Ultrasonography patterns indicating the presence of gout. (a) Double contour sign: transversal ultrasound imaging of the knee joint in the anterior intercondile area. The double contour image is shown as an anechoic line paralleling bony contour femoral cartilage. B-mode, linear transducers with a frequency of 9 MHz. C, knee condyles. (b) Hyperechoic images: longitudinal ultrasound imaging of the dorsal aspect of the first metatarsal phalangeal joint. The hyperechoic cloudy area represents monosodium urate deposits within the thickened synovial membrane (arrows). B-mode, linear transducers with a frequency of 9 MHz. MH, metatarsal head. (c) Power-Doppler signal: longitudinal view, dorsal aspect of an asymptomatic first metatarsal phalangeal joints. The Doppler signal may be seen even seen in hyperechoic synovial areas. Transducer with a frequency of 14 MHz in grey scale and colour Doppler with a frequency of 7.5 MHz.