Implication of cerebral circulation time in intracranial stenosis measured by digital subtraction angiography on cerebral blood flow estimation measured by arterial spin labeling

Intervention for symptomatic vertebrobasilar disease

Disease of the vertebral (VA) and basilar arteries (BA) can lead to stroke of the posterior circulation and may warrant management strategies which differ from the anterior circulation. The mechanism and location of the disease determine its natural history and therefore affect the relative risks and benefits of the possible treatment options. Vertebrobasilar (VB) atherosclerotic disease is a source of both hemodynamic and embolic posterior circulation stroke. Advances in medical therapy have decreased the rate of stroke after initial symptomatic presentation. Antiplatelet therapy, blood pressure control, and optimization of secondary risk factors can reduce recurrent stroke risk in both intracranial and extracranial VB disease. However, symptomatic intracranial disease is still associated with a high risk of subsequent stroke, particularly those with hemodynamic compromise who represent a higher risk population. Patients with hemodynamic impairment may benefit from judicious application of endovascular and microsurgical interventions to augment blood flow. Stenting, angioplasty alone, bypass surgery, and endarterectomy, represent endovascular and surgical tools available to address medically refractory VB disease. Apart from atherosclerotic disease, dissection is another etiology of VB stroke, most frequently affecting the extracranial VA. Treatment is predominantly antithrombotic therapy although surgical or endovascular intervention can be required in rare cases of persistent embolism or hemodynamic compromise. In contrast, extrinsic compromise of the VA represents a separate extracranial pathology and is best treated with mechanistically targeted surgeries or extracranial bypass.

Video-based education improves the image quality of diagnostic percutaneous cerebral angiography among elderly patients

Objective

Digital subtraction angiography (DSA) is considered the gold standard for cerebral vasculature observation and is increasingly applied among the elderly population. The aim of this study is to determine whether the use of a video-based education system can improve the image quality of percutaneous cerebral angiography.

Method

This study is a single-blinded prospective cohort trial. One hundred and sixty patients (≥65 years old) were enrolled in this study. Eighty patients were provided with video-based education as intervention. Eighty age-matched controls only received regular education. The DSA image quality was assessed between control and intervention groups. It was rated by two readers on a 5-point scale, independently.

Results

No differences were found between control and intervention groups in baseline characteristics (P > 0.05). The mean overall image quality was significantly higher in patients receiving video-based education than in controls (P < 0.05), and the same trends were found in the respective assessment of each artery (left and right carotid/vertebral artery; P < 0.05). Moreover, the operation time and radiation doses were quite comparable between the two groups (P > 0.05).

Conclusions

This study indicated that video-based education helps elderly patients to acquire improved DSA image quality. It encourages the application of this approach in practice.

Quantification of cerebral perfusion and cerebrovascular reserve using Turbo-QUASAR arterial spin labeling MRI

Purpose

To compare cerebral blood flow (CBF) and cerebrovascular reserve (CVR) quantification from Turbo‐QUASAR (quantitative signal targeting with alternating radiofrequency labeling of arterial regions) arterial spin labeling (ASL) and single post‐labeling delay pseudo‐continuous ASL (PCASL).

Methods

A model‐based method was developed to quantify CBF and arterial transit time (ATT) from Turbo‐QUASAR, including a correction for magnetization transfer effects caused by the repeated labeling pulses. Simulations were performed to assess the accuracy of the model‐based method. Data from an in vivo experiment conducted on a healthy cohort were retrospectively analyzed to compare the CBF and CVR (induced by acetazolamide) measurement from Turbo‐QUASAR and PCASL on the basis of global and regional differences. The quality of the two ASL data sets was examined using the coefficient of variation (CoV).

Results

The model‐based method for Turbo‐QUASAR was accurate for CBF estimation (relative error was 8% for signal‐to‐noise ratio = 5) in simulations if the bolus duration was known. In the in vivo experiment, the mean global CVR estimated by Turbo‐QUASAR and PCASL was between 63% and 64% and not significantly different. Although global CBF values of the two ASL techniques were not significantly different, regional CBF differences were found in deep gray matter in both pre‐ and postacetazolamide conditions. The CoV of Turbo‐QUASAR data was significantly higher than PCASL.

