Dual Isotope Myocardial Perfusion SPECT Research Articles

Optimization and comparison of simultaneous and separate acquisition protocols for dual isotope myocardial perfusion SPECT

Dual-isotope simultaneous-acquisition (DISA) rest-stress myocardial perfusion SPECT (MPS) protocols offer a number of advantages over separate acquisition. However, crosstalk contamination due to scatter in the patient and interactions in the collimator degrade image quality. Compensation can reduce the effects of crosstalk, but does not entirely eliminate image degradations. Optimizing acquisition parameters could further reduce the impact of crosstalk. In this paper we investigate the optimization of the rest Tl-201 energy window width and relative injected activities using the ideal observer (IO), a realistic digital phantom population and Monte Carlo (MC) simulated Tc-99m and Tl-201 projections as a means to improve image quality. We compared performance on a perfusion defect detection task for Tl-201 acquisition energy window widths varying from 4 to 40 keV centered at 72 keV for a camera with a 9% energy resolution. We also investigated 7 different relative injected activities, defined as the ratio of Tc-99m and Tl-201 activities, while keeping the total effective dose constant at 13.5 mSv. For each energy window and relative injected activity, we computed the IO test statistics using a Markov chain Monte Carlo (MCMC) method for an ensemble of 1,620 triplets of fixed and reversible defect-present, and defect-absent noisy images modeling realistic background variations. The volume under the 3-class receiver operating characteristic (ROC) surface (VUS) was estimated and served as the figure of merit. For simultaneous acquisition, the IO suggested that relative Tc-to-Tl injected activity ratios of 2.6–5 and acquisition energy window widths of 16–22% were optimal. For separate acquisition, we observed a broad range of optimal relative injected activities from 2.6 to 12.1 and acquisition energy window of widths 16–22%. A negative correlation between Tl-201 injected activity and the width of the Tl-201 energy window was observed in these ranges. The results also suggested that DISA methods could potentially provide image quality as good as that obtained with separate acquisition protocols. We compared observer performance for the optimized protocols and the current clinical protocol using separate acquisition. The current clinical protocols provided better performance at a cost of injecting the patient with approximately double the injected activity of Tc-99m and Tl-201, resulting in substantially increased radiation dose.

Design of a digital phantom population for myocardial perfusion SPECT imaging research

Digital phantoms and Monte Carlo (MC) simulations have become important tools for optimizing and evaluating instrumentation, acquisition and processing methods for myocardial perfusion SPECT (MPS). In this work, we designed a new adult digital phantom population and generated corresponding Tc-99m and Tl-201 projections for use in MPS research. The population is based on the three-dimensional XCAT phantom with organ parameters sampled from the Emory PET Torso Model Database. Phantoms included three variations each in body size, heart size, and subcutaneous adipose tissue level, for a total of 27 phantoms of each gender. The SimSET MC code and angular response functions were used to model interactions in the body and the collimator-detector system, respectively. We divided each phantom into seven organs, each simulated separately, allowing use of post-simulation summing to efficiently model uptake variations. Also, we adapted and used a criterion based on the relative Poisson effective count level to determine the required number of simulated photons for each simulated organ. This technique provided a quantitative estimate of the true noise in the simulated projection data, including residual MC simulation noise. Projections were generated in 1 keV wide energy windows from 48–184 keV assuming perfect energy resolution to permit study of the effects of window width, energy resolution, and crosstalk in the context of dual isotope MPS. We have developed a comprehensive method for efficiently simulating realistic projections for a realistic population of phantoms in the context of MPS imaging. The new phantom population and realistic database of simulated projections will be useful in performing mathematical and human observer studies to evaluate various acquisition and processing methods such as optimizing the energy window width, investigating the effect of energy resolution on image quality and evaluating compensation methods for degrading factors such as crosstalk in the context of single and dual isotope MPS.

Evaluation of simultaneous 201Tl/99mTc dual-isotope cardiac SPECT imaging with model-based crosstalk compensation using canine studies

