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PubMed1980

Investigations of thallium-exposed workers in cement factories.

Thallium and its compounds have a high toxic potency. For the production of particularly resistant sorts of cement, additives containing thallium, among other things, are employed. In conformity with our present toxicological knowledge, the determination of the concentration of thallium in the urine must be considered a suitable parameter for the assessment of the presence of thallium in the body. Occupational-medical preventive examinations were carried out in a total of 128 male employees from all areas of production in three cement factories. An exposure of these employees to thallium was objectified by analyses of the roasted pyrites employed and the dust from the electric filter. The study included the questioning of the employees with respect to their previous history of health, and also a physical examination aimed at detecting clinical symptoms of a possible effect of thallium. The analysis of thallium was carried out in samples of "spontaneous" urine. The analytical method employed was flameless atomic absorption spectroscopy (carbon-rod atomizer). In part, the group of persons investigated revealed excretions of thallium slightly or moderately above the normal level (range: < 0.3-6.3 micrograms/g creatinine). As the upper normal limit of thallium excretion, we computed a value of 1.1 micrograms/g creatinine. In no case, however, did the case history data or the findings of the physical examination reveal any indication of the symptoms characteristic of thallium poisoning.

Adolescent↗
PubMedDate not supplied

Planar and tomographic imaging with technetium 99m-labeled tetrofosmin: correlation with thallium 201 and coronary angiography.

This study compared the results of planar and single-photon emission computed tomographic (SPECT) imaging with tetrofosmin with those of 201Tl and coronary angiography. In three normal volunteers the images were normal by both 201Tl and tetrofosmin (planar and SPECT). In 23 patients with coronary artery disease, the images were abnormal in 20 patients by SPECT tetrofosmin, in 19 by planar tetrofosmin, in 20 by SPECT thallium, and in 18 by planar thallium (difference not significant). Both planar and SPECT images were divided into five segments per patient. There were 58 perfusion defects by SPECT tetrofosmin, 50 by planar tetrofosmin (difference not significant), 47 by SPECT thallium, and 42 by planar thallium (difference not significant). Perfusion defects were reversible in 47 segments (36%) by SPECT tetrofosmin, 35 (27%) by planar tetrofosmin, 31 (24%) by SPECT thallium (p < 0.05 vs SPECT tetrofosmin), and 31 (24%) by planar thallium (difference not significant). Among the 23 patients with coronary artery disease, 19 underwent coronary angiography. In these patients there were 32 diseased coronary arteries. Perfusion defects were present in 21 territories (66%) by SPECT tetrofosmin, 19 (59%) by planar tetrofosmin, 20 (63%) by SPECT thallium, and 18 (56%) by planar thallium. There was agreement between thallium and tetrofosmin in 108 of 130 segments (kappa statistics = 0.69 +/- 0.06). The images, especially with SPECT, are better with tetrofosmin than with 201Tl. Thus myocardial imaging with tetrofosmin provides results that are at least as good as those of 201Tl. Slightly more abnormal segments and more reversible defects are detected by tetrofosmin than by thallium imaging, especially with SPECT imaging.

Adult↗
PubMed1996

Reduced probability of orthodromically evoked action potential firing in CA1 pyramidal cells of guinea pig hippocampal slices after acute thallium exposure.

We investigated the effect of thallium ions on extracellular field potentials in the CA1 region of guinea pig hippocampal slices in a matched-pair experimental setup. Somatic and dendritic responses evoked by paired-pulse stimulation of the Schaffer collateral-commissural pathway were recorded before, during and after acute thallium exposure and compared to field potentials from nontreated control slices recorded simultaneously. Thallium reduced the orthodromically evoked population spike reversibly in a clear concentration-effect relationship. In contrast, the field excitatory postsynaptic potential fEPSP, as well as the presynaptic fiber volley of the afferent pathway, were not affected by thallium. Furthermore, the paired-pulse facilitation was reversibly reduced during thallium exposure. Input-output relations clearly demonstrated that thallium did not interfere with the presynaptic transmitter release mechanisms or the postsynaptic transmitter receptor sensitivity, but had a predominant postsynaptic target site. Additionally, any influence of thallium ions on the somatic and/or axonal membrane excitability could be excluded, as the antidromically evoked responses after alvear stimulation were not diminished by thallium. Therefore, the main effect of thallium was a decoupling of the somatic from the dendritic activity at the CA1 pyramidal cells. We conclude that the toxic influence of thallium ions in the guinea pig hippocampus must be confined to intracellular somatic mechanisms. Interactions with intracellular organelles and an impairment of their calcium storage capacity are supposed.

