Ultrasound Localisation Microscopy – ULM for High-Resolution Vascular Imaging of the Brain

Ultrasound Localisation Microscopy or ULM is a microbubble-enabled imaging mode that enables users of the Iconeus One functional ultrasound system to non-invasively image blood vessels in the brain in incredible detail. The first paper on the technique was published in 2015, in the paper “Ultrafast Ultrasound Localization Microscopy for Deep Super-Resolution Vascular Imaging” published in Nature and coauthored by Iconeus cofounder Mickael Tanter.

High-resolution imaging of the vascular structure of the brain using Ultrasound Localisation Microscopy (ULM).

High-resolution imaging of the vascular structure of the brain using Ultrasound Localisation Microscopy (ULM).

The Ultrasound Localisation Microscopy Technique

ULM uses injected microbubbles as a contrast agent to greatly enhance the resolution of functional ultrasound in preclinical imaging of animal models. The process involves:

  1. Injecting microbubbles into the blood stream and detecting them using fUS at ultrafast framerate.
  2. For each frame captured, i.e. at every time point, images of the microbubbles are isolated by subtracting slowly-changing signals from the tissue
  3. The location of each micro-bubble is pin-pointed and their trajectories tracked and superimposed to create a highly resolved localisation map.

What Does Ultrasound Localisation Microscopy Tell Us?

  • High-resolution maps – Capable of an in-plane resolution of around 5µm, ULM allows you to generate high-resolution vascular maps of the brain revealing blood vessel structure
  • Micro-bubble tracking – Count, track and analyse each micro-bubble as they travel through blood vessels indicating the direction of flow of blood
  • Blood velocity quantification – measure the blood velocity in the mm/s range including direction of flow, and this distinguish between different types of blood vessels

3D Mapping

Iconeus successfully demonstrated ULM could be expanded to 3 dimensions in 2022 using 2D transducers such as Row-Column Addressed (RCA) probes. This advancement will facilitate even more comprehensive analysis of brain structures and functions.

The Future of Ultrasound Localisation Microscopy

Iconeus are working on reducing the temporal resolution and making the technology suitable for clinical applications.