Optical technique detects malaria early
TRIESTE, Italy – Rapid detection of malaria, particularly in remote parts of the world, is not always possible because current methods are slow and require precise instrumentation and highly skilled microscopic analysis.
“A new diagnostic tool was urgently needed,” said Dr. Dan Cojoc, a researcher at the Materials Technology Institute of the National Research Council. “With a fast, portable, low-cost and accurate diagnostic tool, physicians can confidently and quickly administer the correct therapy.”
Now, using a technique called secondary speckle sensing microscopy, malaria can be diagnosed with greater accuracy and in as little as 30 minutes. Developed by Cojoc and his colleagues, including malaria experts from Israel and Spain, the new microscopy system uses “speckle imaging,” an optical sensing technique that measures the difference between how laser light bounces off the membranes of healthy and infected red blood cells. They compared the apparently random light scattering (speckling) as it built up from multiple images of 25 cell samples (12 healthy, 13 infected), and a clear statistical pattern emerged – identifying cells that harbored the parasite responsible for malaria.
The difference between an infected red blood cell (top) and a healthy cell (bottom) is revealed by secondary speckle sensing microscopy, in part by considering the dynamics of the correlation value (CV), which indicates the similarity between two patterns. One thousand CVs are calculated from pairs of consecutive speckles acquired in 1 s. As shown in the chart at right, the CV oscillation range for the infected cell (top, 0.36) is almost three times larger than that of the healthy red blood cell (bottom, 0.13). Indicated by the arrow in the top left image of the infected cell, a parasite life-cycle stage of malaria called “trophozoite” can be seen. Courtesy of Dan Cojoc, Materials Technology Institute, National Research Council, Italy.
Malaria is most common in warm, wet climates where mosquitoes thrive. The deadly disease claims nearly 1 million lives a year, mostly those of African children.
By applying secondary speckle sensing microscopy to an automated high-throughput system, the researchers delivered results not only in a short amount of time, but also without the need for highly trained technicians or a well-equipped hospital laboratory. The current diagnostic gold standard for malaria, Giemsa-stained blood smear, requires skilled medical professionals trained to identify the signs of a parasite throughout its life cycle; diagnosis typically takes eight to 10 hours.
The microscopy technique begins with illuminating red blood cells with a tilted laser beam to produce a time-varied speckle pattern field based on the cells’ thermal vibration and the movement of their membranes – traits that differ in healthy and diseased states. The speckle patterns are inspected under the microscope and recorded on a camera at a high frame rate. Using two automated analytical methods – “fuzzy logic” and “principal component analysis” – scientists scour a set of speckle parameters to extract statistical information about changes in red blood cells’ membranes and their flickering movements. Then they can make a diagnosis between healthy and diseased cells based on statistical correlations in speckle patterns.
Timely diagnosis maximizes the likelihood of life-saving treatment and minimizes the chances that an inappropriate therapy will be given, helping to combat the growing problem of drug-resistant malaria.
Although preliminary results have proved encouraging, further study is needed to validate the results and refine the method. If the positive outcomes hold up, field studies or clinical trials of secondary speckle sensing microscopy may be deployed as early as 2013.
The research appears in Biomedical Optics Express (doi: 10.1364/BOE.3.000991).
- The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
- speckle imaging
- A technique for obtaining improved resolution of images produced by large telescopes and distorted by the effects of atmospheric turbulence. Many individual exposures are recorded at high speeds by a low-light-level camera and digitized for computer processing by means of a series of encoded masks.
- speckle pattern
- A power intensity pattern produced by the mutual interference of partially coherent beams that are subject to minute temporal and spatial fluctuations.
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