Action Potentials↗
PubMed1987

Comparison of electrocardiography and thallium-201 myocardial scintigraphy for the detection of ergonovine-induced coronary artery spasm: angiographic correlation.

This study was performed to determine the sensitivity of thallium imaging vs ECG monitoring for detecting coronary artery spasm noninvasively following intravenous ergonovine administration as compared to simultaneous coronary angiography. Thirty-two patients with insignificant coronary artery disease and chest pain underwent 12-lead ECG monitoring, thallium imaging, and coronary arteriography following the administration of 0.05, 0.1, 0.2, and 0.3 mg of ergonovine given 5 minutes apart or until chest pain occurred. One minute following the last dose of ergonovine, 2.5 mCi of thallium-201 was injected intravenously, and a final ECG was recorded and repeat coronary arteriography performed. Within 10 minutes following the injection of thallium, imaging was performed in the 40-degree and 70-degree left anterior oblique and anterior projections. The ECG, thallium study, and coronary arteriogram were read blindly and results were compared. The ECG, angiogram, and thallium study were read as positive if the following occurred, respectively: greater than or equal to 1 mm ST segment elevation, depression, or T wave reversal; greater than 50% vessel narrowing,; and reversible perfusion defect. Five patients were excluded from analysis because of either catheter-induced spasm, suboptimal thallium studies, or protocol violations. Of the 27 patients included for analysis, six had chest pain, five had a positive angiogram, five had a positive thallium study, and one had a positive ECG. The sensitivity of thallium vs ECG monitoring was 80% vs 25%, and the accuracy was 92% vs 80%. We conclude that thallium imaging greatly increases the noninvasive detection of ergonovine-induced coronary spasm as compared with the ECG with no loss of accuracy.

Adult↗
PubMed1991

Two-dimensional Doppler echocardiographic correlation of dipyridamole-thallium stress testing with isometric handgrip.

To determine how frequently new wall-motion abnormalities that are indicative of ischemia accompany thallium redistribution, 47 consecutive patients underwent two-dimensional echocardiography during routine dipyridamole-thallium stress testing. A secondary aim of the study was to determine whether the addition of isometric handgrip exercises to the standard dipyridamole imaging protocol increased the frequency of wall-motion abnormalities or thallium redistribution. Echocardiograms and thallium scans were independently interpreted, and wall-motion abnormalities that appeared with dipyridamole, handgrip exercise, or both were compared with results of thallium imaging. Five of 24 patients with thallium redistribution had new wall-motion abnormalities, and the extent (number of segments) of thallium redistribution in these five patients was significantly greater than in those who did not have well-motion abnormalities (p less than 0.03). The addition of isometric handgrip exercises to the imaging protocol did not distinguish between patients with and without new wall-motion abnormalities or thallium redistribution. Thus new wall-motion abnormalities infrequently accompany thallium redistribution in routine dipyridamole stress testing in spite of the addition of handgrip exercises, but when new wall-motion abnormalities are present, they are associated with a greater area of thallium redistribution.

Coronary Disease↗
PubMed1985

Myocardial kinetics of thallium-201 after stress in normal and perfusion-reduced canine myocardium.

