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PubMed1985

Quantitative split dose thallium-201 imaging with exercise: a technique for obtaining rest and exercise perfusion images in one setting and markedly reducing the study time.

In the current study, a technique for performing serial thallium imaging after two separate tracer injections was applied to exercise thallium imaging, thus allowing the acquisition of rest and exercise images within 1 hour. Twenty-four patients with and 10 patients without significant coronary artery disease were studied. One mCi of thallium-201 was injected intravenously and imaging was performed at rest in three projections. The patient was then stressed and an additional 1 mCi of thallium injected during exercise. Images in the same three projections were collected. After computer realignment, the rest image was subtracted from the exercise image to produce an image representing perfusion during exercise. All 24 patients with coronary artery disease had a positive study, while 9 of 10 without disease had a negative study. The images were then interpreted using a computer method designed to quantitate regional myocardial thallium distribution and redistribution. With quantitative interpretation, 23 of 24 patients with coronary disease had a positive study, while only 1 without disease had a positive study. With qualitative interpretation, 39 (89%) of 44 stenosed coronary arteries demonstrated thallium defects in corresponding myocardial segments, while 54 (93%) of 58 nonstenosed coronary arteries did not. With quantitative interpretation, 38 (86%) of 44 stenosed coronary arteries demonstrated thallium defects in corresponding myocardial segments, while 53 (91%) of 58 nonstenosed coronary arteries did not. A split dose thallium imaging technique that allows imaging before and immediately after exercise, thus markedly reducing the study time, has been validated.

Adult↗
PubMed1986

Determination of the quantitative thallium imaging variables that optimize detection of coronary artery disease.

Although quantification of exercise thallium images has been previously reported, the relative value of different imaging variables for detection of coronary artery disease has not been analyzed in a large group of patients with cardiac catheterization data. Regional initial thallium uptake, redistribution and clearance on thallium study were measured in 325 patients also undergoing cardiac catheterization (281 patients with and 44 patients without coronary artery disease). Normal values were defined in 55 other clinically normal subjects. When five myocardial segments were analyzed in each view, the respective values for sensitivity and specificity were 95 and 50% for initial thallium uptake, 60 and 87% for redistribution and 74 and 66% for clearance. Initial thallium uptake was the most sensitive but least specific (p less than 0.001), whereas redistribution was the least sensitive and most specific (p less than 0.001). Using stepwise logistic regression analysis, the best correlate of coronary artery disease was initial thallium uptake. Addition of redistribution to a mathematical model of the probability of coronary artery disease did not alter sensitivity, but increased specificity from 50 to 70% (p less than 0.001). Once initial uptake and redistribution were considered, myocardial thallium clearance provided no additional improvement in the correlation. Excluding the two basal segments in each view from the analysis increased the specificity from 70 to 80% (p less than 0.001) without affecting sensitivity. Of the 15 patients (5%) with coronary disease not detected using this approach, none had left main disease and 10 (67%) had one vessel disease. A combination of variables derived from quantification of exercise thallium images provides a superior sensitivity and specificity for the detection of coronary artery disease compared with the use of a single variable.

Adult↗
PubMed2001

The higher likelihood of developing cardiomegaly during follow-up in patients with syndrome X and abnormal thallium-201 myocardial perfusion SPECT.

'Syndrome X' describes patients with exertional chest pain and a normal coronary arteriogram. In some patients, acute myocardial ischemia can be demonstrated by regional myocardial perfusion defects on thallium-201 exercise test. However, some patients with typical angina have normal perfusion on thallium-201 heart scintigraphy. It is not clear whether there are different prognoses for patients with normal and abnormal thallium studies. In this study, the clinical features, long term follow-up and clinical results of syndrome X patients with normal and abnormal thallium studies were evaluated to determine the differences between these two groups. Fifty-nine patients (52 males, seven females, mean age 62+/-6 years) with syndrome X were enrolled and divided into two groups on the basis of results of thallium-201 heart scintigraphy. Group I was comprised of 22 patients with normal thallium-201 perfusion scan and group II was comprised of 37 patients with abnormal thallium-201 heart scan. All subjects received coronary arteriography, exercise test, thallium-201 myocardial SPECT, ejection fraction of left ventricle, echocardiography, blood analysis and long term follow-up with questionnaire for 10 years. Lower maximal rate-pressure product and higher angina scores were found in group II. More patients developed cardiomegaly (nine of 33 patients) in group II than in group I (one of 21 patients). Both groups, however, were at low risk for cardiac events (cardiac death or myocardial infarction).

