MRI scans can distinguish different tissues in the body

The magnetic resonance imaging (MRI) scanners currently used for this job in hospitals are large and expensive.

But Princeton University is looking for ways to make scanners cheaper and smaller without affecting performance.

The breakthrough is down to a new way of detecting magnetic signals from water, its researchers told New Scientist magazine.

Portable imaging

But they stressed that there were still major hurdles to overcome before the technology could be used in a clinical setting.

To make images, conventional MRI scanners apply a strong magnetic field to the body.

From this, it can figure out the water content of any tissue it scans.

Different types of tissues within organs have different water contents, so this gives a detailed impression of the structures beneath the skin.

Water is composed of hydrogen and oxygen atoms - and when exposed to a strong magnetic field, the hydrogen atoms all become aligned in one particular direction.

A short pulse of radiowave energy sent through the tissue "knocks" the nuclei of these atoms out of alignment, but when the pulse ends, they snap back into place again.

During this "realignment", radiowaves are emitted - it is these that are captured and measured, and which allow computers to determine the water content of each section of tissue scanned.

It's interesting, but it's a long way to go before it becomes a viable imaging system Professor Peter Morris from Nottingham University's MRI centre

But conventional MRI scanners need to use big magnets that have to be chilled by complicated cooling systems, which is expensive.

Igor Savukov and Michael Romalis have shown that a device called an atomic magnetometer can detect magnetic signals from water without giant magnets or complicated cooling systems.

The atomic magnetometer is basically a small (4cm) glass container filled with hot, vaporised potassium suspended in a gas. With the help of lasers, it is possible to work out the magnetic signals of water samples nearby by looking at how the potassium atoms move within the glass container.

However, the magnetometer and the sample being analysed have to sit inside bulky shields to avoid background "noise" or interference from the surrounding environment, pointed out the researchers.

Eventually it should be possible to do away with the shielding and build a hand-held MRI machine that images tissues inside the body as easily as a digital camera takes a photo, they told New Scientist.

Professor Peter Morris from Nottingham University's MRI centre said: "It's interesting, but it's a long way to go before it becomes a viable imaging system.

"I don't think the big manufacturers of conventional MRI scanners will be quaking in their boots yet."

He said as well as overcoming the problem of background noise, the new device might have difficulty imaging deeper structures within the body.