The scintigraphic evaluation of myocardial infarction and regional ventricular performance using technetium-99m hexakis (t-butylisonitrile) technetium (I) (TBI): a new myocardial imaging agent

Technetium-99m hexakis (t-butylisonitrile) technetium (I) (99mTc-TBI) is a new myocardial perfusion imaging agent. To determine its potential in the evaluation of myocardial infarction, 15 patients with suspected or confirmed acute infarction were studied by bedside imaging in the coronary care unit. Good-quality planar scintigrams in multiple projections were obtained in 13 patients. Gated perfusion studies were performed in 14 patients, and for comparison 13 of these were restudied 24-72 h later by standard gated equilibrium blood pool radionuclide ventriculography. Conventional and planar scintigraphic criteria for myocardial infarction (acute or old) agreed in 12 (92%) patients (k = 0.81, p less than 0.05). All the infarctions detected by scintigraphy were associated with electrocardiographic Q-waves. Localization of infarction by the electrocardiogram and scintigraphy exhibited moderate agreement (k = 0.49, p less than 0.1). Regional wall motion analysis by standard radionuclide ventriculography and gated 99mTc-TBI scintigraphy were in complete agreement for 25 (64%) of 39 left ventricular segments (k = 0.35, p less than 0.05). However, in 7 other segments, associated with areas of infarction, regional wall motion abnormalities were noted only on gated 99mTc-TBI scintigraphy. Therefore, 99mTc-TBI scintigraphy can readily provide data on regional myocardial perfusion and wall motion, permitting detection and localization of areas of myocardial infarction. The superior imaging properties, ready availability and low cost of 99mTc point to the considerable potential value of 99mTc-TBI in assessing patients with suspected or confirmed myocardial infarction.     

Clinical evaluation of the 99mTc-labeled myocardial imaging agent,hexakis (t-butylisonitrile)-technetium

^99mTc-TBI myocardial perfusion imaging has been studied in 7 normal subjects and 24 patients with coronary artery disease. Scintigraphic data revealed that ^99mTc-TBI myocardial perfusion imaging is more sensitive than ECG in detecting myocardial infarction. In comparing ^99mTc-TBI imaging with contrast angiography, its' sensitivity for the diagnosis of coronary artery disease was 91.7%.     

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.     

The utilization of Tc-99m-TBI as a myocardial perfusion agent in exercise studies: Comparison with Tl-201 thallous chloride and examination of its biodistribution in humans

Twenty-four patients were studied with both ²⁰¹Tl-thallous chloride and ^99mTc-TBI scintigraphy following exercise. Comparison of the two agents in detecting segmental myocardial ischemia and scar was made in 18 patients with evidence of coronary artery disease on ²⁰¹Tl-thallous chloride scintigraphy. Agreement between the two studies was observed in 77% (125 of 162) of left ventricular segments, suggesting that ^99mTc-TBI can be used as a myocardial perfusion agent. Limitations were related to early high background activity from lungs and liver. The high lung activity and early myocardial redistribution within the 1st hour contributed to the failure of ^99mTc-TBI to detect 16 segmental defects seen in the immediate post-exercise thallous chloride scan. Persistently high liver activity additionally affected accurate interpretation in the left ventricular segments close to the diaphargm. Improvement in the accuracy of ^99mTc-TBI stress studies might be achieved with tomographic imaging to reduce the problem of background activity or by the development of ^99mTc-labeled isonitrile analogues with rapid lung and liver clearance.     

