Smartphone-based fluorescence imager for PpIX-based PDT treatment planning: System design and initial results

In clinical delivery of PDT, in-situ measurement of PpIX concentration is rarely done, and yet point-probe measurements have shown extreme heterogeneity exists between patients and between lesions. Direct measurements of PpIX can provide guidance in PDT, informing critical decisions about treatment time and retreatment or further skin preparation. In this work, we present a smartphone-based fluorescence imaging system to map PpIX concentration onto a 2D image for the use in PDT treatment optimization. The hand-held system utilizes a custom application on an iPhone 6s in conjunction with a 3D-printed measurement base containing custom miniaturized light source and electronics and filter system. The prototype has been produced and tested in phantoms and in pre-clinical evaluation. Intralipid phantom measurements detected clinicallyrelevant concentrations of PpIX within the 0.05μM - 4μM range. Preclinical tests on mice showed the ability to detect PpIX concentration for topically applied ALA within 20-30 minute incubation. These results showcase the viability of the system to map pixel intensities to PpIX concentrations and perform in-vivo detection within a clinically relevant timeframe. Clinical trials are in preparation with results expected in the next few months.