Terms Starting with Letter: C Ca-125 A tumor marker. It is 80% positive in ovarian cancer, and 20% positive in nongynecologic cancers. There are also a few (~5%) false positives. calibration cylinder A cylinder containing a known amount of radioactivity that is used to calibrate a radiation detector, such as those found in a PET scanner. cancer Popular terminology for any malignant neoplasm. carbocyanines Having both a favorable photochemical properties and low photosensitization, these fluorescent dyes are used in optical imaging as contrast agents. carcinoma Any of the various types of malignant neoplasm occurring in epithelial tissue and glands. caspases A group of enzymes involved in proteolysis (breakdown of proteins into simpler soluble substances) during cellular apoptosis. catecholamines An important group of neurotransmitter molecules containing a catechol nucleus. The principle catecholamines are dopamine, adrenaline (epinephrine) and noradrenaline (norepinephrine). Catecholamines are found in various regions of the central and peripheral nervous systems and are of particular importance in the sympathetic nervous system. CBF Cerebral blood flow. Strict definition is blood flow in units of ml/min. By convention CBF refers to ml/min/g tissue which is more correctly called perfusion (i.e., blood flow per mass of tissue). LCBF refers to a local or regional value. CBV Cerebral blood volume. Conventionally given in units of ml/g tissue. LCBV refers to a local or regional value. CCD Camera A CCD is a charge-coupled device – a silicon chip whose surface is divided into light- sensitive pixels. When a photon (light particle) hits a pixel, it registers a tiny electric charge that can be counted. With large pixel arrays and high sensitivity, CCDs can create high- resolution images under a variety of light conditions. A CCD camera incorporates a CCD to take such pictures. (Xenogen website, Glossary) cell surface receptor Used in intercellular communication, a cell surface receptor is a protein or polysaccharide on the surface of cells that recognizes specific molecular messenger compounds. cerebellum A large brain mass occupying the inferior and posterior aspects of the cranium; it consists of two hemispheres united by a central portion, the vermis. The cerebellum assists the motor cortex and basal ganglia by making body movements smooth and coordinated. cerebral blood flow See CBF. cerebral blood volume See CBV. chelate Of or relating to heterocyclic ring containing a metal ion attached by coordinate bonds to at least two other non-metal ions in the same molecule. They are used to detoxify metals or in building target molecules by attaching metals to the target molecules. chromophore A chemical group (as in an azo group) capable of absorbing specific light frequencies thus imparting the color of the compound. Due to this property, they have the potential to be used in optical imaging. chromosome The structural unit of the genetic material consisting of either a single, linear (eukaryotes) or a single, circular (prokaryotes) double stranded DNA molecule and associated proteins. clone A genetically identical copy of a DNA sequence, cell or entire organism. cloning The production of genetically identical cells from a single ancestor. The production of identical copies of a single gene or DNA segment. codon A triplet of three nucleotides in RNA or DNA that specifies a particular amino acid during protein synthesis. coenzyme A nonprotein molecule that is utilized in enzyme catalysis and that is regenerated in subsequent reactions. coincidence detection The simultaneous or near simultaneous detection of two events such as the two annihilation photons by two detectors. Typically, the events fall within 0.5 to 20 nanoseconds of each other. This coincidence event helps to position the location of the annihilation event during the process of image reconstruction. cold nodule A nodule with lower uptake of radioactive tracer than the surrounding cells. combinatorial chemistry. Highly parallel or split-pool chemical synthesis, resulting in thousands to millions of compounds. complementary DNA DNA that is copied from an mRNA template by reverse transcriptase therefore lacking the introns present in genomic DNA. (cDNA) confocal microscopy Method of optical microscopy by which structures in the focal plane are visible and those outside the focal plane are suppressed. Scanning of the focal plane through the object being imaged enables the collection of three-dimensional microscopic image data sets. congenital existing at birth contrast agent A medical imaging enhancer including molecular probes, nonspecific flow and perfusion agents or radiopaque dyes. cyclotron A cyclotron is a particle accelerator in which charged particles travel in a succession of circular orbits of increasing radii (spiral) under the influence of a magnetic field and are accelerated by traversing an electric field produced by a radio-frequency generator. The cyclotron helps to produce positron emitting isotopes by bombarding a stable target isotope with the accelerated particles. cyst An abnormal sac containing gas, fluid, or a semisolid material with a membranous lining. cytokine Any of numerous secreted, small proteins that bind to cell-surface receptors on certain cells to trigger their differentiation or proliferation. cytoplasm The viscious contents of the cell that are contained within the plasma membrane and excluding the nucleus. cytosine (C). One of the bases found in nucleic acids. cytosine deaminase Reporter gene product used for positron emission tomography (PET), magnetic resonance (MR) imaging, and MR spectroscopy that catalyzes the activation of the pro-drug fluorocytosine to the lethal drug fluorouracil.