Influence of peak exercise heart rate on normal thallium-201 myocardial clearance

Measurement of myocardial clearance rates between initial and delayed images is a major justification for adding computer quantification to the interpretation of exercise 201TI images. To clarify the range of normal thallium clearance and its relationship to the level of exercise achieved, exercise thallium images in 89 normal subjects were analyzed: 45 asymptomatic subjects with less than 1% probability of coronary artery disease (CAD) (Group I), and 44 patients with chest pain found to have no significant CAD on angiography (Group II). Mean initial regional thallium uptake was similar in the two groups, but myocardial thallium clearance (mean +/- 1 s.d.) was slower in Group II, expressed as a longer half-life in the myocardium (8.2 +/- 7.6 hr compared with 3.4 +/- 0.7 hr p less than 0.001). Analysis of variance using ten clinical and exercise variables as covariates showed that the slower clearance in Group II was related to a lower peak exercise heart rate (HR) (154 +/- 27 compared with 183 +/- 11, respectively, p less than 0.001). By linear regression analysis, a decrease in peak HR of 1 beat/min was associated with a slower thallium clearance (longer half-life) of 0.05 hr. Using this formula, the clearance value in each patient was then corrected for peak exercise heart rate by decreasing measured clearance by 0.05 hr multiplied by the amount peak exercise heart rate which was below 183 (the mean value in Group I). There were no differences in the "corrected" clearance between the two groups. We conclude that thallium myocardial clearance after exercise is related in part to factors other than the presence of CAD, being slower when peak exercise HR is lower. Therefore, thallium clearance rates alone uncorrected for peak exercise heart rate should be used with caution when diagnosing CAD.     

Evaluation of myocardial uptake of thallium-201 in whole body scintigraphy

Whole body scintigraphy (WBS) was performed to assess the myocardial uptake in the dipyridamole (DP), exercise loading (EX) and thallium-201 (Tl-201) myocardial scintigraphy. DP-WBS was studied in 15 patients (pts), EX-WBS was studied in 17 pts and resting (RE)-WBS was studied in 20 pts. All pts had some kinds of heart disease clinically, but their myocardial scintigraphy showed no abnormal findings. DP-WBS and EX-WBS were performed both immediately (early image DP-E, EX-E) and 3 hours later (delayed image EX-D, DP-D) after injection of Tl-201. RE-WBS were performed immediately (early image REST) after injection of Tl-201 only. The percent myocardial uptake, background ratio of the myocardium and washout ratio of some organs were calculated from the ROIs (region of interest) over the whole body, heart, lung, mediastinum, abdomen and thighs. The myocardial uptake of DP-E was 9.1 +/- 1.4%, myocardial uptake of EX-E was 6.3 +/- 0.8% and myocardial uptake of REST was 7.1 +/- 1.2%. The thighs uptake of DP-E was 10.4 +/- 1.1%, thighs uptake of EX-E was 25.3 +/- 2.6% and thighs uptake of EX-E was 25.3 +/- 2.6% and thighs uptake of REST was 10.1 +/- 1.5%. The percent myocardial uptake of DP-E was not only higher than that of EX-E (p less than 0.001) but also higher than that of REST (p less than 0.01). Thus, we conclude that DP scintigraphy showed clearer myocardial image than EX scintigraphy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sex-specific criteria for interpretation of thallium-201 myocardial uptake and washout studies

A study was undertaken to determine the effect of gender on criteria for the quantitative analysis of exercise-redistribution 201Tl myocardial scintigraphy. The studies of 26 normal females and 23 normal males were subjected to bilinear interpolative background subtraction and horizontal profile analysis. Significant sexual differences were found in both regional uptake ratios and washout rates. These differences primarily reflected a proportionately decreased anterior and upper septal uptake in females, and faster washout in females. Faster myocardial 201Tl washout rates in females could not be clearly ascribed to either a physiological or artifactual explanation. It is concluded that since important differences exist between males and females in the detected pattern of 201Tl myocardial uptake and washout, sex-specific criteria may enhance the predictive accuracy of exercise-redistribution 201Tl myocardial scintigraphy.     

Tumour uptake of thallium-201 chloride

The uptake of ²⁰¹Tl-chloride in tumours has recently been investigated in several authors' laboratories. We are reporting studies on the uptake in malignant melanoma in mice. Generally, we confirm the published data qualitatively in finding higher uptake in tumour than in muscle. We confirm the rapid blood clearance and high kidney concentration, but we did not measure the myocardial uptake. We observed the concentrations in kidney muscle and tumour to rise during the first four hours while that in the liver fell from one hour onwards. We did not observe markedly higher uptake in melanin rich tumour than in other tumours.     

