Noninvasive Imaging for Supporting Basic Research

Imaging has long been indispensable in clinical practice. Increasingly, in vivo imaging of small laboratory animals (i.e., mice and rats) has emerged as a critical component of preclinical biomedical research as well (Beckman et al. 2007; Cherry 2006; Gross and Piwnica-Worms 2006; Pomper 2005). Small-animal imaging provides a noninvasive means of assaying biological structure and function in vivo, yielding quantitative, spatially and temporally indexed information on normal and diseased tissues such as tumors. Importantly, because of its noninvasive nature, imaging allows serial (i.e., longitudinal) assay of rodent models of human cancer and cardiovascular, neurological, and other diseases over the entire natural history of the disease process, from inception to progression, and monitoring of the effectiveness of treatment or other interventions (with each animal serving as its own control and thereby reducing biological variability). This also serves to minimize the number of experimental animals required for a particular study. With the ongoing development of genetically engineered (i.e., transgenic and knock out) rodent models of cancer and other critical diseases (Malakoff 2000), such models are increasingly more realistic in recapitulating the natural history and clinical sequelae of the corresponding human disease and the ability to track these disease models long-term is therefore invaluable. Importantly, in contrast to cell or tissue culture-based experiments, studies in intact animals incorporate all of the interacting physiological factors – neuronal, hormonal, nutritional, immunological, etc. – present in the complex in vivo milieu. Intact whole-animal models also facilitate investigation of systemic aspects of disease such as cancer metastasis, which are difficult or impossible to replicate in ex vivo systems. Further, because many of the same imaging modalities – magnetic resonance imaging and spectroscopic imaging (MRI and MRSI), positron emission tomography (PET), single-photon emission computed tomography (SPECT), transmission computed tomography (CT), and ultrasound (US) – used in the clinic are also used in the laboratory setting, the findings of small-animal imaging are readily translatable to patients.