Keywords: Quantitative Imaging, Fat, T2 mapping

Motivation: Skeletal muscle inflammation/necrosis and fat infiltration are strong indicators of disease activity and progression in many neuromuscular disorders. They can be assessed by muscle T₂ relaxometry and water-fat separation techniques, respectively.

Goal(s): Develop a method for simultaneous water-fat separation and T₂ quantification.

Approach: The chemical-shift encoding multiple overlapping-echo detachment (CSE-MOLED) sequence was designed for MRI data acquisition, and synthetic data and deep learning were used for image reconstruction.

Results: The experiments showed that accurate T₂ maps of water and fat and proton density fat fraction maps (PDFF) can be fast and simultaneously acquired by CSE-MOLED.

Impact: A new MRI method is proposed for fast and simultaneous T₂ and PDFF mapping, which may help improve the clinical diagnosis of neuromuscular diseases.

Keywords: Myocardium, Cardiovascular, Myocardial Perfusion Imaging

Motivation: As perfusion images are typically acquired over 60 heart beats, respiratory motion is unavoidable. Motion compromises spatio-temporal reconstructions. 

Goal(s): Residual undersampling artifacts and contrast variation make deformation field estimation challenging. This work aims to get an accurate deformation field from the auxiliary reconstruction and incorporate it into the forward reconstruction model to improve perfusion images. 

Approach: To obtain high-quality images for motion estimation, the fixed-angle spiral navigator is used to extract temporal basis. The rigid and non-rigid motion corrections are jointly incorporated into the subspace reconstruction.

Results: Motion-corrected whole-heart first-pass spiral myocardial perfusion imaging with a high resolution of 1.3 mm² is achieved.

Impact: The proposed navigator-guided subspace motion correction reconstruction pipeline substantially improves the image quality, sharpness, and alignment of the 1.3mm² high-resolution spiral myocardial perfusion imaging, benefiting voxel-wise perfusion quantification crucial for assessing ischemic heart disease.

Keywords: Motion Correction, New Devices, Pilot Tone, Low Field

Motivation: With Pilot Tone, it is challenging to extract weak modulations, specifically those related to cardiac motion, at lower B0 field strengths (<1.5T).

Goal(s): To enable the use of cardiac Pilot Tone at low-fields (0.55T).

Approach: We utilize high-amplitude pilot tone transmission in conjunction with interference mitigation to eliminate ensuing image artifacts.

Results: We demonstrate robust extraction of cardiac pilot-tone signals at 0.55T. We demonstrate ability to track motion with real-time MRI, and demonstrate the ability to separate cardiac and respiratory phases with retrospective binning. Compared to ECG, the measured timing standard deviation was 36ms for Cartesian and 47ms for spiral acquisitions.

Impact: This work makes it possible to extract cardiac motion from Pilot Tone at 0.55T, which was not possible before. Pilot Tone could potentially replace ECG gating, simplify the clinical workflow, and serve for scanners that do not employ ECG.

Keywords: MR Fingerprinting, MR Fingerprinting

Motivation: Single breath-hold simultaneous T1, T2 and ADC abdominal Magnetic Resonance Fingerprinting (MRF) in liver would allow for fast and comprehensive liver tissue characterization.

Goal(s): To develop a fast MRF sequence for T1, T2 and ADC quantification on liver tissue in a single breath-hold at 3T

Approach: Radial spoiled-GRE ~16-second acquisition with magnetization preparation modules for T1, T2 and ADC encoding was proposed, with an optimized diffusion-preparation module. Sequence was evaluated in phantoms and in 11 healthy subjects.

Results: T1, T2 and ADC quantification shows good correlation with reference maps in phantoms and good agreement in vivo against clinical scans.

Impact: Simultaneous quantification of T1, T2 and ADC in liver tissue in a single-scan is now possible with this proposed MRF sequence, allowing for a more comprehensive evaluation of hepatic disease through co-registered multiparametric imaging. 

Keywords: Quantitative Imaging, Low-Field MRI, liver

Motivation: Evaluation of patients with fatty liver disease can benefit from low-field scanners due to their larger bore size and reduced cost. However, fat is a cofounding factor for liver T1 mapping, and there is currently no reliable water-only T1 mapping method for low B0 field strengths. 

Goal(s): To develop a practical water-only liver T1 mapping method at 0.55T.
 

Approach: Inversion recovery preparation combined with a 3-echo bSSFP spiral out-in-out-in (OIOI) readout was used to obtain water/fat separated images and quantify water-only T1.

Results: The proposed water-only T1 mapping method is insensitive to liver PDFF, compared to Cartesian MOLLI and water-fat in-phase T1 values. 

Impact: For patients with fatty liver disease, this new method provides reliable water-only T1 mapping at low field strength (0.55T). This method may be incorporated into clinical protocols as an indicator of liver inflammation, fibrosis, and stiffness. 

