Correlation of false negative myocardial infarct scintigraphy with postmortem studies

Negative myocardial infarct scintigrams with 99mtechnetium stannous pyrophosphate (99mTc-PYP) were obtained in two patients with acute massive transmural infarct. Both patients died soon after scintigraphy. Because necropsy was performed within hours after death, we were able to correlate the distribution of the tracer within the acutely infarcted tissue with the myocardial scintigram. The clinical implication is that a single myocardial scintigram may be grossly inaccurate in detecting and quantifying infarct size. The scintigraphic findings should always be correlated with the electrocardiographic and enzymatic findings in evaluating patients with possible myocardial infarct.     

Myocardial scintigraphy by infarct-avid radiotracers

Specific radioindicators are sequestered by acute myocardial infarctions, and their uptake is detectable by external detection systems, such as the Anger scintillation camera. The resultant scintigraphic image may be used to estimate infarct size, although inferior and subendocardial infarcts may pose difficulties. Infarct localization as to anatomic area of the heart is also reasonably accurate.The majority of the clinical experience has been with technetium chelates, particularly ^99mTc-tetracycline and ^99mTc-pyrophosphate. Optimal imaging with ^99mTc-tetracycline is within the first 3 days after infarction, with gradual return to normal of the scintigraphic appearance after this time. While larger infarcts remain positive for longer periods of time, significant uptake or reappearance of uptake after the initial period may be helpful in the identification of reinfarction or extension after an initial infarct. Tetracycline appears to be sequestered only by acutely infarcted myocardium, and therefore is a sensitive agent for distinguishing normal, previously infarcted, and ischemic myocardium from acutely infarcted myocardium.The major clinical experience has been with ^99mTc-pyrophosphate, a bone-seeking radionuclide. The major advantage of ^99mTc-pyrophosphate over ^99mTc-tetracycline is the earlier imaging interval. Optimal scans are obtained at 1–2 days after infarction and only 90 min after the administration of ^99mTc-pyrophosphate (as opposed to 24 hr with ^99mTc-tetracycline). While ^99mTc-pyrophosphate is a quite sensitive indicator of infarction, there is suggestive evidence that ischemic as well as infarcted myocardium sequesters the agent. In addition, various other conditions, including cardioversion, rib fractures, left ventricular aneurysms, and breast tumors may cause uptake of ^99mTc-pyrophosphate and lead to false positive myocardial infarct scintigrams. Thus, while only a few patients with negative scans who have been imaged at the appropriate time will turn out to have clinically detectable infarcts, a somewhat larger number without infarction will have positive scans, particularly those patients with unstable angina pectoris but without clinical infarction.While the final role of acute myocardial scintigraphy remains to be determined, its contribution to the further understanding of the pathogenesis of ischemia and infarction, as well as its clinical utility, has been significant.     

Tritiated digoxin. XX. Tissue distribution in experimental myocardial infarction

The role and potential hazards of digitalis glycoside administration in acute myocardial infarction remain controversial. We investigated the concentration of tritiated digoxin in normal, ischemic, and infarcted left ventricular myocardium of the dog after ligation of the anterior interventricular coronary artery. The normal homogeneous distribution of tritiated digoxin in the normal canine left ventricle was altered following acute myocardial infarction. The ischemic and infarcted zones exhibited a marked diminution in digoxin concentration. Oxidative phosphorylation determinations confirmed tissue hypoxia in the infarcted zone. The gradient of digoxin concentration between normal, ischemic, and infarcted zones of myocardium may potentiate the development of an arrhythmia in the electrically unstable infarcted myocardium.     