Despite the emerging use of quantitative computer programs for assessing myocardial thallium uptake and clearance after exercise, little is known about the kinetics of thallium after exercise stress. Accordingly, 11 mongrel dogs with experimental left anterior descending coronary stenoses were given thallium during norepinephrine infusion to simulate exercise. The infusion was discontinued and thallium activity was monitored regionally using miniature radiation detectors for 3 hours. Heart rate, arterial pressure and double product all increased significantly during norepinephrine infusion. The mean fractional myocardial thallium clearance was lower (0.47 +/- 0.03 [+/- standard error of the mean]) for the stenosis zone than for the no-stenosis zone (0.57 +/- 0.03) (p less than 0.0001). The stress blood flow ratio (stenosis/no-stenosis zone = 0.27 +/- 0.06) was significantly lower than the final thallium activity ratio (0.68 +/- 0.07) (p less than 0.001), consistent with thallium redistribution occurring over the 3-hour period. Myocardial thallium activity in the stenosis zone peaked in a mean of 2.2 minutes, then washed out biexponentially with a final decay constant of 0.0035 +/- 0.0005 min-1. Myocardial thallium activity in the no-stenosis zone peaked within 1 minute in all dogs, then washed out biexponentially, with a final decay constant of 0.0043 +/- 0.0003 (p less than 0.001 compared with stenosis zone). In conclusion, fractional clearance of thallium can differentiate myocardium distal to a coronary artery stenosis from that supplied by a normal coronary vessel.

Animals↗
PubMed1989

Prognostic importance of silent myocardial ischemia detected by intravenous dipyridamole thallium myocardial imaging in asymptomatic patients with coronary artery disease.

One hundred seven asymptomatic patients who underwent intravenous dipyridamole thallium imaging were evaluated to determine prognostic indicators of subsequent cardiac events over an average follow-up period of 14 +/- 10 months. Univariate analysis of 18 clinical, scintigraphic and angiographic variables revealed that a reversible thallium defect, a combined fixed and reversible thallium defect, number of segmental thallium defects and extent of coronary artery disease were significant predictors of subsequent cardiac events. Of the 13 patients who died or had a nonfatal infarction, 12 had a reversible thallium defect. Stepwise logistic regression analysis selected a reversible thallium defect as the only significant predictor of cardiac events. When death or myocardial infarction was the outcome variable, a combined fixed and reversible thallium defect was the only predictor of outcome. In patients without previous myocardial infarction, the cardiac event rate was significantly greater in those with an abnormal versus normal thallium scan (55% versus 12%, p less than 0.001). Thus, intravenous dipyridamole thallium scintigraphy is a useful noninvasive test to risk stratify asymptomatic patients with coronary artery disease. A reversible thallium defect most likely indicates silent myocardial ischemia in a sizable fraction of patients in this clinical subset and is associated with an unfavorable prognosis.

Aged↗
PubMed1991

Thallium-201 for assessment of myocardial viability: quantitative comparison of 24-hour redistribution imaging with imaging after reinjection at rest.

Redistribution thallium-201 imaging 2 to 4 h after exercise may be incomplete and therefore may be inadequate to fully assess myocardial variability. Late redistribution imaging 24 h after exercise has been proposed to overcome this limitation of thallium stress imaging. However, because of poor count density the image quality on these studies is often suboptimal. In the present study the diagnostic information on 24-h planar thallium redistribution images was compared with that on images obtained after a reinjection of thallium at rest. Eighty-four patients with a stress thallium-201 defect had delayed redistribution imaging after 2 to 4 h and 24 h later, and again after an injection of thallium at rest. Defect reversibility on 24-h redistribution images was compared quantitatively with that on images after injection of thallium at rest. The quality of thallium images at rest was consistently better than that of 24-h redistribution images. Poor quality studies occurred in 13% of 24-h redistribution images compared with 0.4% of the studies at rest. Significantly more defect reversibility was detected on images after the reinjection at rest. Of 41 patients who appeared to have a fixed defect at 2- to 4-h redistribution imaging, 11 (27%) had a reversible defect by 24-h redistribution imaging compared with 29 (71%) after thallium-201 reinjection. No clinical variables at the time of stress testing were predictive of late defect reversibility. It is concluded that in patients with fixed a thallium defect at 2 to 4 h after exercise, reimaging after a reinjection at rest provides better diagnostic information than does 24-h late redistribution imaging.

Adult↗
PubMed2001

Relation of thallium uptake to morphologic features of chronic ischemic heart disease: evidence for myocardial remodeling in noninfarcted myocardium.