Value of gated SPECT in the analysis of regional wall motion of the interventricular septum after coronary artery bypass grafting

Purpose The aim of this study was the evaluation of septal wall motion, perfusion and wall thickening after CABG in two groups of consecutive patients, one with grafted left anterior coronary artery and no history of myocardial infarction, and the other with previous anteroseptal myocardial infarction and impaired septal motion before surgery. The issue addressed was the ability of gated SPECT to differentiate between true paradoxical septal motion, characterised by paradoxical wall motion, depressed ejection fraction (EF), poor viability and compromised wall thickening, and pseudo-paradoxical motion, characterised by abnormal wall motion and regional EF but preserved perfusion and wall thickening.Methods One hundred and thirty-two patients with previous anterior myocardial infarction, 82 patients with left anterior descending coronary disease and no history of myocardial infarction and 27 normal subjects underwent rest gated SPECT after ^99mTc-sestamibi injection, according to the standard QGS protocol. Quantitative regional EF, regional perfusion, regional wall motion and regional wall thickening were determined using a 20-segment model.Results Despite the presence of similar regional wall motion impairment in patients with and patients without septal infarction, in terms of regional EF (2.5%±3% vs 1.9%±4.9% p=NS) and inward septal motion (3±4.9 mm vs 2.3±6.1 mm p=NS), significant differences were observed in both perfusion (74.7%±6.2% vs 63.3%±13%, p>0.0001) and regional wall thickening (17.2%±7.4% vs 12.6%±7.2%, p>0.0001).Conclusion Gated SPECT with perfusion tracers can reliably differentiate pseudo-paradoxical from true paradoxical septal motion in patients with previous CABG, and it may be the method of choice for evaluating left ventricular performance in this patient population.     

Detection of residual wall motion after myocardial infarction by gated technetium-99m tetrofosmin SPET: a comparison with contrast ventriculography

The differentiation of residual viability from necrotic myocardium in patients with a prior myocardial infarction is important when deciding whether revascularization is indicated. Myocardial viability can be assessed by studying perfusion and regional wall motion. Gated single-photon emission tomography (SPET) imaging allows the simultaneous assessment of perfusion and function through a single study. The aim of this study was to analyse the concordance between wall motion score derived by gated SPET and by contrast ventriculography. Furthermore, the agreement between myocardial perfusion and regional myocardial wall motion was analysed for both techniques. We studied a homogeneous group of 26 consecutive patients with a prior myocardial infarction, using both gated technetium-99m tetrofosmin SPET and contrast ventriculography. A seven-segment model of the left ventricle was employed to score regional myocardial wall motion on images obtained with gated SPET and contrast ventriculography using a four-point scale. Contrast ventriculography was performed within 2 weeks of the gated SPET study. Prevalence of abnormal wall motion (akinetic or dyskinetic) was 24/182 (13%) for gated SPET and 25/182 (14%) for contrast ventriculography (P=NS). There was a high agreement (80%) in wall motion score between gated SPET and contrast ventriculography (3=0.67, P<0.001). The agreement was better in segments with normal or mild to moderate hypoperfusion (82%, 3=0.69) than in those with severe hypoperfusion (67%, 3=0.56). The agreement between myocardial perfusion and myocardial wall motion was 89% (162/182), 3=0.57, for gated SPET and 80% (145/182), 3=0.21, for contrast ventriculography. The relation between the summed wall motion scores per patient on gated SPET and contrast ventriculography was excellent (y=0.81x+2.9, r=0.82, P<0.01). Thirteen (43%) out of 30 segments with severely diminished or no myocardial perfusion showed normal or hypokinetic wall motion on gated SPET, suggesting residual myocardial viability in malperfused regions. Our results suggest that gated SPET imaging is a reliable tool for the assessment of regional wall motion in post-myocardial infarction patients. Furthermore, in patients with a previous myocardial infarction, gated SPET imaging has the potential to detect preserved wall motion in regions with fixed perfusion defects, which might be indicative of residual myocardial viability.     

