An investigation of the use of haematoporphyrin and helium-neon laser excitation for the detection of cancers by means of fluorescent endoscopy

摘要

In this study the use of a He-Ne laser as excitationudsource in fluorescent endoscopy is investigatedudFluorescence endoscopy is based on the principle ofudinjecting a fluorescent tumour localiser prior toudexamination with a fibre-optic endoscope. Tumours markedudby the fluorescent localiser can then be identified by theuddetection of the characteristic fluorescence output of theudlocaliser. The localiser examined in this research isudHaematoporphyrin or Hp.ududPrevious studies with Hp have generally utilised theudviolet portion of the visible spectrum (400nm) to exciteudfluorescence Spectroscopic studies carried out in thisudproject reveal that He-Ne laser light (632 8nm) can beudused to excite Hp fluorescence. It is shown that 632nmudexcitation possesses significant advantages over the useudof violet light for the detection of small tumours deeplyudembedded in healthy tissue.ududOne such type of tumour is early small cell carcinomaudof the tracheo-bronchial (TB) tract. These tumours mayudonly be a few millimetres in extent and up to 0 5mm thickudSuch a small tumour will have very small amounts of the Hpudmarker material. This combined with the fact that Hp has audvery low excitation efficiency at 630nm will result in audvery low fluorescent emission. To detect such a low leveludlight signal a highly efficient illumination and detectionudsystem is required Such a system has been developed andudis described in chapter 3. In vitro experimentationuddemonstrates that the system can detect fluorescence fromudconcentrations of Hp down to as low as 0 01 pg/ml inudmethanol and 0 1 /¿g/ml in water.ududA comprehensive mathematical model has been developedudto predict the response of the detection system for theuddetection of early small cell^TB tumours. The modeludpredicts that the instrument can detect tumours as low asud2 5mm in extent and 0 3mm thick embedded deep within theudsubmucosa of the TB tract.ududIn order to measure the response of the instrument inudconditions which simulate a clinical environment audtumour-tissue phantom has been developed. Experimentsudcarried out on the phantom with the endoscopic apparatusudyield results in very good agreement with those predictedudby the model.ududIn conclusion it has been shown that He-Ne laserudlight can be used as an effective excitation source inudfluorescent endoscopy for the detection of previouslyudundetectable tumours. The use of He-Ne laser excitation inudfluorescent endoscopy could then play a role in the cancerudscreening of high risk sections of the population.