A 58-year-old man with a history of lung cancer presents with acute-onset thoracic back pain. An AP X-ray of the thoracic spine is obtained. On careful examination, the structure marked **B** (pedicle) appears as a normal round cortical "owl-eye" shadow on the right side, but is absent on the left side at the level of T6. Which of the following is the most appropriate next step in management?