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Biomedical subjects

N S MacDonald

Publications and source records attributed to N S MacDonald.

11 recordsLinked to original sources
PubMed1977

Production by compact cyclotron of radiochemically pure iodine-123 as iodide for synthesis of radiodiagnostic agents.

Iodine-123-labeled radiopharmaceuticals are desirable because they give a high flux of 159-keV photons and a low radiation exposure per millicurie. Procedures suited to a compact cyclotron were developed to produce 50-mCi batches of radiochemically pure iodine-123 as iodide. Iodine-123 is separated from proton-irradiated tellurium-124 by distillation. Aqueous iodide is readily obtained by reduction with thiosulfate. Anhydrous iodide is extracted from the distillate iwth methyl ethyl ketone. The procedures for isolating radiochemically pure iodide are trouble-free, convenient, and reliable. Iodine-123-labeled o-iodohippurate and 16-iodo-9-hexadecenoic acid prepared from our iodide are now being used in clinical trials.

Iodine Radioisotopes↗
PubMed1976

Collimation for imaging the myocardium.

Line-source response functions and modulation transfer functions (MTFs) were used to compare the resolution obtained with four myocardial-imaging agents: 129Cs, 43K, 13N-ammonia, and 81Rb contamination. When an Anger camera with pinhole collimator was used, the order of decreasing resolution was 129Cs, 43K, 13N, and 81Rb. Two techniques were employed to determine the extent to which spatial resolution could be improved. The first, involving the addition of lateral shielding, improved the MTFs for all the agents studied. The second, which utilized a subtraction mode, gave the best overall results. With the second method the MTF curves for 129Cs and 43K became very similar and were superior to both 81Rb and 13N. Both techniques were found useful in improving the spatial resolution of certain myocardial-imaging agents by reducing or eliminating the effects of penetration of the pinhole collimator walls by high-energy photons.

Cesium Radioisotopes↗
PubMed1976

Imaging small pulmonary ischemic lesions after radioactive carbon monoxide inhalation.

A new method is described for imaging small ischemic regions in the lung immediately after a single breath of radioactive carbon monoxide (11CO). A tungsten-collimated scintillation camera is used to visualize the 0.51-MeV annihilation photons due to the 11C. In normal dogs the entire field is cleared of 11CO within 10 sec. However, in dogs with experimentally occluded 2-mm-diam segmental arteries, the ischemic but well-ventilated segment appears as a region of persistent high radioactivity, due most likely to temporary entrapment of 11CO-labeled red blood cells in the ischemic region. This technique also provides a simple noninvasive means for instantly labeling the systemic circulation without left heart catheterization.

Animals↗
PubMed1976

Experimental basis of myocardial imaging with 123I-labeled hexadecenoic acid.

Progress in myocardial perfusion imaging has been slowed by the lack or radiopharmaceuticals with suitable physical and biologic characteristics. Hexadecenoic acid, terminally labeled with 123I, partially overcomes these limitations by providing a compound that concentrates in the myocardium in proportion to relative regional blood flow and carries a gamma-emitter with desirable detection and imaging qualities. After intravenous injection in experimental animals, the clearance half-times of hexadecenoic acid for blood and myocardium are 1.7 and 20 min, respectively. These values compare favorably with 18-carbon fatty-acid analogs labeled with 11C. In acute and chronic infarction, similar distribution patterns are found for hexadecenoic acid and 43K, which indicates that hexadecenoic acid is a suitable substitute for the potassium analogs now in use for myocardial imaging. Because of the high count rates obtainable with 123I-hexadecenoic acid, good-guality images can be acquired in as little as 2-3 min per view. Iodine-123-hexadecenoic acid is potentially a useful radiopharmaceutical for clinical application.

Animals↗
PubMed1975

Myocardial extraction of labeled long-chain fatty acid analogs (38509).

The single circulation myocardial extraction of terminally iodinated hexadecenoic acid (77 plus or minus 11.0%) is approximately two times the extraction of 18 carbon fatty acids (33 plus or minus 5.2%) prepared by iodination of double bonds. The results compare favorably with natural 28 carbon steraic (70 plus or minus 7.5%) and oleic (61 plus or minus 7.8%) acids labeled with carbon-11 in the carboxyl group. It is concluded that terminally radioiodinated long chain fatty acids can be used as substitues for in vivo investigations of fatty acid distribution and in particular may be useful as a regional mycardial blood flow indicator.

Animals↗
PubMedDate not supplied

Lymphocyte involvement in rheumatoid arthritis. Studies during thoracic duct drainage.

Grip strength, ring size, duration of morning stiffness, and the number of tender joints improved significantly in 9 patients with severe rheumatoid arthritis during prolonged continuous removal of thoracic duct lymphocytes through a surgical fistula. There was no improvement in 4 subjects in whom surgery failed to establish satisfactory lymph drainage. Reinfusion of unlabeled or 51Cr-labeled autologous lymphocytes resulted in transient exacerbation of disease activity in 3 subjects. Following reinfusion, some 51Cr-labeled lymphocytes could be found in the inflamed synovium and synovial fluid by autoradiography, and radioactivity was detected over the joints by surface counting of gamma radiation. Active rheumatoid arthritis recurred in all subjects at variable intervals after cessation of lymph drainage. These findings are compatible with the hypothesis that some of the lymphocytes in the thoracic duct lymph are essential for the continued activity of the inflammation associated with rheumatoid arthritis.

Adult↗