OBJECTIVES: The aim of this study was to investigate the disparity between the extent of myocardial injury as assessed by thallium and the severity of left ventricular (LV) dysfunction in chronic ischemic heart disease. BACKGROUND: Although it is believed that thallium differentiates between viable and nonviable myocardium, in some patients with chronic ischemic heart disease, viable regions by thallium may fail to improve function after revascularization. METHODS: Thirteen transplant candidates with chronic ischemic heart disease (LV ejection fraction = 14 +/- 6% at rest) were studied prospectively with stress-redistribution-reinjection thallium single-photon emission computed tomography. We examined pretransplantation quantitative thallium uptake and post-transplantation extent and the histological distribution of collagen replacement in infarcted and noninfarcted myocardium and in 13 age-matched control hearts. RESULTS: The volume fraction of collagen varied inversely with wall thickness (r = -0.70, p < 0.001) and was higher in irreversible (30.9 +/- 15.8%) compared with reversible (20.2 +/- 12.6%, p < 0.001) or normal thallium segments (15.0 +/- 8.7%, p < 0.001). The irreversible thallium segments had lower wall thickness and more severe coronary artery narrowing (9.7 +/- 2.8 mm and 95 +/- 8%) compared with reversible (11.7 +/- 2.7 mm and 87 +/- 13%, p < 0.001) and normal thallium segments (12.8 +/- 2.6 mm and 80 +/- 14%, p < 0.001). Mean volume fraction of collagen was significantly lower in noninfarcted than it was in infarcted segments (13 +/- 6% vs. 36 +/- 13%, p < 0.001) but exceeded that in the control hearts (4 +/- 2%, p < 0.001). Noninfarcted segments had predominantly interstitial fibrosis with either microscopic or patchy areas of replacement fibrosis. CONCLUSIONS: In chronic ischemic heart disease with severe LV dysfunction, patterns of normal, reversible and irreversible thallium uptake correlated with the magnitude of collagen replacement, segmental wall thickness and severity of coronary artery narrowing. The finding of scattered areas of replacement fibrosis in noninfarcted myocardium may explain the observed disparity between LV contractile dysfunction and the extent of myocardial injury assessed by thallium.

Adult↗
PubMed1987

Myocardial uptake and clearance of thallium-201 in normal subjects: comparison of dipyridamole-induced hyperemia with exercise stress.

Thallium-201 uptake and clearance after dipyridamole infusion may differ from that after exercise stress because the hemodynamic effects of these two interventions are different. In this study of normal volunteers, thallium kinetics after dipyridamole (n = 13) were determined from three serial image sets (early, intermediate and delayed) and from serial blood samples and compared with thallium kinetics after exercise (n = 15). Absolute myocardial thallium uptake was greater after dipyridamole compared with exercise (p less than 0.0001), although the relative myocardial distribution was similar. The myocardial clearance (%/h) of thallium was slower after dipyridamole than it was after exercise. Comparing dipyridamole and exercise, the differences in clearance were large from the early to the intermediate image (anterior, -11 +/- 17 versus 24 +/- 5, p = 0.0005; 50 degrees left anterior oblique, -7 +/- 11 versus 15 +/- 8, p = 0.004; 70 degrees left anterior oblique, 3 +/- 9 versus 21 +/- 6, p = 0.001). In contrast, the differences in clearance were small from the intermediate to the delayed image (anterior, 15 +/- 4 versus 20 +/- 2, p = 0.025; 50 degrees left anterior oblique, 15 +/- 4 versus 19 +/- 3, p = 0.13; 70 degrees left anterior oblique, 15 +/- 3 versus 18 +/- 2, p = 0.047). Thallium uptake and clearance in the liver, splanchnic region and spleen were greater after dipyridamole (p less than 0.001). Blood thallium levels were greater after dipyridamole (p less than 0.05) and cleared more slowly (p = 0.07). Thus, myocardial thallium-201 uptake and clearance after dipyridamole infusion differ from thallium kinetics after exercise. This difference is, in part, related to associated differences in extracardiac and blood kinetics. Diagnostic criteria for the detection of abnormal thallium-201 clearance must be specific for the type of intervention.

Adult↗
PubMed1998

Diagnostic accuracy and prognostic value of combined dipyridamole-exercise thallium imaging in hemodialysis patients.

