Q. A 54-year-old male presents to your clinic for an urgent visit with severe left lower limb pain, numbness, and inability to control his urination, beginning 3 hours ago. His pain started two weeks ago following lifting a large bag of soil while doing yard work. At first, the pain was a constant dull ache in the left lower back, which got better with rest and got worse with activity. Three hours ago, following lifting his bag off the floor, the pain suddenly became excruciating, with radiation to the left lower limb and numbness in the leg and foot. When he tried to reach his phone to call EMS, he noticed that he had difficulty with walking. A few minutes later, with the first urination urge, he could not voluntarily stop his urine. On physical examination, he has hypesthesia (reduced sensation) in the dorsal aspect of both legs and dorsum of both feet, saddle hypesthesia, bilateral weakness in plantar flexion of feet, weak Achilles tendon reflex, and laxity in the anal sphincter. What is the best diagnostic modality for this patient?