Serial myocardial scintigraphy after a single dose of thallium-201 in men after acute myocardial infarction

Serial myocardial scintigraphy after a single dose of thallium-201 in the period immediately after myocardial infarction may demonstrate redistribution of thallium-201 into perfusion defects that were evident in the initial scan. This study tested the hypothesis that evaluation of this redistribution, available within hours of infarction, could provide a more accurate estimate of the eventual perfusion defect than a single thallium-201 Image obtained immediately after infarction. The study group comprised 14 patients with a diagnosis on admission of probable acute myocardial infarction. The patients received thallium-201 a mean of 1.3 hours after admission to the coronary care unit. Imaging began 10 minutes after the thallium injection and was repeated 4 to 8 hours later.Eight patients with acute myocardial infarction had a definite reduction in one or more perfusion defects on serial scintigraphy, possibly indicating reperfusion of transiently Ischemic zones. Two patients with acute infarction had an increase in perfusion defects in a second study performed 6 hours after the initial scintigram. In the interval between scans, one patient had a cardiac arrest with clinical evidence of infarct extension after successful resuscitation; the other sustained a lateral extension of the infarct. One patient with acute aortic dissection had normal scans on both studies. All three patients with unstable angina had an abnormal initial scan; on repeat scan, the thallium-201 defect was unchanged in one patient, increased in one and decreased in the third. In the patients with myocardial infarction, repeat thallium-201 scans corresponded more nearly than the initial scans to the extent of technetilum-99m stannous pyrophosphate uptake by the heart.These data suggest that serial myocardial imaging with thallium-201 immediately after myocardial infarction can overcome some of the limitations of a single thallium-201 scintigram and may be useful in delineating ischemic from infarcted myocardium in the postinfarction period.     

抗心肌肌凝蛋白抗体亲大鼠梗塞心肌特性的研究

目的　探讨抗心肌肌凝蛋白单克隆抗体 (antimyosinantibody ,AMA)亲梗塞心肌的特点。方法　心肌梗死大鼠静脉注射放射性锝 99m标记的抗心肌肌凝蛋白单克隆抗体 (99mTc AMA) ,观察注射时间 ,梗死时间和梗塞区对梗塞心肌摄取AMA的影响。结果　注射后 2h梗塞心肌开始摄取AMA ,以后摄取逐渐增加 ,2 4h达到高峰。心肌梗死后 2 0d ,梗塞心肌持续摄取AMA ,期间心肌梗死后 1～ 5d摄取最强 ,梗塞中央区以及梗塞区内层摄取强于其他梗塞区域。结论　急性心肌梗死大鼠梗塞心肌特异性地摄取AMA ,注射AMA后摄取迅速、持久 ,受心肌梗死时间影响较小 ,梗塞中央区内层心肌摄取最强 ,AMA具有亲梗塞心肌的特性。     

Differential accumulation of radiopaque contrast material in acute myocardial infarction

The differential accumulation of radiographic contrast materials in ischemically damaged and normal myocardium was assessed with direct measurement (fluorescent excitation analysis) of the iodine content of tissue samples from dogs with 48 hour old myocardial infarctions. Tissue samples were obtained 10, 30, 60 and 180 minutes after the intraveneus administration of 2 ml/kg body weight of diatrizoate meglumine and sodium (Renografin-76). At all time intervals, the iodine concentration of infarcted tissue was at least threefold greater than that of normal myocardium. At 180 minutes the ratio between iodine concentration in infarcted myocardium and that in normal myocardium was 8.5 and between that in infarcted myocardium and that in blood was 2.6. The iodine concentration in the liver was similar to or greater than that in the infarcted area at time intervals after 10 minutes. These results suggest that the intraveneus administration of contrast material may facilitate the identification of acutely infarcted myocardium with computerized X-ray transmission tomography.     

Early quantification of experimental myocardial infarction with technetium-99m glucoheptonate: scintigraphic and anatomic studies.

