Phonon probe in nanoscale ultrasound imaging tissues


Visual signs of the disease can often be detected within affected tissues, and advances in histopathology have provided clinicians with powerful diagnostic tools to detect these signs. Microscopes are the cornerstone of this trade and, although they have proven to be extremely useful, they have some limitations. They are effectively 2D imaging devices that do not offer a good perspective on the volumetric nature of things on small scales and only detect light, which cannot perceive clinically important properties such as tissue rigidity.

The fiber optic imaging sensor has a diameter of 125 micrometers, about the size of a human hair, which is shown in perspective against a penny. A microscope image shows the true scale of the device and its ability to conduct light.

Now, researchers at the University of Nottingham in England have developed a nanoscopic ultrasound imaging system that can be combined with conventional optical devices to visualize cells and their components in a new way. The image probe is so small that it can barely be seen on a small coin.

Unlike light, ultrasound imaging can provide nuances about the 3D structure of what is observed. In addition, since sound generates waves within the tissues it comes in contact with, detecting the properties of these waves can provide a lot of information about the nature of the tissues themselves. “We believe that the system’s ability to measure the rigidity of a specimen, its biocompatibility and its endoscopic potential, while accessing the nanoscale, are what differentiate it. These characteristics make up the technology for future measurements inside of the body; towards the ultimate goal of minimally invasive diagnosis of the point of care, “said Dr. Salvatore La Cavera III, one of the leaders of the team that developed the new device.

The small size of the new probe allows it to be used alongside optical components of conventional endoscopes and the two imaging modalities can be combined to provide a more complete assessment of the tissue. As the photons of light bouncing from the tissue are represented as bright spots on a screen, so are the phonons in the ultrasound probe. Because the technology adapts to the tips of fiber optics, it can be used to visualize difficult-to-achieve goals such as those in the gastrointestinal tract.

Conventional microscope images of model biological cells (top). The phonon probe reproduces 3D images of objects (color is height). Simultaneously, the probe detected stiffness-related measurements that are mapped in green in the upper left (lower) image. The white flake bar is 10 micrometers long.

The ultrasonic probe has an unusual feature that allows it to make a 2D image on a microscopic scale, but in the 3rd dimension it represents it on a much more impressive nanoscale.

Some details about the operation of the new device, according to the University of Nottingham:

The new ultrasound imaging system uses two lasers that emit short pulses of energy to stimulate and detect vibrations in a specimen. One of the laser pulses is absorbed by a layer of metal (a nanotransducer (which works by converting energy from one shape to another)) made at the tip of the fiber; a process that causes high-frequency phonons (sound particles) to bombard the specimen. Then, a second laser pulse collides with the sound waves, a process known as Brillouin scattering. By detecting these “collided” laser pulses, the shape of the traveling sound wave can be recreated and visually visualized.

The detected sound wave encodes information about the rigidity of a material and even its geometry. The Nottingham team was the first to demonstrate this dual capability using powder lasers and fiber optics.

Open access study a Nature magazine Light: science and applications: 3D Phonon images with a fiber probe

Via: University of Nottingham

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