Posts from: January 2013
Phosphorescence lifetime imaging microscopy (PLIM) allows substances or tissues with different phosphorescence lifetimes to be identified with high spatial resolution. PLIM hasn’t found many practical applications so far, but it could be useful as a way of measuring oxygen concentration in tissues. Depth resolved images can be obtained using multi-photon excitation, a technique which ensures that all the signal comes from the focal plane. Unfortunately, relatively long phosphorescent lifetimes make the point-by-point scanning used in multi-photon microscopy very time consuming. Attempts to improve the frame rate using parallel excitation can result in cross-talk between pixels and blurring of the image. Now, a group from Cornell University has devised a way to acquire parallel excitation PLIM images which are free from cross-talk.
Fibre bundle endomicroscopes usually operate in fluorescence mode: the tissue is stained with a fluorescent dye which, when illuminated at a certain wavelength, emits light at a longer wavelength. Collecting this fluorescent emission tends to produce clear, high contrast images, and also allows back-reflections from the fibre bundle to be removed using wavelength selective filters. Reflectance mode endomicroscopes, which create an image from the light back-scattered from the tissue, have been demonstrated several times, but have found little practical application. Now, Cha et al. from John Hopkins University have developed a dual-mode device that simultaneously collects both fluorescence and reflectance images. They have used this device to measure the efficacy of gene transfection – the deliberate insertion of genes into cancerous cells.