Aged↗
PubMedDate not supplied

Quantitative thallium-201 and technetium 99m sestamibi tomography at rest in detection of myocardial viability in patients with chronic ischemic left ventricular dysfunction.

BACKGROUND: This study was designed to determine the most effective quantitative threshold for thallium-201 and technetium 99m sestamibi uptake on tomographic imaging after rest injection for the detection of myocardial viability in patients with chronic myocardial infarction. METHODS AND RESULTS: Thallium and sestamibi cardiac tomography at rest was performed in 43 patients with chronic myocardial infarction and impaired left ventricular (LV) function undergoing coronary revascularization. In all patients, echocardiography and radionuclide angiography were performed at baseline and repeated 12 months later to evaluate recovery of regional LV function and LV ejection fraction, respectively. Optimal threshold cutoff points to separate reversible from irreversible dysfunction were determined by receiver operating characteristic analysis. When all dysfunctional segments were considered, the best cutoff point in the identification of reversible LV dysfunction for both thallium and sestamibi activity was 67%. When only akinetic or dyskinetic segments were considered, the best cutoff point in the identification of reversible LV dysfunction was 58% for thallium and 55% for sestamibi. In these segments, the area under the receiving operating characteristic curves constructed for thallium and sestamibi activity were 0.74+/-0.05 and 0.75+/-0.04, respectively (P = not significant). LV ejection fraction was 33%+/-7% at baseline and increased to 37%+/-7% after revascularization (P<.0001). A significant relation between the number of akinetic or dyskinetic but viable myocardial segments and revascularization-induced changes in LV ejection fraction was observed for both thallium (r = 0.60, P<.0001) and sestamibi (r = 0.64, P<.0001) imaging. CONCLUSIONS: In patients with chronic myocardial infarction, quantitative analysis of thallium and sestamibi activity on tomographic imaging at rest predicts recovery of regional and global LV dysfunction after revascularization procedures. The most effective quantitative threshold for detecting reversible LV dysfunction is comparable for thallium and sestamibi tomographic imaging. However, the optimal cutoff point is different for both tracers when all dysfunctional segments are considered or when the analysis is focused only on segments with more severe functional impairment (i.e., akinetic or dyskinetic segments).

Chronic Disease↗
PubMed2000

Thallium poisoning during pregnancy: a case report and comprehensive literature review.

BACKGROUND: Thallium salts were once used to treat a variety of disorders such as tuberculosis, sexually transmitted diseases, and ringworm of the scalp. Although the clinical manifestations and treatment of patients with thallium poisoning are well characterized, little information is available on the outcome of pregnancy in thallium-poisoned women. A case of thallium poisoning that began during the first trimester of pregnancy and resulted in fetal demise is reported. METHODS: An extensive literature search identified reported cases of thallium poisoning during pregnancy from 1903 until the present time. All articles were obtained, translated, and abstracted using a standardized data collection form. References were hand-searched and abstracted to identify additional cases. RESULTS: From a total of 25 cases identified, only 18 met satisfactory criteria for inclusion. Five exposures occurred during the first trimester, 5 during the second trimester, and 8 during the third trimester. Mothers developed classic signs and symptoms of thallium poisoning. Summary of these cases demonstrates a range of fetal effects from severe toxicity with residual sequelae to outwardly normal development. Interestingly, some newborns appeared normal despite severe maternal toxicity. The only consistent effect identified was a trend toward prematurity and low birth weight in children exposed during early gestation. CONCLUSIONS: These cases document the transfer of thallium both across the placenta and in breast milk. Insufficient data are available to evaluate prognostic markers of fetal outcome, or the risks and benefits of various treatment regimens in pregnant patients with thallium poisoning.

Adult↗
PubMed1989

A comparison of myocardial thallium-201 image quality after either dipyridamole or exercise stress.

