Keywords: Low-Field MRI, Low-Field MRI

Motivation: The 64mT Hyperfine Swoop (Hyperfine Inc. Guilford CT) is a first-of-kind point-of-care (POC) commercial system to allow ‘patient-to-scanner’ imaging.

Goal(s): We report an independent technical benchmark analysis of this system’s power consumption in this study (pass-through measures of W, kWh, and A).

Approach: Performance benchmarks of MR systems power consumption was measured per-pulse sequence using consumer-grade instrumentation under continuous monitoring. Custom acquisition protocol using two portable 120V_AC NEMA-standard power banks were examined.

Results: A look-up benchmark table of empirical surge current draw (with 120V_AC), its implicit advisory, and a potentially viable protocol run example without 'wall' i.e. via stand-alone power supply are reported. 

Impact: POC-MR Instrumentation power benchmark considerations on a per-pulse-sequence power consumption basis provide key insights into protocol deployment, scheduling, and optimal scan resource management considerations in resource-limited settings. Successful pulse sequence protocol implementation with under resource-limited setting was also demonstrated.

Keywords: Low-Field MRI, Brain, Small vessel disease

Motivation: Field-cycling MRI makes it possible to characterise the clinical potential of endogenous spin-lattice R₁ image contrast that arises at ultra-low-magnetic field strengths.

Goal(s): Our goal was to examine the extent translated motion correction and denoising approaches improve the utility of R₁ mapping performed at ultra-low field.

Approach: : Improvements in sensitivity to differences in R₁ between tissue types and fitting accuracy were determined across brain and head tissues. 

Results: Improvements in sensitivity and goodness of fit were observed. Significant difference in R₁ values between regions of white matter and confluent small vessel disease were observed between 0.2 - 200 mT. 

Impact: The improvement in sensitivity of R₁ mapping using translated motion correction and denoising approaches provides new opportunities to assess the clinical potential of new endogenous image contrast mechanism at ultra-low field strengths. 

Keywords: Low-Field MRI, Low-Field MRI, denoising

Motivation: Low-field MRI holds the promise of expanding access to healthcare. The low signal-to-noise ratio (SNR) poses a significant challenge to acquiring diagnostically useful information in a reasonable scanning time. 

Goal(s): To overcome the challenge of low SNR in low-field MRI, achieving fast, self-supervised denoising.

Approach: A rapid 4D-denoising method utilizing the Zero-Shot-Noise2Noise framework is proposed, without the need for intensive network training.

Results: This method provides fast denoising in just 10-20 seconds per case and significantly boosts SNR efficiency, reducing the number of measrued TIs and TEs needed for precise, high-quality T₁/T₂ mapping.

Impact: This study's fast 4D-denoising approach revolutionizes low-field MRI by enhancing SNR without extensive training datasets, enabling faster, more efficient imaging and broadening diagnostic accessibility in resource-limited settings.

Keywords: Low-Field MRI, Simulations

Motivation: Accurate and precise simulation of low field MR, as well as simulation of high field MR with arbitrary granularity.

Goal(s): To assess and address the limitations in the Magnetic Resonance Integral Equation (MARIE) suite that prevent successful low field simulation.

Approach: We achieved these goals using a number of numerical analysis techniques, such as Taylor series approximations and Kahan summation.

Results: We successfully identified and addressed the limitations of MARIE, which we attributed to catastrophic loss of numerical precision. In doing so, we enabled low frequency and fine mesh simulation.

Impact: Low field and detailed simulation of coils would enable many applications, such as coil optimization, synthetic generation of MR data for machine learning algorithms, computational pulse sequence optimization, accurate safety assessments in simulation, among many other applications.

Keywords: Low-Field MRI, Low-Field MRI, Spatial encoding field, Evaluation method

Motivation: For non-linear encoding technology for portable MRI, the evaluation of encoding capability is by checking the image quality, which is time-consuming and hard to integrate into an optimization process. 

Goal(s): Here, we aim to propose a fast evaluation method for the encoding capability of rotational spatial encoding magnetic field (rSEM). 

Approach: The filling factor of local k-spaces is proposed to evaluate the encoding capability of an rSEM with non-linear gradients. 

Results: The proposed evaluation of encoding capability is fast and agrees with the resultant image quality.  It was used for angle selections to accelerate imaging, showing improved image quality experimentally. 

Impact: A rapid evaluation method for the encoding capability of rSEMs with non-linear gradients is validated using simulation and experimental data. It allows fast evaluations of SEMs without checking the image quality in a design process, which accelerate the optimization. 