Conclusion

Both ASL techniques were effective for quantifying CBF and CVR, despite the regional differences observed. Although CBF estimated from Turbo‐QUASAR demonstrated a higher variability than PCASL, Turbo‐QUASAR offers the advantage of being able to measure and control for variation in ATT.

Low Frequency Systemic Hemodynamic "Noise" in Resting State BOLD fMRI: Characteristics, Causes, Implications, Mitigation Strategies, and Applications

Advances in functional magnetic resonance imaging (fMRI) acquisition have improved signal to noise to the point where the physiology of the subject is the dominant noise source in resting state fMRI data (rsfMRI). Among these systemic, non-neuronal physiological signals, respiration and to some degree cardiac fluctuations can be removed through modeling, or in the case of newer, faster acquisitions such as simultaneous multislice acquisition, simple spectral filtering. However, significant low frequency physiological oscillation (∼0.01-0.15 Hz) remains in the signal. This is problematic, as it is the precise frequency band occupied by the neuronally modulated hemodynamic responses used to study brain connectivity, precluding its removal by spectral filtering. The source of this signal, and its method of production and propagation in the body, have not been conclusively determined. Here, we summarize the defining characteristics of the systemic low frequency noise signal, and review some current theories about the signal source and the evidence supporting them. The strength and distribution of the systemic LFO signal make characterizing and removing it essential for accurate quantification, especially for resting state connectivity, when no stimulation can be compared with the signal. Widespread correlated non-neuronal signals obscure and distort the more localized patterns of neuronal correlations between interacting brain regions; they may even cause apparent connectivity between regions with no neuronal interaction. Here, we discuss a simple method we have developed to parse the global, moving, blood-borne signal from the stationary, neuronal connectivity signals, substantially reducing the negative correlations that result from global signal regression. Finally, we will discuss some of the uses to which the moving systemic low frequency oscillation can be put if we consider it a "signal" carrying information, rather than simply "noise" complicating the interpretation of resting state connectivity. Properly utilizing this signal may offer insights into subtle hemodynamic alterations that can be used as early indicators of circulatory dysfunction in a number of neuropsychiatric conditions, such as prodromal stroke, moyamoya, and Alzheimer's disease.

Cerebral Perfusion Insufficiency and Relationships with Cognitive Deficits in Alzheimer's Disease: A Multiparametric Neuroimaging Study

Micro- or macro-circulatory insufficiency has a negative impact in patients with Alzheimer’s disease (AD). This study used arterial spin-labeled magnetic resonance imaging (ASL-MRI) and ethylcysteinate dimer single-photon emission computed tomography (ECD-SPECT) in 50 patients with AD and 30 age-matched controls to investigate how hypoperfusion patterns were associated with gray matter atrophy and clinical data. All participants completed 3DT1-MRI, ECD-SPECT and ASL-MRI examinations. Medial temporal cortex (MTC) volumes were correlated with regional signals showing significantly lower relative cerebral blood flow (rCBF) in ASL-MRI or perfusion index (PI) in ECD-SPECT. Neurobehavioral scores served as the outcome measures. Regions with lower PI showed spatial similarities with atrophy in the medial, anterior and superior temporal lobes, posterior cingulate cortex and angular gyrus, while regions showing lower rCBF were localized to the distal branches of posterior cerebral artery territories (posterior parietal and inferior temporal lobe) and watershed areas (angular gyrus, precuneus, posterior cingulate gyrus and middle frontal cortex). rCBF values in watershed areas correlated with MTC volumes and language composite scores. Precuneus and angular gyrus hypoperfusion were associated with the corresponding cortical atrophy. Macro- or micro-vasculature perfusion integrities and cortical atrophy determined the overall perfusion imaging topography and contributed differently to the clinical outcomes.