Time-gated fluorescence imaging of chloroaluminum phthalocyanine tetrasulfonate in a tissue phantom

Abstract

Phthalocyanine derivatives are currently under investigation for use in Photodynamic Therapy, which is a promising treatment for cancer. These materials, which display preferential uptake in cancerous cells, also exhibit high fluorescence yields, and can be used for tumour detection. Problems with steady-state fluorescence techniques such as background autofluorescence can be eliminated by the use of time-resolved techniques. Improved contrast can be obtained with time-resolved techniques because of the differing lifetimes between endogenous and exogenous photosensitisers. An imaging system was constructed using a fast (200 psec) gated CCD camera and a pulsed 635 nm laser diode. A tissue phantom was assembled to test the system by drilling thirty-six wells of varying diameter and depth (10 mm to 1 mm) into a block of polymethyl methacrylate (PMMA). The system was used to record images of chloroaluminum phthalocyanine tetrasulfonate within the wells at differing concentrations in phosphate buffer. A mixture of 1) Intralipid to mimic tissue scatter, 2) Evans blue to mimic tissue absorption, and 3) zinc phthalocyanine tetrasulfonate to mimic healthy tissue autofluorescence of varying depth was placed on top of the PMMA block. These results contribute to the precision of a time-gated imaging system to image living organisms using fluorescence lifetimes.

The use of chloroaluminium phthalocyanine tetrasulfonate (AlPcTS) for time-delayed fluorescence imaging

“…The time-gated imaging system has been described previously (Gundy et al 2003), with the exception of a Nikkor 50 mm f/1.4 lens being used to image an area of 9.0 cm × 9.0 cm for the experiments. The images were collected by an integrated, gateable intensified 4 Picos CCD camera system (Stanford Computer Optics, Munich, Germany).…”

“…Since light penetration increases with increasing wavelength, phthalocyanines would allow for deeper tumour detection compared to first-generation photosensitizers, such as haematoporphyrin derivatives, which have weak absorption in the red (Sharman et al 1999). Some phthalocyanine derivatives, such as chloroaluminium phthalocyanine tetrasulfonate (AlPcTS), also exhibit longer lifetimes (∼7.5 ns) that would still be able to be detected after a delay time of a few nanoseconds (Gundy et al 2003).…”