Keywords: Data Acquisition, Diffusion/other diffusion imaging techniques, Distortion correction

Motivation: 7T provides higher SNR compared to clinical field strengths, but susceptibility-induced distortion compromises diffusion imaging at 7T. Current methods to accurately correct distortion require doubling of scan time.

Goal(s): Develop an efficient acquisition scheme to enable distortion correction of multi-direction diffusion images without increased scan time.

Approach: Two ‘half-density’ acquisitions with opposing phase-encoding directions are collected, such that their gradient orientations uniformly sub-sample the sphere in a complementary manner. Spherical harmonics are used to interpolate image pairs for distortion correction.

Results: The proposed method provides distortion correction comparable to the full blip-up/blip-down approach, in half the acquisition time, while retaining the orientation density.

Impact: As the clinical benefits of 7T become established, it is crucial for all sequence types to be available for use. The methods proposed here enable advanced distortion-corrected diffusion imaging to be routinely and efficiently included in 7T imaging protocols.

Keywords: Data Acquisition, Heart, cardiac triggering

Motivation: Contactless cardiac triggering makes cardiac and cardiovascular MRI (cMRI) more accessible by improving patient comfort, reducing complexity, facilitating swift workflow, and increasing patient throughput.

Goal(s): In this work we demonstrate feasibility of contactless cardiac trigger detection using an in-bore camera in two routine cMRI sequences.

Approach: Building on an existing in-bore camera hardware we developed a cardiac trigger detection method for cMRI that extracts a remote photoplethysmography (rPPG) signal acquired at the patient’s forehead. The quality of the acquired MR images is compared with ECG triggering.

Results: rPPG and ECG triggering delivered comparable image quality in the majority of study volunteers.

Impact: The presented work provides evidence that cMRI is feasible with contactless, camera-based cardiac signal detection. The proposed method allows cMRI without placement of ECG electrodes, thus increasing accessibility of cardiac MR.

Keywords: Data Acquisition, Data Acquisition

Motivation: Conventional gradient echo SWI has a slow acquisition speed, thus limiting the minimal scan time achievable. However, accelerated 3D-EPI sequence can perform fast MR acquisition.

Goal(s): In this study, we evaluated the feasibility of SWI-EPI to generate ultra-fast susceptibility weighted images.

Approach: SWI-EPI combines a 3D (muti-shot) EPI sequence with CAIPIRINHA acceleration to significantly reduce the scan time.

Results: A significant reduction in scan time (up to 70%) was achieved with similar image quality and without any apparent artefacts, thus confirming the feasibility of ultra-fast SWI for future clinical neuro-applications at 3T.

Impact: This study demonstrates the feasibility of ultra-fast SWI-EPI at 3T.

Keywords: Data Acquisition, Data Acquisition, Low-field MRI, Acquisition Methods, Cardiovascular

Motivation: Volumetric real-time MRI is desirable to accurately characterize beat-to-beat cardiac function in patients with arrythmia or heart failure.

Goal(s): To identify practical data sampling strategies for volumetric real-time MRI and evaluate cardiac volume measurements against gated reference scans.

Approach: We focus on stack-of-spirals bSSFP at 0.55T. We use simulations and in-vivo experiments to compare three sampling strategies that minimize eddy currents.

Results: A Gaussian distribution of the stack-of-spirals was found to provide the best real-time image quality and most accurate LV volumes, with under-estimation of end-diastolic volume by 7.44% and over-estimation of end-systolic volume by 18.33%.

Impact: Beat-to-beat cardiac function is important to measure in the context of arrhythmia, cardiac stress testing and in interventional MRI, where real-time volumetric coverage will facilitate assessment and monitoring of cardiac function.

Keywords: Data Acquisition, Quantitative Imaging

Motivation: Spiral is the most efficient k-space coverage strategies in current MR gradient systems with robustness to motion and flow, but the implementation of long spiral trajectories keeps challenging due to accumulated off resonance effect and local susceptibility.

Goal(s): SPTI is proposed for artifact- and distortion-free spiral imaging and quantification.

Approach: Modified segmented spiral readout and subspace reconstruction were performed in SPTI technique.

Results: SPTI sequence was validated in a phantom study and feasibility was evaluated on a brain volunteer. In human study, SPTI method showed consistent results with MRF-EPTI on quantitative mapping, including PD, T₁, T₂ and T₂^*.

Impact: SPTI method can simultaneously quantify PD, T₁, T₂ and T₂^* mapping and is potential to expand to other body regions, especially in the liver and cardiac MRI.

Keywords: Data Acquisition, Diffusion/other diffusion imaging techniques

Motivation: Diffusion-weighted MRI suffers from limited spatial resolution, residual geometric distortion, and long acquisition.

Goal(s): To develop high spatial-angular-temporal resolution DW-MRI at 7T.

