Synopsis
Studies have found collateral circulation was correlated with progression of stroke and clinical outcome. Many advanced imaging
approaches appeared regarding the intracranial collaterals, including DSA, CT and MR. Specifically, the newly developed MR sequences,
including multiphase contrast enhanced MR angiography, ASL and vessel-encoded
ASL etc. have been used in the visualization of collaterals. Additionally, some conventional MR sequences have also been found useful. Learning what MR can do in the field of collaterals is of paramount
importance. Application of MR techniques in intracranial
collaterals may help elucidate pathophysiological characteristics of
collaterals and enhance the therapeutic and prognostic performance in stroke
patients.
TARGET AUDIENCE
This talk will be beneficial to radiologists who
are interested in intracranial collaterals and advanced imaging of it, as well
as neurosurgeons and ER physicians.
OUTCOME/OBJECTIVES
By discussing the advanced MR imaging of
intracranial collaterals, this talk will help radiologists and clinicians to
optimize the evaluation of stroke patients, and add evidence to the planning of
individualized treatment.PURPOSE
In the past several years, many advanced imaging
approaches appeared regarding the intracranial collaterals [1]. Studies have found collateral circulation was correlated with
progression of stroke and clinical outcome [2]. Learning what MR can do in the field of collaterals is of paramount
importance.METHODS
In this talk, we
discussed MR imaging in the intracranial collaterals mainly from two aspects:
clinical importance of collaterals and existing methods to image collaterals. In
the former part, we listed several clinical trials concerning the clinical
significance of intracranial collaterals and the impact of collaterals in
stroke. In the latter part, we discussed several approaches to image
collaterals, with focus on what MR can do in this field. Specifically, we
discussed newly developed MR sequences, including multiphase contrast enhanced
MR angiography, ASL and vessel-encoded ASL etc. In addition, some conventional
sequences were found useful in visualization of collaterals. Finally, molecular
imaging was discussed as a novel approach to better understand the intracranial
collaterals.RESULTS
Analogy to CTA, multiphase contrast enhanced MR
angiography provide temporal resolution to detect collateral flow filling
pathway and velocity [3].
It can be assessed with grading scale similar to that of DSA collateral grades.
Arterial spin labeling (ASL) plays an important role in collateral perfusion
evaluation, recently [4].
Delayed retrograde flow can be visualized by multi-delay ASL and quantitatively
measured attributing to the development of 3D pseudo-continuous ASL. Arterial
transit artifacts is a feasible imaging markers of favorable collaterals which
can be seen in single delay ASL [5]. Vessel-encoded ASL provides valuable information of
collateral origination. Besides, a number of imaging markers can be easily
identified on conventional sequences including fluid attenuated inversion
recovery, post-contrast T1WI and susceptibility imaging [6]. Molecular MR imaging is a novel approach to
visualize collateral vessels directly by newly developed nanoparticles for
recruited collateral vessels [7].DISCUSSION
Intracranial collaterals are critical to reserve blood
flow for brain ischemia. Capacity of collaterals determines penumbra in acute
stroke and hemodynamic status in chronic settings. Intracranial collaterals
have served as triage for patients’ selection in recent clinical trials. Due to
the diminutive anatomic routes especially for secondary collateral and
angiogenesis, imaging is pivotal for understanding the pathophysiology of
collaterals. MRI techniques can display collaterals from imaging of collateral
vessels as well as from hemodynamic and metabolic mechanisms. Each imaging
modality characterized unique advantages and has disadvantages. Understanding
application of conventional and advanced neuroimaging in intracranial
collaterals will support exploring determinants of collateral blood flow and
the potential therapeutic targets in cerebrovascular disease.CONCLUSION
Application of MR techniques in intracranial
collaterals may help elucidate pathophysiological characteristics of
collaterals and enhance the therapeutic and prognostic performance in stroke
patients.Acknowledgements
None.References
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