Effect of ribose on thallium-201 myocardial redistribution

Myocardial 201Tl redistribution after transient ischemia may be too slow to allow identification of a reversible myocardial defect within the routine 201Tl imaging period. To determine whether 201Tl redistribution could be affected by a metabolic intervention, intravenous ribose was administered postischemia. Seventeen domestic swine were subjected to a 10-min ischemic period followed by either a 30-min i.v. ribose (n = 8) or saline (n = 9) infusion. Thallium-201 was injected during ischemia and myocardial 201Tl activity was continuously monitored in ischemic and nonischemic regions with miniature CdTe radiation detection probes. Coronary flow in the ischemic region was reduced to 25% of that in the nonischemic regions in both saline and ribose groups. The 201Tl time-activity curves demonstrated a significant enhancement of % 201Tl redistribution in the ribose-treated animals at the end of ribose infusion: Ribose (48 +/- 11%), Saline (20 +/- 4%), p less than 0.05. Alteration of 201Tl kinetics by ribose may permit earlier recognition of 201Tl myocardial redistribution after transient ischemia.     

Tumour uptake of thallium-201 chloride.

The uptake of 201Tl-chloride in tumours has recently been investigated in several authors' laboratories. We are reporting studies on the uptake in malignant melanoma in mice. Generally, we confirm the published data qualitatively in finding higher uptake in tumour than in muscles. We confirm the rapid blood clearance and high kidney concentration, but we did not measure the myocardial uptake. We observed the concentrations in kidney muscle and tumour to rise during the first four hours while that in the liver fell from one hour onwards. We did not observe markedly higher uptake in melanin rich tumour than in other tumours.     

Effect of aminophylline on thallium-201 washout rate during myocardial perfusion imaging with dipyridamole

Thallium-201 myocardial perfusion imaging with dipyridamole was performed on 78 patients (pts) with suspected coronary artery disease (CAD). Twenty eight pts had normal coronary arteries (control group), and 50 pts had 50% or greater stenosis in one or more major coronary arteries (CAD group). In control group, aminophylline (Am) was infused intravenously on 12 pts during dipyridamole testing. Mean washout rate (WR) of these 12 pts was greater than that of 16 pts without Am (42% vs 35%, p less than 0.01). Then normal limit of WR was defined separately from the pts of control group with and without Am. The sensitivity for detecting the pts with CAD by WR analysis which normal limit was calculated separately with and without Am was 92% (46/50). When normal limit of WR was determined from all pts in control group, the sensitivity decreased to 84% (42/50). Am significantly affected thallium-201 washout during dipyridamole testing. WR of CAD pts should be estimated by specific set of normal limit with and without Am.     

Effects of myocardial revascularization on regional thallium-201 uptake and systolic function in regions with reverse redistribution on tomographic thallium-201 imaging at rest in patients with chronic coronary artery disease

Objectives  There is growing evidence that myocardial segments with reverse redistribution are viable in patients with chronic coronary artery disease. The aim of this study was to assess the effects of myocardial revascularization on systolic function and thallium-201 uptake in such segments. Methods  Rest-redistribution thallium-201 tomography before and after myocardial revascularization was performed in 47 patients with chronic coronary artery disease. Regional function was evaluated by two-dimensional echocardiography before and after revascularization according to a 3-point scale (1=normal, 2=hypokinetic, 3=a/dyskinetic). Improvement of dysfunctional segments was defined when systolic function score decreased ≥1 after revascularization. Reverse redistribution was defined as ≥8% decrease in relative thallium-201 uptake between rest and redistribution images. Results  Reverse redistribution was found in 27 (57%) of 47 patients, corresponding to 60 (11%) of 564 myocardial segments. Of such segments, 24 (40%) had normal systolic function, 19 (32%) were hypokinetic, and 17 (28%) were a/dyskinetic. Thirty-six segments underwent myocardial revascularization, and reverse redistribution was no longer present in 86% of them subsequent to the procedure. Of 26 dyssynergic segments with reverse redistribution subjected to revascularization, 18 (69%) improved at follow-up. Conclusions  The findings of the present study indicate that reverse redistribution is a reversible phenomenon and is often associated with improvement of systolic function following revascularization in patients with chronic coronary artery disease.     

