fUS

Functional Ultrasound Imaging (fUS)

Scan applications

fMRI was very dominant due to its noninvasive nature and high spatial resolution. A later creation, Functional Ultrasound imaging (fUS), uses high-frequency ultrasound waves to detect microvascular dynamics with high sensitivity.

This works via High-frequency sound waves, that are transmitted as ‘plane waves’ into the tissue. These waves interact with moving red blood cells, causing a frequency shift (Doppler effect) that is detected by the transducer. The strength of the reflected waves is transmitted back as an echo from a 2D plane, proportional to the amount of red blood cells in that region (this also tells us the local cerebral blood volume, CBV).

In research, it is used to map brain activity at fine spatial scales. Whilst in clinical settings, it is used to: assess stroke, investigate neurodegenerative diseases, and monitor brain function during surgery.

Its advantages are that it has a high spatial resolution (100 micrometers) and a temporal resolution (up to 100 milliseconds). It also has no magnetic field constraints, which makes it safer for patients with metal implants or pacemakers and has lower operational costs compared to MRI. b

fUS - therapy applications

The blood-brain barrier (BBB) is a protective layer of tightly joined cells that lines the blood vessels in the brain and prevents toxins and infectious agents, from diffusing into the surrounding brain tissue.

However, this also prevents many medications from entering the brain, for this reason one can temporarily opening the brain barrier via fUS to treat neurological conditions like brain cancer or alzheimer.

The opening usually lasts for about 4hrs. Microbubbles (small, gas filled particles) are injected in the bloodstream. When exposed to high energy FUS, which creates mechanical vibrations in the vessels, these microbubbles oscillate and create mechanical stress on the blood vessel walls. This disrupts the tight junctions of the BBB temporarily, enabling molecules up to 150kDa to pass.

The main difference with fUS is that here it is high-energy focused ultrasound meaning that the energy applied is higher.

GIF Хайфу, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commonsimage reference Creative Commons Attribution-Share Alike 4.0 International MelOSA72 14 April 2023 https://upload.wikimedia.org/wikipedia/commons/6/6c/BBB_disruption_by_focused_ultrasound.png

Page updated

Google Sites

Report abuse