Detection of residual wall motion after myocardial infarction by gated technetium-99m tetrofosmin SPET: a comparison with contrast ventriculography

The differentiation of residual viability from necrotic myocardium in patients with a prior myocardial infarction is important when deciding whether revascularization is indicated. Myocardial viability can be assessed by studying perfusion and regional wall motion. Gated single-photon emission tomography (SPET) imaging allows the simultaneous assessment of perfusion and function through a single study. The aim of this study was to analyse the concordance between wall motion score derived by gated SPET and by contrast ventriculography. Furthermore, the agreement between myocardial perfusion and regional myocardial wall motion was analysed for both techniques. We studied a homogeneous group of 26 consecutive patients with a prior myocardial infarction, using both gated technetium-99m tetrofosmin SPET and contrast ventriculography. A seven-segment model of the left ventricle was employed to score regional myocardial wall motion on images obtained with gated SPET and contrast ventriculography using a four-point scale. Contrast ventriculography was performed within 2 weeks of the gated SPET study. Prevalence of abnormal wall motion (akinetic or dyskinetic) was 24/182 (13%) for gated SPET and 25/182 (14%) for contrast ventriculography (P = NS). There was a high agreement (80%) in wall motion score between gated SPET and contrast ventriculography (kappa = 0.67, P < 0.001). The agreement was better in segments with normal or mild to moderate hypoperfusion (82%, kappa = 0.69) than in those with severe hypoperfusion (67%, kappa = 0.56). The agreement between myocardial perfusion and myocardial wall motion was 89% (162/182), kappa = 0.57, for gated SPET and 80% (145/182), kappa = 0.21, for contrast ventriculography. The relation between the summed wall motion scores per patient on gated SPET and contrast ventriculography was excellent (y = 0.81x + 2.9, r = 0.82, P < 0.01). Thirteen (43%) out of 30 segments with severely diminished or no myocardial perfusion showed normal or hypokinetic wall motion on gated SPET, suggesting residual myocardial viability in malperfused regions. Our results suggest that gated SPET imaging is a reliable tool for the assessment of regional wall motion in post-myocardial infarction patients. Furthermore, in patients with a previous myocardial infarction, gated SPET imaging has the potential to detect preserved wall motion in regions with fixed perfusion defects, which might be indicative of residual myocardial viability.     

Quantitative analysis of technetium 99m 2-methoxyisobutyl isonitrile single-photon emission computed tomography and isosorbide dinitrate infusion in assessment of myocardial viability before and after revascularization

Background

Assessment of viable myocardium in territories of hypoperfused myocardium is important for predicting functional recovery after revascularization. This study was designed to evaluate quantitative analysis of ^99mTc-labeled 2-methoxyisobutyl isonitrile (MIBI) myocardial perfusion imaging combined with isosorbide dinitrate (ISDN) infusion to detect myocardial viability in patients with chronic coronary artery disease before and after revascularization.

Methods and Results

Twenty-seven consecutive patients with previous myocardial infarction and left ventricular dysfunction (left ventricular ejection fraction 35.2%±13.5%) referred for coronary artery bypass (CABG) were studied with ^99mTc-labeled MIBI single-photon emission computed tomograpy at rest and during ISDN infusion before CABG followed by resting imaging after CABG. Quantitative analysis was performed with circumferential profiles. Left ventricular function (global and regional) was assessed by radionuclide ventriculography before and after CABG. Out of 212 abnormal perfusion segments with resting ^99mTc-labeled MIBI SPECT, 99 segments (47%) showed improved uptake of ^99mTc-labeled MIBI during ISDN infusion. The mean ratio of myocardial uptake was 0.58±0.25 (resting 0.53±0.23; p<0.05). After CABG, of 212 segments with hypoperfusion, 108 segments (51%; p>0.05 vs ISDN) showed improved uptake of ^99mTc-labeled MIBI. The mean ratio of myocardial uptake was 0.60±0.26 (resting 0.53±0.23; p<0.05). The concordance between the improvement of post-CABG wall motion and that of pre-CABG ISDN perfusion imaging was 83%, between the improvement of wall motion and perfusion imaging after CABG 94%, and between the improvement of pre-CABG ISDN and post-CABG perfusion imaging 83%, respectively.

