Desai MA, Peterson JJ, Garner HW, Kransdorf MJ. Clinical utility of dual-energy CT for evaluation of tophaceous gout. Radiographics. 2011;31(5):1365–75– discussion 1376–7.
This is an excellent article discussing the use to dual-energy CT scan for the diagnosis and quantification of tophi. This technique can differentiate between calcium and urate crystals.
I've had several diagnostic occasions when this would have been helpful. These situations include known gout but with new joint pain in an atypical location (spine), or presentation; patients with a clinical diagnosis of gout unresponsive to usual therapy who refuse aspiration; and finally some other interesting cases I can't discuss due to privacy concerns. I also have had many patients with massive tophacous burden and being able to confirm their resolution more objectively would have been reassuring.
I have not had a chance to use it yet, as it is not available at the local, rural hospital.