Keywords: Phantoms, Phantoms

Motivation: There is not a commercially available musculoskeletal (MSK) relaxometry phantom.

Goal(s): Develop a dedicated MSK relaxometry phantom for T1, T2, and T1rho measurement quality assurance.

Approach: A cylindrical phantom with 12 vials containing modulated T1 and T2 samples was created, with an MR-visible thermometer for temperature tracking. Phantom stands were used for consistent positioning. MRI/NMR measurements were collected for longitudinal stability and temperature dependence.

Results: MRI measurements were in good agreement between two vendors with CVs<3% and demonstrated longitudinal stability with CVs<3% over a 3-month period. NMR measurements showed clear changes in T1, T2, and T1rho with changing temperature.

Impact: A stable MSK relaxometry phantom prototype was successfully developed and characterized, including changes with temperature. With harmonized measurement protocols, this phantom will facilitate the use of quantitative relaxometry MRI in large-scale multi-site multi-vendor trials.

Keywords: Phantoms, Phantoms, image quality evaluation

Motivation: The typical MRI phantoms with simple geometric inserts in homogenous background do not allow in-depth evaluation of MR image characteristics necessary for assessing advanced imaging and reconstruction techniques.

Goal(s): To develop phantoms that can produce images with realistic anatomical structure that are more suitable for thorough evaluation of MR image characteristics.

Approach: We developed an approach to construct novel anthropomorphic phantoms using 3D-printing technique and use an example to demonstrate the utilization of this phantom for image quality evaluation.

Results: The phantom created with this approach can produce images resembling original MRI images acquired on human subjects.

Impact: The phantom generated using the proposed approach allows in-depth evaluation of MR image characteristics utilizing images with realistic anatomical structure, which may be especially beneficial for developing and evaluating advanced data acquisition and reconstruction techniques.

Keywords: Phantoms, Phantoms, Motion

Motivation: The development of motion tracking and correction methods requires suitable motion phantoms.

Goal(s): The design, fabrication, assembly and testing of a modular dynamic torso phantom.

Approach: The phantom consists of a saline-filled acrylic shell, with dimensions comparable to a human torso and three distinct interior motion modules. Two linear piezo stages are used to mimic breathing motion of the chest wall and the abdominal organs including the heart, respectively. A pneumatic system is used to move a heart mock-up to represent cardiac motion.

Results: The motion capabilities and MR compatibility of the phantom are validated in 3 T MRI experiments.

Impact: This work presents the development of a dynamic torso phantom for MR applications, i.e. a scientific instrument that can serve as ground truth for the investigation and characterization of novel motion compensation and tracking methods.

Keywords: Phantoms, Phantoms, Validation, Temperature mapping, Dynamic

Motivation: MRI-guided radiofrequency ablation of cardiac arrhythmias holds promise to monitor the lesion formation process, however lacks validation tools.

Goal(s): To develop a phantom for quantitative validation of catheter ablation procedures.

Approach: In this study, a phantom composed of polyvinyl alcohol (PVA) with temperature sensitive properties has been developed for validation of the attained ablation temperature.

Results: Post-ablation T₁ maps were acquired and converted into temperature maps, based on the characterization of the reference phantoms.

Impact: This work demonstrates a validation phantom for temperature validation after radiofrequency ablation procedures. This can offer an effective tool for MR methods development as well as procedural training, shortening procedural times and improving patient outcomes.

Keywords: Phantoms, Phantoms

Motivation: Overcome the high cost, lack of customisation and low global uptake of standard MRI imaging phantoms.

Goal(s): Design an affordable open-source MRI imaging phantom, imaging protocols and analysis tools demonstrated, showcasing their efficacy through the evaluation of slice profile and spatial resolution assessment.

Approach: A complex, multilayered phantom is designed with careful material selection aimed at low cost (US$500 worth of materials) and accessible construction principles. Slice profile and resolution measurements were performed using a double-wedge and a coarse resolution grid, respectively.

Results: This study has successfully produced an affordable open-source imaging phantom with detailed MRI assessment protocols.

