Keywords: Data Acquisition, Data Acquisition

Motivation: This study is motivated by the creation of high-resolution T1-weighting whole brain images in considerably less time (1 minute) than currently required for standard MP-RAGE (~4 minutes).

Goal(s): The sampling efficient 3D-Yarnball trajectory offers a potential imaging solution, but trajectory/sequence design and reconstruction aspects remain to be explored.  

Approach: Variably under-sampled Yarnball trajectories with 2-10 ms duration were compared in healthy brain, along with different methods of steady-state sequence excitation. Iterative, off-resonance correcting, wavelet-regularized reconstruction was applied to Yarnball for the first time.   

Results: Yarnball sequence and reconstruction consideration enabled high-quality 0.77 mm isotropic whole brain images in 1 minute 

Impact: The image acquisition, sequence, and reconstruction investigation of this work enabled robust, high-quality 0.77 mm isotropic T1-weighted whole brain images in just over 1 minute.  The goal of this work is to facilitate considerably shorter MRI protocols. 

Keywords: Data Acquisition, Data Acquisition, Fetal

Motivation: Fetal MRI is an important tool for antenatal diagnosis, allowing to assess appropriate growth with T2-weighted TSE sequences. Involuntary fetal motion is frozen in-plane with single-shot sequences, but 3D inconsistencies remain and are currently mostly addressed with offline slice-to-volume reconstruction.

Goal(s): The goal of this work is to integrate slice-to-volume reconstruction into a clinical fetal low-field scan.

Approach: A Gadgetron-based real-time pipeline including quality control, decision support, 3D reconstruction and transfer back to the scanner was implemented.

Results: The steps of the pipeline were successfully tested in-vivo in low-field fetal MRI.

Impact: The complete integration of Slice-to-Volume reconstruction into the normal clinical workflow and the resulting availability of high resolution 3D volumes during the scan overcomes challenges and current barriers of fetal MRI.

Keywords: Data Acquisition, Vessels, Ghosting suppression, Sequence design, Low-rank reconstruction

Motivation: Ghost artifact of large vessels impede the use of echo-planar imaging(EPI) for accelerated MR Angiography(MRA) or MR Venography(MRV) acquisitions.

Goal(s): To analyze the physical principles of flow-related ghost, and develop targeted technical approaches to suppress the artifact, enabling EPI-based rapid and high-fidelity simultaneous MRAV.

Approach: By employing techniques including point-spread function modeling, alternating flow-compensation scheme, flow-related phase-based reconstruction, and automatic detection and correction algorithms, rapid in-vivo vascular imaging were achieved.

Results: DEPSAV-II achieved cerebral MRAV with suppressed ghost artifacts and comparable vascular depiction with GRE-based methods in 6 minutes, thereby improving the accessibility of comprehensive vascular examination in routine clinical practices.

Impact: Developed a suite of techniques to overcome flow-related ghosting of large vessels which tackling EPI-based rapid arteriovenous-imaging methods.
DEPSAV-II’s simultaneous MRAV and significant time-reduction may benefit clinical studies and practices like small vessel diseases requiring comprehensive arterial and venous examination.

Keywords: Data Acquisition, Data Acquisition, Spiral TSE, HASTE, Abdominal imaging

Motivation: Conventional Cartesian HASTE may be susceptible to image blurring, resolution loss, and artifacts in abdominal imaging.

Goal(s): To develop a 2D T₂-weighted abdominal spiral HASTE technique to achieve better image sharpness, reduced scan time, and reduced power deposition compared to Cartesian HASTE.

Approach: A variable-flip-angle refocusing RF series was designed and employed to maintain high signal-intensity at middle- and late-echoes with a smooth signal-evolution compared to a constant-flip-angle scheme. Variable-density spiral-ring trajectories combined with L1-ESPIRiT reconstruction were performed to accelerate the data acquisition.

Results: Whole-abdomen spiral HASTE images were acquired with 1.5×1.5×6 mm³ spatial-resolution and 25 slices in a 7-second acquisition at 3T.

Impact: This work highlights the utilization of spiral-ring TSE acquisition along with variable-flip-angle RF pulses and L1-ESPIRiT reconstruction for accelerated single-shot abdominal imaging, providing images with improved image sharpness, shorter scan time, and reduced power deposition over conventional Cartesian HASTE.

Keywords: Pulse Sequence Design, Tissue Characterization

Motivation: Wideband bright-blood late gadolinium enhancement (LGE) enables artifact-free imaging of myocardial scars in patients with implantable cardioverter defibrillators (ICDs). Unfortunately, the poor scar-blood contrast makes it difficult to depict subendocardial scars.

Goal(s): To improve myocardial scar visualization and localization in ICD patients.

