Fluorescence imaging of vascular endothelial growth factor in tumors for mice embedded in a turbid medium

Abstract

We demonstrate the feasibility of fluorescence imaging of deeply seated tumors using mice injected with an angiogenesis tracer, a vascular endothelial growth factor conjugated with the infrared dye cyanine 7 (VEGF/Cy7). Our optical-only imaging reconstruction method separately estimates the target depth, and then applies this information to reconstruct functional information such as fluorophore concentration. Fluorescence targets with concentrations as low as sub-25 nM are well reconstructed at depths up to 2 cm in both homogeneous and heterogeneous media with this technique.

Figure 1

Diagram of the frequency-domain system with optical probe and arrangements for imaging experiments. Legend: OS is oscillator; LD is laser diode; LO is local oscillator; BP is bandpass; Pre-amp is preamplifier; Amp is amplifier; CSF is collimation system and filter; PMT is photomultiplier tube; and PC is personal computer. Measurement and reference signals are collected by the computer, and the optical switches are controlled by the same computer. Four laser diodes were in the system, but only one was used for the reported experiments.

Figure 2

(a) The diagram of detection optics (CSF in Fig. 1). (b) Diagram of the optical probe.

Figure 3

Reconstructed fluorescence image of a 50-nM Cy7 target in 2.0-nM background at 1.6-cm reconstructed depth. The first slice is reconstructed at 0.6 cm depth and the last one is at 3.6 cm. The increment in each slice is 0.5 cm in depth.

Figure 4

The reconstructed depth using the optical estimation algorithm plotted against the experimentally measured depth for different concentrations of targets at several depths.

Figure 5

The concentrations of fluorophores reconstructed at reconstructed depths for the cases shown in Fig. 4.

Figure 6

Reconstructed fluorescence image of a 100-nM Cy7 target embedded in chicken breast. The first slice is reconstructed at 0.65 cm depth and the last one is at 3.65 cm. The increment in each slice is 0.5 cm in depth.

Figure 7

Plot of the reconstructed depths for the tumors in two mice versus experimentally measured depths.

Figure 8

Reconstructed fluorescence images of tumor marked with VEGF∕Cy7 conjugate in mouse 1 at different reconstructed depths: (a) 0.43 cm, (b) 1.02 cm, (c) 1.46 cm, and (d) 2.0 cm. The rest of the slices in each figure correspond to coarse mesh in the background region. The depth is shown in the title of each subimage.

Figure 9

Reconstructed fluorescence images of tumor marked with VEGF∕Cy7 conjugate for mouse 2 at different reconstructed depths: (a) 0.51 cm, (b) 1.05 cm, (c) 1.53 cm, and (d) 2.0 cm. The rest of the slices in each figure correspond to coarse mesh in the background region. The depth is shown in the title of each subimage.