Keywords: Data Processing, Low-Field MRI

Motivation: Applying the component imaging method to low-field MRI systems will face a main problem: low-SNR image data.

Goal(s): An optimized inversion method is proposed, aiming to give better results for image data with low SNR.

Approach: This paper proposes an optimized inversion method with the formula of the optimization problem combining intra- and inter-voxel constraints.

Results: The optimized method shows a better convergence rate avoiding the fragmentation of component images and the appearance of pseudo peaks in the spectrum.

Impact: This multi-component imaging approach can provide sub-voxel characterization and be applied to numerous applications of popular portable low-field MRI systems.

Keywords: Low-Field MRI, Susceptibility, Routine Protocols

Motivation: To investigate the performance of modernized low-field MRI relative to traditional systems for imaging near metallic devices within the clinical context.

Goal(s): To evaluate whether low-field MRI can offer a significant reduction in artifacts when using routine clinical protocols.

Approach: The artifact characteristics of 0.5 T, 1.5 T, and 3 T MRIs are compared in this ASTM F2119-07-based phantom study of common passive metallic devices.

Results: Low-field MRI demonstrated the capability to reduce susceptibility artifacts when imaging near metal-containing medical devices. However, artifact produced by some pulse sequences diverged from the anticipated field-dependence, highlighting the sizable effects of clinical protocolling.

Impact: This phantom study demonstrates that low-field MRI can image metallic devices with reduced artifact relative to 1.5/3 T systems using routine clinical protocols, highlighting opportunities for future in vivo studies involving implants and imaging in areas with magnetic susceptibility distortions.

Keywords: Low-Field MRI, Low-Field MRI, denoising, self-supervised learning, zero-shot learning, low SNR

Motivation: Low SNR per unit-time in low-field MRI results in noisy images when targeting both clinically acceptable resolution and acquisition times which may limit their diagnostic effectiveness.

Goal(s): We seek to improve low-field MRI SNR by means of deep-learning while overcoming the limitations of traditional supervised learning and without compromising denoising performance.

Approach: We build on:1)self-supervised method enabling training without having to collect ‘noise-free’ data and 2)zero-shot concept to achieve dataset-free and scan-specific denoising.Additionally,we adopted simplified architecture for fast training times.

Results: Our method showed high denoising performance for different SNR levels and contrasts within few seconds of processing time competing with well-established BM4D.

Impact: Our proposed denoising method, based on self-supervised zero-shot deep-learning, enables high-performance denoising within short processing times. This approach shows promise for speedy acquisitions and enhanced imaged quality in low-field, point-of-care settings.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Commercially available open source electronics will help lower the cost and increase accessibility of MRI scanners.

Goal(s): Here we characterise the performance of a commercially available, partially open source RF amplifier designed for low field (<100 mT) MRI

Approach: We examine the gain linearity and frequency stability of the RF amplifier and examine the behaviour of the RF amplifier when transmitting in to a 50 ohm load and RF coil.

Results: The RF amplifier performs well and has sufficient power for low field applications, making it an attractive open source option for low field MRI systems.

Impact: Commercially available open-source electronics will help fundamentally address the cost and access issues hampering the wide step adoption of MRI in low resource settings. In this work we characterise a commercial, partially open-source RF amplifier for low field MRI.

Keywords: Low-Field MRI, Low-Field MRI, Short T2, hard tissue, extremity imaging

Motivation: We have previously demonstrated the versatility of a portable 72mT extremity MRI scanner. Hard tissue imaging would enhance the system’s potential, but this remains to be demonstrated in low-field systems (<0.1T)

Goal(s): To explore the possibility of imaging samples with T2*<1ms, comparable to those bone or ligament.

Approach: We programmed a PETRA sequence into the MaRCoS opens-source console, and we compared images of short and long T2* samples resulting from PETRA and Spin Echo. 

Results: Image reconstructions show that samples with T2* as low as 800us can be successfully imaged with PETRA in conditions where Spin Echo outputs mostly noise. 

Impact: By successfully capturing signals from short T2* tissues, our research enhances  our 72mT portable MRI scanner utility designed for extremity imaging.

Keywords: Low-Field MRI, Contrast Agent, Low-Field MRI

Motivation: Point-of-care MRI systems have the potential to increase access to imaging. Contrast agents could enhance tissue differentiation at the ultra-low fields of these devices.

Goal(s): To characterize the performance of Gadolinium contrast agents on an FDA cleared, point-of-care MRI system to inform sequence optimization for in vivo imaging. 

