Photo by: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute via NASA Jet Propulsion Laboratory
Spectral imaging, which enables collection of more color information than a typical camera, reveals the properties of tissues or other biological material that the naked eye would miss.Scientists from several universities in China have teamed up to design a new smartphone-compatible device that enables easy and economical acquisition of spectral images of ordinary objects, with potential applications in point-of-care medical diagnosis.
The device could be used for detecting oxygen saturation in a patient's blood, determining whether meat is fresh and even the level of freshness, as well as identifying fruits that are perfectly ripe among other applications.It could also make it easier to collect spectral data for scientific studies in the field.
In a report that published in the journal Biomedical Optics Express, a publication of The Optical Society, the research team comprising of experts from China's Hainan University, Zhejiang University and Beijing University of Chemical technology reveal how they used off-the-shelf components to make the new pencil-like spectrometer.They demonstrated its ability to acquire and transmit spectral images of a person's hand, bananas, and pork.It can detect a range of wavelengths between 400 and 676 nm (nanometers) at 186 spots simultaneously, with a wavelength resolution of about 17 nm.
According to the report's first author, Fuhong Cai of Hainan University, China, the easiest way to use a spectrometer is by waving it over the target area.Cai says the already existing home-made portable spectrometers use a smartphone camera for acquiring data alongside a phone cradle carrying other necessary optics, which he argues is not efficient. "The cradle is hard to align properly and makes it cumbersome to wave the smartphone over the body," he observed.
For their spectrometer, Cai and his team avoided the smartphone camera and went for a complementary metal-oxide-semiconductor camera (which is commercially available).The CMOS camera wirelessly transmits data to a smartphone.
With this approach, the researchers were able to assemble the components into a cylindrical imaging device weighing only 140 grams (5 ounces) and measuring about the length of a smartphone, and just over 3 centimeters (1.18 inches) in diameter.
The scientists say all components used are available commercially and can be acquired for a total of less than US$300.For the light source, they used an array of white light LEDs, which they connected to an optical lens tube that carries the CMOS detector and other optical parts necessary for spectral imaging.
The spectrometer is held like a pencil and moved across the target area to scan and image an object.Through this manual push-broom scanning method, a sequence of spectral images is accumulated.The pictures are then sent to a computer or smartphone where software compiles the data into a 3D spectral image data cube.
The research team tested the spectrometer on bananas to detect ripeness and on a piece of pork to detect levels of myoglobin – the iron-rich protein that gives meat its color.They also tried it on a human hand, obtaining 200 spectral images in the form of a 16-second video.The 3D spectral models enabled the scientists to distinguish the palm and five fingers and see the distribution of hemoglobin in various parts of the hand.
The scientists from China expressed their interest in perfecting the compact imaging spectrometer for use in monitoring the environment. "Currently, we are developing distributed spectral cameras that could help conduct a wide range of oceanic surveys, like detecting dissolved organic materials in water or pigments that give early signs of harmful algal blooms," says Cai. "Given the imaging spectrometer can be attached to any camera, we are also exploring the idea of connecting it to an autonomous vehicle to make a remote ocean sensing system," he added.
Anyone can assemble the prototype because it uses commercially-available components.However, this also limits the resolution and sensitivity of the device.For one, the prototype can only resolve wavelengths that differ by 17 nanometers and above.
Dan Wang of Beijing University of Chemical Technology, China, who was part of the research party, says the team expects to make significant spectral resolution improvements in the future by replacing the camera with one that has a longer focal length among other enhancements. "These improvements will expand the possible applications of the device," he pointed out.
They also intend to develop software that will make the spectral imager much more useful. "We would like to come up with ways of employing machine learning algorithms to analyze the massive amounts of data that the portable spectral imager could collect," says Sailing He of Zhejiang University, China, who took part in making the prototype. "We will also be developing software for smartphones that uses the data from spectral imaging to measure the freshness of meat, for example," he went on.
In the future, you might be able to walk into a grocery store with a smartphone accompanied by a compact spectrometer and walk out with only the freshest products.
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