Keywords: Low-Field MRI, Low-Field MRI, cardiovascular,aortic imaging

Motivation: Bright-blood and black-blood imaging are relevant for assessing aortic pathologies. Research on aortic imaging at 0.55T which could potentially make MRI more accessible and affordable is scarce.

Goal(s): To evaluate the feasibility of a novel non-contrast enhanced simultaneous bright- and black-blood aorta imaging at 0.55T at systole and diastole.

Approach: Five healthy volunteers were scanned at 0.55T with the proposed accelerated and non-rigid motion-compensated sequence (iT2prep-BOOST). Adiabatic, MLEV4 and MLEV8 T2-preparation pulses were compared.

Results: Good image quality was obtained for simultaneous acquisition of 3D bright- and black-blood aorta imaging at 0.55T at systole and diastole with the proposed iT2prep-BOOST and MLEV8 T2-preparation.

Impact: The proposed approach enables 3D simultaneous bright- and black-blood aorta imaging at 0.55T during a fast free-breathing scan and thus shows promise for the detection of different aortic diseases, potentially making aortic MRI more accessible and affordable.

Keywords: Low-Field MRI, Low-Field MRI, Heart, Cardiovascular, Pulse sequence design

Motivation: CMR has not seen widespread adoption beyond large urban academic centers. The reasons for this limited uptake include the cost and time-intensive nature of CMR. 5D Free-Running CMR using self-navigation (5D CMR) implemented on a low-field clinical scanner may help bridge this gap.

Goal(s): Investigate the feasibility of cardiac function measurements using 5D CMR on a 0.55T system.

Approach: 5D CMR data were collected in 10 adult subjects and compared to results from reference 2D cines. Right- and left-ventricular ejection fraction and left atrial volume were ascertained.

Results: 5D CMR allowed for time-efficient and concordant measurements when compared to the 2D reference method.

Impact: 5D Free-Running whole-heart CMR without the need for ECG, breath-holding, navigators, or complex scan plane planning enables a highly simplified and time-efficient assessment of myocardial function on a 0.55T clinical system in under 8 min.

Keywords: Low-Field MRI, Low-Field MRI, Lung, Tissue Characterization, Reader Performance Study

Motivation: Although MRI has had low adoption in lung imaging due to susceptibility artifacts, limiting its utility in pulmonary parenchymal imaging, low-field MRI (0.55T) has potential to address those limitations.  

Goal(s): However, its thoracic diagnostic capabilities remain indeterminate, so our goal was to compare its ability to detect common lung pathologies to chest CT and provide comparable quantitative measurements.

Approach: Structures and pathologies were measured with both modalities, and two radiologists identified lung pathologies with MRI only.

Results: Results indicated that readers were able to detect pathologies using 0.55T MRI, serving as a first step in exploring 0.55T MRI as an alternative modality.

Impact: Our study revealed potential for 0.55T MRI as an emerging tool for MR-based anatomic evaluation of the lung, and its limitations. This can expand lung imaging options and potentially provide better tissue characterization for diagnoses like lung cancer.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: 0.55T MRI may be a promising platform for quantitative multiparametric liver imaging with improved cost-effectiveness and robustness.

Goal(s): This study demonstrates the feasibility of rapid free-breathing 3D MRI of the liver with simultaneous quantification of PDFF, R2*, and water-specific T1 at 0.55 Tesla.

Approach: We tested free-breathing GraspT1-Dixon sequence with in vivo experiment and the quantitative maps are validated using R2* and PDFF phantoms.

Results: We show that (1)the estimated parameters are accurate; (2)the influence of fat on liver T1 mapping can be effectively mitigated to ensure accurate and robust T1 quantification; and (3)R2* mapping may be insensitive to respiratory motion at 0.55T.

Impact: 0.55T MRI offers a cost-effective platform for quantitative multiparametric MRI of the liver to improve the management of various chronic disease conditions. In particular, the improved magnetic field homogeneity at 0.55T may enable more robust estimation of R2* maps.

Keywords: Low-Field MRI, Lung

Motivation: Parametric mapping may enable early detection and monitoring of pulmonary diseases but is hampered by low signal levels, short T₂/T₂* values, and susceptibility artifacts.

Goal(s): This project aims to develop an MRF approach for simultaneous 2D T₁, T₂, and M₀ mapping in the lungs on a commercial 0.55T scanner.

Approach: MRF data were acquired in five healthy subjects during a 16s breathhold, repeated at end-inspiration and end-expiration, and reconstructed using a deep image prior.

Results: Feasibility of lung MRF at 0.55T was demonstrated in healthy subjects, with lung T₁ of 868±57ms (expiration) and 806±59ms (inspiration), and T₂ of 54.1±3.2ms (expiration) and 58.7±4.0ms (inspiration).

Impact: This study demonstrates the feasibility of MR Fingerprinting for 2D T₁, T₂, and M₀ mapping of the lung parenchyma at 0.55T in healthy subjects, which may have future clinical implications for various pulmonary diseases including asthma, emphysema, and cystic fibrosis.

