.6
Results Phantom Mk II
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.