Mri scan

Does anyone know why an MRI of breast is done before the result of biopsy comes

Don’t know in all honesty, I didn’t have a scan at all apart from the ultrasound at diagnosis. I had grade 2 micropapillary with 3 lymph nodes with cancer, the lymph nodes were clear on the ultrasound, maybe it depends on whether they think it’s contained? 
I would love a ct or mri just for my peace of mind as this is my 2nd cancer in 6 yrs.