One picture holds this word together: a sound that is really there but sits above the line where our hearing stops. Because it is so high, it travels in a narrow beam and bounces back off whatever it meets. Everything else the word names is a use people found for that: catch the echo and you get a picture of the inside of a body; send in more of it and it can work on the tissue itself.
這個字可以想成一種「越過我們聽力那條線」的聲音。它確實存在，只是我們聽不到。因為頻率很高，它走得很直，碰到東西會乾淨地彈回來。這個字的其他用法，都是人把這個特點拿來用的結果。接住回音，就能看見身體裡面；送進去多一點，就能對組織本身做事。所以先看見這個畫面，後面兩種用法就不用分開背。
From the word’s history
Wiktionary gives the word as ultra- + sound: ultra- marks going beyond a limit, and here the limit is human hearing.
字源資料把這個字拆成 ultra- 加 sound。ultra- 表示越過某條界線，而這裡被越過的界線，就是人耳聽得到的範圍。
Wiktionary entry for ultrasound, supplied in packet (source_ref kaikki:3f6f69a190036ae4:865718381)
登入就可以看每一支怎麼連回核心畫面。