Originally Published MPMN June 2009

NEED TO KNOW

University Researchers Develop Fastest Camera in the West

Bob Michaels

Taking pictures of cells is crucial for distinguishing healthy ones from diseased ones or for recording neural activity, blood content, or cellular communication. However, the frame rate of even the fastest conventional cameras is too slow to capture the types of high-speed events that occur in the body. By developing a camera that can capture millions or even billions of images continuously, a group of shutterbugs at the University of California Los Angeles (UCLA; www.ee.ucla.edu) is out to change that.

Under team leader Bahram Jalali, a professor of electrical engineering at UCLA’s Henry Samueli School of Engineering and Applied Science, the team consisting of Keisuke Goda and Kevin Tsia have developed a continuously running camera that shoots images approximately one thousand times faster than existing cameras. In one second, the camera can capture 6.1 million shots with a shutter speed of
440 trillionths of a second, which is incomparably faster than the 11 frames per second achieved by high-end digital single-lens reflex cameras.
The invention is based on serial time-encoded amplified microscopy (STEAM). “The new imager starts with a supercontinuum laser pulse—an ultrashort bundle of photons that lasts but a few picoseconds,” explains Jalali. “What makes these pulses special is that they have a broad optical spectrum spanning a wide range of colors.”
Before illuminating an object, the pulse is spread into a 2-D rainbow pattern so that every pixel of the image is assigned a different color, or wavelength, Jalali says. When the 2-D rainbow reflects from the object, the image is copied onto the color spectrum of the pulse. The pixels, or bright spots, reflect their own assigned wavelength while dark ones do not. The picoseconds-long pulse that contains the image is then stretched in time and amplified using a technique called amplified dispersive Fourier transform.
In contrast to conventional cameras, the UCLA team’s device does not rely on charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) technology. “Once the image has been converted to a 1-D serial data stream, one no longer needs a CCD or CMOS photo sensor array,” Jalali remarks. “All that is needed is a single-pixel sensor. In essence, the image is converted to an optical data stream traveling through an optical fiber. So, the camera is replaced by a receiver similar to that used in fiber-optic networks that form the backbone of the Internet.”
The researchers think that the technology may find use in medical applications such as flow cytometry, a technique used to analyze blood. “By virtue of its image amplification feature, STEAM is able to take pictures at high frame rates without the need for intense illumination of the sample,” Jalali states. “In other words, it can capture millions of pictures per second at low light levels.” This, he says, is ideal for microscopy, where high-intensity illumination of the sample is prohibited because the illumination light can damage the sample when it is focused onto a small field of view. “This phenomenon is similar to how ordinary sunlight can burn paper when it is focused into a small spot by a lens,” he adds.
While current flow cytometers can count cells
and record information about their size, they cannot takes pictures of each cell because traditional cameras are not fast enough and sensitive enough. Very rare, diseased cells are rogue cells. Finding diseased cells is like looking for a needle in a haystack, Jalali muses. “You need to analyze billions of cells—the entire haystack.” STEAM promises to do just that. By being integrated into devices such as flow cytometers and taking a picture of every cell at low light levels without damaging them, the camera may enable scientists to catch the rare ones that are precursors to diseases such as cancer.
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