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Evaluation of 2 Scatter Correction Methods Using a Striatal Phantom for Quantitative Brain SPECT

Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland

Objective:

Scatter correction is an important factor in quantitative SPECT. In this study, we evaluated 2 methods of scatter correction for brain SPECT. The first is based on thresholding the energy spectrum (ES), and the second is based on a modification of the transmission-dependent convolution subtraction (TDCS) method.

Methods:

SPECT imaging of a skull striatal phantom was performed using a triple-head camera with and without scatter correction. The striatal compartments were filled with ¹²³I, and the brain shell cavity (background) was filled with varying concentrations of ¹²³I to obtain striatal-to-background ratios of 2, 5, 10, 15, 20, and 25 to 1, respectively, which were considered to be the expected ratios. SPECT-measured ratios of striatal-to-background counts were determined with scatter correction (both ES and TDCS methods) and without scatter correction and were then compared with the expected ratios.

Results:

Without scatter correction, measured striatal-to-background ratios were underestimated by an average of 41.7%, compared with the expected ratios. The ES method of scatter correction underestimated the striatal-to-background ratios by an average of 27.4%, a significant improvement (P < 0.04) over those without scatter correction. With the TDCS method of scatter correction, the ratios were underestimated by only 3.3% (P < 0.03). TDCS ratios were significantly (P < 0.04) higher than ES ratios and were nearly identical to the expected ratios.

Conclusion:

These results suggest that scatter correction significantly improves the striatal-to-background ratios. The TDCS method appears to correct scatter more effectively than does the ES method for the striatal phantom, thus providing more accurate quantification.

Key Words: brain SPECT; scatter correction; striatal phantom