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.     

Significance of diffuse slow washout in dipyridamole loading thallium-201 myocardial perfusion scintigraphy

To assess the significance of diffuse slow washout (DSW) in dipyridamole loading thallium-201 myocardial perfusion scintigraphy, 382 patients were studied. DSW were observed in 69 (24%) of 285 patients with perfusion defects, 5 (5%) of 97 patients without perfusion defects. There was significant relation between DSW and perfusion defects (p less than 0.01). Coronary angiography showed multivessel disease in 84% single vessel disease in 12% of patients with DSW and multivessel disease in 28%, single vessel disease in 50% of patients without DSW. During a mean follow up period of 29 months, initial CABG or PTCA were done in 41%, cardiac death occurred in 12%, nonfatal cardiac events occurred in 7% of patients with DSW and perfusion defects. In patients without DSW, initial CABG or PTCA were done in 11%, cardiac death occurred in 7%, nonfatal cardiac events occurred in 5%. Patients without perfusion defects had good prognosis regardless of the presence or absence of DSW. In conclusion, DSW indicates serious cardiac ischemia in patients with perfusion defects. DSW does not indicate cardiac ischemia in patients without perfusion defects.     

Methods of background subtraction in myocardial perfusion imaging with thallium-201: a comparative study in the presence of an artefact

For thallium imaging quantitation, a simulation study has been made using different methods of interpolation for background subtraction and studying their behaviour in the presence of an artefact. Two artefacts were used, one simulating hepatic or splenic uptake and the other diaphragmatic activity. The interpolative methods used were three classic techniques using standard masks. Their algorithms were modified so that they could also be used with arbitrarily shaped masks enclosing myocardium, and a comparison between the original and modified methods was made. Our results show an improvement when using the modified algorithms adapted to the arbitrarily outlined mask.     

Clinical implications of diffuse slow washout of thallium-201 in exercise stress myocardial SPECT

Clinical implications of diffuse slow washout of thallium-201 (DSWO) in exercise-redistribution myocardial SPECT were studied. Thallium-201 washout rate was calculated by Bull's-eye method. DSWO was defined as having abnormal thallium-201 washout rate (less than 30% per 3 hours) in more than two thirds of each coronary artery (CA) area. OF 974 patients whose exercise heart rate exceeded 120/min, 51 (5.2%) showed DSWO and coronary angiography was performed in 43. Twenty-three patients (53%) showed triple vessel disease (3VD), 8 (19%) showed single or double vessel disease (1VD/2VD) and 12 (28%) showed normal CA. Patients with normal CA consisted of 6 patients with hypertrophic cardiomyopathy (HCM), 5 with hypertension (HT) and one with electrocardiographic abnormality only. The causes of DSWO were assessed from the history of effort angina (EA) and congestive heart failure (CHF), delayed fill-in of the perfusion defect and the ratio of lung to heart thallium-201 activity (L/M) at exercise as an indicator of the left ventricular (LV) function. High prevalence of EA (74%), high incidence of scintigraphic delayed fill-in (83%) and normal L/M suggested diffuse LV ischemia as the cause of DSWO in 3VD. On the other hand in patients with 1VD/2VD, LV dysfunction at exercise was considered as the cause of DSWO because of low prevalence of EA (13%) and scintigraphic delayed fill-in (13%) (p less than 0.01, p less than 0.005 each vs 3VD), and high L/M (p less than 0.001 vs 3VD) and high prevalence of CHF (38%, NS).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Analysis of thallium-201 "washout" from parametric color coded images

We developed a parametric washout image which color codes regional washout, and blindly compared enhanced perfusion images in multiple projections with regional washout graphs and images in 25 patients. Washout images permitted true spatial and anatomic assessment of regions viewed en face as well as those seen in tangent, making possible the exclusion of non-coronary irregularities and permitting evaluation of washout over the apparent cavity. "Cavitary" washout was abnormal in 10 of 12 patients with apparent cavitary dilation on the post stress image, but in none without this finding. The distribution and rotation of washout abnormalities seen over the cavity when viewed en face, and the long delay between the termination of stress and post-exercise image acquisition, suggest that apparent cavitary dilation is often related to improved visibility of the 201T1 deficient blood pool due to relative ischemia of the overlying myocardial wall.     

