Dual isotope myocardial scintigraphy (201thallium at rest/99 M technetium tetrofosmin with exercise) in the detection of reversible hypoperfusion

The dual-isotope technique (rest 201Tl and stress 99mTc-sestamibi) is useful to assess myocardial perfusion in coronary disease patients. 99mTc-labeled tetrofosmin is a radiopharmaceutical whose characteristics are similar to sestamibi. Thus, we decided to use it to detect reversible myocardial hypoperfusion in patients with a background of myocardial infarction and ischemia. A sequential dual-isotope scintigraphy (3 mCi rest 201Tl and 25 mCi stress 99mTc-tetrofosmin) with 24-hour 201Tl redistribution (RD) was performed in 20 patients with previously confirmed myocardial infarction and clinical and ergometric signs of ischemia. Each patient also underwent a stress-redistribution protocol with redistribution at 4 and 24 hours post injection with 201Tl scintigraphy within two weeks of the first study. The qualitative uptake analysis showed no significant differences in the number of myocardial segments with severe reduction of tracer uptake on stress that improved at rest or in RD images, even if 24-hour RD images were considered. The quantitative global uptake analysis showed a similar defect reversibility with both protocols; however if 24-hour RD images were considered the uptake improvement was significant only when compared with the rest 201Tl images in dual-isotope scintigraphy protocol (75+/-8% vs. 81+/-9% of peak activity, rest vs. 24-hour RD; p<0.01) and not when compared with the 4-hour RD in the 201Tl scintigraphy. On the other hand, when only the segments with severely reduced uptake (<50% of peak activity) were analyzed, the 24-hour RD improved myocardial uptake significantly (p<0.001 vs. rest and vs 4-hour RD) in both protocols. We conclude that a sequential dual-isotope rest 201Tl/stress 99mTc-tetrofosmin scintigraphy is comparable with stress-redistribution 201Tl scintigraphy to detect reversible myocardial hypoperfusion; however in both cases, the addition of 24-hour images increases its usefulness in severely hypoperfused segments, if the uptake of the radiopharmaceutic is quantified.     

Nitrate administration to enhance the detection of myocardial viability by technetium-99m tetrofosmin single-photon emission tomography

A comparison was performed between technetium-99m tetrofosmin myocardial perfusion tomography at baseline and after nitrate administration, using a 2-day protocol, and rest-reinjection thallium-201 single-photon emission tomography (SPET) studies in order to assess whether nitrates enhance the detection of viable myocardium with^99mTc-tetrofosmin. Fifteen patients with coronary artery disease, previous myocardial infarction and a left ventricular ejection fraction <40% underwent²⁰¹T1 rest-injection and^99mTc-tetrofosmin. baseline-postnitroglycerin (0.4 mg sublingually) SPET studies, within 48 h. Tomograms based on the three spatial planes were divided into 15 segments and regional tracer uptake was quantitatively analysed. Viability was defined as presence of tracer uptake >50% of peak activity on baseline studies or after reversibility. The percentage of peak activity of^99mTc-tetrofosmin at baseline correlated with that of 201T1 (r=0.82,P <0.001). On baseline^99mTc-tetrofosmin studies, 73 of the 225 segments that were analysed had <50% of peal. activity. Fifteen percent of these segments showed reversibility after nitrate administration, with an increase in^99mTc-tetrofosmin uptake from 40%±9% to 57%±9% of peak activity (P=0.003). All reversible segments after nitrate administration had viability criteria on²⁰¹Tl studies, but 20 segments that were non-viable on^99mTc-tetrofosmin. studies were viable on²⁰¹Tl studies. Using a threshold value of >40% of peak activity, only seven segments remained non-viable on^99mTc-tetrofosmin studies. Overall agreement between^99mTc-tetrofosmin with nitrates and²⁰¹Tl-reinjection regarding the presence of myocardial viability was 90%. Detection of myocardial viability with^99mTc-tetrofosmin. was enhanced after nitrate administration, correlating with viability criteria observed on thallium studies.     

