Step 1: When a prosthetic implant sits within the breast, any technique that depends on penetrating X-rays struggles because the implant casts a dense shadow over the parenchyma that must be assessed.
Step 2: Magnetic resonance imaging sidesteps this problem entirely. It produces high contrast pictures of soft tissue using magnetic fields rather than radiation, and the implant does not obscure the surrounding glandular tissue or the implant shell itself.
Step 3: This makes MRI the modality of choice both for screening the augmented breast and for telling apart fibrous scar from recurrent malignancy after conservation surgery.
Step 4: The remaining options either are blocked by the implant or give insufficient anatomical resolution.
\[\boxed{\text{MRI scan}}\]