Technical Note: Determining regions of interest for CCD camera-based fiber optic luminescence dosimetry by examining signal-to-noise ratio

Purpose: The goal of this work was to develop a method for determining regions of interest (ROIs) based on signal-to-noise ratio (SNR) for the analysis of charge-coupled device (CCD) images used in luminescence-based radiation dosimetry. Methods: The ROI determination method was developed using images containing high-and low-intensity signals taken with a CCD-based, fiber optic plastic scintillation detector system. A series of threshold intensity values was defined for each signal, and ROIs were fitted around the pixels that exceeded each threshold. The SNR for each ROI was calculated and the relationship between SNR and ROI area was examined. Results: The SNR was found to increase rapidly over small ROIs for both signal levels. After reaching a maximum, the SNR of the low-intensity signal decreased steadily over larger ROIs, but the high-intensity SNR did not decrease appreciably over the ROI sizes studied. The spatial extent of the normalized images showed intensity independence, suggesting that a fixed ROI is useful for varying signal levels. Conclusions: The method described here constitutes a simple yet effective method for defining ROIs based on SNR that could enhance the low-level detection capabilities of CCD-based luminescence dosimetry systems.