Myocardial uptake of thallium-201 diethyldithiocarbamate (201TI-DDC) in cultured heart cells and in humans

We assessed the feasibility of SPECT imaging with ²⁰¹Tl-diethyldithiocarbamate (²⁰¹Tl-DDC), a new cerebral blood flow tracer with little redistribution, expecting to observe less extensive redistribution than with ²⁰¹Tl-chloride. Myocardial sections were obtained in three patients presenting with documented coronary artery disease and injected at peak exercise with 100 MBq ²⁰¹Tl-DDC. In two patients there was a clear redistribution phenomenon at four h after injection. In cultured myocardial cells of newborn rats, the uptake and washout of ²⁰¹Tl-chloride and ²⁰¹Tl-DDC were compared. The ²⁰¹Tl-DDC uptake was lower than ²⁰¹Tl-chloride (transmembrane gradients were respectively 89±10 and 4.1±0.2, mean±sem, n=14, P<0.001). After 2 h washout in a Tl free medium, the retention of ²⁰¹Tl-chloride in the cells was 4% vs 19% for ²⁰¹Tl-DDC. It is concluded that although myocardial imaging is feasible with ²⁰¹Tl-DDC, this agent redistributes significantly with time.     

Influence of propranolol on uptake of radioiodinated heptadecanoic acid and thallium-201 in the dog heart

In an experimental study, the influence of propranolol on myocardial uptake of radioiodinated heptadecanoic acid (¹³¹I-HDA) and thallium-201 (²⁰¹Tl) in the dog heart was assessed. Uptake of ¹³¹I-HDA and ²⁰¹Tl was evaluated in ten control dogs and in ten dogs 20 min after IV administration of propranolol (0.15 mg/kg). In both groups, four healthy dogs were studied and six dogs were studied after coronary artery occlusion. It was shown that both total uptake of ¹³¹I-HDA and ²⁰¹Tl did not alter significantly, regardless of significant changes in hemodynamic parameters and total arterial plasma FFA levels. However, distribution of both ¹³¹I-HDA and ²⁰¹Tl was markedly affected by propranolol, since the endocardial to epicardial ratio showed significantly higher values in the ischemic myocardial regions. The results of our study indicate that propranolol (1) preserves myocardial perfusion in the normal and acutely ischemic dog heart, and (2) gives a more favorable distribution in the ischemic myocardial region towards the subendocardial layers.     

Tumor grade-related thallium-201 uptake in chondrosarcomas

Objectives  

Diagnosis of low-grade chondrosarcoma, especially discrimination between enchondroma and low-grade chondrosarcoma, may be difficult pathologically. The aim of this study was to evaluate the value of thallium-201 (Tl-201) scintigraphy in the diagnosis of chondrosarcoma and to investigate whether there was a correlation between Tl-201 uptake and tumor grade.     

Quantification of rotational thallium-201 myocardial tomography

A comprehensive method is described for quantification of the relative 3-dimensional distribution of Tl-201 in the myocardium, following stress and subsequent washout. The method uses maximal-count circumferential profiles of well-defined long- and short-axis tomograms to determine the 3-dimensional distribution of Tl-201; it then maps this distribution onto a 2-dimensional polar representation. Abnormal thallium distribution or washout is identified by automatic computer comparison of each patient's profile with the corresponding lower limits of normal profiles. Abnormality is expressed as a percentage of the entire myocardium by use of polar maps for extent and severity. The binary extent map expresses the degree of abnormality. Preliminary criteria for abnormality were derived from the tomographic results of 25 normals and 28 patients with documented coronary artery disease. The results were normal in 23 of the 25 normals and were abnormal in 25 of the 28 CAD patients. In addition, the computer output correctly localized the presence or absence of disease in 46 of 56 coronary circulations.     

