Assessment of myocardial viability with 201Tl myocardial SPECT 24 hours after injection]

Recently many investigators reported that conventional stress-redistribution myocardial scintigraphy with 201Tl underestimated the presence of ischemic but viable myocardium. We studied the usefulness of 24 hour 201Tl myocardial single photon emission computed tomography (SPECT) to assess myocardial viability and investigated the factors affect to the quality of 24 hour SPECT images. Study patients were consisted with 70 patients with old myocardial infarction (OMI), 72 patients with angina pectoris without OMI (AP) and 43 patients with angiographically proven normal coronary arteries. To obtain SPECT images, 10 minute and 4 hour imagings were sampled 30 seconds per projection. Twenty-four hour imaging was sampled 60 seconds per projection. Twenty-four hour images were visually interpreted as good, moderate and poor quality. Then study patients were divided into 2 groups, group A with good 24 hour images and group B with moderate or poor 24 hour images. One hundred and fifty-eight patients (85.4%) of study patients had 24 hour SPECT images on a good quality. Only 4 patients (2.2%) had poor quality SPECT. All of these 4 patients had broad myocardial infarction. In patients with OMI 61 patients (87.1%), in AP 63 patients (87.5%) and in normal 35 patients (81.4%) had a good 24 hour SPECT. Total sampling counts and myocardial ROI counts were significantly higher in group A than in group B. Body weight was significantly higher and there were more male patients in group B than in group A. Late redistribution was seen in 20 patients (28.5%) with OMI and in 11 patients (15.3%) with AP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Detection of myocardial viability using rest-redistribution thallium-201 imaging in a stress 99Tcm-tetrofosmin/rest thallium-201 dual-isotope protocol

This study investigated the utility of optional thallium-201 (201Tl) imaging for detecting myocardial viability in the stress 99Tcm-tetrofosmin/rest 201Tl dual-isotope protocol. Seventy-nine patients with old myocardial infarction and 25 patients with acute myocardial infarction underwent acquisition of three consecutive 201Tl images (early, intermediate and delayed) using the dual-isotope protocol. A polar map was created and defect scores (extent and severity) were determined by comparison with normal control data. Fluorodeoxyglucose positron emission tomography was also performed in 16 patients with old myocardial infarction. In patients with old infarction, the severity score decreased significantly from the early to the intermediate images, and decreased further on the delayed images. In patients with acute infarction, the score increased from the early to the intermediate images, but not on the delayed images. Regional uptake on the delayed images showed a better correlation with the fluorodeoxyglucose images than that on the early images. Redistribution on the delayed images was exclusively observed in the myocardial segments with less uptake than that estimated by fluorodeoxyglucose. In conclusion, addition of delayed 201Tl imaging to the dual-isotope protocol could improve the sensitivity for detecting myocardial viability.     

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.     

Malignant thymoma detected by thallium-201 myocardial scintigraphy

We present two cases of malignant thymoma which showed a remarkable accumulation of thallium-201 chloride on myocardial scintigraphy. A 69 year-old man underwent stress 201Tl scintigraphy to evaluate myocardial ischemia and abnormal accumulation of thallium activity was observed in the anterior mediastinum by chance. It was more clearly visualized on delayed image. Moreover, abnormal uptake of 67Ga citrate was also observed in the same region. In another 68 year-old woman, there was high uptake on 201Tl scintigraphy, but no abnormal uptake using 67Ga. The diagnosis of malignant thymoma was confirmed by operation in each patient. These two cases had no abnormality in the mediastinum on the chest X-ray film and one of them had no uptake of 67Ga, 201Tl scintigraphy was more useful to detect malignant thymoma.     

The clinical impact of thallium-201 reinjection scintigraphy for detection of myocardial viability

In a clinical study, the value of thallium-201 reinjection was studied in 139 patients with suspected or known coronary artery disease who showed one or more persistent defects after conventional stress-redistribution imaging. Fifty-nine (42%) patients had sustained a Q-wave myocardial infarction. Sixty-eight (49%) patients showed a reversible defect in at least one myocardial segment at redistribution, while 71 (51%) had persistent defects only. Following reinjection additional segmental filling-in was seen in 95 (68%) patients, including 50 of the 68 (74%) patients with reversible defects and 45 of the 71(63%) with persistent defects only. On the immediately post-exercise images, 458 (47%) of 973 segments showed perfusion defects. At redistribution 105 (23%) of the 458 defects showed filling-in, whereas of the remaining 353 persistent defects 164 (46%) resolved additionally after reinjection. Thirteen (10%) of 133 Q-wave related defects showed filling-in at redistribution compared with 22 (27%) of 82 remote defects (P = 0.001). After reinjection additional filling-in of defects was seen in 47 (39%) of 120 Q-wave related defects compared with 35 (58%) or 60 remote defects (P = 0.015). Overall, 60 (45%) of 133 Q-wave related defects resolved compared with 57 (70%) of 82 remote defects (P = 0.005). Thus reinjection of thallium-201 (1) revealed reversible defects in 63% of patients with only persistent defects at redistribution, (2) demonstrated additional filling-in in 74% of patients who already showed reversible defects at redistribution, (3) showed viability in 46% of segments initially classified as persistent, and (4) demonstrated filling-in in 39% of Q-wave related segments, although this was less conspicuous than in remote segments. Offprint requests to: E.K.J. Pauwels     

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.     

