Temporal Diffusion Spectroscopy MRI in Predicting the CPS of PD-L1 Expression and the Efficacy of Neoadjuvant Therapy

The goal of this observational study is to explore the application of temporal diffusion spectroscopy MRI in head and neck squamous cell carcinoma (HNSCC). The main questions it aims to answer are: * If the quantitative parameters of temporal diffusion spectroscopy MRI can predict the comprehensive positive score (CPS) of pathological PD-L1 expression in HNSCC? * If the quantitative parameters of temporal diffusion spectroscopy MRI can predict the efficacy of neoadjuvant therapy in HNSCC? Participants will receive head and neck MRI, including T2WI, T1WI, diffusion-weighted imaging (DWI), oscillating gradient spin echo (OGSE) and pulsed gradient spin echo (PGSE) sequence before and after neoadjuvant therapy. There is not a comparison group in our study.