Figure 2.

 Hypothetical model for the interaction between Doppler ultrasound and amount of synovial flow. (A) The synovial vessels are ranked on the x axis with increasing ability to be detected by Doppler to the right. An overlap between vessels of the normal synovium and inflamed synovium is expected. Thresholds for detection of flow for low, medium, and high sensitivity Doppler are shown with dashed lines. In this model only high sensitivity Doppler will detect flow in a normal synovium and then will detect only a few vessels. (B) After contrast injection, all vessels have an increased ability to be detected by Doppler. The bars have increased in height and some vessels have crossed the Doppler thresholds. According to the model no Doppler activity will be found in normal joints before or after contrast injection if a medium sensitivity Doppler is used. Also, if a contrast study on patients with rheumatoid arthritis does not include mildly inflamed joints, then contrast injection will not result in additional joints becoming Doppler positive.