MRCP2-3020

A 78-year-old man with a history of prostatic carcinoma presents to the Emergency Department with complaints of lower back pain and heavy legs with reduced sensation. On examination, he has percussion tenderness of his spine, loss of sensation up to the umbilicus, a distended bladder, and reduced anal tone. He also has significantly reduced power in his lower legs, hyperreflexia, and upgoing plantar responses. What is the most suitable investigation to request?