Use of paramagnetic chelated metal derivatives of polysaccharides and spin-labeled polysaccharides as contrast agents in magnetic resonance imaging.

Soluble and insoluble polysaccharides were derivatized with diethylenetriaminepentaacetic acid (DTPA) and/or spin-labeled with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). Polysaccharides derivatized with DTPA were prepared via cyanogen bromide activation, coupling to a diamine linker, and to DTPA anhydride. Spin-labeled polysaccharides were also prepared via cyanogen bromide activation. The extent of derivatization for dextran (18 kDa) was about 120 glucose units per DTPA, and for cellulose and starch about 15-30 units per DTPA. For spin-labeled polysaccharides, the average loading ranged from 1 nitroxide per 16 glucose units for starch to 181 for dextran (82 kDa). These derivatized paramagnetic polysaccharides were shown to be more effective relaxants than the small paramagnetic molecules alone. Both soluble and insoluble polysaccharide-linker-DTPA-Gd(III) complexes were effectively cleared from the body (rats) after oral administration. After intravenous administration, the biodistribution of dextran-linker-DTPA-Gd(III) complexes differed significantly from that of GdDTPA. Reduction of the nitroxide by ascorbic acid was retarded in the polysaccharide derivatives, particularly in starch derivatized with both nitroxide and linker-DTPA-Cu(II). These agents showed contrast enhancement in the gastrointestinal tract of rabbits.

Issues in the evaluation of a community psychogeriatric service.

The need for evaluation of community psychogeriatric programs is stressed. The results of the evaluation of an outpatient service, with a liaison component, based in a community general hospital are presented. The use of treatment outcome scales, user satisfaction surveys, and a study of cost effectiveness are discussed. The issues of needs assessment, service models, staffing, target population, and the role of the family physician are addressed. It is recommended that evaluation processes be initiated by psychogeriatric services and that program data collection be developed in a manner that allows for service comparability, the assessment of ongoing community needs and the determining of program effectiveness.

Characterization and in vivo distribution of 99mTc- and 111In-labelled magnetite.

Magnetite (Fe3O4) particles 0.1-0.5 microns in diameter doped with either 99mTc or 111In have been prepared and characterized by electron microscopy and Mössbauer spectroscopy. The time courses of their distributions after injection into rats were determined, including studies by gamma-camera imaging; the main targets were the liver and lung. The radiolabelled magnetic agents may be of value in research studies combining radio- and magnetic resonance imaging procedures.

Technetium-99m d,l-HM-PAO: a new radiopharmaceutical for SPECT imaging of regional cerebral blood perfusion.

Following investigation of a large number of new ligands based upon propylene amine oxime (PnAO) the d,l-diastereoisomer of hexamethyl propyleneamine oxime (HM-PAO) was selected as the preferred ligand for 99mTc as a tracer for cerebral perfusion imaging. The neutral, lipophilic 99mTc complex of d,l-HM-PAO was formed in high yield by stannous reduction of 99Mo/99mTc generator eluate using a kit formulation of the ligand. Two minutes following i.v. administration of this complex in rats, 2.25% of the injected dose appears in the brain. Little washout of the tracer is observed up to 24 hr postinjection. By qualitative autoradiographic comparison with iodoantipyrine this new radiopharmaceutical displays blood flow dependent brain uptake with little redistribution of the tracer over time. The lipophilic 99mTc complex converts slowly in vitro to a secondary complex. This conversion process may account for the ability of [99mTc]d,l-HM-PAO to be retained within the brain without redistribution.