Keywords: Quantitative Imaging, Relaxometry, quantitative, MRS, T1T2 maps

Motivation: Water-referenced metabolite quantification in MRS often relies upon fixed water-relaxation reference times, ignoring differences in relaxation across the brain and lifespan.

Goal(s): To develop a water relaxometry atlas to integrate location- and age-appropriate relaxation values into the MRS analysis workflow.

Approach: DESPOT was used to collected quantitative T₁ and T₂ images in a cohort of 52 subjects aged 20-70 years old, and morphed to standard-space to generate a relaxometry aging atlas. We also perform a parcel-wise assessment of age-related relaxation changes.

Results: The high-resolution water relaxometry aging atlas indicates significant changes in water relaxometry across the lifespan in many brain regions.

Impact: Access to whole-brain relaxometry reference values, with appropriate consideration of aging, is vital to accurate water-referenced metabolite quantification in MRS.

Keywords: Data Acquisition, Data Acquisition, images reconsturction

Motivation: The motivation behind this project was to address critical gaps in our  Hyperpolarized (HP) ¹³C MRI.

Goal(s): The primary goal of this study was to develop and implement a set of tools and methods to support HP ¹³C MRI. These tools aimed to facilitate real-time data processing, improve image quality, and enable precise quantification of metabolic processes.

Approach: We created the HP ¹³C RTHawk reconstruction toolbox. These tools included functions for data reading, gridding, coil combination, DICOM writing, B₁₊ and B₀ calibration.

Results: The RTHAWK toolbox significantly enhanced the capabilities of HP ¹³C MRI, empowering researchers to obtain higher-quality images.

Impact: The study have far-reaching implications for scientists. By enhancing the capabilities of HP ¹³C MRI, the toolbox enables more precise  studies. This not only broadens our understanding of  but also paves the way for improved diagnostic procedures and treatment strategies.

Keywords: Pulse Sequence Design, Brain

Motivation: To develop a sequence for high-quality concurrent measurement of BOLD signal changes (fMRI) and biochemicals metabolite concentrations (fMRS).

Goal(s): To implement parallel imaging with inline image reconstruction to improve fMRI image quality in concurrent fMRI-fMRS experiments at 7 T.

Approach: We modified an fMRS-fMRI sequence to start by acquiring reference lines for GRAPPA reconstruction. Then each TR consists of a semiLASER acquisition for single-voxel MRS, and a GRAPPA-accelerated 3D EPI acquisition.

Results: We obtained sufficient tSNR (30) map for the 3D EPI and a high SNR (59) and a narrow linewidth (9 Hz) for the spectrum.

Impact: The modified concurrent fMRI-fMRS pulse sequence enhances the fMRI component to enable whole-brain coverage, reduced distortion, and high spatial resolution, providing a powerful tool for neuroscientists to study the dynamics of neurochemicals simultaneous with the BOLD signal.

Keywords: Image Reconstruction, PET/MR, Artificial Intelligence, Joint reconstruction

Motivation: PET suffers from a low signal-to-noise ratio. Meanwhile, the k-space data acquisition process in MRI is time-consuming by PET-MRI systems.

Goal(s): We aim to accelerate MRI and improve PET image quality.

Approach: This paper proposed a novel joint reconstruction model by diffusion stochastic differential equations based on learning the joint probability distribution of PET and MRI.

Results: Compare the results underscore the qualitative and quantitative improvements our model brings to PET and MRI reconstruction, surpassing the current state-of-the-art methodologies.

Impact: Joint PET-MRI reconstruction is a challenge in the PET-MRI system. This studies focused on the relationship extends beyond edges. In this study, PET is generated from MRI by learning joint probability distribution as the relationship.

Keywords: Quantitative Imaging, Non-Proton, Data Analysis

Motivation: Sodium homeostasis is altered in abdominal pathologies such as cancer and cardiovascular disease, but established quantification techniques require an invasive biopsy.

Goal(s): Quantification of abdominal sodium content and T₂* relaxation in abdominal organs and fluid-filled structures using ²³Na-MRI.

Approach: Proton and sodium imaging of the abdomen was performed in 18 healthy volunteers using a 3D cones sequence and a sodium-tuned body coil on a clinical 3 T system. 

Results: Mean total sodium concentration and long T₂* relaxation times were measured in 8 organs and fluid-filled structures; results agreed with previously published work in human and animal models.

Impact: Quantitative ²³Na-MRI measurements in healthy volunteers will serve as a baseline to evaluate pathological changes in hypertension and kidney tumour characterisation. This may assist in the assessment of treatment efficacy, thereby reducing the need for invasive biopsy techniques.

Keywords: Data Acquisition, Hyperpolarized MR (Gas), ventilation imaging, rapid acquisition

Motivation: The acquisition time of ventilation imaging with ¹²⁹Xe MRI under breath-hold condition (~10s) is still too long, and might be intolerable for patients with severe pulmonary diseases.

Goal(s): To develop a rapid method for ventilation imaging in human by using ¹²⁹Xe MRI, enabling assessment of ventilation function changes caused by lung diseases.

