MRIs and even less expensive imaging like X-rays aren’t usually advised in the first few weeks following a back injury or back pain. This isn’t true if there’s any reason to suspect a fracture. In the majority of cases acute back pain patients get better in one to two weeks after the start of pain.
Red flags that suggest the need for medical referral include:
Other red flags come out as time goes by. For example, failure to get better despite conservative care. Sometimes other symptoms start to develop after a couple of weeks or months that help point to a more serious problem that requires further medical care.