3.0 T MRI arterial spin labeling and magnetic resonance spectroscopy technology in the application of Alzheimer's disease

MRS in neurodegenerative dementias, prodromal syndromes and at-risk states: A systematic review of the literature

BACKGROUND

In recent years, MRS has benefited from increased MRI field strengths, new acquisition protocols and new processing techniques. This review aims to determine how this has altered our understanding of MRS neurometabolic markers in neurodegenerative dementias.

METHODS

Our systematic review of human in vivo MRS literature since 2002 pertains to Alzheimer's disease (AD), dementia with Lewy bodies (DLB), Parkinson's disease dementia, frontotemporal dementia (FTD), prodromal and 'at-risk' states. Studies using field strengths of 3 T or more were included.

RESULTS

Of 85 studies, AD and/or mild cognitive impairment (MCI) were the most common conditions of interest (58 papers, 68%). Only 14 (16%) studies included other dementia syndromes and 13 (15%) investigated 'at-risk' cohorts. Earlier findings of lower N-acetylaspartate and higher myo-inositol were confirmed. Additionally, lower choline and creatine in AD and MCI were reported, though inconsistently. Previously challenging-to-measure metabolites (glutathione, glutamate and gamma-aminobutyric acid) were reportedly lower in AD, FTD and DLB compared with controls.

DISCUSSION

Increasing field strength alongside targeted acquisition protocols has revealed additional metabolite changes. Most studies were small and regional metabolite differences between dementia types may not have been captured due to the predominant placement of voxels in the posterior cingulate cortex. The standard of data collection, quality control and analysis is improving due to greater consensus regarding acquisition and processing techniques. Ongoing harmonization of techniques, creation of larger and longitudinal cohorts, and placement of MRS voxels in more diverse regions will strengthen future research.

Neuroimaging modalities in the detection of Alzheimer's disease-associated biomarkers

Alzheimer's disease (AD) is the most common cause of dementia. Neuropathological changes in AD patients occur up to 10-20 years before the emergence of clinical symptoms. Specific diagnosis and appropriate intervention strategies are crucial during the phase of mild cognitive impairment (MCI) and AD. The detection of biomarkers has emerged as a promising tool for tracking the efficacy of potential therapies, making an early disease diagnosis, and prejudging treatment prognosis. Specifically, multiple neuroimaging modalities, including magnetic resonance imaging (MRI), positron emission tomography, optical imaging, and single photon emission-computed tomography, have provided a few potential biomarkers for clinical application. The MRI modalities described in this review include structural MRI, functional MRI, diffusion tensor imaging, magnetic resonance spectroscopy, and arterial spin labelling. These techniques allow the detection of presymptomatic diagnostic biomarkers in the brains of cognitively normal elderly people and might also be used to monitor AD disease progression after the onset of clinical symptoms. This review highlights potential biomarkers, merits, and demerits of different neuroimaging modalities and their clinical value in MCI and AD patients. Further studies are necessary to explore more biomarkers and overcome the limitations of multiple neuroimaging modalities for inclusion in diagnostic criteria for AD.

The Utility of Arterial Spin Labeling MRI in Medial Temporal Lobe as a Vascular Biomarker in Alzheimer's Disease Spectrum: A Systematic Review and Meta-Analysis

We sought to systematically review and meta-analy the role of cerebral blood flow (CBF) in the medial temporal lobe (MTL) using arterial spin labeling magnetic resonance imaging (ASL-MRI) and compare this in patients with Alzheimer's disease (AD), individuals with mild cognitive impairment (MCI), and cognitively normal adults (CN). The prevalence of AD is increasing and leading to high healthcare costs. A potential biomarker that can identify people at risk of developing AD, whilst cognition is normal or only mildly affected, will enable risk-stratification and potential therapeutic interventions in the future. All studies investigated the role of CBF in the MTL and compared this among AD, MCI, and CN participants. A total of 26 studies were included in the systematic review and 11 in the meta-analysis. Three separate meta-analyses were conducted. Four studies compared CBF in the hippocampus of AD compared with the CN group and showed that AD participants had 2.8 mL/min/100 g lower perfusion compared with the CN group. Eight studies compared perfusion in the hippocampus of MCI vs. CN group, which showed no difference. Three studies compared perfusion in the MTL of MCI vs. CN participants and showed no statistically significant differences. CBF measured via ASL-MRI showed impairment in AD compared with the CN group in subregions of the MTL. CBF difference was significant in hippocampus between the AD and CN groups. However, MCI and CN group showed no significant difference in subregions of MTL.