Approach: We propose a 2D breath-hold single-shot ECG-triggered gradient echo wideband joint black- and bright-blood (wideband SPOT) LGE sequence to improve scar visualization and localization, while limiting ICD-artifacts. Wideband was implemented in an adiabatic inversion pulse and in an adiabatic T2 preparation.

Results: Wideband SPOT successfully suppressed ICD-artifacts while improving scar detection, and provided same image quality than reference wideband bright-blood.

Impact: This new technology will enable radiologists and cardiologists to detect and localize myocardial scars more accurately in ICD patients by eliminating ICD hyperintensity artifacts and enhancing scar tissue with unprecedented contrast.

Keywords: Pulse Sequence Design, Pulse Sequence Design

Motivation: Vibration of gradient coils is a source of loud acoustics, signal dropout, field distortion, and potential system damage particularly at mechanical resonant frequencies.

Goal(s): To design safe spiral gradient waveforms which avoid mechanical resonant frequencies and their resulting severe vibrations.

Approach: Instantaneous gradient frequency during spiral readout is estimated as the rotational frequency of a circle at the current k-space radius and gradient amplitude. Amplitude is limited to drop through resonant bands quickly. A convex problem for spiral rewinders is formed minimizing the DFT at resonant frequencies.

Results: Coil vibration was significantly reduced using safe spirals, and gradient field oscillations were minimized.

Impact: Frequency constrained “safe” spiral waveforms were shown to avoid specified frequency bands, reducing gradient vibrations and k-space oscillations without degrading image quality. Such waveforms could potentially prolong gradient coil lifetime, reduce acoustic discomfort, and remove artefacts from persisting k-space oscillations.

Keywords: Parallel Imaging, Parallel Imaging

Motivation: This research explores the potential for temporally varying N-periodic bSSFP banding artifacts as a new dimension alongside coils for parallel imaging. 

Goal(s): Our goal is to leverage the temporally varying spatial modulation of a 2-periodic bSSFP acquisition to improve parallel imaging performance over a straightforward bSSFP approach.

Approach: We optimize imaging parameters using computational simulations and validate our methodology through in-vivo experiments in brain.

Results: Our findings demonstrate that the banding artifacts from 2-periodic bSSFP can serve as additional spatial encoding information in parallel imaging applications to reduce scan time.

Impact: Periodically varying bSSFP banding patterns can be exploited to achieve improved parallel imaging performance, creating opportunities for new experimental designs in accelerated imaging.

Keywords: Image Reconstruction, Image Reconstruction, open source vendor-independent sequences

Motivation: To enhance efficiency, transparency, and reproducibility of data acquisition and reconstruction in large-scale MRI studies.

Goal(s): To establish an open-source, cross-platform, easy-to-learn data acquisition and reconstruction workflow.

Approach: The Pulseq framework is extended to integrate Siemens’ “Image Calculation Environment” (ICE) and Gadgetron. To validate the workflow, MPRAGE and EPI sequences were developed using the extended Pulseq and executed on three Siemens scanners with comparison to the corresponding product sequences.

Results: The preliminary results show that Gadgetron had comparable reconstruction performance to ICE, and Pulseq sequences generally produced image quality comparable to product sequences. Online Gadgetron and ICE produce images within seconds/minutes after measurements.

Impact: An open-source, cross-platform MRI data acquisition and reconstruction workflow is established by extending the Pulseq framework to link to reconstruction tools. The preliminary results indicate that this workflow has the potential to enable efficient, transparent, reproducible data acquisition and reconstruction.

Keywords: New Trajectories & Spatial Encoding Methods, Data Acquisition

Motivation: Several diseases influence the human vocal fold oscillation which can currently only be studied with superficial stroboscopic imaging.

Goal(s): We aim to develop a technique that allows the full characterization of the vocal fold oscillation with sub-millisecond sub-millimeter resolution.

Approach: ZTE MRI allows to freeze sub-ms dynamic signal changes in k-space. With synchronization data from a microphone, we retrospectively gate ZTE MRI data of the larynx acquired during singing using a total variation constraint in the time domain to reconstruct the vocal fold motion.

Results: 3D vocal fold oscillations can be visualized with ultra-high spatial (0.8mm) and temporal (670μs) resolution.

Impact: This work aims to improve the understanding of the VF oscillation under various physiological and pathological conditions, and might have applications in 3D dynamic MRI of other oscillatory body motions.

Keywords: New Trajectories & Spatial Encoding Methods, New Trajectories & Spatial Encoding Methods, ZTE, Dynamic MRI, Quiet MRI

Motivation: Existing Zero TE methods are constrained due to gradient slew limits between spokes, which hinders their use in dynamic imaging applications.

Goal(s): We aim to improve temporal k-space sampling in time by increasing the possible angular distance between consecutive spokes via continuously-slewed gradients, while still maintaining minimal gradient refocusing and minimal acoustic noise.

