A 55-year-old female who was recently diagnosed with type 2 diabetes presented with central weight gain over the last 8 months, associated with fatigue and weakness. She also noticed multiple body bruises. On examination her blood pressure is 157/94. Her labs showed: high free urinary cortisol, high morning 8 am cortisol level after administration of 1mg dexamethasone, and low ACTH. What is the most appropriate next step in evaluation ?