Reduction of Fe(III), Mn(IV), and toxic metals at 100 degrees C by Pyrobaculum islandicum.
(33/1995)
It has recently been noted that a diversity of hyperthermophilic microorganisms have the ability to reduce Fe(III) with hydrogen as the electron donor, but the reduction of Fe(III) or other metals by these organisms has not been previously examined in detail. When Pyrobaculum islandicum was grown at 100 degrees C in a medium with hydrogen as the electron donor and Fe(III)-citrate as the electron acceptor, the increase in cell numbers of P. islandicum per mole of Fe(III) reduced was found to be ca. 10-fold higher than previously reported. Poorly crystalline Fe(III) oxide could also serve as the electron acceptor for growth on hydrogen. The stoichiometry of hydrogen uptake and Fe(III) oxide reduction was consistent with the oxidation of 1 mol of hydrogen resulting in the reduction of 2 mol of Fe(III). The poorly crystalline Fe(III) oxide was reduced to extracellular magnetite. P. islandicum could not effectively reduce the crystalline Fe(III) oxide minerals goethite and hematite. In addition to using hydrogen as an electron donor for Fe(III) reduction, P. islandicum grew via Fe(III) reduction in media in which peptone and yeast extract served as potential electron donors. The closely related species P. aerophilum grew via Fe(III) reduction in a similar complex medium. Cell suspensions of P. islandicum reduced the following metals with hydrogen as the electron donor: U(VI), Tc(VII), Cr(VI), Co(III), and Mn(IV). The reduction of these metals was dependent upon the presence of cells and hydrogen. The metalloids arsenate and selenate were not reduced. U(VI) was reduced to the insoluble U(IV) mineral uraninite, which was extracellular. Tc(VII) was reduced to insoluble Tc(IV) or Tc(V). Cr(VI) was reduced to the less toxic, less soluble Cr(III). Co(III) was reduced to Co(II). Mn(IV) was reduced to Mn(II) with the formation of manganese carbonate. These results demonstrate that biological reduction may contribute to the speciation of metals in hydrothermal environments and could account for such phenomena as magnetite accumulation and the formation of uranium deposits at ca. 100 degrees C. Reduction of toxic metals with hyperthermophilic microorganisms or their enzymes might be applied to the remediation of metal-contaminated waters or waste streams. (+info)
Structural characterization of a bridged 99Tc-Sn-dimethylglyoxime complex: implications for the chemistry of 99mTc-radiopharmaceuticals prepared by the Sn (II) reduction of pertechnetate.
(34/1995)
Reduction of pertechnetate by tin(II) in the presence of dimethylglyoxime is shown, by single crystal x-ray analysis, to yield a technetium-tin-dimethylglyoxime complex in which tin and technetium are intimately connected by a triple bridging arrangement. One bridge consists of a single oxygen atom and it is hypothesized that this bridge arises from the inner sphere reduction of technetium by tin(II), the electrons being transferred through a technetium "yl" oxygen which eventually becomes the bridging atom. Two additional bridges arise from two dimethylglyoxime ligands that function as bidentate nitrogen donors towards Tc and monodentate oxygen donors towards Sn. The tin atom can thus be viewed as providing a three-pronged "cap" on one end of the Tc-dimethylglyoxime complex. The additional coordination sites around Tc are occupied by the two nitrogens of a third dimethylglyoxime ligand, making the Tc seven-coordinate. The additional coordination sites around Sn are occupied by three chloride anions, giving the Sn a fac octahedral coordination environment. From indirect evidence the oxidation states of tin and technetium are tentatively assigned to be IV and V, respectively. Since most 99mTc-radiopharmaceuticals are synthesized by the tin(II) reduction of pertechnetate, it is likely that the Sn-O-Tc linkage described in this work is an important feature of the chemistry of these species. This linkage also provides a ready rationale for the close association of tin and technetium observed in many 99mTc-radiopharmaceuticals. (+info)
Radionuclide analysis of drug-induced blood-pool changes in liver and other organs.
