Precise visualization of cricopharyngeal dysfunction after radiation therapy for nasopharyngeal carcinoma using ultrasound-guided balloon catheter dilatation: a case description - Ouyang, Yao; Zhou, Ying; Tian, Jiafa; Lai, Junmei; Guo, Xiuxiu; Zhang, Weiwei; Ren, Dingyuan (Quantitative Imaging in Medicine and Surgery, 2022)