Keywords: Non-Proton, Non-Proton, Spectroscopy, carbon-13

Motivation: To develop a safe MR method to non-invasively measure skeletal muscle glycogen levels in humans.

Goal(s): To reduce SAR without degrading the spectral quality of the ¹H-decoupled C1-glycogen peak in ¹³C MRS.

Approach: To introduce the two-pulse phase-modulated (TPPM) ¹H decoupling scheme, which is widely used for ¹³C NMR of organic solids, into the ¹³C MRS pulse sequence for a clinical scanner.

Results: The ¹H-decoupled C1-glycogen peak could be obtained from a solution phantom using a clinical 3T scanner while reducing SAR with shortening the duration of the TPPM ¹H decoupling during ¹³C FID acquisition.

Impact: ¹³C MRS with the TPPM ¹H decoupling for measuring human skeletal muscle glycogen levels may be more advantageous at high magnetic fields due to the lower SAR, leading to higher SNR or shorter scan times.

Keywords: Non-Proton, Non-Proton, 23Na, Sodium, Triple Quantum (TQ)

Motivation: Sodium TQ-signal is potential viable biomarker for cell viability. However, TQ acquisition requires phase-cycling sequences with long scan times, which currently hinder clinical application.

Goal(s): We present a novel method to estimate the TQ-signal directly from the FID without phase-cycling.

Approach: Compare the our method's TQ-signal with the TQTPPI sequence and theoretical prediction. Investigate the impact of noisy data on our method and provide a proof-of-concept imaging sequence.

Results: The TQ-signal of our method was in close agreement with the TQTPPI TQ-signal and the theoretical prediction. Even for low SNR, our method performed well. Proof-of-concept imaging with our method was successfully demonstrated.

Impact: With our method scan time of sodium TQ imaging can be dramatically reduced. This approach may expand TQ imaging applications and thus may leverage the full potential of sodium TQ signal.

Keywords: Deuterium, Deuterium, Deuterium Metabolic Imaging, 7T, human brain, Magnetic Resonance Spectroscopic Imaging

Motivation: Sufficiently high spatial resolution for metabolic mapping of brain glucose metabolism is crucial as regional differences are present in many severe brain diseases, such as dementia, tumors and schizophrenia.

Goal(s): To increase spatial resolution for whole brain deuterium metabolic imaging without prolonging scan times.

Approach: Implement density-weighted concentric ring trajectory for ²H FID-MRSI readout to achieve 2.5-fold increase in spatial resolution while maintaining sufficient SNR. 

Results: Contrast-enhanced metabolic maps were acquired using CRT with significantly higher (+33%,p<0.01) Glx concentrations in GM regions compared to WM, while no differences were observed using lower resolution phase-encoded MRSI. 

Impact: Increased spatial resolution for dynamic deuterium metabolic imaging is crucially needed as many severe brain pathologies feature regional differences in brain glucose metabolism. However, prolonged scan times ultimately limit the achievable spatial resolution using conventional methods for whole brain DMI.

Keywords: Non-Proton, Non-Proton

Motivation: Perfluorooctyl bromide (PFOB) can be used to visualize the inflammatory reaction after myocardial infarction with ¹⁹F MRI, but effective methods for its imaging in large animals in vivo are still missing.

Goal(s): To develop a Hadamard-encoded sequence that removes the chemical shift artifacts of PFOB and increases the ¹⁹F SNR for application in large animal experiments.

Approach: A 3D center-out radial FLASH-sequence was developed and compared to a Cartesian FLASH-sequence in PFOB-phantoms. The radial sequence was tested in a pig after PFOB injection.

Results: Lowering TE increased the SNR by a factor of 2.4, which allowed to reconstruct ¹⁹F images of the animal.

Impact: Hadamard-encoded radial 19F MRI optimally uses the available multi-spectral information of PFOB which makes it the ideal candidate for monocyte tracking in large animals.

Keywords: Hyperpolarized MR (Non-Gas), Hyperpolarized MR (Non-Gas), multi echo, bSSFP, radial readout

Motivation: 3D Metabolic imaging of hyperpolarized (HP) ¹³C agents demands specialized signal excitation and acquisition strategies.

Goal(s): This study introduces the combination of multi-echo bSSFP and radial readout with a spiral phyllotaxis pattern to rapidly image ¹³C-labeled contrast agents.

Approach: We implemented the novel sequence in a rodent in vivo experiment using HP [1-¹³C]pyruvate.

Results: Employing iterative signal decomposition and radial data reconstruction, we successfully captured the global signal dynamics with an unprecedented temporal resolution of 16 ms. Besides, we generated concentration maps for pyruvate, lactate, alanine, and calculated area-under-the-curve (AUC) metabolite ratio maps for Lac/Pyr and Ala/Pyr.

Impact: Hyperpolarized ¹³C 3D metabolic MRI is challenging due to the short-living magnetization. With 3D spiral phyllotaxis radial multi-echo bSSFP MRI and post-scan metabolite separation, large areas of interest can be acquired and reconstructed into signal time-curves and 3D metabolite maps.