BackgroundSimultaneous 201Tl/99mTc-sestamibi dual-isotope myocardial perfusion SPECT imaging can reduce imaging time and produce perfectly registered rest/stress images. However, crosstalk from 99mTc into 201Tl images can significantly reduce 201Tl image quality. We have developed a model-based compensation (MBC) method to compensate for this crosstalk. The method has previously been validated with phantom and simulation studies. In this study, we evaluated the MBC method using a canine model. MethodsLeft anterior descending or left circumflex coronary artery stenoses were created in 50 adult mongrel dogs weighing 20-30 kg. The dogs were injected with 111 MBq (3 mCi) of 201Tl at rest, and a SPECT study acquired. Stress was induced by administering adenosine to the dog, followed by injection of 740 MBq (20 mCi) of 99mTc-sestamibi at peak stress. A second SPECT study was performed with data acquired in both 201Tl and 99mTc energy windows to provide simultaneous dual-isotope projection data. The images were reconstructed using the ordered-subsets expectation-maximization reconstruction algorithm with compensation for attenuation, scatter, and detector response. For simultaneously acquired 201Tl data, we also applied the MBC method to compensate for crosstalk contamination from 99mTc. ResultsWithout compensation, 99mTc crosstalk increased the estimated 201Tl activity concentration in the rest images and reduced defect contrast. After MBC, the 201Tl images were in good agreement with the registered single-isotope images and ex vivo count data. The ischemic (IS) to non-ischemic (NIS) region 201Tl activity concentration ratios were computed for single-isotope and dual-isotope studies. The correlation with ex vivo IS-NIS ratios was 0.815 after MBC, compared to the 0.495 from data without compensation. In addition, the regression line for the IS-NIS ratios with MBC was almost parallel to the line of identity with a slope of 0.93, compared to a slope of 0.45 without compensation. ConclusionsThese results demonstrate that model-based crosstalk compensation can provide substantial reduction of crosstalk effects in simultaneously acquired myocardial perfusion SPECT images in living biological systems.

Improved accuracy of myocardial perfusion SPECT for detection of coronary artery disease by machine learning in a large population

ObjectiveWe aimed to improve the diagnostic accuracy of myocardial perfusion SPECT (MPS) by integrating clinical data and quantitative image features with machine learning (ML) algorithms. Methods1,181 rest 201Tl/stress 99mTc-sestamibi dual-isotope MPS studies [713 consecutive cases with correlating invasive coronary angiography (ICA) and suspected coronary artery disease (CAD) and 468 with low likelihood (LLk) of CAD <5%] were considered. Cases with stenosis <70% by ICA and LLk of CAD were considered normal. Total stress perfusion deficit (TPD) for supine/prone data, stress/rest perfusion change, and transient ischemic dilatation were derived by automated perfusion quantification software and were combined with age, sex, and post-electrocardiogram CAD probability by a boosted ensemble ML algorithm (LogitBoost). The diagnostic accuracy of the model for prediction of obstructive CAD ≥70% was compared to standard prone/supine quantification and to visual analysis by two experienced readers utilizing all imaging, quantitative, and clinical data. Tenfold stratified cross-validation was performed. ResultsThe diagnostic accuracy of ML (87.3% ± 2.1%) was similar to Expert 1 (86.0% ± 2.1%), but superior to combined supine/prone TPD (82.8% ± 2.2%) and Expert 2 (82.1% ± 2.2%) (P < .01). The receiver operator characteristic areas under curve for ML algorithm (0.94 ± 0.01) were higher than those for TPD and both visual readers (P < .001). The sensitivity of ML algorithm (78.9% ± 4.2%) was similar to TPD (75.6% ± 4.4%) and Expert 1 (76.3% ± 4.3%), but higher than that of Expert 2 (71.1% ± 4.6%), (P < .01). The specificity of ML algorithm (92.1% ± 2.2%) was similar to Expert 1 (91.4% ± 2.2%) and Expert 2 (88.3% ± 2.5%), but higher than TPD (86.8% ± 2.6%), (P < .01). ConclusionML significantly improves diagnostic performance of MPS by computational integration of quantitative perfusion and clinical data to the level rivaling expert analysis.

Optimisation of Simultaneous Tl-201/Tc-99m Dual Isotope Reconstruction with Monte-Carlo-Based Scatter Correction

Simultaneous Tl-201/Tc-99m dual isotope myocardial perfusion SPECT is seriously hampered by down-scatter from Tc-99m into the Tl-201 energy window. This paper presents and optimises the ordered-subsets-expectation-maximisation-(OS-EM-) based reconstruction algorithm, which corrects the down-scatter using an efficient Monte Carlo (MC) simulator. The algorithm starts by first reconstructing the Tc-99m image with attenuation, collimator response, and MC-based scatter correction. The reconstructed Tc-99m image is then used as an input for an efficient MC-based down-scatter simulation of Tc-99m photons into the Tl-201 window. This down-scatter estimate is finally used in the Tl-201 reconstruction to correct the crosstalk between the two isotopes. The mathematical 4D NCAT phantom and physical cardiac phantoms were used to optimise the number of OS-EM iterations where the scatter estimate is updated and the number of MC simulated photons. The results showed that two scatter update iterations and 105 simulated photons are enough for the Tc-99m and Tl-201 reconstructions, whereas 106 simulated photons are needed to generate good quality down-scatter estimates. With these parameters, the entire Tl-201/Tc-99m dual isotope reconstruction can be accomplished in less than 3 minutes.

