How X-rays see through your skin - Ge Wang

譯者: Ann Chen 審譯者: 庭芝 梁

In 1895, a physicist named Wilhelm Roentgen

1895 年，一位物理學家 名叫威廉·倫琴

was doing experiments with a cathode tube,

使用一個陰極射線管 進行實驗

a glass container in which a beam of electrons lights up a fluorescent window.

在這個玻璃容器裡面， 有一串電子束點亮一個螢光屏幕

他用硬紙板包住整個管子

He had wrapped cardboard around the tube

to keep the fluorescent light from escaping,

以防止螢光散出

when something peculiar happened.

這時發生了一件奇怪的事

Another screen outside the tube was glowing.

在管子外面的 另一個螢幕居然發亮了

In other words, invisible rays had passed through the cardboard.

換言之，有看不見的射線 穿透了硬紙板

Wilhelm had no idea what those rays were, so he called them X-rays,

威廉不清楚那射線是什麼 於是他就稱它為 X-射線

and his discovery eventually won him a Nobel Prize.

他的發現後來 使他獲得了諾貝爾獎

Here's what we now know was happening.

我們目前所了解 當初發生的情況是這樣的：

當陰極射線管內的高能量電子

When high energy electrons in the cathode tube

hit a metal component,

撞擊一個金屬物質時

they either got slowed down and released extra energy,

電子的速度會變慢， 而釋放出多餘的能量

or kicked off electrons from the atoms they hit,

也可能會將金屬原子 碰撞出電子

which triggered a reshuffling that again released energy.

這會引發電子重新排列 而後釋出能量

In both cases, the energy was emitted in the form of X-rays,

這兩種情形，被釋出的能量 會以 X-射線呈現

which is a type of electromagnetic radiation

X-射線是一種電磁波

with higher energy than visible light, and lower energy than Gamma rays.

能量比可見光高 而比伽馬射線低

X-rays are powerful enough to fly through many kinds of matter

X-射線能量很強 可以穿透許多物質

as if they are semi-transparent,

讓這些物質 看起來像半透明一樣

and they're particularly useful for medical applications

X-射線在醫學領域特別有用

because they can make images of organs, like bones, without harming them,

因為它們能呈現器官的影像 - 例如骨頭 ，卻不會造成傷害

although they do have a small chance

然而，它們確實會有很小的機會

of causing mutations in reproductive organs,

可造成生殖器官

and tissues like the thyroid,

及以及體內組織 (如甲狀腺) 的突變

which is why lead aprons are often used to block them.

這就是為什麼要用鉛衣 來阻擋它們的理由

When X-rays interact with matter, they collide with electrons.

當 X-射線與物質交互作用時 它們與電子碰撞

Sometimes, the X-ray transfers all of its energy to the matter and gets absorbed.

有時候，X-射線會將全部能量 移轉給物質而被吸收

Other times, it only transfers some of its energy,

也有些時候，它只移轉一部分能量

and the rest is scattered.

而其餘的能量都散射掉

The frequency of these outcomes

發生這些結果的頻率

depends on how many electrons the X-rays are likely to hit.

全看 X-射線 可能撞擊電子的數量而定

Collisions are more likely if a material is dense,

以下的情形較容易產生碰撞： 當物質的密度高

or if it's made of elements with higher atomic numbers,

或者物質是由 原子數較高的元素所構成

which means more electrons.

也就是說這些物質 具有較多的電子

Bones are dense and full of calcium, which has a relatively high atomic number,

例如骨頭的結構緻密， 且富含鈣質，具有相對較高的原子序

so they absorb X-rays pretty well.

所以它們容易吸收 X-射線

Soft tissue, on the other hand, isn't as dense,

相對地，其他軟組織 結構較不緻密

and contains mostly lower atomic number elements,

大多數是包含 原子序較低的元素

like carbon, hydrogen, and oxygen.

例如碳、氫和氧

So more of the X-rays penetrate tissues like lungs and muscles,

因此，多數的 X-射線 會穿透如肺及肌肉的組織

darkening the film.

而使底片變暗

These 2-D pictures are only useful up to a point, though.

然而，這些 2-D 影像 的功能也僅止於此

When X-rays travel through the body,

當 X-射線穿過身體

they can interact with many atoms along the path.

在行經途中能與 許多原子交互作用

What is recorded on the film reflects the sum of all those interactions.

這些交互作用的總和 最後會記錄呈現在底片上

It's like trying to print 100 pages of a novel on a single sheet of paper.

這就像試著把 100 頁的小說 印在一張紙上

To see what's really going on,

為了能夠更進一步的瞭解

you would have to take X-ray views from many angles around the body

必須環繞身體的許多角度 照攝 X 光片

and use them to construct an internal image.

然後將它們組成 身體內部的影像

And that's something doctors do all the time

這就是醫生常做的一種檢查

in a procedure called a CT, Computed Tomography scan,

稱為 CT，電腦斷層掃描

another Nobel Prize winning invention.

這是另一項獲得諾貝爾獎的發明

Think of CT like this.

試著用以下的方式來想像 CT：

With just one X-ray,

如果只靠一張 X 光片

you might be able to see the density change due to a solid tumor in a patient,

也許能看到病人 因體內腫瘤所產生的密度改變

but you wouldn't know how deep it is beneath the surface.

但無法知道它在體表下有多深

However, if you take X-rays from multiple angles,

然而，如果從多重角度照 X 光片

you should be able to find the tumor's position and shape.

便能夠知道腫瘤的位置及形狀

A CT scanner works by sending a fan or cone of X-rays through a patient

電腦斷層掃描是將一個扇形或 錐狀的 X-射線射出，

to an array of detectors.

穿透病人之後， 由排成陣列的感應器接收

The X-ray beam is rotated around the patient,

X-射線環繞病人旋轉

and often also moved down the patient's body,

也經常會移動到病人身體下方

with the X-ray source tracing a spiral trajectory.

X-射線光源 沿著螺旋軌跡行進

Spiral CT scans produce data that can be processed into cross sections

螺旋電腦斷層掃描產生的數據 能被處理成橫斷面影像

detailed enough to spot anatomical features, tumors,

精細到可以標記出 解剖學上的特徵、腫瘤、

blood clots, and infections.

血塊及感染

CT scans can even detect heart disease and cavities

電腦斷層掃描甚至可以查出

in mummies buried thousands of years ago.

數千年前埋葬的木乃伊 的心臟疾病及蛀牙

So what began as Roentgen's happy accident has become a medical marvel.

當初倫琴的意外發現 如今已變成醫學奇蹟

Hospitals and clinics now conduct over 100 millions scans each year worldwide

現在，全世界的醫院和診所 每年執行超過一億次的掃描

to treat diseases and save lives.

來治療疾病及拯救生命