Keywords: New Devices, Motion Correction, Biofeedback

Motivation: Biofeedback during radiotherapy simulation and treatment on conventional linacs improves the accuracy and reproducibility of patient alignment, especially those using breath-hold. However, commercial devices cannot operate in MR environments.

Goal(s): The goal of this study was to develop an MR-compatible biofeedback device and test its utility in volunteer studies.

Approach: The device consists of a single-board computer and addressable LED strip, which was automatically controlled by tracking anatomic motion in CINE MR images.

Results: Initial volunteer studies using the device in an MR linac demonstrated that biofeedback-guided breath-hold resulted in more accurate and consistent target alignment compared to self-guided breath-hold.

Impact: MR-compatible biofeedback devices can facilitate and improve breath-hold techniques for MR-guided radiotherapy simulation and treatment. Furthermore, incorporation of CINE MR images to measure changes in internal anatomy improves target alignment relative to existing devices that use surface imaging.

Keywords: Phantoms, Phantoms, ASL, perfusion

Motivation: During longitudinal studies it is important to ensure quality assurance of MRI data. Here we use a commercially available perfusion phantom for QA of ASL in a 40-patient placebo-control study.

Goal(s): The goal of this study was to assess the utility of a perfusion phantom for QA of ASL MRI in a clinical trial setting.

Approach: Inversion recovery T1 measurements and pseudo-continuous ASL at 3 different phantom flow rates were scanned periodically on a 3T MRI system over a 36 month period.

Results: Once data due to errant phantom behaviour was discounted, the QA metric of labelling efficiency was in a reasonable range.

Impact: By acquiring independent T1 measures of the phantom’s perfusate, then computing ASL perfusion maps and comparing against the phantom’s pump flow rate, a useful QA metric can be established that can provide confidence in acquired subject ASL data.

Keywords: Safety, Safety

Motivation: MR safety guidance formulated by experts from the MR community build upon a combination of experience and technical expertise. MR safety guidance may benefit from assessment based on general workplace safety practices.

Goal(s): To critically assess MR safety guidance and practices using the hierarchy of hazard controls.

Approach: MR safety practices were scored using a 5-point scale derived from the hierarchy of hazard controls, in several areas of risk for MR personnel, patients, and non-MR personnel.

Results: Hazard controls for non-MR personnel had consistently high effectiveness scores, while those for for MR personnel and patients had moderate effectiveness scores, with a greater range.

Impact: The analysis presented in this work could serve as a tool to analyse choices made in the deployment of safety measures, to motivate decision- or policy-making, or as a tool for assessment of MR safety programs.

Keywords: High-Field MRI, High-Field MRI, 7T, 3DTOF, Non-contrast MRA, High gradient performance, microvascular

Motivation: Non-contrast 3DTOF demonstrates visualizing the cerebral microvasculature at 7T MRI, but the scan time is too long, typically about 10 minutes due to requiring high spatial resolution.

Goal(s): Our goal was to reduce the acquisition time by a factor of 2.

Approach: We utilize FLEXA on the high gradient performance system at 7T.

Results: Comparable image quality to 3DTOF was obtained with FLEXA technique with a factor of 2 decrease in acquisition time.

Impact: The improvement in acquisition speed through FLEXA comes from the strategy of short TR with thin slab and opens new standard for scan protocol optimization at 7T MRA.

Keywords: Phantoms, Whole Body, Whole-body diffusion-weighted imaging

Motivation: Poor signal-to-noise ratio (SNR) of whole-body diffusion-weighted images (WB-DWI) impacts the diagnostic exam quality in whole-body MRI. Evaluating SNR of WB-DWI using healthy volunteers is challenging when developing imaging protocols for multi-centre studies. 

Goal(s): Develop a phantom for assessing whether a proposed WB-DWI protocol will provide adequate SNR in patient examinations.

Approach: A phantom was developed which replicated relevant MR properties of WB-MRI patients. We measured SNR using the phantom and qualitatively graded SNR in subjects. 

Results: Good correlation was found between the phantom and the subject data and a discrimination threshold between good and poor quality exams was determined.

