Welcome, Freesia. I don't know anything about requesting the slices to be thinner, but hopefully someone else will. The contrast is used to make lesions, or any abnormalities, appear brighter and easier to see. My brain MRIs have always been done with and without contrast, but I had no contrast when I had my spine imaged. I don't see why you couldn't request your next MRI to be done with & without contrast. They'll image you first without, pull you out, and inject you with the contrast material before the next scan. Good luck to you!