A schematic diagram of the LED-FOD system showing the use of a PXI controller to process the signal from the photomultiplier and to control the operation of the LED source.
The schematic diagram of the measurement on the LED stimulated scintillation signal as a function of tensile stress in a FOD with 1 mm diameter.
Measured spectra as a relative intensity in photomultiplier counts as a function of wavelength. Curve (a) shows the LED emission spectrum measured after the emitted light has passed through 10 m of fiber. Curve (b) shows the spectrum of the scintillation light measured next to a 10 mm scintillator when it is stimulated by the LED light of curve (a). Curve (a) shows the spectrum of the light measured just before it passes through the filter shown in the complete LED-FOD system of Fig. 1.
The dependence of the LED stimulated scintillation signal as a function of tensile stress in a FOD, in which an initial linear decrease is followed by “catastrophic” failure. Also shown is the corresponding force in newton.
The LED driving voltage for a fixed driving current of 1 mA as a function of ambient temperature (error bars are 1 mV). This enables the LED to be used as a sensor of the system temperature instead of using an external temperature sensor.
A time trace of the FOD reading showing the correlation between the LED stimulated scintillation signal (labeled as “LED”) and the signal from the brachytherapy source (labeled as “source”) after mechanical compression of the extension cables. Both signals change after the mechanical compression of the extension cables was introduced at 80 s.
The linear relation between the LED stimulated scintillation signal and the brachytherapy source generated signal as a function of compression force applied to the fiber optic 400 mm from the scintillator end. This is the typical location of the entrance of a urethral catheter. The error bars correspond to 0.5% of the reading.
The correlation between the LED stimulated scintillation signal and the brachytherapy source stimulated signal due to the effect of bending of the extension cables alone (labeled as “Extension” in the figure). The lower part of the curve (labeled as “FOD”) refers to additional bending of the FOD cable near the scintillator while maintaining the maximum bending of the extension cables. The error bars shown correspond to 0.5% of the reading. The slopes of the lines are different for the two cases. The numbers shown for each data point are the bending diameter in units of mm.
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