Approach: We parameterize the k-space trajectory using sequential rotations of an arc in k-space, then optimize the rotation angles over metrics for sampling uniformity and refocusing.

Results: We demonstrate a proof-of-concept of this trajectory and show improvement over radial ZTE in k-space coverage metrics and reconstructions for various temporal resolutions.

Impact: By improving temporal k-space sampling for Zero-TE MRI, our work enables quiet, dynamic imaging with flexible temporal resolution. Potential applications include quiet DCE or respiratory motion-resolved imaging for neonates and other sound-sensitive populations.

Keywords: Software Tools, New Devices, Open-Source

Motivation: Commercial MRI scanners have limited accessibility due to high costs and the proprietary nature of the hardware and software platforms.

Goal(s): To develop a comprehensive console software for community-built low-field MRI systems that is solely based on open-source components and provides a user interface similar to commercial systems.

Approach: The console software was programmed in the Python programming language. The platform is divided into three decoupled services that 1) provide the interface for scan planning and visualization, 2) run the scanner control, and 3) perform the image reconstruction.

Results: The architecture is described, providing a starting point for utilizing it in other projects.

Impact: The development of open-source MRI software and hardware will help to disseminate fundamental knowledge about the construction of MRI scanners. The software platform described in this work may serve as foundation for future community initiatives on building open-source scanners.

Keywords: New Signal Preparation Schemes, Pulse Sequence Design, SMS, PME, Diffusion

Motivation: Both the recently introduced patterned multislice excitation (PME) technique and SMS acquisition can be used for faster imaging. Combining these would reduce imaging times further.

Goal(s): To demonstrate that the PME is compatible with SMS imaging.

Approach: Four RF pulses were combined to achieve acceleration from both SMS and PME. To limit peak RF amplitude, pulse components were time-shifted. The approach was demonstrated using diffusion weighted (DW) imaging at 3T.

Results: Close to fourfold acceleration was successfully implemented by combining twofold SMS and PME and evaluated for DW MRI performance versus twofold acceleration based on PME only.

Impact: Recently introduced PME approach and SMS can be combined to accelerate the acquisition.

Keywords: MR Fingerprinting, MR Fingerprinting

Motivation: Transmit-inhomogeneities at ultra-high-field cause realized/effective flip-angles to strongly deviate from the nominal. In quantitative MRI, retrospective correction is possible but leads to spatially varying efficiency for parameter estimation. Parallel-transmit enables spatio-temporal modulation of excitation pulses in MR Fingerprinting (PTX-MRF), potentially improving encoding power by filling in regions of poor precision achieved with a static configuration.

Goal(s): Investigate an MRF prototype sequence with temporal modulation of parallel-transmit shims.

Approach: We sequentially apply different transmit-shims to modulate realized flip-angles and employ temporal low-rank for reconstruction of singular-component-images.

Results: We explored the potential and key requirements for PTX-MRF, showing that parallel-transmit could prove advantageous for MRF.

Impact: This work is an explorative step towards addressing transmit-field inhomogeneities at ultra-high-field. Its impact is mainly indicating new directions worthwhile investigating, supported by evidence from phantom experiments.

Keywords: Image Reconstruction, Image Reconstruction, nonlinear gradient

Motivation: The local B₀ coil array has been shown to speed up 2D Cartesian MRI and provides a platform for investigating the most efficient B₀ encoding fields. Nevertheless, optimizing the rapid modulations for accelerating volumetric scans without introducing additional artifacts becomes more challenging.

Goal(s): We explore distinct nonlinear modulation B₀ fields and reconstruct artifact-free accelerated images.

Approach: With a recent RKHS framework, the k-space efficiency maps for various modulation fields are analyzed, and a novel auto-calibration reconstruction method is introduced.

Results: Our k-space analysis provides insights validating optimal modulation fields, and the ex-vivo and in-vivo scans demonstrate the robustness of the proposed reconstruction technique.

Impact: We demonstrate the RKHS formalism as a valuable tool for understanding 3D MRI scans encoded with nonlinear modulation fields. Our auto-calibration reconstruction, analogous to GRAPPA in parallel imaging, offers a promising approach for image acceleration with rapid B₀ modulation.

Keywords: Pulse Sequence Design, Fat, fat/water separation, data acquisition, liver, pulse sequence design, software tools

Motivation: 2D sequential chemical-shift-encoded acquisitions with centric encoding and flip-angle modulation (FAM) enables motion-robust and high-SNR liver fat quantification. Originally developed in a single vendor, the performance and relative simplicity of FAM motivate vendor-neutral implementation and validation.

Goal(s): Implement FAM in the vendor-neutral framework Pulseq, and determine its feasibility, bias, and reproducibility in a multi-center, multi-vendor study.

Approach: Pulseq-FAM was applied in two centers with two vendors on a phantom with controlled PDFF/T1_water values, and in volunteers during free breathing.