Impact: This project's affordable, open-source MRI phantom and specialised assessment protocol benefit researchers by reducing costs and encouraging collaboration. The findings on slice profiles and resolution parameters enhance MRI research, improving imaging outcomes and accessibility.

Keywords: Phantoms, Phantoms, Phantom, 3D Printing, Cardiac Interventions

Motivation: Both technological development as well as procedural training of interventional cardiac MR (iCMR) procedures require anatomically realistic models. Animal studies are undesirable and becoming virtually impossible due to legal and ethical restrictions.

Goal(s): To develop a realistic cardiac phantom that can be 3D printed using standard MR-visible support material.

Approach: Material properties were determined and an anatomically realistic cardiac model was developed and constructed using 3D printing. Imaging features were assessed and an MR-guided cardiac intervention was simulated experimentally.

Results: A simple and realistic MR-visible cardiac phantom has been presented for technological development and training purposes, to improve MR-guided cardiac interventions.

Impact: The proposed phantom facilitates the development, testing and validation of novel technologies to improve MR-guided cardiac interventions, can be used for procedural training purposes, and may ultimately contribute to the improvement of clinical outcome.

Keywords: Phantoms, Elastography, MRE, Hydrogel, Phantoms

Motivation: MRE is utilized  to assess tissue stiffness in vivo, however, robust validation in tissue-mimicking phantoms is needed.

Goal(s): Create hydrogel liver phantoms of varying stiffness, characterize them with MRE and compare MRE with a mechanical reference standard. Utilize pulsatile flow to mimic cardiac motion.

Approach: Flow phantoms of varying stiffness were created. Stiffness from mechanical test was compared to MRE. Cardiac tagging visualized motion inside each phantom.

Results: MRE shear stiffness showed agreement with indenter stiffness and cardiac motion decreased with stiffness.

Impact: Advances in MRE have led to its increasing use to determine tissue stiffness in vivo, however, robust validation in tissue mimicking phantoms has yet to be achieved. The proposed methodology may help to assess the quantitative performance of MRE.

Keywords: PET/MR, PET/MR

Motivation: AD patients must undergo repeated visits for amyloid and tau radiotracer imaging, leading to high costs and dose concerns due to PET's inability to simultaneously acquire multiple radiotracers during a single session.

Goal(s): Using PET/MRI scans, we used deep learning to create separate amyloid and tau PET images from a simulated combined dual-tracer image.

Approach: We simulated a combined amyloid-tau image by blending co-registered list-mode data and employed a 2.5D U-Net architecture for effective separation.

Results: Mixed-dose models, incorporating physics-inspired data augmentation and MR information, exhibited enhanced anatomical preservation and reduced variability in quantitative metrics.

Impact: The demonstrated separation of a simulated combined amyloid and tau PET/MRI study into its individual components using DL may allow for simultaneous injection of multiple radiotracers in a single acquisition, streamlining the imaging process for AD patients.

Keywords: Multimodal, Non-Array RF Coils, Antennas & Waveguides

Motivation: By the need to address the limitations of low-field MRI, such as low SNR and insensitive frequency tuning. 

Goal(s): We proposed a design of multimodal surface coil that can enhance the B1 efficiency while reducing the associated electric field. 

Approach: Through both electromagnetic simulation and bench testing, the performance of this novel coil design technique was evaluated and compared with the conventional surface coil and solenoid coil. 

Results: The results affirmed the superior performance of the proposed multimodal surface coil design in terms of B1 efficiency and frequency tuning over the surface coil and solenoid coil at the low field of 0.5T.

Impact: The proposed multimodal surface coil design improves B1 efficiency compared with the conventional surface coil and solenoid coil at 0.5T. It also mitigates frequency tuning challenges and has the potential to enhance the quality of low-field MRI in clinical diagnosis.

Keywords: Hybrid & Novel Systems Technology, Multimodal, TMS, EEG, fMRI

Motivation: The motivation for this research study is to improve the efficacy of transcranial magnetic stimulation.

Goal(s): The specific goals of this study are to establish a closed-loop TMS-EEG-fMRI system and to investigate brain state-dependent EEG-TMS responses in relation to concurrent fMRI measurements.