Discriminant analysis of thallium-201 myocardial scintigrams

In a group of 207 patients undergoing coronary angiography, myocardial scintigrams have been performed at rest (n = 95), after exercise testing (n = 50) or after dipyridamole vasodilation (n = 62). Pictures recorded in anterior and 45 degrees left anterior oblique projections have been analysed according to a model which divides each projection into 5 territories. Thallium uptake has been visually assessed using a three grade scale: 0 = normal uptake, + = sightly abnormal uptake, ++ = evident hypoactivity. With reference to angiography, sensitivity and specificity for prediction of coronary artery disease have been calculated in a classical way using three different criteria of positivity of increasing severity, and by a computerized method based on discriminant analysis. In the first case, sensitivity and specificity were highly dependent one on the other and, as could be expected, varied in opposite directions, a high sensitivity (89 to 100%) being only achieved by accepting a lack of specificity (33 to 57%). Discriminant analysis, on the contrary, provided for each type of protocol: rest, stress, dipyridamole and redistribution, a single optimized combination of sensitivity (74 to 87%) and specificity (92 to 100%). The corresponding point, when located on the receiver operating characteristics (ROC) diagram, demonstrated a clear improvement in diagnostic accuracy. The same method has been applied for discrimination, not only between normals and abnormals, but also between normals and patients with and without myocardial infarction (correct diagnosis in 50 to 68% of cases), and between normals and patients with single-, double- or triple-vessel disease (correct diagnosis in 17 to 65% of cases) with a high specificity (correct classification of normals in 86 to 100% of cases).     

New etiology for intestinal uptake of thallium-201

A patient with both rest and exercise thallium images for unstable angina demonstrated marked large intestinal uptake of thallium. However, the thallium uptake in the large intestine was noted only after exercise. The only change in the patient status between the two studies was the administration of verapamil. Thus, verapamil administration has been demonstrated to be a new cause for gut uptake of thallium.     

Analysis of papillary muscle images on planar thallium-201 myocardial scintigrams in various heart diseases

²⁰¹Tl myocardial imaging can, noninvasively, visualize the various cardiac structures; such as the left ventricle, right ventricle and, occasionally, the atrium. We have noted that certain patients exhibit a prominent appearance of the papillary muscle on a scintigram. Thus, we analyzed ²⁰¹Tl myocardial scintigrams for evidence of activity which corresponded to the anterolateral (A-PM) and posteromedial (P-PM) papillary muscles.Twenty normal subjects, 81 patients with ischemic heart disease (IHD), 11 with hypertrophic cardiomyopathy (HCM) and 13 with dilated cardiomyopathy (DCM) were examined. Patients with DCM had rest imaging only, while the remaining ones performed exercise studies. The prevalence of a positive A-PM image was not high (9%–23%) and there was no significant difference among groups. The P-PM was seen in only 15% of the normal group and in 18% of the HCM group, while the prevalence was high in the IHD (34.6%) and DCM (53.8%) groups. In the IHD, the positive images of the P-PM were largely from the subgroup with single vessel left anterior descending (LAD) coronary artery disease (78.9%). However, even in the presence of a defect in the left ventricular wall supplied by the LAD coronary artery, the patients with multi-vessel coronary artery disease did not tend to disclose the P-PM on the scinti-gram (30.8%). Thus, we conclude that positive P-PM imaging on a planar ²⁰¹Tl myocardial scintigram is frequently observed under some cardiac states and seems to be related to reduced wall motion, sound blood supply to the P-PM and the existence of a defect in the anterior left ventricular wall overlapping the P-PM. When we analyze the planar ²⁰¹Tl myocardial scintigram, not only the left and right ventricles, but also the PM should be assessed.     

The effect of glucose-insulin-potassium on thallium-201 myocardial redistribution

Intravenous infusion of glucose-insulin-potassium (GIK) has been shown to alter the net rate of clearance of ²⁰¹Tl from transiently ischemic and normally perfused canine myocardium. This study was performed to determine if GIK would also decrease the extent of thallium redistribution after transient myocardial ischemia. Six anesthetized, open-chest dogs underwent two studies, one with GIK and another with saline infusion. The left anterior descending coronary artery was occluded, ²⁰¹Tl injected, and the occlusion released 5-min later. An i.v. infusion of either GIK (4 dogs) or saline (2 dogs) was then begun and continued for the 120-min duration of serial myocardial imaging using a standard scintillation camera. The experiment was then repeated with an infusion of saline (4 dogs) or GIK (2 dogs). The dose of ²⁰¹Tl for the second study was at least 5 times more than was used for the first study.The serial 2-min images were then displayed on computer and regions of interest were drawn over the areas of transient ischemia (TI) and normal perfusion (NP). The ratio of average counts per picture element for the area of TI compared to NP was calculated. One hundred and twenty minutes after ²⁰¹Tl administration, the change in the TI/NP ratio (% fill-in) was significantly less for the GIK infusion compared to saline infusion (control) 15.4 ± 4.0% vs 26.2 ± 6.0% (mean ± SE) (P < 0.01), respectively. Therefore, GIK infusion appeared to decrease the extent of thallium redistribution compared to saline control.