Rest Myocardial Perfusion SPECT Research Articles

The preoperative myocardial perfusion and internal mammary artery graft blood flow relationship in patients with ischemic cardiomyopathy

Objective. The purpose of this study was to determine the association between preoperative myocardial perfusion data (obtained by SPECT) with transit time blood flow characteristics in left internal mammary artery (LIMA) to left anterior descending artery (LAD) grafts in patients with ischemic cardiomyopathy.Methods. The study group consisted of 57 patients with ischemic cardiomyopathy. Intraoperative transit-time flow measurement (TTFM) of LIMA-LAD grafts were performed in all patients. All patients were also examined with preoperative stress and rest myocardial perfusion SPECT with 99m Tc-MIBI. Anastomotic patency was considered satisfactory with a normal waveform of blood flow, diastolic-dominant blood filling, and a mean flow value greater than 11.5 ml/min.Results. All 57 patients with LIMA-LAD grafts were divided into two groups; those with graft satisfactory patency (n = 40) and those with unsatisfactory patency (n = 17) as determined by TTFM. We found differences among these groups in values of global summed rest score (20.7 ± 7.5 vs. 29.8 ± 4.0; p = 0.002), global total perfusion deficit (TPD) at rest (32.0 ± 11.4 vs. 43.0 ± 7.2; p = 0.01), and regional TPD at rest in the LAD territory (20.7 ± 7.5 vs. 29.8 ± 4.0; p = 0.002). Additionally, the flow characteristics were different in patients with and without surgical left ventricle reconstruction (Q (ml/min): 17 (11.5, 40.8) vs. 47 (25, 69.5), p = 0.013; PI: 3.9 (3.2, 7.4) vs. 2.4 (2.0, 3.6), p = 0.001; DF (%): 63.5 (44.5, 70.8) vs. 74 (66.0, 79.7), p = 0.019). TPD at rest was the best predictor of the LIMA-LAD graft satisfactory: area under curve = 0.771, cut-off value = 26.85 with 83.3% sensitivity and 78.1% specificity.Conclusions. Preoperative myocardial perfusion characteristics are associated with blood flow in LIMA-LAD graft in patients with ischemic cardiomyopathy. TPD at rest (assessed globally and in the LAD region) as well as global SRS value are potential predictors of early graft failure.

Myocardial Perfusion SPECT and ATTR imaging 2021 in Germany: Results of the 9th Survey.

This paper presents the results of the 9th survey of myocardial perfusion SPECT (MPS) from the reporting year 2021. 218 questionnaires (131 practices (PR), 58 hospitals (HO), 29 university hospitals (UH)) were evaluated. Results of the last survey 2018 are set in squared brackets. MPS data from a total of 133,057 [145,930] patients (-8.8%) with 131,868 [143,707] stress and 106,546 [121,899] rest MPS were analysed. A comparison with official data revealed that 54% all MPS were recorded. From 2018 to 2021, official data showed a every year an increase in MPS numbers. On average, 610 [502] MPS patients (+22%) were examined in each department. 74% [69%] of the responders reported an increase or no changes in their MPS patient numbers. Ambulatory care cardiologists represented as always, the mayor referral group (68% [69%]). For the first time, pharmacological stress was more frequently applied than ergometry (42% [51]). Regadenoson was mostly used. The use of the different protocols remained nearly unchanged. Two-day protocols were predominantly applied (49% [48%]). A shift from multi-headed cameras (58% [72%]) to SPECT-CT systems (24% [17%]) was found. Attenuation correction was performed in 33% [26%] of all MPS. 88% [86%] of all stress, 88% [87%] of all rest and 87% [83%] of all stress and rest MPS were acquired as gated SPECT. 72% [67%] of all departments performed scoring by default. The number of departments without scoring decreased to 13% [16%]. The MPS Study 2021 shows that the long-term positive development of MPS imaging in Germany is continuing. The COVID-19 pandemia did not change this trend. The procedural and technical details of MPS imaging reveal a high level of guideline conformity.