Impact: A phantom can be used to assess the SNR of WB-DWI protocols and shows good correlation with qualitative image quality, enabling faster, quantitative optimisation of SNR in WB-DWI protocols when setting up multi-centre studies.

Keywords: PET/MR, PET/MR, MR Priors, Motion Correction

Motivation: Using MR-priors in PET reconstruction has been performed in numerous studies. While MR-priors provide more SNR and better resolution ti PET-images, without considering motion there may be misalignment between PET and MR images which leads to crosstalk artifacts. Another concern is mismatch between MR and PET images which can potentially affect the final PET image.

Goal(s): To compare the two most-widely used PET recon with MR-priors methods: the Bowsher's method and MRgBSREM.

Approach: We created an MR-series with severe line artifacts and used in as MR-priors in both methods.

Results: We have shown that MRgBSREM handles these mismatches better than the Bowsher’s method.

Impact: MRgBSREM is more robust to mismatches between PET and MR. This is achieved by adding a PET-seed image to identify similar-voxels which avoids the situation in which voxels with significantly different PET-uptake would be considered similar based only on MR-images.

Keywords: Neurofluids, Brain, Volumetric strain; Brain tissue deformation

Motivation: The heartbeat causes deformations and volumetric strain in the surrounding brain tissue which can be observed using Displacement Encoding with Stimulated Echoes (DENSE) MRI. Local variations in volumetric strain reveal both expansion and compression in individual voxels or regions.

Goal(s): To offer insights into the heterogeneous patterns seen in volumetric strain maps.

Approach: Volumetric strain data of nine subjects was included and clustered (k-means) into four clusters.

Results: Both expanding and compressing clusters were found in all subjects. Compressing clusters were mostly found at the periphery of the brain and possibly reflect structures facilitating fluid movement (sulci and veins). 

Impact: Clustering volumetric strain data into individual clusters with similar voxels reveals distinct volumetric strain profiles in DENSE data. Potentially, these clusters can be used to cleanup DENSE data from fluid-related artifacts to make the data specifically reflect brain tissue strains.     

Keywords: In Silico, Artifacts

Motivation: RF shielding up to 95% in stents creates image artifacts that can impact an accurate diagnosis of vessel patency after stent implantation. 

Goal(s): The association between design parameters of novel venous stents and their RF shielding properties were investigated.

Approach: Therefore, field simulations and measurements were performed of the relative induced B₁ in venous stents with different lengths and cell geometries. 

Results: Edge length of the stent cells and their orientation relative to the B₁ transmit field determine the amount of RF shielding.

Impact: The work provides information about the correlation of venous stent geometries and RF shielding artifacts. Sequence parameters e.g. excitation flip angle could be adapted for different stent models to possibly achieve higher intraluminal signal in post-implantation MRI venography.

Keywords: Gradients, Gradients

Motivation: To assess diffusion metrics on a cellular scale necessitates much higher gradient amplitudes. A local nonlinear breast gradient coil needs methods of controlling the field variation during the coil design stage.

Goal(s): Control the y-axis gradient variation of a double layer local breast gradient coil to achieve far above 1T/m in the whole target region. 

Approach: Incorporation of a constraint to control the variation of the gradient along the y-axis with a double-layer current-carrying surface.

Results: A non-linear local human breast gradient coil with a gradient strength between 1.61 and 3.74 T/m for a current of 650 A was designed.

Impact: The coil design with a subsequent implementation paves the way to the application of novel diffusion imaging techniques for the detection and characterization of breast cancer.

Keywords: Phantoms, Precision & Accuracy, 3D Printing, Phantoms, Quantification, Material Characterisation

Motivation: 3D printed materials offer the capability of manufacturing custom phantoms or coil prototypes. While materials for other modalities (such as CT) are widely available, the same cannot be said for MRI.

Goal(s): The goal of this project was to characterise a wide range of 3D printed materials for use in MRI. 

Approach: Using standardised sample sizes, and relaxation property mapping sequences.

Results: Some materials, such as Nylon, proved invisible to MRI. Other materials, such as OrganLike, showed relaxation properties similar to those in the brain at 3T. 

Impact: 3D printing offers the potential to rapidly create low cost, reproducible prototypes for MRI. This work provides an extensive list of the properties of materials, aiding others in narrowing down a material of choice. 