Keywords: Hyperpolarized MR (Non-Gas), Hyperpolarized MR (Non-Gas), B1 correction, B0 correction

Motivation: B₀ and B₁ inhomogeneities affect signal quantification and kinetic modelling but are challenging to map and correct for in hyperpolarized MRI due to the signal being exogenous and non-renewable.

Goal(s): Develop a fully-integrated B₀ and B₁ mapping method that does not require specialized pulse sequence programming, additional hardware, nor any additional carbon-13 dose.

Approach: Varying echo times and flip angles in the imaging sequence.

Results: The in-vivo field maps agreed well with independently acquired maps and could correct for B0 off-resonance blurring and B₁ inhomogeneity.

Impact: A fully-integrated B₀ and B₁ mapping and correction method for hyperpolarized carbon-13 MRI is presented and validated in vivo. This method is readily implemented and can improve image quality, helping ¹³C metabolic imaging become more robust for clinical studies.

Keywords: Non-Proton, Non-Proton

Motivation: Sodium MRI (²³Na-MRI) holds significant potential, but its clinical use is still limited due to challenges arising from low signal-to-noise ratio (SNR). Balanced steady-state free precession (bSSFP) sequences are particularly suited for ²³Na-MRI, being highly SNR efficient, but there are opportunities to extract more signal components.

Goal(s): We aim to improve SNR in sodium bSSFP acquisitions and produce additional tissue contrasts.

Approach: We propose a strategy to extract additional information from a series of phase-cycled bSSFP images using different linear combinations.

Results: Three different signal components were extracted from phase-cycled bSSFP data and combined. Results showed an SNR boost in fluid.

Impact: This offers a simple way to improve the SNR in sodium MRI images, with potential applications being pathologies that alter biofluid sodium concentrations.

Keywords: Hyperpolarized MR (Non-Gas), Hyperpolarized MR (Non-Gas)

Motivation: Fully sampled 3DspCSI acquisition limits the temporal resolution for dynamic imaging  

Goal(s): Our goal was to reconstruct highly under-sampled 3DspCSI without significant image artifacts

Approach: We proposed a low rank plus local sparse (LLS) reconstruction with two types of configurations to reconstruct the under-sampled 3DspCSI data

Results: proposed methods with both types of configurations can effectively reduce the image artifacts due to under-sampling. Type 2 configuration performs slightly better than Type 1 with less image artifacts due to the distinct patterns along the slice dimension

Impact: With the proposed LLS reconstruction, an effective acceleration of 4 can be achieved for 3DspCSI without significant image artifacts. The improvement in temporal resolution helps to quantify the metabolite kinetics during a fixed imaging window with hyperpolarized ¹³C agents

Keywords: Deuterium, Deuterium, DMI,MRSI,SSFP

Motivation: DMI's faces a poor SNR, and the detection of vital Glx/lactate metabolites in the brain tumor can be compromised.

Goal(s): This research aims to determine whether the optimized CSI-SSFP imaging method is effective for detecting the four biomarkers (HDO, Glucose, Glx, and Lactate) with improved SNR compared to traditional CSI in rodent brains.

Approach: The approach involves comparing DMI SNR using both traditional CSI and CSI-SSFP for monitoring and imaging the metabolism of injected [6,6’-²H₂]-glucose in healthy mouse brains.

Results: CSI-SSFP highlights substantial enhancement of 2-3 times in SNR for Glx and lactate.

Impact: DMI is promising to assess the Warburg effect associated with cancer. The CSI-SSFP method provides several folds of SNR improvement, which is critical to improve sensitivity and resolution aiming for imaging intra-tumor heterogeneity and metabolic reprograming in brain tumors.

Keywords: Non-Proton, Spectroscopy, Phosphorus, 31P, pH, magnesium, brain

Motivation: The reliability of conventional ³¹P MRS-based methods for the determination of pH and magnesium ion content (Mg) is hampered when applied to pathologies due to their calibration for physiological conditions.

Goal(s): The aim of this study was the advancement of a novel approach for pH and Mg mapping to improve its reliability for application in vivo.

Approach: This advancement was performed by incorporating an additional input parameter into the approach and tested on in vivo ³¹P MRSI brain datasets.

Results: Compared to the original algorithm, the advanced version resulted in robust mapping of pH and Mg yielding homogeneous brain maps for healthy volunteers.

Impact: The advancement of a novel approach for the in vivo determination of pH and magnesium ion content under different chemical conditions improves its reliability and can now potentially be used for the investigation of pathologies such as cancer.

Keywords: Hyperpolarized MR (Gas), Hyperpolarized MR (Gas)

Motivation: Manufacturer-supplied transmitter calibrations are unsuitable for ¹²⁹Xe MRI due to the transient nature of its magnetization, but existing ¹²⁹Xe calibration protocols exhibit incomplete spoiling that adversely affects accuracy in flip angle measurements.