The Role of Myocardial Perfusion Imaging in Patients with Diabetes Mellitus

Abstract Diabetes mellitus is a complex pathology with increasing incidence, associated with an increased risk of coronary heart disease. Myocardial perfusion imaging (MPI) is an important diagnostic tool for the evaluation of coronary artery disease (CAD), with a high prognostic value. Objective. The aim of this study was to evaluate the role of stress-rest MPI in the assessment of patients with DM and suspected or confirmed CAD. Method. We performed a retrospective analysis of 128 patients who underwent stress-rest MPI in our department, all of them with coronary angiography (CA) available. All patients underwent stress rest myocardial perfusion SPECT using a 1-day or 2-day protocol. The radiopharmaceuticals used were 99m-Tc-MIBI or tetrofosmin. The study was performed with a gated protocol SPECT, synchronous with the ECG, using a dual-head gamma camera. Patients were divided in 4 subgroups based on the presence of DM and of significant CA changes. Results. In the group of patients with significant coronary disease on CA and previously diagnosed DM, number of perfusion defects on the stress-rest MPI were higher and also the presence of systolic disfunction and the severity of defects. Our results support the idea that the severity and extent of myocardial perfusion defects are greater in diabetic patients than in non-diabetic patients. Conclusions. We can consider myocardial perfusion SPECT with 99mTc-labeled agents as a feasible method for the diagnosis and evaluation of CAD and for the management of diabetic patients.

Simulating dose reduction for myocardial perfusion SPECT using a Poisson resampling method.

The purpose of this study was to determine the lowest Tl-201 dose that does not reduce the image quality of myocardial perfusion SPECT (MPS) by Poisson resampling simulation. One hundred and twelve consecutive MPS data from patients with suspected or known coronary artery disease were collected retrospectively. Stress and rest MPS data were resampled using the Poisson method with 33%, 50%, 67%, and 100% count settings. Two nuclear medicine physicians assessed the image quality of reconstructed data visually by giving grades from - 2 to + 2. The summed stress score (SSS), summed rest score (SRS), and summed difference score (SDS) were obtained on the workstation. Image quality grades and semi-quantitative scores were then compared among these resampled images. The proportions of "adequate" image quality were 0.48, 0.75, 0.92, and 0.96 for the groups of images with 33%, 50%, 67%, and 100% data, respectively. The quality of the resampled images was significantly degraded at 50% and 33% count settings, while the image quality was not different between 67 and 100% count settings. We also found that high body mass index further decreased image quality at 33% count setting. Among the semi-quantitative parameters, SSS and SRS showed a tendency to increase with a decline in count. Based on the simulation results, Tl-201 dose for MPS can be reduced to 74MBq without significant loss of image quality. However, the SSS and SRS can be changed significantly, and it needs to be further verified under the different conditions.

Myocardial Perfusion SPECT 2018 in Germany: Results of the 8th Survey.

This paper presents the results of the 8th survey of myocardial perfusion SPECT (MPS) from the reporting year 2018. 291 questionnaires (184 practices (PR), 77 hospitals (HO), 30 university hospitals (UH)) were evaluated. Results of the last survey from 2015 are set in squared brackets. MPS of 145 930 [121 939] patients were reported (+ 19.6 %). 76 % [78 %] of all patients were studied in PR, 16 % [14 %] in HO, and 8 % [8 %] in UH, mostly with a 2-day-protocol 48 % [50 %]. 99.96 % [98 %] of all MPS were performed with Tc-99 m radiopharmaceuticals and in 0.04 % with Tl-201.A pharmacological stress test was applied in 49 % [43 %] (23 % [22 %] adenosine, 26 % [20 %] regadenoson, dipyridamole or dobutamine together < 1 % [1 %]). Attenuation correction was performed in 26 % [25 %] of all MPS, gated SPECT in 86 % [80 %] of stress MPS, in 87 % [78 %] of rest and in 83 % [76 %] of all stress and rest MPS. 67 % [53 %] of the departments performed MPS scoring by default, whereas 16 % [24 %] did not apply this feature at all.69 % [60 %] reported an increase or no changes in their MPS patient numbers. One hundred twenty-six departments which participated in the surveys from 2009 to 2018 reported an increase in MPS by 44 %. 69 % [70 %] of the MPS were requested by ambulatory care cardiologists. The 2018 MPS survey reveals a high-grade adherence of routine MPS practice to current guidelines. The positive development in MPS performance and MPS numbers observed since 2012 remains ongoing.

