The influence of attenuation and scatter compensation on the apparent distribution of Tc-99m sestamibi in cardiac slices.

BACKGROUND: Our objective was to study the differences in relative count distributions in the left ventricular walls with attenuation compensation (AC) versus AC and triple-energy-window scatter compensation (SC), compared with standard filtered backprojection (FBP). METHODS AND RESULTS: Two hundred patients identified as having normal cardiac perfusion with FBP after undergoing either pharmacologically or physiologically induced stress were included in this study. Projection data were reconstructed with FBP, 10 iterations of ordered-subset expectation-maximization (OSEM) with AC, and OSEM with AC+SC. A comparison was made of average percentage of maximum counts within each of 9 regions of CEqual (Marconi Medical Systems, Inc, Cleveland, Ohio) polar maps (ie, the apex, 4 midventricular regions, and 4 basal regions). Compared with OSEM(AC), a slight decrease at the apex exists when SC is included. The elevated inferior-to-anterior count ratio in the midventricular and basal regions noted with OSEM(AC) decreased to close to 1.0 with OSEM(AC+SC). The anterior-to-lateral ratio for both regions was closest to 1.0 for OSEM(AC+SC). In the midventricular region, the lateral-to-septal ratio decreased further below 1.0 with OSEM(AC+SC) than it did with OSEM(AC). This was the only basal ratio not to improve to close to 1.0 with OSEM(AC+SC). In a subset of patients identified at the time of clinical reading as having a possible attenuation-caused decrease in the inferior region, AC elevated the inferior-to-anterior ratio to above 1.0 for the midventricular region. AC+SC resulted in a ratio of near 1.0 for this region. In another subset of patients identified as having anterior attenuation artifacts, compensation methods (either AC or AC+SC) failed to show an improvement compared with FBP. CONCLUSIONS: AC and SC improve the uniformity of the polar map, especially by bringing the inferior-to-anterior ratio closer to 1.0. Further investigation is necessary to determine the cause of the increased midventricular septal polar map count. In addition, the subset of patients identified as having breast-like attenuation artifacts causing a decreased polar map count in the anterior wall (relative to the inferior wall) also needs further attention.

The effect of ischemic injury on the cardiac transport of Tc-99m N-NOET in the isolated rabbit heart.

BACKGROUND: Bis (N-ethoxy, N-ethyl dithiocarbamato) nitrido technetium-99m (V) (TcN-NOET) is a neutral lipophilic myocardial perfusion agent. The effect of ischemic injury on the cardiac transport of TcN-NOET and thallium-201 was determined in isolated rabbit hearts. METHODS AND RESULTS: The multiple indicator dilution method was used to determine the maximum (Emax) and net extraction (Enet, at 5 minutes) of TcN-NOET and TI-201 at control and after 10 minutes (n = 4) or 45 minutes (n = 4) of no-flow ischemia. After 10 minutes of ischemia the mean Emax for T1-201 was unchanged, 0.86 +/- 0.03 vs 0.85 +/- 0.02, whereas TI-201 Enet showed a small decrease from 0.46 +/- 0.03 to 0.40 +/- 0.03, P < .001. Forty-five minutes of ischemia mildly reduced Emax for TI-201 (0.87 +/- 0.04 to 0.74 +/- 0.04, P < .001) and severely reduced Enet (0.46 +/-0.03 vs 0.16 +/- 0.04, P < .001). Neither Emax nor Enet for TcN-NOET was significantly affected by 10 minutes of ischemia (0.54 +/- 0.04 vs 0.58 +/- 0.03 and 0.24 +/- 0.04 vs 0.26 +/- 0.04, respectively). However, severe ischemic injury caused significant reductions versus control in both Emax (0.59 +/- 0.06 vs 0.42 +/- 0.05, P < .001) and Enet (0.27 +/- 0.03 vs 0.18 +/- 0.05, P < .01). CONCLUSIONS: TcN-NOET is a new myocardial perfusion agent with moderate myocardial extraction. Although less sensitive than TI-201 to mild ischemic injury, TcN-NOET extraction and retention are decreased by severe ischemic injury, making uptake of TcN-NOET a possible marker of myocardial viability.