Recent advances in understanding of the pathophysiology of myocardial necrosis indicate the need for a noninvasive method that will allow detection and quantification of infarcts in the first few hours after the onset of infarction. Myocardial infarct scintigraphy using technetium-99m glucoheptonate is capable of detecting infarction in dogs and man within 4 to 6 hours of onset. Studies were performed in 45 dogs with acute myocardial infarction: 28 with with an anterior infarct, 5 with an inferior infarct, 6 with an anterior infarct studied after infusion of mannitol and 6 with ligation of the left anterior descending coronary coronary artery and reperfusion of the ischemic area. The dogs were given 20 m Ci of technetium-99m glucoheptonate 1 hour after coronary occlusion, subjected to imaging 5 to 9 hours later and then killed. The experiments revealed that (1) scintigraphic infarct size correlated with infarct weight for anterior (r = 0.85) and inferior (r = 0.88) infarcts; (2) technetium-99m glucoheptonate also concentrated in a rim of myocardium around the infarct that probably represented the ischemic zone; and (3) technetium-99m glucoheptonate uptake by infarcted myocardium could be greatly increased with mannitol and reperfusion.     

Scintigraphy of acute myocardial infarction with ligands of 99mTc-phosphate

Of the wide range of radiopharmaceuticals which accumulate in acutely myocardial tissue and subsequently enable its scintigraphic detection compounds of 99mtechnetium phosphate have proven clinically practicable in numerous investigations. As opposed to the similarly non-invasive method of myocardial scintigraphy with ionic tracers (201thallium scintigraphy), infarct detection through positive delineation is possible, at the earliest, six to twelve hours faster the onset of pain and meaningful for those in whom the classical ECG and enzyme changes are equivocally diagnostic and for patients with delayed hospital admissions. After approximately one week the concentration of activity in the necrotic zone and, in turn, its detectability, declines. Persistent activity is indicative of extensive infarction and poor prognosis. The sensitivity of the infarct scintigram, which is primarily carried out with 99mTc-pyrophosphate or 99mTc-methylendiphosphonate, is about 86% with small and sudbendocardial infarcts more frequently eluding detection. The method corresponds with electrocardiographic assessment of localization. The combination with 201thallium scintigraphy is useful in differentiating remote from acute infarction and in detection of right ventricular involvement associated with inferior infarction. In spite of a good correlation between the experimentally-determined infarct weight and scintigraphic findings, clinical investigations employing conventional methods of measurement (scintillation camera) have not been able to yield an early and accurate quantification of the appearance may occur, for example, in unstable angina pectoris. Thus, a negative infarct scintigram carried out at the optimal time of uptake assumes its most useful role in ruling out acute myocardial infraction in the presence of otherwise equivocal clinical findings.     

Myocardial imaging in the noninvasive evaluation of patients with suspected ischemic heart disease.

Three noninvasive radioactive tracer techniques for evaluating patients with ischemic heart disease are described: (1) myocaridal perfusion imaging, (2) acute infarct imaging, and (3) the gated blood pool scan. Myocardial perfusion imaging with tracers that distribute in the myocardium in relation to regional blood flow allows detection of patients with transmural and nontransmural infarction by the finding of decreased tracer concentration in the affected region of the myocardium. If these tracers are injected at the time of maximal stress to patients with significant coronary arterial stenosis but without infarction, areas of transient ischemia can be identified as zones of decreased tracer concentration not found when an examination is performed at rest. Acute infarct imaging with tracers that localize in acutely damaged tissue permits separation of patients with acute myocardial necrosis from those without infarction and those with more chronic damage. The gated blood pool scan permits assessment of left ventricular function and regional wall motion. The measurement of ventricular volumes, ejection fraction and regional wall motion adds significantly to the determination of hemodynamic variables in assessing patients with acute infarction. The technique also permits detection of right ventricular dysfunction. Performance of a combination of these radioactive tracer techniques is often advantageous, particularly in patients with suspected infarction. The techniques can establish whether infarction is present, whether it is acute, where the damage is located and how extensive it is; they can also provide a measure of the effect of this damage on left ventricular function.     

