Early photon tomography allows fluorescence detection of lung carcinomas and disease progression in mice in vivo

Abstract

Imaging of targeted fluorescent probes offers significant advantages for investigating disease and tissue function in animal models in vivo. Conversely, macroscopic tomographic imaging is challenging because of the high scatter of light in biological tissue and the ill-posed nature of the reconstruction mathematics. In this work, we use the earliest-transmitted photons through Lewis Lung Carcinoma bearing mice, thereby dramatically reducing the effect of tissue scattering. By using a fluorescent probe sensitive to cysteine proteases, the method yielded outstanding imaging performance compared with conventional approaches. Accurate visualization of biochemical abnormalities was achieved, not only in the primary tumor, but also in the surrounding tissue related to cancer progression and inflammatory response at the organ level. These findings were confirmed histologically and with ex vivo fluorescence microscopy. The imaging fidelity demonstrated underscores a method that can use a wide range of fluorescent probes to accurately visualize cellular-and molecular-level events in whole animals in vivo. (5)] or identifying proteins and molecular pathways of development, function, and disease in vivo. Further enhanced by sensing of spectrally separated fluorescent molecules, fluorescence microscopy currently offers unparalleled insights in the study of cellular and protein interactions. In principle, fluorescence technology could be similarly used to study normal and diseased tissues at the whole-organ and live-animal level. However, there remain significant challenges in imaging beyond a few hundred micrometers in depth because of the high degree of light scatter in tissues, which arises from photon interactions with cellular membranes and organelles. Currently, fluorescence macroscopic imaging is largely performed by illuminating tissue at the fluorochrome's excitation wavelength and detecting the emission from within the animal's body by using appropriate spectral filters. Photographic and planar-fluorescence-imaging implementations of this approach offer only 2-dimensional views and largely qualitative data, because they do not consider the nonlinear relation of photon strength to lesion depth and tissue optical properties. In response, tomographic approaches have been developed to overcome the limitations of these methods (6-8). Optical tomography utilizes multiprojection measurements and physical models of photon propagation to quantitatively retrieve fluorochrome biodistribution in tissues. However, the physical limits of imaging performance of current tomographic implementations ultimately depend on the tissue optical properties-primarily scattering-which leads to a highly ill-posed (i.e., inaccurate) inverse problem that reduces the spatial resolution and yields images that are highly dependent on the particulars of the reconstruction algorithm used.To develop a next-generation optical tomographic method that can selectively reduce the effects of tissue scattering to improve imaging accuracy, we developed a sy...

Adaptive wide-field optical tomography

“…Figure 12(a) and 12(b) shows ∼200% increase in the number of s-d pairs for excitation signal and ∼80% in the fluorescence signal at the early gates, with a smaller yet significant improvement for the maximum gate (∼25% for fluorescence field, 15% for excitation field). The improvement in the time-gated signal at the early gates and the late gates establishes the advantages of this imaging technique for high-resolution optical reconstruction [23][24][25] and lifetime multiplexing applications, respectively.…”

Computed Tomography-guided Time-domain Diffuse Fluorescence Tomography in Small Animals for Localization of Cancer Biomarkers

“…However, CCD cameras have a limited dynamic range and read-out noise limits their ultimate sensitivity. The second design avoids the potential limitations of CCD camera detection by employing highly sensitive single-photon counting technology based on the use of such detectors as photomultiplier tubes or avalanche photodiodes [10][11][12][13] . The drawback of these more sensitive detection methods is that each detector can only collect light at a single point; therefore, to achieve dense tissue sampling, either many detectors have to be used (which is very expensive), or many projections have to be imaged with the same detector (which can be time consuming).…”

“…The majority of research groups have invested in charge-coupled device (CCD)-based systems that provide abundant tissue-sampling but suboptimal sensitivity [4][5][6][7][8][9] , while our group and a few others [10][11][12][13] have pursued systems based on very high sensitivity detectors, that at this time allow dense tissue sampling to be achieved only at the cost of low imaging throughput. Here we demonstrate the methodology for applying single-photon detection technology in a fluorescence tomography system to localize a cancerous brain lesion in a mouse model.…”

Advances in cellular, subcellular, and nanoscale imaging in vitro and in vivo

“…This idea was first described by Turner et al in 2005, named ''diffuse optical tomography by use of early photons'' (48). The reconstruction of the imaged volume in this form of tomography mostly requires the rotation of the object (47). Recently, the group of Vasilis Ntziachristos in Munich has further developed this technique in order to meet future requirements (Table 1).…”

“…as ''ballistic'' photons, but will experience a certain degree of ''snaking'' that will increase the propagation path to the detector as the photon deviates from the straight ballistic route. To exemplify the effect of tissue light scattering, REVIEW ARTICLE a 2.2-cm path was found to broaden a 100 fs laser pulse to 1.5 ns (47). As a longer path implies an increased time-offlight of the photon, its effective lifetime will increase.…”