Background Early detection of inflammation at diagnosis of rheumatoid arthritis (RA) or in remission of RA is important to optimise treatment in order to prevent joint damage and disability. Recent studies in ultrasound (US) indicate that US, especially power Doppler (PD), is more sensitive to detect inflammation than physical examination. Early diagnosis and treatment monitoring could be achieved by a more sensitive power Doppler (PD) method to detect early increased vascularisation. Inspired by recent breakthrough work in high-frame rate Doppler US imaging that was shown to be more sensitive to low flows associated with vascularisation , we systemically explored this method for its application in diagnosing and monitoring RA.
Objectives (i) To compare the minimal flow velocity that can be detected with the high-frame rate Doppler US technique and a conventional clinical US machine using a flow phantom. (ii) To show visual differences between high-frame rate PDUS and conventional PDUS in healthy volunteers assuming that high-frame rate PDUS would detect more vascularisation in MCP2 joints.
Methods In a flow phantom filled with tissue mimicking material  and a vessel diameter of 700 μm, we tested the PDUS performance of conventional PDUS (Esaote MyLab60) and a custom high-frame rate PD imaging technique (Verasonics Vantage). Settings for both methods were optimised to detect lowest flows (continuous PDUS signal) by adjusting pulse repetition frequency (PRF), velocity range, wall filters, frequency and gain. Subsequently we included six healthy volunteers and we performed conventional PDUS and high-frame rate PDUS of the MCP2 joint. The US images were graded on power Doppler (PD; 0–3) according to a semi-quantitatively scoring system of Naredo et al.
Results In the flow phantom we could detect a flow velocity of 2.5 mm/s with the conventional PDUS. With the high-frame rate PDUS the lowest detectable flow was 0.5 mm/s. Results in healthy volunteers (n=6) showed no PD signal in MCP2 joints using conventional PDUS (Figure 1A). With high-frame rate PDUS (Figure 1B) the median PD grade was 2 (IQR: 2 - 2).
Conclusions In a flow phantom we could detect five times lower flows with the high-frame rate PDUS technique than with conventional PDUS. Contrary to conventional PDUS, we detected a positive PD signal in all healthy volunteers with high-frame rate PDUS. Therefore, high-frame rate PDUS is more sensitive to vascularisation. Further evaluation whether this will facilitate early diagnosis and monitoring in RA is needed.
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Ten Cate DF, Luime JJ, van der Ven M, Hazes JM, Kooiman K, de Jong N, et al. Very different performance of the power Doppler modalities of several ultrasound machines ascertained by a microvessel flow phantom. Arthritis Res Ther. 2013;15(5):R162.
Disclosure of Interest None declared
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