Cell therapy enhances function of remote non-infarcted myocardium

Cell transplantation improves cardiac function after myocardial infarction; however, the underlying mechanisms are not well-understood. Therefore, the goals of this study were to determine if neonatal rat cardiomyocytes transplanted into adult rat hearts 1 week after infarction would, after 8–10 weeks: 1) improve global myocardial function, 2) contract in a Ca²⁺ dependent manner, 3) influence mechanical properties of remote uninjured myocardium and 4) alter passive mechanical properties of infarct regions. The cardiomyocytes formed small grafts of ultrastructurally maturing myocardium that enhanced fractional shortening compared to non-treated infarcted hearts. Chemically demembranated tissue strips of cardiomyocyte grafts produced force when activated by Ca²⁺, whereas scar tissue did not. Furthermore, the Ca²⁺ sensitivity of force was greater in cardiomyocyte grafts compared to control myocardium. Surprisingly, cardiomyocytes grafts isolated in the infarct zone increased Ca²⁺ sensitivity of remote uninjured myocardium to levels greater than either remote myocardium from non-treated infarcted hearts or sham-operated controls. Enhanced calcium sensitivity was associated with decreased phosphorylation of cTnT, tropomyosin and MLC2, but not changes in myosin or troponin isoforms. Passive compliance of grafts resembled normal myocardium, while infarct tissue distant from grafts had compliance typical of scar. Thus, cardiomyocyte grafts are contractile, improve local tissue compliance and enhance calcium sensitivity of remote myocardium. Because the volume of remote myocardium greatly exceeds that of the grafts, this enhanced calcium sensitivity may be a major contributor to global improvements in ventricular function after cell transplantation.     

Delineation of acute myocardial infarction with dysprosium DTPA-BMA: influence of dose of magnetic susceptibility contrast medium.

OBJECTIVES. The contrast enhancement of acutely infarcted myocardium produced by the nonionic magnetic susceptibility-enhancing agent dysprosium diethylenetriamine pentaacetic acid-bis-methylamide (DyDTPA-BMA [S-043 Injection]) was assessed in the current study to establish the lowest dose that would yield optimal contrast between normal and acutely infarcted myocardium. BACKGROUND. Magnetic susceptibility contrast agents enhance differences between normal and ischemic tissue by reducing the signal of the normally perfused tissue to which they distribute. METHODS. Acute myocardial infarctions were produced by ligation of the left coronary artery. At 3 to 4 h after occlusion, a dose of 0.1, 0.3 or 0.5 mmol/kg of DyDTPA-BMA was injected intravenously into eight rats each in group 1, 2 or 3, respectively; a fourth group of seven rats served as a control group. Nuclear magnetic resonance (NMR) transverse relaxation time (T2)-weighted images (electrocardiographically gated to every 5th beat, echo delay time [TE] = 60 ms) were acquired before and for 1 h after administration of contrast agent. RESULTS. Images obtained before the injection of contrast agent showed moderate differences in signal intensity between normal and infarcted myocardium (p < 0.05). The contrast enhancement and the duration of delineation between infarcted and normal myocardium produced by this agent were dose dependent. At doses of 0.1, 0.3 and 0.5 mmol/kg, DyDTPA-BMA produced signal loss in normal myocardium: 63 +/- 5%, 41 +/- 4% and 28 +/- 4% of the baseline values, respectively, without any significant reduction in signal intensity of the infarcted region. The reduction in signal of normal myocardium and delineation of the infarct persisted for 5 min at a dose of 0.1 mmol/kg, for 20 min at a dose of 0.3 mmol/kg and for 40 min at a dose of 0.5 mmol/kg. No change in signal intensity or signal intensity ratio between normal and infarcted myocardium was observed in the control group during the same observation period. CONCLUSIONS. These results suggest that low doses of this agent, comparable to those of longitudinal relaxation time (T1)-enhancing agents, can delineate acutely infarcted myocardium. A dose of 0.3 mmol/kg of DyDTPA-BMA (S-043 Injection) provides reasonably persistent demarcation of acute myocardial infarction. Because this dose dramatically suppresses the NMR signal of normal myocardium, it shows the infarcted region as a region of high intensity (bright spot) on NMR images.     

