How to see with sound - Jacques S. Abramowicz

翻译人员: Kai Liu 校对人员: Helen Chang

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

在一片漆黑的洞穴里 蝙蝠难以看得清楚

But even with their eyes shut,

但即便闭上眼

they can navigate rocky topography at incredible speeds.

蝙蝠依然能以惊人的速度穿越岩石地形

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

这是因为蝙蝠不单用眼睛去看路

but rather, by its ears.

而是用耳朵

It may seem impossible to see with sound,

似乎不可能用声音去看东西

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

但蝙蝠、海军军官和医生经常这样做

using the unique properties of ultrasound.

他们借助了超声波( Ultrasound )的特性

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

分子在空气、水或者是其他介质中 以脉冲波的形式振动

or any other medium vibrate in a pulsing wave.

进而产生声音

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

波峰间的距离决定了波的频率

measured as cycles per second, or hertz.

用每秒完成周期的次数 赫兹( hertz )来衡量

This means that over the same amount of time,

也就是说，在相同的时间里

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

高频率的波比低频率波完成更多的周期

This is especially true of ultrasound,

尤其是超声波

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

它包含了所有每秒完成 2万次以上周期的声波

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

人类听不到也无法发出如此高频的声音

but our flying friend can.

但我们的蝙蝠朋友就可以做到

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

当环境太暗看不清时 它会发出高峰值的超声波

Since the wave cycles are happening so quickly,

因为这种波的周期特别短

wave after wave rapidly bounces off nearby surfaces.

波又从附近的表面很快地反射回来

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

波的高峰遍布洞穴里的每一个角落

producing an echo that carries a lot of information.

产生携带大量信息的回声

By sensing the nuances in this chain of echoes,

通过感受一系列回声的细微差别

our bat can create an internal map of its environment.

蝙蝠就可以画出洞穴内部环境的地图

This is how bats use sound to see,

这就是蝙蝠用声音看东西的原理

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

这个过程启发了人类尝试做同样的事

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

在第一次世界大战中 法国科学家向海洋发射超声波

to detect nearby enemy submarines.

来探测敌方附近的潜水艇

This early form of SONAR was a huge success,

这个声呐雏形取得了巨大的成功

in large part because sound waves travel even faster through mediums

很大程度上因为一些介质 有更多紧密联系的分子，比如说水

with more tightly packed molecules, like water.

声波在这样的介质里传播地更快

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

在20世纪50年代 医学专业人员开始用这项技术做实验

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

以非侵入的方式检查病人身体的内部

Today, ultrasound imaging is used to evaluate organ damage,

今天超声成像被用来 评估器官损伤的情况

measure tissue thickness, and detect gallbladder stones, tumors,

测量组织厚度，探测 胆囊结石、肿瘤和血栓

and blood clots.

But to explore how this tool works in practice,

但要想弄明白如何 在实践中应用这项技术

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

让我们来看一种最出名的用途

胎儿超声

First, the skin is covered with conductive gel.

首先，皮肤由导电凝胶所覆盖

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

因为在穿过空气时 声波会损失一些速度和清晰度

this gooey substance ensures an airtight seal

这种黏性物质确保

身体和仪器棒之间 发射超声波的位置气密密封

between the body and the wand emitting ultrasound waves.

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

然后仪器操作员把超声束发射到体内

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

波穿过像尿液、血液、羊水这样的液体

without creating any echoes.

不产生任何回声

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

但当碰到固体结构时，波反弹回去

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

回声在成像屏幕上以点的形式呈现

Objects like bones reflect the most waves,

像骨头这样的物质反射大部分的波

appearing as tightly packed dots forming bright white shapes.

并以紧密点构成亮白形状

Less dense objects appear in fainter shades of gray,

密度较小的物质 以较模糊灰色的形状出现

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

慢慢地 显示出胎儿内部器官的图像

To get a complete picture,

要想得到完整的图像

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

波需要在病人身体里 到达不同深度的地方

bypassing some tissues while echoing off others.

绕开某些组织 并在其他部位反射

Since longer, low frequency waves actually penetrate deeper

因为长波、低频率波实际上 比于短波、高频率波渗透地更深

than short, high frequency ones,

multiple frequencies are often used together

操作员经常混用多种频率的波

and composited into a life-like image.

合成逼真的图像

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

这样操作员就可以放大 关注不同部位

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

因为超声仪器实时 发射并收到一系列的波

the machine can even visualize movement.

机器甚至可以把动作可视化

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

医用超声波的频率 在2百万到1千万赫兹之间

over a hundred times higher than human ears can hear.

在人耳能听到频率的100倍以上

These incredibly high frequencies create detailed images

这些非常高频的波合成了详细的图像

that allow doctors to diagnose the smallest developmental deviations

医生可以借此诊断

脑部、心脏、脊柱还有其他部位 最细微的发育性偏斜

in the brain, heart, spine, and more.

Even outside of pre-natal care,

即便在非产前检查的领域

medical ultrasound has huge advantages over similar technologies.

医用超声波仍比同类技术更具优势

Unlike radiation-based imaging or invasive surgical procedures,

不像辐射成像或侵入性手术

ultrasound has no known negative side effects when used properly.

只要使用得当 超声没有明显的副作用

At very high levels, the heat caused by ultrasound waves

具有很高能量的超声波产生的热量 可以毁坏敏感组织

can damage sensitive tissues,

but technicians typically use the lowest levels possible.

但是技师通常尽可能使用 最低能量的超声波

And since modern ultrasound machines can be small and portable,

因为现代超声仪器体积小且易于携带

doctors can use them in the field—

医生可以在工作场景下使用它们

allowing them to see clearly in any medical emergency.

这让医生们在任何紧急情况下 都可以看得一清二楚