BACKGROUND: Non-invasive detection of coronary artery disease in dialysis patients, a major cause of mortality, often remains difficult. The aim of the study was to test the diagnostic and prognostic accuracies of combined dipyridamole-exercise thallium imaging in dialysis patients. METHODS: Dipyridamole-exercise thallium imaging and coronary angiography were both performed prospectively in 60 asymptomatic hemodialysis patients who were followed up, long term, by recording any major coronary event. RESULTS: Coronary angiography was abnormal in 13 patients (21%), and there was abnormal thallium uptake in 17 patients. Sensitivity, specificity, positive and negative predictive values, and overall accuracy of thallium to detect a coronary artery disease were 92, 89, 71, 98 and 90%, respectively. After a median follow-up of 2.8 years, 12 patients experienced at least one major coronary event (4 cardiac deaths, 5 myocardial infarctions and 3 revascularizations). Eight of the 17 patients with abnormal thallium uptake (47%) suffered a coronary event, compared to only 4 of the 43 patients (9%) with a normal thallium uptake (P < 0.001). The positive prognostic predictive value of thallium imaging was 47% and its negative predictive value was 91%. The probability of survival free of coronary events was significantly higher in patients with normal thallium uptake than in those with abnormal thallium uptake (crude risk ratio 7.6; P < 0.001) even after adjustment for several risk factors for cardiovascular disease (adjusted risk ratio 9.2; P < 0.005). CONCLUSION: In dialysis patients, combined dipyridamole-exercise thallium imaging is an accurate method for detecting coronary stenosis and for predicting future coronary events.

Adult↗
PubMed1999

Comparative efficacy of thallium adsorption by activated charcoal, prussian blue, and sodium polystyrene sulfonate.

BACKGROUND: Although Prussian blue is considered the antidote of choice for thallium poisoning, the lack of a Food and Drug Administration-approved pharmaceutical formulation has led to the search for other adsorbents. Activated charcoal has been demonstrated to adsorb thallium in vitro, and the similarity between thallium and potassium has led some authors to consider the use of sodium polystyrene sulfonate as a potential adsorbent. This experiment was designed to compare the relative thallium binding efficacy of these agents in a standard isotherm model. METHODS: A standard aqueous solution of thallium acetate buffered to pH 7.0 was agitated at 25 degrees C with activated charcoal, Prussian blue, or sodium polystyrene sulfonate at adsorbent:thallium ratios ranging from 1.5:1 to 100:1. In order to further simulate physiologic conditions, all trials were repeated in a solution containing 4 mmol/L potassium phosphate. After thorough agitation, the mixtures were allowed to settle and were centrifuged and filtered through a 0.22-micron filter. Supernatant thallium concentrations were measured by atomic absorption spectrophotometry. Langmuir isotherms were used to calculate the maximal adsorptive capacity of each adsorbent, using linear regression with Pearson's correlation coefficients (r). Maximal adsorptive capacities were compared statistically with a p < 0.05 considered significant. RESULTS: The maximal adsorptive capacities defined as milligrams of thallium per gram of adsorbent (shown with linear regression p and r values) were as follows: activated charcoal, 59.7 mg/g (p = 0.005, r = 0.995); Prussian blue, 72.7 mg/g (p = 0.004, r = 0.996); and sodium polystyrene sulfonate, 713 mg/g (p = 0.049, r = 0.951). All three values were statistically different from each other. At a physiologic potassium concentration, the maximal adsorptive capacities for activated charcoal and Prussian blue were essentially unchanged (58.3 mg/g and 69.8 mg/g, respectively, p > 0.05 for each vs trials without potassium), while the maximal adsorptive capacity for sodium polystyrene sulfonate fell to 39.1 mg/g (p = 0.003, r = 0.997, p = 0.005 vs sodium polystyrene sulfonate without potassium). CONCLUSIONS: This in vitro study confirms the utility of Prussian blue and activated charcoal as thallium adsorbents. Although sodium polystyrene sulfonate demonstrates exceptional in vitro adsorption of thallium, its greater affinity for potassium probably renders it clinically ineffective.

Adsorption↗
PubMed1985

Effect of hyperaemia on thallium-201 redistribution in normal canine myocardium.