Approach: 150 single TMS pulses are delivered while monitoring TMS-elicited network activity using interleaved fMRI acquisition. Data processing involves extracting EEG phase information, preprocessing of fMRI data, and statistical analysis using SPM12.

Results: Significantly increased fMRI signal was detected in the M1 and SMA under specific EEG phase conditions. These results illustrate the relationship between TMS, EEG phases, and BOLD responses

Impact: The results of this study have important implications for the field of non-invasive brain stimulation and neuroimaging. The development of a closed-loop TMS-EEG-fMRI system holds the potential to revolutionize the treatment of various brain disorders by personalizing TMS interventions.

Keywords: Multimodal, High-Field MRI, EEG, fMRI, EEG-fMRI, 7T, laminar

Motivation: The combination of BOLD-fMRI at 7T with EEG could bring novel insights to neuroscience. However, the combination has remained challenging due to accentuated artifacts and RF-coil constraints.

Goal(s): To implement a first-of-its-kind 7T EEG-fMRI framework combining key developments from recent studies, and assess its safety, data quality and functional sensitivity in humans.

Approach: Extensive tests in phantom and humans(N=8) including field mapping, structural MRI and fMRI (1.6 and 0.8mm-resolution) acquired with+without EEG. Comparisons of data quality and functional sensitivity.

Results: The framework proved safe and feasible with fMRI down to sub-mm resolution, with moderate quality losses and potentially negligible impact on functional sensitivity.

Impact: This study characterizes the feasibility of 7T-EEG-fMRI with high sensitivity and acceleration capabilities, which could bring valuable insights to research in e.g. laminar functional connectivity, or localization of epileptogenic sources and their propagation pathways, for clinical diagnostic and pre-surgical planning.

Keywords: Multimodal, Elastography, Cross-validation

Motivation: Magnetic resonance elastography (MRE) and ultrasound time-harmonic elastography (USE-THE) have not been cross-validated yet. Since their results are in 3D and 2D, respectively, aligning them is difficult.

Goal(s): To cross-validate MRE and USE-THE in the brain based on a common atlas space.

Approach: An optical system tracked the position of fiducial markers derived from MRE during USE-THE measurements. Consequently, the resulting spatial alignment of both measurements allowed direct comparison.

Results: Stiffness was averaged over the whole field-of-view and over five anatomical regions. Globally, agreement was good (ICC=0.6982) and regionally, it was acceptable based on a Wilcoxon signed test (p>0.05).

Impact: Agreement between cerebral MRE and USE will facilitate multi-modal neural tissue characterization. Combined MRE-USE could benefit from high spatial resolution of MRE and high temporal resolution of USE-THE.

Keywords: PET/MR, Parallel Imaging, MR-PET 7T array

Motivation: We are developing the Human Dynamic NeuroChemical Connectome, a high spatio-temporal resolution brain PET (HSTR-BrainPET) scanner integrated with a 7T MR system

Goal(s): To build a 16-channel PET-compatible RF coil with parallel transmit capability based on an 8-channel test array for high-resolution imaging.

Approach: We designed and built multi-channel transmit-receive coils with RF screen that fits inside the spherical geometry of the PET camera. Coil performance was characterized with and without PET modules present.

Results: The performance of the 8-channel coil was satisfactory. Preliminary tests with the 16-channel array showed some loss in sensitivity in the CP mode.

Impact: By designing a 16-channel transmit-receive RF head coil and RF screen that both conform to the novel spherical geometry PET camera, we can acquire high-quality MR data simultaneously with PET data while also minimizing 511 keV photon attenuation.  

Keywords: Hybrid & Novel Systems Technology, Multimodal, Optical Imaging, Calcium

Motivation: BOLD fMRI is widely used as an indirect measure of neuronal activity. However, the spatial and temporal specificity of the BOLD signal is still under debate.
 

Goal(s): Being able to measure both hemodynamics and neuronal activity simultaneously with fMRI can help to improve interpretation of the BOLD signal.

Approach: A combined in-bore setup for concurrent intrinsic optical imaging, calcium imaging and ultra-high field fMRI in rats was designed.
 

