Luna, I'm just seeing this thread so I'm sending good thoughts your way for your MRI, I recently went through the MRI for the lumbar of my back. I had to have an Open sided MRI as I'm EXTREMELY claustrophobic and too big for standard MRI tubes.
I have a bulged/herniated disc at L5/S1 along with some degeneration along L3 through S1. I opted for the microlumbar discectomy as my sciatic pain spread to my left leg while waiting to be seen by a neurosurgeon and I needed to get my live back to the abnormal that I'm accustomed to sooner than later. I ride a comfort bike (Trek Navigator 50) and you can do anything you want and physically can accomplish on your Townie. My longest ride has been 118 miles with some hills etc. It took me all day to do it and I've accomplished multiple centuries (7) and a total of 23 metric centuries (including the full centuries) last year before my back went out. I have over 7200 miles including road, trainer and stationary bike since July 2005. Luckily my Primary care physician said he believes I'll be able to get back on my bike eventually (he's a cyclist thank the gods) I don't believe the comfort bike had anything to do with my back problems (other than possibly lifting it on and off the front bus rack at times) I also watched my 2 grandsons under the age of 3 before this happened and had a back injury in 1988 so I don't believe it was the bike.
Good luck with whatever they say you do have, if you can do the PT good luck. My back situation was progressing and I knew the longer it took to get the less invasive surgery I've opted for, the less chance of it being successful. (my back went out day before Thanksgiving and I only finally got to see a surgeon/specialist in late March. It wasn't going to be for another week but when my pain went to BOTH legs I threw a fit about it taking so long to be seen) I'm scheduled for surgery 11 May now. Hopefully you won't have to take the same route, but if you do, find someone afterwards that knows sports medicine. I think you'll find out you can ride again too. My doctor said I would need to be more upright instead of bent over so it's probably just as well I'm ALREADY ON the Navigator. Anyways, once you get healed and cleared by a doctor, ride like you stole it girl.