High-resolution microvessel imaging using novel beamforming techniques and no microbubbles!

Michael Oelze – oelze@illinois.edu
X (Twitter): @Oelze_Url

University of Illinois at Urbana-Champaign
Urbana, IL 61801
United States

Zhengchang Kou
University of Illinois at Urbana-Champaign
Urbana, IL 61801
United States

Popular version of 1pBAb7 – Contrast-Free Microvessel Imaging Using Null Subtraction Imaging Combined with Harmonic Imaging
Presented at the 186th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0026780

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

Bubbles? We don’t need no stinking bubbles!

In recent years, super resolution imaging techniques for imaging the microvasculature have been developed and demonstrated for applications such as functional ultrasound imaging in mice and assessing Alzheimer’s disease in pre-clinical models. While these novel super resolution techniques have produced images with incredible detail and vessel contrast, one drawback to the approach is the need to inject contrast agents, which consist of small gas-filled microbubbles. This reduces the clinical application and adoption of these techniques. Furthermore, the time required to construct these images can take hours because it involves localizing and tracking individual microbubbles as they progress through the vasculature.

FIGURE 1: Video of 3D rendering of rat brain using traditional approaches at a fundamental frequency (top left) and at twice the fundamental frequency (bottom left) compared to using our novel approach (NSI) at a fundamental frequency (top right) and at twice the fundamental frequency (bottom right) (please note this will be a playable video online)

In our novel approach to microvessel imaging, we don’t need no stinking microbubbles! Instead, we utilize a novel nonlinear beamforming approach that allows fast reconstructions with much better spatial resolution. This allows us to approach super resolution without the need to inject microbubbles into the body. Along with the beamforming approach we also use a pulse inversion scheme, where we transmit with one frequency and receive with twice the transmit frequency. This allows a doubling of the spatial resolution over receiving with the same transmit frequency. However, the use of pulse inversion scheme can introduce unwanted clutter into the image. With our novel beamforming approach, clutter is greatly reduced or eliminated from the images.

FIGURE 2 Single image frames comparing traditional power Doppler methods (left) with our novel approach (right).

We demonstrated our new technology in a rat brain (both 2D and a 3D rendering) and rabbit kidney and compared our images to traditional beamforming approaches without the use of contrast agents. The video shows a 3D rendering of the microvasculature of a rat brain and the corresponding figure shows a particular frame of the 3D rendering. We showed that our approach eliminates the clutter produced by the pulse inversion scheme, increases the contrast of microvessel images, results in more observable vessels, and produces a much finer spatial resolution better than one fourth of a wavelength. The time to reconstruct the images using our novel technique was a fraction of the time needed for current super resolution techniques that rely on localizing and tracking microbubbles in the vasculature. Therefore, our novel approach could provide microbubble-free technology to produce high-resolution power Doppler images of the microvasculature with the potential for clinical applications.