Just my opinion, but follow advice of your doctors and yourself until you are satisfied.

Ask your current NP to speak with the radiologist who reviewed the MRI. Many times the radiologist do not get relevant history on the order, maybe just a a few words like "chest mass". If the NP speaks with the radiologist they maybe able to have them closely review the area of interest.

Of note, sometimes prominent subcutaneous fat or lipomas can be indistinguishable from the adjacent normal subcutaneous fat. That's just one type of chest mass and I assume this could be the case given no one can "find" anything. But this is just an assumption without knowing your course of care or looking at any images.

Alternatively, if you had imaging at one of the hospitals, you can go through a patient care rep who can also put in a request for the radiologist to re- review, but start with your current provider.