Keywords: High-Field MRI, Bone, Diabetes bone, UTE-MRI, MMF, Exchange rate

Motivation: Increased risk of fractures in patients with type-2 diabetes mellitus (T2DM) despite higher average bone mineral density is unexplained with routine diagnostic tools like DEXA and CT. 

Goal(s): This study aimed to examine the feasibility of using ultrashort echo time (UTE) magnetization transfer (MT) modeling to detect the potential differences between T2DM and normal rats.

Approach: The macromolecular fraction (MMF) and proton exchange rate (k_ab) from UTE-MT modeling on the tibial bone of Zucker diabetic fatty (ZDF) and Zucker lean (ZL) rats were compared.

Results: There was a significant difference in MMF and k_ab measures between the two groups.

Impact: The MMF and kab measures can detect potential bone alternations related to T2DM which may help to better understand the pathogenesis of T2DM bone fractures. 

Keywords: Phantoms, Quantitative Imaging, Reproducibility

Motivation: Variability and bias of diffusion parameters need to be assessed to separate the measurement-induced variability from biological effects.

Goal(s): Our goal was to assess the bias and variability of mean diffusivity (MD) from the Diffusion Tensor Model using a traceable phantom.

Approach: The NIST/QIBA phantom was scanned multiple times using two different head coils on the same system. The differences between MD measured using different head coils and bias to NIST-reported values were investigated.

Results: A significant difference in measured MD with two coils can be found across multiple vials. Both coils introduce non-negligible bias to NIST-reported values for lower MD values.

Impact: Using traceable phantoms is essential in the development of Diffusion MRI-based Quantitative Imaging Biomarkers (QIBs). Different head coils can introduce significant differences across MD values and should be treated as confounding factors in QIBs studies.

Keywords: System Imperfections, System Imperfections: Measurement & Correction, Vendor-Neutral Automated Quality Assurance

Motivation: Ensuring comparable performance of MR protocols across vendors and over time duration.

Goal(s): To implement an easy-to-use vendor-independent quality control pulse sequences and data analysis routines.

Approach: Relying on Pulseq as a vendor-independent MR pulse sequence environment, we implemented the established quality assurance protocols (ACR/fBIRN). Following the image reconstruction from the acquired data, performed either on the scanner or off-line in Gadgetron, images are analyzed by the open-source Matlab pipeline.

Results: The proposed protocol has been tested on three 3T Siemens scanners with over a decade difference in the manufacturing date and has been successfully executed on a 3T GE scanner.

Impact: The proposed protocol and post-processing scripts allow for easy and streamlined quality assurance, contributing an essential component for Pulseq to become usable in large scale multicenter imaging studies.

Keywords: High-Field MRI, High-Field MRI

Motivation: Ultra-high field MRI of the brain suffers from an increased B₁⁺ inhomogeneity as well as involuntary motion artifacts when very high spatial resolution is targeted.

Goal(s): Integration of a FatNav technique into pTx Universal Pulse sequences would be beneficial to reach the best image quality at very high resolution.

Approach: An MP(2)RAGE sequence using GRAPE pTx universal pulses was modified to integrate a FatNav module. High-resolution protocols were acquired in vivo on the brain.

Results: Very high-quality images were obtained throughout the brain and cerebellum thanks to FatNav motion correction and pTx Universal Pulses.

Impact: The ultra-high field community targetting high-resolution protocols on the whole brain would benefit from a FatNav-enabled PASTEUR package to bring robust protocols against B₁⁺ inhomogeneities and involuntary motion of the head.

Keywords: Parallel Transmit & Multiband, Brain, bSSFP, parallel transmission, transmit field inhomogeneity

Motivation: Elimination of the transmit field inhomogeneity effects in the brain for T₂ contrast at 7T.

Goal(s): Removing the transmit field inhomogeneity effects in balanced steady state free precession acquisitions using Bilateral Orthogonality Generative Acquisitions method.

Approach: Bilateral Orthogonality Generative Acquisitions method is implemented  at dual channel parallel transmit 7T system using several balanced steady state free precession acquisitions with varying scan parameters to eliminate the transmit field inhomogeneity effects and reduce the banding artifacts effects via different combining schemes in the final image.

