Herein, we review mechanisms regulating cerebral blood flow (CBF), with specific focus on humans We revisit important concepts from the older literature and describe the interaction of various mechanisms of cerebrovascular control We amalgamate this broad scope of information into a brief review, rather than detailing any one mechanism or area of research The relationship between regulatory mechanisms is emphasized, but the following three broad categories of control are explicated: (1) the effect of blood gases and neuronal metabolism on CBF; (2) buffering of CBF with changes in blood pressure, termed cerebral autoregulation; and (3) the role of the autonomic nervous system in CBF regulation With respect to these control mechanisms, we provide evidence against several canonized paradigms of CBF control Specifically, we corroborate the following four key theses: (1) that cerebral autoregulation does not maintain constant perfusion through a mean arterial pressure range of 60–150 mmHg; (2) that there is important stimulatory synergism and regulatory interdependence of arterial blood gases and blood pressure on CBF regulation; (3) that cerebral autoregulation and cerebrovascular sensitivity to changes in arterial blood gases are not modulated solely at the pial arterioles; and (4) that neurogenic control of the cerebral vasculature is an important player in autoregulatory function and, crucially, acts to buffer surges in perfusion pressure Finally, we summarize the state of our knowledge with respect to these areas, outline important gaps in the literature and suggest avenues for future research

https://physoc.onlinelibrary.wiley.com/doi/epdf/10.1113/jphysiol.2013.268953

Integrative regulation of human brain blood flow

Clinical applications of 7 T MRI in the brain.

Over 20?000 MR systems are currently installed worldwide and, although the majority operate at magnetic fields of 1.5?T and below (i.e. about 70%), experience with 3-T (in high-field clinical diagnostic imaging and research) and 7-T (research only) human MR scanners points to a future in functional and metabolic MR diagnostics. Complementary to previous studies, this review attempts to provide an overview of ultrahigh-field MR research with special emphasis on emerging clinical applications at 7?T. We provide a short summary of the technical development and the current status of installed MR systems. The advantages and challenges of ultrahigh-field MRI and MRS are discussed with special emphasis on radiofrequency inhomogeneity, relaxation times, signal-to-noise improvements, susceptibility effects, chemical shifts, specific absorption rate and other safety issues. In terms of applications, we focus on the topics most likely to gain significantly from 7-T MR, i.e. brain imaging and spectroscopy and musculoskeletal imaging, but also body imaging, which is particularly challenging. Examples are given to demonstrate the advantages of susceptibility-weighted imaging, time-of-flight MR angiography, high-resolution functional MRI, 1H and 31P MRSI in the human brain, sodium and functional imaging of cartilage and the first results (and artefacts) using an eight-channel body array, suggesting future areas of research that should be intensified in order to fully explore the potential of 7-T MR systems for use in clinical diagnosis. Copyright (C) 2011 John Wiley & Sons, Ltd. (Less)

/pdf/7-t-mr-from-research-to-clinical-applications-3tstzcbwkt.pdf

7-T MR—from research to clinical applications?

Summary Cerebral blood flow (CBF) is regulated by vasomotor, chemical, metabolic, and neurogenic mechanisms. Even though the innervation of cerebral arteries is quite extensively described and reviewed in the literature, its role in regulation of CBF in humans remains controversial. We believe that insufficient attention has so far been focused on the potential role of the innervation of the cerebral vasculature in cerebral autoregulation in humans. We have performed an extensive search and selection of available literature on electrical, chemical, and surgical manipulations of the sympathetic innervation of cerebral arteries, and the effects of circulation sympathetically active agents on CBF. Studies on (surgical) ganglion block show a role of sympathetic tone in preventing increases in CBF in humans, which are consistent with the view based on animal studies. Both direct innervation of the cerebral arteries from cervical ganglia and stimulation of adrenergic receptors by circulating sympathomimetics prevent sudden increases of CBF associated with hypertension and hypercapnia. We postulate that under normal physiological conditions neurogenic control has little influence on cerebral autoregulation as other methods of control (vasomotor, chemical, and metabolic) are dominant. In severely challenging circumstances, such as delayed cerebral ischaemia after subarachnoid haemorrhage, these methods might be overwhelmed, increasing the relative importance of neurogenic, sympathetic control of CBF. This insight might lead to future therapeutic possibilities.

Sympathetic regulation of cerebral blood flow in humans: a review

With more than 40 installed MR systems worldwide operating at 7 Tesla or higher, ultra-high-field (UHF) imaging has been established as a platform for clinically oriented research in recent years. Along with technical developments that, in part, have also been successfully transferred to lower field strengths, MR imaging and spectroscopy at UHF have demonstrated capabilities and potentials for clinical diagnostics in a variety of studies. In terms of applications, this overview article focuses on already achieved advantages for in vivo imaging, i.e., in imaging the brain and joints of the musculoskeletal system, but also considers developments in body imaging, which is particularly challenging. Furthermore, new applications for clinical diagnostics such as X-nuclei imaging and spectroscopy, which only really become feasible at ultra-high magnetic fields, will be presented.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/jmri.24573

MRI at 7 tesla and above: Demonstrated and potential capabilities

The purpose of this study was to analyze human lenticulostriate arteries (LSAs) obtained non-invasively by 7.0-T MRI. A three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA) technique was used with an investigational 7.0-T MRI scanner with a radio-frequency coil that was optimized and designed for angiographic purposes. We obtained images from 16 healthy volunteers (8 males and 8 females, mean age 21 +/- 2.7 years). For direct comparison of LSA images with digital subtraction angiography (DSA), we also obtained 7.0-T MRA and DSA images from one patient, a 27-year-old woman with a posterior fossa arteriovenous malformation (AVM). We then analyzed the characteristics of LSAs using a custom data analysis method with MatLab for quantitative analysis. Analysis of LSA images included shape and number of branches and origins, findings that are essential and useful for quantification of LSA abnormalities in both healthy controls and patients. Ultra-high-field MRA provided clear anatomic delineation of the LSAs, thereby suggesting that 7.0-T MRA may be a promising technique for microvascular imaging of the LSAs.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/mrm.21786

Imaging and analysis of lenticulostriate arteries using 7.0-Tesla magnetic resonance angiography.

