Using radioactive drugs to see inside your body - Pedro Brugarolas

譯者: Lilian Chiu 審譯者: Helen Chang

This syringe contains a radioactive form of glucose known as FDG.

這支注射器內有放射性形式的葡萄糖，

即氟化去氧葡萄糖（FDG）。

The doctor will soon inject its contents into her patient’s arm,

醫生馬上就要把這內容物 注射到病人的手臂中，

whom she’s testing for cancer using a PET scanner.

用正子斷層掃瞄 來為病人做癌症檢測。

The FDG will quickly circulate through his body.

FDG 很快就會透過循環 遍佈病人的全身。

If he has a tumor,

如果他有腫瘤，

cancer cells within it will take up a significant portion of the FDG,

腫瘤內的癌細胞 會吸收大量的 FDG，

which will act as a beacon for the scanner.

FDG 扮演的角色是 掃瞄器要偵測的信號 。

PET tracers such as FDG

正子斷層掃瞄的示蹤劑，如 FDG，

are among the most remarkable tools in medical diagnostics,

是醫療診斷最了不起的工具之一，

and their life begins in a particle accelerator,

它們是僅僅幾小時之前 從粒子加速器產生出來的。

just hours earlier.

The particle accelerator in question is called a cyclotron,

這裡談到的粒子加速器 叫做「粒子迴旋加速器」。

and it’s often housed in a bunker within hospitals.

它通常被放置在醫院 放射線室的掩體中。

It uses electromagnetic fields to propel charged particles

它用電磁場將帶電粒子加速，

like protons faster and faster along a spiraling path.

如質子，會延著螺旋路徑移動， 且速度越來越快。

When the protons reach their maximum speed,

當質子的速度達到最快時，

they shoot out onto a target that contains a few milliliters of a type of water

它們會被射向一個目標， 目標內含有幾毫升的一種水，

with a heavy form of oxygen called oxygen-18.

帶著重氧形式的氧氣， 稱為「氧-18」。

When a proton slams into one of these heavier oxygen atoms,

當質子撞上了 這些比較重的氧原子，

it kicks out another subatomic particle called a neutron.

便會踢掉另一個 亞原子粒子，即中子。

This impact turns oxygen-18 into fluorine-18,

這種衝擊會把氧-18 轉變成氟-18，

a radioactive isotope that can be detected on a PET scan.

它是一種放射性同位素， 正子斷層掃瞄器可以偵測到它。

In a little under two hours,

不到兩個小時，

about half the fluorine will be gone due to radioactive decay,

大約一半的氟因放射性衰變而消失，

so the clock is ticking to get the scan done.

所以，掃瞄必須要盡快完成。

So how can fluorine-18 be used to detect diseases?

所以，要如何 用氟-18 來偵測疾病？

Radiochemists at the hospital can use a series of chemical reactions

醫院中的放射能化學家 能使用一連串的化學反應

to attach the radioactive fluorine to different molecules,

將放射性氟附著到不同的分子上，

creating radiotracers.

創造出放射性示蹤劑。

The identity of the tracer depends on what doctors want to observe.

至於要用什麼來當示蹤劑， 就要看醫生想要觀察什麼了。

FDG is a common one because the rate at which cells consume glucose

FDG 是常用的示蹤劑， 因為細胞吸收葡萄糖的速度很快，

can signal the presence of cancer;

能夠呈現出是否癌症、 感染的所在位置，

the location of an infection;

or the slowing brain function of dementia.

或是失智症患者減緩的腦功能。

The FDG is now ready for the patient’s scan.

現在，病人掃瞄要用的 FDG 已經準備好了。

When a radiolabeled tracer enters the body,

有放射性標記的示蹤劑 在進入身體之後，

it travels through the circulatory system and gets taken up by its target—

就會透過循環系統移動， 並被目標吸收——

whether that's a protein in the brain, cancer cells, or otherwise.

目標有可能是腦中的蛋白質、 癌症細胞，或其他東西。

Within a few minutes,

在幾分鐘之內，

a significant amount of the tracer has found its way to the target area

相當大量的示蹤劑 就找到了目標區域，

and the rest has cleared from circulation.

其他的示蹤劑則不再 存在於循環當中。

Now the doctors can see their target using a PET,

現在，使用「正子斷層掃瞄」， 也就是 PET、掃瞄器，

or positron emission tomography, scanner.

醫生就可以看見他們的目標。

The radiation that the tracer emits is what makes this possible.

這種方式之所以可行， 是因為示蹤劑會放出放射線。

The isotopes used in PET decay by positron emission.

正子斷層掃瞄中所使用的同位素， 會因為釋放陽電子而衰變。

Positrons are essentially electrons with positive charge.

基本上，陽電子就是 帶著正電的電子。

When emitted, a positron collides with an electron

釋放時，陽電子會撞擊到

來自周圍其他分子的電子。

from another molecule in its surroundings.

This causes a tiny nuclear reaction

結果會造成小型的核反應，

in which the mass of the two particles is converted into two high-energy photons,

在反應中，這兩個粒子 會被轉換成兩個高能光子，

similar to X-rays,

很類似 X 光，

that shoot out in opposite directions.

朝相反方向射出。

These photons will then impact an array

接著，這些光子會撞擊

of paired radiation detectors in the scanner walls.

掃瞄牆上的成對放射線偵測器。

The software in the scanner uses those detectors

掃瞄器中的軟體會使用這些偵測器

to estimate where inside the body the collision occurred

來估計撞擊發生在 身體中的哪個位置，

and create a 3D map of the tracer’s distribution.

再繪製出示蹤劑分佈的 3D 地圖。

PET scans can detect the spread of cancer

比起其他種類的照影技術，

before it can be spotted with other types of imaging.

正子斷層掃瞄能更早 偵測出癌症的擴散。

They’re also revolutionizing the diagnosis of Alzheimer’s disease

它也為阿茲海默症的 診斷帶來了革命，

by allowing doctors to see amyloid,

讓醫生可以看見澱粉體，

the telltale protein buildup that otherwise couldn’t be confirmed

要不然，這種具有指示 用途的蛋白質增長，

without an autopsy.

就一定得要靠解剖才能確認。

Meanwhile, researchers are actively working to develop new tracers

同時，研究者也致力於 開發新的示蹤劑，

and expand the possibilities of what PET scans can be used for.

將正子斷層掃瞄應用到 更多可能的用途上。

But with all this talk of radiation and nuclear reactions inside the body,

但，為了掃瞄，身體中得要有 上述這些放射線和核反應，

are these scans safe?

這樣安全嗎？

Even though no amount of ionizing radiation is completely safe,

雖然，不論游離輻射的劑量多少， 都不可能完全安全，

the amount of radiation the body receives during a PET scan is actually quite low.

在正子斷層掃瞄時身體 接收到的放射線量其實相當低。

One scan is comparable to what you’re exposed to over two or three years

一次掃瞄接觸到的放射線，等同於

暴露在天然的放射線來源 （如氡氣）兩到三年的量；

from natural radioactive sources, like radon gas;

or the amount a pilot would rack up

或飛行員在飛渡大西洋 二十到三十次之後

from cosmic radiation after 20 to 30 transatlantic flights.

所接收到的累計宇宙輻射量。

Most patients feel that those risks are acceptable

大部分的病人可以接受這樣的風險，

for the chance to diagnose and treat their illnesses.

因為可以換到診斷 和治療他們疾病的機會。