More than 30 % of the patients seeking emergency care have symptoms related to reduced blood oxygenation, possibly indicating stroke, heart failure or similar conditions. Therefore, it would be advantageous to be able to image the oxygenation in the body. It is known that deoxygenated blood absorbs red light of a specific wavelength (700 nanometres) to a much greater extent than oxygenated blood. Measuring the light absorption at that wavelength can thus reveal the oxygenation level. Unfortunately, body tissue scatters the light in all directions, making it impossible to tell where the absorption took place.
A research team within the Wallenberg Centre for Quantum Technology (WACQT) now tries to solve this problem by pointing an ultrasound pulse to the location to be measured. The ultrasound shifts the wavelength of the light by a small amount, and by analyzing the wavelength-shifted light for different positions of the ultrasound pulse, they expect to be able to form an image of the oxygenation level. In order to filter out the tiny amount of wavelength-shifted light from the much stronger unshifted light, they use a crystal with a specific quantum structure designed by the Quantum Information Group at Lund University. The crystal strongly suppresses light at the unshifted wavelength – and also slows down the shifted light to just a few kilometres per second.
“This means it comes out long after any remaining unshifted light, and effectively can be distinguished from it,” says principal investigator Stefan Kröll.
In this way, the team has managed to achieve measurements almost free from background noise, as described in an article in Biomedical Optics Express. The technique is developed by industrial PhD student David Hill at the medical start-up company SpectraCure AB together with the Quantum Information Group at Lund University.