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X射线如何“看穿”你

How X-rays see through your skin - Ge Wang

《TED教育》 值得分享的课程
In 1895, a physicist named Wilhelm Roentgen
1895年 一位名为威廉·伦琴的物理学家
was doing experiments with a cathode tube,
正在用阴极射线管做实验
a glass container in which
阴极射线管是一个玻璃容器
a beam of electrons lights up a fluorescent window.
其中的电子束能使荧光屏发光
He had wrapped cardboard around the tube
伦琴用纸板包裹住射线管
to keep the fluorescent light from escaping,
以防止荧光照到管外
when something peculiar happened.
这时奇怪的事情发生了
Another screen outside the tube was glowing.
射线管外部的一块荧光屏发着光
In other words, invisible rays had passed through the cardboard.
换句话说 有不可见光透过了纸板
Wilhelm had no idea what those rays were, so he called them X-rays,
伦琴不知道那是什么 所以称之为X射线
and his discovery eventually won him a Nobel Prize.
这一发现最终为他赢得了诺贝尔奖
Here’s what we now know was happening.
我们来解释一下这是怎么回事
When high energy electrons in the cathode tube hit a metal component,
当阴极射线管中的高能电子撞击金属部件时
they either got slowed down and released extra energy,
它们要么运行受阻变慢 释放多余能量
or kicked off electrons from the atoms they hit, which triggered a reshuffling
要么将金属原子的电子撞出
that again released energy.
引发再次释放能量的结构重组
In both cases, the energy was emitted in the form of X-rays,
两种情况下 能量都以X射线的形式释放
which is a type of electromagnetic radiation
X射线 是一种能量高于可见光
with higher energy than visible light, and lower energy than Gamma rays.
低于γ射线的电磁辐射
X-rays are powerful enough to fly through many kinds of matter
X射线非常强大 能穿透很多物质
as if they are semi-transparent,
仿佛那些东西都是半透明的
and they’re particularly useful for medical applications
它在医疗领域尤为有用
because they can make images of organs, like bones,
因为它能在不损伤器官的情况下
without harming them,
对骨骼等器官进行成像
although they do have a small chance
虽然确实存在很小的可能性
of causing mutations in reproductive organs, and tissues like the thyroid,
会导致生殖器官 甲状腺等组织的突变
which is why lead aprons are often used to block them.
所以人们常会穿上铅围裙来防护
When X-rays interact with matter, they collide with electrons.
当X射线与物体发生相互作用时 它们撞击电子
Sometimes, the X-ray transfers all of its energy to the matter and gets absorbed.
有时 X射线的所有能量转移到物体上并被吸收
Other times, it only transfers some of its energy, and the rest is scattered.
其他时候 只转移了部分能量 剩余的发生了散射
The frequency of these outcomes
以上不同情况的发生频率
depends on how many electrons the X-rays are likely to hit.
取决于X射线可能会撞击到的电子数量
Collisions are more likely if a material is dense,
如果物体比较致密 或其构成元素的原子序数较高
or if it’s made of elements with higher atomic numbers,
即意味着电子数也更多
which means more electrons.
那就更可能发生碰撞
Bones are dense and full of calcium,
骨骼致密且富含钙质
which has a relatively high atomic number,
相对来说钙原子序数较高
so they absorb X-rays pretty well.
所以它能很好地吸收X射线
Soft tissue, on the other hand, isn’t as dense,
而软组织就没那么致密
and contains mostly lower atomic number elements,
其构成元素也大多是低原子序数的
like carbon, hydrogen, and oxygen.
比如 碳 氢 氧
So more of the X-rays penetrate tissues like lungs and muscles,
所以对于肺 肌肉等 更多的X射线穿透了组织
darkening the film.
使影像变暗
These 2-D pictures are only useful up to a point, though.
但这些2D图像的用途比较有限
When X-rays travel through the body,
当X射线穿越人体
they can interact with many atoms along the path.
一路上会和很多原子发生相互作用
What is recorded on the film reflects the sum of all those interactions.
在X光片上记录的 是这些相互作用的总和
It’s like trying to print 100 pages of a novel on a single sheet of paper.
这就好比 要在一页纸上打印出100页的小说
To see what’s really going on,
想获知准确信息的话
you would have to take X-ray views from many angles around the body
必须从身体的多个角度 拍摄多张X光片
and use them to construct an internal image.
并以此构建出身体的内部图像
And that’s something doctors do all the time in a procedure called a CT,
其实这就是医生们一直在用的CT检查
Computed Tomography scan,
即电子计算机断层扫描
another Nobel Prize winning invention.
是另一项荣获诺贝尔奖的发明
Think of CT like this.
可以这样来理解CT
With just one X-ray,
如果只拍一张X光片
you might be able to see the density change due to a solid tumor in a patient,
由于患者的实体肿瘤 你可能会发现光片上的密度变化
but you wouldn’t know how deep it is beneath the surface.
但是你无法获知肿瘤距离体表的深度
However, if you take X-rays from multiple angles,
然而 如果拍摄多个角度的X光片
you should be able to find the tumor’s position and shape.
就应该可以探测到肿瘤的位置和形状
A CT scanner works by sending a fan or cone of X-rays
CT扫描的原理是 向病人发射扇形或锥形的X光束
through a patient to an array of detectors.
光束透过人体后由探测器接收
The X-ray beam is rotated around the patient,
X光束绕病人旋转
and often also moved down the patient’s body,
通常 病人躺着的扫描床还会向下移动
with the X-ray source tracing a spiral trajectory.
使X射线扫描轨迹呈螺旋状
Spiral CT scans produce data
螺旋CT的成像数据
that can be processed into cross sections detailed enough to
经处理后可得到详尽的横断面信息
spot anatomical features, tumors, blood clots, and infections.
能从中看到解剖结构 肿瘤 血栓 感染
CT scans can even detect heart disease and cavities
CT扫描甚至能在掩埋千年的木乃伊中
in mummies buried thousands of years ago.
发现心脏病和龋齿
So what began as Roentgen’s happy accident has become a medical marvel.
始于伦琴的意外惊喜发现 成了医学上的奇迹
Hospitals and clinics
现今 全球范围内
now conduct over 100 millions scans each year worldwide
每年在医院和诊所进行的扫描超过1亿次
to treat diseases and save lives.
用以治疗疾病 挽救生命

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视频概述

X射线是怎么发现的,它的应用有哪些,CT又是什么?

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视频来源

https://www.youtube.com/watch?v=gsV7SJDDCY4

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