Evaluation of Salvaged Myocardium After Acute Myocardial Infarction Using Single Photon Emission Computed Tomography After 201Tl-Glucose-Insulin Infusion

Application of Monte Carlo Algorithms to Cardiac Imaging Reconstruction

Monte Carlo algorithms have a growing impact on nuclear medicine reconstruction processes. One of the main limitations of myocardial perfusion imaging (MPI) is the effective mitigation of the scattering component, which is particularly challenging in Single Photon Emission Computed Tomography (SPECT). In SPECT, no timing information can be retrieved to locate the primary source photons. Monte Carlo methods allow an event-by-event simulation of the scattering kinematics, which can be incorporated into a model of the imaging system response. This approach was adopted in the late Nineties by several authors, and recently took advantage of the increased computational power made available by high-performance CPUs and GPUs. These recent developments enable a fast image reconstruction with improved image quality, compared to deterministic approaches. Deterministic approaches are based on energy-windowing of the detector response, and on the cumulative estimate and subtraction of the scattering component. In this paper, we review the main strategies and algorithms to correct the scattering effect in SPECT and focus on Monte Carlo developments, which nowadays allow the threedimensional reconstruction of SPECT cardiac images in a few seconds.

Serial dual single-photon emission computed tomography of thallium-201 and iodine-123 beta-methyliodophenyl pentadecanoic acid scintigraphy can predict functional recovery of patients with coronary artery disease after coronary artery bypass graft surgery

BACKGROUND

A mismatch between thallium-201 ((201)Tl) and iodine-123 ((123)I)-beta-methyl iodophenyl pentadecanoic acid (BMIPP) dual single-photon emission computed tomography (SPECT) reflects a dysfunctional but viable myocardium, such as stunned or hibernating myocardium, in patients with coronary artery disease (CAD). However, the cardiac function does not always improve after revascularization. The present study aimed to determine whether serial (201)Tl and (123)I-BMIPP dual SPECT can predict improvements in cardiac function after coronary artery bypass graft surgery (CABG) in patients with CAD.

MATERIALS AND METHODS

The study included 98 patients with CAD requiring CABG and having a left ventricular ejection fraction (LVEF) less than 50%. The total defect score (TDS) was calculated from (201)Tl and (123)I-BMIPP dual-SPECT images acquired before and 3 weeks after CABG. The LVEF, left ventricular end-diastolic volume index, and end-systolic volume index were determined by means of contrast left ventriculography before and 6 months after CABG.

RESULTS

After 6 months, LVEF improved by 5% or more in 62 patients (group A) but did not improve in the remaining 36 patients (group B). Baseline Tl-TDS was significantly lower (9.1±4.6 vs. 14.6±6.5, P<0.001), and the mismatch score (BMIPP-TDS-Tl-TDS) was significantly higher (6.9±4.2 vs. 4.2±3.9, P=0.002) in group A than in group B. The extent of change in BMIPP-TDS 3 weeks after CABG compared with that before (delta-BMIPP-TDS) was significantly greater in group A than in group B (-5.9±3.0 vs. 2.8±4.3, P<0.001). Stepwise multivariate analysis selected delta-BMIPP-TDS as a significant independent predictor of improvement in LVEF at 6 months after CABG (multivariate β-coefficient=-0.718, P<0.001). The degree of change in LVEF 6 months after CABG compared with that before significantly and negatively correlated with delta-BMIPP-TDS (r=-0.631, P<0.001).

CONCLUSION

The delta-BMIPP-TDS evaluated by serial (201)Tl and (123)I-BMIPP dual SPECT can predict improvements in cardiac function during the chronic phase of CAD.

Evaluation of myocardial viability with thallium-201 infusion MPSPECT after oral glucose application in patients with chronic coronary artery disease

AIM

The aim of this study was to evaluate the myocardial viability in nondiabetic patients with chronic coronary artery disease (CCAD) or past myocardial infarction (MI), using thallium-201 infusion myocardial perfusion single-photon emission computed tomography (MPSPECT) imaging after oral glucose application (Glu+Tl-infusion).

