Microtesla MRI of the human brain combined with MEG

Abstract

One of the challenges in functional brain imaging is integration of complementary imaging modalities, such as magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). MEG, which uses highly sensitive superconducting quantum interference devices (SQUIDs) to directly measure magnetic fields of neuronal currents, cannot be combined with conventional high-field MRI in a single instrument. Indirect matching of MEG and MRI data leads to significant co-registration errors. A recently proposed imaging method--SQUID-based microtesla MRI--can be naturally combined with MEG in the same system to directly provide structural maps for MEG-localized sources. It enables easy and accurate integration of MEG and MRI/fMRI, because microtesla MR images can be precisely matched to structural images provided by high-field MRI and other techniques. Here we report the first images of the human brain by microtesla MRI, together with auditory MEG (functional) data, recorded using the same seven-channel SQUID system during the same imaging session. The images were acquired at 46 microT measurement field with pre-polarization at 30 mT. We also estimated transverse relaxation times for different tissues at microtesla fields. Our results demonstrate feasibility and potential of human brain imaging by microtesla MRI. They also show that two new types of imaging equipment--low-cost systems for anatomical MRI of the human brain at microtesla fields, and more advanced instruments for combined functional (MEG) and structural (microtesla MRI) brain imaging--are practical.

Kinetic inductance magnetometer

“…U ltrasensitive magnetic detection is utilized in a variety of applications, such as magnetoencephalography 1 , magnetocardiography 2 , ultra-low-field NMR 3 and magnetic resonance imaging (ULF NMR and MRI) [4][5][6] , exploration of magnetic minerals 7 and a wide range of other scientific purposes. The most established method is to use superconducting quantum interference devices (SQUIDs) based on low critical temperature superconducting materials 8,9 as the sensor, featuring field sensitivity in the fT Hz À 1/2 regime or below.…”

Adaptive suppression of power line interference in ultra-low field magnetic resonance imaging in an unshielded environment

“…In order to verify this method in a wider frequency range, we chose the 1D imaging frequencies at 1.3 kHz and 4.8 kHz, because the 1~2 kHz range is a typical frequency range of the hybrid MRI-MEG application [11,12], and 4.8 kHz is a common imaging frequency of ULF MRI. To evaluate the robustness of the adaptive suppression in the case of low SNR, we applied frequency encoding gradients in this experiment to make the signal amplitude comparable to those of the noise peaks.…”

“…Hyperpolarization techniques, which significantly enhance spin population difference, were introduced in LF/ULF nuclear magnetic resonance (NMR) and MRI systems to obtain stronger SNR [5][6][7]. Some potential applications of ULF MRI have been demonstrated compared with high field MRI, e.g., enhanced contrast between cancerous and surrounding tissues [8,9], the possibility of imaging in the presence of metallic objects [10], the hybrid biomagnetic imaging of MRI and magnetoencephalography (MEG) [11,12] and the feasibility of neuronal current imaging [13][14][15]. Most of these advantages were achieved in a magnetically shielded room (MSR), which is costly, or in a shielded room made from aluminum a few millimeters thick.…”

Is There a Place for Clinical Neurophysiology Assessments in Synucleinopathies?

“…While MEG may be super i o r t o E E G e s p e c i a l l y f o r f u n c t i o n a l connectivity studies, its high cost and the impossibility to combine it directly with structural MRI remain important obstacles. In this respect the development of ultra low field MRI (ULF MRI) could be a very interesting new approach [103]. If this technology can be further developed high quality integrated structural and functional studies of brain networks may become feasible.…”