Rethinking MRI scans
Feb 23, 2009 1 comment
Biomedical engineers in Switzerland have discovered a new way of using magnetic resonance imaging (MRI) scanners to produce images with more uniform quality. This technique could also remove the need for patients to be placed in a narrow tube, making the experience less intimidating, especially for children.
In a standard MRI scan, a magnetic field is applied to a body, causing the magnetic moments of hydrogen atoms to align. Following this, a radio frequency is targeted at the area to be imaged, knocking the moments out of alignment. As the hydrogen atoms relax they emit radio waves and these can be mapped to form images of the interior of the body.
Since the first MRI scan produced a blurry image of a human body in 1977, the machinery has been refined to produce high-quality medical images, particularly of soft tissues that are not well depicted in X-rays. However, an unpleasant aspect of the process is that radio wave interaction has to take place at close quarters with the patient; this is on account of the short range of standing radio waves.
Now, in a radical rethink of the process, a team led by David Brunner of the University of Zurich has demonstrated a new way of manipulating hydrogen atoms to produce images by using travelling radio waves sent and received by an antenna. Operators will now be able to produce clearer images over larger areas of the body, and the new technique would free up space around the patient, say the researchers.
Long range MRI
Brunner and his colleagues have scrapped the radio coils of classic MRI scanners and replaced them with a waveguide and remote antenna. Apart from this, their MRI technique remains unchanged from the classic process. Essentially, they have replaced a standing radio wave interaction with travelling radio wave interaction, which has a range of metres.
We had hit a bit of a wall with using higher fields so this has now broken open the ceiling for obtaining higher quality images. Philip Grandinetti, Ohio State University
In their demonstration, Brunner and his team placed the cylindrical waveguide into a 7 Tesla scanner and placed an antenna at one of the ends. They used this arrangement to generate images of the lower leg of a human volunteer. Reporting their results in Nature (457.07752), they compare their images with those from a traditional scan and show a much improved resolution.
According to the researchers this amendment to the traditional MRI scan would not require any alteration to existing equipment beyond the introduction of a waveguide and antenna. “The technology is quite simple and in some ways actually simpler than the existing solutions. It is also arguably safer because the transmitter is further removed from the patient,” said Klauss Pruessmann, one of the researchers at the University of Zurich.
Philip Grandinetti, an MRI researcher at Ohio State University, told physicsworld.com, “In theory, hospital implementation could be almost immediate. We had hit a bit of a wall with using higher fields so this has now broken open the ceiling for obtaining higher quality images.”
Within the European Union, a hindrance may come from the legislation of 2004 set to restrict occupational exposure to electromagnetic fields. After being met with considerable protest by the MRI community, implementation of the MRI and Physical Agents (EMF) Directive has been postponed until 2012 to allow a more amicable solution to be sought. But given the 7 Tesla fields required by this new technique, compared with the 3 Tesla of ‘standard’ machines, adoption of this new technique could face political barriers.
“We will use travelling-wave approach for uniform coverage of large volumes, such as the entire head, for neuroscientific studies. We will also investigate the combination of travelling-wave excitation with close-range array detection, which would combine uniform and safe excitation with sensitivity benefits of array detection,” Pruessmann told physicsworld.com.
About the author
James Dacey is a reporter for physicsworld.com