Thallium reinjection versus standard stress/delay redistribution imaging for prediction of cardiac events.

OBJECTIVES: The purpose of this study was to compare thallium reinjection with standard stress/delay redistribution for the prediction of cardiac events. BACKGROUND: Although thallium reinjection enhances the detection of viable myocardium, its contribution to prognosis over stress/delay redistribution in a general referral population has not been clearly evaluated. METHODS: This retrospective analysis included 366 consecutive patients with coronary artery disease who underwent stress/delay redistribution imaging and thallium reinjection scintigraphy, with a mean follow-up of 33+/-12 months. RESULTS: Cardiac events occurred in 48 patients (40 deaths, 8 myocardial infarctions). Of the 366 original patients, 159 demonstrated ischemia by stress/delay redistribution, 107 showed ischemia by reinjection only, and 100 showed infarction only. Cardiac events occurred in 20 patients (12.6%) with stress/delay redistribution, 13 patients (12%) with ischemia detected by thallium reinjection only and 15 patients (15%) with infarction only. The size of the reversible thallium defect by either stress/delay redistribution imaging or reinjection scintigraphy did not predict cardiac events. Independent predictors of cardiac events included left ventricular cavity size, the size of the abnormal perfusion defect and patient age. CONCLUSIONS: Thallium reinjection does not contribute independent prognostic utility for cardiac events when compared with stress/delay redistribution. Left ventricular dilation and the size of the post-stress defect were predictors of cardiac events.

An investigation of the estimation of ejection fractions and cardiac volumes by a quantitative gated SPECT software package in simulated gated SPECT images.

BACKGROUND: The purpose of this investigation was to determine the accuracy of the estimation of ejection fractions (EFs) and left ventricular volumes from a commercially available software package (Quantitative Gated SPECT [QGS]) as a function of different true EFs, count level in the acquisitions, severity and location of perfusion defects, increasing hepatic activity, and modified wall motion. METHODS AND RESULTS: The dynamic mathematic cardiac-torso digital phantom was used to create three-dimensional source and attenuation maps representing the distribution of a technetium-99m-labeled cardiac perfusion agent in the chest. Three hearts with varying end-systolic volumes were used to investigate different EFs. Perfusion defects were created as localized uptake within selected portions of the cardiac walls, scaled to the desired fraction of the normal wall uptake, and subtracted from the normal distribution. The hepatic uptake was increased up to five times of the normal heart uptake to investigate the influence of a "hot" liver. Alteration of lateral wall motion was also investigated. A three-dimensional projector that included the influence of distance-dependent spatial resolution and nonuniform attenuation was then used to create projection images. The projections were scaled to the desired acquisition count level, and Poisson noise was added. Automatic determination of EF slightly overestimated the true EF for normal count levels by 3% to 7% of the true EF and underestimated the true EF by up to 9% for very low count levels for 180-degree reconstructions. The accuracy for determining the volumes was not as high as for the EFs (an average error of 12% was observed). The calculated EFs were relatively accurate for perfusion defects of 50% or less. When perfusion defects exceeded 50%, extracardiac counts were included in the heart contours, causing larger underestimations of EF. With removal of the extracardiac counts, the EFs increased. With a hepatic uptake of two or more times the heart uptake, no meaningful EF could be obtained. Either drawing a single region of interest for every slice or use of the manual mode with constrain option could remarkably improve the estimation. The accuracy of the calculation of EF and volumes for the heart with stationary wall was fairly high but decreased significantly when coupled with perfusion defects. CONCLUSION: It is concluded that the QGS program evaluates the functional parameter of EF accurately. The biggest limitations occurred in determining the appropriate cardiac contour if areas with very high extracardiac counts were present in the heart slices, and when a greater than 50% decrease occurred in uptake for perfusion defects.

Intracoronary Doppler assessment of moderate coronary artery disease: comparison with 201Tl imaging and coronary angiography. FACTS Study Group.

