Keywords: Pulse Sequence Design, Pulse Sequence Design, Arterial Spin Labelling; Spectroscopy

Motivation: Single voxel spectroscopy allows us to measure the metabolite signal within a voxel in the brain. There are strides to mathematically segment this signal based on tissue type: grey matter, white matter, and cerebral spinal fluid. However, blood is also an important component to this signal as the brain is heavily vascularized. 

Goal(s): We wish to better understand the MR signal contribution coming from blood in the brain.

Approach: Borrowing from imaging-based pCASL, we’ve combined the RF tagging pulse train to a standard PRESS sequence, creating SVS-pCASL.

Results: With our preliminary testing, we observed an ASL effect on the unsuppressed water signal.

Impact: MRS provides us with useful information regarding the metabolite signals. However, one key component is overlooked, blood. Combining pCASL RF tagging with PRESS to create SVS-pCASL, our preliminary results show an ASL effect on unsuppressed water signal in the brain.

Keywords: Pulse Sequence Design, Pulse Sequence Design, Pulseq, reproducable, open, open-source, UHF, 7T, Philips

Motivation: Conventional MRI vendor-specific sequence development limits research transferability and reproducibility. Harmonized frameworks, like Pulseq, overcome these limitations - but Pulseq was not supported yet on Philips MRI scanners.

Goal(s): To develop a fully-compliant Pulseq interpreter for Philips MRI systems, facilitating the use of open-source sequences previously incompatible with these platforms.

Approach: Custom adaptation of Pulseq for the Philips R5.4 platform, followed by validation with standard imaging sequences using a field camera and phantom/in vivo scans, and comparison with native sequences.

Results: Demonstration of the first Philips-compatible Pulseq interpreter, evidenced by successful scans at 7T, marking a leap in cross-vendor research capabilities.

Impact: The successful adaptation of Pulseq sequences to Philips MRI system enables researchers to deploy and disseminate advanced MRI techniques universally, fostering cross-vendor collaboration and accelerating the evolution of MRI technology.

Keywords: Pulse Sequence Design, Multi-Contrast, Rapid imaging

Motivation: The T2w and T2FLAIR are extremely versatile MRI contrasts and paramount to asses a wide range of pathologies in neuroimaging.

Goal(s): A highly efficient acquisition strategy is proposed that jointly acquires T2w and T2FLAIR full brain data in a little more than half a minute.

Approach: Single shot FSE readouts, inversion pulses and saturation bands are strategically interleaved to maximize sampling efficiency and avoid dummy TRs. Prospective motion correction is added to increase robustness.

Results: Volunteer results comparing different protocols, a motion experiment and a pediatric scan are presented. Acceptable image quality was achieved even under severe motion.

Impact: A half minute, motion robust, whole brain T2w and T2FLAIR scan is very interesting for clinical neuroimaging. It is potentially very useful for acute MR, pediatric imaging, screening, disease progression or treatment monitoring.

Keywords: Pulse Sequence Design, Pulse Sequence Design

Motivation: While current multi-contrast imaging technique spoiled gradient recalled echo (SPGR) requires a long acquisition time and with a relatively low signal-to-noise ratio (SNR), an efficient three-dimensional (3D) dual-pathway sequence may improve image quality with a reduced scan time.

Goal(s): Our goal is to demonstrate an image quality improvement in multi-contrast imaging with our proposed 3D double-echo steady-state echo-planar imaging (DESS-EPI) sequence.

Approach: We design and implement a 3D DESS-EPI sequence and  evaluate SNR and contrast-to-noise ratio (CNR) of acquired images.

Results: Our results demonstrate the potential advantages of the 3D DESS-EPI sequence in terms of imaging quality and efficiency.

Impact: The improvement in time efficiency and image quality using our 3D DESS-EPI sequence illustrates the prospective benefits in multi-contrast imaging, which is appropriate for temperature mapping, quantitative mapping, field mapping, susceptibility-weighted imaging (SWI) and quantitative susceptibility mapping (QSM).

