Evaluation of bone surface roughness by a pulsed laser technique

For hard tissues such as bone, ultrasonic waves generated by pulsed laser techniques mainly originate from the solid surface and are affected by surface roughness. These waves may serve as indicators for evaluating bone diseases. This study examined the relationship between bone surface roughness and laser-induced ultrasonic wave characteristics. A pulsed laser (1064 nm, 2.5 ns, 81.5 mW) was focused on hydroxyapatite (HAp) and bovine cortical bone samples placed in degassed water. Infrared light was chosen for potential in vivo applications. Ultrasonic waves were detected using a hollow-focus PVDF transducer. The surface roughness (Ra) values of HAp samples were 0.05, 0.08, 0.28, 0.44, and 0.92 μm; the bone sample had an Ra of 0.39 μm. Ry values were 0.3, 0.7, 3.0, 4.7, and 9.6 μm for HAp samples, and 4.6 μm for bone samples. In HAp, wave amplitude increased with Ra, and higher amplitudes tended to show lower frequency components. Despite differences in material properties, the bone sample showed a similar amplitude—Ra trend. These results suggest that PA amplitude may be a useful indicator of surface roughness in hard biological tissues.