Exercise and dipyridamole provide two mechanistically different stress techniques for thallium-201 imaging. To date, comparisons of the two have relied solely on assessments of clinical results. However, because diagnostic accuracy ultimately depends on image quality, this study was undertaken to compare the image quality obtained by both techniques. The left anterior oblique images of 30 patients, who had thallium imaging after intravenous dipyridamole (0.56 mg kg-1 over 4 min) were compared with those of 30 patients who were imaged after symptom limited, Bruce protocol, treadmill exercise in the same time period. Myocardial and lung-background thallium uptake were compared after stress and on redistribution. The ratio of the best segmental myocardial thallium uptake (M) to that in a fixed lung-background region (B) was taken as an index (M/B) of image quality. Myocardial thallium uptake was significantly higher after dipyridamole than after exercise (P less than 0.001). Lung-background thallium uptake, however, was also higher (P less than 0.001) so that the resulting image quality indices (M/B) were similar (P = NS). The redistribution images gave the same results. In both techniques myocardial and lung-background thallium uptake counts dropped significantly from stress to redistribution images, but because they declined at similar rates, the resulting image quality index (M/B) remained unchanged. Adverse effects occurred less frequently in the dipyridamole stressed group. Thallium images performed after dipyridamole stress are at least equivalent in image quality to those after exercise stress. This technical study further strengthens the clinical case for the use of the dipyridamole stress technique in routine diagnostic imaging.

Dipyridamole↗
PubMed1986

Complementary role of thallium-201 scintigraphy to predischarge exercise electrocardiography for patients stratification after a first myocardial infarction.

The value of a predischarge exercise test combined with thallium-201 myocardial scintigraphy in detecting patients with severe multivessel disease (MVD) was studied in 58 consecutive patients discharged after a first acute myocardial infarction. Twelve electrocardiographic, clinical and scintigraphic variables were analysed. Angiography at one month revealed MVD (greater than 70% narrowing in vessels unrelated to infarction) in 26 patients (45%). ST segment depression of 1mm or greater, thallium defects in multiple vascular distributions (MVTL), and reversible thallium defects in a vascular distribution different from the infarct related vessel predicted patients at risk for MVD (predictive value respectively of 68%, 65% and 75%). The other variables were not significantly associated with the presence of MVD. Only ST segment depression and thallium defects in multiple vascular distributions emerged as independent predictors of MVD. Their combination yielded a 77% sensitivity and a 59% specificity for MVD. Combination of thallium imaging with the predischarge exercise ECG significantly improved the stratification provided by the exercise test alone (P less than 0.05). A positive thallium scan (MVTl defects) associated with a positive ECG (ST depression) carried a risk for MVD of 80% in the population studied. When both tests were negative, MVD was infrequent (risk 22%). Because improvement in the stratification of patients is not as clear as expected from studies performed at a later stage, it appears that exercise thallium scintigraphy at a submaximal level one or two weeks after infarction does not provide optimal information. Predischarge exercise thallium-201 scintigraphy, however, is superior to an exercise tolerance test alone in separating patients into those with high and low risk of MVD.

Electrocardiography↗
PubMed1994

Does routine stress-thallium cardiac scanning reduce postoperative cardiac complications?

OBJECTIVE: Prophylactic cardiac revascularization in patients with ischemic myocardium could reduce postoperative cardiac complications after aortic reconstruction. However, the effectiveness of this approach has not been documented. SUMMARY BACKGROUND DATA: Stress-thallium scanning can identify patients with ischemic myocardium. Morbidity and mortality after aortic reconstruction appears to be largely caused by co-existent coronary artery disease, and patients who have had recent cardiac revascularization have few postoperative cardiac complications. METHODS: Preoperative stress-thallium scanning was evaluated prospectively in 146 patients undergoing aortic reconstruction. Patients with positive studies underwent coronary arteriography and cardiac revascularization, when appropriate. Postoperative cardiac complications and long-term survival in these patients were compared with results from 172 similar patients undergoing aortic reconstruction without stress-thallium scanning. Results also were analyzed to determine predictors of postoperative cardiac events. RESULTS: Forty-one per cent of patients undergoing stress-thallium testing underwent coronary arteriography, and 11.6% had cardiac revascularization. In contrast, 14.7% of patients treated without stress-thallium testing had coronary arteriography, and 4.1% had revascularization (p < 0.01). Despite this, cardiac mortality, serious cardiac complications, and long-term cardiac mortality were similar in both groups. Only advanced age and intraoperative complications (but not a positive stress-thallium test) predicted postoperative cardiac events. CONCLUSIONS: Preoperative stress-thallium testing confirmed a high incidence of significant coronary artery disease in patients undergoing aortic reconstruction, but prophylactic cardiac intervention does not reduce operative or long-term mortality. Thus, the risk and expense of routine stress-thallium testing and subsequent cardiac revascularization cannot be justified.

