Laser imaging beats the bends

21 Nov 2007

A laser-based system can diagnose decompression sickness in seconds, before the onset of physical symptoms.

Decompression sickness is a well-documented risk for divers and other people who experience sudden changes in pressure, but it's usually not detected until clinical symptoms appear. The new device could allow advance warning of the sickness by spotting microbubbles of nitrogen as small as 6 µm across in blood and tissues.

"This is a fresh idea, a technique that has not been used to detect microbubbles in blood before now," Kirill Larin of the University of Houston told optics.org. "Each test only takes a few seconds and is completely non-invasive."

Most microbubbles in the blood stream of people suffering from decompression sickness are between 5 and 15 µm, about the size of a red blood cell, and readily spotted by the technique.

The system uses optical coherence tomography (OCT), an interferometric technique that uses lasers to build up images of tissue just below the skin. In Larin's current prototype, a 1330 nm laser source with a spectral width of 110 nm and a power of 10 mW scans the subject at a scanning rate of 15 kHz. The light is delivered to an interferometer, one arm of which includes the test sample. The resulting interferogram is digitized using 14-bit analog-to-digital conversion, and the machine produces a 2D OCT image of the microbubbles present along with a graphical read out.

Applied to the skin of a returning diver, pilot or astronaut, the technique could reveal the presence of microbubbles in seconds, so medical steps or time in a decompression chamber could be arranged before other symptoms appear.

Larin and his colleagues are now preparing for detailed animal and clinical trials to determine exactly how much advance warning the technique could provide and identify which areas of medical practice could benefit most.

"A noninvasive technique to detect microbubbles in blood and tissues has significant clinical importance, since they a potentially serious problem in a range of medical procedures including open heart surgeries, orthopedic surgery, and various laser ablation and laproscopic procedures," Larin commented. "Gas embolism can even occur during intravenous antibiotic delivery at home."

Larin believes that other applications, including imaging, diagnostic and therapeutic applications that use microbubbles for contrast or as drug delivery vehicles, will also benefit from a system able to both detect and size moving or stationary bubbles.