Keywords: High-Field MRI, Parallel Transmit & Multiband, whole-body, abdomen, kT-points, free-breathing, 3D, RPE acquisition

Motivation: Flip angle variations or voids are problematic at 7T, especially when large fields of excitation are needed, such as for the entire abdomen.

Goal(s): To homogeneously excite the whole abdomen using dynamic pTx and to investigate the minimal number of kT-points necessary.

Approach: Dynamic pTx is applied in the abdomen using a 32-Tx-channel whole-body array and free-breathing relative B₁⁺ mapping.

Results: The preliminary data indicates that exciting the whole abdomen is feasible and that dynamic pTx yields sufficient FA homogeneity in all subjects.

Impact: The preliminary data indicates that exciting the whole abdomen is feasible and that dynamic pTx yields sufficient FA homogeneity in all subjects.

Keywords: High-Field MRI, RF Pulse Design & Fields, High-Field MRI, pTx, B1+ mapping, neural networks

Motivation: B₁⁺ -maps needed for subject-specific pTx can be derived from localizers using a neural network (NN), omitting separate B₁⁺-mapping. Ideally, a single, general NN applicable to all UHF sites is highly desired.

Goal(s): Investigate the robustness of a neural network predicted B₁⁺-field maps. Utilizing receive profiles from an 8Tx/32Rx head coil as neural network input.

Approach: Comparing the performance on data from identical and different commercial head coils across multiple MRI sites.

Results: Achieving SSIMs as high as 96% and RMSEs as low as 2.7%, with error mapping predominantly localizing discrepancies at the cranial margins, suggesting that larger datasets could enhance Gaussian convergence.  

Impact: The study suggests that a single NN trained by a large B₁⁺ library for one type of pTx head coil may be disseminated to other UHF sites that use the same coil. This will enable a fast, streamlined pTx calibration.

Keywords: RF Arrays & Systems, RF Arrays & Systems, Ultra highfield, 7T, coil comparison, pTx, transmit efficiency

Motivation: A standardized pTx body array would be highly beneficial for 7T, especially as a step toward achieving an extension of the existing 7T CE label/FDA clearance to whole-body MRI.

Goal(s): To compare the transmit performance (Tx efficiency/coverage) of 5 different existing body coils containing different element types.

Approach: Measure relative and absolute B₁⁺ maps and evaluate them regarding the Tx efficiency and Tx heat-foot coverage.

Results: The B₁⁺ efficiency was similar for all local coil concepts with some differences in heat-foot excitation coverage. The remote array achieved the largest heat-foot excitation coverage and can achieve similarly high flip angles as the local arrays.

Impact: B₁⁺ efficiency was similar for all local coil concepts with some differences in excitation coverage. The remote array achieved the largest excitation coverage and can achieve similarly high flip angles as the local arrays if sufficient transmit power is available.

Keywords: System Imperfections, System Imperfections: Measurement & Correction

Motivation: Successful multi-coil B₀ field control relies on reproducible hardware placement. 

Goal(s): Our goal was to detect hardware misplacements from MC-generated field patterns alone (i.e. without field probes) to allow spatial transformations for correction. 

Approach: We co-registered unique field maps before and after hardware displacements to derive the underlying translation and rotation parameters. 

Results: In simulation and preliminary scanner validation, hardware misplacements were detected with sub-millimeter/sub-degree precision. 

Impact: Field-based spatial self-registration for multi-coil field inserts is expected to allow optimal B₀ field control even with differences in hardware placement, thus preserving the best shim performance. 

Keywords: High-Field MRI, High-Field MRI, X-nuclei, SAR, VOP

Motivation: Managing peak local SAR for pTx-enabled studies at UHF is challenging, especially for multinuclear acquisitions.

Goal(s): To evaluate the feasibility and potential advantages of multinuclear VOPs for pTx optimizations in multinuclear studies.

Approach: Simulation data was used to perform L-curve analyses to quantify the achievable minimal excitation errors at different peak 10g local SAR levels using both mononuclear and multinuclear VOPs.

Results: Multinuclear VOPs can substantially improve excitation performance at a set peak 10g local SAR level in multinuclear acquisitions by preserving the spatial correlation between the 10g local SAR resulting from each individual nucleus’s excitation.

Impact: The improved ¹H excitation performance enabled through multinuclear VOPs can lead to improved image quality and reduced scan times for a variety of multinuclear imaging applications.

Keywords: System Imperfections, System Imperfections: Measurement & Correction, B1 shim

Motivation: To develop a method for fast per-patient calibration of B1 shim parameters.

Goal(s): To reduce scan time for per-patient B1 shimming calibration to improve patient throughput.