Results: T₂ contrast was obtained without the transmit field inhomogeneity effects but residual banding artifacts exists in the final images.

Impact: T₂ contrast can be achieved without the transmit field inhomogeneity effects in the brain using balanced steady state free precession sequence.

Keywords: Bioeffects & Magnetic Fields, Artifacts

Motivation: Inhomogeneity in measured multi-gradient echo (mGRE) field data corrupts reconstructions of quantitative susceptibility maps by obscuring the tissue field of interest with strong background field.

Goal(s): To extend the voxel spread function (VSF) library implementation to a nonzero phase offset and demonstrate improvements on QSM.

Approach: The measured field was estimated and inhomogeneity contributions computed using the extended library implementation. The inhomogeneity field was then estimated and subtracted from the total field to reduce the influence of strong background fields in the QSM reconstruction

Results: Inhomogeneity-informed field-fitting for QSM is shown to improve total field reconstructions of the brain, carotid, and cervical spine.

Impact: The voxel spread function (VSF) library implementation is extended to include initial phase offset contributions and reduce the effect of field inhomogeneity in quantitative susceptibility map (QSM) reconstruction.

Keywords: RF Arrays & Systems, RF Arrays & Systems, intraoral, dental, maxillofacial, RF coil

Motivation: In dental diagnostics MRI provides an improved soft tissue contrast for endodontic, craniomaxillofacial and implant applications with better visibility of anatomical structures.

Goal(s): An intraoral coil array is introduced for dental MRI to investigate feasibility, achievable signal gain and parallel acquisition performance.

Approach: Coil element size, material, and shape properties are investigated with respect to image SNR. The array is adjusted to the dental anatomy on a 3D phantom to estimate the sensitivity and the g factor of parallel imaging.

Results: Intraoral coil array improves SNR, spatial resolution and provides a homogenous B₁ receive profile. It allows parallel imaging to minimize measurement time.

Impact: Intraoral coil arrays can enhance MRI of small dental structures, required for endodontics, while increasing the spatial coverage in oral cavity. Compared to single-loop coils, a more homogeneous receive sensitivity can be achieved and parallel imaging becomes feasible.

Keywords: Neurofluids, Alzheimer's Disease, Aging, Brain, Blood Vessels, Cardiovascular, Dementia, Flow, Neuro, Neurodegeneration, Neurofluids, Velocity & Flow

Motivation: Cardiac driven motions may affect Alzheimer's Disease.

Goal(s): The goal was to provide preliminary results on the success of measuring the displacement and strain of brain tissues due to Cardiac Arterial Pulsations (CAPs) using DENSE (Displacement ENcoding with Stimulated Echoes) in patients with AD and age-comparable controls.

Approach: DENSE scan data from a sample of 133 volunteers was processed and evaluated for trends in the derived displacement and strain information.

Results: High variability was found in the displacement measures, and future work is needed to determine the confounding factors behind the variability and to what degree those factors can be minimized going forward

Impact: DENSE MR was used to measure displacement of brain tissue from cardiac effects in Alzheimer’s disease (AD) patients and age-comparable controls. Preliminary results are inconclusive and future work is needed to determine what confounding factors are affecting the displacement measures.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: Hyperpolarized ¹³C MR imaging is of particular interest in cancer applications such as tumor staging and monitoring treatment response as it provides unique real-time metabolic information.

Goal(s): This work is to develop a novel double-tuned RF coil that can achieve uniform excitation and highly sensitive acquisition for ¹H/¹³C MR imaging at 7T.

Approach: The numerical electromagnetic simulation was utilized to evaluate the feasibility and performance in s-parameters and B₁⁺ field distributions. The bench tests were conducted to further validate the performance.

Results: These simulated and measured results indicated that the development of an efficient ¹H/¹³C RF coil for MR imaging at 7T.

Impact: A novel double-tuned RF coil system that can achieve uniform excitation and highly sensitive acquisition for ¹H/¹³C MR imaging at 7T was developed. This coil system has the potential to be used for hyperpolarized ¹³C MRI at ultra-high field.