RESUMO
Phantoms are frequently used in medical imaging systems to test hardware, reconstruction algorithms, and the interpretation of data. This report describes and characterizes the use of powdered graphite as a means of adding a significant reactive component or permittivity to useful phantom media for electrical impedance imaging. The phantom materials produced have usable complex admittivity at the electrical impedance tomography (EIT) frequencies from a few kilohertz to 1 MHz, as measured by our EIT system (ACT4) and by a commercial bioimpedance analyzer (BIS 4000, Xitron). We have also studied a commercial ultrasound coupling gel, which is highly electrically conductive and semisolid but that permits objects to move within it. The mixture of agar-graphite and gel-graphite, increases in permittivity and conductivity are proportional to the graphite concentration. We also report the use of a porous polymer membrane to simulate skin. A thin layer of this membrane increased resistance and the characteristic frequency of the phantoms, providing a promising candidate to simulate the effect of skin and the layered structure of a breast or other anatomical structure. The graphite also provides a realistic level of "speckle" in ultrasound images of the phantom, which may be useful in developing dual-mode imaging systems with ultrasound and the EIT.
Assuntos
Grafite , Imagens de Fantasmas , Tomografia/métodos , Ágar , Impedância Elétrica , Géis , Humanos , Polímeros , Porosidade , SulfonasRESUMO
Two new classes of tricyclic-based corticotropin-releasing factor (CRF(1)) receptor-1 antagonists were designed by constraining known 1H-pyrrolo[2,3-b]pyridine and 1H-pyrazolo[3,4-b]pyridine ligands. Pyrrole- and pyrazole-based molecules 19g and 22a, respectively, were discovered that potently bind the recombinant CRF(1) receptor (K(i) = 3.5, 2.9 nM) and inhibit adrenocorticotropic hormone (ACTH) release from rat pituitary cell culture (IC(50) = 14, 6.8 nM). These compounds show good oral bioavailabity (F = 24%, 7.0%) and serum half-lives in rats (t(1/2) = 6.3, 12 h) and penetrate the rat brain ([brain]/[plasma] = 0.27, 0.52) but tend toward large volumes of distribution (V(D) = 38, 44 L kg(-1)) and rapid clearances (CL = 70, 43 mL min(-1) kg(-1)). When given orally, both the pyrazole and the pyrrole leads dose-dependently inhibit stress-induced ACTH release in vivo. ACTH reductions of 84-86% were observed for 30 mg kg(-1) doses.
Assuntos
Compostos Heterocíclicos com 3 Anéis/síntese química , Pirazóis/síntese química , Piridinas/síntese química , Pirróis/síntese química , Receptores de Hormônio Liberador da Corticotropina/antagonistas & inibidores , Acenaftenos , Hormônio Adrenocorticotrópico/antagonistas & inibidores , Animais , Disponibilidade Biológica , Barreira Hematoencefálica/metabolismo , Células Cultivadas , AMP Cíclico/biossíntese , Compostos Heterocíclicos com 3 Anéis/farmacocinética , Compostos Heterocíclicos com 3 Anéis/farmacologia , Humanos , Técnicas In Vitro , Masculino , Camundongos , Hipófise/citologia , Pirazóis/farmacocinética , Pirazóis/farmacologia , Piridinas/farmacocinética , Piridinas/farmacologia , Pirróis/farmacocinética , Pirróis/farmacologia , Ensaio Radioligante , Ratos , Ratos Sprague-Dawley , Receptores de Hormônio Liberador da Corticotropina/metabolismo , Estresse Psicológico/metabolismo , Relação Estrutura-AtividadeRESUMO
A new method for stereospecific synthesis of P-chiral phosphorothioates based on intramolecular nucleophile catalysis was developed.
Assuntos
Oligonucleotídeos Antissenso/química , Oligonucleotídeos Antissenso/síntese química , Tionucleotídeos/química , Tionucleotídeos/síntese química , Catálise , Estrutura Molecular , EstereoisomerismoRESUMO
A modular strategy has been applied to synthesize large, porous, self-assembling capsules. The coupling of tricyclic building blocks incorporating glycoluril hydrogen-bonding units and derivatives of triethylbenzene produces monomers which readily form homo- and heterodimeric assemblies (calculated structure is shown). Large guests can be trapped while small solvent molecules flow freely through the pores of the capsules.