A tissue-fraction estimation-based segmentation method for quantitative dopamine transporter SPECT

Abstract

Quantitative measures of dopamine transporter (DaT) uptake in caudate, putamen, and globus pallidus (GP) have potential as biomarkers for measuring the severity of Parkinson disease. Reliable quantification of this uptake requires accurate segmentation of the considered regions. However, segmentation of these regions from DaT-SPECT images is challenging, a major reason being partial-volume effects (PVEs), which arise from the limited system resolution and reconstruction of images over finite-sized voxel grids. The latter leads to tissue-fraction effects (TFEs). Thus, there is an important need for methods that can account for the PVEs, including the TFEs, and accurately segment DaT-SPECT images. The purpose of this study is to design and objectively evaluate a fully automated tissue-fraction estimation-based segmentation method that segments the caudate, putamen, and GP from DaT-SPECT images. The proposed method estimates the posterior mean of the fractional volumes occupied by the caudate, putamen, and GP within each voxel of a 3-D DaT-SPECT image. The estimate is obtained by minimizing a cost function based on the binary cross-entropy loss between the true and estimated fractional volumes over a population of SPECT images. Evaluations using clinically guided highly realistic simulation studies show that the proposed method accurately segmented the caudate, putamen, and GP with high mean Dice similarity coefficients ~ 0.80 and significantly outperformed (p < 0.01) all other considered segmentation methods. Further, objective evaluation of the proposed method on the task of quantifying regional uptake shows that the method yielded reliable quantification with low ensemble normalized root mean square error (NRMSE) < 20% for all the considered regions. The results motivate further evaluation of the method with physical-phantom and patient studies.