The specific effect of hyperaemia on thallium redistribution is not known. Therefore we evaluated the effect of initial (group A) and delayed (group B) hyperaemia on thallium kinetics in normal canine myocardium. In group A dogs (n = 14) adenosine was infused into the left circumflex artery (LCx) prior to thallium injection and was continued for either 5, 30 or 120 min after thallium administration. In group B dogs (n = 10) LCx adenosine was begun 10 min post thallium injection and continued for 2 h. Radioactive microspheres were injected simultaneously with thallium and just prior to death in all but the 5 min experiments. The region of the left anterior descending artery (LAD) served as a normal control for each heart. The mean LCx/LAD flow ratio in all group A hearts was 3.81 +/- 1.24 (SD) and the final thallium LCx/LAD ratios averaged 2.29 +/- 0.26, 1.52 +/- 0.27 and 0.93 +/- 0.16 at 5, 30 and 120 min respectively, which represents a significant redistribution of thallium (p less than 0.05). In group B hearts, the mean LCx/LAD flow ratio was 1.06 +/- 0.07 during thallium injection and after LCx adenosine infusion the flow ratio rose to 2.91 +/- 0.75 (p less than 0.001). This resulted in a final thallium LCx/LAD ratio of 0.96 +/- 0.07 which was significantly less than the initial microsphere determined flow ratio (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1998

Noninvasive diagnosis of gastroesophageal inflammation using dipyridamole thallium-201 tomography.

OBJECTIVE: Esophagitis, a complication of GERD, and gastric erosions are common findings in dyspeptic patients. Unfortunately, these findings cannot be predicted based on symptoms alone and require endoscopy for an accurate diagnosis. Noninvasive diagnosis of other gastrointestinal pathology by radiopharmaceuticals (GA 67, Tc 99m pertechnetate) has previously been studied. We hypothesized that endoscopically documented esophagitis and/or gastric erosions could also be detected by using dipyridamole thallium-201 imaging and, if they were of sufficient accuracy, could serve as a useful, noninvasive screening test for esophagitis and/or gastric erosions. METHODS: A pilot study was undertaken in 12 patients undergoing endoscopy for symptoms of GERD or dyspepsia. Esophagitis was defined as the presence of either erosions or ulceration and gastric erosions were defined as discrete mucosal breaks measuring > or = 1 mm. Dipyridamole thallium-201 imaging was performed the following day on all 12 patients. A standard dose of dipyridamole (0.56 mg/kg) was infused over 4 min, followed by a 3-mCi dose of thallium-201. Initial stress tomographic images and reinjection (1 mCi) resting tomographic images 3-4 h later were obtained using a gamma camera. Tomographic images were read blinded to the endoscopy results. Thallium-201 uptake was graded on a 0-3+ scale using the liver uptake as the internal comparative standard (2+ = uptake equal to the liver). Abnormal thallium uptake was defined as > or = 2+ in the area of the esophagus or stomach. RESULTS: Seven women and five men (mean age 41 yr, range 25-60 yr) were studied. Eight patients were taking histamine-2 receptor antagonists and none were on proton pump inhibitors, or promotility agents. All five patients with endoscopic esophagitis had a positive thallium-201 tomographic image. Seven patients had no evidence of esophagitis, and three had positive thallium-201 tomograms. Dipyridamole thallium-201 imaging sensitivity, specificity, and positive and negative predictive values for esophagitis were 100%, 57%, 63%, and 100%, respectively. All three patients with gastric erosions had positive thallium-201 tomograms. Six of nine patients without gastric erosions had positive tomograms. The sensitivity, specificity, and positive and negative predictive values of DT 201 gastric erosions were 100%, 33%, 33%, and 100%, respectively. CONCLUSIONS: Dipyridamole thallium-201 tomographic imaging has good sensitivity (100%) in detecting esophagogastric mucosal erosions, but its poor specificity (33-57%) results in an unacceptable accuracy as a screening test. Additionally, the cost of radiopharmaceuticals requires that sensitivity and specificity be at least equal to that of endoscopy for this test to be clinically valuable as a screening test. However, a noninvasive test for these diseases is inherently appealing, and further research in this area seems to be warranted.

Adult↗
PubMed1994

Myocardial viability in patients with chronic coronary artery disease. Comparison of 99mTc-sestamibi with thallium reinjection and [18F]fluorodeoxyglucose.

