Portable microscope images the flow of individual blood cells noninvasively

A new optical microscopy device developed by researchers at the Israel Institute of Technology (Technion; Haifa, Israel) involves shining light through the skin to reveal the same information that a traditional blood test yields—but in real time. The device, which is about the size of a shoebox, provides high-resolution images of individual blood cells coursing through veins without the need for fluorescent dyes.

The microscope, which could eliminate a long wait-time for blood test results, might help spotlight warning signs (i.e., high white blood cell count) before a patient develops severe medical problems.  The microscope's portability could also enable doctors in rural areas without easy access to medical labs to screen large populations for common blood disorders, notes Lior Golan, a graduate student in the biomedical engineering department at Technion.

Using the microscope, the researchers imaged blood flowing through a vessel in the lower lip of a volunteer. They then measured the average diameter of the red and white blood cells and also calculated the percent volume of the different cell types (key for many medical diagnoses).

An in-vivo image shows red blood cells within a microvessel
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. (Image courtesy of Biomedical Optics Express)

The device relies on spectrally encoded confocal microscopy (SECM), which creates images by splitting a light beam into its constituent colors. The colors are spread out in a line from red to violet--like a rainbow. To scan blood cells in motion, a probe is pressed against the skin of a patient and the 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 color of the scattered light carries spatial information, and computer programs interpret the signal over time to create 2D images of the blood cells.

Currently, other blood-scanning systems with cellular resolution do exist, but they rely on bulky equipment or potentially harmful fluorescent dyes that must be injected into the bloodstream. "Since the blood cells are in constant motion, their appearance is distinctively different from the static tissue surrounding them," explains Golan. The team's technique also takes advantage of the one-way flow of cells to create a compact probe that can quickly image large numbers of cells while remaining stationary against the skin.

A portable microscope relies on spectrally encoded confocal microscopy
A portable microscope relies on spectrally encoded confocal microscopy. A single line within a blood vessel is imaged with multiple colors of light that encode lateral positions (a), and a single cell crossing the spectral line produces a 2D image with one axis encoded by wavelength and the other by time (b). (Image courtesy of Biomedical Optics Express)

At first, the narrow field of view of the microscope made it difficult for the team to locate suitable capillary vessels to image. To solve this, they added a green LED and camera to the system to provide 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," notes Golan. "Adjusting the imaging depth of the probe for imaging a small capillary is still a challenge we will address in future research."

The researchers are also working on a second-generation system with higher penetration depth--one that might expand the range of possible imaging sites beyond the inside lip, which was selected as a test site since it was rich in blood vessels, has no pigment to block light, and doesn't lose blood flow in trauma patients. The team hopes to produce a thumb-size prototype within the next year as well, notes Golan.

For more information on the work, please visit http://www.opticsinfobase.org/boe/abstract.cfm?uri=boe-3-6-1455.

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