Regularized Image Reconstruction Algorithms for Dual-Isotope Myocardial Perfusion SPECT (MPS) Imaging Using a Cross-Tracer Prior

In simultaneous dual-isotope myocardial perfusion SPECT (MPS) imaging, data are simultaneously acquired to determine the distributions of two radioactive isotopes. The goal of this work was to develop penalized maximum likelihood (PML) algorithms for a novel cross-tracer prior that exploits the fact that the two images reconstructed from simultaneous dual-isotope MPS projection data are perfectly registered in space. We first formulated the simultaneous dual-isotope MPS reconstruction problem as a joint estimation problem. A cross-tracer prior that couples voxel values on both images was then proposed. We developed an iterative algorithm to reconstruct the MPS images that converges to the maximum a posteriori solution for this prior based on separable surrogate functions. To accelerate the convergence, we developed a fast algorithm for the cross-tracer prior based on the complete data OS-EM (COSEM) framework. The proposed algorithm was compared qualitatively and quantitatively to a single-tracer version of the prior that did not include the cross-tracer term. Quantitative evaluations included comparisons of mean and standard deviation images as well as assessment of image fidelity using the mean square error. We also evaluated the cross tracer prior using a three-class observer study with respect to the three-class MPS diagnostic task, i.e., classifying patients as having either no defect, reversible defect, or fixed defects. For this study, a comparison with conventional ordered subsets-expectation maximization (OS-EM) reconstruction with postfiltering was performed. The comparisons to the single-tracer prior demonstrated similar resolution for areas of the image with large intensity changes and reduced noise in uniform regions. The cross-tracer prior was also superior to the single-tracer version in terms of restoring image fidelity. Results of the three-class observer study showed that the proposed cross-tracer prior and the convergent algorithms improved the image quality of dual-isotope MPS images compared to OS-EM.

Application of Three-Class ROC Analysis to Task-Based Image Quality Assessment of Simultaneous Dual-Isotope Myocardial Perfusion SPECT (MPS)

The diagnosis of cardiac disease using dual-isotope myocardial perfusion SPECT (MPS) is based on the defect status in both stress and rest images, and can be modeled as a three-class task of classifying patients as having no, reversible, or fixed perfusion defects. Simultaneous acquisition protocols for dual-isotope MPS imaging have gained much interest due to their advantages including perfect registration of the (201)Tl and (99m)Tc images in space and time, increased patient comfort, and higher clinical throughput. As a result of simultaneous acquisition, however, crosstalk contamination, where photons emitted by one isotope contribute to the image of the other isotope, degrades image quality. Minimizing the crosstalk is important in obtaining the best possible image quality. One way to minimize the crosstalk is to optimize the injected activity of the two isotopes by considering the three-class nature of the diagnostic problem. To effectively do so, we have previously developed a three-class receiver operating characteristic (ROC) analysis methodology that extends and unifies the decision theoretic, linear discriminant analysis, and psychophysical foundations of binary ROC analysis in a three-class paradigm. In this work, we applied the proposed three-class ROC methodology to the assessment of the image quality of simultaneous dual-isotope MPS imaging techniques and the determination of the optimal injected activity combination. In addition to this application, the rapid development of diagnostic imaging techniques has produced an increasing number of clinical diagnostic tasks that involve not only disease detection, but also disease characterization and are thus multiclass tasks. This paper provides a practical example of the application of the proposed three-class ROC analysis methodology to medical problems.

Normalization of Negative T Waves in the Chronic Stage of Q Wave Anterior Myocardial Infarction as a Predictor of Myocardial Viability