Conclusion

ISDN infusion can improve the uptake of ^99mTc-labeled MIBI in hypoperfused myocardium and increase the efficiency of ^99mTc-labeled MIBI in the detection of viable myocardium in patients with previous myocardial infarction and left ventricular dysfunction.     

Estimate of myocardial salvage in late presentation acute myocardial infarction by comparing functional and perfusion abnormalities in predischarge gated SPECT

Purpose We hypothesized that, because of persistent stunning, the extent of post-treatment functional abnormalities detected using gated single-photon emission computed tomography (SPECT) could be representative of the initial risk area in acute myocardial infarction (AMI) treated by reperfusion therapy. Materials and methods In 48 AMI patients, we acquired two ^99mTc-sestamibi gated SPECT studies (at admission with tracer injection before treatment and at discharge 5 to 10 days later). We assessed the myocardial salvage defined by the admission minus predischarge summed rest score, and we compared it with the value obtained by subtracting the extent of perfusion defect from the extent of wall motion or wall thickening abnormalities in predischarge gated SPECT. Myocardial salvage was expressed as salvage index (salvaged myocardium divided by initial risk area). Results There was a good correlation between summed rest score salvage index and wall motion (Spearman’s ρ = 0.754, p < 0.0001) or wall thickening salvage index (Spearman’s ρ = 0.798, p < 0.0001). The wall thickening salvage index was able to classify correctly the patients that had a summed rest score salvage index ≥ 0.10 with 73% sensitivity, 88% specificity, and 83% accuracy. The wall motion salvage index was highly sensitive (91%) but poorly specific (13%, p < 0.002 vs wall thickening salvage index) and less accurate (69%, p < 0.05 vs wall thickening salvage index). Conclusions ^99mTc-sestamibi gated SPECT allows assessing myocardial salvage using only post-treatment data. The salvage index derived using wall thickening as surrogate of admission perfusion defect correlates well with the salvage index measured by comparing pre- and post-treatment perfusion defects.     

Evaluation of left ventricular wall motion, volumes, and ejection fraction by gated myocardial tomography with technetium 99m-labeled tetrofosmin: A comparison with cine magnetic resonance imaging

Background  Whether left ventricular function can be assessed accurately by gated single photon emission computed tomography (SPECT) in patients with myocardial infarction and severe perfusion defects is not well known. Methods and Results  Twenty-five patients with an acute myocardial infarction underwent ^99mTc-labeled tetrofosmin (^99mTc-tetrofosmin) gated SPECT and cine magnetic resonance imaging (MRI). Wall motion was assessed in 13 left ventricular segments using a 5-point scoring system ranging from 3 (normal) to-1 (dyskinetic). Exact agreement for wall motion scores between gated SPECT and MRI was excellent (92%, kappa=0.82). Furthermore, correlations between the two techniques were also good for end-diastolic volume (r=0.81, P<.0001), end-systolic volume (r=0.92, P<.0001), and ejection fraction (r=0.93, P<.0001). Conclusion  In patients with a recent myocardial infarction, ^99mTc-tetrofosmin gated SPECT provides reliable evaluation of global and regional ventricular function and volumes.     

Prediction of functional recovery after revascularization using quantitative gated myocardial perfusion SPECT: a multi-center cohort study in Japan

