Conventional UItrasound Imaging
Ultrasound imaging is a commonly used technique used to visualise internal organs, blood vessels and tissue inside the human body. In clinical applications it provides real-time imaging that help doctors diagnose, monitor and treat various conditions. It does this by using emitting high-frequency sound waves with a point focus from a transducer that bounce back off internal structures. The transducer also picks up these echoes and translates them into images.
Functional Ultrasound Imaging
Functional ultrasound (fUS) works in the same way, but uses plane waves, thus generating a complete 2D image in one scan. By using a succession of plane waves in different angles, it is possible to reconstruct high-quality images with enhanced sensitivity, enabling the detection of subtle changes in blood flow across the whole brain. More details about how this technique works can be found in the paper “Functional Ultrasound Imaging of the Brain”, co-authored by Iconeus founder Mickael Tanter, published in Nature Methods (2011).
Comparison of conventional and functional ultrasound imaging
Iconeus employs a transducer that generates pulses (plane waves) at about 5kHz, allowing imaging of the entire brain in a single scan.
In this context, fUS offers an alternative to fMRI and has the advantage that it can be used on awake and mobile animals and provides a lower start up and operational cost option.
Tomography – Isometric volume of the brain vasculature (50 x 50 x 50µm)
How Functional Ultrasound Works
As mentioned, each ultrasound pulse produces an echo or backscatter from bodily tissues. Low frequency quasi-static echoes can be subtracted from high frequency signals produced by moving red blood cells. The mean intensity of this signal is known as the Power Doppler value which is proportional to the relative number of red blood cells in a unit volume, and consequently to the cerebral blood volume (CBV). The high sensitivity of functional ultrasound allows imaging of the tiniest blood vessels, where the red blood cells move extremely slowly, which is impossible to capture using conventional ultrasound.
Brain activity is closely related to the dilation of blood vessels supplying neurons involved or the neurovascular coupling, indicates that the cerebral blood volume (CBV) measured by functional ultrasound can be directly related to neuronal activity. The Iconeus One software then converts the complex datasets into easy-to-understand images and video, revealing brain activity in real time.
Functional ultrasound providing a window into brain activity
Summary
Functional ultrasound is a non-invasive technique used to visualise blood flow in the brain that can be directly related to neural activity. It has the spatial and temporal resolution to image the smallest blood vessels in real time, detecting the exact location and intensity of haemodynamic responses to stimuli or therapeutic treatments. This allows researchers to map sensory processing making the Iconeus One functional ultrasound a powerful tool for neuroscientists to study disease mechanisms. Drug effects or brain plasticity in the context of preclinical research.