Disconnection from prediction: A systematic review on the role of right temporoparietal junction in aberrant predictive processing

The right temporoparietal junction (rTPJ) is a brain area that plays a critical role in a variety of cognitive functions. Although different theoretical proposals tried to explain the ubiquitous role of rTPJ, recent evidence suggests that rTPJ may be a fundamental cortical region involved in different kinds of predictions. This systematic review aims to better investigate the potential role of rTPJ under a predictive processing perspective, providing an overview of cognitive impairments in neurological patients as the consequence of structural or functional disconnections or damage of rTPJ. Results confirm the involvement of rTPJ across several tasks and neurological pathologies. RTPJ, via its connections with other brain networks, would integrate diverse information and update internal models of the world. Against traditional views, which tend to focus on distinct domains, we argue that the role of rTPJ can be parsimoniously interpreted as a key hub involved in domain-general predictions. This alternative account of rTPJ role in aberrant predictive processing opens different perspectives, stimulating new hypotheses in basic research and clinical contexts.

Chemical genetic activation of the cholinergic basal forebrain hippocampal circuit rescues memory loss in Alzheimer's disease

Background

The degeneration of the cholinergic circuit from the basal forebrain to the hippocampus contributes to memory loss in patients suffering from Alzheimer’s disease (AD). However, the internal relationships between the acetylcholine (Ach) cycle and memory decline during the early stages of AD currently remain unknown. Here, we investigate the mechanisms underlying the activation of the cholinergic circuit and its impact on learning and memory using APP/PS1 mice models.

Methods

Novel object recognition and Morris water maze tests were used to measure learning and memory function. Magnetic resonance spectrum (MRS) imaging was applied to longitudinally track changes in neurochemical metabolism in APP/PS1 mice aged 2, 4, 6, and 8 months. The number of neurons and the deposition of Aβ plaques were measured using Nissl, immunohistochemistry, and Thioflavin S staining. We then employed a chemogenetic strategy to selectively activate the cholinergic circuit from the medial septal nucleus (MS) and the vertical limb of the diagonal band nucleus (VDB) on the basal forebrain to the hippocampus. MRS and immunoblotting techniques were used to measure the neurochemical metabolism levels and cholinergic-related proteins, respectively.

Results

We found that the levels of choline (Cho) in the basal forebrain were markedly higher compared to other brain regions and that its decrease along with N-acetyl aspartate (NAA) levels in the hippocampus was accompanied by memory deficits in APP/PS1 mice aged 4, 6, and 8 months. In terms of pathology, we observed that the deposition of Aβ plaques gradually aggravated throughout the cerebral cortex and hippocampus in APP/PS1 mice aged 6 and 8 months, while no Aβ deposition was detected in the basal forebrain. In contrast, the activity of choline acetyltransferase (ChAT) enzyme in the basal forebrain was decreased at 6 months of age and the cholinergic neurons were lost in the basal forebrain at 8 months of age. In addition, the activation of the cholinergic circuit from the MS and VDB to the hippocampus using chemical genetics is able to improve learning and reduce memory impairment in APP/PS1 mice. Similarly, the levels of Cho in the basal forebrain; NAA in the hippocampus, as well as the expression of ChAT and vesicular acetylcholine transporter (vAchT) in the basal forebrain; and muscarinic acetylcholine receptor 2 (CHRM2) in the hippocampus all increased.

Conclusions

These findings demonstrate that the neurochemical Cho and NAA of the cholinergic circuit can be used as biomarkers to enable the early diagnosis of AD. In addition, memory impairment in APP/PS1 mice can be attenuated using chemical genetics-driven Ach cycle activity of the cholinergic circuit.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-00994-w.

