The application of continuous laser (coherent) light onto cells or tissue without the addition of any reporter molecules results in a high level of contrast from amplitude, phase and polarisation scattering events.
An interesting technique arising from inelastic scattering is Raman spectroscopy, which is sensitive to vibrational excitations of molecular bonds. Since the energy of the vibrational interaction is specific to the type of bond being excited, Raman spectra provide a chemical “fingerprint” of the material being studied. For biomedical imaging, Raman spectra provide insight into the composition of cells and tissues, including their lipid, protein and DNA content, as well as chemical modifications of these molecules occurring in response to oxidative stress and chemotherapy. Studies of living cells are enabled by imaging chambers that maintain temperature, humidity and atmosphere compatible with cell culture.
Exciting opportunities for imaging early cancer, or dysplasia, also arise from quantitative phase imaging and polarisation-resolved properties of tissue. The potential of phase and polarisation dependent contrast is currently being explored in tissue mimicking phantoms and also in ex vivo tissue, with a view to future clinical application through endoscopy in the oesophagus and lung.
Raman: Ben Woodhams, Dr Jakub Surmacki
Optical phase and polarisation: Travis Sawyer, Dr James Joseph, Dr Catherine Fitzpatrick, Dr George Gordon.
Prof. Tim Wilkinson, Prof. Ian White (Department of Engineering, University of Cambridge); Dr Lexi Haslehurst, Prof. Bruce Ponder (CRUK CI/ Department of Oncology, University of Cambridge).