Comparison of technetium 99m-tetrofosmin and thallium-201 single photon emission computed tomographic imaging for the assessment of viable myocardium in patients with left ventricular dysfunction

Background  Tetrofosmin is a new technetium 99m-labeled myocardial perfusion agent that has demonstrated favorable imaging characteristics in recent clinical trials. However, it is not certain whether ^99mTc-tetrofosmin compared with thallium 201 would underestimate myocardial viability in regions with left ventricular dysfunction. Methods  To this end 15 patients (mean age 52±7 years) with coronary artery disease and left ventricular dysfunction (ejection fraction 35%±8%) documented on angiography underwent both quantitative rest-redistribution ²⁰¹TI and rest ^99mTc-tetrofosmin single photon emission computed tomography imaging. Results  Of 240 total segments on rest-redistribution ²⁰¹TI protocol 139 (58%) segments had irreversible ²⁰¹TI defects. Of these segments 79 (57%) had only mild to moderate reduction of ²⁰¹TI uptake (51% to 85% of normal uptake), whereas the remaining 60 (43%) had severely reduced tracer uptake (≤50% of normal uptake). On ^99mTc-tetrofosmin protocol 180 (75%) segments had abnormal ^99mTc-tetrofosmin uptake; of these segments 120 (67%) had mild to moderate reduction of ^99mTc-tetrofosmin uptake, whereas 60 (33%) had severely reduced activity. Among hypokinetic regions concordance between ²⁰¹TI and ^99mTc-tetrofosmin regarding myocardial viability with a cutoff point of 50% of peak activity was obtained in 28 (90%) of 31 segments (K′=0.80), leaving only 3 of 31 regions discordant (p=NS). Similarly, among akinetic or dyskinetic regions concordance between the two tracers regarding myocardial viability was achieved in 54 (93%) regions (K′=0.75), leaving only 4 of the 58 regions discordant (p=NS). Conclusions  These data show that when the severity of uptake was considered within abnormal segments, a similar amount of ²⁰¹TI viable regions were observed by ^99mTc-tetrofosmin. Thus these two agents may provide comparable information about myocardial viability when quantitative analysis of defect severity is performed.     

A comparison of resting images from two myocardial perfusion tracers

We have compared stress-redistribution and delayed rest thallium-201 with rest technetium-99m methoxyisobutylisonitrile (MIBI) tomograms in order to compare the tracers for the assessment of myocardial viability and to validate a rapid protocol combining the two tracers. We studied 30 consecutive patients with known or suspected coronary artery disease [group 1: 16 with normal left ventricular function, mean left ventricular ejection fraction (LVEF) 55%, SD 6%; group 2: 14 with abnormal function, mean LVEF 28%, SD 8%].²⁰¹Tl was injected during infusion of adenosine followed by acquisition of conventional stress and redistribution tomograms. On a separate day,²⁰¹Tl was injected at rest with imaging 4 h later.^99mTc-MIBI was then given at rest and imaging was performed. Three images were compared: redistribution²⁰¹Tl, rest²⁰¹Tl, and rest^99mTc-MIBI. Tracer activity was classified visually and quantitatively in nine segments and segments with>50% activity were defined as containing clinically significant viable myocardium. Mean (±SD) global tracer uptake as a percentage of maximum was similar in group 1 (rest²⁰¹Tl 69%±12%, redistribution²⁰¹Tl 69%±15%, rest^99mTc-MIBI 70%±13%, ANOVAP>0.05), but in group 2 mean tracer uptake was significantly greater in the rest²⁰¹Tl images (59%±16%) than in redistribution²⁰¹Tl images (53%±17%) or rest^99mTc-MIBI images (53%±19%) (ANOVAP=0.02). Overall agreement for regional uptake score was excellent ( from 0.79 to 0.84), although there were a significant number of segments with less uptake shown by redistribution²⁰¹Tl and by rest^99mTc-MIBI than by rest²⁰¹Tl in group 2 (P<0.001). The number of segments with significant viable myocardium in group 1 was very similar between the three images (P>0.05) but in group 2 rest²⁰¹Tl identified significantly more segments as viable than the other images (McNemarP<0.001). Thus²⁰¹Tl and^99mTc-MIBI provide similar information in patients without prior infarction and with normal left ventricular function (group 1), and a rapid protocol with stress²⁰¹Tl injection and imaging followed immediately by rest^99mTc-MIBI injection and imaging is feasible. In patients with abnormal left ventricular function and prior infarction (group 2),^99mTc-MIBI may underestimate the extent of clinically significant viable myocardium.     