The objective of this study is to investigate the neural activities in the human brain after stellate ganglion block (SGB) treatment using functional magnetic resonance imaging (fMRI). Thirteen healthy female volunteers from the local community participated in the study. An echo planar imaging sequence for fMRI has used to examine the effect on the cerebral cortex before and after SGB stimulation at 1.5T MRI. We used 6 mL of 1 % mepivacaine hydrochloride as a local anesthetic. Two control groups with and without a saline injection were also included. FMRI data were processed using statistical parametric mapping. The blood-oxygen-level-dependent fMRI signal intensities increased in contralateral anterior cingulate cortex, hypothalamus, ventral putamen, and parahippocampal gyrus after SGB stimulation, while the signal intensities had decreased in contralateral thalamus and dorsal putamen, and ipsilateral caudate nucleus. In the saline control group, the signal intensities in ipsilateral posterior putamen and superior temporal gyrus and both insular cortices have increased significantly. The present study could show the changes by SGB in the several important brain areas associated with sympathetic nervous system. The non-invasive and repeatable imaging technique of fMRI could provide some useful information for better understanding of the neural mechanisms involved in SGB treatments.

Effect of Stellate Ganglion Block on the Cerebral Cortex: A Functional Magnetic Resonance Imaging Study

Background: Several studies have shown that stellate ganglion block (SGB) is an effective treatment for certain cerebrovascular related diseases; however, the direct effect of SGB on the cerebral vasculature is still unknown. The present study investigated the effect of SGB on the cerebral vascular system using magnetic resonance angiography. Methods: Time-of-flight magnetic resonance angiography images of 19 healthy female volunteers (mean ages of 46.4 8.9yr)wereobtainedbeforeandafterSGBwith1.5-Tmagnetic resonance imaging. The authors determined successful interruptionofsympatheticinnervationtotheheadwiththeappearance of Horner syndrome and conjunctival injection. We measuredchangesintheaveragesignalintensityanddiameterofthe major intracranial and extracranial arteries and their branches, which were presented with mean (SE). Results: The signal intensity changes were observed mainly in the ipsilateral extracranial vessels; the external carotid artery (11.2%, P 0.001) and its downstream branches, such as the occipital artery (9.5%, P 0.001) and superficial temporal artery (14.1%, P 0.001). In contrast, the intensities of the intracranial arteries did not change with the exception of the ipsilateral ophthalmic artery, which increased significantly (10.0%, P 0.008). After SGB, only the diameter of the ipsilateral external carotid artery was significantly increased (26.5%, P 0.001). Conclusions: We were able to observe significant changes in the extracranial vessels, whereas the intracranial vessels were relatively unaffected (except for the ophthalmic artery), demonstrating that both perivascular nerve control and sympathetic nerve control mechanisms may contribute to the control of intracranialandextracranialbloodvessels,respectively,afterSGB.

/pdf/effect-of-stellate-ganglion-block-on-the-cerebrovascular-3jck9opi3z.pdf

Effect of stellate ganglion block on the cerebrovascular system: magnetic resonance angiography study.

Purpose:

To visualize the perforating arteries originating from basilar artery (BA) by using ultra-high resolution 7T MR angiography (MRA) and optimizing MR parameters as well as radio frequency (RF) coils, which may provide important information for neurosurgery and understanding diseases of the pons, but was unable to clearly visualize with conventional MRA techniques.



Materials and Methods:

Seven healthy volunteers (five males and two females, age [mean ± SD] = 28.71 ± 7.54 years) were scanned using optimized MR parameters to obtain images of pontine arteries (PAs) originating from the main trunk of BA. Two different volume coils and a phased array coil were designed and compared for this study. The images obtained at 7T MRA were compared with those at 1.5T and 3T MRA.



Results:

The results showed that PA imaging at 7T MRI consistently provided clearly identifiable vessels, which were difficult to visualize in MR angiograms obtained at 1.5T and 3T MRIs. Volume RF coils had higher sensitivity for the center of the brain, which enhanced PA imaging compared to phased array coil. The average number of PA branches in all seven subjects observable by 7T MRA was 7.14 ± 2.79, and the visualized PA branches were found to mainly propagating on the surface of the pons.



Conclusion:

We have demonstrated that ultra-high resolution 7T MRA could delineate the PAs using optimized imaging parameters and volume RF coils compared to commercially available 1.5T and 3T MRIs. J. Magn. Reson. Imaging 2010;32:544–550. © 2010 Wiley-Liss, Inc.

Non-invasive visualization of basilar artery perforators with 7T MR angiography.

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Papers

Imaging and analysis of lenticulostriate arteries using 7.0-Tesla magnetic resonance angiography.

Effect of Stellate Ganglion Block on the Cerebral Cortex: A Functional Magnetic Resonance Imaging Study

Effect of stellate ganglion block on the cerebrovascular system: magnetic resonance angiography study.

Non-invasive visualization of basilar artery perforators with 7T MR angiography.