Approach: Longitudinal relaxivities of six FDA approved gadolinium contrast agents were characterized at 64 mT on a point-of-care MRI device and used to optimize T1 imaging of white matter and CSF. 

Results: Longitudinal relaxivities increased at 64 mT compared to their 3 T values. Simulations showed enhancement could be well visualized within feasible sequence parameters. 

Impact: Point-of-care MRI systems have the potential to impact patient care by increasing access to imaging. This work explores the feasibility of contrast-enhanced imaging with FDA-approved agents at ultra-low field on a point-of-care MRI. 

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Single-sided MRI offers flexibility for the movements of the field-of-view (FoV) with respect to the magnet. This adds a degree-of-freedom for signal encoding especially when the gradients are non-linear.

Goal(s): We aim to optimize the trajectory of the FoV within a non-linear magnet field, generated by a single-sided magnet array for good signal encoding.

Approach: Genetic algorithm was used for the optimization. The fitness function includes the filling area of local k-spaces, an indicator of the encoding capability of non-linear gradient field.

Results: The optimized trajectories result in improved signal encoding and thus improved image quality.

Impact: This work provides an additional degree of freedom to encode signals using single-sided magnet/arrays besides the gradients of field patterns, to improve image quality. It extends the possibility to use a moving single-sided magnet/arrays for imaging.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: The field cycling (FC) scanner introduces an extra degree of freedom for adjusting the B0 field strength during both polarization and readout. However, the ideal readout Larmor frequency remains unexplored.

Goal(s): To investigate the optimal readout Larmor frequency for the non-uniform B0 (NuBo) scanner regarding SNR, T2*, and T2 dephasing. 

Approach: Controlled experiments at two Larmor frequencies, 1MHz and 2MHz, were conducted. Echo trains at these two frequencies were acquired.

Results: Results show that readout at a lower Larmor frequency could benefit from a longer echo train, and longer T2*, but with the penalty of a smaller initial signal amplitude.

Impact: This research conducted a comparison of the trade-off between SNR, T2* and T2 decay across various readout Larmor frequencies, potentially offering insights for researchers in the field of field cycling in the future.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Low-Field MR (LF-MRI) offers greater accessibility and reduced sensitivity to susceptibility artifacts, but it suffers from low SNR. As a result, novel denoising techniques hold great promise to improve image quality and promote broader clinical applications of LF-MRI.

Goal(s): This work introduces a novel MRI denoising technique that is based on self-supervised deep learning without requiring high SNR references.

Approach: Our technique, called SNAC-DL, employs a Self-supervised Network for Adaptive Convolutional Dictionary Learning using a complex-valued coil-to-coil ($\mathbb{C}$C2C) training strategy.

Results: SNAC-DL has been tested for lung MRI denoising at 0.55T to demonstrate efficient denoising while preserving the underlying image structure.

Impact: The proposed denoising technique holds significant potential to improve image quality for LF-MRI. This is expected to facilitate the broad adoption of LF-MRI to improve cost-effectiveness and enable new clinical applications that are traditionally challenging at high field strengths.

Keywords: Low-Field MRI, Low-Field MRI, Elastography

Motivation: To our knowledge, concomitant field effects in MRE have not been investigated yet, which might become of importance when translating MRE to low field MR systems.

Goal(s): Propose a framework to investigate concomitant field effects on MRE, in particular Hadamard-encoded 3D MRE at 0.55T.

Approach: A 6x6 encoding scheme is proposed to study the effects of concomitant fields on 3D MRE at 0.55T in phantom experiments.

Results: Phantom experiments demonstrated that the effects of concomitant fields on 3D Hadamard-encoded MRE at 0.55T are negligible.

Impact: A framework to assess concomitant field effects in MRE, in particular Hadamard-encoded 3D MRE at 0.55T in phantom experiments.

Keywords: Low-Field MRI, New Devices, Feild mapping robot

Motivation:  Measurement of  parameters like magnetic field and temperature inside a magnet bore is of interest at all MR magnetic field strengths to characterize the system and use that information for downstream image quality improvement or to determine safety thresholds.

Goal(s): Build and test a simple 3D movement robot.

Approach:   we design, build and test a simple 3D movement robot with a sensor holder as a standalone system using a Raspberry Pi and a 16 channel ADC hat.

Results:   The robot is capable of sub-millimeter measurements. We demonstrate the 3D field mapping of a 50mT scanner as an example use of the robot.

Impact:  We designed and built a $2000 3D field mapping robot to map a very low field scanner’s magnet. The system is standalone exploiting Raspberry Pi’s system on a chip architecture and is scalable to include 16 analog inputs (sensors).