BACKGROUND: 99mTc-sestamibi and thallium imaging have similar accuracy when used for diagnostic purposes, but whether sestamibi provides accurate information regarding myocardial viability in patients with chronic coronary artery disease has not been established. Since there is minimal redistribution of sestamibi over time, it may overestimate nonviable myocardium in patients with left ventricular dysfunction, in whom blood flow may be reduced at rest. METHODS AND RESULTS: We studied 54 patients with chronic coronary artery disease with a mean ejection fraction of 34 +/- 14%. Patients underwent stress/redistribution/reinjection thallium tomography and, within a mean of 5 days, same-day rest/stress sestamibi imaging using the same exercise protocol and with patients achieving the same exercise duration. Of the 111 reversible thallium defects on either the redistribution or reinjection study, 40 (36%) were determined to be irreversible on the rest/stress sestamibi study, whereas only 3 of 63 irreversible thallium defects despite reinjection (5%) were classified to be reversible by sestamibi imaging. The concordance regarding reversibility of myocardial defects between thallium stress/redistribution/reinjection and same day rest/stress sestamibi studies was 75%. A subgroup of 25 patients also underwent positron emission tomography (PET) studies with 15O-labeled water and [18F]fluorodeoxyglucose (FDG) at rest after an oral glucose load. As in the overall group of 54 patients, there was concordance between thallium and sestamibi imaging regarding defect reversibility in 51 of 73 regions (70%). In the remaining 22 discordant regions (30%), 18 (82%) appeared irreversible by sestamibi imaging but were reversible by thallium imaging. Myocardial viability was confirmed in 17 of 18 regions, as evidenced by normal FDG uptake (10 regions) or FDG/blood flow mismatch (7 regions) on PET. These regions were present in 16 of the 25 patients studied (64%). We then explored methods to improve the sestamibi results. First, when the 18 discordant regions with irreversible sestamibi defects were further analyzed according to the severity of defects, 14 (78%) demonstrated only mild-to-moderate reduction in sestamibi activity (51% to 85% of normal activity), suggestive of predominantly viable myocardium, and the overall concordance between thallium and sestamibi studies increased to 93%. Second, when an additional 4-hour redistribution image was acquired in 18 patients after the injection of sestamibi at rest, 6 of 16 discordant irreversible regions (38%) on the rest/stress sestamibi study became reversible, thereby increasing the concordance between thallium and sestamibi studies to 82%. CONCLUSIONS: These data indicate that same-day rest/stress sestamibi imaging will incorrectly identify 36% of myocardial regions as being irreversibly impaired and nonviable compared with both thallium redistribution/reinjection and PET. However, the identification of reversible and viable myocardium can be greatly enhanced with sestamibi if an additional redistribution image is acquired after the rest sestamibi injection or if the severity of reduction in sestamibi activity within irreversible defects is considered.

Adult↗
PubMed1989

Combining clinical and thallium data optimizes preoperative assessment of cardiac risk before major vascular surgery.

STUDY OBJECTIVE: To determine whether clinical markers and preoperative dipyridamole-thallium imaging are both useful in predicting ischemic events after vascular surgery. DESIGN: Retrospective, observational study. SETTING: University medical center. PATIENTS: Two hundred fifty-four consecutive patients referred to a nuclear cardiology laboratory before surgery. Forty-four patients had surgery cancelled or postponed after clinical evaluation and dipyridamole-thallium imaging. Surgery was not confirmed for ten. Two hundred patients receiving prompt vascular surgery were the study group. MEASUREMENTS AND MAIN RESULTS: Thirty patients (15%) had early postoperative cardiac ischemic events, with cardiac death in 6 (3%) and nonfatal myocardial infarction in 9 (4.5%). Logistic regression identified five clinical predictors (Q waves, history of ventricular ectopic activity, diabetes, advanced age, angina) and two dipyridamole-thallium predictors of postoperative events. Of patients with none of the clinical variables (n = 64), only 2 (3.1%; 95% CI, 0% to 8%) had ischemic events with no cardiac deaths. Ten of twenty (50%; 95% CI, 29% to 71%) patients with three or more clinical markers had events. Eighteen of one hundred sixteen (15.5%; 95% CI, 7% to 21%) patients with either 1 or 2 clinical predictors had events. Within this group, 2 of 62 (3.2%; 95% CI, 0% to 8%) patients without thallium redistribution had events compared with 16 events in 54 patients (29.6%; 95% CI, 16% to 44%) with thallium redistribution. The multivariate model using both clinical and thallium variables showed significantly higher specificity at equivalent sensitivity levels than models using either clinical or thallium variables alone. CONCLUSIONS: Preoperative dipyridamole-thallium imaging appears most useful to stratify vascular patients determined to be at intermediate risk by clinical evaluation. For patients with one or two clinical predictors, thallium redistribution correlates with substantial change in probability of events. For nearly half the patients, however, thallium imaging may have been unnecessary because of very high or low cardiac risk predicted by clinical information alone.

