Keywords: Arterial Spin Labelling, Perfusion, FAIR, whole-kidney coverage, quantitative imaging, biomarkers

Motivation: Flow-sensitive alternative inversion (FAIR) is one of the recommended arterial spin labeling (ASL) schemes for renal perfusion. Although FAIR can provide robust measurements, it suffers from partial-kidney coverage especially when aorta is close to or even at the same level of kidney in anterior-posterior (A/P) direction.

Goal(s): To obtain whole-kidney perfusion measurements using 3D FAIR despite anatomy differences within population.

Approach: Two additional labeling strategies of 3D FAIR were proposed and tested in healthy volunteers.

Results: Both strategies generated robust and high-quality perfusion maps with whole-kidney coverage within a feasible clinical scan time, which is challenging for existing 3D FAIR and pCASL implementations.

Impact: Our labeling strategies in 3D FAIR ASL could be valuable for early detection, diagnosis, differentiation, and management of renal diseases, including chronic kidney disease and acute kidney injury, despite individual anatomy differences between patients.

Keywords: Arterial Spin Labelling, Perfusion, PET/MR

Motivation: Arterial spin labeling (ASL) MRI with a single post-labeling delay may not be appropriate for quantifying cerebral blood flow (CBF) in older participants or individuals with Alzheimer’s disease (AD).

Goal(s): To evaluate reliability of multi-delay versus single-delay ASL and their associations with [¹⁵O]water positron emission tomography (PET) using simultaneous PET/MRI in older adults.

Approach: We investigated 4-week test-retest reliability using intra-class correlation (ICC) and assessed Spearman’s correlations between ASL and PET in young and older controls (n=12) and AD patients (n=3).

Results: ICC values were similar between ASL approaches but exhibited regional differences. Multi-delay ASL-based CBF was correlated with PET in more regions-of-interest.

Impact: Multi-delay arterial spin labeling MRI provides CBF measures with good intermediate-term reliability that are strongly correlated with gold-standard [15O]water PET when studying older adults and AD patients.

Keywords: Arterial Spin Labelling, Arterial spin labelling

Motivation: We have recently shown that a PCASL-bSSFP sequence provides high quality perfusion images of the lung. However, the perfusion signal is dependent on the respective cardiac cycle.

Goal(s): Our aim was to further increase the perfusion signal of the lung parenchyma and/or to shorten the examination time using a new PCASL approach with multiple labeling.

Approach: Four volunteers were examined using an ECG-triggered multiple labeling PCASL-bSSFP sequence with different number of labeling pulses, post labeling delays and repetition delays.

Results: The PCASL sequence with multiple labeling appears to provide a higher perfusion signal of the lung parenchyma, reducing sensitivity to cardiac cycle variations.

Impact: The new PCASL approach with multiple labeling appears to provide a significantly higher perfusion signal of the lung than measurements with single labeling pulse. The sequence makes the PCASL technique more robust and faster for future application in clinical practice.

Keywords: Arterial Spin Labelling, Arterial spin labelling

Motivation: Arterial spin labeling (ASL) is vulnerable to motion and off-resonance, which may result in unstable image quality, particularly in children.

Goal(s): To propose an automatic image quality assessment model for 3D ASL in children.

Approach: The proposed model was trained and validated on 51 3D ASL scans from children, and was compared to a previously developed reference method. The performance was evaluated using AUC and 5-fold cross-validation tests.

Results: The proposed model yielded 8%-11% higher AUC, accuracy, and F1 score compared to the reference method.

Impact: The proposed model for assessing image quality in children's ASL may offer a valuable tool for clinics and studies on brain development with a large cohort.

Keywords: Arterial Spin Labelling, Arterial spin labelling, Asymmetric magnetization transfer

Motivation:  This study explores the asymmetric magnetization transfer (MT) effects on recently developed blood-brain barrier integrity (BBB-ASL) technique, with a focus on different neck labeling gradient polarities.

Goal(s): Validation of the asymmetric MT effect in BBB-ASL.

Approach: BBB-ASL parameters of arrival transit time (ATT), intra-voxel transit time (ITT), exchange time (Tex) and CBF were estimated by our custom MATLAB program based on a two-compartment model.

Results: Asymmetric MT effect changes not only depending on physical factors but also on the severity of the tissue. The difference might be related to changes in ITT and ATT.
 

Impact: This study explores the asymmetric magnetization transfer (MT) effects on BBB-ASL with MCAO model rats. Asymmetric MT effect changes not only depending on physical factors such as magnetic field inhomogeneity but also on the severity of the tissue.

Keywords: Arterial Spin Labelling, Arterial spin labelling, renal transplantation

Motivation: Renal interstitial fibrosis, a prevalent, irreversible, progressive chronic kidney injury, emerges as a crucial prognostic determinant for kidney transplantation. 

Goal(s): To explore the feasibility and performance of arterial spin labeling (ASL) in evaluating the degree of renal fibrosis after renal transplantation.

