Hi,
I suppose that because you have dense breasts,all the tests that you have done, including the Breast-Specific Gamma Imaging (BSGI), still do not give a clear picture for the Breast Specialist to make a proper evaluation.
I think that you should follow the Breast Specialist recommendation wanting to pursue this matter.
The MRI is an excellent tool to detect abnormalities in dense breast tissue,but you know that to have an accurate diagnosis,would be to have a biopsy,because this procedure is the only way to know for sure what's going on.
Best wishes...
I am not sure of what a BSGI is...? Regardless, it sounds to me like the breast specialist is suggesting an early follow up and/or another modality to confirm the diagnosis. Dense fibroglandular tissue can be difficult to diagnosis for Radiologists or Breast Specialists, and often they will recommend more information from another modality (ultrasound or MRI) or be more aggresive and recommend a biopsy. It is your choice for which advice/procedure to follow. Personally, I would go with whatever is recommended for you from your doctors!
Best wishes....