The Finnish researcher Jaakko Nieminen has developed a new device for researching the brain. Nieminen's hybrid MEG-MRI device produces more accurate data and makes it easier to diagnose brain diseases, sources from Aalto University report.
Magnetic resonance imaging (MRI) produces images of the human body with excellent soft-tissue contrast. Magnetic fields used for MRI typically exceed 1 Tesla. Magnetoencephalography (MEG) is a tool for functional brain imaging: an array of highly sensitive superconducting quantum interference device (SQUID) sensors is used to measure the weak magnetic field around the head produced by neuronal activity in the brain. It has been demonstrated that SQUID sensors can be used to measure also MR signals if amplitudes of the MRI fields are reduced and a prepolarization approach is applied. Ultra-low-field (ULF) MRI detects signals in fields around 100 mT and typically utilizes SQUID sensors for signal readout. The use of the same sensors in MEG and MRI offers significant benefits and has permitted to develop a single device capable of both MEG and MRI, according to the thesis recently published by the Department of Biomedical Engineering and Computational Science at Aalto University in Finland.
The thesis develops several techniques for ULF MRI and its combination with MEG. It shows that the origin of MR signals can be encoded by preparing the sample consecutively with spatially different polarizing fields. It is also demonstrated that by carefully designing the polarizing-field time course, contrast in ULF MRI can be improved. “This Thesis provides also a general method to reconstruct images, when the magnetic fields within the imaging region are nonlinear. In addition, this thesis describes how to design self-shielded polarizing coils with weak stray fields. Finally, a device for hybrid MEG-MRI was developed based on a commercially available whole-head MEG system”, according to the university.
The polarization-encoding method may ultimately enable MRI without phase encoding and become essential when developing new kinds of magnetic imaging. The contrast enhancement achieved with time-dependent polarizing fields may be useful when ULF MRI is applied for new purposes. In ULF MRI, the encoding gradients are relatively strong, therefore conventional reconstruction methods produce image artifacts, whereas the newly developed general reconstruction method performs much better, outlines the thesis. The self-shielded polarizing coils are essential when ULF MRI is performed inside magnetically shielded rooms, since otherwise strong eddy currents may be induced in the conductive shielding layers. “The instrumentation developed for hybrid MEG-MRI has been successfully used for brain imaging and establishes a solid basis for future research.”
Nieminen underlined that his hybrid MEG-MRI makes it possible to observe changes in the brain more accurately: “The device helps to observe things that are not visible from a traditional magnetic image. Also it does not make additional mistakes caused by measurements being taken with two different methods.”
“Nieminen's innovation produces higher quality images and achieves a unprecedented level of contrast”, university sources suggested, “making it easier to identify the characteristics of the brain's different tissues and, for example, to diagnose cancers. This will help the work of radiologists and neurosurgeons”.
In addition, the hybrid MEG-MRI device is more patient-friendly than traditional MRI. Thanks to its lower magnetic field it can also be used for imaging patients with pacemakers. “The new device is expected to come into regular use in the next few years. Nieminen's research group at Aalto University is now among the leaders in the field of brain imaging”, university sources concluded.