MATERIALS AND METHODS

In this study, 33 nondiabetic patients (three female, 30 male, mean age: 55.24+/-11 years, range: 33-77 years) with MI history or known CCAD were included. Rest/redistribution/24 h-late-MPSPECT imaging was performed for all patients. In all patients in whom fixed perfusion defect was observed on any wall of the left ventriculi, after 24 h-late-MPSPECT imaging, 75 g oral glucose was given. Thirty minutes later, 1 mCi thallium-201 in 100 ml of physiological saline solution was applied in a period of 20 min by slow infusion. After infusion at the 10th minute, MPSPECT imaging was performed. Perfusion was evaluated visually for a total of 3432 segments with the 26-segment 5-point scoring technique. Scoring measured perfusion as 0 = no perfusion defect, 1 = mildly reduced, 2 = moderately reduced, 3 = severely reduced, and 4 = absent uptake. Scores '0 and 1' were considered normal and scores '2-4' were considered abnormal.

RESULTS

For serum insulin levels measured after glucose application, a significant increase was determined, according to the period before glucose application (P<0.001). When compared with rest MPSPECT images, segmental perfusion improvement both in redistribution and in the 24 h-late-MPSPECT images were 16.3 and 18.3%, respectively. This ratio was found to be 27.2% for Glu+Tl-infusion images. The ratios of segments in which perfusion was worsening were calculated to be 9.4, 14.5, and 7.3%, respectively, for redistribution, 24 h-late-MPSPECT, and Glu+Tl-infusion images. When this evaluation was made for all three vessel areas, again the highest perfusion improvement and the lowest perfusion worsening were detected for Glu+Tl-infusion images. In addition, when this evaluation was made for the three vessel areas according to the coronary narrowing degree, again the highest perfusion improvement was detected for Glu+Tl-infusion images, in segments in the left anterior descending artery, and right coronary artery areas with >/=90% narrowing. In rest images, in segments with segmental scores of 3 and 4, when the total reversibility ratio was evaluated, this ratio was calculated to be 0.7% for redistribution images and 4.5% for 24 h-late-MPSPECT. The highest total reversibility ratio in these segments was detected with Glu+Tl-infusion images to be 10.3%. When we evaluated the patients with respect to the MI history time, the highest segmental perfusion improvement was detected in patients with 0-3 months of MI history.

CONCLUSION

We conclude that in nondiabetic patients who are known to have CCAD or past MI history, Glu+Tl-infusion is an easily applicable method that gives better results for the evaluation of myocardial viability.

123I-MIBG imaging can be used to evaluate microvascular disturbance caused by embolization by microdebris after rotational atherectomy

BACKGROUND

During rotational atherectomy (RA), the coronary atherosclerotic plaque is largely pulverized into microdebris, which may cause serious hemodynamic instability owing to significant segmental left ventricular asynergy embolization of the distal microvasculature by atheromatous debris and associated vasospasm.

OBJECTIVE

To evaluate the usefulness of 123I-metaiodobenzylguanidine (123I-MIBG) in the examination of microvascular embolization after RA.

