NAVLE（北美执业兽医考题）Day 769

A 9-year old male Queensland Heeler presents with a four day history of progressive tetraparesis. Physical exam showed him to be weakly ambulatory with support. As part of your initial workup, you take chest X-rays which are shown below. Which of the following next steps is the most appropriate test to confirm your clinical suspicion about the cause of the dog's signs?
一只9岁的雄性昆士兰赫利犬由于持续4天进行性的四肢轻瘫前来就诊。体格检查显示他可以在有帮助的情况下虚弱的站立。你为他拍摄了胸腔X光片作为初步诊断检查的一部分，结果如下图。以下哪项是能够帮助你确立诊断的最合适的下一步检查？