A hyperspectral approach for recovering agent excretion biodistributions using whole-body fluorescence cryo-imaging

Understanding the uptake and clearance kinetics of new drugs and contrast agents is an important aspect of drug development that typically involves a combination of imaging and analysis of harvested organs. Although these techniques are well-established and can be quantitative, they generally do not preserve high resolution biodistribution information. In this context, fluorescence whole-body cryo-imaging is a promising technique for recovering 3D drug/agent biodistributions at a high resolution throughout an entire study animal at specific time points. A common challenge associated with fluorescence imaging in tissue is that agent signal can be confounded by endogenous fluorescence signal which is often observed in the visible window. One method to address this issue is to acquire hyperspectral images and spectrally unmix agent signal from confounding autofluorescence signals using known spectral bases. Herein, we apply hyperspectral whole-body cryo-imaging and spectral unmixing to examine the distribution of multiple fluorescent agents in excretion organ regions.

Evaluating uptake of multiple fluorescent contrast agents in brain tumors simultaneously using whole animal multi-spectral cryo-imaging

MRI images of gadolinium-based contrast agents (GBCA's) acquired before surgery are often registered to patients and used to guide surgical resection of intracranial tumors. Yet, the accuracy of these MR images in describing the surgical field degrades as surgery progresses; a well-recognized problem which has prompted efforts to develop new techniques that provide updated guidance information on residual tumor location. These efforts span a wide array of technologies, including image updating with deformation models, intraoperative MRI, and fluorescence guided surgery, among others. However, introduction of a straightforward technique that provides surgeons with a current view of GBCA distribution in real time remains an important goal. In this context, development of a fluorescent agent that recapitulates the kinetic behavior of GBCA's could provide familiar information directly in the surgical field in real time. To advance this strategy, we have begun identifying fluorescent contrast agents that show similar kinetic behavior to GBCA's. Using a novel hyperspectral whole body cryo-imaging system, we acquired high-resolution 3-D volumes of the distribution of multiple candidate fluorophores in whole heads bearing orthotopic brain tumors. Preliminary results reveal significant differences in the distribution of candidate optical agents, some of which show strong similarity to the GBCA uptake. Identification and eventual translation of a reliable GBCA-optical analog could improve and simplify surgical resection of brain tumors.

Multi-angle projection imaging of short-wave infrared (SWIR) fluorescence for small animal optical tomography

Short-wave infrared imaging in tissue in the 1000-2000 nm range is characterized by reduced photon scatter and comparable or higher absorption compared to the NIR-I regime. These characteristics have implications for the performance of fluorescence molecular tomography (FMT) techniques, potentially improving the resolution of sub-surface structure, possibly at the expense of depth sensitivity. To examine these questions, we have developed a SWIR small animal fluorescence tomography system. This instrument acquires multi-angle SWIR projection images of a stationary platform through a rotating gantry technique. These images are then processed for tomographic reconstruction of the SWIR fluorescence activity. Herein, we describe the development of this system and show multi-angle images from a mouse carcass containing a SWIR-specific fluorophore inclusion.