DATSCAN

Quantitation Vs Image Reading Mike Avison Bradford Royal Infirmary

Overview

• Simple quantitation of SPECT slices implemented on Odyssey • How reproducible is it?

• How does it correlate with radiologist reports?

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. 2.34 mm pixel size) – Brain-reach offset in Y direction

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

From vertex to lowest slice

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

Arc and Orbit

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

Check Sinogram

Check Cine

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)

Reformatting

Occipito-frontal orientation Define slices

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

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

Give the operator instructions about selecting slices for processing

Allow the operator to modify their selection

Tell the operator how to place ROIs

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

Formulae

Striatal to background uptake ratios

ratio right



C right

/

area right



C bg

/

area bg C bg

/

area bg ratio combined



C combined

/

area combined



C bg

/

area bg C bg

/

area bg

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

Controversy, shaped ROIs?

– Use shaped ROIs to cut out extra-striatal tissues? • Which bits to include?

• What margin?

• Operator dependant!

Reproducibility?

Intra-operator repeatability – One patient processed 10 times –

LEFT : 0.90 - 0.92

–

RIGHT : 0.95 – 0.96

–

GLOBAL: 0.93 – 0.94

– Standard deviation ~= 0.07% of the mean

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

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)

Quantitation vs Qualitative Report 1.8

1.6

1.4

1.2

1 0.8

0.6

0.4

0.2

0 -0.5

Normal n = 30 0.5

Abnormal 1.5

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)

Next Step

• Audit of patient outcome in progress.

• Compare uptake with outcome instead of qualitative image interpretation.