A5079930346- Advanced MRI Techniques and Applications
- Atomic and Subatomic Physics Research
- Medical Imaging Techniques and Applications
- Advanced NMR Techniques and Applications
- NMR spectroscopy and applications
- Electrical and Bioimpedance Tomography
- Geophysical and Geoelectrical Methods
- Physics of Superconductivity and Magnetism
- Scientific Research and Discoveries
- Nuclear Physics and Applications
- Magnetic Field Sensors Techniques
- Advanced Neuroimaging Techniques and Applications
- Quantum and electron transport phenomena
- Geophysical Methods and Applications
- Biomedical and Engineering Education
- Seismic Waves and Analysis
- Electromagnetic Simulation and Numerical Methods
- Ultrasound and Hyperthermia Applications
- Functional Brain Connectivity Studies
- Electrostatics and Colloid Interactions
- Magnetic Properties and Applications
- Electromagnetic Scattering and Analysis
- Photoacoustic and Ultrasonic Imaging
- Seismic Imaging and Inversion Techniques
- Electrowetting and Microfluidic Technologies
Aalto University
2011-2021
Tieto (Finland)
2018
VTT Technical Research Centre of Finland
2018
University of California, Berkeley
2014
Abstract Ultra‐low‐field MRI uses microtesla fields for signal encoding and sensitive superconducting quantum interference devices detection. Similarly, modern magnetoencephalography (MEG) systems use arrays comprising hundreds of device channels to measure the magnetic field generated by neuronal activity. In this article, hybrid MEG‐MRI instrumentation based on a commercial whole‐head MEG is described. The combination ultra‐low‐field in single expected significantly reduce coregistration...
Globally, the demand for improved health care delivery while managing escalating costs is a major challenge. Measuring biomagnetic fields that emanate from human brain already impacts treatment of epilepsy, tumours and other disorders. This roadmap explores how superconducting technologies are poised to impact care. Biomagnetism study magnetic biological origin. Biomagnetic typically very weak, often in femtotesla range, making their measurement challenging. The earliest vivo measurements...
Surface currents provide a general way to model static magnetic fields in source-free volumes. To facilitate the use of surface magneto-quasistatic problems, we have implemented set computational tools Python package named bfieldtools. In this work, describe physical and principles toolset. be able work with arbitrary shape, discretize on triangle meshes using piecewise-linear stream functions. We apply analytical discretizations integral equations obtain field potentials associated discrete...
We present a novel open-source Python software package, bfieldtools, for magneto-quasistatic calculations with current densities on surfaces of arbitrary shape. The core functionality the relies stream-function representation surface-current density and its discretization triangle mesh. Although this technique is well-known in certain fields, to date related implementations have not been published or limited specific applications. With we aimed produce general, easy-to-use well-documented...
Eddy currents induced by applied magnetic-field pulses have been a common issue in ultra-low-field magnetic resonance imaging. In particular, relatively large prepolarizing field-applied before each signal acquisition sequence to increase the signal-induces walls of surrounding conductive shielded room. The transient generated eddy may cause severe image distortions and loss, especially with coils designed for vivo We derive theory thin conducting structures enclosures provide intuitive...
In the context of biomagnetism, a magnetically shielded room (MSR) is designed for shielding against external magnetic fields. Recently, several applications, such as combined structural resonance imaging (MRI) and functional magnetoencephalography (MEG), have emerged that require applying relatively strong fields inside MSR. These induce eddy currents magnetize MSR walls are made materials with high permeability conductivity. magnetization generate secondary disturb, e.g., MEG-MRI by...
Pulse-induced transients such as eddy currents can cause problems in measurement techniques where a signal is acquired after an applied preparatory pulse. In ultra-low-field magnetic resonance imaging, performed fields typically of the order 100 μT, signal-to-noise ratio enhanced part by prepolarizing proton spins with pulse much larger field and detecting Superconducting QUantum Interference Device (SQUID). The turn-off, however, induce large shielded room, producing inhomogeneous...
The prototypes of ultra-low-field (ULF) MRI scanners developed in recent years represent new, innovative, cost-effective and safer systems, which are suitable to be integrated multi-modal (Magnetoencephalography MRI) devices. Integrated ULF-MRI MEG could an ideal solution obtain functional (MEG) anatomical (ULF information the same environment, without errors that may limit source reconstruction accuracy. However, low resolution signal-to-noise ratio (SNR) ULF images, as well their limited...