Twenty-four-hour thallium-201 late redistribution imaging enhances the detection of myocardial viability after myocardial infarction

BACKGROUND: Thallium-201 (201Tl) myocardial perfusion imaging has been widely used for evaluation of myocardial ischemia/viability after myocardial infarction. The 3- to 4-h early redistribution imaging has underestimated a considerable part of viable myocardium, while the 24-h late redistribution imaging may enhance the detection of myocardial ischemia/viability, but remains controversial. METHODS: Thirty-eighty patients with myocardial infarction underwent the initial, 3-h, and 24-h redistribution imaging after intravenous injection of 148-185 MBq 201Tl. Image quality analysis was performed using a four-grade model: excellent, good, moderate, and poor. The initial and 3-h images, the initial and 24-h images, and the 3- and 24-h images were compared double-blinded. RESULTS: The 3- and 24-h images showed no significant differences in image quality according to the four-grade model (P=.3580). Out of the 194 abnormal segments based on the initial imaging, 60 (31%) segments improved by at least one grade on the 3-h imaging, while 86 (44%) segments improved by at least one grade on the 24-h imaging. The 24-h late imaging detected more viable myocardium than the 3-h imaging did, with a significant difference (chi2=7.4235, P=.0064). There were 164 abnormal segments on the 3-h imaging, with an average 30% (48) segments improved by at least one grade on the 24-h imaging. There were 134 initial abnormal segments without any improvement on the 3-h imaging. Out of these segments, the 24-h late redistribution imaging detected additional redistribution in 30 segments, taking up 22%. The mean global score on the 3-h imaging significantly decreased compared to that on the initial imaging (t=5.71, P<.0001), and the mean global score on the 24-h imaging further decreased significantly compared to that on the 3-h imaging (t=6.28, P<.0001). CONCLUSIONS: Twenty-four-hour late 201Tl imaging, with satisfactory image quality, enhances the detection of myocardial viability after myocardial infarction.     

Thallium-201 myocardial scintigraphic evidence of ischemia in a patient with angina pectoris and normal coronary arteriogram: Significance of thallium-201 washout analysis

We present a patient who had anginal pain and an abnormal exercise electrocardiogram but a normal coronary arteriogram. We thought that myocardial ischemia was responsible for this symptom in view of the exercise left ventriculogram, exercise thallium-201 myocardial scintigraphy and effect of nitroglycerin on the anginal pain. The left ventriculogram at rest was normal but exercise worsened the entire left ventricular wall motion. Exercise thallium-201 myocardial images showed minimal reduction of radio-activity in the anterior, apical, antero-lateral and postero-lateral wall. Myocardial thallium-201 washout analysis revealed washout abnormalities all over the left ventricular myocardium similar to those of triple vessel disease, supporting the exercise left ventriculographic finding. Myocardial thallium-201 washout analysis as well as the visual method should be performed in patients with angina pectoris and normal coronary arteriograms.     

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).     

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.     

Assessment of myocardial viability in patients with myocardial infarction using twenty-four hour thallium-201 late redistribution imaging

BACKGROUND: Rest thallium-201 (201Tl) myocardial perfusion imaging has been widely used for evaluation of myocardial ischemia/viability after myocardial infarction, but the ideal timing for imaging after injection to maximally estimate viability is not well established. METHODS: Thirty-six patients with myocardial infarction underwent the initial, 3 h, and 24 h redistribution imaging after intravenous injection of 148-185 MBq 201Tl. The initial and 3 h images, the initial and 24 h images, and the 3 and 24 h images were compared double-blinded. RESULTS: Out of the 184 abnormal segments based on the initial imaging, 56 (30%) segments improved by at least 1 grade on the 3 h imaging while 78 (42%) segments improved by at least 1 grade on the 24 h imaging. The 24 h late imaging detected more viable myocardium than the 3 h imaging did, with a significant difference (chi2= 5.680, p = 0.017). There were 158 abnormal segments on the 3 h imaging, with average 28% (44) segments improved by at least 1 grade on the 24 h imaging. There were 128 initial abnormal segments with no improvement on the 3 h imaging. Out of these segments, the 24 h late redistribution imaging detected additional redistribution in 26 segments, taking up 20%. CONCLUSIONS: Twenty-four hour late 201Tl imaging will demonstrated additional redistribution in patients who have incompletely reversible defects on early redistribution imaging at 3h.     

Usefulness of resting thallium-201 delayed imaging for detecting myocardial viability in patients with previous myocardial infarction

To test the feasibility of resting thallium-201 (²⁰¹Tl) initial and delayed scintigraphy for detecting the area of viable myocardium, we performed single photon emission computed tomography (SPECT) in 57 patients with previous myocardial infarction (MI). All had received coronary arteriography (CAG) and left ventriculography (LVG). Initial and delayed myocardial imagings were carried out 10 min and 2 hours, respectively, after the injection of²⁰¹Tl at rest. Redistribution was judged by visual interpretation and/or the circumferential profile curve, and found in the infarcted or its adjacent area in 40 of the 57 cases (70.2%). A negative washout (net increase of²⁰¹Tl uptake in delayed image) was detected in 17 of these 40 cases. In 10 of the 57 patients, both exercise and rest-injected²⁰¹Tl myocardial images were obtained at exercise and rest, and compared visually. The areas of abnormal perfusion were smaller in the resting delayed images than those seen after exercise in 9 of the 10 cases, and were equal in one case. Thus, resting²⁰¹Tl delayed myocardial scintigraphy appears to reduce the underestimation of the size of the viable myocardium by the usual²⁰¹Tl images obtained after exercise or by single initial images obtained at rest in patients with previous MI.     

