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New technique lets MRI scanner see individual cells

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Saturday, May 17, 2003
By Anne McIlroy
The Globe and Mail

Canadian researchers have found a way to use ordinary hospital MRI scanners to see individual white blood cells, a discovery that could lead to the earlier diagnosis of diseases such as cancer and multiple sclerosis.

The researchers' work has given scientists studying spinal-cord injuries, MS, cancer and other illnesses a new tool to look at how those diseases begin and progress in laboratory animals.

MRI scanners are used in hospitals around the world as a non-invasive way (no blood samples or biopsies) to get a picture of internal organs and tissues, but they are not powerful enough to see individual cells.

This means that they can see the end results of a disease such as cancer, but cannot detect the earlier stages at a cellular level. "You see the tumour or the lesions, but it is really way too late at that stage, in our opinion," says Paula Foster-Gareau, a biologist at the Robarts Research Institute in London, Ont.

If doctors could see individual cells with an MRI, they could more easily tell if a case of cancer that had been in remission had returned. They might also be able to see if drugs they had administered were working properly.

Dr. Foster-Gareau and biophysicist Brian Rutt, also at the Robarts Research Institute, say they have found a way to trick MRI machines into seeing white blood cells, which fight infection and help clear away cellular debris, and play a role in many illnesses.

"We feed white blood cells iron oxide particles," she said. She grew white blood cells known as macrophages in a culture and then added iron oxide. Macrophages gobble up foreign material in the body, so they quickly absorbed the iron oxide.

An MRI scanner uses radio waves and a strong magnetic field rather than X-rays to provide detailed pictures of internal organs and tissues. Because iron oxide is magnetic, it causes a distortion in the magnetic field that can be picked up by the scanner.

The Robarts team also developed custom hardware that allowed the MRI scanner at the London Health Sciences Centre to see cells that had been fed iron oxide. They looked like black dots, Dr. Foster-Gareau said. "Each dot represented a single cell."

Macrophages play a role in spinal cord injuries, although there is a debate over which type of macrophage has a positive role and which type has a negative role. The technique developed by Dr. Foster-Gareau and Dr. Rutt would allow researchers to study in lab animals what happens, at a cellular level, in the first moments after a spinal cord injury occurs.

Macrophages are also involved in multiple sclerosis, a disease that damages the fatty tissue called myelin that helps nerve fibres conduct electrical impulses. Dr. Foster-Gareau says researchers would now be able to study the lesions they believe macrophages cause at the early stages of the illness.

Researchers around the world are working to find ways to make MRI scanners more effective. Other groups have imaged individual cells, but by using far more powerful machines than are used at hospitals.

The team at the Robarts institute, which focuses on developing new approaches to investigating and understanding neurological, cardiovascular and immune disorders, was the first to image individual cells using a modified version of technology that is widely available. Their discovery was published this month in a scientific journal called Magnetic Resonance in Medicine.

Iron oxide is already used as what is known as a contrast agent in MRI scans. A patient is injected with the substance so that doctors can get a clearer picture of what is happening in his liver, where macrophages take it up. A healthy liver will look black in a scan, but the area where a tumour has invaded will not change colour.

Doctors do not see individual liver cells because they do not have a specially adapted MRI scanner like the one used in London and because they are not looking for them. They are after the big picture, not what is happening at the cellular level.

The new technique, at this point, works best with macrophages. But the Robarts team is working on ways to get other kinds of cells, such as tumour cells, to absorb iron oxide.

So far, the research has involved only animals. If it is eventually used in humans, it would also involve injecting iron oxide into the body. The other possibility is to take white blood cells out of someone's body, feed the cells iron oxide and then reinject them.

Anne McIlroy is The Globe and Mail's science reporter.
 

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