Scientists combine Bessel beam two-photon microscopy with high throughput analysis for faster and more precise measurements of blood flow

The brain is perhaps the most sensitive organ with respect to changes in blood flow and oxygen supply. Even brief interruptions in capillary flow (or "stalling") can indicate acute neurological issues; evidence suggests that chronic conditions like Alzheimer’s and Parkinson’s diseases are closely related to stalling events. Thus, investigating the effects of stalling could lead to the development of therapies for such disorders.  

However, despite tremendous advances in medical imaging over the past few decades, identification of stalling in capillaries remains a formidable challenge. Optical coherence tomography (OCT) is currently the best available method to monitor capillaries within a small volume. But this approach suffers from poor temporal resolution, meaning that it can only capture long stalling events. Also, analyzing data gathered via OCT to determine stalling events requires extensive manual work.

In a recent study published in the SPIE journal Neurophotonics, a research team led by Dr. John Giblin from Boston University, United States, sought to address these issues. Using a custom setup, the researchers showcased the potential of a technique called Bessel beam two-photon microscopy to obtain volumetric images of brain capillaries. In addition, the team proposed an innovative analysis approach to semi-automate the identification of stalling events.

Compared to OCT, the proposed approach using Bessel beam two-photon microscopy could generate images much faster, providing better temporal resolution. However, the larger amount of data produced by this setup only exacerbated the problem of data analysis. Thus, the team came up with a method to make the identification of stalling events easier.

The proposed analysis procedure relies on the fact that the intensity along a stalled capillary in a two-photon image would remain relatively unchanged. The researchers implemented an algorithm to calculate the between-frame intensity correlation for individual capillaries; high correlation implies that the capillary has stalled. By visualizing the calculated correlation instead of the raw intensity image, the researchers found it much easier and quicker to identify stalling events.

Taken together, the findings of this study demonstrate the power of Bessel beam two-photon microscopy to explore the intricate workings of the brain's circulatory system and its implications for neurological health.
Neurophotonics Associate Editor Ji Yi, a professor of ophthalmology and biomedical engineering at the Johns Hopkins University

In the near future, fully automated methods to detect stalling will hopefully help scientists investigate, diagnose, and assess the treatment of brain diseases.


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