The main goal of this study is to determine if static or dynamic [18F]NaF PET/CT (positron emitting tomography) can identify the source of lower backpain in at least 20% of the patients experiencing lower backpain, yet could not be diagnosed from MRI or CT scans.

Patients with chronic lower backpain are routinely scanned with MR and/or CT to diagnos the source of pain. Larger studies have reported that approximately 20% of patients are given a certain diagnosis from the scans and in the majority of cases the source of the pain is not determined. The use of [18F]NaF PET/CT to map bone perfusion and metabolism is a routine clinical scan that can potentially identify the source of lower backpain in MRI and CT negative patients.

Hypothesis: That [18F]NaF PET/CT bone metabolism and bone perfusion images would contain information that allow the correct diagnosis in at least 20% of patients where MRI and CT images did not reveal pathology.

Inclusion Criteria:

• Over 18 years
• Chronic lower back pain with no concrete diagnosis after MRI and/or CT
• Under the the care of Rigshospitalets centre for Rheumatology and Spine Disease

Exclusion Criteria:

• previous operation in the lower back area
• Known inflammatory related illness or progressive rheumatism

Patients with chronic lower back pain where the source could not be identified on MRI scans