Reconstruction of absorption and fluorescence contrast for scanning time-domain fluorescence mammography

Abstract

We report on the reconstruction of absorption and fluorescence from measured time-domain diffuse reflectance and transmittance of laser and fluorescence radiation. Measurements were taken on slab-like, diffusely scattering and fluorescent phantoms containing fluorescent inhomogeneities, using fs laser pulses (l = 730 nm) and time correlated single photon counting. The source was scanned across the entrance face of the phantom, and at each source position data were collected in transmission and reflection at various detector positions. These measurements simulate in vivo data that will be obtained employing a scanning, time-domain fluorescence mammograph, where the breast is gently compressed between two parallel glass plates, and source and detector optical fibers scan synchronously at various source-detector offsets, allowing to record laser and fluorescence mammograms. The diffusion equations for the propagation of the laser and fluorescence radiation were solved in frequency domain by the finite element method. Measured time-resolved phantom data were Fourier-transformed to frequency domain prior to image reconstruction. Signal-to-noise ratios were high enough to use several data sets simultaneously in the reconstruction process belonging to various modulation frequencies up to several hundred MHz. To obtain the spatial distribution of the fluorescent contrast agent the Born approximation of the fluorescence diffusion equation was used.