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MRI machine tracks brain's metabolism

September 21, 2004 By Helen Pilcher This article courtesy of Nature News.

Powerful imager scans patients with strongest-ever magnetic field.

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An unusually powerful magnetic resonance imaging (MRI) machine was unveiled today that should reveal not just the anatomy but also the metabolism of the human brain, say scientists at the University of Illinois at Chicago.

If it lives up to its promise, the machine should help researchers to probe how the brain thinks, learns, fights disease and responds to experimental therapies. But it will involve exposing patients to stronger magnetic fields than ever before.

MRI uses a combination of magnetism, radio waves and computing power to peer inside the body. Patients lie inside a large circular magnet. When turned on, the magnetic field causes the nuclei of certain atoms, including hydrogen, to line up. A pulse of radio waves is then sent through the magnetic field. The aligned nuclei absorb this radiation and emit it again, producing a signal that reveals the structure of the molecules in which the atoms sit.

Most MRI machines use magnets with field strengths of around 3 tesla (equivalent to around 30 fridge magnets). This allows researchers to image water molecules and create pictures of anatomical structures within the body.

At 9.4 tesla, the new machine's magnetic field is more than three times as strong. This will enable scientists to capture signals not just from molecules containing hydrogen, but also from the body's metabolic building blocks: sodium, phosphorus, carbon, nitrogen and oxygen atoms. This should allow them to watch metabolism in action.

Early warnings

Such detailed images should help doctors to spot the subtle changes in brain chemistry that precede disease, allowing them to offer treatments earlier.

It will also allow scientists to study how drugs are metabolised inside the brain, and map the molecular changes that accompany learning, says MRI researcher Penny Gowland from the University of Nottingham.

The researchers must now apply for approval to use their machine on patients. In the United States, the maximum approved magnetic field strength for an MRI scanner is 8 tesla.

Gowland thinks that the machine, which exposes patients to strong magnetic fields for around 20 minutes at a time, should be safe.

For some years after MRI was first used on patients in the 1970s, researchers worried that the magnetic fields involved were exerting unusual forces on the body's blood supply, possibly leading to cardiovascular problems. But human subjects have been exposed to magnetic fields of up to 8 tesla without any noticeable adverse effects, says Gowland.

However, Anthony Swerdlow, an epidemiologist and chair of the National Radiological Protection Board's Advisory Group on Non-Ionising Radiation, thinks more safety research is needed.

"We've no reason to think that there are any adverse health effects," he says. But he adds that there haven't been any long-term studies following up those exposed to high-strength magnetic fields. Carrying out such studies would help to allay any fears, he says.


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