Clinical comparison between thallium-201 and Tc-99m-methoxy isobutyl isonitrile (hexamibi) myocardial perfusion imaging for detection of coronary artery disease

^99mTc-hexamibi (methoxy isobutyl isonitrile) is a new ^99mTc-hexakis analog that can be used as a myocardial perfusion imaging agent. The purposes of this study were to compare ^99mTc-hexamibi to ²⁰¹Tl-thallous chloride myocardial stress scintigraphy in patients referred for investigation of chest pain and to evaluate the sensitivity of ^99mTc-hexamibi in detection of coronary artery disease. One hundred patients were prospectively studied with both ²⁰¹Tl and ^99mTc-hexamibi planar imaging. Sixty five patients had a current coronary angiography. There was a total of 97 significantly (70%) stenosed major coronary arteries. ^99mTc-hexamibi (25 mCi) study was done within a week of the ²⁰¹Tl scan with similar double products upon standard treadmil stress testing. Rest studies with ^99mTc-hexamibi were obtained 24–48 h after the stress test using the same acquisition parameters and dose. Analysis was performed blind by three observers. The left ventricle was divided into five segments in each image. Analysis of ²⁰¹Tl and ^99mTc-hexamibi results in 1500 left ventricle segments showed an overall agreement in 1326/1500 (88.4%) segments. Correlation between the patient diagnosis on the ²⁰¹Tl and ^99mTc-hexamibi studies showed an agreement in 89 patients (89%). ²⁰¹Tl revealed myocardial uptake defects in 526 segments, detecting 72 out of 97 (74.2%) significantly stenosed coronary arteries and ^99mTc-hexamibi detected 513 segments corresponding to 68 (70.1%) stenosed arteries (no significant statistical difference). In conclusion, these results show a good correlation between ²⁰¹Tl and ^99mTc-hexamibi myocardial imaging in the detection of significant coronary artery disease.     

Technetium-99m teboroxime scintigraphy

In order to evaluate the clinical value of a new myocardial perfusion tracer, a series of 30 patients (25 male, 5 female, mean age 56 years) referred for thallium 201 stress/redistribution scintigraphy has been studied using stress/rest (n = 7) or rest/stress (n = 23) protocols with technetium 99m teboroxime (Cardiotec SQUIBB). In all cases coronary artery disease was known or highly probable, with a history of myocardial infarction in 18 cases. Medical treatment was not discontinued at the time of stress testing, and coronary angiography was available in 27 patients. Exercise tests for both tracers were carried out on a bicycle ergometer during the same day, and the levels of exercise achieved for the ²⁰¹Tl study were very similar to those achieved for 99^mTc-teboroxime. Studies performed in three planar projections were evaluated using a model with four territories septal and anterior assumed to correspond to the left anterior descending artery, lateral and lateroposterior (left circonflex), inferior and posterior (right coronary artery) and apex. Classification of results was normal, ischaemic, infarcted and infarcted with ischaemia. On comparison with the ²⁰¹Tl results, agreement was found in 86% (37/43) of normal regions and in 82% (63/77) of abnormal regions. Relative to documented coronary artery lesions (27 patients), sensitivity and specificity of ²⁰¹Tl and ^99mTc-teboroxime for exact correspondence between arteries and territories were respectively: ²⁰¹Tl: sensitivity 64%, specificity 60%; ^99mTc-teboroxime: sensitivity 62%, specificity 77%. These results, obtained in a given clinical context, indicate the ability of Cardiotec to evaluate myocardial perfusion with a significant saving in time, since the complete study duration (stress and rest) was: ²⁰¹Tl, 4 h 35 min±21 min; ^99mTc-teboroxime, 1 h 52 min ±29 min. Nevertheless, the high liver uptake was responsible for 68% of non-evauble inferior segments and the limited acquisition time makes the applicability of SPET questionable.     