We investigated whether spontaneous normalization of negative T waves (TWN) on infarct-related ECG leads (IRLs) in the chronic phase of Q wave anterior myocardial infarction (MI) could be a predictor of residual viability in infarct areas. We prospectively studied 35 patients (age 60 ± 8.6 years) in the chronic phase of Q wave anterior MI. Spontaneous TWN (group A, n = 23) were defined as negative T waves that became upright (≧0.15 mV) in ≧2 IRLs. The presence of negative T waves (group B, n = 12) was defined as symmetric or biphasic negative T wave of ≧0.15 mV. All patients underwent same-day rest ²⁰¹Tl-stress ^99mTc sestamibi dual-isotope myocardial perfusion SPECT and 24-hour ²⁰¹Tl reinjection imaging for ischemia and viability analysis. On scintigraphic examination, ischemic or viable myocardial segments were found in 18 patients (78%) with TWN and 4 patients (33%) of group B (p = 0.013). The use of TWN as a parameter had a marked influence on the sensitivity (82%), specificity (62%), positive (78%) and negative (67%) predictive values and accuracy (74%) of the diagnosis of viable myocardium. If we add the criterion of positive T waves in aVR with negative T waves to our criteria, we found that sensitivity (90%), positive (80%) and negative (80%) predictive values and accuracy (80%) increased. The results of our study suggest that analysis of TWN on IRLs is an accurate marker of residual viability and/or persistent peri-infarct ischemia in patients in the chronic stage of Q wave anterior MI, and therefore optimizes the diagnostic and therapeutic strategies after MI.

Comparison of extent and severity of quantitative perfusion defects on rest Tl-201 and rest Tc-99m sestamibi myocardial perfusion SPECT

Background: Rest Tl-201 (Tl) myocardial perfusion SPECT (MPS) has been widely used alone or in dual isotope MPS, but the direct comparison of quantitative perfusion defect (PD) on rest Tl and rest sestamibi (MIBI) MPS has not been evaluated in depth. Methods: 162 pts in a randomized clinical trial with known or suspected CAD ( ≥4/20 segments with reversible defects, age 40–76, 34 F) underwent same day rest Tl followed immediately by rest MIBI injection and MPS 1 hr later. The same protocol was repeated in 56 pts of the placebo group (with no clinical changes or coronary interventions) at day 60. Reconstruction using Butterworth filtered backprojection, cutoff /order 0.55 / 5.00 for MIBI and 0.50 / 10.00 for Tl, sex and isotope specific normal limits were used. PD extent (% of pixels abnormal) and severity (mean number of standard deviations by which counts of abnormal pixels fell below normal profile) were determined by QPS. Correlation and regression analysis were performed. Results: The linear correlation between rest Tl and rest MIBI showed high agreement as follows: N = 162 R 2 Rt MSE Regression Extent MIBI-TI 0.93;*> 2.91 MIBI ext = 1.03 TI ext + 1.32 Severity MIBI-TI 0.90;*> 0.20 MIBI sev = 1.04 TI sev + 0.06 Repeated scans at day 60 showed similar results for MIBI and Tl agreement, and good inter scan reproducibility (MIBI day 0 vs day 60). * N = 56 R 2 Rt MSE Interscan R 2-MIBI Rt MSE Extent MIBI-TI 0.96 * 2.42 Extent 0.94 * 2.69 Severity MIBI-TI 0.92 * 0.18 Severity 0.94 * 0.16 * (p < 0.0001) Conclusion: Quantitative analysis of perfusion defect extent and severity on same day rest Tl and rest MIBI MPS shows excellent correlation which is as high as the reproducibility of day 0 vs day 60 MIBI. These findings indicate that a rest Tl / rest MIBI protocol may be useful in same day assessment of changes in myocardial perfusion with therapeutic interventions.

Prognostic relevance of symptoms versus objective evidence of coronary artery disease in diabetic patients.

Little is known about the prognostic significance of silent versus symptomatic coronary artery disease (CAD) in diabetic patients. We therefore assessed the incidence of scintigraphic evidence of CAD in diabetic patients without known CAD and the impact of symptoms and scintigraphic findings on prognosis. A consecutive series of 1737 diabetic patients without known CAD underwent dual-isotope myocardial perfusion SPECT (MPS) and 1430 were followed-up for a median of 2 (1-8.5) years. Critical events were defined as myocardial infarction or cardiac death. Objective evidence of CAD was found in 39% of 826 asymptomatic diabetic patients, in 51% of 151 diabetic patients with shortness of breath (SOB), and in 44% of 760 diabetic patients with angina. During follow-up, 98 critical events occurred. Annual critical event rates were 2.2% in asymptomatic, 3.2% in angina, and 7.7% in diabetic patients with shortness of breath ( p < 0.001 versus other groups). With MPS evidence of CAD, critical event rates increased to 3.4% (asymptomatic), 5.6% (angina), and 13.2% (SOB) ( p </= 0.009 versus no evidence of CAD). Age, hypertension, shortness of breath, scarring and ischaemia were independent predictors of critical events. MPS findings added incremental information to prescan information regarding outcome prediction. In asymptomatic diabetic patients, the rate of objective evidence of CAD and annual critical events were similar to those found in diabetic patients with angina. The outcome was three times worse in diabetic patients with shortness of breath. MPS findings were strongly predictive of outcome and proved valuable for risk stratification.