Aged↗
PubMed1995

Usefulness of dipyridamole-thallium imaging in 257 patients with atherosclerotic vascular disease.

We evaluated the usefulness of dipyridamole-thallium imaging for the detection of ischaemic heart disease in 257 patients with atherosclerotic vascular disease (80 patients with arteriosclerosis obliterans, 81 patients with aneurysm of the abdominal aorta, 60 patients with aneurysm of the thoracic aorta and 36 patients with dissecting aortic aneurysm). Clinical evidence of ischaemic heart disease was found in 69 of 257 (27%) patients, including 32 patients with arteriosclerosis obliterans, 23 with aneurysm of the abdominal aorta, 9 with aneurysm of the thoracic aorta and 5 with dissecting aortic aneurysm. Dipyridamole-thallium imaging identified myocardial ischaemia in 49 of 69 (71%) patients with clinical evidence of ischaemic heart disease. Dipyridamole-thallium imaging showed positive results in 67 of 81 (83%) patients with aneurysm of the abdominal aorta. In patients with no clinical evidence of ischaemic heart disease, the results of dipyridamole-thallium imaging were positive in 39 of 188 (21%) patients. Dipyridamole-thallium imaging was positive in 90 of the 257 (35%) patients as a whole. When we combined the patients with positive dipyridamole-thallium imaging with those with negative dipyridamole-thallium imaging but who had clinical evidence of ischaemic heart disease, 42% of all patients had evidence of ischaemic heart disease. Our findings suggest that atherosclerotic vascular disease is strongly associated with ischaemic heart disease and that dipyridamole-thallium imaging is useful for the detection of ischaemic heart disease.

Aged↗
PubMed1988

Thallium kinetics in rat cardiac transplant rejection.

Cardiac transplant rejection is a very complex process involving both cellular and vascular injury. Recently, thallium imaging has been used to assess acute transplant rejection. It has been suggested that changes in thallium kinetics might be a sensitive indicator of transplant rejection. Accordingly, thallium kinetics were assessed in vivo in acute untreated rat heterotopic (cervical) transplant rejection. Male Lewis rats weighing 225-250 g received heterotopic heart transplants from syngeneic Lewis rats (group A; n = 13), or allogeneic Brown Norway rats (group B; n = 11). Rats were imaged serially on the 2nd and the 7th postoperative days. Serial cardiac thallium content was determined utilizing data collected every 150 sec for 2 hr. The data were fit to a monoexponential curve and the decay rate constant (/sec) derived. By day 7 all group B hearts had histological evidence of severe acute rejection, and demonstrated decreased global contraction. Group A hearts showed normal histology and contractility. However, thallium uptakes and washout of the two groups were the same. Peak thallium uptake of group B was +/- 3758 1166 counts compared with 3553 +/- 950 counts in the control group A (P = 0.6395); The 2-hr percentage of washout was 12.1 +/- 1.04 compared with 12.1 +/- 9.3 (P = 1.0000); and the decay constant was -0.00002065 +/- 0.00001799 compared with -0.00002202 +/- 0.00001508 (P = 0.8409). These data indicate that in vivo global thallium kinetics are preserved during mild-to-severe acute transplant rejection. These findings suggest that the complex cellular and extracellular processes of acute rejection limit the usefulness of thallium kinetics in the detection of acute transplant rejection.

Animals↗
PubMed2004

Cerebrospinal fluid analysis in fatal thallium poisoning: evidence for delayed distribution into the central nervous system.

