Multimodality Biomolecular Imaging Guest Editor

Discoveries in the field of molecular biology over the past two decades have radically altered how bioengineers approach biological and diagnostic imaging. The genetic and biochemical mechanisms underlying cancer, for example, provide new opportunities for detection, classification, and treatment of multiform, complex disease processes. Cancer is a principal application of molecular imaging, as we see from papers in this issue, for good reasonVoncology represents 37% of all clinical imaging in the United States. Medical imaging was originally developed a century ago as a tool for viewing gross anatomy noninvasively; the applications were diagnosis and surgical planning. As technology improved, the number of medical imaging modalities expanded to meet the growing need for more detailed diagnostic information with greater sensitivity and improving spatial resolution. For the past several decades, it has been possible to image functional properties of the body such as cardiac dynamics, blood volume and flow, metabolic activity, and biochemical features. Medicine now utilizes a broad range of modalities to generate image contrast for the specific information required to accurately diagnose diseases in patients with variable physiological characteristics. Recently, imaging scientists have sought to combine diverse data from simultaneous imaging acquisitions to more accurately blend the anatomical and functional information; to improve quantitative estimation of substrate uptake, blood flow, and like features; or to use data from one modality to improve the image reconstruction of another. Molecular imaging represents the next phase in the evolution of medical imaging. It incorporates genomic and proteomic advances into existing multimodality imaging approaches. The premise offered by molecular biology through the systems-biology perspective on disease management is that the phenotype of cells, and indeed whole organisms, can be predicted when they are considered products of genes interacting with their environment. Thus, a greater understanding of how cells react to and control environmental factors is possible with in vivo imaging tools. Molecular imaging allows us to see the interactions of signaling molecules with sites on cell membranes and extracellular matrix that characterize normal and pathological biological processes. One goal in cancer molecular imaging is to visualize the dynamics of genetic mutations and secondary changes in gene expression that predict tumor growth and metastatic potential. Such information would enable earlier detection in patients and the design of more individualized treatment strategies. However, cancer has also been viewed as an inappropriate response of cells to their environment. Thus, despite its genetic etiology, environmental factors promoting tumor progression also are targeted by molecular imaging techniques. Accordingly, molecular imaging is valued as an in situ tool for basic research and drug discovery as much as it is for clinically diagnosis. Many approaches to molecular imaging are designed around exogenous molecular probes (targeted contrast agents) that bind preferentially to macromolecules or cell membrane structures, or they are transported into the cell, all in response to specific biological stimuli. Probes introduced into the blood stream accumulate at Molecular imaging represents the next phase in the evolutionofmedical imaging and this issue describes many aspects of imaging technologies that can be combined to efficiently enhance diagnostic performance.