Keywords: Quantitative Imaging, Relaxometry, Fetal Brain, T2 mapping

Motivation: Unpredictable and intense motion poses serious challenges to quantitative imaging of the fetal brain.

Goal(s): To evaluate the value of single-shot multiple overlapping-echo detachment acquisition (MOLED) imaging technique in accurately T₂ mapping the developing fetal brain.

Approach: Single-shot MOLED imaging was utilized for motion-robust T₂ mapping in the developing fetal brain. The method was tested on phantom and in vivo, and a scan-rescan assessment was performed on nine fetuses.

Results: MOLED T₂ mapping strongly agreed with single-echo spin echo T₂ (r = 0.996 in phantom). The median intra-subject coefficient of variation of T₂ values between scan-rescan tests across the nine subjects is 1.385%.

Impact: MOLED is a motion-robust, accurate, and repeatable method for T₂ mapping of the whole developing fetal brain in only a few seconds. This method makes it feasible to use T₂ maps to quantify early myelination in the fetal brain.

Keywords: MR Fingerprinting, MR Fingerprinting, Liver, Respiratory Motion, Scanner Feedback

Motivation: Abdominal MRF can require long breath-holds. Free-breathing MRF with retrospective binning and offline reconstruction does not guarantee adequate map quality.

Goal(s): Develop a self-binning, self-terminating MRF sequence for free-breathing abdominal imaging, providing real-time adjustments to the acquisition for improved image quality.

Approach: The proposed MRF sequence monitors respiratory states in real-time, adapts or extends the acquisition based on reconstruction feedback, and performs iterative conjugate gradient reconstruction online.

Results: The free-breathing approach shows promising results mitigating motion artifacts, producing similar maps to conventional breath-hold results. Sequence termination commands are processed within 0.55 seconds, while reconstruction is completed within 22 seconds.

Impact: This work enables free-breathing abdominal MRF scans with real-time control and online reconstruction. This approach potentially allows for shorter scans with improved map quality without breath-holds. New strategies for real-time control and adaptive MRF imaging can now be investigated.

Keywords: White Matter, Brain

Motivation: T2-FLAIR is an essential contrast for clinical neuroimaging. However, the inherently long scan time limits its application in screening. 

Goal(s): We aim to accelerate 3D T2-FLAIR scan while maintaining sufficient image quality.

Approach: We developed a framework that simultaneously learns a sampling pattern and a fully 3D deep learning reconstruction neural network. This allows exploiting the optimization space in both sampling and reconstruction.

Results: Learned sampling pattern with MoDL reconstruction trained with added Gaussian noise was able to provide high quality T2-FLAIR scan with 1x1x1.6mm resolution in 1 min 39s.

Impact: This work confirms the feasibility of a short 3D T2-FLAIR scan, provides insights for optimization strategies, and could lead to clinical implementation.

Keywords: Data Acquisition, Diffusion Tensor Imaging, Simultaneouse Multi-Slice; Navigator-gated Acqusition

Motivation: Low scanning efficiency of stimulated echo acquisition mode (STEAM) diffusion tensor cardiac magnetic resonance images (DT-CMR) limits its clinical translation.

Goal(s): We aimed to improve the slice coverage efficiency of DT-CMR utilizing simultaneous multi-slice (SMS) techniques. 

Approach: The navigator-gated (Nav) SMS STEAM acquisition, integrated with a biofeedback system, was introduced, enabling controlled breathing and respiratory motion compensation. 

Results: Nav SMS STEAM acquisition reduced scanning time by 46±6% compared to single-band (SB) acquisition. No significant difference in global mean MD and FA was observed, but a lower median |E2A| was noted for the SMS basal slice. 

Impact: Our proposed Nav SMS STEAM acquisition would reduce the total breath-hold duration of STEAM DT-CMR acquisitions, enhancing clinical feasibility. Improved efficiency could also lead to whole heart coverage in DT-CMR scans, essential for example, in myocardial infarction.

Keywords: Data Acquisition, Data Acquisition, Fetal

Motivation: Fetal MRI plays an important role in clinical and research settings. The variability of the fetal position and extensive fetal motion, however, create challenges limiting the use of fetal MRI mainly to specialist centres.

Goal(s): Real-time fully automatic planning of true radiological fetal brain planes for anatomical TSE scans.

Approach: Deep-learning based detection of key landmarks in the fetal brain on a whole-uterus EPI scan enables the subsequent automatic calculation of the radiological plane for the TSE scan.

Results: Prospective results on three fetal MRI scans on a clinical low-field 0.55T MRI scanner illustrate the ability of the framework to perform diagnostic planning.

Impact: Fully automated planning of radiological planes for low-field fetal MRI demonstrates time efficiency and carries the potential to significantly widen accessibility to fetal MRI beyond specialist centres.