Optimized 3D co-registration of ultra-low-field and high-field magnetic resonance images

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 in multi-modal (Magnetoencephalography and MRI) devices. Integrated ULF-MRI and MEG scanners could represent an ideal solution to obtain functional (MEG) and anatomical (ULF MRI) information in the same environment, without errors that may limit source reconstruction accuracy. However, the low resolution and signal-to-noise ratio (SNR) of ULF images, as well as their limited coverage, do not generally allow for the construction of an accurate individual volume conductor model suitable for MEG localization. Thus, for practical usage, a high-field (HF) MRI image is also acquired, and the HF-MRI images are co-registered to the ULF-MRI ones. We address here this issue through an optimized pipeline (SWIM-Sliding WIndow grouping supporting Mutual information). The co-registration is performed by an affine transformation, the parameters of which are estimated using Normalized Mutual Information as the cost function, and Adaptive Simulated Annealing as the minimization algorithm. The sub-voxel resolution of the ULF images is handled by a sliding-window approach applying multiple grouping strategies to down-sample HF MRI to the ULF-MRI resolution. The pipeline has been tested on phantom and real data from different ULF-MRI devices, and comparison with well-known toolboxes for fMRI analysis has been performed. Our pipeline always outperformed the fMRI toolboxes (FSL and SPM). The HF-ULF MRI co-registration obtained by means of our pipeline could lead to an effective integration of ULF MRI with MEG, with the aim of improving localization accuracy, but also to help exploit ULF MRI in tumor imaging

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

High-Tc SQUIDs for magnetophysiology - development of a magnetometer system and measurements of evoked fields from hippocampal neurons in vitro

This thesis concerns development of a system based on a high-transition-temperature superconducting quantum interference device (high-Tc SQUID) magnetometer. The system has been designed and used for magnetic field recordings from brain slices, i.e. magnetophysiology.Magnetophysiology is a complementary method to electrophysiology, which is routinely used today. One aim of magnetophysiology is to aid in the assessment of the full nature of the signals in magnetoencephalography (MEG), which is a method for multi-channel whole-head recordings of magnetic fields from the brain.Dipole models of post-synaptic currents have been used to determine the magnetic fields above hippocampal slices. These simulations indicate that a high-Tc SQUID system with a sensor-to-sample separation as small as 65 \ub5m would have superior signal-to-noise ratio compared with the low-Tc SQUID systems previously used elsewhere.A directly-coupled magnetometer with a side length of 2~mm has been fabricated from a YBa2Cu3O7-δ thin film. The large input washer was composed of strips of 5 \ub5m width in order to prevent flux-trapping. The magnetic field noise of the magnetometer was 0.75 pT/Hz1/2 and the effective area was 0.071 mm2.A successful method has been developed for the ∼20 min transportation of the slices to the measurement lab.Evoked magnetic fields from transverse hippocampal slices from rats have been recorded. The magnetic fields were ∼5 pT and showed a high correlation with the excitatory post-synaptic potential measured in close connection to the magnetic field recordings.With further development of the system, it may be possible to verify a higher signal-to-noise ratio than experienced in low-Tc SQUID systems. This would enable fewer averages, resulting in shorter experiments. Magnetic field studies of less dense brain structures than the hippocampus could be possible

High-Tc SQUID gradiometer system for immunoassays

A high-Tc dc SQUID (superconducting quantum interference device) gradiometer was developed for magnetic immunoassays where magnetic nanoparticles are used as markers to detect biological reactions. The gradiometer was fabricated on a 5 × 10 mm2 SrTiO3 bicrystal substrate and has a gradiometer resolution of 2.1 pT cm−1 Hz−1/2. A magnetic signal was detected from a sample of 1 μl of Fe3O4 nanoparticles in a 40 mg ml−1 solution kept in a microcavity fabricated on Si wafers with Si3N4 membranes using MEMS (micro-electro-mechanical-systems) technology. It was found that volumes as small as 0.3 nl in principle would be detectable with our present device. This corresponds to a total number of particles of 2.2 × 107. The estimated average dipole moment per particle is 4.8 × 10−22 Am2. We are aiming at reading out immunoassays by detecting the Brownian relaxation of magnetic nanoparticles, and we also intend to integrate MEMS technology into our system

HTS SQUID measurements of evoked magnetic fields from transverse hippocampal slices

We have developed a high-transition-temperature superconducting quantum interference device system aimed at neuromagnetic measurements of evoked fields from in vitro brain slices. Recordings from transverse hippocampal slices from rat have been performed and they showed neuromagnetic fields of ∼ 5 p

Development of a High-Tc SQUID-Based System for Neurophysiology Studies In-Vitro

In this paper we report on the development of a system based on a high-T c SQUID (HTS) sensor for measurements of the neuromagnetic field generated by neurons inside tissue slices. SQUIDs have successfully been measured inside the system. The system white noise level is lower than 7 pT/Hz 1/2 , which is only slightly higher than previously reported 4.5 pT/Hz 1/2 for the same kind of SQUID measured inside a superconducting shield. \ua9 2006 IOP Publishing Ltd