Regional heterogeneity in cardiac sympathetic innervation in acute myocardial infarction: relationship with myocardial oedema on magnetic resonance

Purpose

To assess the relationships between myocardial structure and function on cardiac magnetic resonance (CMR) imaging and sympathetic tone on ¹²³I-metaiodobenzylguanidine (¹²³I-MIBG) scintigraphy early after myocardial infarction (MI).

Methods

Ten patients underwent ¹²³I-MIBG and ^99mTc-tetrofosmin rest cadmium zinc telluride scintigraphy 4?±?1 days after MI. The segmental left ventricular (LV) relative radiotracer uptake of both ^99mTc-tetrofosmin and early ¹²³I-MIBG was calculated. The day after scintigraphy, on CMR imaging, the extent of ischaemia-related oedema and of myocardial fibrosis (late gadolinium enhancement, LGE) was assessed. Accordingly, the extent of oedema and LGE was evaluated for each segment and segmental wall thickening determined. Based on LGE distribution, LV segments were categorized as "infarcted" (56 segments), "adjacent" (66 segments) or "remote" (48 segments).

Results

Infarcted segments showed a more depressed systolic wall thickening and greater extent of oedema than adjacent segments (p?<?0.001) and remote segments (p?<?0.001). Interestingly, while uptake of ^99mTc-tetrofosmin was significantly depressed only in infarcted segments (p?<?0.001 vs. both adjacent and remote segments), uptake of ¹²³I-MIBG was impaired not only in infarcted segments (p?<?0.001 vs. remote) but also in adjacent segments (p?=?0.024 vs. remote segments). At the regional level, after correction for ^99mTc-tetrofosmin and LGE distribution, segmental ¹²³I-MIBG uptake (p?<?0.001) remained an independent predictor of ischaemia-related oedema.

Conclusion

After acute MI the regional impairment of sympathetic tone extends beyond the area of altered myocardial perfusion and is associated with myocardial oedema.     

Assessment of myocardial perfusion and viability with technetium-99m methoxyisobutylisonitrile and thallium-201 rest redistribution in chronic coronary artery disease

We compare thallium-201 rest redistribution and fluorine-18 fluorodeoxyglucose ([¹⁸F]FDG) for the assessment of myocardial viability within technetium-99m methoxyisobutylisonitrile (MIBI) perfusion defects in 27 patients with chronic stable coronary artery disease. The following studies were performed: (1) stress^99mTc-MIBI, (2) rest^99mTc-MIBI, (3)²⁰¹T1 rest-redistribution single-photon emission tomography, (4) [¹⁸F]FDG positron emission tomography. The left ventricle was devided into 11 segments on matched tomographic images. The segment with the highest activity at stress was taken as the reference (activity=100%). Perfusion defects at^99mTc-MIBI rest were classified as severe (activity<50%), moderate (activity 50%–60%) or mild (activity 60%–85%). Uptakes of [¹⁸F]FDG and rest-redistributed²⁰¹Tl were recognized as significant if they exceeded 50% of that in the reference segment. Among the 33 segments with severe^99mTc-MIBI rest perfusion defects, 21 had significant [¹⁸F]FDG and 10 significant rest-redistributed²⁰¹Tl uptake. As regards the 37 segments with moderate defects, [¹⁸F]FDG was present in 29 and²⁰¹Tl in 31, while of the 134 segments with mild defects, 128 showed [¹⁸F]FDG uptake, and 131,²⁰¹Tl uptake. In conclusion, there is an inverse relationship between the severity of^99mTc-MIBI perfusion defects and the uptake of rest-redistributed²⁰¹Tl and [¹⁸F]FDG. Both tracers are adequate markers of viability in mild and moderate defects; in severe defects²⁰¹Tl might underestimate the presence of viability as assessed by [¹⁸F]FDG.     

