An ultrasound coupled handheld-probe-based optical fluorescence molecular tomography (FMT) system has been in
development for the purpose of quantifying the production of Protoporphyrin IX (PPIX) in aminolevulinic acid
treated (ALA), Basal Cell Carcinoma (BCC) in vivo. The design couples fiber-based spectral sampling of PPIX
fluorescence emission with a high frequency ultrasound imaging system, allowing regionally localized fluorescence
intensities to be quantified . The optical data are obtained by sequential excitation of the tissue with a 633nm
laser, at four source locations and five parallel detections at each of the five interspersed detection locations. This
method of acquisition permits fluorescence detection for both superficial and deep locations in ultrasound field. The
optical boundary data, tissue layers segmented from ultrasound image and diffusion theory are used to estimate the
fluorescence in tissue layers. To improve the recovery of the fluorescence signal of PPIX, eliminating tissue autofluorescence
is of great importance. Here the approach was to utilize measurements which straddled the steep Qband
excitation peak of PPIX, via the integration of an additional laser source, exciting at 637 nm; a wavelength
with a 2 fold lower PPIX excitation value than 633nm.The auto-fluorescence spectrum acquired from the 637 nm
laser is then used to spectrally decouple the fluorescence data and produce an accurate fluorescence emission signal,
because the two wavelengths have very similar auto-fluorescence but substantially different PPIX excitation levels.
The accuracy of this method, using a single source detector pair setup, is verified through animal tumor model
experiments, and the result is compared to different methods of fluorescence signal recovery.