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Application of Laser Speckle Imaging to Ischemic Stroke Research

   |  July 12, 2022

Currently, the ischemia models employed in most research are imperfect in causing a sustained reduction in blood flow. In some cases, it is possible that spontaneous reperfusion may occur right after occlusion, leading to infarct size variability.[1] As a result, it is important to monitor cerebral blood flow using Laser Speckle Imaging (LSCI) in ischemic stroke models to document adequate sustained occlusion and to monitor reperfusion, providing more insight into the development of stroke treatment.

Introduction to Ischemic Stroke Research

Stroke is a prevalent deadly medical condition in most countries, with ischemic stroke being the most common type. In the past 20 years, considerable progress has been made in ischemic stroke studies, but large gaps of knowledge about ischemic stroke treatment remain. By using the Laser Speckle Imaging (LSCI) technology, preclinical studies are done to advance the development of ischemic stroke treatment.

Mechanism of Laser Speckle Imaging (LSCI)

The fundamental concept of LSCI is to generate the interference patterns of reflected or scattered light from an illuminating surface, then in return produces a granular effect, also known as the laser speckle. The movement of speckle pattern corresponds to the movement of an object that is associated with the idea of speckle fluctuation triggered by blood flow velocity.[2]

In this case, if blood flow is restricted, the real-time image will show highly enhanced speckle contrast. On the contrary, the speckle pattern will appear to be more gradual and blurred out due to high blood flow.

Using Laser Speckle Imaging in Ischemic Stroke Research

As the most important indicator of ischemic stroke is the decrease in cerebral blood flow (CBF), LSCI is adopted to monitor the spatio-temporal CBF changes after the onset of stroke in the temporary ischemia models. Besides, it delivers real time high spatio-temporal resolution information before, during, and immediately after the ischemia surgery. This feature is conducive to the competitiveness of the research paper because it greatly reduces the experiment duration, and at the same time provides more meaningful data to enhance the validity of the experiment.

Most Laser Speckle Imaging stroke pre-clinical studies focus on ischemia as focal ischemic stroke in animals is typically induced by occlusion of the middle cerebral artery. Different models of middle cerebral artery occlusion (MCAO) require different surgical methods. For example, the common ones are the suture and embolic methods. The intraluminal suture MCAO model is one of the most widely utilized experimental focal cerebral ischemia models to induce vascular endothelial injury which mimics a clinical ischemic stroke.[3]

The high-quality quantized data provided by LSCI maintains the quality and increases the success rate of the MCAO models. The model is proved to be successful only if the measured CBF changes are over 70 %. Apart from testing the models, LSCI conducts ongoing examinations on post-surgical conditions to assess the recovery rate and improvements in perfusion.

The LSCI-guided MCAO model setup, which can be modified according to immediate feedback and correction offered by the LSCI technology, can be completed in about a month from the beginner to have the skill. Without the assistance of LSCI, it may take 4 months to 6 months to complete the set-up.

Successful Case

It has always been challenging for researchers to achieve a successful animal model of stroke, for example, to create a stable infarct volume in the MCAO model due to the variances in animal weight, brain vascular anatomy, suture material, filament insertion depth, and surgical operations.

So far, laser doppler flowmetry (LDF) has been the most widely-used intraoperative method to check the cerebral blood flow (CBF) drop immediately after the surgery. However, due to the high sensitivity to motion and the absence of spatial resolution, LDF in most cases can only be used for postsurgical confirmation.
LSCI offers cerebral blood flow (CBF) markers to guide suture insertion during the surgery that allow researchers to adjust the filament insertion depth accordingly to improve the consistency of infarct volume and reduce mortality. There are many successful cases which rely on the guidance of LSCI to improve the stability of the model.

Westlake Laboratory of Life Sciences and Biomedicine

This client aimed at assessing perinatal arterial embolic stroke induced by occluding the dMCA using SIMPLeR(embolic stroke induced by magnetic nanoparticle-coated red blood cells).[4]

However, technical challenges still remained for precise embolism control in the mechanistic studies of brain damage and repair after perinatal arterial ischemic stroke (PAIS). LSCI provided a measure of blood flow velocity by quantifying the extent of blurring of dynamic speckles caused by the motion of red blood cells through the vessels.

Application of LSCI to Ischemic Stroke Model Research
Application of Laser Speckle Imaging to Ischemic Stroke Research

As vindicated by our client, “the traditional pathological sectioning methods and neurological assessment tools are unable to accommodate the needs of the MCAO models. This is because there are disparities between different types of infarcts even though their clinical symptoms are similar. Compared to other imaging technologies, LSCI greatly enhances the success rate of the experiment and collects a wide field of CBF data in the whole brain. ”

[1] Kuriakose D, Xiao Z. Pathophysiology and Treatment of Stroke: Present Status and Future Perspectives. Int J Mol Sci. 2020 Oct 15;21(20):7609. doi: 10.3390/ijms21207609. PMID: 33076218; PMCID: PMC7589849.

[2] B. David,‘Laser Doppler, speckle and related techniques for blood perfusion mapping, Physiological Measurement (2001).

[3] L. Yuan, and L. Hongyang, and L. Hangdao, T. Shanbao,‘Photothrombotic Ischemia: A Minimally Invasive and Reproducible Photochemical Cortical Lesion Model for Mouse Stroke Studies’, J Vis Exp (2013)

[4] Precise control of embolic stroke with magnetized red blood cells in mice,Communications Biology volume 5, Article number: 136 (2022), https://www.nature.com/articles/s42003-022-03082-9

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