Attenuation-corrected rest thallium-201/stress technetium 99m sestamibi myocardial SPECT in normals

Background  Rest thallium-201/stress technetium 99m sestamibi protocol is widely used in the clinical setting. Although attenuation correction (AC) represents an important recent development in cardiac single photon emission computed tomography (SPECT) imaging, adjacent extracardiac activity can affect the myocardial count density distribution on AC images, particularly with ²⁰¹Tl. The aims of this study were to compare normal distribution between AC rest ²⁰¹Tl and stress ^99mTc-sestamibi SPECT images as well as to evaluate the effect of extracardiac activity on AC SPECT images with ^99mTc and ²⁰¹Tl. Methods and Results  A phantom measurement and a study of 21 patients with low likelihood of coronary artery disease were performed with a triple-head SPECT system equipped with a americium 241 line source. In the phantom study, the presence of extracardiac activity increased the inferior-to-anterior ratios, particularly with ²⁰¹Tl (1.01 to 1.32). In the clinical data, reduced count density with ²⁰¹Tl compared to ^99mTc-sestamibi was observed in most of the noninferior segments. On an individual segment basis, 37 (20%) of 189 segments from 11 (52%) of 21 subjects showed reduced count density on the ²⁰¹Tl image compared to ^99mTc-sestamibi by >10% of peak activity. Conclusions  There is a significant difference in myocardial count density distribution between ^99mTc-sestamibi and ²⁰¹Tl on AC SPECT images, indicating that a careful image interpretation that considers the different normal count density distribution between the tracers and/or a tracer specific normal database is necessary, especially when defect reversibility is of concern. Further work should aim for the incorporation of scatter correction combined with attenuation correction. Supported by Mitsubishi Research Institute, Japan.     

A comparison of rest sestamibi and rest-redistribution thallium single photon emission tomography: Possible implications for myocardial viability detection in infarcted patients

Thirty patients (26 men, 4 women, mean age 61 ± 8 years) who had suffered myocardial infarction 15 ± 6 months previously, were submitted to (1) standard stress-redistribution thallium-201 single photon emission tomography (SPET), (2) rest-redistribution²⁰¹Tl SPET and (3) stress-rest technetium-99m sestamibi SPET. Uptake modifications in relation to exercise-induced defects were evaluated in a total of 390 myocardial segments. Tracer uptake was scored as normal (=0), mildly reduced (=1), apparently reduced (=2), severely reduced (=3) or absent (=4). Comparison of stress studies failed to show any statistical difference (58% segmental abnormalities with sestamibi vs 61% with thallium). Uptake abnormalities (score 1–4) were detected in 55% of the segments wiliest sestamibi, 55% with standard thallium redistribution, 55% with early imaging after thallium injection at rest and 54% with 3-h delayed rest imaging (P = NS). Absence of tracer uptake (score = 4) under resting conditions was recorded in 75 (19%) segments with standard²⁰¹Tl redistribution, 75 (19%) with rest sestamibi, 70 (18%) with rest²⁰¹Tl imaging and 62 (16%) with rst-rdistruion²⁰¹Tl (P<0.05 vs other imaging modalities). Thus, 3-h delayed rest thallium imaging detected reversibility of uptake defects in a significantly higher number of myocardial segments. This finding might have important implications for both tracer and technique selection when myocardial viability is the main clinical issue.     

