Fluorescent multi-sensor fiber-optic probes for spatially resolvedmonitoring of Interstitial Photodynamic Therapy
were absolute calibrated using an integrating cylinder. The dynamic response was evaluated and showed linear responsivity in the test range from 1 - 60 mW•cm-2. Sensor-probe and optoelectronic readout provides an accuracy of better than 10%.
An integrating cylinder composed of high-density polyurethane with a measured multiplication factor (M) of
38 has been developed for absolute calibration of fluence rate probes designed for monitoring of photodynamic
therapy (PDT) and other light-based therapies.
Photodynamic Therapy (PDT) is a minimally invasive treatment that uses a photosensitive drug into convert triplet state
oxygen (3O2) to singlet oxygen (1O2) to destroy malignant tissue. A fiber-optic system based on frequency domain
detection of phosphorescence quenching by 3O2 is described which optically measures the distribution of 3O2 in the
treatment volume during PDT to permit adjustments of treatment parameters to improve outcome. A specially designed
fiber optic probe containing phosphorescent sensors embedded along its length permit spatially resolved measurements.
Each sensor is composed of a phosphorescent metalloporphyrin compound that emits a characteristic spectrum. Four
candidate sensors with high absorption at the excitation wavelength of 405nm and emission in the 650nm to 700nm
region are considered. The dependence of phosphorescence lifetime (τ) on 3O2 concentration is described by the
linearized Stern-Volmer relationship as being inversely proportional. Determination of τ, and hence 3O2 concentration,
is accomplished in the frequency domain by means of phase-modulation detection of the phosphorescence signal due to
an amplitude modulated excitation. The τ's of each sensor are recovered by performing global non-linear least squares
fit on the measured phase and modulation index over a range of frequencies and wavelengths. With the τ of each sensor
known, the oxygen concentration at each sensor's location can be determined with the Stern-Volmer relationship.
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