The quest for a universal signature for cancerous tissue may have taken a step forward with a fast three-dimensional imaging device. This uses ultrasonic emissions to highlight variations in electrical conductivity between healthy and diseased tissue, and it could also avoid the need for painful biopsies.
The technique, called Hall Effect Imaging (HEI), relies on the interaction between ultrasonic vibrations and strong magnetic fields to map the dielectric properties of the body. "What I'm hoping to have is something as sensitive and specific as MRI, but with the speed of ultrasound," says the technique's inventor, Han Wen, who is based at the National Institutes of Health in Bethesda, Maryland.
Wen hopes his HEI will complement magnetic resonance imaging (MRI) which uses nuclear magnetic resonance to produce tissue density maps of the body.
"Some published results suggest that breast tumours trigger large changes in tissue electrical parameters," he explains. This technique should work with other cancers since this change happens in all other tumours, he adds.
HEI works when an oscillating electric pulse is sent through the body while it is exposed to a strong magnetic field. This makes charged particles in the tissue vibrate. If the frequency of the pulse is high enough, then the vibrations can be detected using ultrasound sensors. By monitoring the intensity and the phase difference between the two signals a high contrast 3D image of the tissue inside the body can be constructed in real time.
Wen discovered the effect accidentally when he noticed unexpected electrical activity during MRI scans.
"The technique of choice for screening breast cancer is X-ray mammography," says Aaron Fenster, director of imaging in the Robarts Research Institute at the University of Western Ontario, London, Canada. He reckons that it will be some years before mammography will be replaced because it has such a high sensitivity, but he says this doesn't rule out the use of HEI.
HEI, says Fenster, appears to have one major advantage over existing techniques. HEI has a high specificity which means that false positives can be ruled out. At the moment, the only way to be completely sure is to take a biopsy.
This is precisely what Wen hopes to avoid with his invention, but HEI is still very much in its infancy. So far, Wen has only successfully tested tissue in the lab: he says it remains to be seen whether the same conductivity differences can be detected in the body. Wen has put together hand-held scanners in his laboratory but needs to build a full-body scanner.
This week a British company, Oxford Instruments, started building the supermagnet needed for the job. Although it is relatively small with a diameter of about 1.5 metres, it will have a massive magnetic field of 6 tesla and will take about a year to build.
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