Terms Starting with Letter: N naked DNA DNA that is not contained within a liposome or virus. Used in some gene therapies. nanomedicine The potential use of nanoparticles for medical diagnosis and treatment of disease. nanoparticle With dimensions on the order of tens of nanometers, nanoparticles have potential biological uses as therapeutic agents and in molecular imaging. near-infrared fluorescence imaging (NIRF) Imaging of fluorescence photons in the near-infrared range (typically 600-900 nm). A fluorochrome is excited by a smaller wavelength photon, and emits a longer wavelength photon. NIRF imaging can be done in reflectance mode or in tomographic mode. necrosis In contrast to apoptosis which is regulated, necrosis is unordered and unregulated cell death. neoplasm An abnormal tissue that grows and forms a distinct mass that is usually benign or malignant. neu Neu is a tyrosine kinase receptor which has been correlated with breast, gastric and ovarian cancer. nodule a small node nonviral vectors A means of getting DNA into cells via nonviral molecules. normalization Normalization refers to the correction of the PET image data for the inherently non uniform efficiency of various detector systems. Although it is possible to do a very good job in mechanically and electronically matching detectors in a PET system, normalization is used to insure that each detector will yield the same number of corrected counts per unit of activity. nuclear receptor Proteins that are ligand-mediated regulators of gene expression. For example, receptors for steroid hormones are nuclear receptors and can be used to image hormones labeled with a imaging agent. nucleic acid A long-chain alternating polymer of deoxyribose or ribose and phophate groups with nitrogenous bases (adenine, thymine, guanine, cytosine or uracil) as side chains. Examples: DNA or RNA. nucleotide The basic chemical unit in nucleic acid. In RNA, a nucleotide is made up of one of four nitrogenous bases linked to ribose. In DNA, the sugar molecule is deoxyribose instead of ribose. nude mouse A mouse strain with a homozygous mutation for the recessive gene nu. This mutation causes the mice to be born aythmic, resulting in the complete lack of t-cell mediated immunity. The lack of immunity allows the mice to be used for the successful introduction and acceptance of foreign implants. The hairlessness is caused by a closely linked mutation in a gene involved in hair formation.