(35/1995)
Although it is possible to repopulate the animal liver with transplanted hepatocytes, the success of such transplants depends, in part, on the number of transplanted cells that enter the hepatic sinusoids. Pharmacologic alteration of hepatic vascular tone, and hence blood volume, can increase the number of cells that are successfully transplanted. Although analysis of changes in vascular beds is helpful for developing strategies for cell transplantation, convenient methods to analyze such changes are lacking. The objective of this study was to determine whether 99mTc-labeled red blood cells could be used to reveal pharmacologically induced blood pool changes in various organs. METHODS: F344 rats were injected with syngeneic labeled red blood cells and subjected to blood pool analysis with gamma camera imaging. Animals were treated with phenylephrine, phentolamine, labetalol, and nitroglycerine. To correlate hepatic blood pool changes with structural alterations at the vascular level, microspheres were injected into the portal circulation of these animals. RESULTS: Phenylephrine significantly increased cardiac and pulmonary blood pools, findings in agreement with its alpha-adrenergic effects. Phentolamine increased the hepatic, splenic, and pulmonary blood pools, whereas labetalol increased only the pulmonary blood pool. Nitroglycerine increased both hepatic and splenic blood pools. Prior administration of phentolamine, labetalol, and nitroglycerine prevented the phenylephrine-induced changes. When microspheres were injected into the portal circulation after nitroglycerine administration, they penetrated more distal locations in the liver lobule. CONCLUSION: These data indicate that it is possible, using radionuclide methods, to noninvasively show pharmacologically induced hemodynamic changes. This finding is potentially useful for studying hepatic physiology and may also have applications for cell therapy. (+info)
Channelized hotelling and human observer correlation for lesion detection in hepatic SPECT imaging.
(36/1995)
Mathematic "model" observers that predict human performance are of interest in medical imaging as substitutes in psychophysical studies. We have examined the correlations between human observers and several forms of the channelized Hotelling observer (CHO) for a tumor detection task with simulated SPECT liver images that were used to study the effects of scatter and scatter correction on detection. METHODS: A receiver operating characteristic (ROC) study was devised to investigate the relative value of a scatter-subtraction strategy in SPECT imaging. The study used simulated images of the biodistribution of 99mTc-labeled FO23C5 anticarcinoembryonic antigen antibodies within the liver. Projection data for 3 separate tumor locations and 5 strategies for handling scatter were obtained using Monte Carlo software applied to an anthropomorphic phantom. The strategies were (a) perfect scatter rejection, (b) no scatter correction, (c) no scatter correction under an assumption of an elevated amount of scatter, (d) an energy-spectrum-based scatter compensation of the normal-scatter case (b), and (e) similar scatter compensation for the elevated-scatter case (c). Image reconstruction approximated current clinical procedures at the University of Massachusetts Medical School. Human performance for each combination of location and strategy was based on averaging the areas under the ROC curve for 7 individuals. A set of 15 signal-to-noise ratios (SNRs) was derived from these averages for comparison with SNRs for CHO models featuring constant-Q and difference-of-gaussian (DOG) filters. RESULTS: The Spearman rank correlation coefficient was 0.92 (P = 0.000001) when comparing task performances for the average human and a constant-Q CHO using 4 square-profile channels. For the DOG version of the CHO, comparison with the average human found a coefficient of 0.84 (P = 0.00005). CONCLUSION: The significant positive correlations found between the rankings of the average human observer and the CHOs for our detection task indicate that a channelized model observer could eventually serve as a replacement for human observers. The specific CHO models we have used are best suited to screen for significant differences between strategies before a human psychophysical study. (+info)
Radioimmunotherapy for the intensification of conditioning before stem cell transplantation: differences in dosimetry and biokinetics of 188Re- and 99mTc-labeled anti-NCA-95 MAbs.
