Sensitive absorption measurements of 99mTc imaging agents using a new fiber optic sensor

Radiopharmaceuticals containing 99m Tc, a gamma emitting radionuclide, are commonly used in nuclear medicine to image specific organs for the purpose of diagnosis. Following injection of a chemical complex of this isotope and concentration of the activity within the organ of interest, scanning with a gamma ray camera provides an image from which diagnostic information can be obtained. Although, in most instances the composition of the injected radiopharmaceutical is known, the chemical form of the agent that is actually responsible for the image has not been identified and may represent an altered form due to in vivo reaction. Sensors that could be implanted in specific organs in order to specify the chemical form of the radioactive complex that is imaging an organ would be especially useful. In order to accomplish this goal, sensors for in vivo monitoring of imaging agents that are used in nuclear medicine are being developed. Such sensors must be multiwavelength since chemical information is contained in the spectrum of agents. A brief outline of the results of our efforts to make highly efficient catheter-sized absorbance sensors is presented.