Open-source magnetic resonance imaging : Improving access, science, and education through global collaboration

The authors would like to thank all the authors that are sharing their work open-source and all the supporters of the Open Source Imaging Initiative (OSI2). The project (21NRM05 and 22HLT02 A4IM) has received funding from the European Partnership on Metrology, co-financed by the European Union's Horizon Europe Research and Innovation Programme and by the Participating States. This research is funded by dtec.bw- Digitalization and Technology Research Center of the Bundeswehr. dtec.bw is funded by the European Union - NextGeneration EU. Part of the image reconstruction used here was developed by the CCP PETMR and CCP SynerBi (https://www.ccppetmr.ac.uk/), UK EPSRC grants EP/P022200/1, EP/M022587/1 and EP/T026693/1. This work made use of computational support by CoSeC, the Computational Science Centre for Research Communities via CCP-SyneRBI and CCPi. RG Nunes acknowledges funding from Fundação para a Ciência e a Tecnologia (grants UIDP/50009/2020 and LA/P/0083/2020). Ruben Pellicer-Guridi has been funded by the European Union's Marie Skłodowska-Curie project nr. 101030868. Open Access funding enabled and organized by Projekt DEAL.Peer reviewe

Versatile quadrature antenna for precise control of large electron spin ensembles in diamond

We present an easily reproducible inexpensive microwave antenna that can generate a strong and homogeneous magnetic field of arbitrary polarization, which enables fast and coherent control of electron spins over a large volume. Unlike preceding works, we present a resonant antenna that maintains its resonant behaviour regardless of the proximity of other experimental hardware components. This robustness is crucial as it enables, amongst others, using microscope objectives with short working distances to perform wide field imaging/sensing with bulk diamonds. The antenna generates a magnetic field strength of 22.3 A/m for 1 W total driving power, which doubles the power efficiency compared with previously reported patch antenna designs. The magnetic field homogeneity in a volume of $0.3 \text{mm}^3$, $0.5 \text{mm}^3$ and $1 \text{mm}^3$ is within 6\%, 8\% and 13\%, respectively. The antenna has a full width at half maximum bandwidth of $\sim$160 MHz and its resonant frequency can be tuned over a 400 MHz range via four capacitors or varactors. The antenna has been tested and found to remain within safe handling temperatures during continuous-wave operation at 8 W. The files required to reproduce this antenna, which can be built on a standard and affordable double sided PCB, are provided open-source. This work facilitates a robust and versatile piece of instrumentation, being particularly appealing for applications such as high sensitivity magnetometry and wide field imaging/sensing with Nitrogen Vacancy centers

T1 mapping in the rat myocardium at 7 Tesla using a modified CINE inversion recovery sequence

Purpose To evaluate the reproducibility and sensitivity of the modified CINE inversion recovery (mCINE-IR) acquisition on rats for measuring the myocardial T1 at 7 Tesla. Materials and Methods The recently published mCINE-IR acquisition on humans was applied on rats for the first time, enabling the possibility of translational studies with an identical sequence. Simulations were used to study signal evolution and heart rate dependency. Gadolinium phantoms, a heart specimen and a healthy rat were used to study reproducibility. Two cryo-infarcted rats were scanned to measure late gadolinium enhancement (LGE). Results In the phantom reproducibility studies the T1 measurements had a maximum coefficient of variation (COV) of 1.3%. For the in vivo reproducibility the COV was below 5% in the anterior cardiac segments. In simulations with phantoms and specimens, a heart rate dependency of approximately 0.5 ms/bpm was present. The T1 maps of the cryo-infarcted rats showed a clear lowering of T1 in de LGE region. Conclusion The results show that mCINE-IR is highly reproducible and that the sensitivity allows detecting T1 changes in the rat myocardium

3D-Spatial encoding with permanent magnets for ultra-low field magnetic resonance imaging

We describe with a theoretical and numerical analysis the use of small permanent magnets moving along prescribed helical paths for 3D spatial encoding and imaging without sample adjustment in ultra-low field magnetic resonance imaging (ULF-MRI). With our developed method the optimal magnet path and orientation for a given encoding magnet number and instrument architecture can be determined. As a proof-of-concept, we studied simple helical magnet paths and lengths for one and two encoding magnets to evaluate the imaging efficiency for a mechanically operated ULF-MRI instrument with permanent magnets. We demonstrate that a single encoding magnet moving around the sample in a single revolution suffices for the generation of a 3D image by back projection

Rotatable small permanent magnet array for ultra-low field nuclear magnetic resonance instrumentation: a concept study

Object We studied the feasibility of generating the variable magnetic fields required for ultra-low field nuclear magnetic resonance relaxometry with dynamically adjustable permanent magnets. Our motivation was to substitute traditional electromagnets by distributed permanent magnets, increasing system portability. Materials and Methods The finite element method (COMSOL® ) was employed for the numerical study of a small permanent magnet array to calculate achievable magnetic field strength, homogeneity, switching time and magnetic forces. A manually operated prototype was simulated and constructed to validate the numerical approach and to verify the generated magnetic field. Results A concentric small permanent magnet array can be used to generate strong sample prepolarisation and variable measurement fields for ultra-low field relaxometry via simple prescribed magnet rotations. Using the array, it is possible to achieve a pre-polarisation field strength above 100 mT and variable measurement fields ranging from 20-50 μT with 200 ppm absolute field homogeneity within a field-of-view of 5 x 5 x 5 cubic centimetres. Conclusions A dynamic small permanent magnet array can generate multiple highly homogeneous magnetic fields required in ultra-low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) instruments. This design can significantly reduce the volume and energy requirements of traditional systems based on electromagnets, improving portability considerably

2D cross-sectional plots of pre-polarisation field B_p along the x-axis (switched on).

<p>For array <i>A</i> with constant fill factor, curve 1 (solid line) corresponds to 12 magnets, curve 2 (dashed line) to 16 and curve 3 (dash-dotted line) to 24 magnets. For array <i>A</i> with constant magnet dimensions (L = 70 cm, d_m = 2.16 cm), curve 4 (dash-dotted line) corresponds to 24 magnets, curve 5 (dashed line) to 16 magnets and curve 6 (solid line) to 12 magnets. (a) In array A with constant fill factor 0.75, the field strength within the field of view (FOV) decreases with the number of magnets, since magnet volume and surface area increase. (b) For array <i>A</i> with constant magnet size, the field strength decreases with decreasing numbers of magnets. (c) Within the FOV the field inhomogeneity decreases slightly with decreasing numbers of magnets for both constant fill factor (c) and magnet size (d). In all cases, the field inhomogeneity within the FOV was well below 0.02% (200 ppm)</p

Comparison of simulated and measured magnetic fields generated by the SPMA prototype.

<p>Comparison of simulated and measured magnetic fields generated by the SPMA prototype.</p