Keywords: Low-Field MRI, Low-Field MRI

Motivation: Ultra-low-field (ULF) MRI technology holds significant promise for advancing medical imaging by offering low-cost and portable solutions for point-of-care applications. These advancements have the potential to improve access to medical imaging in resource-limited settings, thereby benefiting underserved populations and enhancing diagnostic capabilities to ultimately improve patient care. 

Goal(s): The implementation of a highly efficient protocol for ULF MRI.

Approach: A 3D bSSFP protocol was implemented and optimized. 

Results: The study successfully implemented bSSFP protocol at 0.05 T and demonstrated its utility for imaging the brain, cervical spine, and knee.

Impact: In this study, a bSSFP protocol was successfully implemented at 0.05 T by  demonstrating its utility for imaging the brain, cervical spine, and knee. These findings enable the potential of high-quality ULF MRI. 

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Magnetic resonance spectroscopy at ultralow-field (B₀ < 0.1T) on portable MRI scanner is challenging due to the low signal-to-noise ratio (SNR) and the impossible spectral separability.

Goal(s): To obtain spectroscopic images of lactate at different concentrations in a phantom on our 46mT Halbach point-of-care MRI scanner and maximize SNR with incorporation of composite refocusing pulses.

Approach: We modified a non-localized Carr-Purcell-Meiboom-Gill (CPMG) echo train sequence to perform 2D J-spectroscopic imaging in lactate phantom with composite refocusing pulses for improved SNR. 

Results: We showed the first steps towards lactate spectroscopic imaging at ultralow-field. 

Impact: The implementation of lactate spectroscopic imaging could add value to the growing list of biomedical applications of low field MR systems, for example in neonatal hypoxic ischemic encephalopathy.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Imaging with a single sided MRI allows for a smaller scanner footprint, making it possible to bring the scanner into the doctor's office.

Goal(s): An xSPEN pulse sequence capable of producing three dimensional images is presented here, allowing for rapid image collection in an inhomogeneous magnetic field.

Approach: An additional phase encode array is incorporated into the xSPEN pulse sequence, allowing for the excited slab to be resolved along the z axis.

Results: A two dimensional multislice technique was converted into a three dimensional volumetric imaging by adding a phase encode array to the spatiotemporal axis.

Impact: A method for rapidly collecting three dimensional images in an inhomogeneous magnetic field is presented here. This technique will help bring MRI into the doctor's office by allowing for higher quality images to be collected in less time.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Developing methods for rapidly imaging in an inhomogeneous magnetic field is necessary for the general adoption of single sided MRI, which would bring MR imaging into the doctor's office.

Goal(s): We aim to develop a fully spatiotemporal pulse sequence for collecting images with a single sided scanner.

Approach: A hyperbolic phase is imparted to the magnetization which results in a time domain signal that is a profile of the phantom. The angle of this profile is rotated to produce an image.

Results: Images with no Fourier encoding were produced and the images could be cropped without aliasing.

Impact: This novel technique allows for rapid imaging in an inhomgeneous magnetic field. Furthermore, this technique allows for improved resolution because the field of view of the images collected with it can be smaller than the object without aliasing.

Keywords: Low-Field MRI, Sparse & Low-Rank Models, Electromagnetic Interference

Motivation: Point-of-care MRI systems need electromagnetic interference (EMI) cancellation with limited passive shielding to improve cost and portability. Existing methods require external hardware or training, which increases costs and design complexity.

Goal(s): This novel solution targeting narrowband EMI is hardware-free, training-free, introduces no white-noise and can be used in conjunction with other methods.

Approach: Exploiting the sparsity, L1-regularized compressed sensing is used to extract EMI from a comb-shaped sampling window that consists of noise-dominated regions in acquisition.

Results: With proof-of-concept implementation, robust EMI cancellation is demonstrated on both simulated and experimental data, with comparable performance to collector-based method despite the lack of extra hardware.

Impact: Point-of-care MRI systems can further push SNR and save scan time by removing narrowband EMI without the cost of additional hardware or training data, enabling new design possibilities for fast, portable, and economically accessible MRI.

Keywords: Low-Field MRI, Low-Field MRI, Relaxometry

Motivation: Low-field MRI holds promise for efficient diagnostics. T₁ mapping is valuable in neuroscience for studying myelination and brain development. To reduce scan time, incoherent, variable density trajectories are often used. 

Goal(s): to reach high image quality and T₁ accuracy for fast T₁ mapping at 64 mT.

Approach: Using the 64-mT, Hyperfine Swoop scanner, we compared T₁ maps acquired with fully sampled and undersampled trajectories (with and without incoherence) and reconstructed them with locally low rank regularization at different regularization factors λ. 

Results: Our findings showed that the most effective approach involves the use of a customized trajectory with λ around 0.004. 

Impact: Since fast and accurate T₁ mapping in the context of low-field MRI is achievable, it would now be interesting to study brain developement in children, that present a unique challenge due to movement.

Keywords: Low-Field MRI, Elastography

Motivation: Magnetic resonance elastography can provided quantitative assessment of tissue mechanical properties, but requires large, expensive, in demand clinical MRI scanners, this motivates a more accessible portable MR technique. 

