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. Credit: Biomedical Optics Express. |
Blood
tests convey vital medical information, but the sight of a needle often
causes anxiety and results take time. A new device developed by a team
of researchers in Israel, however, can reveal much the same information
as traditional blood test in real-time, simply by shining a light
through the skin. This optical instrument, no bigger than a breadbox, is
able to provide high-resolution images of blood coursing through our
veins without the need for harsh and short-lived fluorescent dyes.
“We
have invented a new optical microscope that can see individual blood
cells as they flow inside our body,” says Lior Golan, a graduate student
in the biomedical engineering department at the Israel Institute of
Technology, or Technion, and one of the authors on a paper describing
the device that is published Monday in the Optical Society’s (OSA)
open-access journal Biomedical Optics Express.
By eliminating a long wait-time for blood test results, the new
microscope might help spotlight warning signs, like high white blood
cell count, before a patient develops severe medical problems. The
portability of the device could also enable doctors in rural areas
without easy access to medical labs to screen large populations for
common blood disorders, Golan notes.
Using
the new microscope, the researchers imaged the blood flowing through a
vessel in the lower lip of a volunteer. 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.
The
device relies on a technique called 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. To scan blood cells in motion, a probe is pressed against the
skin of a patient and the rainbow-like 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 are far less practical, relying on bulky equipment or potentially
harmful fluorescent dyes that must 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 says. “Since the blood
cells are in constant motion, their appearance is distinctively
different from the static tissue surrounding them.” 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.
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,
the researchers 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.
The
new system 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.
Additional
steps include work to miniaturize the system for ease of transport and
use. “Currently, the probe is a bench-top laboratory version about the
size of a small shoebox,” says Golan. “We hope to have a thumb-size
prototype within the next year.”
Noninvasive imaging of flowing blood cells using label-free spectrally encoded flow cytometry
Source: Optical Society of America