The neurologic manifestations of thallium poisoning include a severely painful ascending peripheral neuropathy, autonomic dysfunction, cranial nerve abnormalities, and a toxic encephalopathy. Although thallium has a short half-life, these neurologic manifestations commonly progress, even as the blood concentration of thallium decreases. This suggests either that thallium persists in neuronal tissues or that it initiates an injury cascade that takes time to fully manifest. As the latter mechanism is consistent with many toxin exposures, the concept of a central nervous system reservoir for thallium is often discounted. A recent case provided a unique opportunity to evaluate this possibility. A 48-year-old man was acutely and chronically thallium poisoned by his common-law wife. During his initial exposures, only gastrointestinal symptoms manifested. Following an acute ingestion, hospitalization was required. Over 3 days, his symptoms rapidly progressed from a severely painful neuropathy to slurred speech, ptosis, confusion, coma, respiratory insufficiency, and death. Because of considerations of alternative diagnoses, 2 lumbar punctures were performed, one on admission and another on the day of his death. Serum thallium concentrations obtained from stored blood samples were paired with spinal fluid concentrations from the same days. On day 1, serum and spinal fluid concentrations were 8700 mu/L and 1200 mu/L, respectively. On day 3, although the serum concentration had fallen to 7200 mu/L, the spinal fluid concentration had increased to 2100 mu/L. This case provides evidence to support the hypothesis that thallium distributes into the central nervous system more slowly than the blood compartment, and this may in part account for the progression of neurologic findings in the setting of decreasing serum concentrations.

Consciousness Disorders↗
PubMed1999

Intracranial mass lesions: sequential thallium and gallium scintigraphy in patients with AIDS.

PURPOSE: To determine the efficacy of sequential thallium and gallium scintigraphy to differentiate intracranial neoplasms (lymphoma and glioma) from other nonmalignant intracranial mass lesions among patients with acquired immunodeficiency syndrome (AIDS). MATERIALS AND METHODS: The authors reviewed the cases of 40 patients with human immunodeficiency virus (HIV) who underwent thallium and gallium scanning to evaluate intracranial mass lesions from October 1991 through November 1997. There was a definitive final diagnosis of the nature of the mass lesions in 21 of these cases. In these 21 cases, the scintigraphic patterns were reviewed and were compared with the final diagnosis. RESULTS: On the basis of results at thallium and gallium scanning, the patients were divided into three groups. Group A included 13 patients (11 with brain tumors [lymphomas and gliomas] and two with progressive multifocal leukoencephalopathy [PML]) with thallium-positive, gallium-positive scans. Group B included five patients with intracranial infections (tuberculosis, Cryptococcus, bacteria) with thallium-negative, gallium-positive scans. Group C included three patients (one with PML and two with infarcts) with thallium-negative, gallium-negative scans. All patients with lymphomas were in group A. The sensitivity and specificity of the thallium-positive, gallium-positive pattern for intracranial malignancy were 100% and 80%, respectively. CONCLUSION: Sequential thallium and gallium scanning helped differentiate tumors from nonmalignant intracranial mass lesions and may help differentiate infections from PML or infarcts.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Risk stratification prior to vascular surgery: does the location of a dipyridamole thallium scintigram defect provide prognostic information?

BACKGROUND: While the value of myocardial scintigraphy using dipyridamole thallium is accepted for risk assessment prior to vascular surgery, it is unknown whether the location of the thallium abnormalities provides prognostic information. METHODS: Records from 435 consecutive patients scheduled for vascular surgery were reviewed and patients with dipyridamole thallium abnormalities involving the anterior distribution (ANTERIOR n = 62), or inferior or inferolateral distribution (INFERIOR n = 105) were assessed for cardiac complications of surgery (death, myocardial infarction, unstable angina or ischemic congestive heart failure). RESULTS: Patients with a normal dipyridamole thallium scintigraphy had few surgical cardiac complications: 2/86 (2%). Patients with an ANTERIOR dipyridamole thallium defect had a 12% incidence of surgical cardiac complications (7/57) without any cardiac deaths, while patients with an INFERIOR dipyridamole thallium defect had a similar incidence of surgical cardiac complications, 18% (18/100; p = 0.65 vs. ANTERIOR) including 4 cardiac deaths. CONCLUSIONS: Significant inferior or inferolateral dipyridamole thallium scintigraphy abnormalities are not associated with a lower risk of cardiac complications following vascular surgery than anterior abnormalities. Rather, any clearly abnormal dipyridamole thallium study is a marker for increased risk of perioperative events and may warrant further evaluation and treatment.