Approach: We developed ky-shift encoding and navigated interleaved EPI (NAViEPI) with consistent echo spacing, enabling efficient sampling and minimal distortion mismatch between echoes. We developed joint reconstruction with locally low-rank regularization, encompassing multi-band slices and multiple diffusion directions.

Results: We achieved (1) whole brain 3-scan trace acquisition at a resolution of 0.5 x 0.5 x 2.0 mm³ and 98 seconds, and (2) 3-shell 126 diffusion encodings with 1.0 mm isotropic resolution and 22 minutes scan time.

Impact: JETS-NAViEPI enables accelerated submillimeter resolution in vivo brain DW-MRI at 7T, offering both clinically relevant 3-scan trace and neuroscientific DTI protocols.

Keywords: Data Acquisition, Quantitative Imaging, T1rho, Reproducibility, TSLs Sampling, Magnetization Preparation

Motivation: Reproducibility of T1rho measurements is crucial for longitudinal studies, as highly reproducible measurements are needed to detect treatment-induced changes in tissue properties. 

Goal(s): To evaluate two novel sampling schemes of spin-locking times (TSLs) to improve the reproducibility of T1rho quantification in inhomogeneous fields (B1/B0) compared to previously reported TSL-sampling schemes.

Approach: T1rho sequences with three different T1rho preparation modules and four TSL-sampling schemes were used for repeated scans of phantom and volunteers to evaluate reproducibility in each case.

Results: The proposed TSL-sampling schemes produced significantly better reproducibility (i.e., lower coefficient of variation) than the previously reported TSL-sampling schemes.
 

Impact: The proposed novel TSL-sampling schemes may enable T1rho relaxation parameter as a robust biomarker of imaging tissues with a slow-motional process despite B1/B0 inhomogeneities.

Keywords: Data Acquisition, Heart, spiral MRI, cardiac CINE, water/fat separation

Motivation: Water/fat separation can be helpful to better distinguish adipose tissue, blood and myocardium in a cardiac cine series. However, inclusion of a multi-echo acquisition in the conventional bSSFP sequence can introduce artifacts and reduce temporal efficiency.

Goal(s): To develop a fast and robust water/fat separation method for time-resolved cardiac cine imaging.

Approach: A spoiled gradient echo sequence with spiral acquisition is proposed to perform the cine acquisition with retrospectively cardiac gating.

Results: The image from the proposed method has shorter scan time, lower artifact level and lower RF deposition compared to a multi-echo bSSFP sequence.

Impact: We demonstrate the feasibility of spiral cardiac cine imaging with water/fat separation, enabling faster scanning while preserving adequate contrast among adipose tissue, blood and myocardium. This sequence also has low RF deposition with much lower SAR level for the patient.

Keywords: Data Acquisition, Vessels

Motivation: The conventional velocity-selective ASL-based (VSASL) MRA couldn’t separate arteries and veins unless additional module is used, which would cause long scan time. In addition, its acquisition efficiency is low since a long waiting time for blood refreshing.

Goal(s): To proposed a VSASL-based sequence for Simultaneous imaging of cerebral Arteries and VEins (SAVE). 

Approach: SAVE uses the waiting period between consecutive shots of VSASL MRA to acquire SWI data. VSASL MRA/MRV were obtained by subtracting Control images from Label images, while SWI images were averaged to increase SNR. 

Results: SAVE-VSASL MRA/MRV can well depict arteries and veins, and SAVE-SWI MRV could depict veins well. 

Impact: The novel sequence can obtain decent VSASL MRA/MRV and SWI MRV images. The combination of the VSASL MRA/MRV and SWI MRV in SAVE should allows separation of arteries and veins by post-processing, that may be useful in clinical settings. 

Keywords: Data Acquisition, Pulse Sequence Design

Motivation: To enable execution of open-source vendor-agnostic pulse sequences on Philips MRI scanners.

Goal(s): To develop a Pulseq interpreter for Philips scanner.

Approach: An intelligent Philips Pulseq interpreter, denoted "p2p" (Pulseq to Philips), was implemented in MATLAB. It converts Pulseq-generated .seq files into a format compatible with Philips sequence objects.

Results: The p2p interpreter was tested with sequences that included arbitrary gradient waveforms including custom spiral waveforms and crusher waveforms spelling out the words ‘Philips Pulseq’, GRE and DW-EPI scans evaluated in phantoms and in vivo.

Impact: Open-source Pulseq format sequences can be executed with minimal adaptations on Philips scanners. The p2p Pulseq Philips interpreter completes the set of interpreters required to implement harmonized pulse sequences across the three major vendor platforms.

Keywords: Pulse Sequence Design, Pulse Sequence Design, accelerated imaging; displacement imaging; diffusion imaging

Motivation: Accelerate spin echo multi-slice MRI.

Goal(s): Combine echo dephasing and rephasing segments of different slices to reduce scan time.

Approach: Use a composite RF pulse to excite upcoming slices while refocusing signal from a current slice.

Results: Implementations at 3 T for spin echo based displacement encoding and spin echo and stimulated echo based DTI show 2-3 fold acceleration.