99mTc-MIBI (RP-30) to define the extent of myocardial Ischemia and evaluate ventricular function

^99mTc-MIBI, a new myocardial perfusion agent, is a technetium labeled isonitrile derivative. We have taken advantage of the physical characteristics of^99mTc to combine at rest, post infarction, ventricular function studies with analysis of perfusion. We have studied at rest and at stress, 22 patients with coronary artery disease selected on the basis of an abnormal coronary angiogram or on the basis of a positive exercise ECG stress test for symptomatic angina. We have also studied, at rest only, 20 patients with a previous myocardial infarction. A comparative thallium planar scintigraphy was obtained for all patients. The sensitivity of^99mTc-MIBI scintigraphy for detecting individual vessel lesions at stress was 88% as compared with 83% for²⁰¹TI. Sensitivity was higher in patients with previous myocardial infarction (93% for the 2 isotopes) than in patients without (85% for^99mTc-MIBI versus 81% for²⁰¹TI). Segmental myocardial correspondence between^99mTc-MIBI and²⁰¹Tl was very close (92%). The overall sensitivity for the detection of acute myocardial infarction reached respectively 91% for^99mTc MIBI and 87% for²⁰¹T1. The specificity in the regions corresponding to arteries not involved was excellent for both tracers as we did not observe any false positive result. This is important information but it does not correspond to the specificity to detect coronary artery disease in the overall patient population. The correlation between first pass left ventricular ejection fraction obtained with^99mTc-MIBI and equilibrium left ventricular ejection fraction obtained with^99mTc red cells was excellent (r = 0.96). It was not as good but was still satisfactory for the right ventricle (r=0.75). By comparison of diastolic and systolic frames., gated tomography provides analysis of regional wall motion and wall thickening. In this preliminary study, we have only limited data collected from a selected population with a high prevalence of coronary artery disease and myocardial infarction. Thus, no definitive conclusion can be drawn on the sensitivity and specificity of these tests when performed in the general population. Further studies analyzing comparatively MIBI scintigrams and angiographic results in a large number appears to be a very promising perfusion agent to document myocardial infarction and myocardial ischemia as well as to provide functional information on global and regional ventricular function.     

Technetium-99m Q4: a prototype cationic perfusion radiotracer with myocardial washout

Technetium-99m Q4 is derived from an existing mixed ligand myocardial tracer (^99mTc-Q3) by the addition of an ester group to promote myocardial washout. Six subjects with single-vessel coronary disease documented by angiography and/or Q wave myocardial infarction documented by electrocardiography were studied with ^99mTc-Q4 injection during exercise and with comparative thallium-201 tomography. Six healthy volunteers were also studied with ^99mTc-Q4 imaging following injection at peak exercise. Tomographic images with ^99mTc-Q4 and ²⁰¹Tl each provided correct assessment of the presence or absence of coronary disease in 22 of 30 myocardial segments (73.3%). Six myocardial segments showed defect reversibility with ^99mTc-Q4, whereas 14 segments showed reversibility with ²⁰¹Tl, but the latter included three segments with no angiographic or electrocardiographic evidence of disease. In both normals and subjects with coronary artery disease, significant global washout of ^99mTc-Q4 was observed over 4 h. For five patients with angiographic evidence of unrevascularized coronary artery stenosis, the ischemic to normal zone count ratio increased from 0.782±0.107 at 45 min postexercise to 0.891±0.115 at 4 h postexercise (P = 0.016), suggesting occurrence of differential washout. It is concluded that addition of an ester group functionality to a previously studied mixed ligand cardiac tracer promotes global and regional myocardial tracer washout. Nevertheless, demonstration of perfusion defect reversibility with comparable frequency to that observed with ²⁰¹Tl stress and reinjection images, required separate injections of ^99mTc-Q4 at peak stress and at rest. Received 4 October and in revised form 19 December 1997     

Technetium-99m-tetrofosmin imaging with incremental nitroglycerin infusion to detect severely ischaemic but viable myocardium: a comparative study with thallium-201

