Microimaging and Sensing
A number of different in vivo imaging techniques are routinely used. These techniques differ in resolution, sensitivity, acquisition time etc.
A major goal of CMIR is to apply to clinical practice the molecular imaging techniques developed here. Mouse transgene imaging, for example, is usually performed in a dedicated �MRI system at higher field strength to demonstrate feasibility, and later optimized for clinically relevant systems at 1.5T. Small animal imaging at 1.5T is done in conjunction with specially designed coils to optimize the signal to noise ratio obtained using the small voxel sizes.
Planar nuclear imaging is an important imaging method to track molecules, cells and viruses in the body. Taking advantage of the geometry/size of rodents, high spatial resolution of about 2-3 mm is achieved routinely for 111In and 99mTc radiopharmaceutical imaging, while yielding markedly higher counts compared to pinhole systems.
CMIR has imaging software in place to acquire high resolution SPECT images for both mice and rats, for 3D localization of 111In and 99mTc label drugs, virus particles used for gene delivery, etc. SPECT aids in quantitation of organ delivery by allowing separation of counts from overlapping organs (especially in the abdomen), and results in higher signal-to-noise ratios.
CT micro-imaging of mice is quite useful for evaluating the phenotypic expression of disease in transgenic mice, for example lung cancers, before molecular imaging of efficacy of novel therapies can be initiated. Currently, 50 micron isotropic voxels can be obtained using our � CT systems.
High resolution metabolite maps are achievable in rodents using 18F-labeled compounds and specially designed small animal PET imagers. Dr. Jack Correias group at MGH, has designed and constructed a 1 mm resolution system, small animal PET imaging is available for assessment of transgene activity.
Near Infrared (Optical) Imaging
We use a number of different optical imaging approaches including photon counting (bioluminescence), fluorescence imaging and tomographic imaging.
Cellular and sub-cellular localization of activated probes helps to define the biological basis of the molecular optical imaging used in whole animal reflectance and tomographic systems. In conjunction with collaborators at the Wellman Laser and Steele Radiobiology Research Laboratories, we have used intravital microscopy to identify relative contributions of stroma and tumor cells in signal from whole tumors.