Contribution of Inflammation and Hypoperfusion to White Matter Hyperintensities-Related Cognitive Impairment

White matter hyperintensities (WMHs) of presumed vascular origin are one of the most important neuroimaging markers of cerebral small vessel disease (CSVD), which are closely associated with cognitive impairment. The aim of this study was to elucidate the pathogenesis of WMHs from the perspective of inflammation and hypoperfusion mechanisms. A total of 65 patients with WMHs and 65 healthy controls were enrolled in this study. Inflammatory markers measurements [hypersensitive C-reactive protein (hsCRP) and lipoprotein-associated phospholipase A2 (Lp-PLA2)], cognitive evaluation, and pseudocontinuous arterial spin labeling (PCASL) MRI scanning were performed in all the subjects. The multivariate logistic regression analysis showed that Lp-PLA2 was an independent risk factor for WMHs. Cerebral blood flow (CBF) in the whole brain, gray matter (GM), white matter (WM), left orbital medial frontal gyrus [MFG.L (orbital part)], left middle temporal gyrus (MTG.L), and right thalamus (Tha.R) in the patients was lower than those in the controls and CBF in the left triangular inferior frontal gyrus [IFG.L (triangular part)] was higher in the patients than in the controls. There was a significant correlation between Lp-PLA2 levels and CBF in the whole brain (R = -0.417, p < 0.001) and GM (R = -0.278, p = 0.025), but not in the WM in the patients. Moreover, CBF in the MFG.L (orbital part) and the Tha.R was, respectively, negatively associated with the trail making test (TMT) and the Stroop color word test (SCWT), suggesting the higher CBF, the better executive function. The CBF in the IFG.L (triangular part) was negatively correlated with attention scores in the Cambridge Cognitive Examination-Chinese Version (CAMCOG-C) subitems (R = -0.288, p = 0.020). Our results revealed the vascular inflammation roles in WMHs, which may through the regulation of CBF in the whole brain and GM. Additionally, CBF changes in different brain regions may imply a potential role in the modulation of cognitive function in different domains.

Early Warning Value of ASL-MRI to Estimate Premorbid Variations in Patients With Early Postoperative Cognitive Dysfunctions

Background: Postoperative cognitive dysfunction (POCD) is a general complication following cardiac and major non-cardiac surgery amongst the elderly, yet its causes and mechanisms are still unknown. The present study aimed to detect whether regional cerebral blood flow (CBF) is altered in the brain before surgery in POCD patients compared with non-POCD (NPOCD) patients, thus, CBF variation may potentially predict the occurrence of early POCD.

Methods: Fifty patients scheduled for spinal stenosis surgery were enrolled in the study. All study participants completed a battery of neuropsychological tests (NPTs) by a well-trained neuropsychologist before the surgery and 1 week after the surgery. POCD was defined when the preoperative to postoperative difference of at least two of the NPTs’ |Z|-scores with reference to a control group exceeded 1.96. Pulsed arterial spin-labeling (ASL) MRI was scanned at least 1 day before surgery. The ASLtbx toolkit and SPM12 were applied to preprocess and correct the images, which were then normalized to the MNI brain template space to obtain standardized cerebral perfusion images.

Results: POCD was identified in 11 out of 50 patients (22%). The CBF of the right superior temporal lobe, right and left middle cingulate gyrus, and the right hippocampus, and parahippocampal gyrus in POCD group was lower than that in NPOCD group (P < 0.001). The CBF of the pars triangularis of inferior frontal gyrus in POCD group was higher than that in NPOCD group (P < 0.001).

Conclusions: These preliminary findings suggest that CBF premorbid alterations may happen in cognitively intact elderly patients that develop early POCD. Alterations of preoperative CBF might be a bio-marker for early POCD that can be detected by noninvasive MRI scans.

