Perfusion Ultrasound Imaging in 3D

Ultrasound is one of the most widely used imaging modalities in modern healthcare and it remains a field in rapid development, mainly due to the new possibilities offered by modern fast electronics, computers, and graphics processors.

Ultrasound provides instantaneous images at the bedside and reveals the intricate human anatomy as well as the body’s function in terms of movement and blood flow. So far, however, the characterization of blood flow in micrometer-sized vessels has been beyond the resolution and sensitivity of commercial ultrasound technology.

Current medical ultrasound systems are diffraction limited to the wavelength of the emitted and received wave. In traditional pulse-echo system with delay-and-sum beamforming, axial and lateral resolutions are approximately one wavelength, which for typical frequencies of 3-15 MHz translates into 0.5 to 0.1 mm, which is far from the resolution needed to visualize the microvasculature and reveal capillary flow.

Current techniques such as super resolution imaging (SRI) have demonstrated images of a mouse ear with a resolution of 20 µm, clearly detailing the arterioles and venules of the mouse ear and their blood flow. The technique uses contrast agent bubbles.

As of now, this has only been possible for a 2-D representation of the data. Here the motion in and out of the imaging plane is neglected, and tissue motion is not an issue due to rodent being fixated. True SRI must be three-dimensional and have the capability of tracking particles with a high resolution in all three dimensions simultaneously to truly visualize the microvasculature, and tissue motion for breathing and pulsation should be compensated for.

A technique and probe design known as Row-Column (RC) arrays, proposes a method of 3-D imaging with high temporal resolution. Such arrays have been researched and developed in a collaboration between DTU Nanotech, BK Ultrasound in Denmark, STI in the US, and Center for Fast Ultrasound (CFU) since 2011.

The project seeks to further develop these new advanced ultrasound techniques for three-dimensional imaging of blood perfusion using (RC) arrays. RC arrays have a larger penetration depth than conventional arrays, and this can translate into a higher investigation frequency for the imaging. Combined with synthetic aperture velocity imaging and tracking of contrast agent bubbles for super resolution imaging can potentially increase the fundamental resolution of ultrasound by a factor of 10-100 times in the blood stream.

The project also seeks to develop these new imaging schemes for performing 3-D imaging using newly developed RC CMUT (Capacitive Micro-machined Ultrasound Transducers) arrays and investigate its use on 3-D printed phantoms from DTU Nanotech.

The project is funded by Innovation Fund Denmark and DTU.