Prognostic significance of follow-up scintigraphy with 99m Tc-pyrophosphate in myocardial infarction (author's transl)]

Using 99m Tc-pyrophosphate there is a positive visualization of a transmural myocardial infarction by a localized tracer activity outside of the skeletal system. The uptake of the tracer in the infarcted area is expressed as percentage of the accumulation over the sternum. It reaches a maximum 48-60 hours after infarct onset and then recedes gradually but not strictly linearly. On the occasion of a control scintigraphy 3-4 weeks after the myocardial infarction and after full mobilization 56 per cent of the investigated patients showed a variable decrease of the tracer activity. On 44 per cent the tracer activity in the infarcted area remained unchanged or even increased slightly, though the infarction could be excluded. At the same time performed haemodynamic investigations with measuring the pulmonary artery pressure at rest and under stress conditions showed a good correlation between the persistence of the tracer activity in the infarcted area and the amount of the pulmonary pressure at rest and during stress, manifesting left ventricular function. So the result of a control scintigraphy 3-4 weeks after myocardial infarction allows to draw prognostic inferences about the further course of the disease.     

Kinetics of thallium-201 in reperfused canine myocardium after coronary artery occlusion

To study the kinetics of thallium-201 in nonsalvaged acutely infarcted myocardium and salvaged myocardium, the tracer was administered after experimental left anterior descending coronary artery reperfusion 2 hours after occlusion. In 19 dogs, thallium activity was then monitored for 4 hours in the reperfused anterior wall and normal posterior wall using miniature cadmium telluride radiation detectors. After sacrifice, 13 of the dogs were found to have an infarcted anterior wall by triphenyltetrazolium-chloride staining. In these dogs, mean (+/- standard deviation) fractional 4 hour thallium clearance was 0.33 +/- 0.08 for the infarct zone and 0.15 +/- 0.06 for the normal control zone (p less than 0.001). When computer-modeled, the clearance curve from the infarct zone was biexponential. The second exponential clearance curve from the infarct zone began 19.1 +/- 3.2 minutes after tracer administration, and was indistinguishable from the monoexponential clearance curve from the normal control zone. Thallium clearance from the blood pool was triexponential, the final exponential clearance curve being indistinguishable from the normal control zone clearance curve. Six dogs were found to have a salvaged noninfarcted anterior wall by triphenyltetrazolium-chloride staining. In these dogs, mean fractional 4 hour thallium clearance was 0.20 +/- 0.07 for the reperfused zone, and 0.19 +/- 0.08 for the normal control zone (p = NS). When computer-modeled, clearance curves for the reperfused and control zones were monoexponential. The monoexponential clearance curve for the salvaged reperfused zone was indistinguishable from the monoexponential clearance curve for normal myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dual radionuclide study of myocardial infarction. Relationships between myocardial uptake of potassium-43, technetium-99m stannous pyrophosphate, regional myocardial blood flow and creatine phosphokinase depletion.

The dual radionuclide myocardial distributions of imaging agents potassium-43 (43K) and technetium-99m stannous pyrophosphate (99mTc-PYP) were studied in a 24-hour closed chest canine infarct preparation. In multiple myocardial biopsies in 20 dogs, tissue levels of both radionuclides were compared to either an index of tissue viability (myocardial creatine phosphokinase [CPK] depletion), or to estimates of regional myocardial blood flow as measured by the microsphere technique. Myocardial 43K uptake in the ischemic and infarcted zone correlated well with both CPK depletion (r = 0.73) and microsphere estimates of relative blood flow. The correlation with microspheres was excellent in the transmural sample (r = 0.93) as well as endocardial (r = 0.97) and epicardial (r = 0.86) portions. On the other hand, 99mTc-PYP myocardial uptake did not correlate with the extent of CPK depletion. Maximal uptake was frequently noted in border zones with only moderate CPK depletion, while lesser degrees of 99mTc-PYP uptake were noted in the central infarct zone where CPK activity was lowest. The relationship of 99mTc-PYP uptake to microsphere regional flow estimates demonstrated that 99mTc-PYP uptake was maximal at flows of 0.3 to 0.4 of normal. At lower flows, 99mTc-PYP uptake fell toward normal levels. A similar relationship was noted between the distributions of 99mTc-PYP and 43K. In relatively high flow border segments (larger than or equal to 0.80 of normal), abnormal 99mTc-PYP uptake of five to six times normal persisted. The transmural distribution of 99mTc-PYP demonstrated that in low flow regions 99mTc-PYP uptake was primarily epicardial, while in the higher flow ischemic periphery of the infarct endocardial uptake predominated. Thus, while there is a direct correlation between cationic 43K myocardial uptake and regional myocardial viability and blood flow, no such direct relationship exists for 99mTc-PYP. This is in part based on the necessity for delivery of the radioactive tracer to the infarct zone.     