Bayesian analysis of stress thallium-201 scintigraphy

The variation of the diagnostic value of stress Tl-201 scintigraphy with prevalence of coronary heart disease (CHD) in the population has been investigated using Bayesian reasoning.From scintigraphic and arteriographic data obtained in 100 consecutive patients presenting with chest pain, the sensitivity of stress Tl-201 scintigraphy for the detection of significant CHD was 90% and the specificity was 88%.From Bayes' Theorem, the posterior probability of having CHD for a given test result was calculated for prevalences of CHD ranging from 1% to 99%. The discriminant value of stress Tl-201 scintigraphy was best when the prevalence of CHD lay between 30% and 70% and maximum for a prevalence of 52%. Thus, stress Tl-201 scintigraphy would be an unsuitable diagnostic test where the prior probability of CHD is low, e.g., population screening programmes, and would add little where the clinical probability of having CHD is already high. However, where the prior probability of having CHD is intermediate stress Tl-201 scintigraphy may provide valuable diagnostic information.     

The clinical impact of thallium-201 reinjection scintigraphy for detection of myocardial viability.

In a clinical study, the value of thallium-201 reinjection was studied in 139 patients with suspected or known coronary artery disease who showed one or more persistent defects after conventional stress-redistribution imaging. Fifty-nine (42%) patients had sustained a Q-wave myocardial infarction. Sixty-eight (49%) patients showed a reversible defect in at least one myocardial segment at redistribution, while 71 (51%) had persistent defects only. Following reinjection additional segmental filling-in was seen in 95 (68%) patients, including 50 of the 68 (74%) patients with reversible defects and 45 of the 71 (63%) with persistent defects only. On the immediately post-exercise images, 458 (47%) of 973 segments showed perfusion defects. At redistribution 105 (23%) of the 458 defects showed filling-in, whereas of the remaining 353 persistent defects 164 (46%) resolved additionally after reinjection. Thirteen (10%) of 133 Q-wave related defects showed filling-in at redistribution compared with 22 (27%) of 82 remote defects (P = 0.001). After reinjection additional filling-in of defects was seen in 47 (39%) of 120 Q-wave related defects compared with 35 (58%) or 60 remote defects (P = 0.015). Overall, 60 (45%) of 133 Q-wave related defects resolved compared with 57 (70%) of 82 remote defects (P = 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

Noninvasive perfusion control by thallium-201 myocardial scintigraphy after coronary artery bypass surgery

Thallium-201 myocardial scintigraphy, which has been shown accurate in the assessment of myocardial perfusion, was employed in the evaluation of 34 patients after coronary artery bypass surgery. In 28 patients (82.4%), there was a clear correspondence in the postoperative studies between the defects shown on scintigraphy and the coronary artery stenosis documented by arteriography. Thallium imaging after coronary artery bypass revealed an increased or newly developed scintigraphic defect in eight of 10 patients with recurrent angina. Follow-up arteriography in these 10 patients revealed occlusion or stenosis of the bypass graft in five, perioperative myocardial infarction in two, and increased stenosis of a preoperatively less occluded artery in two. In 24 patients with postoperative clinical improvement or relief of angina,²⁰¹Tl scintigraphy revealed complete normalization of thallium uptake in three, improvement of uptake in 17, and unchanged uptake defects in four. Presented at the 5. Herbsttagung der Deutschen Gesellschaft für Kreislaufforschung, October 28, 1978, Berlin.     

Pharmacokinetics of thallium-201 in normal individuals after routine myocardial scintigraphy

Data of pharmacokinetic distribution of and radiation dose from 201Tl chloride used in routine myocardial scintigraphy are based on animal studies or on small groups of humans not exercised. In order to obtain data under routine conditions pharmacokinetics of 201Tl were measured in 15 individuals who had undergone diagnostic myocardial scintigraphy and were classified as normal. Ventral and dorsal whole-body scans were acquired until 9 days after injection. Conjugate pixels were averaged geometrically. Percentage values of total administered dose were obtained for total body and 13 organs by using a calculation method that takes into account the differentiation of overlapping organs.     