BACKGROUND: Coronary angiography may not reliably predict whether a stenosis causes exercise-induced ischemia. Intracoronary Doppler ultrasound may enhance diagnostic accuracy by providing a physiological assessment of stenosis severity. The goal of this study was to compare intracoronary Doppler ultrasound with both 201Tl imaging and coronary angiography. METHODS AND RESULTS: Fifty-five patients with 67 stenotic coronary arteries underwent coronary angiography with intracoronary Doppler ultrasound and had exercise 201Tl testing within a 1-week period. Coronary flow reserve was measured, and analyses were performed by independent core laboratories. The mean stenosis was 59+/-12%; 51 of 67 stenoses were intermediate in severity (40% to 70%). A coronary flow reserve < 1.7 predicted the presence of a stress 201Tl defect in 56 of 67 stenoses (agreement=84%; kappa=0.67; 95% CI=0.48 to 0.86). In the patients who achieved 75% of their predicted maximum heart rate, the Doppler and 201Tl imaging data agreed in 46 of 52 stenoses (agreement=88%; kappa=0.77; 95%CI=0.57 to 0.97). Scatter was evident when angiography was compared with coronary flow reserve (r=.43), and the angiogram did not reliably predict the results of the 201Tl stress test (kappa=0.21; agreement=57% to 63%). CONCLUSIONS: Doppler-derived coronary flow reserve accurately predicts the presence of exercise-induced ischemia on stress 201Tl imaging, and coronary angiography does not reliably assess the physiological significance of an intermediate coronary stenosis.

Estimation of attenuation maps from scatter and photopeak window single photon-emission computed tomographic images of technetium 99m-labeled sestamibi.

BACKGROUND: In single photon-emission computed tomographic imaging of the chest, nonuniform attenuation correction requires use of a patient-specific attenuation map. The aim of this study was to determine whether an estimate of the regions of the lungs and nonpulmonary tissues of the chest could be obtained by segmenting the photopeak and Compton scatter window images in a phantom and in patients to estimate patient-specific attenuation maps. METHODS AND RESULTS: The photopeak and scatter window slices from 16 consecutive 99mTc-labeled sestamibi perfusion studies were segmented interactively. In these studies, visually reasonable regions could be obtained by estimating a "cold" lung region from scatter window data with additional anatomic information of the myocardium region, the backbone and sternum locations, the liver, and the rib cage from the photopeak window data. In an anthropomorphic torso phantom study and a patient study, comparison was made between the attenuation maps based on segmentation of the emission images and transmission imaging with a slant-hole collimator. It was determined that good agreement in the estimation of the body regions can be achieved with segmentation of the emission images in both the phantom and patient data. Attenuation correction using the maximum-likelihood expectation maximization method was performed on the phantom and the patient data. In both studies, attenuation correction with the segmented attenuation map improved uniformity of the inferior wall region in comparison with the other walls. CONCLUSIONS: The estimation of patient-specific attenuation maps by segmenting the scatter and photopeak window slices of 99mTc-labeled sestamibi studies may be a way of reducing the loss of specificity due to attenuation artifacts. The potential limitations on the accuracy of correction inherent in the method due to the estimation of the regions and assignment of the attenuation coefficients need to be determined further, and the method needs to be further automated before it can be considered for routine clinical use.

Effects of acute ischemia and reperfusion on the myocardial kinetics of technetium 99m-labeled tetrofosmin and thallium-201.

