X-rays must be reasonably proximate to the initiation of a course of treatment. Unless more specific X-ray evidence is warranted, an X-ray is considered reasonably proximate if it was taken no more than 12 months prior to or 3 months following the initiation of a course of chiropractic treatment. 

In certain cases of chronic subluxation (e.g., scoliosis), an older X-ray may be accepted provided the beneficiary's record indicates the condition existed longer than 12 months and there is a reasonable basis for concluding that the condition is permanent. 

You may use a previous computed tomography (CT) scan and/or magnetic resonance imaging (MRI) of the spine in lieu of an X-ray when it demonstrates a subluxation of the spine. The timeframe specified for X-rays is applicable for MRIs and CT scans.