Feasibility of 3D photoacoustic tomography for the assessment of rheumatoid arthritis.

OBJECTIVES

To assess whether 3D photoacoustic tomography (PAT) using the Fabry-Perot (FP) scanner can (1) reliably detect synovitis in participants with rheumatoid arthritis (RA), and (2) assess the severity of active inflammation.

METHODS

A total of 247 3D-PAT images of the finger and wrist joint from 11 healthy volunteers and 9 patients with RA were obtained using the FP scanner. Patients underwent power doppler ultrasound (PDUS) assessment of RA disease activity. The 3D-PAT images were acquired over a 15 × 15 × 10 mm3 volume in <15 s. The images were assessed quantitatively by segmentation of the vasculature using k-means clustering followed by skeletonization to measure vascular path length (PAT-VPL). Patient and volunteer PAT-VPL were compared using t-tests and area under the receiver operating characteristic curve (ROC-AUC).

RESULTS

The 3D-PAT differentiates between unaffected and affected joints in patients with RA, showing a statistically significant difference in PAT-VPL (unaffected joint: 11.88 mm, affected joints: 45.7 mm, P < .001). The ROC-AUC was 0.91 (95% confidence interval [CI]: 0.81-0.96), with sensitivity and specificity of 86% (95% CI: 72%-95%) and 78% (95% CI: 60%-90%), respectively. PAT-VPL was associated with PDUS-based clinical severity grade, with a correlation coefficient of 0.74 (95% CI: 0.67-0.8). Significant differences in PAT-VPL were observed between each clinical severity group.

CONCLUSIONS

The FP scanner generates rapid high-resolution quantitative 3D-PAT images of the synovial microvasculature that can be used to distinguish between inflamed and non-inflamed joints, and assess the severity of active inflammation.

ADVANCES IN KNOWLEDGE: The 3D-PAT FP scanner reliably distinguishes between affected and unaffected finger and wrist joints in patients with rheumatoid arthritis. Compared to previous 2D PAT scanners used to image joint inflammation, it offers superior image quality and the prospect of mitigating operator-dependent variations in probe positioning by virtue of its 3D imaging capability.