How to see with sound - Jacques S. Abramowicz

譯者: Lilian Chiu 審譯者: Amanda Zhu

In a pitch-black cave, bats can’t see much.

在一片漆黑的洞穴裡， 蝙蝠能看見的不多。

But even with their eyes shut,

但就算閉著眼睛，

they can navigate rocky topography at incredible speeds.

牠們也能在崎嶇的地形快速飛行。

This is because a bat’s flight isn’t just guided by its eyes,

那是因為蝙蝠 不只是用眼睛來引導飛行，

but rather, by its ears.

牠們還要靠耳朵。

It may seem impossible to see with sound,

靠聲音來「看」似乎是不可能的，

but bats, naval officers, and doctors do it all the time,

但蝙蝠、海軍軍官， 以及醫生都經常這麼做，

using the unique properties of ultrasound.

靠的就是超音波的特性。

All sound is created when molecules in the air, water,

聲音的產生是因為空氣、水，

or any other medium vibrate in a pulsing wave.

或其他介質中的分子在波中振動。

The distance between each peak determines the wave’s frequency,

波峰之間的距離決定了波的頻率，

measured as cycles per second, or hertz.

測量單位是每秒完成的週期數，

也就是赫茲。

This means that over the same amount of time,

意思就是，在同樣的時間中，

a high frequency wave will complete more cycles than a low frequency one.

高頻率的波能完成的週期數

會比低頻率的波更多。

This is especially true of ultrasound,

對超音波更是如此，

which includes any sound wave exceeding 20,000 cycles per second.

頻率超過每秒兩萬個週期的聲波 都算是超音波。

Humans can't hear or produce sounds with such high frequencies,

人類無法聽見或發出 這麼高頻率的聲音，

but our flying friend can.

但我們這位會飛的朋友可以。

When it’s too dark to see, he emits an ultrasound wave with tall peaks.

當太黑看不見時，

牠就會發出波峰很高的超音波。

Since the wave cycles are happening so quickly,

因為波的週期出現得非常快，

wave after wave rapidly bounces off nearby surfaces.

所以一個接著一個的波 會快速撞擊附近的表面後反彈。

Each wave’s tall peak hits every nook and cranny,

每一個波的高波峰 都深入到表面的凹陷和縫隙中，

producing an echo that carries a lot of information.

產生帶著許多資訊的迴音。

By sensing the nuances in this chain of echoes,

蝙蝠能感測到 這一連串迴音的細微差異，

our bat can create an internal map of its environment.

因而在腦裡畫出這個環境的地圖。

This is how bats use sound to see,

這就是蝙蝠靠聲音來看的方式。

and the process inspired humans to try and do the same.

人類從這個方式得到靈感， 而試圖做同樣的事。

In World War One, French scientists sent ultrasound beams into the ocean

第一次世界大戰時，

法國科學家朝海洋發射超音波束，

to detect nearby enemy submarines.

以偵測鄰近的敵人潛艇。

This early form of SONAR was a huge success,

這種早期的聲納十分成功，

in large part because sound waves travel even faster through mediums

很大一部分的原因是聲波的行進速度

在像水這種分子 更緊實的介質中會更快。

with more tightly packed molecules, like water.

In the 1950s, medical professionals began to experiment with this technique

1950 年代，

醫療專業人員開始實驗這種技術，

as a non-invasive way to see inside a patient’s body.

用非侵入性的方式 來檢視病人的體內。

Today, ultrasound imaging is used to evaluate organ damage,

現今，超音波造影 可用來評估器官的損傷、

measure tissue thickness, and detect gallbladder stones, tumors,

測量組織厚度，

並偵測膽結石、腫瘤，以及血栓。

and blood clots.

But to explore how this tool works in practice,

為了探究這項工具實際上怎麼運作，

let’s consider its most well-known use— the fetal ultrasound.

我們就以它最知名的用途來說明——

胎兒超音波。

First, the skin is covered with conductive gel.

首先，皮膚上要塗抹傳導性凝膠。

Since sound waves lose speed and clarity when traveling through air,

因為聲波穿過空氣時 會失去速度和清晰度，

this gooey substance ensures an airtight seal

而這種黏答答的物質

能確保身體和發射超音波的魔杖之間

between the body and the wand emitting ultrasound waves.

能完全無縫相接。

Then the machine operator begins sending ultrasound beams into the body.

接著，操作儀器的人便開始 將超音波束送入身體。

The waves pass through liquids like urine, blood, and amniotic fluid

超音波會穿過液體， 比如尿液、血液，以及羊水，

without creating any echoes.

而不會產生任何迴音。

But when a wave encounters a solid structure, it bounces back.

但當超音波遇到固態的結構時，

就會反彈回來。

This echo is rendered as a dot on the imaging screen.

這迴音就會成為 造影螢幕上的一個點。

Objects like bones reflect the most waves,

骨頭這類物體會反射的波最多，

appearing as tightly packed dots forming bright white shapes.

呈現出來的結果就是密集的點，

形成明亮、白色的形狀。

Less dense objects appear in fainter shades of gray,

密度較低的物體 呈現出來則是較模糊的灰影。

slowly creating an image of the fetus’s internal organs.

慢慢創造出胎兒內部器官的影像。

To get a complete picture,

要得到完整的影像，

waves need to reach different depths in the patient’s body,

波必須要能夠觸及 病人體內各種不同的深度，

bypassing some tissues while echoing off others.

繞過一些組織，

並在某些組織上反彈產生迴音。

Since longer, low frequency waves actually penetrate deeper

較低頻率的長波能夠進入的深度

than short, high frequency ones,

比高頻率的短波更深，

multiple frequencies are often used together

因此通常會同時使用多種頻率，

and composited into a life-like image.

組合出栩栩如生的影像。

The operator can then zoom in and focus on different areas.

接著，操作機器的人可以針對 不同的區域放大影像。

And since ultrasound machines send and receive cascades of waves in real time,

因為超音波機器

能夠即時發送和接收一連串的波，

the machine can even visualize movement.

甚至可以把動作作視覺化呈現。

The waves used for medical ultrasound range from 2 million to 10 million hertz—

醫療超音波所使用的波，

範圍從兩百萬到一千萬赫茲不等。

over a hundred times higher than human ears can hear.

比人類耳朵能聽到的聲音 還要高一百倍以上。

These incredibly high frequencies create detailed images

這些超高的頻率能創造 很細緻的影像，

that allow doctors to diagnose the smallest developmental deviations

讓醫生能夠診斷出 大腦、心臟、脊椎等等

in the brain, heart, spine, and more.

在發育上極細微的偏差，

Even outside of pre-natal care,

在產前醫療以外的領域，

medical ultrasound has huge advantages over similar technologies.

醫療用超音波也比其他 類似技術更有優勢。

Unlike radiation-based imaging or invasive surgical procedures,

不像要用到輻射的造影技術

或者侵入性手術，

ultrasound has no known negative side effects when used properly.

超音波在使用恰當的情況下 沒有任何已知的不良副作用。

At very high levels, the heat caused by ultrasound waves

高強度超音波所產生的熱

can damage sensitive tissues,

可能會傷害到敏感的組織，

but technicians typically use the lowest levels possible.

但技術人員通常會 盡可能用最低的強度。

And since modern ultrasound machines can be small and portable,

因為現代的超音波機器 可以做得很小、可攜帶，

doctors can use them in the field—

醫生可以在外頭使用——

allowing them to see clearly in any medical emergency.

讓他們在任何醫療緊急狀況時 都能看得很清楚。