Recent advances in arterial spin labeling perfusion MRI in patients with vascular cognitive impairment

Arterial Spin Labeling: Key Concepts and Progress Towards Use as a Clinical Tool

Arterial spin labeling (ASL), a non-invasive MRI technique, has emerged as a valuable tool for researchers that can measure blood flow and related parameters. This review aims to provide a qualitative overview of the technical principles and recent developments in ASL and to highlight its potential clinical applications. A growing literature demonstrates impressive ASL sensitivity to a range of neuropathologies and treatment responses. Despite its potential, challenges persist in the translation of ASL to widespread clinical use, including the lack of standardization and the limited availability of comprehensive training. As experience with ASL continues to grow, the final stage of translation will require moving beyond single site observational studies to multi-site experience and measurement of the added contribution of ASL to patient care and outcomes.

The effect of post-labeling delay on cerebral blood flow is influenced by age and sex: a study based on arterial spin-labeling magnetic resonance imaging

Background

Whether the effect of post-labeling delay (PLD) on cerebral blood flow (CBF) is influenced by age and sex in adults is unknown. In this study, we mainly aimed to explore the potential influence of age and sex on the effect of PLD on CBF.

Methods

This prospective study enrolled 90 healthy adult volunteers (49.47±15.63 years of age; age range, 20-77 years; 47 female; 43 male). All participants underwent 3-dimensional (3D) pseudo-continuous arterial spin labeling (ASL) imaging with 3 different PLDs (1,525, 2,025, and 2,525 ms). The CBF values for each PLD, the arterial transit time (ATT), and the spatial coefficient of variation (spatial CoV) were computed for 21 regions of interest (ROIs) in every participant. Multivariate regression analysis was conducted to assess the potential influence of age and sex on the effect of PLD on CBF and the relationships among CBF, ATT, PLD, age, sex, and spatial CoV.

Results

The CBF increased for 7.32 to 9.87 mL/100 g/min as the PLD increased per 1 second in the global gray matter, bilateral frontal, temporal lobes, the vascular territories of bilateral anterior and middle carotid artery. When the age increased per 1 year, the speed of the changes for CBF decreased for 0.26 to 0.3 mL/100 g/min/s in these regions. However, the CBF decreased for 12 to 17 mL/100 g/min as the PLD increased per 1 second in the bilateral limbic lobes, insula, and deep gray matter. In these regions, the speed of the changes for CBF increased for 0.2 to 0.28 mL/100 g/min/s as the age increased per 1 year. Furthermore, compared to the female, the speed of the changes for CBF decreased for 3.58 to 4.6 mL/100 g/min/s for the male in global gray matter, bilateral frontal, limbic lobes, and the vascular territories of bilateral anterior carotid artery, and the speed increased 4.49 to 5.09 mL/100 g/min/s for the male in the limbic lobes. In addition, the CBF decreased with aging and the CBF tended to be higher in females compared to males. At the same time, we found that the ATT of all ROIs increased with age and manifested higher in males than females. Moreover, we found that CBF decreased with the increase of ATT, and the effect of ATT on CBF was less influenced by PLD. Finally, we found that the spatial CoV of ASL in certain regions increased with the increase of ATT and age, and was greater in males.

Conclusions

The effect of PLD on CBF can be influenced by age and sex. The relationships among CBF, ATT, PLD, age, sex, and spatial CoV found in this study may have certain significance for the study of ASL imaging in the future.

Reduced cerebral blood flow and cognitive dysfunction following isolated cerebellar infarction: two case reports

Cognitive impairment in focal cerebellar disorders has been widely recognized and is described as cerebellar cognitive affective syndrome (CCAS). However, the relationship between CCAS and crossed cerebello-cerebral diaschisis (CCD) has rarely been discussed. The present report describes the uncommon phenomenon of CCD in two cases with isolated cerebellar infarction, and discuss its contribution to cognitive impairment. Cognitive performance was examined using the CCAS scale and a battery of neuropsychological assessments. Moreover, the relative distribution of cerebral and cerebellar blood flow was measured using three-dimensional arterial spin labeling imaging. Case 1 showed deficits in general cognition and had impaired language, episodic memory, and executive function. Case 2 showed deficits in general cognition at baseline, and cognitive deterioration of visuospatial abilities, language, episodic memory, and executive function was observed at the 3-month follow-up. Both cases met the diagnosis criteria of CCAS. Reduced cerebral blood flow was observed in the cerebral hemisphere contralateral to the cerebellar infarction at baseline in Case 1, and at the 3-month follow-up in Case 2. The present report describes cognitive decline after isolated cerebellar infarction in combination with contralateral cerebral hypoperfusion, as measured using quantitative arterial spin labeling. One possible mechanism involves the functional depression of cerebello-cerebral pathways.

A 3D-printed phantom for quality-controlled reproducibility measurements of arterial spin labeled perfusion

PURPOSE

To develop a portable MR perfusion phantom for quality-controlled assessment and reproducibility of arterial spin labeled (ASL) perfusion measurement.

METHODS

A 3D-printed perfusion phantom was developed that mimics the branching of arterial vessels, capillaries, and a chamber containing cellulose sponge representing tissue characteristics. A peristaltic pump circulated distilled water through the phantom, and was first evaluated at 300, 400, and 500 mL/min. Longitudinal reproducibility of perfusion was performed using 2D pseudo-continuous ASL at 20 post-label delays (PLDs, ranging between 0.2 and 7.8 s at 0.4-s intervals) over a period of 16 weeks, with three repetitions each week. Multi-PLD data were fitted into a general kinetic model for perfusion quantification (f) and arterial transit time (ATT). Intraclass correlation coefficient was used to assess intersession reproducibility.

