Your case is exactly what mine was. In my case, my surgeon scheduled a pouchoscopy (also known as an endoscopy) every six months. Each time, he looked for cancer, inflammation, and any abnormalities. Only once did he take some small biopsies for a closer look, and those were clear. We kept to this schedule for two years, and then moved to a pouchoscopy just once a year. So I kind of graduated!! Now that I go in only once a year, he follows up with an annual CT scan of my chest and abdominal area to cover my liver, lungs, kidneys, and anything else in there. This protocol will only continue for five years, then I am clear. It could be that my surgeon is extra vigilant because my cancer was in a tricky spot and almost unnoticeable during regular colonoscopies, except that my gastroenterologist felt something during a digital exam and with sharp eyes noticed something "funny looking" on the camera screen that turned out to be my cancer, and from there it was a long journey. I am perfectly fine now.
If you trust you doctor / surgeon, you could write a list of questions for your next appointment to determine if further, or more regular, investigation is necessary. I have never had an MRI related to my cancer or for my j pouch, and none of the surgeons or oncologist prior to surgery suggested it. You could ask for a pouchoscopy and see what the results are, especially if you are really concerned. Put your mind at ease. Stress on the unknown is not good for you.
Before one of my pouchoscopies, I asked my surgeon to take photos inside my pouch and of the "owl's eyes" so I could see it. He did, and when I woke up I had a few photos to take home and they looked clear and very interesting. I don't know if all doctors will do this (might be cost involved) but mine did. He doesn't ever ask his patients to prep; I am allowed to have a light breakfast on the morning. I guess he uses a special hose to flush my pouch clean! Not everyone asks to be sedated, but I do because I couldn't get through it otherwise. Besides, when I wake up in recovery I am given a bunch of cookies and juice, so there's that.