BACKGROUND: Effects of no-flow ischemia and reperfusion on myocardial extraction and retention of 99mTc-labeled tetrofosmin and 201Tl were investigated in seven isolated, blood-perfused rat hearts with isotope dilution studies at constant coronary perfusion. METHODS AND RESULTS: After a control injection of tracers, no-flow ischemia was induced for 20 minutes. After coronary reflow, tracers were injected. Both maximal fractional extraction and capillary permeability-surface area product for tetrofosmin were significantly less than those for 201Tl (maximal fractional extraction 0.30 +/- 0.01 and 0.70 +/- 0.09, respectively, p < 0.001; capillary permeability-surface area product 0.66 +/- 0.14 and 2.29 +/- 0.61, respectively, p < 0.001). After no-flow ischemia-reperfusion, both maximal fractional extraction and capillary permeability-surface area product decreased for both tetrofosmin and 201Tl (decreases in maximal fractional extraction of 23% and 7%, respectively; decreases in capillary permeability-surface area product of 27% and 16%, respectively), although the difference reached statistical significance only for tetrofosmin. Net extraction at 5 minutes of both tracers decreased significantly after no-flow ischemia-reperfusion (tetrofosmin 20% decrease, p < 0.01; 201Tl 23% decrease, p < 0.02). Early (0 to 5 minutes) washout of tetrofosmin did not change after no-flow ischemia-reperfusion, whereas the 201Tl value increased significantly. Although late (5 to 19 minutes) washout of both tracers increased significantly after no-flow ischemia-reperfusion, the myocardial clearance rates for tetrofosmin were always significantly less than those noted for 201Tl. CONCLUSIONS: The myocardial uptake of tetrofosmin is depressed (independent of blood flow) after severe ischemic injury, apparently resulting mainly from decreased transcapillary exchange. In contrast, the depressed uptake of 201Tl is related more to an accelerated early washout from injured myocardium than to a fairly stable initial transcapillary exchange.

Prognostic utility of increased pulmonary thallium uptake in patients without ischemia.

BACKGROUND: Although the combination of increased pulmonary thallium uptake and ischemia has demonstrated prognostic utility, the value of pulmonary uptake independent of ischemia has not been evaluated critically. Accordingly, our purpose was to evaluate the prognostic utility of thallium lung uptake in patients who do not have stress-induced defects. METHODS AND RESULTS: We studied 184 patients who were divided into three groups. Patients with increased pulmonary uptake were grouped into either the normal perfusion (n = 48) or fixed defect (n = 44) scan group and were compared with a third group (n = 92) of control patients who had normal scans and no lung uptake. During a mean follow-up of 23 +/- 13 months, there were 13 cardiac events (death or myocardial infarction) and the incidence per year was 0.6%, 2%, and 12% in the control, normal, and fixed defect groups, respectively (p < 0.00001). Life table analysis demonstrated greater event-free survival rates in the control and normal groups compared with the group with fixed defects. A Cox regression analysis showed that the number of fixed defects (infarct segments) was the most important independent prognostic factor (p < 0.00001) for future cardiac events. CONCLUSION: In patients with increased pulmonary thallium uptake and no stress perfusion defects, the prognosis is similar to that of control patients. However, patients with infarct segments and lung uptake have a significantly worse prognosis.

Transmission imaging of large attenuators using a slant hole collimator on a three-headed SPECT system.

By combining conjugate views, truncation-free attenuation profiles of patients can be obtained by using slant hole collimators on three-headed SPECT systems. The alterations in reconstruction algorithms necessary for use with slant hole collimators and potential image artifacts are discussed. Based on an evaluation of the size of objects that can be imaged without truncation and the size of the overlap region in the conjugate views, a 15 degrees slant angle was determined to be optimal. Studies with a 30 degrees slant hole collimator verified the ability of slant hole transmission imaging to provide accurate, truncation-free attenuation maps of a 56 cm lateral width phantom. The center of rotation was determined to be dependent on the slant angle and radius of rotation of the slant collimator. These studies also demonstrated that the spatial resolution in the transaxial plane of the attenuation maps depends on radius of rotation of the slant hole collimator, but does not depend on the radius of rotation of an uncollimated transmission source. A multiline transmission source was investigated for use with estimating the attenuation map in Tc-99m labeled sestamibi perfusion imaging.

Teboroxime is a marker of reperfusion after myocardial infarction.

BACKGROUND: It has been shown that serial teboroxime imaging can rapidly assess coronary perfusion in viable myocardial distributions. However, the myocardial uptake of teboroxime after reperfusion of acutely infarcted myocardium has not been critically evaluated. The study object was to assess whether teboroxime uptake in acutely infarcted myocardium is linearly related to blood flow. METHODS AND RESULTS: Seventeen New Zealand rabbits underwent occlusion of the left circumflex coronary artery for 1 hour. The animals were reperfused for 2 hours and, just before they were killed, teboroxime was injected. The infarct was delineated by triphenyltetrazolium chloride staining. Normalized blood flow and myocardial teboroxime distribution in the infarcted myocardium was determined by gamma well counting. Ex vivo planar images of the left ventricle were also acquired. Transmural myocardial infarction was documented in all 17 rabbits. The mean infarct size +/- one standard deviation was 25.5% +/- 10.7% (range, 11.9% to 43.3%). There was a direct linear relationship between normalized reperfusion flow and myocardial teboroxime distribution in the infarct zone (r = 0.91). A direct linear relationship between defect size and normalized infarct zone reperfusion was also evident on the ex vivo planar studies (r = 0.70). CONCLUSION: This study shows that the initial uptake of teboroxime in acutely infarcted myocardium is linearly related to blood flow. Teboroxime has properties that are well suited for the early evaluation of infarct zone perfusion.

