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Treatment monitoring of Aminolevunilic-acid (ALA) - Photodynamic Therapy (PDT) of basal-cell
carcinoma (BCC) calls for superficial and subsurface imaging techniques. While superficial imagers exist
for this purpose, their ability to assess PpIX levels in thick lesions is poor; additionally few treatment
centers have the capability to measure ALA-induced PpIX production. An area of active research is to
improve treatments to deeper and nodular BCCs, because treatment is least effective in these.
The goal of this work was to understand the logistics and technical capabilities to quantify PpIX at depths
over 1mm, using a novel hybrid ultrasound-guided, fiber-based fluorescence molecular spectroscopictomography
system. This system utilizes a 633nm excitation laser and detection using filtered
spectrometers. Source and detection fibers are collinear so that their imaging plane matches that of
ultrasound transducer. Validation with phantoms and tumor-simulating fluorescent inclusions in mice
showed sensitivity to fluorophore concentrations as low as 0.025μg/ml at 4mm depth from surface, as
presented in previous years.
Image-guided quantification of ALA-induced PpIX production was completed in subcutaneous xenograft
epidermoid cancer tumor model A431 in nude mice. A total of 32 animals were imaged in-vivo, using
several time points, including pre-ALA, 4-hours post-ALA, and 24-hours post-ALA administration. On
average, PpIX production in tumors increased by over 10-fold, 4-hours post-ALA. Statistical analysis of
PpIX fluorescence showed significant difference among all groups; p<0.05. Results were validated by exvivo
imaging of resected tumors. Details of imaging, analysis and results will be presented to illustrate
variability and the potential for imaging these values at depth.
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