29Prognostic safety of automatic cancellation of rest myocardial perfusion scan by machine learning: a report from multicenter REFINE SPECT registry of new generation SPECT

Abstract Background We aimed to develop a machine learning (ML) computer score derived from stress imaging and clinical data, which indicates if the rest scan could be automatically and safely canceled in the routine stress/rest myocardial perfusion SPECT (MPS). Methods A total of 20414 stress/rest cases from the REFINE SPECT registry collected from 5 sites in 3 countries with Tc-99m-based MPS images, clinical data, and clinical follow-up were included in the study. All images were automatically processed at our Medical Center. The automatically generated myocardial contours were checked by experienced technologists. In total, 93 variables (26 clinical, 17 stress-test, and 50 stress-imaging variables) were used to build a LogitBoost model for prediction of adverse events (AE), including coronary revascularization, death, myocardial infarction, and unstable angina. 10-fold cross-validation was performed to separate test from validation data for the assessment of ML. The overall ML predictive performance was compared to quantitative (stress total perfusion deficit [TPD]) by the area under the receiver operating characteristic curves (AUC). ML cut-off (ML1) to simulate the decision of cancellation of the rest scan was set to result in the same % of normal scans as these determined by the normal clinical reader diagnosis on a 4-point scale in the whole population, or the same % of scans with visual summed stress scores (SSS) = 0 in the subpopulation with available SSS. A second ML cutoff (ML2) was established to achieve a 1% annual risk of AE. The annual risk of AE of the normal ML score was compared with normal clinical diagnosis and with the finding of SSS = 0. Results The mean follow-up interval was 4.7±1.5 years. Overall, 3542 AE were observed (3.7% annual risk). The AUC for AE was higher for ML (0.780±0.005) than for stress TPD (0.698±0.006) (p&lt;0.001). Normal clinical diagnosis was reported in 60% cases. In 70% (14242 scans) with available segmental scores, 53% had SSS=0. ML1 and ML2 thresholds were compared with normal visual diagnosis and with SSS = 0 for AE (Figure). ML1 achieved a lower annual risk (1.5%) than normal clinical diagnosis (2.1%) or SSS = 0 (1.6% versus 2.3%) (p&lt;0.001). The more conservative ML2 threshold with a 1% annual risk of AE resulted in a 40% canceling rate. Figure 1 Conclusion ML could be used to automatically cancel the rest MPS scan with the same proportion as using normal visual MPS reading, but with significantly lower AE rate in stress-only scans. Acknowledgement/Funding R01HL089765 from the National Heart, Lung, and Blood Institute/National Institutes of Health (NHLBI/NIH)

Myocardial perfusion SPECT 2015 in Germany. Results of the 7th survey.