Physiologic properties of myocardial perfusion tracers.

Accurate noninvasive assessment of coronary blood flow is dependent on the physiologic properties of the perfusion agent as well as the physical imaging properties of its radiolabel. Perfusion agents can accurately assess variable levels of flow by having a high myocardial extraction and retention. Based on extraction values, teboroxime can best determine hyperemic flow, but only if imaged very early after injection. In contrast, sestamibi has the lowest peak extraction and has diminished linear uptake at hyperemic flows. However, sestamibi has stable tissue distribution and good linear uptake over physiologic levels of flow, which make for good clinical utility. 201Tl has extraction properties that are slightly less than those for teboroxime, but its clinical myocardial retention is much higher. Therefore, all three perfusion agents can adequately evaluate variable levels of coronary flow. Uptake of the cationic perfusion agents 201Tl and sestamibi can be used for the assessment of myocardial viability, whereas uptake of the neutral compound teboroxime appears to be related to the level of coronary flow regardless of myocyte function.

Interaction of technetium 99m-labeled teboroxime with red blood cells reduces the compound's extraction and increases apparent cardiac washout.

BACKGROUND: 99mTc-labeled teboroxime shows high myocardial extraction in both in vivo animal and in vitro cell culture and isolated heart studies. Whereas in vivo studies show rapid myocardial clearance of teboroxime, in vitro cell culture and isolated heart studies show slower washout comparable to that of 201Tl. Binding of teboroxime to blood components may contribute to these conflicting results. METHODS AND RESULTS: We measured teboroxime extraction in the isolated blood-perfused rabbit heart after injection in saline solution, brief incubation in red blood cell perfusate, or 4-hour incubation with human red blood cells. Teboroxime in saline solution showed high extraction (Emax = 0.89 +/- 0.02; Enet = 0.69 +/- 0.02), whereas brief incubation in perfusate (Emax = 0.60 +/- 0.06; Enet = 0.48 +/- 0.05) or prolonged incubation with human red blood cells (Emax = 0.43 +/- 0.09; Enet = 0.38 +/- 0.07) resulted in reduced extraction. Teboroxime clearance was similar for all groups and was slower than 201Tl clearance. Analysis of total residual cardiac teboroxime (comparable to external imaging) showed that teboroxime clearance was biexponential. Reduced extraction of teboroxime in red blood cells resulted in an increased size of the rapidly clearing (unextracted) fraction, giving the appearance of rapid myocardial washout. CONCLUSIONS: Teboroxime has a high myocardial extraction. Binding to blood components reduces teboroxime extraction and increases the rate of cardiac teboroxime clearance.

Use of sequential teboroxime imaging for the detection of coronary artery occlusion and reperfusion in ischemic and infarcted myocardium.

Nine Yorkshire pigs underwent coronary artery occlusion followed by 2 hours of reperfusion. In five pigs (group A) the occlusion time was 15 minutes and in four pigs (group B) the occlusion time was 1 hour. Teboroxime was administered and images were acquired at baseline, and following occlusion and reperfusion. Infarct size was determined by triphenyl tetrazolium staining. Normalized regional myocardial blood flow, as determined by radio-labeled microspheres, was 0.26 +/- 0.09 following occlusion and 0.83 +/- 0.07 following reperfusion (p < 0.01). Significant differences were found between the defect/normal scan ratios on the baseline and occlusion scans (1.0 +/- 0.03 vs 0.54 +/- 0.10; p < 0.01) and between the occlusion and reperfusion scans (0.54 +/- 0.10 vs 0.97 +/- 0.17; p < 0.01). This is the first study to demonstrate that rapid sequential teboroxime imaging can detect acute coronary occlusion and reperfusion to both ischemic and infarcted myocardium. Teboroxime may be an excellent tracer for the early evaluation of infarct artery patency in patients receiving thrombolytic therapy.

