Intracranial Collaterals: The Role of MRI
Xin Lou1

1Chinese PLA General Hospital, China

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

1. Heit, J.J., G. Zaharchuk and M. Wintermark, Advanced Neuroimaging of Acute Ischemic Stroke: Penumbra and Collateral Assessment. Neuroimaging Clin N Am, 2018. 28(4): p. 585-597.

2. Kao, Y.J., E.A. Oyarzabal, H. Zhang, et al., Role of Genetic Variation in Collateral Circulation in the Evolution of Acute Stroke: A Multimodal Magnetic Resonance Imaging Study. Stroke, 2017. 48(3): p. 754-761.

3. Hernandez-Perez, M., J. Puig, G. Blasco, et al., Dynamic Magnetic Resonance Angiography Provides Collateral Circulation and Hemodynamic Information in Acute Ischemic Stroke. Stroke, 2016. 47(2): p. 531-4.

4. Lyu, J., N. Ma, D.S. Liebeskind, et al., Arterial Spin Labeling Magnetic Resonance Imaging Estimation of Antegrade and Collateral Flow in Unilateral Middle Cerebral Artery Stenosis. Stroke, 2016. 47(2): p. 428-33.

5. Zaharchuk, G., H.M. Do, M.P. Marks, et al., Arterial spin-labeling MRI can identify the presence and intensity of collateral perfusion in patients with moyamoya disease. Stroke, 2011. 42(9): p. 2485-91.

6. Lee, K.Y., S.H. Suh and S.J. Ahn, Significance of hyperintense arteries on Gd-enhanced 3D T1W black-blood imaging in acute stroke. Eur Radiol, 2019. 29(3): p. 1329-1337.

7. Wang, T., Y. Hou, B. Bu, et al., Timely Visualization of the Collaterals Formed during Acute Ischemic Stroke with Fe3 O4 Nanoparticle-based MR Imaging Probe. Small, 2018. 14(23): p. e1800573.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)