All About Imaging

We often want to look inside a body or a cell and find out what's going on.

The problem with biology is that it’s complicated.  Even a single cell contains millions of tiny structures; a whole human being is even worse.  So if we need to know about one object in a cell or a person we need to be able to pick that object out amongst all the others.  Your mother is a familiar face, but could you pick her out in this lot ... ?

Imaging_about_crowd
Can you spot mum?

Actually it's a lot more challenging than this!

In a single cell the structures are absolutely tiny; in a person they are buried inside the body.  Not only do we have to make them bigger and stand out against the background, but we sometimes have to look inside a body; and we’re not very transparent – mother always said we were better doors than windows!

Imaging_About_betterdoor
People are not very transparent - we need to find ways of looking through them.

 

To make things even more difficult.

Modern medicine is often more interested in what’s going on than what’s there. These days we want to know how fast the tumour cells are dividing, or how much food they are using each hour.  The answer to all these issues is contrast.

Take a look at the picture below - what do you see?

Imaging_About_dog
Good dog.

A black dog.  Now what happens if I take the same photo at night?

Black dog at night
Black dog at night; a picture postcard scene.

 

 

 

 

 

 

 

 

If we still want to see what the dog is up to, we need to make the dog show up against the black of the night.  We need a contrast agent.

When Sherlock Holmes met the Hound of the Baskervilles, he could see the dog quite clearly despite the pitch black of the Dartmoor night.

 

Imaging_About_hound
Bad dog.

 

 

He could see The Hound, because the person controlling it had painted it with phosphorus.  The phosphorus glowed in the dark providing contrast between the dog and the night.  In imaging the phorphorus would be called a contrast agent.  Contrast agents help us pick-out the thing we're interested in even when it's surrounded by loads of other stuff.

There are lots of contrast agents in modern medical imaging: some are radioactive, some are metallic and some are simply bubbles of air.  Some work at tiny scales which can only be seen through a microscope - some work in a whole human body.  Imaging has changed a lot over the years - find out more.  In this section we will explore: microscopes, MRI, nuclear medicine, X-rays, and ultrasound.

 

*Hound of the Baskervilles Image courtesy of Randall Stock.