METHODS AND RESULTS

Nineteen patients with stable effort angina pectoris who had undergone RA were evaluated in this study. Left ventricular ejection fraction (LVEF) was determined by left ventriculography immediately before and after RA. The serum concentration of creatine phosphokinase (CPK), creatine phosphokinase-myocardial band (CPK-MB) isozyme, and cardiac troponin-T was determined after RA. 99mTc-methoxyiso-butylisonitrile (99mTc-MIBI) and 123I-MIBG scintigraphic examinations were also performed 1 day after RA. The regional defect score (RDS) was determined from 99mTc-MIBI scintigraphic findings, while early and delayed RDS, heart-to-mediastinum count ratios (H/M ratios), and washout rate (WR) were determined from 123I-MIBG scintigraphy. After RA, the left ventriculographic LVEF mildly decreased by <10% in ten patients (group A), but it decreased by >10% in the remaining nine patients (group B). There were no differences in baseline clinical characteristics between the two groups. The CPK, CPK-MB isozyme, troponin-T, RDS by 99mTc-MIBI, H/M ratios, and WR after RA were similar in the two groups. However, the RDSs determined from early and delayed 123I-MIBG in group A were significantly lower than those in group B (4.5 +/- 3.8 vs. 13.4 +/- 10.8, P < 0.05; 9.0 +/- 6.3 vs. 17.7 +/- 10.0, P < 0.05, respectively). Moreover, there were significant correlations between delta LVEF and troponin-T (r = 0.54, P < 0.05) and RDSs of early and delayed 123I-MIBG (r = 0.46, P < 0.05; r = 0.64, P < 0.05, respectively).

CONCLUSIONS

These findings suggest that 123I-MIBG imaging can be used to evaluate microvascular disturbance caused by embolization by microdebris after RA.

Prediction of functional improvement of ischemic myocardium with (123I-BMIPP SPECT and 99mTc-tetrofosmin SPECT imaging: a study of patients with large acute myocardial infarction and receiving revascularization therapy

BACKGROUND

(18)F-fluorodeoxyglucose (FDG) positron-emission tomography (PET) is assumed to be the most useful method of evaluating the viability of the myocardium, but its use is limited by the need for a cyclotron. In the present study, the ability of a combination of (99m)Tc-tetrofosmin (TF) and (123)I-beta-methyliodophenyl pentadecanoic acid (BMIPP) single-photon emission computed tomography (SPECT), a combination of (18)F-FDG PET and (123)I-BMIPP SPECT, and a combination of (18)F-FDG PET and (99m)Tc-TF SPECT were compared to predict functional improvement of ischemic myocardium after a large acute myocardial infarction (AMI).

METHODS AND RESULTS

Ten patients with large AMI were studied by (99m)Tc-TF SPECT, (123)I-BMIPP SPECT and (18)F-FDG PET within 3 weeks. Six months later, (99m)Tc-TF imaging was performed. All patients underwent successful revascularization, and had no restenosis. Regional tracer uptake was scored using a 4-point scale in 20 segments of the SPECT and PET images. When the defect score of (123)I-BMIPP SPECT exceeded the defect score of (99m)Tc-TF SPECT or (18)F-FDG PET by 1 point or more, and when the defect score of (99m)Tc-TF SPECT exceeded the defect score of (18)F-FDG PET by 1 point or more, the segment was considered to show mismatching. When the defect score was the same in 2 tracers, the segment was considered to show matching. (99m)Tc-TF imaging at 3 weeks and 6 months used quantitative gated SPECT (QGS) to score wall motion using a 6-point scale (-1= dyskinesis, 0= akinesis, 1= severe hypokinesis, 2= moderate hypokinesis, 3= mild hypokinesis, and 4= normokinesis). The sensitivity of the combination of (123)I-BMIPP and (99m)Tc-TF imaging in predicting functional improvement was 61%, that of (18)F-FDG PET and (123)I-BMIPP SPECT was 94%, and that of (18)F-FDG PET and (99m)Tc-TF SPECT was 76%. The specificity of the combination of (123)I-BMIPP and (99m)Tc-TF imaging in predicting functional improvement was 83%, that of (18)F-FDG PET and (123)I-BMIPP SPECT was 40%, and that of (18)F-FDG PET and (99m)Tc-TF SPECT was 49%. The accuracy of the combination of (123)I-BMIPP and (99m)Tc-TF imaging in predicting functional improvement was 70%, that of (18)F-FDG PET and (123)I-BMIPP SPECT was 71%, and that of (18)F-FDG PET and (99m)Tc-TF SPECT was 63%.

CONCLUSION

The combination of (123)I-BMIPP and (99m)Tc-TF imaging is a practical modality for predicting the functional improvement of ischemic myocardium after a large AMI.