Division of Medical Engineering, Research Center for Medical Sciences, The Jikei University School of Medicine, 3-25-8, Nishi-shinbashi, Minato-ku, Tokyo 105-8461, Japan.
Department of Neurology, The Jikei University School of Medicine, 3-25-8, Nishi-shinbashi, Minato-ku, Tokyo 105-8461, Japan.
Ultrasonics. 2015 May;59:94-101. doi: 10.1016/j.ultras.2015.01.017. Epub 2015 Feb 7.
For safe and efficient sonothrombolysis therapies, accurate estimation of ultrasound transmittance through the human skull is essential. The present study clarifies uncertainty surrounding this transmittance and experimentally verifies the equalization of transmittance through the modulation of ultrasound frequency. By changing three factors (ultrasound frequency, the thickness of a bone-phantom plate, and the distance between a transducer and a bone-phantom plate), we measured the intensity of ultrasound passing through the plate. Two activating methods, sinusoidal waves at 500 kHz and modulated waves, were compared. When we changed (1) the distance between a transducer and a bone-phantom plate and (2) the thickness of the bone-phantom plate, ultrasound transmittance through the plates substantially fluctuated. The substantial fluctuation in transmittance was observed also for a cut piece of human temporal skull bone. This fluctuation significantly declined for the modulated wave. In conclusion, modulation of ultrasound frequency can equalize the transmittance with an approximately 30-65% fluctuation drop and an approximately 40% fluctuation drop for a bone-phantom plate and for a cut piece of skull bone, respectively. By using modulated waves, we can develop safer and more effective sonothrombolysis therapies.
为了实现安全、高效的超声溶栓治疗，精确估计超声通过人体颅骨的透射率至关重要。本研究阐明了该透射率的不确定性，并通过调制超声频率来验证透射率的均衡性。通过改变三个因素（超声频率、骨仿体板的厚度以及换能器与骨仿体板之间的距离），我们测量了穿过板的超声强度。比较了两种激发方法，即 500 kHz 的正弦波和调制波。当我们改变（1）换能器与骨仿体板之间的距离和（2）骨仿体板的厚度时，板的超声透射率会发生显著波动。在人颞骨的切骨样本中也观察到了透射率的显著波动。调制波显著降低了透射率的波动。总之，调制超声频率可以均衡透射率，使波动分别降低约 30-65%和 40%，对于骨仿体板和颅骨切片分别如此。通过使用调制波，我们可以开发更安全、更有效的超声溶栓治疗。