Backgrounds  Prediction of left ventricular functional recovery is important after myocardial infarction. The impact of quantitative perfusion and motion analyses with gated single-photon emission computed tomography (SPECT) on predictive ability has not been clearly defined in multi-center studies. Methods  A total of 252 patients with recent myocardial infarction (n = 74) and old myocardial infarction (n = 175) were registered from 25 institutions. All patients underwent resting gated SPECT using ^99mTc-hexakis-2-methoxy-isobutyl isonitrile (MIBI) and repeated the study after revascularization after an average follow-up period of 132 ± 81 days. Visual and quantitative assessment of perfusion and wall motion were performed in 5,040 segments. Results  Non-gated segmental percent uptake and end-systolic (ES) percent uptake were good predictors of wall motion recovery and significantly differed between improved and non-improved groups (66 ± 17% and 55 ± 18%, p < 0.0001 for non-gated; 64 ± 16% and 51 ± 17% for ES percent uptake, p < 0.0001). The area under the curve of receiver operating characteristics curve for non-gated percent uptake, ES percent uptake, end-diastolic percent uptake and visual perfusion defect score was 0.70, 0.71, 0.61, and 0.56, respectively. Sensitivity and specificity of percent uptake were 68% and 64% for non-gated map and 80% and 52% for ES percent uptake map. An optimal threshold for predicting segmental improvement was 63% for non-gated and 52% for ES percent uptake values. Conclusion  Segmental ^99mTc-MIBI uptake provided a useful predictor of wall motion improvement. Application of quantitative approach with non-gated and ES percent uptake enhanced predictive accuracy over visual analysis particularly in a multi-center study.     

Evaluation of left ventricular function using gated planar myocardial imaging with Tc-99m-MIBI

A quantitative index of left ventricular wall motion obtained from ECG-gated planar myocardial images has been developed. Five normal controls and 39 patients with heart disease received an injection of Tc-99m-MIBI (550-740 MBq) at rest, and ECG-gated planar scintigraphy (LAO view) was performed 3 h later. Mean End-diastolic (ED) and end-systolic (ES) myocardial activities were measured using circumferential profile analysis and %count increase (CI) was determined according to the following formula; (ES count-ED count)/(ED count) x 100. The global %CI was compared with the EF obtained from contrast ventriculography (LVG; n = 29) and radionuclide ventriculography using Tc-99m-labelled RBC (RNV; n = 24). The regional %CI was compared with left ventricular wall motion assessed by LVG. The global %CI was correlated well with EF by LVG (r = 0.70) and EF by RNV (r = 0.75). The regional %CI significantly decreased in accordance with wall motion on LVG worsened at impaired region. In conclusion, gated perfusion imaging with Tc-99m-MIBI provides useful information on ventricular function in addition to myocardial perfusion.     

Acute oral trimetazidine administration increases resting technetium 99m sestamibi uptake in hibernating myocardium

Background  Trimetazidine is an antiischemic drug protecting the myocardium from ischemic damage through the preservation of mitochondrial oxidative metabolism, without any hemodynamic effect. ^99mTc-sestamibi is accumulated by myocytes according to mitochondrial function. As mitochondrial metabolism is thought to be present in hibernating myocardium, the aim of the study was to investigate trimetazidine effects on infarcted and eventually hibernating myocardial areas by means of ^99mTc-sestamibi perfusional scintigraphy, comparing them to postoperative recovery of wall motion. Methods and Results  Twelve patients with previous myocardial infarction underwent 2 perfusion imaging tomographic studies at rest with ^99mTc-sestamibi, receiving placebo or trimetazidine (60 mg orally), and subsequently underwent revascularization procedures. An echocardiographic study was carried out before and >3 months after revascularization. At polar map analysis of placebo scan, infarcted vascular territories (wall motion score index: 2.65±0.31) showed 73.7%±10.4% of the territory with activity <2.5 SD from the mean of normals, for a severity (expressed as the sum of the standard deviations below average normal values in all abnormal pixels) of 833.8±345.7. Polar map analysis of the trimetazidine scan showed tracer uptake increased significantly in 11 of them, by 8.2%±3.0% (p<0.001) and by 180.3±111.0 SD (p<0.001), respectively. Postoperative wall motion score index improved significantly in 9 of these territories (−0.9±0.4, p<0.001). Conclusions  Trimetazidine-associated increase in ^99mTc-sestamibi uptake in infarcted but viable myocardial areas is probably related to an improvement in mitochondrial oxidative metabolism that is essential to ^99mTc-sestamibi retention. Additionally, coupling trimetazidine administration to ^99mTc-sestamibi perfusional scintigraphy may represent a means of detecting viable myocardium.     