Goal(s): We sought to develop a new spoiling-gradient configuration for ¹²⁹Xe MRI transmit calibration that corrects the incomplete spoiling and improves accuracy.

Approach: Spoiling configurations were simulated, tested, and optimized in a water phantom. The optimal configuration was tested in subjects who underwent ¹²⁹Xe MRI with both calibration schemes.

Results: A configuration that increases spoiling-gradient moment with each FID corrected the incomplete spoiling and improved the accuracy of flip angle measurements.

Impact: Implementing a ¹²⁹Xe MRI transmit calibration that increases spoiling-gradient moment with each FID acquisition improves accuracy in flip angle calculations, thereby ensuring consistently optimal image quality for all subjects and advancing the clinical utility of ¹²⁹Xe MRI.

Keywords: Hyperpolarized MR (Non-Gas), Metabolism, carbon-13 imaging, x-nuclei MRI, metabolic imaging, flexible RF coil, CSI

Motivation: For hyperpolarized ¹³C metabolic imaging studies, a challenge is to achieve high temporal resolution without decreasing spatial and/or spectral resolution. 

Goal(s): To accelerate hyperpolarized ¹³C MRI by combining a 2D Chemical Shift Imaging (CSI) sequence with SENSitivity Encoding (SENSE) reconstruction.

Approach: Due to the low natural abundance of ¹³C, the sensitivity maps needed for SENSE reconstruction cannot be pre-acquired. As such, in this work, the novel approach of using sodium sensitivity maps was demonstrated.

Results: SENSE reconstruction corrected aliased images, where in-vivo metabolic information was acquired with a 4-fold temporal acceleration.

Impact: As hyperpolarized ¹³C metabolic imaging is clinically translated, there is a need for easy-to-implement, fast, and robust imaging techniques. Therefore, this study implemented a novel ¹³C technique to accelerate Chemical Shift Imaging: a ubiquitous and robust sequence.

Keywords: Hyperpolarized MR (Gas), Image Reconstruction

Motivation: 3D hyperpolarized ¹²⁹Xe gas exchange imaging is limited by low SNR and long breath-holds, which is problematic for patients with dyspnea and/or low gas transfer. Compressed sensing (CS) reconstruction can accelerate ¹²⁹Xe MRI whilst improving SNR.

Goal(s): To assess whether gas exchange ratio maps are quantitatively preserved with CS dissolved ¹²⁹Xe imaging and investigate the feasibility of reduced-cost natural abundance (NA) CS dissolved ¹²⁹Xe imaging.

Approach: CS-reconstructed gas exchange ratios were evaluated in healthy volunteers and COPD patients and prospectively with NA ¹²⁹Xe.

Results: CS increased image SNR, allowed 3-fold acquisition acceleration and maintained ratio map fidelity, even with NA ¹²⁹Xe.

Impact: Compressed sensing reconstruction of dissolved ¹²⁹Xe spectroscopic imaging improved image quality even with decreased scan time, whilst preserving key gas exchange metrics. This will benefit patients with breathlessness and/or low gas transfer and enables natural abundance dissolved ¹²⁹Xe imaging.

Keywords: Deuterium, Deuterium

Motivation: Abdominal imaging of orally-administered deuterium-labelled tracers can be hindered by artifacts arising from excessive stomach signal.

Goal(s): To establish and optimize methods for acquisition of abdominal deuterium metabolic imaging in conjunction with orally-administered tracers.

Approach: A flexible transmit-receive surface coil was used to image naturally abundant deuterium in healthy volunteers and orally-administered D₂O in a patient with renal cancer.

Results: Water and lipid peaks were repeatably fit with high confidence both in unlocalised spectra and voxels extracted from MRSI in the liver, kidney, and spleen. Artifacts were minimal even 12 minutes after tracer ingestion.

Impact: Feasibility of abdominal deuterium imaging at 3T was demonstrated using a flexible surface coil.  We obtained consistent water measurements in healthy volunteers and good images in a patient with a left-sided renal tumour even just 12 min after drinking D₂O.

Keywords: Non-Proton, Non-Proton

Motivation: Motivation is to unleash the clinical potential of sodium (²³Na) MRI.

Goal(s): Main goal is to answer the key question about what the optimal sequence encoding is?

Approach: 3D sodium sampling schemes were designed, implemented and compared in simulations and experimentally in the human brain and porcine abdomen.

Results: (1) While encoding schemes differ in sampling efficiency, 15ms-Density-Adapted Radial is SNR optimal.
(2) Clinically reasonable acquisition parameters are: total scan time ~10min., nominal matrix size=80³, readout duration=15ms, TR=30ms, flip angle=60°.

Impact: Sodium MRI holds great clinical potential for diagnosing and monitoring of stroke, cancer, etc. Devising and comparing the optimal acquisition will help the sodium field to improve SNR, hence facilitating clinical studies and adoption.