SummaryAimThe working group Cardiovascular Nuclear Medicine of the German Society of Nuclear Medicine presents the results of the 7th survey of myocardial perfusion SPECT (MPS) of the reporting year 2015.Method268 questionnaires (173 practices [PR], 67 hospitals [HO], 28 university hospitals [UH]) were evaluated. Results of the last survey from 2012 are set in squared brackets.ResultsMPS of 121 939 [105 941] patients were reported. 98 % [95 %] of all MPS were performed with Tc-99m radiopharmaceuticals and 2 % [5 %] with Tl-201. 78 % [79 %] of all patients were studied in PR, 14 % [15 %] in HO, and 8 % [6 %] in UH. A pharmacological stress test was performed in 43 % [39 %] (22 % [24 %] adenosine, 20 % [9 %] regadenoson, 1% [6 %] dipyridamole or dobutamine). Attenuation correction was applied in 25 % [2009: 10 %] of MPS. Gated SPECT was performed in 78 % [70 %] of all rest MPS, in 80 % [73 %] of all stress and in 76 % [67 %] of all stress and rest MPS. 53 % [33 %] of all nuclear medicine departments performed MPS scoring by default, whereas 24 % [41 %] did not apply any quantification. 31 % [26 %] of all departments noticed an increase in their counted MPS and 29 % [29 %] no changes. Data from 89 departments which participated in all surveys showed an increase in MPS count of 11.1 % (PR: 12.2 %, HO: 4.8 %, UH: 18.4 %). 70 % [60 %] of the MPS were requested by ambulatory care cardiologists.ConclusionThe 2015 MPS survey reveals a high-grade adherence of routine MPS practice to current guidelines. The positive trend in MPS performance and number of MPS already observed in 2012 continues. Educational training remains necessary in the field of SPECT scoring.

Appearance of thoracic aortic aneurysm on myocardial perfusion imaging

We present the case of a 65-year-old man with dyspnea and chest discomfort referred for dipyridamole myocardial perfusion scintigraphy. 99mTc-sestamibi cardiac gated SPECT images showed an irreversible hypoperfusion in the mid-ventricular portion of anteroseptal wall, a suspicious reversible hypoperfusion in the apical slices of inferolateral wall, and left ventricle dilatation with a ejection fraction of 40%. In addition, a decreased radiotracer uptake was seen in the posterior region of the left hemithorax in the rotating (cine) images of the stress and rest myocardial perfusion SPECT (Fig. 1). Also, the review of all the raw data demonstrated

Surgical Ventricular Restoration Improves the Left Ventricle Basal Wall Function Using Quantitative Gated Spect

It is not clear whether surgical ventricular restoration (SVR) or procedures approaching mitral complex for controlling functional mitral regurgitation (MR) affect the regional left ventricular wall function. The purpose of the present study was to evaluate the regional LV function after SVR using overlapping left ventriculoplasty (OLVP) using quantitative gated myocardial perfusion SPECT (QGS). Forty-one heart failure patients, including those with ischemic cardiomyopathy (ICM) (n = 25) and non-ICM (NICM) (n = 16), underwent SVR and/or papillary muscle approximation (PMA). The rest myocardial perfusion SPECT were performed before and early after operation (mean 25.8 ± 10.6 days). These patients were divided into 4 groups based on the surgical procedures (SVR and/or PMA) and etiology of patients (ICM or NICM) as follows: SVR (with or without PMA) of ICM, SVR of NICM, PMA of ICM and PMA of NICM groups. The regional wall thickening was compared before and after the operation between the four groups. NYHA functional classes were improved after the operation in all four groups. MR grade was also improved in three groups other than SVR of the ICM group. The left ventricular basal wall thickening was improved postoperatively in following three groups (SVR of ICM: 12.7 ± 3.8% to 16.5 ± 4.6% p <0.05, PMA of ICM: 11.1 ± 4.3% to 14.9 ± 4.8% p <0.05, SVR of NICM: 5.8 ± 6.6% to 12.3 ± 6.4% p <0.05), whereas PMA of the NICM group did not show an improvement. Wall thickening in the middle and distal levels was not improved in all groups. OLVP improved NYHA functional classes, and also improved the regional wall function at the basal level of the left ventricle. In contrast, lone PMA did not improve or impair the regional wall function at any of the levels.

