Optimizing MRI signal-to-noise ratio for quadrature unmatched RF coils: two preamplifiers are better than one.

Using separate preamplifiers for the two outputs of a quadrature receive coil (and then combining the preamplifier outputs in a quadrature hybrid) provides a better signal-to-noise ratio (SNR) than is obtained by directly combining the quadrature outputs in a hybrid followed by a single preamplifier. The advantage of the two-preamplifier configuration increases when the body coil impedance changes and is no longer matched to 50 ohms. Using 0.4 dB noise figure preamplifiers, theory predicts 1.53, 0.42, 0, 0.42, and 1.53 dB SNR advantage of the two-preamplifier configuration over the one-preamplifier arrangement at body coil impedances of 12.5, 25, 50, 100, and 200 ohms, respectively. Experimental hot/cold resistor noise figure measurements indicate 2.86, 0.65, 0.36, 0.83, and 1.40 dB noise figure advantage for the two preamplifier configuration relative to the one-preamplifier configuration at those impedances. Empirical gains larger than theoretically calculated are attributable to insertion losses of various circuit elements, such as the quadrature hybrid, for the one-preamplifier configuration.

Immunochemical analysis of insect carbohydrate antigenic determinants: recognition of a terminal alpha-linked N-acetylgalactosamine-containing epitope of Calliphora vicina neutral glyco(sphingo)lipids and detection in additional orthopteran and dipteran species.

A cloned mouse hybridoma was established that secreted a monoclonal antibody directed against certain neutral glycosphingolipids of the third-instar larvae of Calliphora vicina (Insecta: Diptera). The isotype of the designated monoclonal antibody CNF-I (Calliphora Neutral Fraction) was determined as IgG3. By the use of purified neutral glycosphingolipids of C. vicina, qualitative thin-layer chromatography immunostaining and semi-quantitative enzyme-linked immunosorbent assay determinations, the epitope was specified as a terminal alpha 1-4-linked N-acetylgalactosamine to subterminal N-acetylgalactosamine, which is present on the components GalNAc alpha 4GalNAc beta 4GlcNAc beta 3Man beta 4Glc beta lCer (N5a) and GalNAc alpha 4GalNAc beta 4-(6' PEtn-)GlcNAc beta 3Man beta 4Glc beta lCer (Nz5a). After enzymatic removal of the terminal alpha-N-acetylgalactosamine residue, the epitope reactivity was destroyed. The distribution of the CNF-I recognized epitope among neutral glycolipids of other insects was shown for: Locusta migratoria (Insecta: Orthoptera); and, Chironomus tentans and Drosophila melanogaster (Insecta: Diptera).