Image Alignment and Normalisation for MR-DUAL SPECT Imaging in Epilepsy

Because the amount of radioactive tracer reaching the brain during the two studies is unknown, the relationship between the counts emitted by corresponding tissues in the two scans is unknown. In simple terms, the overall brightness of the two scans is different:
 


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Orthogonal slices through registered MRI (left), SPECT scan 'A' (middle column) and SPECT scan 'B' (right column).
The two SPECT scans are displayed with the same colour table and intensity range to illustrate the overall difference in tracer reaching the brain during the two studies.

To reveal localised changes we must normalise the uptake in the two SPECT studies. The key issue here is that there are localised regions of change in the uptake of tissue in the two scans and also changes due to imaging artefact. The problem is to recover a normalisation estimate for the majority of unchanged tissue in the brain . Once normalisation is carried out, subtraction of the two sets of image values can reveal possible regions of epileptic fous:

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Orthogonal slices through registered MRI (left), SPECT scan 'A' ,SPECT scan 'B' (normalised to 'A') and their difference
(displayed with a green-red colour table to illustrate increase and decrease respectively).
Note: Regions of increase in the temporal lobe and also reconstruction artfeacts in the last slice of SPECT 'A'.


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