Keywords: Pulse Sequence Design, Pulse Sequence Design

Motivation: The selection of cerebrospinal fluid (CSF) as a zero-reference can yield significant and interpretable susceptibility measurements in quantitative susceptibility mapping (QSM).

Goal(s): Our goal is to develop a 3D dual-pathway sequence capable of achieving acquisition of multi-contrast images with a reduced scan time and improving image quality. These images will be used in selecting the zero reference in QSM.

Approach: We implement a 3D double-echo steady-state echo-planar imaging (DESS-EPI) sequence with fly-back gradients, designed to generate multi-contrast images while eliminating Nyquist artifact.

Results: Our preliminary findings indicate the feasibility of utilizing multi-echo images in QSM and global CSF segmentation.

Impact: The use of global CSF as a reference in QSM can enhance susceptibility measurements. The development of our modified 3D DESS-EPI sequence improves image quality, reduces scan time, and shows promise for global CSF segmentation in QSM.

Keywords: Pulse Sequence Design, New Signal Preparation Schemes

Motivation: Determination of T2 typically depends on spin-echo based relaxometry. Partially spoiled non-balanced gradient echo imaging also allows T2-mapping but requires two data sets from two different steady states, making it prone to motion artefacts. 

Goal(s): To determine T2 from a single T2-weighted steady state.

Approach: A combination of partial spoiling and oscillating steady state imaging was optimized using Bloch simulations, implemented on a human whole-body MR-scanner and tested on a test object and in vivo.

Results: Partially spoiled oscillating steady state imaging allowed generating phase images similar to partially spoiled non-balanced SSFP imaging without the need to sequentially establish two different steady states.

Impact: Partially spoiled gradient echo imaging allows T2-mapping without using large flip angles but requires data from two different steady states.  By combining partial spoiling with oscillating steady state imaging T2 can be determined from one single oscillating steady state.

Keywords: Pulse Sequence Design, Pulse Sequence Design

Motivation: Conventional 2D-TSE offers superior tissue contrast compared to 3D-TSE, but its slice thickness is restricted by SNR and slice profile of RF pulse.

Goal(s): Our objective was to achieve 0.4mm isotropic T2-weighted imaging with high contrast and high SNR.

Approach: Amplitude and phase modulated gSlider pulses were developed and incorporated into 2D-TSE. Their performances were evaluated in phantom and in vivo.

Results: The gSlider-TSE achieved 0.4mm isotropic imaging with high accuracy. The SNR was comparable to 8 times averaged conventional 2D-TSE image.

Impact: The gSlider-TSE provides high-resolution isotropic imaging with submillimeter slice thickness and high SNR, while preserving the high contrast of conventional 2D-TSE.

Keywords: Pulse Sequence Design, Tumor, Stack-of-stars Acquisition

Motivation: Sequences from the T1RESS family offer increased lesion conspicuity in contrast-enhanced brain examinations. Recently, radial variants have been developed to improve motion robustness.

Goal(s): To enable broader clinical utilization of radial T1RESS sequences.

Approach: Dynamic imaging is enabled through combination with GRASP reconstruction. Fat/water separation is achieved by integrating the multi-echo Dixon technique. Further scan acceleration is achieved by applying 1D GRAPPA along the kz dimension.

Results: The proposed extensions are demonstrated for brain imaging at 3T in volunteers and patients, revealing dynamic lesion-enhancement patterns, successful fat/water separation, and supplementary scan acceleration with comparable quality and lesion conspicuity.

Impact: The proposed technical extensions of radial stack-of-stars T1RESS sequences, including dynamic reconstruction, fat/water separation, and parallel imaging, will enable broader clinical utilization of this novel sequence family and may result in noticeably improved sensitivity for lesion detection throughout the body.

