Structural characterization of a bridged 99Tc-Sn-dimethylglyoxime complex: implications for the chemistry of 99mTc-radiopharmaceuticals prepared by the Sn (II) reduction of pertechnetate.
(25/1315)
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)
In vivo dynamic real-time monitoring and quantification of platelet-thrombus formation: use of a local isotope detector.
(26/1315)
Current methods for monitoring thrombosis and thrombus growth are invasive and provide only single-time-point data. Animal models rely mainly on flow changes as a surrogate of thrombus formation. Our aim was to validate a unique potentially noninvasive system to detect and quantify dynamic thrombus formation in vivo by using a porcine model of carotid artery injury. Thrombus growth was monitored by deposition of autologous (111)In-labeled platelet activity over the injured artery by use of miniaturized gamma detectors and Doppler blood flow. Counts were recorded at 2-minute intervals for 2 hours. The technique was validated by comparing standard antithrombotic agents against controls. Platelet recruitment was detected before significant change in flow. Thrombus formation, calculated as the area under the curve (platelets x minutes x 10(6)), was greatest for control animals (11.7+/-1.28), followed by animals treated with aspirin (6.13+/-0.91, P<0.05), heparin (2.45+/-0.34, P<0.05), and hirudin (0.2+/-0.01, P<0.01 compared with heparin). The rate of platelet deposition was assessed as the slope of the curve in the first 30 minutes (platelets x 10(6) per minute) for the following treatment groups of animals: control, 3.53+/-0.34; aspirin, 1.67+/-0. 34 (P<0.01); heparin, 1.55+/-0.3 (P<0.01); and hirudin, 0.25+/-0.03 (P<0.001). There was no statistical difference between heparin and aspirin treatments. Change in flow was assessed as reduction from baseline: control, >99+/-0.34%; aspirin, 39+/-9.1%; heparin, 36+/-12. 5%; and hirudin, 17+/-5.4%. There was no statistical difference between the aspirin- and heparin-treated groups. Morphometric analysis revealed >99+/-0.63% occlusion of the luminal area with thrombus for the control group, 43+/-14.3% for the aspirin-treated group, 30+/-5.6% for the heparin-treated group, and <10+/-1.8% for the hirudin-treated group. Assessment of platelet-thrombus formation with this technique was more sensitive than change in flow in determining antithrombotic efficacy, and thrombus formation was detected earlier. This study validates a new quantitative, sensitive, potentially noninvasive, portable, in vivo monitoring of dynamic thrombus growth, which appears applicable to phase II studies in humans. (+info)
Radionuclide computed tomography of the body using routine radiopharmaceuticals. I. System characterization.
(27/1315)
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)
Radionuclide computed tomography of the body using routine radiopharmaceuticals. II. Clinical applications.
(28/1315)
A whole-body computed tomography system for single-photon emitters was used to investigate the clinical utility of this imaging modality. We have explored its application in brain, lung, liver, kidney, cardiac, bone, and gallium imaging in over 200 patients. Brain images demonstrated better lesion contrast than that in standard scintiphotos. Images of the lung and liver showed radionuclide distribution that was not readily apparent in standard scintiphotos. Moderate or strongly positive pyrophosphate myocardial images demonstrate the potential for infarct quantitation. ECG-gated cardiac blood-pool images in cross section, displayed in cine formate, permit evaluation of segmental motion of the free and septal walls of both ventricles. These results suggest significant clinical potential for this imaging modality using standard radiopharmaceuticals, but some increase in system sensitivity will likely be necessary to realize the full benefit of the technique. (+info)
Registration of planar emission images with reprojected CT data.
