Laboratory for Experimental Biological Imaging Systems (EBIS)
Director: Dr. Daniel Razansky
The main direction of the Laboratory for Experimental Biological Imaging Systems (EBIS) is the development of new imaging approaches that allow non-invasive or minimally invasive interrogations of function and gene-expression in living subjects. The ultimate goal is to allow anatomic, functional and molecular imaging at various scales in intact tissues, whole animals and organs. Our particular focus is the development of novel probing and tomographic techniques using broad range of available spectra, from diffuse light and photoacoustics to ultrasonics and microwaves. We often use a combination between several imaging methods and existing modalities like MRI and CT in order to increase the amount of useful information provided by our images.This technology, when combined with appropriate molecular markers and probes can enable probing of disease and function, noninvasive visualization of development and morphogenesis as well as elucidation of expression patterns in vivo. It is expected that our new imaging systems will enable detection and characterization of disease states even before anatomic changes become apparent. They could also revolutionarize drug discovery and development by real-time in-vivo monitoring of drug effects at the molecular level in intact tissues. Below are some examples of applications that enable us to move forward in all aspects of this multi-disciplinary research.
Imaging Protease Activity
Systematic efforts are under way to develop novel technologies that would allow molecular sensing in intact organisms in vivo. Using near-infrared fluorescent molecular beacons and inversion techniques that take into account the diffuse nature of photon propagation in tissue, we were able to develop a series of new tomographic modalities based on optical and optoacoustic approaches that make it possible to obtain three-dimensional in vivo images of molecular bio-markers. In an example below, a protease activity in orthopic gliomas is visualized using Fluorescence Molecular Tomography (FMT). This system was used to three dimensionally image enzyme-activatable fluorochromes, within animal bodies. It was found that fluorescence activity can be detected with high positional accuracy in deep tissues, that molecular specificities of different beacons towards enzymes can be resolved and that tomography of beacon activation is linearly related to enzyme concentration.The new tomographic imaging methods offer a range of new capabilities for studying biological function; for example, identifying molecular-expression patterns by multispectral imaging or continuously monitoring the efficacy of therapeutic drugs.
Drug Responses
The ability to non-invasively image molecular processes in-vivo is an emerging reality using different reporter and detection approaches. Molecular imaging has been heralded to lead to earlier detection than current anatomical imaging approaches, which typically detect late stage abnormalities. Another important prospect of molecular imaging is the ability to examine and quantify treatment responses in-vivo by monitoring specific primary molecules or downstream targets. Therapeutic efficacy could then be probed dynamically on time-scales of hours to days. This is in contrast to the mainstay of today's healthcare with traditionally late end points of drug efficacy, a practice that often impairs prompt revision and exclusion of ineffective treatment strategies with potentially lethal results.Tomographic techniques based on accurate modeling of photon propagation in tissues and subsequent mathematical inversion have the possibility to overcome the limitations of planar imaging, and provide quantitative three-dimensional information of optical contrast. Figure below shows images of apoptotic tumor response following treatment obtained in-vivo from an animal implanted with a sensitive (left side) and resistant (right side) Lewis Lung Carcinoma tumors.
Multi-Spectral Optoacoustic Tomography (MSOT)
Optoacoustic (or photoacoustic) tomography is a hybrid imaging modality that has recently demonstrated unprecedented high-resolution imaging of chromophore distribution and vasculature deep in tissues of small animals. Optoacoustic imaging relies on detection of ultrasonic signals induced by absorption of pulsed light. The amplitude of the generated broadband ultrasound waves reflects local optical absorption properties of tissue. Since scattering of ultrasonic waves in biological tissues is extremely weak, as compared to that of light, biomedical optoacoustic imaging combines high optical absorption contrast with good spatial resolution limited only by ultrasonic diffraction. Originally, optoacoustic imaging of tissues targeted endogenous tissue contrast, primarily resolving oxy- and deoxy-hemoglobin and different vascular structures. We have developed a Multi-Spectral Optoacoustic Tomography (MSOT) method, capable of high resolution 3D visualization of molecular probes located deep in scattering living tissues. The method is therefore capable of simultaneously deliver anatomical, functional and molecular information with both high resolution and penetration capabilities. In the figure below, we resolve three-dimensional fluorescence probe distribution deep in wild-type Balb/c mouse with below 150 microns spatial resolution and 25 fmol sensitivity. As opposed to most previous optoacoustic studies, assuming planar illumination and nearly homogenous light distribution within appropriately selected sections of tissue, we have applied an imaging configuration suitable for whole-body small animal imaging applications.
Mesoscopic Fluorescence Tomography (MFT)
Real-time whole body in-vivo imaging techniques at dimensions that lie between optical microscopy (below 0.5 mm) and macroscopy (above 1cm) are currently not adequate to follow the dynamics and coordination of animal development; e.g., developing insects, animal embryos or small animal extremities. By utilizing a photon transport description using a modified Fermi simplification to the Fokker-Planck approximation, we demonstrate that fluorescence tomography can yield whole body visualization of three-dimensional structures of developing Drosophila tissues in-vivo and over time. In particular, we follow the morphogenesis of GFP-expressing salivary glands and wing imaginal discs in the opaque Drosophila pupae in real time. Our mesoscopic technique is based on a modified standard laboratory microscope and comes to fill the gap that exists between optical microscopy and current state-of-the art optical macroscopy. While the resolution of the approach is exchanged for penetration depth, the method adds ‘time’ as a new dimension in the study of morphological changes during metamorphosis and potentially as a response to mutations and internal or external stimuli.