Keywords: Pulse Sequence Design, Spectroscopy, J-editing lactate

Motivation: Metabolites exhibiting J-coupling (like lactate) can be selectively detected against overlapping signals using multi-quantum filtering (MQF). Accurate modelling of such spin systems under realistic RF and gradient pulses is crucial for optimizing signal yield, background suppression and quantification.
 

Goal(s): Improve MQF sequences to mitigate the inherent 50 % signal loss of double-quantum filters.

Approach: The effect of realistic RF-pulses (hard/selective, various phases) and gradients on an AX₃ system’s higher-order coherences was investigated. Semi-LASER-based spin-echo sequences were simulated in pyGAMMA and tested on a 7T scanner.

Results: Quadruple-quantum coherences maintain near-100 % signal, outperforming traditional DQF.  Simulations and phantom experiments agreed within 6 %.

Impact: Quadruple-quantum filtering of lactate can retain its full signal, promising faster and more precise lactate quantification in human tissues. This could significantly improve the monitoring of glycolytic and oxidative metabolism and thus the understanding of underlying mechanisms in disease.

Keywords: Pulse Sequence Design, Pulse Sequence Design

Motivation: The current practice of MRI acceleration commonly subsamples K-space along the Phase Encoding (PE) direction, but this approach does not fully address the need for further reduction in scan time.

Goal(s): Our goal was to develop a Frequency Encoding (FE) subsampling technique that reduces scan time while maintaining image quality.

Approach: We introduced the Double Lobe Gradient (DOGE) readout approach, which manipulates the readout gradient waveform to subsample along the FE direction.

Results: The verification of DOGE readout on b-SSFP resulted in a significant reduction of 40% in readout time and 20% reduction in repetition time (TR), while maintaining comparable image quality.

Impact: Our approach exhibits compatibility with existing MRI acceleration techniques, thereby enhancing scan efficiency. Moreover, its potential applicability to other pulse sequences to reduce scan duration could bear substantial implications for clinical practice, potentially revolutionizing patient experience and diagnostic accuracy.

Keywords: Pulse Sequence Design, Cardiovascular

Motivation: Designing optimal gradient waveforms is a convex problem. They must satisfy gradient hardware constraints, physiological constraints, and being time-optimal.

Goal(s): By shortening TE, we are more robust to motion artifact and less vulnerable to field inhomogeneities. By shortening TR and consequently TA, we can potentially minimize banding artifacts and obtain shorter scan time, increasing motion artifact robustness.

Approach: The gradient optimized method “GrOpt” was integrated directly into free-running 3D-radial-bSSFP and GRE acquisitions at 3T

Results: We achieved 14.0 %, 5.7% and 5.4% reduction in TE, TR and TA for bSSFP and 25.1%, 6.6% and 6.5% reduction in TE, TR and TA for GRE, .

Impact: In 3D-radial-bSSFP, CVX achieves 14.0%, 5.7% and 5.4% reduction in TE, TR and TA, respectively. In 3D-radial-GRE, 25.1%, 6.6% and 6.5% reduction in TE, TR and TA was obtained, reducing the effect of inhomogeneities, motions, eddy current and scan time.

Keywords: Pulse Sequence Design, Arterial spin labelling, multiple-TE ASL

Motivation: To assess the blood-CSF barrier on a Siemens platform using a multi-TE 3D RARE stack-of-spirals ASL sequence. 

Goal(s): To obtain high-quality fitted blood-to-csf time images. 

Approach: A 3D RARE pCASL sequence with multiple-TE acquisitions was used to collect ASL images. To cope with the low SNR issue in blood-CSF barrier ASL imaging, a denoising technique of locally adaptive low rank regularization with collaborative data selection was applied to images. 

Results: The fitted blood-to-csf time images generated from denoised control and label images showed significantly improved image quality. The Bland-Altman Plot shows a good agreement between the test and retest scans using the sequence. 

