Science & Environment

New probe 'lights up' blood clots in single scan

A blood clot highlighted in an MRI scan Image copyright Paul Caravan
Image caption The technique easily picked out a blood clot in the corotid artery of this rat

A new probe that sticks to blood clots so they can be seen in a PET scan has proved successful in rats - and will be tested in humans later this year, according to researchers in the US.

They say the technique can scan the entire body and pinpoint the location of large and small blood clots.

This would offer an advantage over present methods, which concentrate on individual parts of the body.

In the rat study, blood clots "lit up" brightly in a whole-body PET scan.

Speaking at a meeting of the American Chemical Society in Boston, the scientists said that if human trials were similarly successful, the technique could be available within a few years.

Peter Caravan, a research chemist at Massachusetts General Hospital, said that in many cases, the blood clots that caused strokes and heart attacks were actually small pieces broken off from a larger clot, somewhere else in the body.

"For instance, a piece of blood clot breaks off in the aorta, which is a big vessel, goes into the brain, into smaller vessels, and causes a stroke.

"So clinicians want to know, where is the culprit lesion [in the brain]... and also where's the source thrombus? Does it remain? Because if it remains, there's a high probability of another event," Dr Caravan told the BBC.

"Our idea is that from a single injection, the probe will travel through the body and find blood clots anywhere."

He and his colleagues made and tested 15 different probes before they found one that worked really well. It consists of a small peptide molecule that binds to the clot protein fibrin, coupled to a radioactive "label" that can be detected in the scanner.

The results in rats, published this week, were particularly promising because of how clearly the blood clots stood out.

"There's very little background signal here - we've got very high conspicuity," Dr Caravan said.

"We're hoping to start studies in humans later this year. And then it will take some years to prove to the regulatory agencies that this is indeed effective and accurate. That's the next stage of the journey."

Image copyright SPL
Image caption Could a PET scan pinpoint blood clots after a stroke?

Prof Jeremy Pearson is the Associate Medical Director (Research) at the British Heart Foundation. He said the results were preliminary, but was impressed by how well-suited the probe was to the task.

"I think there is mileage in this," Prof Pearson told BBC News.

"Clearly, it doesn't work for emergencies. But for people who have had a stroke and you want to find the thrombus a day or two later, it could be very useful.

"The disadvantage of any PET scanning technology is that you're exposing the patient to extra radiation. But there are plenty of examples now... where PET imaging is a useful adjunct - the additional radiation dose is not significant and it's outweighed by the benefits you might get."

He suggested that the scan could prove particularly valuable in searching for smaller clots.

"It really does have an advantage there, because your scan will pick up something wherever it is. I don't know that you'd do a whole body, but if you're looking across a whole limb, or a head and neck - that would be very helpful.

"You might well pick up things that you hadn't anticipated, you didn't know where they were, and you want to do something about it."

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