Paradoxical uptake of F-18 fluorodeoxyglucose by successfully reperfused myocardium during the sub-acute phase in patients with acute myocardial infarction

Cardiac 18F-FDG Positron Emission Tomography: An Accurate Tool to Monitor In vivo Metabolic and Functional Alterations in Murine Myocardial Infarction

Cardiac monitoring after murine myocardial infarction, using serial non-invasive cardiac 18F-FDG positron emissions tomography (PET) represents a suitable and accurate tool for in vivo studies. Cardiac PET imaging enables tracking metabolic alterations, heart function parameters and provides correlations of the infarct size to histology. ECG-gated 18F-FDG PET scans using a dedicated small-animal PET scanner were performed in mice at baseline, 3, 14, and 30 days after myocardial infarct (MI) by permanent ligation of the left anterior descending (LAD) artery. The percentage of the injected dose per gram (%ID/g) in the heart, left ventricular metabolic volume (LVMV), myocardial defect, and left ventricular function parameters: end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), and the ejection fraction (EF%) were estimated. PET assessment of the defect positively correlates with post-infarct histology at 3 and 30 days. Infarcted murine hearts show an immediate decrease in LVMV and an increase in %ID/g early after infarction, diminishing in the remodeling process. This study of serial cardiac PET scans provides insight for murine myocardial infarction models by novel infarct surrogate parameters. It depicts that serial PET imaging is a valid, accurate, and multimodal non-invasive assessment.

Reproducibility and accuracy of non-invasive measurement of infarct size in mice with high-resolution PET/CT

BACKGROUND

This study assessed the reproducibility and accuracy of 2-deoxy-2[(18)F]fluoro-D-glucose ((18)F-FDG) for non-invasive quantification of myocardial infarct size in mice by a high-resolution positron emission tomography (PET)/computed tomography (CT) system.

METHODS AND RESULTS

Mice were studied by (18)F-FDG PET/CT 1 week after induction of myocardial infarction by permanent coronary occlusion or sham procedure. In a subset of mice, PET/CT was repeated 2 days apart to assess the reproducibility of infarct size measurements. Histological analysis was used as reference method to validate imaging data. The average difference in infarct size measurements between the first and the second study was -0.42% ± 2.07% (95% confidence interval -2.6 to 1.75) with a repeatability coefficient of 4.05%. At Bland-Altman analysis, the lower and upper limits of agreement between the two repeated studies were -4.46% and 3.63%, respectively, and no correlation between difference and mean was found (P = .89). The concordance correlation coefficient was 0.99 (P < .001) and the intraclass coefficient of correlation was 0.99. A high correlation between PET/CT and histology was found for measurement of infarct size (P < .001). Using Bland-Altman analysis, the mean difference in infarct size measurement (PET/CT minus histology) was 1.9% (95% confidence interval 0.94% to 2.86%).

CONCLUSIONS

In a mice model of permanent coronary occlusion non-invasive measurement of infarct size with high-resolution (18)F-FDG, PET/CT has excellent reproducibility and accuracy. These findings support the use of this methodology in serial studies.

Myocardial viability assessment using nuclear imaging

Myocardial assessment continues to be an issue in patients with coronary artery disease and left ventricular dysfunction. Nuclear imaging has long played an important role in this field. In particular, PET imaging using 18F-fluorodeoxyglucose is regarded as the metabolic gold standard of tissue viability, which has been supported by a wide clinical experience. Viability assessment using SPECT techniques has gained more wide-spread clinical acceptance than PET, because it is more widely available at lower cost. Moreover, technical advances in SPECT technology such as gated-SPECT further improve the diagnostic accuracy of the test. However, other imaging techniques such as dobutamine echocardiography have recently emerged as competitors to nuclear imaging. It is also important to note that they sometimes may work in a complementary fashion to nuclear imaging, indicating that an appropriate use of these techniques may significantly improve their overall accuracy. In keeping these circumstances in mind, further efforts are necessary to further improve the diagnostic performance of nuclear imaging as a reliable viability test.

14 C-deoxyglucose imaging overestimates myocardial viability in subacute infarction of rats

Clinical studies using 18F-fluorodeoxyglucose suggest that this tracer may overestimate myocardial viability. This study aimed to elucidate whether 2-deoxyglucose accurately indicates myocardial viability at the early phase of myocardial infarction. Autoradiography with 14C-deoxyglucose was performed in fasting rats whose left coronary artery was occluded for 60 min and then reperfused. 14C-deoxyglucose was injected 30 min after the reperfusion (acute; n=10) or 1 week later (subacute; n=9). Infarction and risk areas were identified by triphenyl tetrazolium chloride or haematoxylin-eosin staining and methylene blue, respectively. Immuno-histochemical staining using anti-glucose transporter 1 and 4 antibodies was performed. At the acute stage, the uptake of deoxyglucose was consistent with the grade of anti-glucose transporter 4 expression. At the subacute stage, the uptake of deoxyglucose in poorly viable myocardium (543.4+/-343.7%: normalized with the uptake at the right ventricle) as well as in the viable one (335.2+/-149.8%) in the risk area was significantly greater than that in the remote area (116.4+/-94.9%, P<0.01). Anti-glucose transporter 1 was expressed in the poorly viable area where inflammatory cells infiltrated. It is concluded that deoxyglucose uptake by inflammatory cells which express anti-glucose transporter 1 causes overestimation of myocardial viability at subacute stage.