Keywords: Low-Field MRI, Low-Field MRI, MR Fingerprinting, T1 Mapping, T2 Mapping, Fat-fraction Quantification

Motivation: Cardiac MRF is a powerful imaging-technique that allows for comprehensive myocardial tissue characterization in a single-scan and has been proposed at 1.5T and 3T. However, cMRF has not been demonstrated at lower-field yet.

Goal(s): Investigate the feasibility of a Dixon-cMRF sequence for simultaneous T1, T2 and fat-fraction quantification at 0.55T.

Approach: Dual-echo spoiled-GRE-acquisition with varying IR-T2-preparation pulses. Experiments were performed on standardized phantoms and with 5 healthy volunteers and compared with spin-echo references.

Results: T1, T2 and fat-fraction Dixon-cMRF at 0.55T was tested with phantoms and with healthy subjects, showing good agreement with reference values in phantom and promising results in healthy subjects.

Impact: The simultaneous quantification of T1, T2 and fat-fraction at 0.55T in a single cardiac-MRF of 15s could provide an alternative to higher field scanners, allowing for a more accessible way to assess cardiovascular disease.

Keywords: Non-Array RF Coils, Antennas & Waveguides, New Devices, Flexible Electronics, 3D-Write Technology

Motivation: MRI receiver coils are often rigid thus cannot conform to every anatomy. This motivates to create flexible, robust, and easy to manufacture coils.

Goal(s): To create scalable and low-cost MRI coils using direct-3D-writing. The coils should conform to different anatomies and be robust to bending and stretching.

Approach: We utilize a fast direct-3D-write method (~8 minutes print time per coil) that uses an easy to modify coil model, and compare performance against a rigid copper coil at 0.55 Tesla.

Results: The flexible printed coil provided 1.8 times higher SNR compared to the reference copper coil due to better form-fitting.

Impact: MRI receiver coils, printed with the direct-3D-write method, can be made flexible to conform to imaging anatomy, while offering scalability and lower cost. This simplifies manufacturing and improves SNR due to better form-fitting.

Keywords: Low-Field MRI, Low-Field MRI, Fat suppression, Dixon, bSSFP

Motivation: Fat suppression is challenging at low field strengths due to small fat frequency shifts. Dixon imaging with bSSFP offers an attractive solution by combining the robust fat-water separation performance of Dixon with the high SNR and scan speed of bSSFP sequence.  However, the distinctive spectral response of bSSFP signals was overlooked in existing Dixon implementations.

Goal(s): This study aims to improve fat suppression with bSSFP sequence at low field by incorporating bSSFP signal model in a two-point Dixon algorithm. 

Approach: Numerical simulations and phantom experiments were performed at 0.55T.

Results: Results suggest that integration of bSSFP signal model can improve fat suppression.

Impact: Our proposed bSSFP-based two-point Dixon method could improve imaging with fat suppression at low field, which has been a challenging task due to small fat frequency shift and low SNR.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: As assessment of liver metastases requires multiple imaging modalities, it is essential to compare diagnostic capabilities and patient experiences of the low-cost 0.55T MRI to conventional imaging techniques.

Goal(s): We analyzed the sensitivity for neuroendocrine tumor metastases detection of gadoxetate-enhanced 0.55T MRI to ⁶⁸Ga-DOTATATE PET/CT and 3.0T MRI while evaluating patient experience

Approach: Patients were imaged on 0.55T MRI with ⁶⁸Ga-DOTATATE PET/CT and/or 3.0T MRI for comparison. Sound pressure levels (SPLmax) were compared between 0.55T and 3.0T.

Results: Hepatobiliary phase imaging at 0.55T showed increased detection rates over ⁶⁸Ga-DOTATATE PET/CT. SPLmax of 0.55T was significantly lower. Patients found the 0.55T MRI less stressful.

Impact: Routine imaging of patients with neuroendocrine tumor metastases is feasible at 0.55T MRI. Low-field MR imaging has the potential to improve patient experience and accessibility without sacrificing diagnostic capability.

Keywords: Low-Field MRI, Low-Field MRI, resting-state, functional connectivity, resting-state network, test-retest reliability

Motivation: Resting state fMRI (rs-fMRI) provides vital neurological information in acute care.

Goal(s): To demonstrate the feasibility of rs-fMRI at 0.5T.

Approach: Repeated rs-fMRI acquisitions of two healthy volunteers (n = 6, n = 4) were acquired at 0.5T using a 31 min EPI based protocol.

Results: All eleven well-established resting state networks were identified. Sensorimotor and language networks were very reliable across scans for both volunteers with intersession intra-class correlation coefficient values > 0.5.

Impact: Resting state fMRI is feasible at 0.5T with an EPI acquisition technique. The functional connectivity detected resembles a 3T database for well-established resting-state networks.

Keywords: Low-Field MRI, Diffusion/other diffusion imaging techniques

Motivation: Single-shot diffusion weighted imaging at 0.5T has low SNR, increased blurring and is limited by spatial resolution.

Goal(s): We want to demonstrate image quality improvement in multi-shot DWI at 0.5T with MUSE DL reconstruction.

Approach: Multi-shot DWI is reconstructed using MUSE algorithm followed by ARDL.