Impact: Blood-CSF barrier ASL implemented in the Siemens platform showed good test-retest reliability with the help of advanced denoising. The denoising technique can be used for ASL applications to provide high-quality images. 

Keywords: Pulse Sequence Design, Cancer, MRS, editing, 2HG, brain, tumor

Motivation: 2HG is an important oncometabolite which is commonly detected using J-difference editing.

Goal(s): Here, we determined the optimal echo time for J-difference editing of 2HG at 3T.

Approach: This was done by evaluating the echo time dependence of the 2HG-edited signal using simulations and in vivo experiments. We also quantified the T2 relaxation of 2HG as well as the co-edited glutamate and glutamine signals

Results: A TE of 90 ms was found to produce the highest signal, however, a TE of 70 ms was found to provide the best separation between 2HG and Glx in poor shimming conditions.

Impact: This optimized J-difference edited sequence could improve MRS measurements of 2HG. This would take MRS one step closer towards clinical applicability which could aid in the diagnosis and treatment monitoring of glioma patients.

Keywords: Pulse Sequence Design, Pulse Sequence Design, ZTE bSSFP

Motivation: Zero Echo-Time MRI has numerous advantages over conventional pulse sequences but also several drawbacks including inefficient k-space sampling and limited PD/T1 contrasts.

Goal(s): Improving the efficiency, SNR and contrasts available with ZTE.

Approach: Utilising a 3D rosette trajectory to combine the best aspects of the ZTE and bSSFP sequences.

Results: Preliminary data indicating the feasibility of the bSSFP ZTE sequence and highlighting limits imposed by current MR hardware.

Impact: Highly efficient sequences enable more useable data to be acquired in a single scan. We present a combined bSSFP ZTE sequence that pushes efficiency to the limits of typical MR hardware. 

Keywords: Pulse Sequence Design, Pulse Sequence Design

Motivation: Ultrashort echo time (UTE) sequences are essential for short T2 imaging, but have resulted in long scan times. Simultaneous multi-slice techniques can reduce scan times, but until the recent development of the PINS-UTE sequence, they been incompatible with UTE sequences.

Goal(s): We aim to optimize the slice profiles of the PINS-UTE sequence.

Approach: We investigate the effects of minimum radiofrequency subpulse duration, repetition time (TR), and gradient areas on in-vivo slice profiles.

Results: A minimum subpulse duration of 153.6 µs, TR of 250 ms with crusher gradients, and spoiler gradients with areas of 11.7 ms*mT/m on in-plane axes resulted in optimal slice profiles.

Impact: Power independent of number of slices (PINS) presaturation enables simultaneous multi-slice ultrashort echo time acquisitions and can reduce scan times for short T2 imaging. In this work, out-of-slice signal artifacts are reduced by optimizing elements of the PINS-UTE sequence.

Keywords: Pulse Sequence Design, Data Acquisition, Image reconstruction, quantitative mapping, fast imaging, compressed sensing, T1rho

Motivation: Magnetization-prepared (MP) 3D gradient-echo (GRE) MRI sequences suffer from T1 relaxation-induced artifacts, necessitating short echo train lengths. Paired phase-cycling (pPC) mitigates this but at the cost of doubled scan time. 

Goal(s): This research introduces inherent phase-cycling (iPC) to 3D MP-GRE sequences, aiming to eliminate T1-related artifacts without extending scan time.

Approach: iPC combines random PC+ and PC- acquisitions within a single 3D sequence. It is demonstrated that iPC, coupled with compressed sensing reconstruction, achieves high-resolution imaging without scan time increase.

Results: iPC significantly reduces ghosting and blurring artifacts compared to pPC, with potential applications in accelerated and artifact-free MRI.

Impact: The iPC MP-GRE sequence improves image quality while reducing scan time and complexity. It promises faster, clearer diagnostic imaging, benefiting medical research and patient care, and opens doors to broader applications in quantitative parameter mapping and beyond.