Fluorescence diagnosis (FD) provides an innovative and promising technique for in-vivo diagnosis of dysplastic tissue and superficial skin tumours. Dr Gerhard Holst reports.
Similar to photodynamic therapy (PDT) a photo-sensitiser or the pro-drug of a photo-sensitiser is applied either topically or systemically which thereafter accumulates with good selectivity in tumour cells.
Irradiation with light induces fluorescence in the photo-sensitiser molecules and so allows the localisation of the tumour.
However, up to now it has been necessary to shade the area of treatment while a fluorescence diagnostic examination took place as otherwise the ambient light would outshine the weak fluorescence light.
Wood's Light
The so-called Wood's Light (a blacklight equipped magnifying glass which is in widespread use in terms of FD) neither provides working under ambient light nor fluorescence quantification or digital image storage.
In addition, the naked eye can only hardly distinguish between photo-sensitiser and background fluorescence due to low contrast.
This is now overcome by a viewing procedure which has been developed and patented by a company named BIOCAM.
Based on this type of investigation BIOCAM recently introduced a new image processing system for fluorescence diagnosis (FD) called DYADERM, which opens a new field of medical imaging technology. Here the sensitiser is not excited to fluorescence by a coherent lighting but by short and intensive flashes of a flashlight.
Fluorescence is recorded using a 12bit CCD camera, so it is possible to create a digital native colour image and the corresponding fluorescence image of the examined lesion directly in succession.
Overlaid images
Further online image processing generates overlaid images with a false colour coding.
The main benefits of DYADERM are therefore: a. non-invasive and early detection of cancer; b. operation under ambient light; c. simultaneous real time display of fluorescence and clinical image; and d. digital data storage for offline image processing or data mining.
The potential of the system strongly depends on the performance of the applied camera system. DYADERM incorporates the pixelfly CCD camera system (PCO AG,) because of its 12bit dynamic resolution (4096 grey scale values instead of 256 of conventional 8 bit cameras), its versatile control functions (via SDK) and its very compact design.
The camera has been optimised in terms of triggering to serve the functionality of the DYADERM system.
The sequence of images show a colour image of the skin of a patient, a fluorescence image clearly showing the skin tumour position and the processed image, where in false colour the tumour position, known from the fluorescence image, is superimposed and blended into the original image.
Due to PC speed this is done online and can be seen nearly simultaneously by the doctor.
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Dr Gerhard Holst is with Research & Development, PCO AG, Kelheim, Germany. www.pco.de