Myocardial kinetics of radiolabeled perfusion agents: basis for perfusion imaging.

The myocardial deposition of radiolabeled perfusion agents permits the noninvasive assessment of regional coronary blood flow. The design of imaging protocols and the optimal interpretation of clinical perfusion studies are based on an understanding of the kinetics of blood-tissue exchange for these compounds. Thallium 201 and the technetium 99m-labeled compounds sestamibi, teboroxime, and tetrofosmin show differing myocardial extraction and retention. This review focuses on studies that used cell culture, isolated heart, and intact animal models that form the basis of our current understanding of the myocardial kinetics of these imaging agents.

Comparison of teboroxime and thallium for the reversibility of exercise-induced myocardial perfusion defects.

To determine the optimal technique for the scintigraphic detection of exercise-induced myocardial perfusion defects, we compared teboroxime scanning to both stress/redistribution thallium imaging and the thallium reinjection method following exercise in 35 patients. The overall concordance for the presence of a perfusion defect between teboroxime and thallium scanning was 91% (p < 0.01) and 89% when teboroxime was compared with stress/reinjection thallium imaging (p < 0.01). More segments per scan with fixed defects were observed with redistribution imaging than with teboroxime or thallium reinjection (2.9 vs 2.0 vs 1.9; p < 0.02). Additionally, more transient defects were present with teboroxime than thallium, but less than with reinjection imaging. One half of the 52 fixed perfusion abnormalities on stress/redistribution thallium imaging demonstrated reversibility with both teboroxime imaging and thallium reinjection scanning, but less than 50% of these segments were concordant. Teboroxime allows for improved detection of reversible perfusion defects compared with stress/redistribution thallium scanning, but more ischemia is noted with thallium reinjection. The variation in the detection of segmental ischemic defects between teboroxime scintigraphy and thallium reinjection scanning probably reflects different physiologic properties and imaging protocols of these perfusion agents.

Comparison of 3- versus 6-minute infusions of adenosine in thallium-201 myocardial perfusion imaging.

Adenosine thallium stress testing has a demonstrated utility in the detection of coronary artery disease. The optimal dose for diagnostic efficacy with minimal side effects has not been critically evaluated. A randomized 3- and 6-minute infusion of adenosine (140 micrograms/kg/min) was performed in 11 subjects. Subjects reported more side effects during the 6-minute infusion protocol (p < 0.05). Hemodynamic changes were not different during either infusion duration. All dysrhythmias began within 2 minutes and therefore the duration of the infusion did not influence their occurrence. Segmental comparison of the stress images demonstrated an 89% agreement. Delayed scans demonstrated a 79% agreement. There was a higher incidence of redistribution following the 6-minute infusion (p = 0.014). We conclude that when side effects necessitate the discontinuation of a 6-minute adenosine infusion, a diagnostic test can still be achieved if 2 to 3 minutes of adenosine have been administered before the thallium injection; however, the amount of viable myocardium may be underestimated.

Myocardial extraction of technetium-99m-[2-(1-methoxybutyl) isonitrile] in the isolated rabbit heart: a myocardial perfusion agent with high extraction and stable retention.

Technetium-99m-[2-(1-methoxybutyl) isonitrile] (MBI) is a potential new compound for the scintigraphic imaging of coronary flow. Evaluation in the blood-perfused isolated rabbit heart model showed this compound to have a myocardial uptake comparable to 201Tl and higher than sestamibi. Although the mean +/- s.d. maximum extraction (Emax) and capillary permeability-surface area product (PScap) of 99mTc-MBI (Emax = 0.45 +/- 0.10, PScap = 1.07 +/- 0.47 ml/min.g) were much less than 201Tl (Emax = 0.71 +/- 0.07, PScap = 2.21 +/- 0.76 ml/min.g, p < 0.0001), the net extraction of 99mTc-MBI (Enet = 0.52 +/- 0.10) was only slightly less than the value for 201Tl (Enet = 0.56 +/- 0.10, p < 0.05). There was no significant difference in the myocardial uptake versus flow between 99mTc-MBI and 201Tl. These data indicate that assessment of relative coronary flow based on the myocardial uptake of 99mTc-MBI should give results comparable to 201Tl. Therefore, 99Tc-MBI may have clinical potential as a radiolabeled myocardial perfusion agent.