Brain hemodynamic changes in amnestic mild cognitive impairment measured by pulsed arterial spin labeling

We used pulsed arterial spin labeling (PASL) to investigate differences in cerebral blood flow (CBF) between 26 patients with amnestic mild cognitive impairment (aMCI) and 27 controls with normal cognition (NC). Hypoperfusion was observed in the right temporal pole of the middle temporal gyrus and the right inferior temporal gyrus in the aMCI compared with NC group. Interestingly, hyperperfusion was observed in the left temporal pole of the middle temporal gyrus, left superior temporal gyrus, bilateral precuneus, postcentral gyrus, right inferior parietal lobule, and right angular gyrus in the aMCI group, which likely resulted from a compensatory mechanism to maintain advanced neural activities. We found that mean CBF in the right inferior temporal gyrus, precuneus, and postcentral gyrus was positively correlated with cognitive ability in the aMCI but not NC group. Collectively, our data indicate that PASL is a useful noninvasive technique for monitoring changes in CBF and predicting cognitive decline in aMCI.

Application of a 3D pseudocontinuous arterial spin-labeled perfusion MRI scan combined with a postlabeling delay value in the diagnosis of neonatal hypoxic-ischemic encephalopathy

BACKGROUND

Currently, there are many studies on the application of the 3D pseudocontinuous arterial spin-labeled (3D-pcASL) perfusion MRI technique for adult brain examinations, but few studies exist on the application of the technique for child brain examinations.

PURPOSE

To explore the application of a 3D-pcASL perfusion MRI scan combined with postlabeling delay (PLD) for assessing neonatal hypoxic-ischemic encephalopathy (HIE).

MATERIALS AND METHODS

Two-hundred neonates diagnosed with neonatal HIE were equally divided into five groups (40/group): 0- to <24-hour-old HIE group, 1- to <3-day-old HIE group, 3- to <7-day-old HIE group, 7- to <15-day-old HIE group and 15- to 28-day-old HIE group; 200 healthy neonates were equivalently divided. All 10 groups received a conventional and a 3D-pcASL perfusion MRI scan. For groups <3 days old, PLD values for the 3D-pcASL cerebral perfusion MRI scan were preset at 1025 ms; in all other groups, PLD values were preset at 1525 ms. CBF values for the 3D-pcASL cerebral perfusion MRI were compared between the HIE and corresponding control groups to determine the distinguishing characteristics of CBF values in HIE neonates.

RESULTS

On the 3D-pcASL cerebral perfusion MRI scan, in the 1- to <3-day-old groups, HIE neonate CBF values were higher than those of controls in all brain regions (excluding the frontal lobe); in the 0- to <24-hour-old and 3- to <7-day-old groups, HIE neonate CBF values were lower than those of corresponding controls in all brain regions; in the 7- to <15-day-old and 15- to 28-day-old groups, there were no significant differences in the CBF values between groups in any brain regions.

CONCLUSIONS

The 3D-pcASL perfusion MRI scan combined with a PLD can assist in the early diagnosis of neonatal HIE, as this method more comprehensively reflects the HIE pathological process.

Functional MRI of brain physiology in aging and neurodegenerative diseases

Brain aging and associated neurodegeneration constitute a major societal challenge as well as one for the neuroimaging community. A full understanding of the physiological mechanisms underlying neurodegeneration still eludes medical researchers, fuelling the development of in vivo neuroimaging markers. Hence it is increasingly recognized that our understanding of neurodegenerative processes likely will depend upon the available information provided by imaging techniques. At the same time, the imaging techniques are often developed in response to the desire to observe certain physiological processes. In this context, functional MRI (fMRI), which has for decades provided information on neuronal activity, has evolved into a large family of techniques well suited for in vivo observations of brain physiology. Given the rapid technical advances in fMRI in recent years, this review aims to summarize the physiological basis of fMRI observations in healthy aging as well as in age-related neurodegeneration. This review focuses on in-vivo human brain imaging studies in this review and on disease features that can be imaged using fMRI methods. In addition to providing detailed literature summaries, this review also discusses future directions in the study of brain physiology using fMRI in the clinical setting.

