Effect of Denoising and Deblurring 18 F-Fluorodeoxyglucose Positron Emission Tomography Images on a Deep Learning Model's Classification Performance for Alzheimer's Disease.

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease. 18 F-fluorodeoxyglucose positron emission tomography ( 18 F-FDG PET) is widely used to predict AD using a deep learning model. However, the effects of noise and blurring on 18 F-FDG PET images were not considered. The performance of a classification model trained using raw, deblurred (by the fast total variation deblurring method), or denoised (by the median modified Wiener filter) 18 F-FDG PET images without or with cropping around the limbic system area using a 3D deep convolutional neural network was investigated. The classification model trained using denoised whole-brain 18 F-FDG PET images achieved classification performance (0.75/0.65/0.79/0.39 for sensitivity/specificity/F1-score/Matthews correlation coefficient (MCC), respectively) higher than that with raw and deblurred 18 F-FDG PET images. The classification model trained using cropped raw 18 F-FDG PET images achieved higher performance (0.78/0.63/0.81/0.40 for sensitivity/specificity/F1-score/MCC) than the whole-brain 18 F-FDG PET images (0.72/0.32/0.71/0.10 for sensitivity/specificity/F1-score/MCC, respectively). The 18 F-FDG PET image deblurring and cropping (0.89/0.67/0.88/0.57 for sensitivity/specificity/F1-score/MCC) procedures were the most helpful for improving performance. For this model, the right middle frontal, middle temporal, insula, and hippocampus areas were the most predictive of AD using the class activation map. Our findings demonstrate that 18 F-FDG PET image preprocessing and cropping improves the explainability and potential clinical applicability of deep learning models.