1 / This is the first study in Vietnam with sufficiently large sample size about the applicable value of six joint power Doppler ultrasound index in evaluating rheumatoid arthritis disease activity 2 / New conclusions of the thesis: Establish the rate of effusion, synovial inflammation, bone erosion and synovial hypervascularization found on ultrasound and six joint power Doppler ultrasound for each disease activity group according to DAS28CRP.