With a hybrid magnetoencephalography (MEG)-MRI device that uses the same sensors for both modalities, co-registration of MRI and MEG data can be replaced by an automatic calibration step. Based on highly accurate signal model ultra-low-field (ULF) MRI, we introduce method eliminates error sources traditional co-registration. The includes complex sensitivity profiles superconducting pickup coils. In ULF are independent sample therefore well-defined. most basic form, spatial information...
Ultra-low-field (ULF) MRI (B0 = 10–100 µT) typically suffers from a low signal-to-noise ratio (SNR). While SNR can be improved by pre-polarization and signal detection using highly sensitive superconducting quantum interference device (SQUID) sensors, we propose to use the inter-dependency of k-space data parallel with up tens sensors readily available in ULF order suppress noise. Furthermore, prior information that an image sparsely represented integrated this consistency constraint further...
We have implemented a new field-tolerant low-critical-temperature superconducting quantum interference device current sensor with submicrometer Josephson junctions. The small junction area enables the fabrication of devices lower noise and higher tolerance against magnetic fields. An application benefitting from these properties is ultra-low-field resonance imaging (ULF MRI). In currently ongoing BREAKBEN project, technology being pushed forward by combining ULF MRI magnetoencephalography in...
Thermal motion of charge carriers in a conducting object causes magnetic field noise that may interfere with sensitive measurements near the object. In this paper, we describe method to compute spectral properties thermal from arbitrarily shaped thin objects. The is based on modeling divergence-free currents surface using stream function and calculating magnetically independent noise-current modes. By doing this, obtain power density as well its spatial correlations frequency dependence. We...
In ultra-low-field (ULF) MRI, applied fields on the order of 100 μT are present during measurement with one or more SQUID sensors. The current noise in coils that produce must be extremely small not to add measurement, especially when measured using magnetometer pickup coils. addition, allow other than most basic pulse sequences, often ramped up and down at millisecond time scales, requiring relatively high voltages a sufficient bandwidth. Since commercial power amplifiers far from...
For ultra-low-field MRI, the spatial-encoding magnetic fields generated by gradient coils can have strong concomitant leading to prominent image distortion. Additionally, using superconducting magnet pre-polarize magnetization improve signal-to-noise ratio of MRI. Yet spatially inhomogeneous remanence field due permanently trapped flux inside a pre-polarizing coil modulates and causes further distortion.We propose two-stage frequency-space (f-x) formulation accurately describe dynamics...
In ultra‐low‐field magnetic resonance imaging, arrays of up to hundreds highly sensitive superconducting quantum interference devices (SQUIDs) can be used detect the weak fields emitted by precessing magnetization. Here, we investigate noise amplification in sensitivity‐encoded MRI at various acceleration rates using a SQUID array consisting 102 magnetometers, gradiometers, or 306 magnetometers and cover whole head. Our results suggest that gradiometers are similar g ‐factor distribution. A...
The visually evoked field (VEF) maps at 80 ms after the stimulus onset.The contour step is 50 fT; red indicates out and blue into head surface.The green arrows depict surface projection of equivalent current dipoles fitted to data.This image from article by Vesanen et al (pp 1795-1804).
Magnetic fields associated with currents flowing in tissue can be measured non-invasively by means of zero-field-encoded ultra-low-field magnetic resonance imaging (ULF MRI) enabling current density (CDI) and possibly conductivity mapping human head tissues. Since applied to a are limited safety regulations only small fraction the passes through relatively high-resistive skull, sufficient signal-to-noise ratio (SNR) may difficult obtain when using this method. In work, we study relationship...
Superconducting QUantum-Interference Devices (SQUIDs) make magnetic resonance imaging (MRI) possible in ultra-low microtesla-range fields. In this work, we investigate the design parameters affecting signal and noise performance of SQUID-based sensors multichannel magnetometers for MRI brain. Besides sensor intrinsics, various sources along with size, geometry number superconducting detector coils are important factors image quality. We derive figures merit based on optimal combination data,...
In low-field and ultra-low-field MRI, concomitant fields can cause severe blurring distortion in traditional Fourier reconstruction. We have developed an improved image reconstruction framework based on our previously published method that uses a frequency–space formulation. It provides more accurate results with the cost of increased computation time. Known inhomogeneity other field nonidealities be incorporated into model to improve quality The will as open source.