Impact: The proposed technique can accelerate 2D multi-slice imaging techniques that rely on multiple RF pulses per slice for signal generation and acquisition. It can be combined with simultaneous multi-slice and SENSE approaches for additional acceleration.

Keywords: Pulse Sequence Design, Pulse Sequence Design

Motivation: Multi-echo steady-state acquisitions (Dual/Triple Echo Steady State) allow for the acquisition of multi-contrast images, but only in a sequential manner, which is time-inefficient, and requires substantial gradient spoiling to avoid banding artifacts.

Goal(s): Our goal was to introduce an alternative multi-contrast acquisition with parallel imaging capabilities.

Approach: By exploiting the effects of partial RF spoiling in Fluctuating Equilibrium MR (FEMR) imaging, we devised a novel acquisition strategy enabling simultaneous acquisition of aliased multi-contrast images and their subsequent reconstruction via SENSE.

Results: Implemented in 3D, our approach yields multiple images in one acquisition while providing flexibility over the acquired imaging contrasts.

Impact: This new acquisition strategy offers more time-efficient multi-contrast imaging while also reducing gradient requirements in comparison to existing approaches, creating new opportunities for rapid quantitative imaging experiments in healthy and diseased tissue.

Keywords: Pulse Sequence Design, Arterial spin labelling, UTE, 4D MRA

Motivation: The conventional multi-phase Pulsed ASL UTE 4D MRA sometimes provides insufficient signal intensity to visualize hemodynamic flow characteristics in late phases.

Goal(s): Our goal is to improve the visibility of multi-phase Pulsed ASL UTE 4D MRA.

Approach: We developed a novel method, Continuous Acquisition Variable TR (CAVTR) UTE 4D MRA pulse sequence which utilizes continuously increasing TR. This new pulse sequence has less signal fluctuation and can avoid late phase signal reduction. We combined CAVTR with view sharing and improved late phase image quality without detriment to temporal resolution.

Results: This novel method can improve clinical usability of non-contrast ASL based UTE 4D-MRA.

Impact: The novel method, Continuous Acquisition Variable TR pulse sequence with View Sharing achieved both high temporal resolution and good visibility of arteries in late phases. This novel method can improve clinical usability of non-contrast ASL based UTE 4D-MRA.

Keywords: Pulse Sequence Design, Pulse Sequence Design, Gradient Array

Motivation: Gradient arrays are superior compared to the conventional MR coils. However, there exists no pulse sequence design algorithm for the optimum use of the gradient array.

Goal(s): This work proposes a novel pulse sequence design schema for the optimum use of the gradient arrays

Approach: The algorithm utilizes a waveform optimization method. This method provides the shortest trapezoidal pulses with three inputs: the area to cover, starting and ending amplitudes.

Results: The algorithm is fit for any gradient array weight matrix with an arbitrary number of channels. It can provide the shortest timing values for any imaging plane while preserving the hardware limits.

Impact: There exists no pulse sequence design algorithm for the optimum use of the gradient array. We present a novel algorithm fit for any gradient array weighting with an arbitrary number of channels while providing the shortest timing values.

Keywords: Pulse Sequence Design, RF Pulse Design & Fields

Motivation: Simultaneous mutli-slice (SMS) techniques can reduce scan times. Power deposition from multiband pulses and outer slice signal from power independent of number of slices (PINS) pulses has hampered thoracic and cardiac SMS imaging.

Goal(s): To reduce power deposition in thoracic and cardiac SMS imaging, thereby reducing scan times and motion artifacts.

Approach: A power independent of finite number of slices (PIFINS) pulse was designed to excite any number of slices over a desired field of view with power deposition comparable to single-band pulse.

Results: The PIFINS pulse was used to simultaneously acquire 3 slices in a cylindrical ACR phantom.

Impact: Reducing scan time in thoracic and cardiac imaging reduces motion artifacts. Acceleration with simultaneous multi-slice has been hampered due to high power deposition. The new pulse presented here will enable SMS thoracic and cardiac imaging with reduced power deposition.

Keywords: Pulse Sequence Design, Software Tools

Motivation: Spatially-tailored excitation is often favorable in MR applications where the region-of-interest only occupies a small portion of the whole FOV.

Goal(s): In this study, we sought to design an inner-volume saturation pulse for steady-state imaging.

Approach: We propose an extension to the AutoDiff tool by Luo et al. Here we use steady-state magnetization error as the design objective instead of one-time excitation error in the original design.

Results: Our proposed pulse design can excite spatially-selective patterns with ultra-short duration(~1.2ms) and high accuracy (error reduced by 50% compared to the original design).

Impact: Our pulse design tool enables highly accurate multi-dimensional spatially-tailored excitations with ultra-short pulses. Such pulses can be plugged into functional MRI sequences, and be played in clinical scenarios where ROI-specific excitations can mitigate motion artifacts and reduce image encoding time.