Is there any way to tell if some capsules were left behind after implants were removed? Maybe MRI, CATscan or Ultrasound?

To visualize a clinically significant breast capsule after explant, the most sensitive radiographic test is MRI, followed by ultrasound. If a thick capsule was left behind, both of these studies have high sensitivity for detection. CAT scan is not thought to be as sensitive, but can be useful in some circumstances.Hope this helps! Sam Jejurikar, MD

Dear MonicaAW,
if your capsules were thin, then there was no need to remove them as your body will remove the remaining capsule and it will not show on MRI or ultrasound. However, in case of capsular contracture capsules are thick and can be easily seen on MRI or ultrasound. Most plastic surgeons will try to remove the entire capsule in case of contracture. 
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Leaving a capsule behind is preferred if it is thin and pliable. If there are calcific components, or silicone granulomatous material, or if the capsule is deforming the breast tissue, then removal of the capsule may be warranted.  If the capsule is left behind, the body will break down and remodel the scar tissue on its own.Kenneth Hughes, MD, ABPS Board Certified Plastic SurgeonLos Angeles, CA

Depending on the qualities of the capsules, they may or may be detected in tests.  If the capsules are thin, they may not be visible even with sensitive tests.  Thickened capsules may be able to been seen from an MRI or ultrasound.

If the capsule is normal (thin) it is likely that all the forms of radiographic imaging you mentioned will not detect a specific capsule (as opposed to "post surgical changes"). On the other hand, if the capsule is thickened and/or calcified, a distinct layer may be  identifiable on the imaging scans you noted mentioned. I hope this helps.