RESULTS

MR perfusion signals acquired in the 3D-printed perfusion phantom agreed well with the experimental conditions, with progressively increasing signal intensities and decreasing ATT for pump flow rates from 300 to 500 mL/min. The perfusion signal at 400 mL/min and the general kinetic model-derived f and ATT maps were similar across all PLDs for both intrasession and intersession reproducibility. Across all 48 experimental time points, the average f was 75.55 ± 3.83 × 10-3  mL/mL/s, the corresponding ATT was 2.10 ± 0.20 s, and the T1 was 1.84 ± 0.102 s. Intraclass correlation coefficient was 0.92 (95% confidence interval 0.83-0.97) for f, 0.96 (0.91-0.99) for ATT, and 0.94 (0.88-0.98) for T1 , demonstrating excellent reproducibility.

CONCLUSION

A simple, portable 3D-printed perfusion phantom with excellent reproducibility of 2D pseudo-continuous ASL measurements was demonstrated that can serve for quality-controlled and reliable measurements of ASL perfusion.

Lower cerebral blood flow predicts cognitive decline in patients with vascular cognitive impairment

INTRODUCTION

Chronic cerebral hypoperfusion is one of the assumed pathophysiological mechanisms underlying vascular cognitive impairment (VCI). We investigated the association between baseline cerebral blood flow (CBF) and cognitive decline after 2 years in patients with VCI and reference participants.

METHODS

One hundred eighty-one participants (mean age 66.3 ± 7.4 years, 43.6% women) underwent arterial spin labeling (ASL) magnetic resonance imaging (MRI) and neuropsychological assessment at baseline and at 2-year follow-up. We determined the association between baseline global and lobar CBF and cognitive decline with multivariable regression analysis.

RESULTS

Lower global CBF at baseline was associated with more global cognitive decline in VCI and reference participants. This association was most profound in the domain of attention/psychomotor speed. Lower temporal and frontal CBF at baseline were associated with more cognitive decline in memory.

DISCUSSION

Our study supports the role of hypoperfusion in the pathophysiological and clinical progression of VCI.

HIGHLIGHTS

Impaired cerebral blood flow (CBF) at baseline is associated with faster cognitive decline in VCI and normal aging. Our results suggest that low CBF precedes and contributes to the development of vascular cognitive impairment. CBF determined by ASL might be used as a biomarker to monitor disease progression or treatment responses in VCI.

Recent advances in mechanistic, therapeutic, and diagnostic research of cerebrovascular diseases: updates from brain & BrainPET 2022

Cerebrovascular dysfunction and diseases are major causes of mortality, morbidity, and poor quality of patient life. Despite the enormous socioeconomic burden imposed by these conditions, therapeutic options remain scarce. However, rigorous preclinical and clinical research has augmented our mechanistic understanding of cerebrovascular diseases and underlying pathophysiological processes, and there is some optimism that novel therapeutic strategies may be developed in the next decade. This special collection comprises preclinical and clinical studies from investigators who presented their work at the Brain & BrainPET 2022 conference. It highlights recent research on cerebrovascular disease mechanisms, diagnosis, and treatments. A focus is set on cerebroprotective strategies during acute and chronic cerebral ischemia and predicting stroke risk and unfavorable outcomes. The special collection also sheds light on emerging novel treatment targets and management strategies in the pursuit of better clinical outcomes for patients with cerebrovascular diseases.

Utilizing Reduced Labeled Proton Clearance to Identify Preclinical Alzheimer Disease with 3D ASL MRI

Addressing the seminal pathophysiology in Alzheimer disease (AD) is the next logical focus for effective intervention, given the initial disappointing and more recent possibly encouraging results of monoclonal antibody trials. Endothelial cell dysfunction-induced blood-brain barrier leak with associated prolonged capillary mean transit time (cMTT) and glymphatic outflow dysfunction is the most proximal events in the degeneration cascade. Sensitive and reproducible markers are required to both identify early disease and assess future treatment trial outcomes. Two participants, with mild cognitive impairment (MCI) and one with AD, were evaluated clinically prior to MRI in this small case series report. From seven 3D turbo gradient and spin echo (TGSE) pulsed arterial spin echo (PASL) MRI sequences six homologous region of interest in bitemporal, bifrontal, and biparietal lobes for each sequence were examined and plotted against time. By choosing late perfusion times during cMTT phase of perfusion linear analysis of signal decay could be utilized. A reference axial FLAIR sequence was also obtained. Slope of the linear analysis correlated to the rate of labeled proton clearance with reduced clearance occurring in AD participants compared to normal participants in our previous study. Whether similar differences in clearance rate extend to either MCI or early AD was investigated. Participants were categorized by clinical phenotype before MRI and compared to previously published phenotype cohorts: n = 18 normal/healthy, n = 6 AD, n = 3 MCI. Significant differences in labeled proton clearance rates between AD and MCI/control phenotypes within bilateral temporal lobes (left p = 0.004, right p = 0.002) and within bilateral frontal lobes AD versus controls (left p = 0.001, right p = 0.008) and AD versus MCI (left p = 0.001, right p = 0.001) were found. This noninvasive MRI technique has potential for identifying MCI transition to AD.