| Autor: |
Kilappa V; Department of Physics, University of Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland., Moilanen P; Department of Physics, University of Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland., Salmi A; Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland., Haeggström E; Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland., Zhao Z; Department of Electrical Engineering, University of Oulu, P.O. Box 4500, 90014 Oulu, Finland., Myllylä R; Department of Electrical Engineering, University of Oulu, P.O. Box 4500, 90014 Oulu, Finland., Timonen J; Department of Physics, University of Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland. |
| Abstrakt: |
The fundamental flexural guided wave (FFGW) enables ultrasonic assessment of cortical bone thickness. In vivo, it is challenging to detect this mode, as its power ratio with respect to disturbing ultrasound is reduced by soft tissue covering the bone. A phase-delayed ultrasound source is proposed to tailor the FFGW excitation in order to improve its power ratio. This situation is analyzed by 2D finite-element simulations. The soft tissue coating (7-mm thick) was simulated as a fluid covering an elastic plate (bone, 2-6 mm thick). A six-element array of emitters on top of the coating was excited by 50-kHz tone bursts so that each emitter was appropriately delayed from the previous one. Response was recorded by an array of receivers on top of the coating, 20-50 mm away from the closest emitter. Simulations predicted that such tailored/phase-delayed excitations should improve the power ratio of FFGW by 23 ± 5 dB, independent of the number of emitters (N). On the other hand, the FFGW magnitude should increase by 5.8 ± 0.5 dB for each doubling of N. This suggests that mode tailoring based on phase-delayed excitation may play a key role in the development of an in vivo FFGW assessment. |