Arterial spin labelling detects posterior cortical hypoperfusion in non-demented patients with Parkinson's disease

While previous studies suggested that perfusion abnormalities in Parkinson's disease (PD) are driven by dementia, our study aimed to identify perfusion underpinning of cognitive alteration in non-demented PD patients. Cerebral blood flow was measured using arterial spin labelling (ASL) in 28 PD patients (age 65 years ± 9.9 SD) and 16 age-matched healthy controls (HC) (age 65 years ± 7.8 SD), who also underwent neurological and cognitive testing. The 3D pseudocontinuous ASL and T2-weighted scans from 22 PD patients and 16 HC were analysed in a voxel-wise manner using SPM8 software. Associations between the ASL values in volumes of interest (VOIs) and behavioural and cognitive measures were assessed by Spearman correlation analysis. Posterior cortical hypoperfusion was found in PD patients compared to HC in the left supramarginal gyrus/superior temporal gyrus (VOI1) and left posterior cingulate/precuneus (VOI2). Positive correlation was revealed between perfusion in the VOI2 and Addenbrooke's Cognitive Examination Revised (ACE-R) scores after filtering out the effect of age, levodopa equivalent dose (LED), and total intracranial volume (TIV) (R = 0.51, p = 0.04). Conversely, negative correlation between VOI1 and ACE-R was detected (R = -0.62, p = 0.01) after regressing out the effects of motor impairment, age, LED, and TIV. In non-demented subjects with PD, blood flow abnormalities in precuneus/posterior cingulate were linked to the level of motor impairment and global cognitive performance. Oppositely, perfusion abnormalities in supramarginal gyrus might serve as a compensatory mechanism for brain degeneration and decreased cognitive performance.

Acute changes in liver tumour perfusion measured non-invasively with arterial spin labelling

BACKGROUND

Non-invasive measures of tumour vascular perfusion are desirable, in order to assess response to vascular targeting (or modifying) therapies. In this study, hepatic arterial spin labelling (ASL) magnetic resonance imaging (MRI) was investigated to measure acute changes in perfusion of colorectal cancer in the liver, in response to vascular disruption therapy with OXi4503.

METHODS

SW1222 and LS174T tumours were established in the liver of MF1 nu/nu mice via intrasplenic injection. Perfusion and R2(*) MRI measurements were acquired with an Agilent 9.4T horizontal bore scanner, before and at 90 min after 40 mg kg(-1) OXi4503.

RESULTS

A significant decrease in SW1222 tumour perfusion was observed (-43±33%, P<0.005). LS174T tumours had a significantly lower baseline level of perfusion. Intrinsic susceptibility MRI showed a significant increase in R2(*) in LS174T tumours (28±25%, P<0.05). An association was found between the change in tumour perfusion and the proximity to large vessels, with pre-treatment blood flow predictive of subsequent response. Histological evaluation confirmed the onset of necrosis and evidence of heterogeneous response between tumour deposits.

CONCLUSIONS

Hepatic ASL-MRI can detect acute response to targeted tumour vascular disruption entirely non-invasively. Hepatic ASL of liver tumours has potential for use in a clinical setting.

A neuroradiologist's guide to arterial spin labeling MRI in clinical practice

Arterial spin labeling (ASL) is a non-invasive MRI technique to measure cerebral blood flow (CBF). This review provides a practical guide and overview of the clinical applications of ASL of the brain, as well its potential pitfalls. The technical and physiological background is also addressed. At present, main areas of interest are cerebrovascular disease, dementia and neuro-oncology. In cerebrovascular disease, ASL is of particular interest owing to its quantitative nature and its capability to determine cerebral arterial territories. In acute stroke, the source of the collateral blood supply in the penumbra may be visualised. In chronic cerebrovascular disease, the extent and severity of compromised cerebral perfusion can be visualised, which may be used to guide therapeutic or preventative intervention. ASL has potential for the detection and follow-up of arteriovenous malformations. In the workup of dementia patients, ASL is proposed as a diagnostic alternative to PET. It can easily be added to the routinely performed structural MRI examination. In patients with established Alzheimer’s disease and frontotemporal dementia, hypoperfusion patterns are seen that are similar to hypometabolism patterns seen with PET. Studies on ASL in brain tumour imaging indicate a high correlation between areas of increased CBF as measured with ASL and increased cerebral blood volume as measured with dynamic susceptibility contrast-enhanced perfusion imaging. Major advantages of ASL for brain tumour imaging are the fact that CBF measurements are not influenced by breakdown of the blood–brain barrier, as well as its quantitative nature, facilitating multicentre and longitudinal studies.