Detection of crystalline material has long been an important indication for ultrasound (gall stones, kidney stones). Urate crystals are radiolucent but are readily seen sonographically.
Chronic hindfoot pain. Tophaceous bursitis. Hyperechoic crystalline material is seen shifting in the retrocalcaneal bursa with light pressure of transducer. Conventional radiograph below obtained on the same day (rotated left, same orientation as ultrasound scan).