Molecular imaging: state of the art

Molecular imaging includes all imaging methods applied in the identification, characterization and assessment "in vivo" of biological processes which occur at the cellular and molecular level. Molecular imaging parallels the remarkable advances achieved in the medical field, culminated in the sequencing of human DNA, the genome project. The understanding of the genetic basis of diseases and of human biology in general, together with the development of new drugs, led to a growing need for novel, sensitive and safe imaging technology to be rapidly translated from animal models into patients. The present evaluation of presence/absence of disease is based on anatomic and morphologic changes, the result of underlying molecular alterations. Direct "in vivo" visualization of these alterations allows early diagnosis before the onset of typical pathologic manifestations. Similarly, short-term effects of therapy can be directly visualized. In a near future, "evidence-based" medicine will become "presymptomatic" medicine. Histopathology will be replaced by "molecular pathology" with genomic implications in disease classification. In the near future the conventional morphologic methods should be supported and then replaced by the new functional and molecular methods with additional information proved useful for the diagnostic approach. In this article, the potentialities and applications of Nuclear Medicine, Magnetic Resonance Imaging, Optical Imaging and Contrast-enhanced Ultrasound are reviewed.