The influence of gating on measurements of myocardium at risk and infarct size during acute myocardial infarction by tomographic technetium 99m-labeled sestamibi imaging

Background

Serial perfusion imaging with ^99mTc-labeled sestamibi has been useful in the assessment of myocardial salvage from reperfusion therapy during acute myocardial infarction. Studies in animal models have shown that discernible perfusion defects can be created by left ventricular asynergy from partial volume effects in the setting of homogenous perfusion tracer distribution. The purpose of this study was to examine the influence of gating on serial perfusion images during acute myocardial infarction to determine the magnitude of potential partial volume effects.

Methods and Results

^99mTc-labeled sestamibi was injected into 18 patients during acute myocardial infarction and 29 patients 5 to 8 days after myocardial infarction. Tomographic imaging was acquired in gated format (16 frames per R-R cycle of the electrocardiogram) for each set of images. All frames were summed to produce ungated images. Tomographic images were quantified on three different thresholds to define the perfusion defect: 50%, 60%, and 70% of maximal counts. Severity of perfusion defects was calculated as the lowest ratio of minimum/maximum counts on five short-axis slices. Regional wall motion was assessed subjectively on the gated images by cine-loop display. Radionuclide ventriculography was performed at 6 weeks. There was a close correlation between perfusion defect size on ungated images and end-diastolic and end-systolic images independent of the quantitative threshold used (r=0.90 to 0.93; p<0.0001 for all correlations). Gated images provided consistently significantly greater estimates of perfusion defect size and severity by a small increment (3% to 9% of the left ventricle; p<0.05 for all comparisons) independently of the quantitative threshold used or the time of imaging (acute or late). Ungated images provided slightly better correlations with left ventricular ejection fraction at 6 weeks independently of the quantitative threshold used and despite significant wall motion abnormalities present on both the acute and final studies.

Conclusions

The differences between perfusion defect size for gated and ungated images were highly significant as a group, but the magnitude of difference was small and not clinically relevant. The larger estimates provided by end-diastolic gated images are opposite the difference expected if partial volume effects were significantly influencing perfusion defect size. Partial volume effects appear to have minimal impact on clinical tomographic imaging during acute myocardial infarction for the quantification of myocardium at risk and infarct size.     

Kinetics of Tc-99m hexakis t-butyl isonitrile in normal and ischemic canine myocardium

Hexakis ^99mTc-tertiary butyl isonitrile (^99mTc-TBI) was studied as a cardiac perfusion imaging agent in nine dogs with partial occlusion of the LAD. Thirty min after applying the stenosis, ^99mTc-TBI was injected into the right atrium (RA) in five dogs and left atrium (LA) in four dogs. Normal and ischemic zone regional myocardial ^99mTc-TBI activites were monitored continuously for 4 h. Dogs with LA injections had minimal and equivalent 4 h fractional clearance from the normal and ischemic zones. Dogs with RA injections had minimal, but significantly lower 4 h fractional ^99mTc clearances in the ischemic zone (0.08±0.08) compared to the normal zone (0.16±0.07, P<0.05). The delayed ischemic zone clearance is probably due to the high initial lung uptake observed after RA injection. Despite the differences in clearance, this minimal amount of redistribution could not be detected on gamma camera images. The minimal myocardial washout and redistribution, and the 140 keV gamma make ^99mTc-TBI a promising cardiac perfusion imaging agent.Dr. Okada is an Established Investigator of the American Heart Association     

Measurement of both left ventricular function and regional myocardial perfusion with 133Xe in dogs