Goal(s): To develop robust experimental protocols for bulk assessment of tissue mechanical properties using portable magnetic resonance and explore clinical applications.

Approach: Effects of phase interference on the MR signal magnitude and phase are investigated to characterize the shear wave velocity for samples with differing mechanical properties under harmonic and transient excitation. 

Results: Preliminary measurements show that a portable MR instrument can be used to quantify the shear wave velocity in homogeneous samples. 

Impact: These results show the potential of a portable magnetic resonance instrument for quantification of  shear mechanical properties in biological tissues. This merits further investigation of applications to the diagnosis of specific diseases which could potentially improve patient outcomes. 

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Limited access to medical equipment makes low-field MRI an interesting option in many settings. One challenge is the prolonged scan time, especially for quantitative imaging. However, parallel imaging is typically not used due to the very high sensitivity of a single solenoid receive coil.

Goal(s): This study aims to accelerate T₁ mapping (used for estimating brain myelination) on a Halbach low-field system.

Approach: A locally low-rank reconstruction was applied to diminish undersampling artifacts from the variable-density random sampling trajectory.

Results: The study highlights the potential for both, fast lower-resolution (2.5mm² in-plane) and higher-resolution (1.5mm² in-plane) T₁ mapping with an acceleration factor of R=4.

Impact: Our study's advanced low-rank reconstruction approach for low-field MRI could transform imaging methods in regions where high-field MRI is inaccessible, enabling precise and fast T₁ brain mapping, which is critical for assessing myelination-related diseases with newfound speed and reliability.

Keywords: Low-Field MRI, Low-Field MRI, Diffusion

Motivation: DWI/DTI are very challenging in portable MRI system, while they play a pivotal role in timely triage, diagnosis and treatment for patients with suspected acute conditions such as stroke. 

Goal(s): To mitigate the effects of eddy currents and achieve multi-directional diffusion-weighted imaging and diffusion tensor imaging in portable MRI system.

Approach: With the three-axis gradient coil accompanied with anti-eddy plate and image-phase based eddy current correction, we applied multi-scaning average to suppress noise and adopted eddy correction to mitigate the motion blurring.

Results: We succeed obtain visible multi-direction diffusion-weighted imaging and DTI imaging in portable MRI system.

Impact: With the three-axis gradient coil accompanied with anti-eddy plate and image-phase based eddy current correction, we succeed in obtaining multi-direction diffusion-weighted imaging and  DTI images with the portable MRI system.

Keywords: Gray Matter, Segmentation, Analysis/Processing, Brain, Data Acquisition, Validation

Motivation: Ultra-low-field MRI scanners offer a cost-effective and portable alternative to high-field neuroimaging.

Goal(s): To quantify between-scanner test-retest reliability of 64mT brain scans, and their correspondence to 3T MRI.

Approach: We scanned 23 healthy participants on two Hyperfine 64mT scanners and a GE 3T scanner using T₁w and T₂w scans at multiple resolutions. We segmented images into 98 structures and estimated their volumes.

Results: We demonstrate excellent reliability of volumetric estimates from ultra-low-field MRI, and high correspondence to high-field scans. The highest reliability and high-field correspondence was obtained using T₂w ultra-low-field scans, super-resolved by combining three orthogonal acquisitions with low through-plane resolution.

Impact: Measures of brain volume from Hyperfine portable ultra-low-field MRI scans show excellent test-retest reliability across scanners, and excellent correspondence to similar estimates from high-field MRI. This enables quantitative analysis of cost-effective and portable neuroimaging in various contexts, including low-resource environments.

Keywords: Low-Field MRI, Simulations

Motivation: Due to its convenience and affordability, ultra-low field MR imaging is growing in popularity. However, poor SNR requires a solution.

Goal(s): This research aims to determine if superconducting coils or low temperature coils are still beneficial in terms of SNR in ultra-low-field MR.

Approach: Our method compares RF coils made from different conductivities. This comparison will help us determine superconductor importance in coil performance.

Results: The findings highlight the significance of superconductor materials and how they can be used to improve imaging performance at lower field strengths.

Impact: This study investigates signal-to-noise ratio (SNR) in superconducting, low temperature and room temperature RF coils for affordable ultra-low-field MR imaging and determines if superconducting or low temperature coils are still beneficial in SNR at 0.07T. It shows how superconductor materials improve imaging performance, especially at lower field strengths.

Keywords: Low-Field MRI, Magnets (B0)

Motivation: The current optimizations of permanent magnet array (PMA) designs are guided by checking field properties, not reflecting the quality of reconstructed images.

Goal(s): We aim to propose indicating parameters for the encoding capability of spatial encoding magnetic fields (SEMs) to guide PMA designs.

Approach: Local k-spaces are pushed to be point-wise. The coverage area of the point-wise k-spaces between the spokes of the maximum and minimum angles is calculated to indicate the encoding capability.

Results: The proposed method is fast, enlarging the optimization space, resulting in SEMs having superior encoding capability with stronger field, higher gradient, and lower NRMSE of the resultant images.

Impact: The proposed point-wise k-space evaluation enlarges the solution space for the PMA optimizations thus significantly improves the performances of the outcomes, i.e., SEMs having superior encoding capability with higher field strength and higher gradient compared to that from conventional approachs.