Results: The qualitative DWI results show improved image quality and less blurring with MUSE ARDL reconstruction.

Impact: Using multi-shot DWI and the MUSE ARDL recon increases spatial resolution and image quality at 0.5T and provides reliable imaging for low SNR DWI acquisitions.

Keywords: Low-Field MRI, Data Acquisition, PROPELLER, Image Reconstruction, Compressed Sensing, NUFFT, Acceleration

Motivation: Mid-field MRI have lower SNR so data acquisition is associated with longer data acquisition time. Therefore, develop fast imaging technique with motion robust data acquisition with minimal SNR penalty due to fast imaging.

Goal(s): Develop a robust image reconstruction technique for compressed sensing (CS) accelerated PROPELLER acquisitions. 

Approach: A new iterative reconstruction technique based on NUFTT and CS for PROPELLER acquisitions. 

Results: MRI imaging of ISMRM-NIST phantom and volunteer scan were acquired and reconstructed with minimal under-sampling artifacts such as haze and streaks with PROPELLER acceleration.

Impact: Compressed sense accelerated PROPELLER can acquire high quality motion robust MRI images at mid-field MRI. Proposed MR image reconstruction technique for compressed sensing accelerated PROPELLER technique can enable acquisitions requiring longer scan time due to SNR.

Keywords: Low-Field MRI, Low-Field MRI, T2*,subcortical brain,SNR

Motivation: Accurate knowledge of T2* relaxation times is important for optimizing contrast and SNR in multi-echo gradient echo sequences.

Goal(s): To measure the nominal T2* relaxation parameter at 0.5 T over subregions in the brain.

Approach: A 2 mm isotropic 3D multi-echo GRE sequence was acquired in 5 healthy volunteers. T2* estimates were computed over regions of interest using a mono-exponential fit.

Results: T2* estimates of gray (86±8 ms) and white (78±5 ms) matter are in good agreement with previously published measurements in the mid-field. In the deep brain, average T2* values ranged between 70±2 ms to  89±5 ms.

Impact: For optimal T2* contrast in the brain at 0.5 T, echoes from multi-echo acquisitions should extend beyond 60 ms. For optimal SNR, echoes should be combined with a target T2* of ~80 ms.

Keywords: In Silico, Relaxometry, Low-Field MRI, Hepatic Steatosis and Iron Overload, HIC, Fat Fraction

Motivation: Multi-spectral fat water models fail to produce reliable fat fraction(FF) estimations for severe iron overload conditions at 1.5T and 3T. Low-field MRIs(<1T) may increase the accuracy in HIC and FF estimations at high iron overload by slowing signal decay but might suffer from lower signal-to-noise ratio(SNR).

Goal(s): Assess the accuracy and robustness of quantifying R2* and FF at 0.75T across various SNR conditions.

Approach: Realistic virtual liver models with concomitant presence of iron overload and hepatic steatosis were used to simulate MRI signals at 0.75T and 1.5T using Monte Carlo simulations.

Results: 0.75T showed improved FF and R2* estimation compared to 1.5T.

Impact: Low-field MRI can increase the accuracy and precision in simultaneous quantification of R2* and FF in the presence of mild-to-severe iron overload. With low-field MRI systems being less expensive and potentially increasing MRI accessibility, they can facilitate the reliable diagnosis.

Keywords: Low-Field MRI, Low-Field MRI, Hardware, Spine

Motivation: MR image quality concerns due to metallic implants may be addressed by preferentially scanning on 0.55T units.

Goal(s): To assess image quality, metallic artifacts, and diagnostic agreement secondary to spinal hardware at 0.55T compared to higher-field imaging.

Approach: Two blinded neuroradiologists independently reviewed 20 0.55T studies and 10 paired high-field studies. Diagnostic efficacy of 0.55T scans was assessed via pick-list, and image quality and metal artifact reduction were assigned scaled ratings.

Results: 0.55T produced studies with high diagnostic efficacy (16/20 studies had complete or near-complete agreement) and equivalent or improved image quality compared to higher-field images.

Impact: Commercial 0.55T MRI systems may improve the appearance of artifacts caused by spinal hardware compared to higher fields, and can be used in routine clinical practice without compromising image quality or diagnostic efficacy.

Keywords: Quantitative Imaging, Breast

Motivation: The fractional T1 differences between healthy and abnormal tissue are significant larger in the ultra-low-field (ULF) regime (<10 mT) compared to high field. 

Goal(s): Despite the challenges of imaging at ULF (predominately low SNR and spatial-temporal resolution), we demonstrate in vivo T1 mapping in the breast at 6.5 mT in 43 minutes.

Approach: A variable flip angle (VFA) method with B1 correction was used. 

Results: T1 mapping of CuSO₄ solutions showed an average T1 deviation <7% compared to reference T1 measurements. Breast phantom T1 mapping was also performed. Finally, this method was applied on two healthy female volunteers.

Impact: This work explores ultra-low field T1 mapping as potential biomarker for low-cost breast imaging. We demonstrate the feasibility of quantitative T1 mapping of the human breast in healthy female volunteers at 6.5 mT using a variable flip angle method.