A technique to measure left ventricular (LV) function and myocardial perfusion was validated in 12 dogs. ¹³³Xe in saline was injected into the left atrium (LA) or LV and two data sets were obtained using gamma camera imaging: 1) A first pass gated scan for LV function; followed by 2) Sequential images for regional myocardial perfusion. LV ejection fraction and wall motion measurements from the ¹³³Xe blood pool images were compared to ejection fraction (r=0.88, P<0.01) and wall motion (r=0.83, P<0.01) data from ^99mTc labeled blood pool scans. The perfusion measurements obtained with the ¹³³Xe method were compared to microsphere data (r=0.79, P<0.01). Measurements after LV ¹³³Xe injection were similar to data following LA injection. Thus, quantitative assessment of global LV function, regional wall motion and myocardial perfusion is possible with LA or LV ¹³³Xe injection and gamma camera imaging.     

Gated 99Tcm-MIBI myocardial function imaging.

The introduction of the 99Tcm isonitrile perfusion agents has provided improved myocardial image quality with conventional imaging equipment allowing improved edge definition on gating. We evaluated left ventricular wall motion in 46 patients using gated 99Tcm-2-methoxy-2-methyl-isopropyl-1-isonitrile (MIBI) scintigraphy. Using a method of myocardial profiles in four axes, global and regional fractional shortening (FS) were assessed. A good correlation was found between FS in the left anterior oblique (LAO) 40 degrees projection and ejection fraction (EF) on gated radionuclide ventriculography (r = 0.81, P less than 0.001). This was improved by using FS in two planes, LAO 40 degrees and anterior (r = 0.88, P less than 0.001). There was also a good correlation between FS in two planes and EF on cine-angiography (r = 0.72, P less than 0.001). There was good intra- and interobserver agreement with the studies. Assessment of myocardial function using gated MIBI imaging and myocardial profiles provides useful additional information to the perfusion scan, thus enhancing the diagnostic usefulness of the agent.     

Limited performance of quantitative assessment of myocardial function by thallium-201 gated myocardial single-photon emission tomography

We investigated the reproducibility between thallium-201 and technetium-99m methoxyisobutylisonitrile (MIBI) gated single-photon emission tomography (SPET) for the assessment of indices of myocardial function such as end-diastolic and end-systolic volume (EDV, ESV), ejection fraction (EF) and wall motion. Rest ²⁰¹Tl (111 MBq) gated SPET was sequentially performed twice in 20 patients. Rest ²⁰¹Tl gated SPET and rest ^99mTc-MIBI (370 MBq) gated SPET were performed 24 h apart in 40 patients. Wall motion was graded using the surface display of the Cedars quantitative gated SPET (QGS) software. EDV, ESV and EF were also measured using the QGS software. The reproducibility of functional assessment on rest ²⁰¹Tl gated SPET was compared with that on ^99mTc-MIBI gated SPET, and also with that between ²⁰¹Tl gated SPET and ^99mTc-MIBI gated SPET performed on the next day. The two standard deviation (2 SD) values for EDV, ESV and EF on the Bland-Altman plot were 29 ml, 19 ml and 12%, respectively, on repeated ²⁰¹Tl gated SPET, compared with 14 ml, 11 ml and 5.3% on repeated ^99mTc-MIBI gated SPET. The correlations were good (r=0.96, 0.97 and 0.87) between the two measurements of EDV, ESV and EF on repeated rest studies with ²⁰¹Tl and ^99mTc-MIBI gated SPET. However, Bland-Altman analysis revealed that the 2 SD values between the two measurements were 31 ml, 23 ml and 12%. We were able to score the wall motion in all cases using the 3D surface display of the QGS on ²⁰¹Tl gated SPET. The kappa value of the wall motion grade on the repeated ²⁰¹Tl study was 0.35, while that of the wall motion grade on the repeated ^99mTc-MIBI study was 0.76. The kappa value was 0.49 for grading of wall motion on repeated rest studies with ²⁰¹Tl and ^99mTc-MIBI. In conclusion, QGS helped determine EDV, ESV, EF and wall motion on ²⁰¹Tl gated SPET. Because the EDV, ESV and EF were less reproducible on repeated ²⁰¹Tl gated SPET or on ²⁰¹Tl gated SPET and ^99mTc-MIBI gated SPET on the next day than on repeated ^99mTc-MIBI gated SPET, functional measurement on ²⁰¹Tl gated SPET did not seem to be interchangeable with that on ^99mTc-MIBI gated SPET. Received 18 May 1999 and in revised form 4 October 1999     