Relation between regional distribution of thallium-201 and myocardial blood flow in normal,acutely ischemic,and infarcted myocardium

Myocardial localization of thallium-201 was compared with direct measurements of myocardial perfusion in normal, acutely ischemic, and recently infarcted myocardium. Studies were performed in 6 chronically instrumented dogs that were subjected to myocardial infarction by occlusion of the proximal left circumflex coronary artery. Four days after myocardial infarction, thallium-201 and 9 ± 1 μm niobium-95-labelled microspheres were injected simultaneously after acute left anterior descending coronary arterial occlusion; the animals were killed 5 minutes later and the entire left ventricle was sectioned into 1 to 2 g samples. Regression analyses between thallium-201 activity and regional myocardial blood flow using all myocardial samples demonstrated a very close linear relation in each dog; r values were 0.98 or greater, indicating that the initial localization of thallium-201 in acutely ischemic and recently infarcted myocardium as a function of regional blood flow was essentially identical. Consequently, in each dog the regional distribution of thallium-201 closely approximated myocardial perfusion over a wide range of blood flow and potentially different local metabolic conditions that may be encountered in the clinical use of the isotope.     

Enhanced detection of ischemic but viable myocardium by QT interval dispersion on treadmill exercise electrocardiograms of patients with healed anterior wall myocardial infarcts

BACKGROUND: The presence of ischemic but viable myocardium in infarcted areas is an important indication for coronary revascularization, but is often difficult to detect with the use of treadmill exercise electrocardiography (ECG). HYPOTHESIS: QT interval dispersion (QTd) is a sensitive method for detecting myocardial ischemia and may improve the accuracy of treadmill exercise ECG testing for detecting ischemic but viable myocardium in infarcted areas. METHODS: Forty-five patients with Q-wave anterior wall myocardial infarctions who underwent treadmill exercise ECG, exercise reinjection thallium-201 (201Tl) scintigraphy, radionuclide angiocardiography, and coronary angiography 1 month after infarction were enrolled in this study. The presence of viable myocardium in the infarct area was determined by exercise reinjection 201Tl scintigraphy. Patients who had no redistribution in the infarct area after reinjection were included in Group 1, and those with redistribution were included in Group 2. RESULTS: QTd immediately after exercise, and the difference between QTd before and immediately after exercise, were significantly greater in Group 2 than in Group 1. The sensitivity, specificity, and accuracy of conventional ST-segment depression criteria for detecting viable myocardium in the infarct area were 48, 64, and 56%, respectively. The measurement of QTd immediately after exercise (abnormal: > or = 70 ms; normal: < 70 ms) improved the sensitivity, specificity, and accuracy to 78, 82, and 80%, respectively. CONCLUSIONS: This novel diagnostic method using QTd-based criteria significantly improves the clinical usefulness of treadmill exercise ECG testing for detecting ischemic but viable myocardium in infarct areas in patients with healed Q-wave anterior wall myocardial infarctions.     

99mTc-imidodiphosphonate: a superior radio-pharmaceutical for in vivo positive myocardial infarct imaging. II: Clinical data

99mTc-Imidodiphosphonate was investigated as a new myocardial infarct imaging agent. In the acute phase, 50 patients admitted to the coronary care unit were serially scanned over a period of 7 days. A mobile gamma camera linked on line to a remote data processor was used. Because of higher uptake in infarcted myocardium and faster blood clearance, superior images than those recorded with 99mTc-pyrophosphate were obtained. Its ease of preparation, low cost, and favourable dosimetry (because of its label with conventional 99mTc) transforms this agent into the present radiopharmaceutical of choice for acute infarct imaging in particular if sizing and follow-up is intended versus time and type of treatment. In this series, no false positive cases were seen. The sensitivity of the method in the detection of full thickness myocardial infarction was 95%. It dropped to 70% in the detection of subendocardial infarction. However, some of these apparent false negative cases may reflect severe ischaemia without infarction. It is postulated that this discrimination may not always be realistic.     