Results: Measurements of BOLD, intrinsic hemodynamic and calcium signals with high temporal and spatial resolution reveal high correlation between these signals with specific characteristics regarding localization, vascularization and fMRI sequence.

Impact: A combined in-bore setup for concurrently recording calcium, intrinsic optical signals and fMRI was developed, which can be used to investigate spatial and temporal characteristics and correlations between brain activation, hemodynamic changes and BOLD signals.

Keywords: PET/MR, PET/MR

Motivation: Juvenile-onset Huntington Disease (JoHD) represents 4-10% of HD cases, has worse prognosis and psychiatric rather than motor symptomatology, compared to the adult form (AoHD). No study has yet investigated morphological and metabolic changes comparing these two forms with PET-MRI.

Goal(s): Are brain structural and metabolic changes different between patients with JoHD and AoHD? Do they evolve differently?

Approach: PET/MRI was acquired on AoHD and JoHD patients. Cortical and subcortical hybrid characteristics were compared between groups and overtime.

Results: POHD had the most remarkable striatum volume loss at baseline. Interestingly, POHD brain cortex volume was relatively spared at baseline if compared to AOHD patients.

Impact: This study provides first evidence that disease-related degeneration in JoHD first affects subcortical regions, where atrophy is more severe compared to AoHD, and ultimately spreads to the cortex, with faster rates of thinning and glucose metabolism changes compared AoHD.

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

Motivation: Uptake in the supratentorial cortex defines clinical amyloid positivity. Because of PET’s low spatial resolution, there is a spill-in effect from adjacent white-matter to gray-matter in amyloid PET scans, which may cause inconsistent rating between trained readers.

Goal(s): Reduce the spill-in effect by using MR priors in PET recon to improve the consistency of reading amyloid PET scans.

Approach: A recently developed PET recon with MR-priors and motion correction is applied to a set of 18F-florbetaben (amyloid) PET/MRI scans and is compared with regular TOF-OSEM PET recon using SUVR.

Results: PET recon with MR priors improves reading of negative amyloid PET scans.

Impact: PET-recon with MR-priors can make identifying negative cases more consistent between readers. Given how common inconsistent ratings are for amyloid-PET, methods that improve the ability to distinguish intermediate amyloid levels may be valuable for the widespread use of this modality.  

Keywords: New Devices, New Devices, Optics

Motivation: RF-induced heating and reduced image signal-to-noise ratio (SNR) due to crosstalk between adjacent cables are problematic in dense receive arrays. RF coils with fiber-optical connection can overcome these problems associated with metallic wires.

Goal(s):  To develop optical signal and power transmission units for MRI.

Approach: An analog photonic link with Mach-Zehnder modulator was constructed for optical signal transmission, and GaAs-based photonic power converters were used for power-over-fiber supply of low-noise-amplifiers (LNA).

Results: Image SNR and signal dynamic range of the photonic link are comparable with coaxial cable connection. Photonic power convertors can supply up to 10 LNAs in the receive chain.

Impact: Fully optical signal and power transmission is feasible for RF coils. It enables extremely dense modular receive arrays by eliminating cable-crosstalk and overcoming RF induced heating problems.

Keywords: Hybrid & Novel Systems Technology, Hybrid & Novel Systems Technology, Magnetic Particle Imaging, MPI

Motivation: The gold-standard for guiding minimally invasive cardiovascular interventions is X-ray (digital subtraction angiography - DSA). Can we reduce the radiation exposure for clinical staff and patients?

Goal(s): The use of alternative radiation-free imaging methods providing all necessary features can reduce the radiation exposure dramatically.

Approach: The imaging modality Magnetic Particle Imaging (MPI) uses iron-oxide-based nanoparticles as tracer for realtime visualization of dynamic processes. In a first step, this technique could be used to support clinical DSA treatment.

Results: In a first study, a lightweight and portable human-sized MPI scanner has been built and successfully tested under realistic conditions with vascular phantoms within a catheter-lab.

Impact: First simultaneous MPI/DSA hybrid imaging in human-sized phantoms demonstrates the feasibility of scaling-up the MPI technology. With a clinical approved tracer, MPI could be ready for clinical routine.