부산대학교 도서관

Photo-acoustic skeletal quantitative ultrasound enables assessment of the fundamental flexural guided wave (FFGW) propagating in bone. This mode, consistent with the F(1,1) tube mode can now be measured through a coating of soft tissue. Interference due to ultrasound propagation in the soft tissue surrounding the bone is reduced by using phase-delayed ultrasound excitation. Photo-acoustic phase-delayed excitation was done on five axisymmetric bone phantoms (1–5 mm wall thickness), coated by a 5 mm thick soft-tissue mimicking layer. A fiber head comprising a linear array of four optical fibers (400 µm diameter), illuminated by pulsed laser diodes (905 nm wavelength) generated ultrasound. This sound was received by a small (10 mm diameter) custom-made piezo transducer from the top surface of the coating. Tuning the phase delay allowed selection of the excited mode(s). FFGW was detected in the 20–40 kHz band when the power ratio between FFGW and interference was tuned to a local maximum. This tuning removed interference and improved SNR of the FFGW mode by >10 dB. Fitting the theoretical F LC (1,1) mode of a liquid-coated (LC) tube to the measured FFGW phase-velocity provided accurate (11% ± 7% rms deviation) estimate for the cortical thickness. These results suggest that photo-acoustic phase-delayed excitation may enable in vivo assessment of cortical thickness based on FFGW.