Approach: ASL was performed on 64 renal transplantation recipients. ASL parameters were obtained and analyzed.

Results: The study revealed a noteworthy negative correlation between the measured renal blood flow values, obtained through ASL, and the degree of interstitial fibrosis in transplanted kidneys. ASL can effectively differentiate various degrees of fibrosis in transplanted kidneys.

Impact: Using ASL technology, it is possible to non-invasively assess the degree of fibrotic changes in transplanted kidneys and the progression of kidney function, thereby achieving early detection, diagnosis, and treatment.

Keywords: Arterial Spin Labelling, Arterial spin labelling

Motivation: Renal imaging using echo planar imaging (EPI) readout may be sensitive to field inhomogeneities and induced ghost artifact. Besides, single inversion time is not enough for renal blood flow (RBF) quantification. Investigation of more stable clinical arterial spin label (ASL) imaging methods is required.

Goal(s): We aimed to design a stable clinical ASL sequence to quantify RBF accurately.

Approach: Multiple inversion time (TIs) readout by turbo spin echo (TSE) was processed, and the repeatability of quantification was evaluated in volunteers  (n=7).

Results: Multiple TIs combined with TSE readout of FAIR-ASL provided more accurate RBF measurement and highly repeatability compare with pcASL-EPI.

Impact: Multi-PLDs readout by TSE may provide a stable clinical ASL-FAIR sequences to accurately quantify RBF.

Keywords: Arterial Spin Labelling, Perfusion

Motivation: 3D-PCASL is a well-established perfusion MRI technique at 3T. Nonetheless, its effectiveness is hampered by increased RF power deposition at 7T limiting the SNR efficiency and labeling duration.

Goal(s): This work investigates the relationship between gray matter perfusion signal and labeling duration aiming to optimize 3D-PCASL SNR efficiency while taking into consideration the increased RF power constraints of 7T MRI.

Approach: SNR efficiency was measured at various labeling durations maintaining scan time to ~6 min and SAR to ~90% of first-level mode limit at 7T.

Results: Optimal SNR efficiency was obtained at labeling duration of ~3 s.

Impact: The result of this work provides optimal labeling duration for 7T 3D PCASL studies with maximum SNR per unit time taking into account first-level mode RF power limits.

Keywords: Arterial Spin Labelling, fMRI

Motivation: The olfactory bulbs (OBs) play a key role in the detection and processing of olfactory information. However, research on human OB function has been limited due to their challenging location for conventional T₂*-weighted BOLD fMRI. 

Goal(s): To explore ASL as an alternative to BOLD for OB functional MRI.

Approach: We utilized ASL with a 16-shot Stack-of-Spirals 3D TSE readout to obtain short-TE functional imaging. We quantified blood flow and subsequently assessed neural activation in the OB using a blocked design olfactory paradigm.

Results: This study quantifies OB blood flow for the first time and demonstrates neural activation in the OB during odor delivery.

Impact: This work highlights ASL's potential for fMRI, especially in challenging areas with high susceptibility and low signal-to-noise ratio, making it a viable option for studying olfactory-related regions where BOLD fMRI faces difficulties.

Keywords: Arterial Spin Labelling, Arterial spin labelling, infant; labeling efficiency; off-resonance

Motivation: The image quality of ASL in infants is variable.

Goal(s): To investigate the labeling efficiency in infant pCASL.

Approach: Labeling efficiency was simulated using the Bloch equation. Prospective scans were performed on 11 subjects, with pCASL at 60mm and 90mm below the AC-PC line, MRA, and B0 map.

Results: Blood flow velocity has negligible effects on the labeling efficiency at the on-resonance frequency. The combined effects of off-resonance and the high blood flow velocity are the primary cause of the variable image quality. pCASL images at 60mm showed improved SNR in 8 /11 infants, compared to that of 90mm.

Impact: This study examined the factors contributing to variable ASL images in infant and provided a preliminary solution by selecting the labeling plane.

Keywords: Arterial Spin Labelling, Perfusion, T1 mappinng

Motivation: Pseudo-continuous Arterial Spin Labeling (PCASL) MRI is a promising technique for assessing renal perfusion. Previous studies have been carried out at 1.5T and 3T field strengths, but a comparison of data acquired at both field strengths has never been performed.

Goal(s): The aim of this work was to assess the effects of field strength on the measured perfusion signal and to evaluate the reproducibility of renal PCASL at both fields

Approach: Healthy volunteers underwent repeated scans on both scanners, spaced a week apart. 

Results: The results showed excellent reproducibility and minimal differences in RBF, ATT and T1 values between visits and field strengths. 

Impact: The similarity in the study results across both field strengths underscore the potential for expanding PCASL-based renal perfusion assessment, increasing the technique accessibility, and widening diagnostic capabilities.  