Age Factors↗
PubMed2005

Lesion size determines accuracy of thallium-201 brain single-photon emission tomography in differentiating between intracranial malignancy and infection in AIDS patients.

BACKGROUND AND PURPOSE: Discrimination between enhancing mass lesions in acquired immunodeficiency syndrome (AIDS) patients with conventional CT and MR imaging remains difficult. We determined the effect of lesion size on thallium-201 brain single-photon emission tomography (SPECT) imaging in differentiating primary brain lymphoma from cerebral toxoplasmosis. METHODS: We retrospectively identified 35 AIDS patients with a total of 48 focal enhancing mass lesions on contrast-enhanced brain CT and/or MR images who subsequently underwent thallium-201 brain SPECT imaging. The thallium index of each lesion was evaluated on the basis of the ratio of mean uptake in the lesion compared with the corresponding contralateral side. Receiver operator curves were drawn to determine the optimal thallium index threshold. The effect of lesion size on scan accuracy was evaluated. RESULTS: Malignant lesions in 20 patients had a mean thallium index of 2.4 (range, 1-11). Infectious lesions in 15 patients had a mean thallium index of 1.6 (range, 1-3.6). Twenty-five lesions were <2 cm (14 malignant, 11 nonmalignant) and 23 lesions were > or =2 cm (14 malignant, 9 nonmalignant). Thallium index was not a significant predictor of malignancy in the lesions <2 cm by using the logistic regression (P = .27). Receiver operator curve analysis by using thallium index of 2 in small lesions yielded 50% sensitivity and 82% specificity. In contrast, thallium index was a significant predictor of malignancy in lesions > or =2 cm (P < .01), yielding 100% sensitivity and 89% specificity. CONCLUSION: Lesion size is a significant determinant of the accuracy of thallium-201 brain SPECT imaging, which should be the initial diagnostic tool for lesions > or =2 cm.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Effect of ischemia-related metabolic factors on thallium exchange in cultured rat myocardial cells.

Failure of the myocardium to take up Thallium-201 is widely used as a diagnostic marker for ischemia or infarction. Although this is commonly related to a reduction in coronary flow or myocardial perfusion, other possible metabolic factors are poorly understood. The present studies investigated the influence of various interventions, designed to simulate the metabolic consequences of ischemia, on thallium-204 uptake and release in cultured myocardial cells. In these cells, where thallium exchanged rapidly (t 1/2 = 5 min.), and 60% of thallium uptake occurred via the sodium pump, thallium uptake was markedly influence by changes in extracellular potassium. Increasing extracellular potassium from a physiologic level of 5 mM to those levels reported to occur in ischemic myocardium (7.5 mM to 18 mM) effected a 25% to 60% reduction in thallium influx. The decrease in thallium influx produced by increasing extracellular potassium was rapid (30 sec.) in onset and readily reversible by restoring extracellular potassium towards normal. Changes in extracellular pH in the range 6.4 to 8.0 had no demonstrable effect on thallium uptake despite the fact that this was accompanied by similar, although less marked, changes in intracellular pH. Addition of adenine nucleosides, adenosine, inosine and hypoxanthine, to the incubating solution in concentrations from 1 nM to 0.1 mM had no effect on thallium influx or efflux in the cells. This observation held true even when 10 microM dipyridamole was used to inhibit nucleoside uptake by the cells. Addition of 1 mM 2, 4-dinitrophenol or 4 mM potassium cyanide to the cultures maximally inhibited 42% of the thallium influx within 30 min.(ABSTRACT TRUNCATED AT 250 WORDS)

2,4-Dinitrophenol↗