Fluorescence tomographic imaging in turbid media using early-arriving photons and Laplace transforms

Abstract

We present a multichannel tomographic technique to detect fluorescent objects embedded in thick (6.4 cm) tissue-like turbid media using early-arriving photons. The experiments use picosecond laser pulses and a streak camera with single photon counting capability to provide short time resolution and high signal-to-noise ratio. The tomographic algorithm is based on the Laplace transform of an analytical diffusion approximation of the photon migration process and provides excellent agreement between the actual positions of the fluorescent objects and the experimental estimates. Submillimeter localization accuracy and 4- to 5-mm resolution are demonstrated. Moreover, objects can be accurately localized when fluorescence background is present. The results show the feasibility of using early-arriving photons to image fluorescent objects embedded in a turbid medium and its potential in clinical applications such as breast tumor detection.

Figure 1

Schematic diagram of experimental apparatus and sample geometry.

Figure 2

Typical streak camera output in phantom experiments. (a) Embedded fluorescent object close to the center of the beaker. (b) Object 1 mm away from the center. Time increases from top to bottom, and detection channels 1 through 8 are displayed from left to right. The light regions are signals.

Figure 3

Determination of the optimal s value, based on a diffusion theory calculation of the signal level. The adequate S/N level, determined by the experimental conditions and desired imaging resolution, is schematically represented by the horizontal dashed line.

Figure 4

Comparison of experimentally estimated object positions with the actual positions. The open symbols are the actual positions of the objects, and the filled symbols are the experimental estimates. The stars denote the collapsed positions when the algorithm cannot resolve the two objects.

Figure 5

Localization result at 10:1 contrast ratio. The open symbols are the actual positions of the objects, and the filled symbols are the experimental estimates.