An automatic method for quantification of myocardium at risk from myocardial perfusion SPECT in patients with acute coronary occlusion

BackgroundIn order to determine myocardial salvage, accurate quantification of myocardium at risk (MaR) is necessary. We present a validated novel automatic segmentation algorithm for quantification of MaR by myocardial perfusion SPECT (MPS) in patients with acute coronary occlusion. Methods and ResultsTwenty-nine patients with coronary occlusion were injected with a perfusion tracer before reperfusion, and underwent rest MPS within 4 hours. The MaR was quantified using the proposed algorithm (Segment software), the software Quantitative Perfusion SPECT (QPS) and by manual segmentation. The Segment MaR algorithm used a threshold of 55% of maximal counts and an a priori model based on normal coronary artery perfusion territories. The MaR was 30 ± 10% left ventricular mass (%LVM) by manual segmentation, 31 ± 12%LVM by Segment, and 36 ± 14%LVM by QPS. There was a good agreement between automatic and manual segmentation for both of the algorithms with a lower bias for Segment (.8 ± 4.0%LVM) than for QPS (5.8 ± 5.8%LVM) when compared to manual segmentation. ConclusionsThe Segment MaR algorithm can be used to correctly assess MaR from MPS images in patients with acute coronary occlusion without access to tracer-specific normal database. The MaR in relation to final infarct size enables determination of myocardial salvage.

Clinical significance of ischemic electrocardiographic changes during stress myocardial perfusion imaging: sub-analysis of the J-ACCESS study

The cardiac event rate among the countries varies according to ethnicity. Some reports have identified that ischemic heart disease often occurs at a low incidence and is often milder in Japan compared to other countries. Therefore, the present study was designed to determine the clinical significance and prediction for cardiac events in patients who showed ischemic ECG changes during stress myocardial perfusion SPECT. Among 4,670 registered patients for Japanese-assessment of cardiac event and survival (J-ACCESS) study, patients with conduction abnormality on baseline were excluded and revascularization within 60 days of SPECT study were censored from the prognostic portion of analysis. Stress and rest myocardial perfusion SPECT imaging with (99m)Tc-tetrofosmin were performed and occurrence and nature of cardiac events were investigated at 1, 2 and 3 years after registration. Both PCI and CABG, as well as recurrent angina and non-severe heart failure were classified as soft events. Cardiac death, non-fatal MI and heart failure requiring hospitalization were classified as major cardiac events, and hard events comprised cardiac death and non-fatal MI. A total of 3,125 patients performed exercise (n = 2,383) or vasodilator (n = 742) stress MPI and significant ischemic ECG changes were obtained in 538 during exercise and 35 during vasodilator stress. Kaplan-Meier analysis revealed that the patients with both ischemic ECG changes and reversible perfusion defect on MPI had significantly higher incidence for major cardiac events, such as cardiac death, non-fatal MI and severe heart failure (P = 0.0038), and for cardiac hard events, such as cardiac death and non-fatal MI (P = 0.0028), in exercise stress. Interestingly, patients without reversible perfusion defect showed significantly fewer events despite presence of ischemic ECG changes. Ischemic ECG changes during exercise stress are well associated with higher incidence of cardiac events in patients demonstrated reversible perfusion defect on MPI.

An Improved Method for Automatic Segmentation of the Left Ventricle in Myocardial Perfusion SPECT

This study describes and validates a new method for automatic segmentation of left ventricular mass (LVM) in myocardial perfusion SPECT (MPS) images. This is important for estimating the size of a perfusion defect as percentage of the left ventricle. A total of 101 patients with known or suspected coronary artery disease underwent both rest and stress MPS and MRI. A new automated algorithm was trained in 20 patients (40 MPS studies) and tested in 81 patients (162 MPS studies). The algorithm, which segmented the left ventricle in the MPS images, is based on Dijkstra's algorithm and finds an optimal mid-mural line through the left ventricular wall. From this line, the endocardium and epicardium are identified on the basis of an individually estimated wall thickness and signal intensity. The algorithm was validated by comparing LVM in both stress and rest MPS, with LVM of the manually segmented left ventricle from MRI as the reference standard. For comparison, LVM was quantified using the software quantitative perfusion SPECT (QPS). The mean difference+/-SD in LVM between MPS and MRI was lower for the new method (6%+/-15% LVM) than for QPS (18%+/-19% LVM) for both mean difference (P<0.001) and SD (P=0.015). Linear regression analysis of LVM, comparing MPS and MRI, yielded R2=0.83 using the new method and R2=0.80 using QPS. Interstudy variability, measured as the coefficient of variance between rest MPS and stress MPS, was 6% for both the new method and QPS. Both the new algorithm and QPS systematically overestimated LVM in hearts with thin myocardium and underestimated LVM in hearts with thick myocardium. The new segmentation algorithm quantifies LVM with a significantly lower bias and variability than does the commercially available QPS software, when compared to manually segmented LVM by MRI. This makes the new algorithm an attractive method to use for estimating the size of the perfusion defect when expressing it as percentage of the left ventricle. This study shows that inaccurate estimation of wall thickness is the main source of error in automatic segmentation.

