1. A method for diagnosing a pain generator or a suspected pain generator in a patient suffering from neck or back pain, the method comprising administering a diagnostic agent comprising a tracer that specifically binds to a pain marker at a location inside of or adjacent to an intervertebral disc in the patient suffering from neck or back pain thereby labeling the pain marker with the diagnostic agent; allowing the labeled pain marker to bind the pain generator or suspected pain generator; and comparing the amount of labeled pain marker in a location inside of or adjacent to the intervertebral disc to a normal range of the labeled pain marker inside of or adjacent to an intervertebral disc via imaging, wherein the amount of the labeled pain marker outside of the normal range indicates the location of and diagnoses the pain generator or suspected pain generator, and the labeled pain marker bound to the pain generator or suspected pain generator can be 30% or higher than the normal range of labeled pain marker or labeled pain generator present, wherein the tracer has a binding affinity of at least 10 8 M −1 , and the pain marker comprises vascular endothelial growth factor, and the diagnostic agent is disposed in a matrix to retain the diagnostic agent at the location inside of or adjacent to the intervertebral disc in the patient, the diagnostic agent being in an amount of at least 35 wt. % of the matrix in microfiber particle form.