The aim of this study was to assess the influence of incremental nitroglycerin infusion (NTG+Inf) on the myocardial uptake of 99mTc-tetrofosmin (TF) in order to determine whether nitrates enhance the detection of viable myocardium with TF in patients with coronary artery disease (CAD) and left ventricular dysfunction. Fifty patients (39 males, 11 females; 54 +/- 11 years) with previous myocardial infarction and left ventricular dysfunction, who had been referred for coronary revascularization procedures, were studied. Myocardial single-photon emission tomography (SPET) images were obtained 1 h after injection of 750 MBq TF at baseline and after NTG+Inf, using a 2 day protocol. NTG+Inf was performed starting at 0.4 microg x kg(-1) x min(-1), with equal increments every 5 min up to 2 microg x kg(-1) x min(-1). Within 1 week of the TF study, rest-redistribution (R-RD) 201Tl SPET was performed after the injection of 111 MBq 201Tl. For each study, quantitative analysis was performed in 17 segments. Viability was defined as the presence of tracer uptake of > 50% of the peak activity on baseline studies or reversibility. There was significant correlation between quantitative regional RD 201Tl activity and TF activity after NTG+Inf (r = 0.90, P < 0.001). Of the 131 segments with severely reduced tracer uptake on resting TF images, 34 (26%) were reversible, showing increased tracer uptake after NTG+Inf (from 41%+/-7% to 57%+/-12% of peak activity; P < 0.001). All reversible segments after NTG+Inf had viability criteria on 201Tl studies. There was 95% concordance between TF with NTG+Inf and RD 201Tl imaging with regard to the presence of myocardial viability. We conclude that TF imaging with incremental NTG+Inf improves the detection of ischaemic but viable myocardium, correlating with the viability criteria observed on 201Tl studies. When the advantages of TF imaging are considered, rest TF imaging with NTG+Inf may be a practical diagnostic protocol in patients with CAD and left ventricular dysfunction who are being considered for revascularization.     

Myocardial uptake of thallium 201 and technetium 99m-labeled sestamibi after ischemia and reperfusion: Comparison by quantitative dual-tracer autoradiography in rabbits

Background  

Myocardial scintigraphy with^99mTc-labeled sestamibi (^99mTc-sestamibi) or²⁰¹Tl is used to assess regional perfusion in acute coronary syndromes associated with metabolic or functional abnormalities, such as acute coronary thrombosis with reperfusion and ischemia at rest. However, the initial uptake of these agents may be affected by a recent ischemic insult because the myocardial retention of these tracers depends on cellular metabolism.     

Quantitative comparison of technetium-99m tetrofosmin and thallium-201 images of the thyroid and abnormal parathyroid glands

The aim of the study was to quantitatively compare the scintigraphic images of the thyroid and abnormal parathyroid glands obtained with technetium-99m tetrofosmin and thallium-201 in patients with hyperparathyroidism. Forty-six patients with hyperparathyroidism underwent ²⁰¹Tl (74 MBq), ^99mTc-pertechnetate (74 MBq) and ^99mTc-tetrofosmin (555–740 MBq) scintigraphy in a single session. Image analysis included the computation of the thyroid/background ratio in the whole study population and the parathyroid/background ratio, parathyroid/thyroid ratio and diagnostic sensitivity in 17 patients who underwent parathyroid surgery. The pertechnetate subtraction technique was used. ²⁰¹Tl and ^99mTc-tetrofosmin showed a similar thyroid/background ratio (1.79±0.41 and 1.81±0.47, respectively, P=NS); however, ^99mTc-tetrofosmin showed a higher parathyroid/background ratio than ²⁰¹Tl (2.06±0.54 vs 1.79± 0.50, P=0.007). Despite the superior quality of ^99mTc-tetrofosmin images, both tracers showed identical sensitivity in detecting enlarged parathyroid glands in patients with primary hyperparathyroidism (89%) and in those with secondary hyperparathyroidism (50%).     