Aged↗
PubMed1982

Serial thallium-201 myocardial imaging after dipyridamole infusion: diagnostic utility in detecting coronary stenoses and relationship to regional wall motion.

After a 4-minute i.v. dipyridamole infusion, 0.14 mg/kg/min, serial thallium-201 scans were obtained in 60 patients undergoing cardiac catheterization. Forty patients had significant (greater than or equal to 50% stenosis) coronary artery disease (CAD), and 20 patients had normal coronary arteries or trivial lesions. The images were graded qualitatively for thallium activity by three observers. Sensitivity was 93% (37 of 40) and specificity was 80% (16 of 20). The sensitivity and specificity of the thallium-201 study were not affected by the extent of CAD, the presence of Q waves, or propranolol therapy. Twenty-seven of 37 patients who had initial defects (73%) had complete thallium redistribution of one or more defects. Patient-by-patient analysis using a regression model of all patients showed that the fate of a segmental thallium defect predicted abnormal wall motion by angiography better than ECG Q waves. The presence of propranolol therapy or collaterals did not significantly affect the thallium redistribution results. We conclude that qualitative interpretation by multiple observers of thallium images after dipyridamole infusion is a highly sensitive and specific test for CAD. After dipyridamole, as with exercise stress, the extent of thallium redistribution is related to the degree of myocardial wall motion abnormality.

Adult↗
PubMed1983

Relationship between segmental thallium-201 uptake and regional myocardial blood flow in patients with coronary artery disease.

The relationship between the spatial distribution of thallium-201 in myocardial perfusion scintigrams and the distribution of left ventricular regional myocardial blood flow was examined in 25 patients undergoing coronary arteriography. Thallium-201 myocardial scintigrams were obtained after symptom-limited exercise and after a 4 hr delay. Regional myocardial blood flow was measured by the xenon-133 clearance method in patients at rest and during rapid atrial pacing to a double product comparable with that achieved during exercise stress testing. Patterns of regional thallium-201 activity and regional myocardial blood flow, recorded in similar left anterior oblique projections, were compared for left ventricular segments supplied by the left anterior descending (LAD) and left circumflex (CIRC) arteries. In 11 patients without significant lesions of the left coronary artery (group 1), thallium-201 was homogeneously distributed in the LAD and CIRC distributions in scintigrams taken during peak exercise; these scintigrams correspond to homogeneous regional myocardial blood flow in the LAD and CIRC regions during pacing-induced stress. In 14 patients with significant lesions of the left coronary artery (group 2), ratios of regional thallium-201 activity in the LAD and CIRC distributions of exercise scintigrams correlated well (r = .84) with ratios of regional myocardial blood flow measured during rapid pacing. Background subtraction altered the relationship between relative thallium-201 uptake and regional myocardial blood flow, causing overestimation of the magnitude of flow reduction on exercise scintigrams. These data indicate that: (1) in patients with normal left coronary arteries, thallium-201 is homogeneously distributed to the left ventricle, reflecting the homogeneous distribution of regional myocardial blood flow over a wide range of mean left ventricular flow rates and (2) in patients with significant lesions of the left coronary artery, the relative spatial distribution of thallium-201 activity in exercise perfusion scintigrams reflects the distribution of regional myocardial blood flow.

Adult↗
PubMed1983

Differences in Thallium-201 uptake in reperfused and nonreperfused myocardial infarction.

The respective importance of flow and cellular viability in determining initial myocardial thallium uptake was studied in reperfused and nonreperfused experimental myocardial infarction. Open-chest dogs were subjected to permanent coronary artery occlusion of 70-minute (n = 3) or 5-hour duration (n = 5), or to a 3-hour temporary occlusion followed by reflow (n = 14). Thallium uptake 10 minutes after intravenous injection was compared directly with radioactive microspheres in myocardial samples from excised hearts. Triphenyl tetrazolium chloride staining was used to differentiate necrotic and viable samples with confirmation by electron microscopy. In nonreperfused infarcts, thallium uptake occurred despite necrosis, and a close correlation was found between thallium uptake and regional myocardial blood flow. In reperfused infarcts, thallium uptake again occurred, but was reduced relative to flow in necrotic myocardium and, to a lesser extent, in reperfused viable areas. However, because of the high levels of reflow, actual thallium uptake was often more than 50% of normal in reperfused necrotic regions. This study demonstrates that the presence of thallium uptake is an unreliable indicator of myocardial injury and that reperfused necrotic tissue may have remarkably high levels of thallium uptake.

