Background/Purpose: In many patients with rheumatoid arthritis (RA) subclinical disease activity can be detected with ultrasound (US), especially using power Doppler US (PDUS).[1-3] However, in our experience, PDUS is highly dependent on type of machine. This is a problem when conducting multicentre trials or in clinical practice.  US machines should be able to detect the blood flow velocities in capillaries as low as 0.5 mm/s. [4-5] The objective of the study was to determine the lowest detectable flow by PDUS of 5 different US machines using microvessel flow phantom.

Methods: The flow phantom, consisted of an acrylic (PMMA) container filled with tissue mimicking material(TMM)[6], with 3 microvessels (150, 1000, 2000 micron). The blood mimicking fluid was based on the recipe by Ramnarine.[7] A syringe pump generated the flows. We tested the Aloka α7, Esaote MyLab60, Philips iU22, Ultrasonix SonixTouch, and VisualSonics Vevo2100. Settings were optimised to detect the lowest flows by adjusting pulse repetition frequency, velocity range, wall filters, frequency and gain. Lowest possible flow was defined as a continuous PDUS signal. Flow velocities were calculated from pump flow setting and microvessel diameter.

Results: Table 1: Lowest detected flow velocity (mm/s), still resulting in a continuous positive PDUS signal; N.D. = none detected.

	Flow velocity
Vessel size (micron) Machine(probe)	2000	1000	150
Aloka α7(UST-5411)	4	2.2	11.1
Esaote MyLab 60 (LA 435)	<0.05	0.06	0.11
Philips iU22 (L9-3)	1	0.56	1.68
Ultrasonix SonixTouch (L14-5/38)	1	0.56	N.D.
Visual Sonics Vevo2100 (MS200)	0.5	0.33	N.D.

Conclusion: The performance of the PDUS modality of 5 US machines for detecting very low flows in small vessels was very different, when tested on a microvessel flow phantom. The large differences found between the machines are partly explained by different lower limits of PRF and wall filter, but also by fundamental differences in processing of the PD signal or internal settings inaccessible to users. In the 150 micron vessel, minimal detectable velocity is higher because of sensitivity issues. The actual flow velocity in the 1000 micron vessel was probably slightly higher than calculated and similar to that in the 2000 micron vessel. A reason for this could be compression by the TMM and a more parabolic flow velocity profile in the 1000 micron vessel, with a relatively high peak flow, as compared to the 2000 micron vessel. Caution should be exercised when conducting a multi-machine trial or when making treatment decisions based on PDUS. Based on the results of our study it would be advisable to standardise and validate US machines both for rheumatological clinical practice and for clinical trials. Our flow phantom could be used for this purpose. References: :[1] Peluso (2011) Ann Rheum Dis [2] Saleem (2011) Ann Rheum Dis [3] Brown (2008) Arthritis Rheum  [4] Stucker (1996) Microvas Res [5] Stucker (2004)  Skin Res Tech [6] Teirlinck (1998) Ultrasonics [7]Ramnarine (1998) Ultrasound Med Biol

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-power-doppler-modalities-of-5-ultrasound-machines-perform-very-differently-ascertained-by-a-microvessel-flow-phantom/