Approach: Zigzag sampling based on the sequence of gradient echo (GRE-zigzag) was developed for ventilation imaging with ¹²⁹Xe MRI.

Results: By using the proposed method, ventilation imaging with a spatial resolution of 4mm×4mm×9mm could be acquired within 2.2 s.

Impact: Zigzag sampling was used for accelerating ventilation imaging with 129Xe MRI, shortening the acquisition time to 2.2s, which might prompt its clinical application, especially for those patients who could not hold the breath for a long time.

Keywords: Data Acquisition, Brain, spectral editing, gaba, glutathione, glutamate

Motivation: Spectral editing methods are widely used to measure γ-aminobutyric acid (GABA), which also co-edits glutamate (Glu) at 2.34 ppm in the sum spectrum (sum=ON+OFF). However, the co-detection of Glu at 2.34 ppm has not been assessed.

Goal(s): We demonstrate the co-editing of Glu without glutamine using HERMES of GABA and glutathione.

Approach: Simulations of HERMES and 1D J-resolved of Glu, glutamine, and GABA, followed by in vivo experiments on 137 participants.

Results: Simulations and in vivo experiments show a Glu-edited signal without overlapping glutamine and GABA signals from both methods. In vivo quantification of Glu show that the two methods are significantly correlated.

Impact: Our study demonstrates a purer measurement of Glu using HERMES without needing a separate acquisition. HERMES provides an opportunity to study Glu/GABA/glutathione concurrently to understand their relationships under homeostasis or drug interventions that might affect the glutamatergic/GABAergic/antioxidant systems.

Keywords: Data Acquisition, Data Acquisition

Motivation: Hyperpolarized ¹³C magnetic resonance spectroscopic imaging (¹³C-MRSI) provides real-time metabolic insights but requires extremely fast and efficient imaging sequences, especially for dynamic measurements.

Goal(s): This work aims to enhance three-dimensional ¹³C radially-sampled echo-planar spectroscopic imaging (rEPSI) to enable dynamic acquisitions.

Approach: A novel algorithm for a 3D Gapped Arrangement of Golden Angles (GAGA) is introduced, combined with sliding window (SW) reconstruction, and tested in simulation and phantom studies.

Results: The algorithm developed for GAGA creates homogeneous k-space sampling distributions for individual temporal subframes, and SW reconstruction successfully recovers the temporal dynamics while displaying only minor temporal flickering and incoherent undersampling artifacts.

Impact: The novel algorithm for a Gapped Arrangement of Golden Angles (GAGA) enables dynamic measurements of volumetric hyperpolarized ¹³C MRSI with a high temporal resolution. Further studies will exploit its potential for the investigation of metabolic processes using dynamic hyperpolarized ¹³C-MRSI.

Keywords: Muscle, Pulse Sequence Design, Sodium imaging

Motivation: The quantitation of sodium MRI depends on the reference tubes located near the inner surface of the RF coil. Hence, the RF flip angle at the reference tubes could be off from the intended 90°, which will result in inaccurate quantitation.

Goal(s): To develop an MR sequence to measure the RF field map while maintaining the short echo time of UTE and sensitivity of 90° excitation.

Approach: A composite 90° RF pulse was chosen and implemented into a 3D UTE sequence.

Results: The flip angle map was measured with enough sensitivity and accuracy, which was used in more accurate sodium quantitation.

Impact: The composite 90° RF pulse can be easily added to an existing 3D UTE sequence, and it has the advantage of short echo time and sensitivity. The measured RF field map will be essential for an accurate sodium quantitation.

Keywords: Other Musculoskeletal, PET/MR, Pain

Motivation: Chronic low back pain (LBP) and persistent hip pain after total hip replacement (THR) are often inadequately treated since conventional imaging techniques as CT or MRI are unable to accurately identify the source of pain in these patients.

Goal(s): To evaluate the clinical value of [18F]FDG PET-MRI for identification of pain generators in LBP and hip pain after THR.

Approach: Randomized controlled trial with either [18F]FDG PET-MRI or standard clinical practice.

Results: [18F]FDG PET-MRI can reveal previously unidentified pain generators in patients with chronic LBP or persistent hip pain after THR, leading to more changes in clinical management compared to standard clinical care.

Impact: [18F]FDG PET-MRI in patients with chronic low back pain or persistent pain after total hip replacement can reveal previously unidentified pain sources. PET-MRI led to more changes in clinical management than in patients receiving standard clinical care.

Keywords: Quantitative Imaging, Spectroscopy, Quantification, LCModel, Glycemia

Motivation: As more clinical MRS studies migrate from 3T to 7T, comparing neurochemical quantification under the same physiological status is of interest.

Goal(s): Our goal was to investigate whether there are systematic biases in neurochemical concentrations obtained with the identical advanced MRS protocol on 3T vs. 7T. 

Approach: Seventeen participants underwent an advanced MRS protocol at 3T and 7T during euglycemic clamps. 