Acute myocardial infarction delineated by noninvasive thallium-201/technetium-99m pyrophosphate tomography

The purpose of this study was to validate different scintigraphic approaches for assessing acute myocardial infarctions. 201Tl, 99Tcm pyrophosphate (PPi) and combined 201Tl/99Tcm PPi tomograms were evaluated in 115 consecutive patients, in 85 of whom clinical examination revealed acute myocardial infarction. The overall sensitivity and specificity for infarct detection was 80% versus 56% for 201Tl alone, 61% versus 97% for 99Tcm PPi alone, and 100% each for the combined 201Tl/99Tcm PPi imaging. The sensitivity for nontransmural infarcts was 57% for 201Tl, 37% for 99Tcm PPi and 100% for combined imaging. The overlay of 201Tl and 99Tcm PPi images increases the observer's confidence in the diagnosis and provides better localization of the infarction. 201Tl alone could localize the infarction in 80%, 99Tcm PPi alone in 49% and 201Tl/99Tcm PPi in 100% of the cases. ECG and 201Tl/99Tcm PPi tomography concurred upon infarct localization in 98% of the patients. Based on the 201Tl/99Tcm accumulation pattern, 94% of the Q-wave infarctions were judged to be transmural and 83% of the non-Q-wave infarctions were judged to be nontransmural. It is concluded that combined 201Tl/99Tcm PPi tomography is highly accurate for determining the presence and location of acute myocardial infarction. This technique appears to be superior to studies where only one radioisotope is used.     

ECG-gated thallium-201 myocardial SPECT in patients with old myocardial infarction compared with ECG-gated blood pool SPECT

We evaluated one of the merits of ECG-gated thallium-201 single photon emission computed tomography (g-T1 SPECT), i.e., the ability to appreciate left ventricular (LV) wall motion. LV wall motion assessed by g-T1 SPECT and by ECG-gated Blood Pool SPECT (g-BP SPECT) was classified into three grades and compared segment by segment. T1-201 uptake by g-T1 SPECT was also classified into three grades and compared with those of wall motion in g-BP SPECT. Fifty patients with prior myocardial infarction were injected intravenously at rest with 111 to 185 M Bq (3 to 5 mCi) of Tl-201. The left ventricular regions were divided into anterior, septal, inferior and lateral segments (50 patients X 4 segments = 200 segments in total). The grades of wall motion and Tl-201 uptake detected by g-Tl SPECT correlated well with those of wall motion in g-BP SPECT (94.5% and 85%, respectively). With g-Tl SPECT it was possible to evaluate left ventricular wall motion, providing clear perfusion images.     

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.     

Reverse redistribution of thallium-201 represents a low-risk finding in thrombolysed patients following myocardial infarction

The aim of the study was to evaluate the prevalence and clinical significance of reverse redistribution on thallium-201 imaging in post-myocardial infarction patients who have undergone thrombolytic therapy. Sixty-two patients aged 35–79 (mean 60) years with proven myocardial infarction who had undergone thrombolysis were studied 6 weeks post infarction. Standard stress and 4-h redistribution imaging was performed with ²⁰¹Tl following treadmill exercise. Separate day rest injection of ²⁰¹T1 was given after sublingual nitroglycerine; imaging was performed at 1 h. Planar images were acquired in three standard views and semiquantitative segmental analysis of the images was performed from the unprocessed images. All patients had radionuclide ventriculography for the assessment of left ventricular ejection fraction and wall motion abnormality. Thirty-three patients also had coronary angiography. ²⁰¹T1 scintigraphy revealed fixed defects in 19 patients, reversible defects in 22, and reverse redistribution in 21. Those with reverse redistribution had a significantly higher exercise capacity (P < 0.01). Mean (SD) left ventricular ejection fraction was 46 (12)% for those with fixed defects, 47 (9)% for those with reversible defects and 45 (15)% for patients with reverse redistribution (P = NS). The regional wall motion abnormality score was 8 (5), 11.8 (2.2) and 14.2 (6) respectively in patients with reverse redistribution, redistribution alone and fixed defects. Regions with reverse redistribution revealed less regional wall motion abnormality compared to the other two groups (P < 0.01). Fifteen patients demonstrated significant ²⁰¹Tl uptake in the region showing reverse redistribution, with rest injection of ²⁰¹Tl following sublingual nitroglycerine, suggesting viable myocardium in that region. Patients with reverse redistribution had less residual stenosis of the infarct-related artery than those with fixed or reversible defects. Reverse redistribution on ²⁰¹T1 scintigraphy is a common phenomenon, even at 6 weeks, in patients with myocardial infarction who have received thrombolytic therapy. Areas with reverse redistribution demonstrate ²⁰¹T1 uptake following rest injection, less regional wall motion abnormality and a more patent infarct-related artery. Thus, reverse redistribution in these patients represents a low risk finding which suggests retained myocardial viability and successful thrombolytic therapy.