Characteristics of supine myocardial perfusion SPECT (MPS) which predict normalization on prone imaging could simplify acquisition and aid image interpretation

Background: Imaging in the prone position is known to differentiate true perfusion defects from abnormalities created by artifacts seen on supine MPS images. If normalization on prone imaging could be predicted, additional prone images could be avoided while maintaining diagnostic accuracy. Methods: Two blinded observers identified 236 coronary vascular areas in 176 patients, 124 men and 52 women, with abnormal or possibly abnormal supine MPS who had prone images after stress performed at UCSF between 9 and 11/03. Nineteen image features based on gender, defect location, intensity, variation at rest MPS (when acquired), evidence of attenuation or motion, cavitary dilation, lung uptake, background activity, counts density and wall motion (WM) were related by multiple logistic regression (LR) and a C4.5 decision tree (DT) analyses to the likelihood of defect normalization on prone imaging. The overall population was divided into test and validation groups. Coronary angiograms within 2 years of MPS were available in 48 patients. Results: Prone images agreed with angiographic findings in 41 of 48 (86%) patients. LR predicted prone image findings in all cases but required input from all 19 factors. In both men and women 10 fold stratified cross validation predicted prone image normalization (p < 0.05) by non-segmental, low intensity, shifting defects, patient motion and low count images, and persistent prone defects by dense, segmental, stress induced defects, cavitary dilation, lung uptake and WM abnormalities. DT analysis simplified the findings and identified image findings and their combination with high predictive accuracies in the validation group, where a dense defect, a low intensity defect with either abnormal WM, or with an abnormal polar map (PM) and segmental defect were predictive of persistence on prone, while a normal PM, or a low intensity defect with either normal WM, or with a normal PM with a non-segmental defect predicted prone normalization with accuracies over 93%. Conclusion: A few critical findings on supine MPS predict the findings on prone images. These findings aid image interpretation and reduce the need for added prone images.

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.

Validation and Evaluation of Model-Based Crosstalk Compensation Method in Simultaneous&amp;lt;tex&amp;gt;$^99rm m$&amp;lt;/tex&amp;gt;Tc Stress and&amp;lt;tex&amp;gt;$^201$&amp;lt;/tex&amp;gt;Tl Rest Myocardial Perfusion SPECT

Simultaneous acquisition of /sup 99m/Tc stress and /sup 201/Tl rest myocardial perfusion SPECT has several potential advantages, but the image quality is degraded by crosstalk between the Tc and Tl data. We have previously developed a crosstalk model that includes estimates of the downscatter and Pb X-ray for use in crosstalk compensation. In this work, we validated the model by comparing the crosstalk from /sup 99m/Tc to the Tl window calculated using a combination of the SimSET-MCNP Monte Carlo simulation codes. We also evaluated the model-based crosstalk compensation method using both simulated data from the 3-D MCAT phantom and experimental data from a physical phantom with a myocardial defect. In these studies, the Tl distributions were reconstructed from crosstalk contaminated data without crosstalk compensation, with compensation using the model-based crosstalk estimate, and with compensation using the known true crosstalk, and were compared with the Tl distribution reconstructed from uncontaminated Tl data. Results show that the model gave good estimates of both the downscatter photons and Pb X-rays in the simultaneous dual-isotopes myocardial perfusion SPECT. The model-based compensation method provided image quality that was significantly improved as compared to no compensation and was very close to that from the separate acquisition.