Effect of age on visualization of right atrium by thallium-201 myocardial scintigraphy]

With Thallium-201 (Tl) myocardial scintigraphy, right atrial (RA) myocardium has been visible in the disease involving the right side of the heart. We have found RA visualization in the elderly patients without the evidence of right heart disease. Therefore, we studied the relation of age to the RA visualization with Tl myocardial scintigraphy performed at rest. Planar images of 291 patients without valvular or congenital heart disease were read by two observers and classified into the three by the degree of RA visualization; RA 0 = not visualized, RA 1+ = moderately visualized, RA 2+ = intensely visualized. The results were as follows: 93.1% of under 50 y.o., 77.8% of fifties, 86.7% of sixties, 50.5% of seventies and 36.7% of over 80 y.o. showed RA 0. 6.9% of under 50 y.o., 22.2% of fifties, 8.3% of sixties, 46.5% of seventies and 36.7% of over 80 y.o. showed RA 1+. None of under 60 y.o., 5.0% of sixties, 3.0% of seventies, and 26.6% of over 80 y.o. showed RA 2+. In conclusion, RA visualization in Tl myocardial scintigraphy, suggesting right heart overload, may increase with aging.     

Assessment of resting thallium-201 reinjection after stress-delayed Tl imaging (I): Comparison with 24-hour scan and regional wall motion

Clinical value of resting reinjection of 1 mCi (37 MBq) of Tl after stress-delayed scan was assessed in comparison with 24 hr delayed scan and regional wall motion (RWM) in 37 patients with coronary artery disease. Of 101 segments with initial perfusion abnormality, concordant findings were observed after Tl reinjection in 67 segments (66%). But redistribution (RD) after Tl reinjection was observed in 19 of the 52 persistent defect (PD) segments (37%), and complete RD was observed 15 of the 43 segments (35%) where 3 hr scan showed incomplete RD. On the other hand, concordant findings were observed on 24 hr delayed scan in 11 of the 20 segments with perfusion abnormality (55%). RD on 24 hr delayed scan was observed in 5 of the 13 PD (38%), but it was not apparent in 3 of the 7 segments where 3 hr scan showed RD. Furthermore the segments which showed RD after Tl reinjection in PD segments tend to have less severe RWM abnormality than the sustained PD segments (RWM score: 1.65 +/- 1.17 vs. 2.29 +/- 1.05, p less than 0.05). These data indicate that Tl reinjection which permits assessment of RD with good quality images on the same day is considered as a valuable means for assessing myocardial viability.     

Detection of lesions in thallium-201 myocardial perfusion scintigraphy

Experimental studies have been made of the lesion detectability in myocardial perfusion studies using thallium-201. A series of images (AP-view) was generated using a convolution of a mathematical model of the left ventricular myocardium and an experimentally determined point spread function. Background was added. Images were simulated with 100k, 200k, and 300k counts for the complete image. Each image contained a lesion with either 0% or 50% of the normal tracer concentration. All images were interpreted by five experienced observers, independently of each other. Their interpretations were analysed using the Kolmogorov-Smirnov two sample test. The true positive fraction (TPF) was hardly affected by changes in count density. The TPF decreased significantly if the lesion tracer concentration changed from 0% to 50% of the normal myocardial tracer concentration. The decrease was independent of the count density. The false positive fraction (FPF) decreased significantly if the count density increased; no difference in FPF was found for a change in lesion tracer concentration. In addition, plots were generated with the TPF and the FPF versus lesion location and of the TPF versus lesion volume. The TPF was lowest for locations far from the camera; FPF was high for these segments. Increase of the count density mainly improved the FPF in these segments. Small lesion were more difficult to detect.     

Radioiodine therapy of hyperthyroidism precludes thallium-201 myocardial scintigraphy

The authors attempted to perform Tl-201 myocardial perfusion scintigraphy in a 42-year-old man 23 and 35 days after he received 9.8 mCi of oral I-131 for documented Graves' disease. Interference from primary and scattered photons from residual thyroid I-131 made Tl-201 myocardial scintigraphy technically impossible. A series of phantom and patient studies using I-131 and Tl-201 were performed, yielding guidelines for planning Tl-201 myocardial scintigraphy following radioiodine therapy.     

Nuclear imaging of bone tumors: thallium-201 scintigraphy

(201)Tl scintigraphy provides important information for the management of patients with bone tumors. Although the role for staging the disease of bone tumors and for differentiation of benign from malignant lesions is limited, (201)Tl scintigraphy reflects the disease activity after treatment and it should be used to determine the treatment response and for early diagnosis of recurrence. Baseline study is essential for future reference to evaluate the response to preoperative chemotherapy and to detect recurrence after surgery. Sequential (201)Tl scintigraphy before and after treatment is useful in assessing the grade of response of the tumor to chemotherapy. The early prediction of chemotherapeutic effect by (201)Tl scintigraphy during treatment will affect the management of patients who do not respond to the therapy. This is of special importance to determine whether the patient needs an amputation or a limb-salvage surgery.