Magnetic resonance imaging (MRI) began its way in 1977, at first producing blurry images of the human body but gradually improving to produce high quality medical images, particularly of soft tissues. During a standard scan, a magnetic field is applied to the body which causes the hydrogen atoms, which are part of the water molecules in our bodies, to align. Special radio frequencies are then targeted at the area to be imaged and the atoms are knocked out of their alignment. As the hydrogen atoms try to return to the alignment, they emit radio waves, which are picked up by the machine and mapped to form images. Current clinical MRI systems normally operate at a field strength of 1.5 Tesla (T), which corresponds to a signal frequency of 64 MHz. Compared to higher fields, the current systems are less precise in measurements and yield images with lower spatial resolution. The test itself takes place in a confined tube in order to better catch the short-wave radio waves emitted.
David Brunner, a Ph.D. student at the University of Zurich, has recently demonstrated a novel way of enticing hydrogen atoms to produce images. He used traveling (propagating) radio waves which were sent and received by an antenna. Brunner says this technique may produce images of larger portions of the body and at the same time free up some space around the patient.
In his research, Brunner searched for the optimal conditions for creating propagating waves. He used a strong magnet with field strength of 7T. The size of the magnet’s tube (58 cm) allowed him to achieve propagation at resonate frequency of 300 MHz. Lined with a conductive material, the magnet’s bore effectively acts as a waveguide. Brunner used an antenna which generated traveling waves that passed through the entire body with nearly no loss. The resonance signals, which were also in the form of traveling waves, were then recorded by the same antenna. These recordings produced MRI images of greater coverage than those previously obtained at such a high field.
Traditional MRI scanning is based on near-field coupling, which means that the detector is placed as close as possible to the body in order to lose as small a portion of the signal as possible. However, with the presence of a strong field, such as 7T, the signal wavelength in the tissue is so short that stationary radiofrequency fields form “node regions,” from which no image information can be obtained. As a result, structures bigger than the wavelength such as the head cannot be fully covered. According to the researchers, the results of their study suggest that scientists should move away from stationary fields and adopt the use of traveling radiofrequency waves. This method, they say, will allow coverage of large parts of the body uniformly, while receiving the signals at a greater distance from the body.
However, the use of this technique is far from being ready for immediate clinical use. Aside from the need to conduct clinical trials, the creation of such strong magnetic fields remains very expensive. Therefore, the device will have to be proven cost effective and safe before it will come to widespread use.
TFOT has previously covered several developments in the MRI scan field. We have recently covered the discovery of a new contrast agent to be used in MRI scans, which was developed at the Delft University of Technology in the Netherlands .We have also brought you the world’s strongest MRI, at 9.4 Tesla, positioned at the University of Illinois in Chicago (UIC).
For more information on the revolutionized MRI scan please visit the ETH website.
Image icon credit: Aerts et al.