Convolutional neural network based attenuation correction for 123I-FP-CIT SPECT with focused striatum imaging

SPECT imaging with I-123-FP-CIT is used for diagnosis of neurodegenerative disorders like Parkinson's disease. Attenuation correction (AC) can be useful for quantitative analysis of I-123-FP-CIT SPECT. Ideally, AC would be performed based on attenuation maps (mu-maps) derived from perfectly registered CT scans. Such mu-maps, however, are most times not available and possible errors in image registration can induce quantitative inaccuracies in AC corrected SPECT images. Earlier, we showed that a convolutional neural network (CNN) based approach allows to estimate SPECT-aligned mu-maps for full brain perfusion imaging using only emission data. Here we investigate the feasibility of similar CNN methods for axially focused I-123-FP-CIT scans. We tested our approach on a high-resolution multi-pinhole prototype clinical SPECT system in a Monte Carlo simulation study. Three CNNs that estimate mu-maps in a voxel-wise, patch-wise and image-wise manner were investigated. As the added value of AC on clinical I-123-FP-CIT scans is still debatable, the impact of AC was also reported to check in which cases CNN based AC could be beneficial. AC using the ground truth mu-maps (GT-AC) and CNN estimated mu-maps (CNN-AC) were compared with the case when no AC was done (No-AC). Results show that the effect of using GT-AC versus CNN-AC or No-AC on striatal shape and symmetry is minimal. Specific binding ratios (SBRs) from localized regions show a deviation from GT-AC <= 2.5% for all three CNN-ACs while No-AC systematically underestimates SBRs by 13.1%. A strong correlation (r >= 0.99) was obtained between GT-AC based SBRs and SBRs from CNN-ACs and No-AC. Absolute quantification (in kBq ml(-1)) shows a deviation from GT-AC within 2.2% for all three CNN-ACs and of 71.7% for No-AC. To conclude, all three CNNs show comparable performance in accurate m-map estimation and I-123-FP-CIT quantification. CNN-estimated m-map can be a promising substitute for CT-based mu-map.

Automated summary

The study investigated the feasibility of CNN methods for axially focused I-123-FP-CIT scans, showing that CNN-AC can significantly improve the quantitative accuracy of localized regions.