Sequential teboroxime imaging during and after balloon occlusion of a coronary artery.

OBJECTIVES: We sought to assess whether sequential teboroxime imaging can rapidly evaluate vessel patency and identify the coronary artery occluded in patients undergoing balloon occlusion of a coronary artery. BACKGROUND: Intravenous thrombolytic therapy results in successful reperfusion of the infarct-related artery in only 50% to 80% of cases. A noninvasive technique to serially evaluate coronary perfusion would identify patients who might benefit from other interventions such as emergency percutaneous transluminal coronary angioplasty, coronary artery bypass grafting or increased intensity of thrombolytic therapy. METHODS: Teboroxime scans were performed during balloon occlusion in 15 nonconsecutive patients undergoing angioplasty of a major coronary artery. Equivalent views were repeated after successful angioplasty. RESULTS: The mean time between balloon occlusion and reperfusion imaging was 1.6 +/- 0.6 h. The mean number of defects decreased significantly from 4.13 +/- 1.01 during balloon occlusion to 0.27 +/- 0.44 after reperfusion (p = 0.0006). There was a 30% decrease in the defect/normal zone count/pixel ratios during balloon occlusion and normalization of these ratios after reperfusion (p = 0.0006). The scans correctly identified all nine left anterior descending coronary artery occlusions and both right coronary artery occlusions. One of the four left circumflex coronary artery occlusions was incorrectly identified as a right coronary artery occlusion by scan criteria. Overall, the scans correctly identified the occluded artery 93% of the time (kappa = 0.88). The scan was 100% accurate for distinguishing occlusion of the left anterior descending coronary artery (n = 9) from occlusions of the left circumflex or right coronary artery (n = 6). CONCLUSIONS: We believe that this is the first clinical study to demonstrate that sequential planar imaging with teboroxime can 1) rapidly detect acute coronary artery occlusion and reperfusion, and 2) identify the occluded coronary artery. A trial comparing rapid sequential teboroxime imaging with coronary angiography in patients receiving thrombolytic therapy for acute myocardial infarction is warranted.

Rapid redistribution of teboroxime.

Teboroxime, a new technetium-99m-labeled myocardial perfusion tracer, possesses rapid myocardial kinetics. Whereas this agent is routinely imaged after separate stress and rest injections, experimental data suggest that teboroxime may rapidly redistribute in the myocardium. Accordingly, we assessed 68 exercise teboroxime scintigrams in which immediate poststress, early delay (5 minutes) and rest images were acquired. Studies were categorized visually as ischemia, infarct or normal based on conventional stress-rest comparison. They were then evaluated for rapid teboroxime redistribution by comparing the stress and early delay images. Quantitative analysis was then performed on 537 myocardial segments. Segments were grouped as ischemia, infarct or normal based on stress-rest comparison, and the degree of normalization of stress-induced defects in the early delay images was determined for each group. Rapid teboroxime redistribution was observed in 20 of 46 scintigrams (48%) considered ischemic, and in 2 of 7 and 2 of 15 scintigrams deemed infarct and normal, respectively. The mean segmental intensity ratio (defined relative to the opposite segment) improved from 0.79 at stress to 0.88 at early delay (p < 0.005) in the group with ischemia and from 0.83 to 0.87 in the group with infarction. The most likely explanation for rapid redistribution of teboroxime is differential washout from the myocardium between areas of disparate flow. It is concluded that rapid redistribution of teboroxime occurs within 5 minutes of a stress injection, giving rise to potentially useful clinical information. Thus, teboroxime imaging should be completed expeditiously to detect areas of relative hypoperfusion.