23 research outputs found
Microtesla MRI of the human brain combined with MEG
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 microtesla 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.Comment: 8 pages, 5 figures - accepted by JM
Recommended from our members
Sequential Read-Out Architecture for Multi-Channel SQUID Systems
The authors describe a novel multi-channel sequential SQUID read-out technique that requires fewer wires than conventional units and also simplifies the electronics significantly. They designed and experimentally tested the sequential read-out electronics with up to 8 channels using LTS 8x8 mm{sup 2} magnetometers with about 3fT/{radical}Hz field resolution. They have investigated noise performance, amplitude-frequency characteristics, and cross-talk of the sequential read-out electronics for 2, 4, and 8 channels. They observed field resolution better than 4fT/{radical}Hz, 6fT/{radical}Hz, and 9fT/{radical}Hz for 2-, 4-, and 8-channel versions, respectively. They observed 10 kHz frequency bandwidth for the 8-channel version using 200 kHz modulation frequency. Cross-talk better than {minus}90dB was measured for this system. A single-channel simulation was used to estimate the field resolution for systems with up to 128 channels. They found that the expected field resolution can be better than 15fT/{radical}Hz, 20fT/{radical}Hz, and 30fT/{radical}Hz for 32-, 64-, and 128-channel systems, respectively, with the sequential read-out technique
In vivo Observation of Tree Drought Response with Low-Field NMR and Neutron Imaging
Using a simple low-field NMR system, we monitored water content in a livingtree in a greenhouse over two months. By continuously running thesystem, we observed changes in tree water content on a scale of halfan hour. The data showed a diurnal change in water content consistentboth with previous NMR and biological observations. Neutron imaging experiments showthat our NMR signal is primarily due to water being rapidly transported through the plant, and not to other sources of hydrogen, such as water in cytoplasm, or water in cell walls. After accountingfor the role of temperature in the observed NMR signal, we demonstratea change in the diurnal signal behavior due to simulated drought conditionsfor the tree. These results illustrate the utility of our system toperform noninvasive measurements of tree water content outside of a temperature controlled environment
Multi-Channel SQUID System for MEG and Ultra-Low-Field MRI
A seven-channel system capable of performing both magnetoencephalography
(MEG) and ultra-low-field magnetic resonance imaging (ULF MRI) is described.
The system consists of seven second-order SQUID gradiometers with 37 mm
diameter and 60 mm baseline, having magnetic field resolution of 1.2-2.8
fT/rtHz. It also includes four sets of coils for 2-D Fourier imaging with
pre-polarization. The system's MEG performance was demonstrated by measurements
of auditory evoked response. The system was also used to obtain a multi-channel
2-D image of a whole human hand at the measurement field of 46 microtesla with
3 by 3 mm resolution.Comment: To appear in Proceedings of 2006 Applied Superconductivity Conferenc
Recommended from our members
Forward model for the superconducting imaging-surface meg system
We have recently completed a novel whole-head MEG system based on the Superconducting Imaging-Surface (SIS) concept originally proposed by van Hulsteyn, et al.[l]. The SIS concept is generally described as a source near a superconducting surface. The source field induces Meissner currents in the superconductor equivalent to a source image 'behind' the surface. A sensor (SQUIDS in our system) placed on the source-side of the SIS will measure the superposed fields from the real and image sources. A second consequence of the Meissner effect is to shield the SQUIDS sensors near the SIS from external or background fields. The shape of the SIS used in our MEG system is a hemisphere with two cut-outs at the nominal ear-locations. A brim is added around the entire periphery with a smooth 0.5 cm radius transition between brim and hemisphere. Benefits of the SIS concept over existing systems include significantly enhanced signal-to-noise as a consequence of the SIS shielding and inherently generating pseudo-first order gradient fields at the sensors. One of the most significant challenges in realizing this system has been to accurately describe how the SIS system impacts the forward physics of any source model. Two approaches have been examined. The first is a hybrid analytical and empirical model using the analytic formalism to describe the hemisphere [1] and a correction matrix derived from empirical measurements to correct for edge effects. This approach proved overly complex and difficult in practice to obtain sufficient empirical data to derive a well-conditioned correction matrix. The second approach, reported here, was to develop a boundary element model (BEM) description of the SIS using the exact as-built geometry. Each element is described by a uniform magnetization arising from a distribution of Meissner currents in the superconductor such that B{perpendicular} = 0 at the surface. B{sub i} at each element is a superposition of the source field and the fields resulting from currents in all other elements. A precision phantom was developed to test the model. Modeled and measured magnetic field distributions agreed with typically less than 1% (< 0.1% in most cases) discrepancy at all SQUID sensors for more than 60 phantom coil positions. The attached figure shows modeled and measured magnetic field distributions for 25 such phantom coils
Multi-sensor system for simultaneous ultra-low-field MRI and MEG
Magnetoencephalography (MEG) and magnetic resonance imaging at ultra-low
fields (ULF MRI) are two methods based on the ability of SQUID (superconducting
quantum interference device) sensors to detect femtotesla magnetic fields.
Combination of these methods will allow simultaneous functional (MEG) and
structural (ULF MRI) imaging of the human brain. In this paper, we report the
first implementation of a multi-sensor SQUID system designed for both MEG and
ULF MRI. We present a multi-channel image of a human hand obtained at 46
microtesla field, as well as results of auditory MEG measurements with the new
system.Comment: To appear in Proceedings of 15th International Conference on
Biomagnetis
Recommended from our members
Weld quality evaluation using a high temperature SQUID array
This paper presents preliminary data for evaluating weld quality using high temperature SQUIDS. The SQUIDS are integrated into an instrument known as the SQUID Array Microscope, or SAMi. The array consists of ll SQUIDs evenly distributed over an 8.25 mm baseline. Welds are detected using SAMi by using an on board coil to induce eddy currents in a conducting sample and measuring the resulting magnetic fields. The concept is that the induced magnetic fields will differ in parts of varying weld quality. The data presented here was collected from three stainless steel parts using SAMi. Each part was either solid, included a good weld, or included a bad weld. The induced magnetic field's magnitude and phase relative to the induction signal were measured. For each sample considered, both the magnitude and phase data were measurably different than the other two samples. These results indicate that it is possible to use SAMi to evaluate weld quality
SQUIDs in biomagnetism : A roadmap towards improved healthcare
This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 686865.Peer reviewedPublisher PD
On a Method For Reconstructing Computed Tomography Datasets from an Unstable Source
As work continues in neutron computed tomography, at Los Alamos Neutron Science Center (LANSCE) and other locations, source reliability over the long imaging times is an issue of increasing importance. Moreover, given the time commitment involved in a single neutron image, it is impractical to simply discard a scan and restart in the event of beam instability. In order to mitigate the cost and time associated with these options, strategies are presented in the current work to produce a successful reconstruction of computed tomography data from an unstable source. The present work uses a high energy neutron tomography dataset from a simulated munition collected at LANSCE to demonstrate the method, which is general enough to be of use in conjunction with unstable X-ray computed tomography sources as well