(29/1315)
Planar gamma-camera imaging is still widely used clinically. Alignment of planar images with images from tomographic modalities, such as CT, or with other planar images would be desirable. Here, we present and evaluate a method for such an alignment, using planar transmission images acquired with the emission images and reprojection of the 3-dimensional CT data. This method permits determination of which CT slice corresponds to a particular row of pixels in the gamma-camera image and which column of pixels in that CT slice corresponds to a particular pixel in the emission data. METHODS: A method based on maximization of the correlation coefficient, previously used for 3-dimensional datasets, was modified to permit 2-dimensional registrations. Planar transmission measurements were obtained using a collimated 99mTc flood source in conjunction with planar emission studies. The CT data were first reprojected to permit the 2-dimensional registration. The registration method was evaluated for its accuracy and reproducibility. RESULTS: For phantom data, the registration errors were -0.1 +/- 1.0 mm for x-translations, 1.0 +/- 1.3 mm for y-translations, and -0.2 +/- 0.3 degrees for rotations. For patient data, the errors were 1.6 +/- 0.8 mm for x-translations, 1.3 +/- 1.0 mm for y-translations, and 0.5 +/- 0.5 degrees for rotations. An examination of the need for rescaling of the attenuation data (to compensate for the different photon energies used in the respective attenuation measurements) showed no significant impact on registration error. When 5 different regions of interest were used for the correlation coefficient calculation, the mean errors attributable to region-of-interest choice alone were 1.0 mm for x-translations, 2.0 mm for y-translations, and 1.2 degrees for rotations. CONCLUSION: In almost all instances, translational registration errors were kept to subpixel levels (pixel size, 2.6 mm) and rotational errors to 1 degrees or less. The 1 exception was in the easily avoidable case of "pitch" rotations of the patient of 2 degrees or more. The modified registration method provides a simple yet reliable way to provide cross-modality evaluation of planar emission data. (+info)
Diagnosis of an enteric duplication with pertechnetate 99mTc scanning.
(30/1315)
A case of enteric duplication is reported in which preoperative pertechnetate (99m)Tc scanning demonstrated localized uptake in the region of the anatomic abnormality. This test is recommended for use in the evaluation of lower gastrointestinal bleeding in infants and children. (+info)
Platelet kinetics in dogs treated with a glycoprotein IIb/IIIa peptide antagonist.
(31/1315)
Platelet glycoprotein IIb/IIIa (GPIIb/IIIa) receptor antagonists have been highly effective inhibitors of platelet aggregation in preclinical studies and in clinical trials. However, decreased platelet counts have been documented in preclinical studies and in some patients receiving GPIIb/IIIa antagonists. We evaluated changes in platelet kinetics and fate in dogs receiving the GPIIb/IIIa receptor antagonist RPR 109891 orally for 4 days. Dogs receiving RPR 109891 had a 22-52% decrease in platelet count with the nadirs at 3-5 days after initiation of treatment. Platelet survival time was reduced by 19%, and platelet half-life was reduced by 63%. Indium-111-labeled platelets were rapidly cleared from the blood within 1 hour after administration of RPR 109891 on treatment days 1 and 2. This clearing was associated with a sharp increase in radioactivity in spleen but not in liver or lung. Platelet clearance was markedly attenuated on treatment days 3 and 4. Platelet counts returned to baseline within 1 week after discontinuation of treatment. These data indicate that RPR 109891 causes rapid and selective sequestration of platelets in the spleen. (+info)
A valid, accurate, office based non-radioactive test for gastric emptying of solids.
(32/1315)
BACKGROUND: Current breath tests for measurement of gastric emptying of solids are expensive, possibly inaccurate, and require cumbersome calculations. AIMS: We wished to validate a simplified solid gastric emptying test using a [(13)C]Spirulina platensis breath test for accurate results relative to scintigraphy. SUBJECTS: Thirty healthy volunteers. METHODS: We measured gastric emptying of egg containing [(13)C]S platensis and (99m)Tc sulphur colloid by breath (13)CO(2) and scintigraphy over six hours. A generalised linear regression model was used to predict t(1/2) and t(LAG) by scintigraphy from breath (13)CO(2) data. The model was cross validated and normative data calculated for a prepacked [(13)C]meal. RESULTS: Regression models using all breath data over six hours, for the first three hours, and for samples at 75, 90, and 180 minutes ("reduced model") predicted t(1/2) and t(LAG) values similar to scintigraphy (t(LAG) 43 (SD 12) min; t(1/2) 100 (20) min). Standard deviations of differences in t(1/2) and t(LAG) between scintigraphy and the "reduced model" were both 10 minutes. Gastric t(1/2) for the prepacked [(13)C]meal was 91 (15) min (10-90% range: 74-118). CONCLUSION: The [(13)C]S platensis breath test and a simple formula using breath (13)CO(2) at baseline, 90, and 180 minutes measured gastric emptying t(1/2) for solids with results that were comparable with scintigraphy. (+info)