99mTc-imidodiphosphonate: a superior radio-pharmaceutical for in vivo positive myocardial infarct imaging. II: Clinical data.

99mTc-Imidodiphosphonate was investigated as a new myocardial infarct imaging agent. In the acute phase, 50 patients admitted to the coronary care unit were serially scanned over a period of 7 days. A mobile gamma camera linked on line to a remote data processor was used. Because of higher uptake in infarcted myocardium and faster blood clearance, superior images than those recorded with 99mTc-pyrophosphate were obtained. Its ease of preparation, low cost, and favourable dosimetry (because of its label with conventional 99mTc) transforms this agent into the present radiopharmaceutical of choice for acute infarct imaging in particular if sizing and follow-up is intended versus time and type of treatment. In this series, no false positive cases were seen. The sensitivity of the method in the detection of full thickness myocardial infarction was 95%. It dropped to 70% in the detection of subendocardial infarction. However, some of these apparent false negative cases may reflect severe ischaemia without infarction. It is postulated that this discrimination may not always be realistic.     

Detection and characterization of acute myocardial infarction in man with use of gated magnetic resonance

To evaluate the capability of magnetic resonance imaging (MRI) in the detection and characterization of alterations in signal intensity and T2 relaxation time in acutely infarcted relative to normal myocardium 16 adult patients and normal volunteers were studied by electrocardiographically gated proton MRI. The seven volunteers were entirely asymptomatic and had no history of cardiovascular abnormality. The nine patients had each suffered an acute myocardial infarction within 5 to 12 days before the MRI studies. The diagnosis in each patient was confirmed by electrocardiographic (ECG) criteria and elevated levels of fractionated creatine kinase (CK) isoenzymes. Electrocardiographically gated MRI was performed with a superconducting system operating at 0.35 tesla. MRI demonstrated infarcted myocardium as a region of high signal intensity relative to that of adjacent normal myocardium; regions of high intensity corresponded anatomically to the site of infarction as defined by the ECG changes. The mean percent difference between normal and infarcted myocardium was substantially greater on 56 msec images (70.2 +/- 21.3%) compared with 28 msec images (27.1 +/- 13.6%). Region of interest analysis revealed that infarcted myocardium had a significantly (p less than .01) prolonged T2 relaxation time (mean T2 = 80.9 msec) relative to that in normal myocardium (mean T2 = 42.3 msec) and relative to the mean T2 of left ventricular myocardium in the volunteers (mean T2 = 42.4 msec). An additional finding for each patient with myocardial infarction was a high intraluminal flow signal on 56 msec images, but this was also observed in normal subjects and is therefore a nonspecific finding.(ABSTRACT TRUNCATED AT 250 WORDS)     

99mTc-imidodiphosphonate: a superior radio-pharmaceutical for in vivo positive myocardial infarct imaging. I: Experimental data.

99mTc-Imidodiphosphonate (99mTc-IDP) was investigated as an agent for nuclear medicine imaging of acute myocardial infarctions. For this purpose a suitable animal model was found. After coronary artery ligation reproducible myocardial infarcts were obtained with 80% of surviving animals. Scans of the myocardial infarcts were recorded with a high resolution gamma camera and good quality images were obtained. 99mTc-IDP ratios for normal and infarcted tissue were calculated and compared with similar data available from other 99mTc-labelled phosphates. With an infarct/normal ratio of 21:1, 99mTc-IDP is so far the best radiopharmaceutical for nuclear medicine imaging of necrosed heart muscle. Images of the myocardial infarcts have been recorded as early as 6 hours after infarction.