伊藤 貴司, 広瀬 昌紀, 河西 千広

Takashi ITOH, Masanori HIROSE, Chihiro KASAI

アロカ株式会社研究所

Research Laboratory, Aloka Co., Ltd.

キーワード : Resolution, Pulse width, Beam width, Degradation, Attenuation

Range and lateral resolution of ultrasonic diagnostic equipment, which largely depends on the pulse width and the beam width of a pulsed ultrasound wave radiated from a transducer, is an important factor in performance evaluation. It is considered that pulse and beam widths propagated in a medium with frequency dependent attenuation are different from those in a nonattenuating medium, hence resolution in living tissues may be inferior to that in water.
In this study, degradation of resolution in a medium whose attenuation coefficient is similar to living tissues was evaluated by computer simulation. A pulse width of -20 dB and a -6 dB beam width, which represent the range and the lateral resolution respectively, were calculated, assuming the transducer diameter, curvature and center frequency to be 13 mm, 75 mm and 3.5 MHz, respectively. By comparing the calculated results for propagation with and without attenuation, the following results were obtained. The pulse width of a wave reflected from a point target which is 150 mm in depth from the transducer, is elongated by about 0.5 μs in an attenuating medium. This means that the range resolution is degraded by about 0.4 mm. On the other hand, the lateral resolution for propagation with and without attenuation showed no significant difference, which suggests that the lateral resolution can be estimated from the result of a continuous wave in a nonattenuating medium.