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DATSCAN Quantitation Vs Image Reading Mike Avison Bradford Royal Infirmary.

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Presentation on theme: "DATSCAN Quantitation Vs Image Reading Mike Avison Bradford Royal Infirmary."— Presentation transcript:

1 DATSCAN Quantitation Vs Image Reading Mike Avison Bradford Royal Infirmary

2 Overview Simple quantitation of SPECT slices implemented on Odyssey How reproducible is it? How does it correlate with radiologist reports?

3 The Acquisition Procedure Acquisition protocol –185MBq imaging 3 hrs PI –LEHR collimators –128x128 matrix –Orbit “as-is” 13cm radius or less – 360º data in 120 frames of 20sec –Mag x2 (i.e mm pixel size) –Brain-reach offset in Y direction

4 Reconstruction (workbench macro) Iterative reconstruciton –OS ML-EM – all –From vertex to lowest slice

5 From vertex to lowest slice

6 Reconstruction (workbench macro) Iterative reconstruciton –OS ML-EM – all –From vertex to lowest slice –Check orbit

7 Arc and Orbit

8 Reconstruction (workbench macro) Iterative reconstruciton –OS ML-EM – all –From vertex to lowest slice –Check orbit –Check sinogram and cine for movement

9 Check Sinogram

10 Check Cine

11 Filter Always the same Butterworth –Order = 4 –Cutoff = 0.33 cycles/2pixels –= 0.7 cycles/cm –(min object size ~= 1x0.5/0.7 = 0.7 cm)

12 Reformatting Occipito-frontal orientation Define slices

13 Quantitative Macro (Pixie) Features –Background information poster at the start –Analyses headers compares with specification –Simple to operate –2 rectangular regions pre-set size –Elliptical background region pre-set size

14 Background information about the processing procedure. Especially the expected slice and ROI dimensions

15 Give the operator instructions about selecting slices for processing

16 Allow the operator to modify their selection

17 Tell the operator how to place ROIs

18 Results are printed on the screen Expected dimensions of the volumes of interest are printed along side the actual values

19 Formulae Striatal to background uptake ratios

20 Controversy – why subtract background? FOR –The box contains some non-striatal tissues –The scale is amplified:- No uptake = 0 Double bg counts = 1 AGAINST –Its cross sectional imaging so there is no overlying background

21 Controversy, shaped ROIs? –Use shaped ROIs to cut out extra-striatal tissues? Which bits to include? What margin? Operator dependant!

22 Reproducibility? Intra-operator repeatability –One patient processed 10 times –LEFT : –RIGHT : 0.95 – 0.96 –GLOBAL: 0.93 – 0.94 –Standard deviation ~= 0.07% of the mean

23 Reproducibility? Selection of Slice Set How sensitive is processing to differences in slice selection? Selected 5 consecutive positions for central slice set (slices 9-13) Range of results = 11% of the mean. LESSON: display max and mean counts for each slice on display during slice selection

24 Reproducibility? Inter-operator variation 2 operators processed all studies –Maximum difference = 0.18 (19% of mean) –Std Dev of differences = 0.10 (11% of mean)

25 Quantitation vs Qualitative Report Combined ratio n = 30

26 Conclusion Robust quantitative system with low intra- and inter-operator variation. Good (but not perfect) separation of normal from abnormal Useful when apparent uptake contradicts shape (dot, comma paradigm)

27 Next Step Audit of patient outcome in progress. Compare uptake with outcome instead of qualitative image interpretation.


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