A 67-year-old man with a history of long-standing poorly controlled hypertension presents to the emergency department with sudden-onset, severe “tearing” chest pain that radiates to the back. He is diaphoretic and anxious. Blood pressure is 190/110 mm Hg in the right arm and 165/95 mm Hg in the left arm. Pulses are asymmetric in the upper extremities. A portable chest X-ray demonstrates a widened mediastinum. He is hemodynamically stable and has normal renal function.

Which of the following is the most appropriate next diagnostic study to confirm the suspected diagnosis?