Photoacoustic tomography of carrageenan-induced arthritis in a rat model.

Laser-based photoacoustic tomography (PAT), a novel, nonionizing, noninvasive, laser-based technology, has been adapted to the diagnosis and imaging of inflammatory arthritis. A commonly used adjuvant induced arthritis model using carrageenan was employed to simulate acute rheumatoid arthritis in rat tail joints. Cross-sectional photoacoustic images of joints affected by acute inflammation were compared to those of the control. The diameter of the periosteum and the optical absorption of intra-articular tissue were measured on each joint image. Significant differences were found on PAT imaging between the affected joints and the control for both variables measured, including enlarged periosteum diameter and enhanced intra-articular optical absorption occurring in the joints affected with carrageenan-induced arthritis. Anatomical correlation with histological sections of imaged joints and microMRI results verified the findings of PAT. This suggests that PAT has the potential for highly sensitive diagnosis and evaluation of pathologic hallmarks of acute inflammatory arthritis.