Measurement of left ventricular ejection fraction from gated technetium-99m sestamibi myocardial images

Left ventricular ejection fraction (LVEF) and single-photon emission tomographic (SPET) imaging of the myocardium can be performed after a single technetium-99m sestamibi (MIBI) injection. Sixty patients underwent SPET imaging with MIBI. Immediately after SPET acquisition ECG-gated^99mTc-MIBI perfusion images were acquired using 24 planar images per R-R interval. A new method for measurement of LVEF from the ECG-gated 99mTc-MIBI perfusion images was developed. To validate the method, LVEF derived from MIBI perfusion images was compared with that from conventional radionuclide ventriculography in all 60 patients. Forty patients had evidence of myocardial infarction and 20 had normal perfusion on MIBI imaging. There was no statistically significant difference between LVEF computed from^99mTc-MIBI perfusion images and that from radionuclide ventriculography (r=0.7062,P<0.001). There was little difference associated with the technique (intraobserver variabilityr=0.9772,P<0.001). Interobserver variability was also good (r-0.8233,P<0.001). LVEF from^99mTc-MIBI perfusion images can be obtained at the same time as assessment of myocardial perfusion and in the same orientation and metabolism of the myocardium, thereby permitting more accurate and realistic prognosis and diagnosis in patients with coronary artery disease.     

The contraction fraction (CF) in myocardial studies with Technetium-99m-isonitril (MIBI) — correlations with radionuclide ventriculography and infarct size measured by SPECT

Criteria for the detection of coronary artery disease in nuclear cardiology include visualization of perfusion defects and functional impairment of contraction. The purpose of this study is to combine both methods in one procedure with the new myocardial perfusion tracer, ^99mTc-methoxy-isobutyl-isonitril (MIBI), reducing time and radiation burden to the patient. Following an uncomplicated recovery, ten patients with first myocardial infarction participated in this study. Radionuclide ventriculography (RNV) was performed at rest and during exercise. Within 2–3 days, 370 MBq ^99mTc-MIBI were injected and SPECT acquisition commenced 1 h later. Data processing included a scar image in polar coordinates. Areas of significantly reduced tracer uptake were expressed as a percentage of the total myocardial area. Directly following SPECT, resting and maximum exercise gated planar LAO images were recorded and the contraction was quantified. The concept of the contraction fraction (CF) rested on the end systolic change in count distribution: their increase in density and their centripetal concentration. For comparison, geometrical inner edge detection techniques were also applied. All algorithms for describing an EF equivalent were verified by computer simulations, showing a perfect correlation over a wide range of preset EFs. When applied to the patient studies only the non geometric methods revealed a good correlation with the ejection fraction (EF) obtained by RNV, and with the infarct size measured by SPECT. The corresponding correlation coefficients (r), standard errors (SEE) and the regression lines read as follows (in %): CF=0.56×EF+24.8; r=0.87; SEE=4.98; CF=-0.53×SPECT+71.5; r=0.93; SEE=4.19. Thus, estimation of the left ventricular function by the above defined CF is feasible, easy to perform and clinically meaningful. In one procedure with ^99mTc-labelled MIBI not only the perfusion abnormalities were detectable, but also any reduction in function by a valied EF equivalent. Although the monochromatic gamma spectrum of the radionuclide provided better tissue penetrating power, the inner edge of the left ventricle was poorly outlined (especially in the stress studies) and does not lend itself to clinical routine practice.Supported in part by the grant LFS28 from the ministry of science, Stuttgart, Federal Republic of Germany