Keywords: Arterial Spin Labelling, Perfusion, Arterial Spin Labelling, Normal Development

Motivation: There is lacking understanding of hemodynamic changes in children and their impact on MRI perfusion quantification.

Goal(s): We aim to investigate age-related hemodynamic changes in developing brain.

Approach: Perfusion parameters from single- and multi-delay Arterial Spin Labeling (ASL) MRI of MR-negative children are analyzed.

Results: We found significant age-dependent differences between perfusion quantification with single- and multi-delay approaches. ATT followed a non-linear distribution in age and was heterogeneous across vascular territories Our findings support the use of multi-delay ASL for improved perfusion assessment in children and provide better understanding of hemodynamic changes in developing brain.

Impact: This is the first study to investigate age-related arterial transit-time changes in children and their impact on perfusion quantification with perfusion MRI. Our findings prompt improved understanding of age-related perfusion changes and standardization of hemodynamic parameters in the pediatric cohort.

Keywords: Arterial Spin Labelling, Perfusion

Motivation: There are few validated noninvasive indicators for renal perfusion and renal function in patients with renal artery stenosis (RAS)

Goal(s): To explore the utility of arterial spin labeling (ASL) as a noninvasive indicator of renal perfusion and function in patients with RAS.

Approach: We evaluated correlations between ASL-measured preoperative renal blood flow (RBF) and renal function, then compared preoperative and postoperative RBF.

Results: ASL-measured RBF was significantly correlated with renal function. ASL was able to evaluate perfusion improvement in patients with RAS after interventional therapy.

Impact: ASL can be used as an indicator of renal function and perfusion in patients with RAS. It can also be used to assess changes in renal perfusion after interventional therapy.

Keywords: Arterial Spin Labelling, Arterial spin labelling, calibrated fMRI, BOLD, multi-echo, sequence, brain

Motivation: Calibrated fMRI quantitatively estimates cerebral metabolic rate of oxygen (CMRO2) by simultaneously measuring cerebral blood flow (CBF) with arterial spin labeling (ASL) and BOLD. Pseudo-continuous ASL (PCASL) with background suppression (BS) and 3D readout is recommended for CBF while multi-echo (ME) 2D BOLD has gained popularity. Nowadays, no calibrated fMRI sequence integrates both.

Goal(s): Our goal is to combine them in a single sequence.

Approach: We introduce a novel dual-acquisition calibrated fMRI sequence integrating BS-PCASL-3D GRASE for CBF and 2D multi-echo EPI BOLD.

Results: Resting-state data in a healthy volunteer showed CBF values concordant with literature and improved BOLD tSNR and connectivity maps.

Impact: We propose a novel sequence for calibrated fMRI that optimizes both CBF and BOLD measurements with a dual acquisition scheme, thus overcoming the limitations of previous ASL-BOLD calibrated fMRI sequences and showing promise for improved accuracy and reliability.

Keywords: Arterial Spin Labelling, Arterial spin labelling, cerebral small vessel disease

Motivation: The blood brain barrier (BBB) is damaged in patients with cerebral small vessel disease (cSVD).

Goal(s): To study the role of subtle BBB impairment in cSVD by measuring water-transport over the vessel wall.

Approach: T₂-prepared time-encoded pCASL was applied in cerebral small vessel disease (cSVD) patients and healthy controls.

Results: T₂ variations between the groups showed no significance in this preliminary sample yet. However, T₂-values tend to decay earlier in VCI patients compared to HC. This suggests earlier water-transport from blood to tissue, possibly referring to stronger BBB impairment. Moreover, broader distributions of T₂-values seem to indicate larger heterogeneity in the VCI-group.

Impact: This study applied T₂-prepared time-encoded pCASL in cerebral small vessel disease (cSVD) patients and healthy controls to study subtle BBB-damage. Although T₂-values showed no significant differences yet, the T₂-values seem to decay earlier in cSVD, suggesting earlier water-transport into tissue.

Keywords: Arterial Spin Labelling, Machine Learning/Artificial Intelligence

Motivation: Hemodynamic disturbance is one of the neuropathological characteristics of Parkinson's disease (PD). Multi-delay arterial spin labeling (m-ASL) MRI can optimize the accuracy of cerebral blood flow (CBF) quantification by taking into account arterial transit time (ATT). 

Goal(s): We aimed to comprehensively explore the detailed abnormalities of hemodynamics in PD and verify the application of m-ASL in PD diagnosis.

Approach: Voxel-based analysis and machine learning approach were applied to this study. 

Results: Our findings identified impaired hemodynamics in PD with regional abnormalities of CBF, ATT and cerebral blood volume, providing complementary depictions of perfusion disruption in PD and highlighting the clinical feasibility of m-ASL.

Impact: Our results provided complementary depictions of perfusion disruption in PD, and validated the promise of m-ASL in the investigation of underlying neurodegeneration and the clinical diagnosis of PD, providing an effective neuroimaging biomarkers for the diagnosis of neurodegenerative diseases.