Feasibility of simultaneous stress sestamibi/rest Tl dual-isotope myocardial perfusion SPECT in the detection of coronary artery disease and the assessment of myocardial viability

Feasibility of simultaneous stress sestamibi/rest Tl dual-isotope myocardial perfusion SPECT in the detection of coronary artery disease and the assessment of myocardial viability

Effect of Chamber Size on Accuracy of Dual Isotope Myocardial Perfusion SPECT

Effect of Chamber Size on Accuracy of Dual Isotope Myocardial Perfusion SPECT

Effect of chamber size on accuracy of dual isotope myocardial perfusion SPECT

Effect of chamber size on accuracy of dual isotope myocardial perfusion SPECT

Prognostic Value of Rest Tl-201/Dipyridamole Stress Tc-99m-MIBI Myocardial Single Photon Emission Computed Tomography (SPECT)

Background and Objectives:Dual isotope myocardial SPECT, rest thallium-201/dipyridamole stress Tc-99m sestamibi is used to diagnose coronary artery disease. We examined predictive value of myocardial SPECT for the prognosis of patients having or suspected coronary artery disease. Materials and Method:We examined 692 patients referred for dipyridamole stress myocardial perfusion SPECT. Cardiac events (hard and soft events were followed up with medical record review and telephone interview. Survival analysis and multivariate Cox proportional hazard model were used to find significant predictors and the incremental predictive value of myocardial SPECT. Patients with coronary angiography (n=246 were analyzed in separate group. Results: There were 4 hard events and 3 soft events in 341 normal SPECT group (1.20%/yr. There were 5 hard events and 21 soft events in 351 abnormal SPECT group (4.69%/yr. Survival curve was separated between normal SPECT group and abnormal SPECT group (p<0.01. In univariate analysis, smoking, history of myocardial infarction, typical chest pain and SPECT findings were important variables. In multivariate analysis, SPECT result was the single most independent predictor. Large reversible perfusion abnormality predicted worse prognosis. In patients with coronary angiography, SPECT did not add statistically significant predictive value to the coronary angiography. Conclusion:Dipyridamole stress Tl-201/ MIBI dual isotope myocardial perfusion SPECT provided excellent prognostic information. Extent of reversible perfusion decrease was the independent predictor of future cardiac events. (Korean Circulation J 1998;28(8 :1260-1271

Assessment of myocardial viability with low dose dobutamine radionuclide ventriculography. Comparison with rest thallium- 201/stress mibi dual isotope myocardial perfusion spect

Assessment of myocardial viability with low dose dobutamine radionuclide ventriculography. Comparison with rest thallium- 201/stress mibi dual isotope myocardial perfusion spect

Reverse redistribution of stress Tc-99m sestamibi in dual isotope myocardial perfusion SPECT as a marker of myocardial viability

Reverse redistribution of stress Tc-99m sestamibi in dual isotope myocardial perfusion SPECT as a marker of myocardial viability

Rest TI-201/adenosine Tc-99m sestamibi separate acquisition dual isotope myocardial perfusion SPECT: Diagnostic efficacy in detection of coronary artery disease in women

Rest TI-201/adenosine Tc-99m sestamibi separate acquisition dual isotope myocardial perfusion SPECT: Diagnostic efficacy in detection of coronary artery disease in women

Diagnostic accuracy of rest T1-201/Stress Tc-99m sestamibi separate acquisition dual isotope myocardial perfusion SPECT in the very elderly

Diagnostic accuracy of rest T1-201/Stress Tc-99m sestamibi separate acquisition dual isotope myocardial perfusion SPECT in the very elderly

Dual-Isotope Myocardial Perfusion Spect with Rest Thallium-201 and Stress Tc-99m Sestamibi

The commercial availability of Tc-99m-labeled myocardial perfusion agents had added choices in the noninvasive clinical assessment of coronary artery disease. Preferential use of Tc-99m sestamibi has been advocated principally due to improved image quality, which results from the combined physical and biological characteristics of this agent. This article reports upon the investigation of another approach for Tc-99m sestamibi SPECT--dual-isotope rest-stress myocardial perfusion SPECT, which takes advantage of the Anger camera's ability to collect date in different energy windows. For the dual-isotope approach, separate radiopharmaceuticals are employed for the rest injection and the stress injection.