Animals↗
PubMed1984

Relationship between regional myocardial blood flow and thallium-201 distribution in the presence of coronary artery stenosis and dipyridamole-induced vasodilation.

This study assesses the relationship between the distribution of thallium-201 and myocardial blood flow during coronary vasodilation induced by intravenous dipyridamole in canine models of partial and complete coronary artery stenosis. 10 dogs were chronically instrumented with catheters in the left atrium and aorta and with a balloon occluder and electromagnetic flow probe on the proximal left circumflex coronary artery. Regional myocardial blood flow was measured during control conditions with radioisotope-labeled microspheres, and the phasic reactive hyperemic response to a 20-s transient occlusion was then recorded. Dipyridamole was then infused intravenously until phasic coronary blood flow increased to match peak hyperemic values. The left circumflex coronary artery was either partially occluded to reduce phasic blood flow to control values (group 1) or it was completely occluded (group 2), and thallium-201 and a second microsphere label were injected. 5 min later, the animals were sacrificed, the left ventricle was sectioned into 1-2-g samples, and thallium-201 activity and regional myocardial blood flow were measured. Curvilinear regression analyses between thallium-201 localization and myocardial blood flow during dipyridamole infusion demonstrated a slightly better fit to a second- as compared with a first-order model, indicating a slight roll-off of thallium activity as myocardial blood flow increases. During the dipyridamole infusion, the increases in phasic blood flow, the distributions of regional myocardial blood flow, and the relationships between thallium-201 localization and regional blood flow were comparable to values previously observed in exercising dogs with similar occlusions. These data provide basic validation that supports the use of intravenous dipyridamole and thallium-201 as an alternative to exercise stress and thallium-201 for evaluating the effects of coronary occlusive lesions on the distribution of regional myocardial blood flow.

Animals↗
PubMed1993

Implications of delayed image on simultaneous thallium-201/technetium-99m pyrophosphate dual emission computed tomography early after acute myocardial infarction.

This study aimed investigate whether thallium-201 and technetium-99m pyrophosphate dual rest-redistribution emission computed tomography early after intracoronary thrombolysis may provide supplementary information for the management of patients with acute myocardial infarction. Fifty patients who received intracoronary thrombolysis underwent simultaneous dual emission computed tomography 3 days after first acute myocardial infarction. All patients who had a technetium-99m pyrophosphate accumulation were selected. Thallium-201/technetium-99m pyrophosphate overlap in the initial and delayed images early after intracoronary thrombolysis identified successful recanalization with sensitivities of 68% and 90% (p < 0.05), specificities of 47% 79% (p < 0.05), positive predictive accuracies of 68% and 88%, negative predictive accuracies of 47% and 80% (p < 0.05), and overall accuracy of 60% and 86% (p < 0.01), respectively. The patients were divided into 3 groups according to the change in thallium-201 uptake from the initial image to the delayed image on dual emission computed tomography: 20 patients had no change in thallium-201 uptake (fixed type), 16 had increases in thallium-201 uptake (redistribution type), and 14 had decreases in thallium-201 uptake (reverse redistribution type). The number of patients with successful recanalization was significantly higher in the redistribution type than in the other types (redistribution type vs reverse redistribution type or fixed type; p < 0.01, respectively). In the redistribution type a frequency of reinfarction in the same infarcted area during the hospital course was significantly higher than in the other types (redistribution type vs reverse redistribution type or fixed type; p < 0.05, respectively), which was mainly due to the patients having high grade residual stenosis. Thus, a thallium-201/technetium-99m pyrophosphate overlap in the delayed image early after acute myocardial infarction can be used as an index for predicting successful early recanalization and probably viable myocardium. In addition, the redistribution patterns on thallium-201 emission computed tomography early after intracoronary thrombolysis can be helpful in identifying patients with successful early recanalization and a high risk subset.

Adult↗