Approach: A key insight is that 1D projections acquired with specific projection orientations are sufficient to capture B1 distribution patterns. By comparing a pair of orthogonal B1 projections in the brain or by measuring average B1 amplitude of a pair of ROIs in a single projection across the breast, left-right B1 symmetry can be measured.

Results: Optimal B1 shim settings can be determined with a total time < 1 second as confirmed by B1 maps.

Impact: The proposed method for per-patient B1 shimming calibration using 1D B1 projections instead of 2D B1 maps can quickly calibrate B1 shimming parameters in less than one second.

Keywords: RF Arrays & Systems, High-Field MRI

Motivation:  Improved RF coil performance is needed to realize the gains from UHF body imaging.

Goal(s): Design a 7T body array with improved stability and increased transmit/receive performance.

Approach: A 32 channel loop-dipole (32LD) array was constructed with a shield allowing for on board electronics. Dipoles were transceivers while loops were coupled in groups of three on transmit while receiving separately.  Comparisons were made with an existing 16LD array.

Results: The 32LD is more stable, has a lower flatter z-profile on transmit, 20% higher central SNR and supports parallel imaging on all axes

Impact: The new 32LD array provides a more robust platform for clinical translation of UHF body imaging while approaching the theoretical gains in SNR and improved parallel imaging performance enabling increased spatiotemporal resolutions at 7T.

Keywords: Hybrid & Novel Systems Technology, Prenatal

Motivation: The development of hardware dedicated to pre-clinical applications that can produce high quality images for small animal MRI systems with limited transmission channels.

Goal(s): a double birdcage coil that can deliver  uniform field for multiple rats, while having only one transmission channel.

Approach: Employing electromagnetic simulations, we devised a geometric arrangement comprising two birdcage coils with a leg distribution rotated relative to each other. This configuration enables the generation of uniform, high-intensity circularly polarized fields.

Results: Uniform magnetic fields were acquired with double birdcage coil with a single excitation port.  These results also showed uniform field  and with similar intensity between two rats.

Impact: By employing double birdcage coils with rotated leg distributions, we achieve the generation of uniform and strong circularly polarized magnetic fields. This breakthrough offers significant advancements in pre-clinical applications and has the potential to improve research in small animal MRI.

Keywords: High-Field MRI, RF Arrays & Systems, Coupling

Motivation: To gain a better understanding of electromagnetic (EM) interactions in RF coil designs by visualizing their EM flow.

Goal(s): Identifying the dominant coupling mechanism in different coil types through visualization of electric and magnetic fields and power flow. 

Approach: Simulating conventional, shielded-coaxial-cable (SCC), twisted pair coils, and square loops (self-decoupled coils) to visualize their EM fields using streamlines.

Results: Diverse coupling behaviors are observed among the coil types, each demonstrating unique dominant mechanisms. A high resemblance in the EM flow between the self-decoupled coil and the SCC and twisted pair coils was found.

Impact: Identifying the dominant coupling mechanism in different coil designs with streamlines can help in adjusting the coil design for maximum interelement decoupling when placed in an array configuration.

Keywords: Gradients, Gradients

Motivation: MRI users rely on vendor-specific means to correct for distortions due to gradient nonlinearity. This study endeavors to measure gradient nonlinearities without a dedicated phantom for MR systems where accurate correction parameters are unavailable.

Goal(s): Develop a nonproprietary gradient nonlinearity measurement procedure.

Approach: We conduct NMR field probe measurements to determine the gradient nonlinearity. A dedicated algorithm detects inconsistencies between the apparent probe positions and seeks the optimal spherical harmonic coefficients correcting for distortions.

Results: We demonstrate the feasibility of the proposed measurement and a reduction of distortions in MR images.

Impact: The proposed nonproprietary approach for measuring gradient nonlinearity induced distortions without a dedicated phantom has the potential to promote accuracy and reproducibility of imaging studies across different MRI systems, if the sites are equipped with a field camera.

Keywords: RF Arrays & Systems, Breast

Motivation: This study addresses the challenge of motion artifacts in free-breathing supine breast MRI using a flexible RF coil, aiming to improve image quality and patient comfort.

Goal(s): The primary goal is to demonstrate the feasibility of motion correction using beat pilot tones (BPT) in combination with the GRICS algorithm, requiring no additional on-patient hardware.

Approach: A volunteer underwent supine breast MRI performing various breathing patterns, while BPT motion signals were extracted. The GRICS algorithm was used for retrospective motion correction.

Results: Motion artifacts were effectively reduced for flat abdominal and normal thoracic breathing. However, heavy thoracic breathing artifacts were insufficiently reduced.

Impact: Motion-corrected supine breast MRI with a flexible coil promises improved diagnostic image quality and increased patient comfort. Further optimization of acquisition and motion-correction techniques for clinical supine breast MRI will ultimately aid in early disease detection and management.

