Multiple myeloma is a disease mainly located in participants bones. Usually a participants physician arrives at this diagnosis by doing blood tests and ordering standard of care imaging tests (18F-FDG PET/CT and maybe additional MRI) to see how many bones (and/or other organs) are affected. While these two imaging tests are already very good, recent research indicates that even more precise imaging methods could be used to diagnose participants disease more precisely. The purpose of this study is to learn if a combined PET/MR scan with a new radiotracer, \[68Ga\]Ga-PentixaFor, can provide more accurate and precise diagnostic information in patients with Multiple Myeloma, a type of cancer primarily affecting the bones. This study aims to improve the accuracy of diagnosing and monitoring Multiple Myeloma using more advanced imaging techniques.