Real time excitation-emission spectra for in vivo disease diagnosis

It has been demonstrated that fluorescence spectroscopy is able to distinguish between diseased and healthy tissue and now is being explored as a potential tool for the diagnosis of disease. This often requires complete characterization of the absorption and fluorescence properties of normal and abnormal tissues over the near UV and visible regions. Such information is often collected and displayed in the form of an excitation emission matrix (EEM). We have designed, fabricated, and tested a compact, transportable EEM system capable of collecting multi-excitation spectra in approximately 600 milliseconds in a reliable manner. This is an increase in data collection speed of at least an order of magnitude over some other previous systems and is an essential advantage when measuring spectroscopic signals in vivo. Spectra can be collected from the same tissue site, without artifacts due to probe displacement caused by heartbeats, breathing and other body motions, and without undue strain on the patience of the physician and patient. A white light source provides simultaneous measurement of diffuse reflectance from the same tissue site on each cycle, giving important additional diagnostic information. Our system uses a 337 nm nitrogen laser to pump a sequence of ten dye cuvettes located on a rotating wheel. The pump is also used as an excitation source, providing a total of eleven excitation wavelengths approximately uniformly spaced in the range 337 to 505 nm. By changing the dyes used, the excitation wavelengths can be varied as required.