mrcp part 1 MCQ (SBA): Phaeochromocytoma

A 34-year-old woman presents with recurrent episodes of palpitations, sweating, tremor, and anxiety lasting 10-20 minutes. She also reports headaches and has noted high blood pressure readings at home. Examination during a symptom-free period is normal, BP 130/85 mmHg. What investigation is most likely to establish the diagnosis?