Keywords: Phantoms, Interventional Devices, Rapid prototyping, medical devices, phantoms, biopsy

Motivation: This study is motivated by the authors to easily, and cheaply, manufacture phantoms and other accessories that is inherently dimensionally accurate, MRI compatible, and visible in MRI images. 

Goal(s): The goal of the study is to develop a manufacturing method to create a MRI-visible localization grid for MR-guided breast biopsies. 

Approach: By hollowing out the part without inclusions of any drainage holes, we can ensure liquid resin is trapped inside the part during the printing process. 

Results: The finished part is shown to be inherently MRI visible as demonstrated on both T1- and T2-weighted images from our MRI biopsy protocol.

Impact: This approach offers an efficient and cost-effective solution for creating MRI-visible objects with high spatial accuracy, which is useful for producing phantoms and other MRI compatible accessories. 

Keywords: Phantoms, Phantoms

Motivation: While soy lecithin has been shown to be a beneficial substance for the production of diffusion phantoms, there is no research to date on whether this applies generally or only to specific product sources of soy lecithin.

Goal(s): To investigate the variability of the MR-related properties of three different types of soy lecithin (SL-1,SL-2,SL-3).

Approach: Aqueous soy lecithin solutions of different concentrations were prepared for all three soy lecithin sources and examined using DWI and Relaxometry.

Results: It was found that the MR-related properties of aqueous soy lecithin solutions are dependent on the type of soy lecithin used.

Impact: This work shows that MR properties of soy lecithin strongly depend on the product source. Related effects must be considered for the production of phantoms with tissue-like relaxation and diffusion properties.

Keywords: Hybrid & Novel Systems Technology, Simulations, spatial encoding

Motivation: Design of accessible scanners may require accounting for substantial magnetic field inhomogeneities, which challenge assumptions used in MRI simulators.

Goal(s): To capture the encoding effects of strong field variations accurately and efficiently, predicting distortions of input images.

Approach: We discretized magnetic fields as usual but extended the MR signal simulation at each grid point from the 0^th-order approximation, which assumes a locally-constant field, to a 1^st-order approximation, which assumes a locally-linear field.

Results: The 1^st-order approximation, which has an analytic solution, better captures strongly varying fields and enables simulations on a coarser grid, greatly improving computational efficiency.

Impact: The simulator enables evaluation of scanner designs with strongly varying magnetic fields. Simulated images can be utilized to generate training data efficiently from existing ground-truth images, enabling exploration of machine-learning techniques prior to the construction of prototype systems.

Keywords: RF Arrays & Systems, RF Arrays & Systems, liquid metal, stretchable RF coils

Motivation: Motivated by the limitations of traditional RF receive coils, this study aims to demonstrate in vivo imaging using a conformal and stretchable, self-tuning liquid metal coil array.

Goal(s): This study’s goal was to demonstrate improved signal-to-noise ratio (SNR) with the stretchable array compared to commercial coils.

Approach: We designed and fabricated a one-dimensional 6-channel stretchable coil array and tested it in vitro and in healthy volunteers using standard knee imaging sequences.

Results: In vitro and in vivo experiments demonstrated an SNR improvement of 4.7x over a dedicated commercial knee coil.

Impact: Our self-tuning stretchable coil array allows for maximized SNR and improved image quality due to its conformal fit and minimized distance from the target anatomy. This concept could also allow for dynamic imaging, leading to enhanced, clinically relevant, MRI applications

Keywords: System Imperfections, Interventional Devices

Motivation: Clinical MRI-guided microwave ablations often suffer from noise due to electromagnetic interference (EMI) between ablation probes and imaging coils. Instead of modifying the clinical microwave ablation system that could compromise FDA-approval, we explore alternative coil designs to mitigate the noise.

Goal(s): Minimize EMI between the microwave ablation probes and imaging coils during clinical MR-guided microwave ablations.

Approach: We applied a band-pass filter, studying the impact of coil size, and investigating efficient coil combinations to reduce interference.

Results: A band-pass filter led to a  89% improvement in field uniformity. Also employing smaller coils can mitigate the ripple effects induced by the ablation probe.

Impact: Our study addresses the critical need to reduce electromagnetic interference (EMI) between microwave ablation probes and imaging coils during clinical MR-guided microwave ablations at 1.5T. Motivated by the interference challenges in current clinical setups, we develop methods to mitigate EMI.

Keywords: High-Field MRI, Pulse Sequence Design, B1+ Mapping, SatTFL, Sandwich, SA2RAGE, 7 Tesla

Motivation: Fast and accurate B₁⁺ mapping is critical for parallel transmission in ultra-high field MRI, but several options exist, and which is the most optimal is unknown.