Results: While most of the mean metabolite levels were comparable at 3T vs. 7T, a few metabolites displayed systematic differences, notably gamma-aminobutyric acid, glucose, taurine and phosphoethanolamine. Utilizing total creatine ratios did not alleviate but exacerbated the biases. 

Impact: Water referenced MRS quantification results in similar neurochemical profiles at 3T vs. 7T, with the exception of a few important metabolites. Selection of the magnetic field for a clinical study should depend on the metabolite-of-interest.

Keywords: Sparse & Low-Rank Models, Spectroscopy, Sodium

Motivation: The ²³Na TQ-signal is a potential biomarker for cell viability but the required phase-cycling leads to long scan times with redundant information.

Goal(s): To investigate the feasibility of undersampling the fixed TQTPPI FID in the second dimension and reconstructing it by either an undersampled fit or two iterative thresholding algorithms.

Approach: Investigation of the feasibility of undersampling the fixed TQTPPI FID in the second dimension and reconstructing it by either an undersampled fit or two iterative thresholding algorithms. 

Results: Undersampled fit successfully reconstructed data up to a 14 undersampling factor, while accuracy of the CS algorithms declined post-Nyquist-limit in both measurement and simulation.

Impact: While undersampled fit was as accurate as CS algorithms in simulations and below the Nyquist-limit it showed more reliable results and outperformed the latter two on measurement data and post-Nyquist limit, suggesting that physics informed reconstruction is advantageous.

Keywords: Motion Correction, Motion Correction

Motivation: Prospective gating potentially reduces respiratory motion-induced degradation in ³¹P liver MRSI at the cost of increased acquisition time. This presents a difficult trade-off, since the protocols are already time-consuming while the effects of motion are yet unknown.

Goal(s): To characterize spectral quality degrading effects of typical respiratory motion on human liver ³¹P MRSI data.

Approach: We analyzed spectra obtained from free breathing human liver ³¹P MRSI scans to determine differences in spectral quality between uncorrected and prospectively gated acquisitions using a respiratory belt.

Results: We found a significant difference in spectral line width between gated and non-gated acquisitions.

Impact: Showing that respiratory motion induces significant degradation of the spectral quality in in vivo liver ³¹P MRSI acquisitions, this study justifies the application and further development of prospective gating, as well as other respiratory motion correction methods.

Keywords: Data Acquisition, Non-Proton

Motivation: Perfluorooctyl bromide (PFOB) is a possible ¹⁹F tracer for monocytes active during myocardial infarction (MI). The method of Hadamard-encoding can mitigate chemical shift artifacts, but spectrally tailored pulses have not been leveraged yet.

Goal(s): The goal of this work is to increase the SNR efficiency of the Hadamard-encoding method for ¹⁹F MRI of PFOB.

Approach: Variable flipangle measurements were performed to measure T₁ and the individual Hadamard-pulses were tailored to better fit the spectrum.

Results: T₁ values are similar for all PFOB resonances ranging between 870 and 970ms. SNR was increased by 10% by using a combination of Gaussian- and sinc-pulses.

Impact: The improvements shown here contribute to making Hadamard-encoding a viable method for imaging PFOB with ¹⁹F MRI. As an alternative to monocyte tracking with PET, this might further our understanding of monocyte behavior during MI.  

Keywords: Artifacts, Data Processing

Motivation: The PET/MR system provides precise anatomical and functional information for neurological disorder detection. 

Goal(s): To mitigate quality degradation caused by reduced radiation exposure of radiopharmaceuticals.

Approach: We proposed a 3D network with spatial brain transformation for whole-brain low-dose PET/MR imaging.

Results: The obtained PSNR and SSIM were 41.96 ± 4.91 dB (p<0.01) and 0.9654 ± 0.0215 (p<0.01), which achieved 19% and 20% improvement, respectively. The VOI analysis of brain regions showed more accurate standardized uptake value distributions. In the future, we hope to apply our method to other multimodal systems, such as PET/CT, to assist clinical brain disease diagnosis and treatment.

Impact: (1) Our approach employs multimodal information fusion to enhance low dose PET/MR whole-brain imaging.
(2) Our method considers spatial brain anatomical alignment information, ensuring the consistency and accuracy of imaging data within brain regions.

Keywords: Quantitative Imaging, Hyperpolarized MR (Gas), Dynamic ventilation imaging

Motivation: High spatiotemporal resolution dynamic ventilation imaging with hyperpolarized ¹²⁹Xe MRI can well-depict the airflow process in the lung during the respiratory. However, there is a lack of quantitative assessment methods that correlate dynamic ventilation images with pulmonary physiology.

Goal(s): We aimed to translate the dynamic ventilation images into quantitative parameters that could assess the ventilation function.

Approach: The signal-time curve was used to explain the airflow rate and optical flow method was utilized to generate airflow field for each frame to depict the orientation and magnitude.

Results: Gas distribution and airflow process could be quantified through dynamic ventilation images. 

Impact: Regional dynamic ventilation function was quantified using signal-time curves and optical flow methods in vivo, and these preliminary results might be helpful for assessing the lung pathological changes that related to airflow restriction, obstruction, or air trapping.