(37/1995)
A new concept is the intensification of preparative regimens for patients with advanced leukemia using monoclonal antibodies (MAbs) with an affinity for beta emitter-labeled bone marrow. 188Re is a high-energy beta emitter that has therapeutic promise. Our first aim was to clarify whether the therapeutic application of 188Re-MAb against nonspecific cross-reacting antigen 95 (NCA-95) can be predicted from biokinetic data derived from 99mTc-labeled NCA-95. Our second aim was to show that a radiation absorbed dose of > or =12 Gy in the bone marrow can be achieved using 188Re-MAb. METHODS: Dosimetric data were obtained for both radiotracers from multiple planar whole-body scans (double-head gamma camera), blood samples, and urine measurements from 12 patients with advanced leukemia. Radiation absorbed doses were calculated using MIRDOSE 3 software. RESULTS: Radiation absorbed doses to bone marrow, liver, spleen, lung, and kidney were 2.24, 0.50, 1.93, 0.05, and 0.90 mGy/MBq, respectively, using 99mTc-MAb and 1.45, 0.43, 1.32, 0.07, and 0.71 mGy/MBq, respectively, using 188Re-MAb. These differences were statistically significant for bone marrow, spleen, and kidney. The main differences were less accumulation of 188Re-MAb in bone marrow (31%+/-13% compared with 52%+/-13%) and faster elimination through urine (25%+/-3% compared with 15%+/-5% after 24 h). On the basis of these data, a mean marrow dose of 14+/-7 Gy was achieved in 12 patients suffering from leukemia after application of approximately 10+/-2 GBq 188Re-MAb. CONCLUSION: Myeloablative radiation absorbed doses can easily be achieved using 188Re-MAb. 99mTc- and 188Re-MAb showed similar whole-body distributions. However, direct prediction of radiation absorbed doses from the 99mTc-MAb, assuming identical biokinetic behavior, is not valid for the 188Re-MAb in a single patient. Therefore, individual dosimetry using 188Re-MAb is needed to calculate therapeutic activity. (+info)
Disposition in rats of N-pyridinium-propyl-cyclam, N-triethylammonium-propyl-cyclam, and N-[Triethylammonium]-3-propyl-[15]ane-N5, potential cartilage imaging agents.
(38/1995)
Quaternary ammonium compounds are known to highly concentrate in articular cartilages after i.v. administration. This property was used to synthesize new potential radiodiagnostic agents for joint imaging. Pharmacokinetic study was performed in rats for three new compounds: N-pyridinium-propyl-cyclam (NPPC), N-triethylammonium-propyl-cyclam (NTPC), and N-[triethylammonium]-3-propyl-[15]ane-N5 (NTP 15-5). After i.v. administration, [(3)H]NPPC and [(3)H]NTPC highly and rapidly concentrated in articular cartilage, this uptake being followed by a single exponential decrease with half-lives of, respectively, 75 and 82 min. Except cartilage, only the kidney was highly labeled. After complexation of (99m)Tc by NPPC, NTPC, and NTP 15-5, only (99m)Tc-NTP 15-5 exhibited a high affinity for cartilage. On the other hand, the pharmacokinetic behavior of (99m)Tc-NTPC and (99m)Tc-NPPC was very different from those of their (3)H-labeled analogs. Concentration in cartilaginous tissues was strongly diminished, and liver and bone were highly labeled. For all labeled species, the major route of excretion was urine, and HPLC analysis showed that [(3)H]NTPC and [(3)H]NPPC were excreted under their unchanged form. On the other hand, no (99m)Tc-NTPC and (99m)Tc-NPPC were found in the urine, the radioactivity being mainly due to free technetium, contrary to (99m)Tc-NTP 15-5, which was excreted in the urine under the complexed form. These data can explain the striking differences observed between the three (99m)Tc-labeled molecules, the lack of concentration of (99m)Tc-NTPC, and (99m)Tc-NPPC in cartilages in comparison with their (3)H-labeled analogs due to an instability in vivo of these technetiated complexes. (+info)
Detection of a large arteriovenous fistula between the internal lliac vessels by radionuclide angiography.
(39/1995)
A patient evaluated for heart failure was found by routine radionuclide angiography to have a large internal iliac arteriovenous fistula of presumed postoperative origin. The value of radionuclide angiography is described with a review of the literature on such unusual cases. (+info)
Radionuclide computed tomography of the body using routine radiopharmaceuticals. I. System characterization.
(40/1995)
A whole-body computed tomography system for single-photon emitters was evaluated from the standpoint of spatial resolution, sensitivity, and thresholds for count densities with reference to standard doses of currently used radiopharmaceuticals in patients. In air and tissue equivalents, spatial resolution was relatively constant throughout the field of view and attentuation correction algorithms returned uniformity of response to within 10%. In a phantom of the human abdomen 1.5-cm spherical "cold" lesions and 1-cm "hot" lesions could be resolved. Aspects of the partial-volume effect were observed and investigated. To detect 1.5 cm-cold lesions in an abdominal phantom, five million events were required. (+info)