Results: At both centers, Pulseq-FAM shows low bias and good reproducibility in the phantom, and excellent motion robustness and image quality in volunteers.

Impact: A vendor-neutral implementation of motion-robust liver fat quantification, as demonstrated in this study, may enable detection, staging, and treatment monitoring of steatotic liver disease with improved availability and standardization.

Keywords: Data Acquisition, New Trajectories & Spatial Encoding Methods

Motivation: Major limitation of lung MRI is respiratory motion which can be overcome by retrospective self-gating approaches.

Goal(s): Achieving sufficient SNR values in the parenchyma is crucial for clinical evaluations and the assessment of physiological parameters.

Approach: This abstract presents a single-petal rosette UTE trajectory that is evaluated for k-space-, as well as image-based, retrospective self-gated lung imaging in comparison to the radial UTE trajectory.

Results: Higher SNR values and sharpness are obtained when using the SPR trajectory, compared to radial UTE sampling approaches at constant temporal resolution.

Impact: This abstract presents a single-petal rosette UTE trajectory (SPR) for 2D self-gated lung imaging, yielding higher SNR and sharpness in comparison to radial UTE sampling approaches.

Keywords: Data Acquisition, Non-Proton

Motivation: Sodium (²³Na) and advanced ¹H MRI provides valuable metabolic information but are not routinely used because of the required additional scan time.

Goal(s): Employ the idle times in ²³Na MRI to perform ¹H measurements, reducing total scan time.

Approach: An interleaved radial amine CEST and sodium pulse sequence was developed to simultaneously acquire acidity or T₂* maps simultaneously with salinity maps in phantoms and in the lower leg during an exercise paradigm.

Results: A scan reduction of 46% relative to sequential acquisitions. Dynamic T₂*, acidity and sodium changes were successfully tracked and in line with the expected physiological responses.

Impact: The achieved scan time reduction could facilitate the inclusion of sodium and advanced 1H imaging in clinical routine. Furthermore, it could benefit functional studies by providing dynamic multinuclear information simultaneously from the same transient state.

Keywords: Data Acquisition, Heart, 3D cardiac image, 3D cine image, localized quadratic encoding

Motivation: A gated 3D cardiac cine MRI will be useful to evaluate cardiac structure and function from different viewing angles, unlike conventional 2D scans covering only specific orientations.

Goal(s): To develop a retrospectively cardiac gated 3D imaging sequence for the cine scan with reasonable breath-hold time and reconstruction speed.

Approach: A bSSFP sequence was combined with Localized Quadratic Encoding RF pulses for the cardiac gated 3D imaging.

Results: The 3D cardiac cine imaging requires around 20 breath-holds and each breath-hold takes around 25 seconds. The images feature similar soft tissue contrast to the conventional 2D bSSFP scanning with isotropic resolution along different viewing angles.

Impact: The proposed method enables a 3D cardiac cine scan with reasonable breath-hold duration and much faster reconstruction speed.

Keywords: Data Acquisition, Brain, Mesoscopic

Motivation: Our previous work provided 0.35×0.35×0.35 mm³ voxel resolution T₂^* dataset where the intracortical angioarchitecture details were captured and analyzed (Gulban et al. 2022). However, this work only covered a third of the brain while requiring two scanning sessions.

Goal(s): Our aim here is to explore reducing the scanning time while expanding the brain coverage to get similar quality data for vascular analyses.

Approach: Our approach consisted of exploring further acceleration for T₂^* imaging and boosting the SNR of T₁ images though denoising instead of multi-run averaging.

Results: Our results suggest that we can reduce the scanning time five-fold while accomplishing whole brain overage.

Impact: We provide a low undersampling 0.35 mm in vivo human brain dataset and a scanning protocol (including 7 T T2*, T1 contrasts) for cortical angioarchitecture studies while delivering a reference dataset to test further acceleration and denoising.

Keywords: New Signal Preparation Schemes, Low-Field MRI

Motivation: Inherently reduced SAR at low B0 fields opens the possibility for sequences employing high B1 to generate contrasts inaccessible on common systems.

Goal(s): Explore generation of magnetization transfer (MT) and inhomogeneous MT (ihMT) contrast using high B1 sequences on low-field MRI system.

Approach: A tuned resonator was used to enhance B1 fields locally within a 0.55T scanner. Rapid gradient-echo based MT/ihMT sequences were tested on ex-vivo lamb brain sample.

Results: Achieved ~9-fold increase in B1, boosting observed MTR/ihMTR. Unexpectedly, RF pulses failed to function at high B1 due to Bloch-Siegert and spin-locking; new pulse designs for this regime will form future work.

Impact: Using high B1 fields at low B0 enables contrasts that were previously off-limits due to safety constraints at high B0. To exploit these with clinical hardware we demonstrate a passive resonator that increases the B1 by a factor of 9.