Molecular imaging shedding new light on disease processes and treatments

Molecular imaging is a rapidly developing field that is enlightening diagnosis, drug development and basic biomedical research, blending techniques ranging from ultrasound to MRI, PET, SPECT and a new process called NIRF.Molecular imaging relies on binding a ligand with a target of interest, then using an imaging system that has resolution, sensitivity and depth penetration appropriate for the disease. NIRF - near-infrared fluorescence - allows optical imaging, using photons emitted in the near-infrared and far-red range. Unlike visible light, these frequencies can be detected through tissue up to 10 cm thick. Resolution is in the sub-millimetre range, and it has been applied clinically in retinal angiography, cardiovascular surgery and gastrointestinal endoscopy.Other imaging systems that reveal molecular targets include the nuclear techniques of SPECT and PET, often combined with CT to enhance their anatomical detail, and MRI, which provides molecular and anatomical information in a single mode. Many imaging agents have already been approved, for example fluorodeoxyglucose to detect tumour cell metabolism with SPECT or PET, iron oxide to highlight liver cancer with MRI, gadofluorine to show lipid-rich atherosclerotic plaques, dopamine receptor ligands for investigation of Parkinson's disease, and a variety of compounds to demonstrate inflammation in arthritis and infectious diseases.Earlier, specific detection of disease is one potential benefit of molecular imaging. For example, MRI can be enhanced with a ligand to highlight abnormal macrophages in lymph nodes to show occult prostate cancer metastases as small as 2 mm. In contrast, conventional MRI detects lymph nodes only when they exceed 8-10 mm. Activated macrophages in atherosclerotic plaques can be detected in a similar way, detecting high-risk lesions to guide treatment or research.The technology can also be used to assist efficient, rational discovery and development of new drugs. Once a drug or prodrug, or its target, is labelled, then it is possible to track the presence, efficacy and distribution of the drug in vivo. In basic research, molecular imaging has helped describe key enzymatic and cellular events in inflammation, angiogenesis, apoptosis, leucocyte and stem cell traffic, and thrombosis.Reference...