Goal(s): To evaluate three FLASH-based volumetric B₁⁺ mapping methods; 2D SatTFL, 3D SA2RAGE and 3D Sandwich.

Approach: We acquired fully sampled absolute B₁⁺ maps at 7T in a realistic human head phantom across multiple transmission voltages to establish a ground truth and assess the dynamic range of each method.

Results: SA2RAGE and Sandwich both enable low-power non-selective RF pulses and maintain accuracy for low B₁⁺ regions. Sandwich has a 60% shorter acquisition time than SA2RAGE.

Impact: This study will help to inform a choice of B₁⁺ mapping sequences when imaging at ultrahigh field.

Keywords: RF Arrays & Systems, Arterial spin labelling

Motivation: To overcome the limitations of a commercially-available single-transmit channel knee coil in terms of B₁⁺ inhomogeneity in the imaging region, and limited coverage in the proximal femoral meta-diaphysis for knee bone marrow arterial spin labeling (ASL) at 7T.

Goal(s): Our goal was to evaluate the B₁⁺ performance of possible transmit array designs, as the first step towards an optimized design for an ASL imaging knee coil.

Approach: 6- and 8-channel multichannel transmit array designs were explored experimentally and in simulation. 

Results: Both evaluated transmit arrays provided more uniform B₁⁺ and better coverage in the labelling region compared to a single-transmit channel knee coil.

Impact: Development of pTx-capable knee coils will greatly improve the quality, reliability, and efficiency of knee ASL imaging at 7T and can provide the clinically critical but currently not available platform for the assessment of knee bone marrow perfusion.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: Conventional hand/wrist coils have larger loop sizes and limited number of elements, resulting in in-sufficient SNR and acceleration capability for imaging small anatomic structures.

Goal(s): To develop a small flexible coil for hand/wrist, which improves spatial resolution, SNR and acceleration with flexibility for brachial plexus imaging as well when combined with other coils.

Approach: A 30-Channel parallel imaging optimized coil was built with the small flexible dual loop, high impedance internal cable baluns, exceptionally low noise preamplifiers and highly flexible mechanical materials.

Results: This study shows higher SNR and improved acceleration capabilities for results for this novel ultra-flexible coil compared to conventional coils.

Impact: This novel coil design provides comfortable fitting, high-resolution and higher acceleration for in-vivo 3T hand/wrist/unilateral brachial plexus imaging.

Keywords: System Imperfections, System Imperfections: Measurement & Correction, Trajectory correction

Motivation: Gradient imperfections typically cause ringing and blurring artifacts in spiral imaging. Gradient impulse response function (GIRF) characterizes the gradient system and can be applied for gradient prediction in image reconstruction. However, the low-pass characteristic of the gradient system could cause a penalty of the achieved resolution.

Goal(s): This work aims to improve the GIRF-based spiral trajectory correction. 

Approach: A joint pre-emphasis and post-processing method was introduced to correct spiral trajectory. The effectiveness of our proposed method was tested on the phantom and in-vivo experiments.

Results: The ringing and blurring artifacts were further mitigated using our proposed method.

Impact: A joint pre-emphasis and post-processing correction strategy was proposed in this study. The results of phantom and in-vivo experiments indicate that our proposed method yields good image quality and effectively reduces the loss of the actual resolution.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: Optimize dipole antennas for 7T MR applications.

Goal(s): Enable compact 300MHz dipole structures for higher-channel arrays.

Approach: Introduce a solenoidal dipole design and evaluate against meander designs using numerical simulations.

Results: Analyze H-field efficiency, electric-field distributions, coupling, and Q-factors in multi-channel arrays.

Impact: The introduction of a solenoidal dipole design overcomes limitations posed by meander structures, enabling shorter and compact 300MHz dipole antennas for 7T MR applications within higher-channel multi-channel arrays, positively impacting MR imaging efficiency and signal quality.

Keywords: RF Pulse Design & Fields, RF Pulse Design & Fields, DAM, 31P, B1 mapping, fast B1, MRSI, X-Nuclei

Motivation: Fast and accurate B1 mapping for ³¹P MRI is challenging due to the low sensitivity of ³¹P nucleus and its long T1 relaxation times.

Goal(s): This study aims to develop a fast B1 mapping approach for ³¹P at 7T.

Approach: A look-up table approach was adopted to enable B1 mapping at short TR. Fast spiral encoding together with weighted averaging was implemented with a GRE sequence to further accelerate the acquisition.

Results: B1 mapping was validated in phantom and in vivo in human calf muscle and brain within a scan time of 10min.

Impact: The presented fast and accurate B1 mapping correction method is particularly suited for moderate to short repetition times, showing promise for future applications in rapid X-nuclei imaging.