Microscope Uses Broadband Light to Track Cell Flow

A novel optical instrument no bigger than a breadbox can take real-time images of blood coursing through our veins without harsh and short-lived fluorescent dyes.

The microscope created at the Israel Institute of Technology, or Technion, could eliminate a long wait for blood test results and might help spotlight warning signs, like high white blood cell count, before a patient develops severe medical problems. The device’s portability could also help doctors in rural areas without easy access to medical labs to screen large populations for common blood disorders, according to Lior Golan, a graduate student in biomedical engineering at the institute.

The device relies on a method called spectrally encoded confocal microscopy, which creates images by splitting a light beam into its constituent colors, spread out in a line of light from red to violet. A probe pressed against the skin of a patient scans blood cells in motion as the rainbowlike line of light is directed across a blood vessel near the surface of the skin. As blood cells cross the line, they scatter light, which is collected and analyzed. The scattered light’s color carries spatial information, and computer programs interpret the signal over time to create two-dimensional images of the blood cells.

The team’s device relies on a technique called spectrally encoded confocal microscopy. (a) A single line within a blood vessel is imaged with multiple colors of light that encode lateral positions. (b) A single cell crossing the spectral line produces a two-dimensional image with one axis encoded by wavelength and the other by time. (Images: Biomedical Optics Express)

The researchers tested the optical device by imaging the blood flowing through a vessel in a volunteer’s lower lip, which was selected as a test site since it is rich in blood vessels, has no pigment to block light, and does not lose blood flow in trauma patients. They successfully measured the average diameter of the red and white blood cells and also calculated the percent volume of the different cell types, a key measurement for many medical diagnoses.

Other blood-scanning systems with cellular resolution currently exist, but they are far less practical because they rely on bulky equipment or require harmful fluorescent dyes to be injected into the bloodstream.

“An important feature of the technique is its reliance on reflected light from the flowing cells to form their images, thus avoiding the use of fluorescent dyes that could be toxic,” Golan said. “Since the blood cells are in constant motion, their appearance is distinctively different from the static tissue surrounding them.”

Their technique takes advantage of the one-way flow of cells to create a compact probe that quickly images large numbers of cells while remaining stationary against the skin.

An in vivo image shows red blood cells within a microvessel. The area occupied by red blood cells in the images can be used to calculate the percent volume of red blood cells, a key measurement for many medical diagnoses.

The narrow field of view of the microscope initially made it difficult for the scientists to locate suitable capillary vessels to image. By adding a green LED and camera to the system, they obtained a wider view in which the blood vessels appeared dark because hemoglobin absorbs green light.

“Unfortunately, the green channel does not help in finding the depth of the blood vessel,” Golan said. “Adjusting the imaging depth of the probe for imaging a small capillary is still a challenge we will address in future research.”

The team is now working on a second-generation system with higher penetration depth, which could expand the possible imaging sites to beyond the inside lip. They are also working toward miniaturizing the system for ease of transport and use.

“Currently, the probe is a benchtop laboratory version about the size of a small shoebox,” Golan said. “We hope to have a thumb-size prototype within the next year.”

The research appeared in the open-access journal Biomedical Optics Express.

For more information, visit: www1.technion.ac.il/en