Realistic photoacoustic simulations of articular cartilage

A simulation method was developed to generate realistic photoacoustic (PA) images for assessing osteoarthritis (OA) progression. OA, a common joint disease characterized by cartilage degradation, leads to disability and work loss. Early OA detection is challenging, and PA imaging shows promise for noninvasive assessment. The proposed simulation method integrated cartilage microstructure and geometry by combining optical and acoustic models. The extracellular matrix (ECM) was generated in the acoustic grid, and varied surface roughness was applied to represent healthy and OA cartilage. Optical absorption coefficients derived from cartilage compositions (water, collagen, proteoglycan) and scattering coefficients derived from Mie theory, and local variations of optical properties for OA cases were included. Monte Carlo methods simulated optical fluence and initial pressure, while 2-D k-Wave modeled acoustic propagation. Validation with in vitro measurements showed that normal cartilage exhibits a smooth, continuous PA signal from strong collagen absorption, whereas OA cartilage shows irregular surfaces, reduced PA signals, and increased local response due to surface damage and collagen loss. Some discrepancies in deeper regions highlight the need for further optimization.