A 59-year-old presents with complaints of low back pain that radiates into the buttocks and thighs. The pain is exacerbated with walking and standing in an erect position. Walking in a flexed position with a cart, walking upstairs, and sitting down relieve his pain. Additional complaints include nonspecific lower extremity numbness and tingling, and lower extremity weakness. Weight-bearing activities exacerbate his neurological symptoms. L1 to L5 myotomes, dermatomes, and reflexes are grossly intact. Straight-leg raise test is negative. Posterior tibial and pedal pulses are 2+ and equal bilaterally and lower extremity capillary refill is brisk at 2 seconds. Which of the following is the modality of choice for confirming the suspected diagnosis?
(A) Doppler ultrasound of the lower extremities
(B) Computed tomography (CT) of the lumbar spine
(C) Magnetic resonance imaging (MRI) of the lumbar spine
(D) Nerve conduction studies of the lower extremities
(E) Radiographs of the lumbar spine