Background/Purpose:

B flow is a vascular ultrasound (US) technique in which the high resolution aspect of gray scale US is optimized to demonstrate movement of one tissue (particularly of erythrocytes) against the background of stationary structures. Though power Doppler can demonstrate relatively low flow structures such as synovial vessels and the neovascularization characteristic of active synovitis, it is in part a flow-direction dependent technique.  B flow has been shown to demonstrate carotid artery stenosis as well as color Doppler techniques while more accurately depicting background non-vascular anatomy ¹. The goal of this study is to evaluate the utility of B flow in the assessment of inflammatory arthritis.

Methods:

In a cohort of 10 patients with CCP positive RA (fulfilling the 2010 EULAR/ACR classification criteria) with at least one swollen joint, 120 joints (wrists and MCP joints) were assessed by gray scale US.    51 of the 120 joints were determined to have grade 1 or greater synovitis and underwent power Doppler and B flow interrogation.  Two sonographers independently scanned all patients with a GE logic E9 and a 15Mhz matrix array transducer for PD imaging. B flow was performed with an 18 MHz transducer with settings for venous flow.  Image scoring for both PD and b flow was performed by the same 2 rheumatologist sonographers (DT and RT) using a reference scoring atlas ²

Results:

51 joints were assessed by PD and B flow.  There was a good to very good agreement between B flow and PD scores (quadratic weighted kappa 0.62 and prevalence-adjusted and bias-adjusted kappa (PABAK) using quadratic weights k= 0.86, p<0.0005).  B flow scores were generally lower than PD scores (median B flow score 1, IQ range 0, 2, median PD score 2, IQ range 1, 2).  28 joints showed perfect agreement between modalities giving a percentage exact agreement of 54.9%. 20 of 51 (39.2%) joints had higher PD scores while only 3 of 51(5.88%) had higher B flow scores. Inter-reader reliability was high in both modalities (b flow intraclass correlation coefficient (ICC) 0.978 vs PD ICC 0.964).

Conclusion:

In this pilot study, B flow correlated well with PD in the assessment of rheumatoid synovitis in small and medium sized joints with similarly excellent inter-rater reliability.  Both ultrasonographers felt that there were fewer sonographic artifacts with B flow imaging compared to PD and this may explain the lower scores seen on B flow.  The ability to clearly demonstrate the background gray scale anatomy while displaying the vascular structures of interest offers advantages over Doppler techniques as artifactual findings can be more clearly recognized and excluded from interpretation.

Funding support provided in part through NIAMS AMP UH2AR067690

References:

1. Clevert,D.A.,Johnson,T., et al., Color Doppler, power Doppler and B-flow ultrasound in the assessment of ICA stenosis:  Comparison with 64-MD-CT angiography. Eur Radiol, 2007. 17:2149-59

2. Hammer, H.B.,et al., Examination of intra and interrater reliability with a new ultrasonographic reference atlas for scoring of synovitis in patients with rheumatoid arthritis. Ann Rheum Dis, 2011.70:1995-98

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/b-flow-a-novel-ultrasound-modality-in-the-assessment-of-synovitis-in-ra/