A thermo-sensitive fluorescent agent based method for excitation light leakage rejection for fluorescence molecular tomography

Abstract

Fluorescence molecular tomography (FMT) is widely used in preclinical oncology research. FMT is the only imaging technique able to provide 3D distribution of fluorescent probes within thick highly scattering media. However, its integration into clinical medicine has been hampered by its low spatial resolution caused by the undetermined and ill-posed nature of its reconstruction algorithm. Another major factor degrading the quality of FMT images is the large backscattered excitation light component leaking through the rejection filters and coinciding with the weak fluorescent signal arising from a low tissue fluorescence concentration. In this paper, we present a new method based on the use of a novel thermo-sensitive fluorescence probe. In fact, the excitation light leakage is accurately estimated from a set of measurements performed at different temperatures and then is corrected for in the tomographic data. The obtained results show a considerable improvement in both spatial resolution and quantitative accuracy of FMT images due to the proper correction of fluorescent signals.

Figure 1.

(a) The instrumentation: (1) CCD camera, (2) filter wheel, (3) light source fiber, (4) galvano-mirrors, (5) agar phantom, (6) laser point illumination, (7) position of the inclusion and thermocouple tip, (8) heating pad and (9) temperature controller. In order to fully demonstrate the efficacy of our method in suppressing excitation leakage, the FT system was set up in reflection mode which yields a higher leakage of the excitation light. Schematic showing the used agar phantom, the tubes containing the ThermoDots and the laser scanning line (red dashed line): (b) side-view and (c) top-view.

Figure 2.

(a) Top view of the phantom showing the two tubes and the position where the profiles are carried-out. (b) Profiles of the fluorescence light obtained during the characterization of ThermoDots. The green and red highlighted areas show the position of the ICG and ThermoDots tubes, respectively. (c) Integral of the fluorescence signals performed at ROIs above the two tubes.

Figure 3.

The fluorescence images acquired using the Standard method and when ThermoDots are present within phantom at T₁ = 15 °C, T₂ = 17 °C and T₃ = 19 °C are presented in the first row. The figure in the second row depicts the profiles along the dashed red lines.

Figure 4.

The excitation light leakage measured using the Standard method (Standard), method 1 (Leak₁), and method 2 (Leak₂) are presented in the first row. The profiles along the dashed red line are presented in the second row.

Figure 5.

The fluorescence data acquired at T₃ = 19 °C corrected using the Standard method (Standard), method 1 (Leak₁), and method 2 (Leak₂) are presented in the first row. The profiles along the dashed red line are presented in the second row.

Figure 6.

The real fluorescence absorption (Real). The reconstructed fluorescence absorption images using: simulated data (Simu), raw data (Raw), and the corrected data using: Standard method (Standard), method 1 (Leak₁), method 2 (Leak₂). In figure, (1)–(3) represent the normalized profiles of the absorption fluorescence (μ_af) along the lines defined by the arrows 1, 2 and 3 on the Real image, respectively. The ratio between the reconstructed profiles is preserved by normalizing them to the maximum of the reconstructed images using simulated data (Simu).