Review Question - QID 214550

A 27-year-old man presents to the emergency department after a motor vehicle accident. He sustained trauma to the left lower extremity and hit the front part of his head. He reports having a headache at the site of injury and pain involving the left lower extremity. He denies any vision changes, nausea, or vomiting. His blood pressure is 135/85 mmHg, pulse is 105/min, and respirations are 20/min with an oxygen saturation of 99% on room air. The patient is alert to person, place, and time. There is tenderness upon palpation of the left leg with ecchymoses in the affected area. Dorsalis pedis and posterior tibial pulses are present and the left lower extremity is warm. Neurological examination of the left leg is notable for mild weakness with pain on plantar- and dorsiflexion. CT head without contrast is unremarkable, and radiography of the left leg demonstrates a tibial fracture. The patient receives a fiberglass splint and is admitted for observation. Approximately 3 hours later, the patient develops a burning pain followed by a "prickling" sensation in the left lower extremity. Pain is precipitated with passive stretch of the calf and a "wood-like" feeling of the left leg. Which of the following is the diagnostic study of choice for this patient?