A new way to monitor blood flow to the brain

Monitoring the proper blood supply to the brain is essential, not only to prevent neurological diseases, but also to treat them
.
Parallel near-infrared interferometric spectroscopy, or πNIRS for short, can make life easier for doctors and patients around the world
.

Blood drives our entire body and is especially important
for brain function.
On average, about 50 ml/min/100 g flows through brain tissue – about 80-90 ml/min/100 g flows through gray matter and 20-30 ml/min/100 g flows through white matter
.
When there is a lack of oxygen, therefore, a lack of proper blood supply, nerve cell death occurs - then we say stroke
.
About 70,000 people in Poland are infected with the disease
every year.

This is why monitoring cerebral blood flow is crucial
in disease prevention and treatment.
Neurology knows many effective methods, but many of them have their weaknesses
.
Now, a team of neuroscientists led by ICTER researchers has developed a technique that can significantly improve the monitoring
of cerebral blood flow in the body.

How is cerebral blood flow monitored?

Cerebral blood flow (CBF) uses about 15% of cardiac output to transport essential substances (oxygen and glucose) to the brain and take away unnecessary substances (products of metabolism).

Any deviation from normal behavior can lead to temporary brain dysfunction and trigger irreversible diseases, with Alzheimer's disease being the most prominent
.
That's why non-invasive monitoring of CBF is so important – we have several practical tools to do just that
.

The first thing that comes to mind is functional magnetic resonance imaging (fMRI), which is probably the most widely used diagnostic test in the world and is also effective
here.
It can monitor local changes in cerebral blood supply and related fluctuations
in neuronal activity in the body.
For example, this technology can provide high-resolution images, but it is quite expensive and difficult to use in young children
.
This is where
the optical approach comes in handy.

Cerebral oxygenation can be evaluated
using functional near-infrared spectroscopy (fNIRS).
This technique enables non-invasive measurement
of regional brain oxygenation through the selective absorption of electromagnetic radiation in the range of 660-940 nm by human chromophores.
It is often used as a tool to help monitor a patient's condition, including during
neurosurgery.

On the other hand, diffusion correlation spectroscopy (DCS) enables continuous monitoring
of blood flow.
Their state-of-the-art improvements are based on continuous wave (CW) lasers, which prevent absolute measurements
.
Interferometric near-infrared spectroscopy (iNIRS) can help in this regard
.
Still, previous studies have shown that this method is too slow to detect immediate changes in blood flow that translate into neuronal activity
.
This is because it is a single-channel system that only measures the intensity
of single-mode light collected from the sample.

Innovation πNIRS

A team of researchers at ICTER decided to modify iNIRS to rely on parallel near-infrared interferometric spectroscopy (πNIRS) for multichannel cerebral blood flow detection
.
To achieve this, it is necessary to change the iNIRS detection system
.
In π NIR, the acquired light signal is recorded by a 2D CMOS camera at an ultra-fast frame rate (~1 MHz
).
Each pixel in the recorded image sequence effectively becomes a separate detection channel
.
Using this method, it is possible to obtain data similar to iNIRS, but much faster - even orders of magnitude!

This improvement, in turn, translates into higher sensitivity of the system and the accuracy of the
detection itself.
It is possible to detect rapid changes in blood flow associated with neuronal activation, for example, in response
to external stimuli or drugs.
The solution may help diagnose CBF-related neuronal diseases and assess the effectiveness of treatments such as neurodegenerative diseases
.

• The project will improve a rapid, non-invasive human brain-blood monitoring system
  .
  Continuous, non-invasive blood flow monitoring can help treat serious brain disorders
  .
  In addition, rapid tests of cerebral blood flow will bring us closer to developing a non-invasive brain-computer interface (BCI)
  that can help people with disabilities.
  Finally, our project will strengthen Poland's tradition of development in diffusion optics, said ICTER's Dawid Borycki
  .
  

Trials have confirmed that this technique can effectively monitor the activity of the prefrontal cortex in the
body.
In addition, due to the development of lidar technology and ultra-fast volumetric imaging of the eye, further improvements can be made, reducing the cost of
CMOS cameras.
Thus, πNIRS technology can monitor changes in cerebral blood flow and absorption from multiple spatial locations
.

Data obtained π near-infrared spectroscopy can be applied to the diagnosis of cerebral circulation disorders, help assess the patient's condition, and predict early and long-term treatment outcomes
.