A method of simultaneous dual-radionuclide cardiac imaging with technetium 99m and thallium 201. I: Analysis of interradionuclide crossover and validation in phantoms

Background  

Simultaneous dual-radionuclide technetium 99m/thallium 201 scintigraphy can potentially produce perfectly aligned stress and rest images in less time than conventional protocols. However, interradionuclide crossover limits diagnostic accuracy. Accordingly, we evaluated^99mTc and²⁰¹Tl crossover in line and heart phantoms.     

Dual-isotope myocardial imaging: feasibility,advantages and limitations

Two hundred and thirty-one patients underwent dual-isotope myocardial imaging (rest thallium-201 followed by stress technetium-99m sestamibi). The feasibility of the procedure was excellent: camera scheduling flexibility was improved and the duration of the procedure was less than that of a classical stress-redistribution procedure. Interpretation of defects due to image attenuation was facilitated by the different attenuation properties of ²⁰¹Tl and ^99mTc-sestamibi in 11 of 19 patients. ²¹⁰Tl cross-over on ^99mTc was found to be 15% ± 3% with doses of ²⁰¹Tl and ^99mTc-sestamibi of 3 and 10 mCi, respectively, and 7% ± 2% with doses of 3 and 20 mCi. This protocol should preferentially be reserved for patients with a history of myocardial infarction and/or a basal left ventricular dysfunction, in whom assessment of myocardial viability is of major interest. Extensive clinical validation of the dual-isotope procedure is required and optimal acquisition and reconstruction parameters should be established.     

Nitrate-augmented myocardial imaging for assessment of myocardial viability

²⁰¹Tl myocardial perfusion imaging is presently done by several possible strategies. Stress/delayed redistribution, stress/redistribution/reinjection, and rest/redistribution imaging can be useful in the clinical assessment of myocardial viability. Unfortunately, the extent of myocardial viability may still be underestimated even by ²⁰¹Tl reinjection imaging, compared with ¹⁸F-fluorodeoxyglucose positron emission tomography. ^99mTc-labeled sestamibi imaging provides results similar to those of ²⁰¹Tl imaging in the detection of coronary artery disease, but several previous studies suggest that stress/rest ^99mTc-labeled sestamibi imaging significantly underestimates myocardial viability. Recently it has been reported that the administration of nitrates, before ²⁰¹Tl reinjection, improves detection of defect reversibility. Several studies also suggested that administration of nitrates before the injection of ^99mTc-labeled sestamibi significantly improved detection of reversibility with this agent, whereas additional studies showed further that this combination improves the predictive accuracy for recovery of left ventricular function and perfusion after coronary revascularization, compared with a standard rest ^99mTc-labeled sestamibi study. Nitrate administration before the injection of ²⁰¹Tl and ^99mTc-labeled sestamibi may thus be a potentially attractive alternative for the evaluation of myocardial viability. Although the available results are encouraging, further studies are needed to evaluate the clinical value of ²⁰¹Tl and ^99mTc-labeled sestamibi imaging, in combination with nitrates, for predicting recovery of left ventricular dysfunction.     

Diagnostic utility of tomographic myocardial perfusion imaging with technetium 99m furifosmin (Q12) compared with thallium 201: Results of a phase III multicenter trial

Background  

Based on physical properties, ^99mTc-labeled perfusion agents offer several advantages over ²⁰¹Tl for myocardial perfusion imaging. The results of in vivo and experimental studies, along with preliminary experience in human subjects, have shown ^99mTc-labeled furifosmin to be a promising new perfusion tracer. The purpose of this study was to evaluate the safety of a new myocardial perfusion agent, ^99mTc-labeled furifosmin (Q12), and determine the concordance of furifosmin perfusion scintigraphy to ²⁰¹Tl imaging. In addition, we sought to determine the normalcy rate of myocardial scintigraphy with furifosmin.     

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.