After 1b low grade endometrial stromal sarcoma hysterectomy operation, should the follow-up monitoring be done with ct/cat or mri?

Your Gyn to guide: CT and MRI provide good images to detect pelvic/abdominal tumors. But your doctor should help you to decide whether either is indicated in your case. Most low grade tumors do not recur, so it is not necessary to do these expensive tests as their yield is very low. So they are not considered useful or helpful for Cancer surveillance in most Cancers .Annual medical checkup is all that I recommend