Influence of SPECT attenuation correction on the quantification of hibernating myocardium as derived from combined myocardial perfusion SPECT and ¹⁸F-FDG PET

[15O]H2O myocardial perfusion positron emission tomography: Added value of relative stress perfusion deficit in the prediction of significant coronary artery stenosis in a mixedpopulation

BACKGROUND

It remains unknown whether estimation of the relative stress perfusion deficit offers added value in the prediction of significant coronary artery stenosis in myocardial perfusion imaging with [15O]H2O positron emission tomography (PET) in a population with high prevalence of established cardiac disease.

METHODS

During eight months, we consecutively included all patients undergoing [15O]H2O PET and subsequent invasive coronary angiography (ICA). Significant stenosis was defined from ICA as fractional flow reserve ≤.8 or coronary artery narrowing of ≥70%. We calculated absolute and relative total perfusion deficits (aTPD and rTPD, respectively) as semiquantitative measures of the extent and severity of reduced stress perfusion. A multivariate logistic regression analysis was performed to test the adjusted associations (odds ratio (OR) with 95% CI) with significant coronary artery stenosis.

RESULTS

Of 800 patients undergoing [15O]H2O PET, 144 underwent ICA, where 142 patients had aTPD of ≥3% and 79 (55%) of these had at least one significant stenosis. In an adjusted analysis, rTPD (OR10% increase = 2.12 (1.44-3.12), P < .001), previous coronary artery bypass grafting (CABG) (OR = .11 (.03-.36), P < .001) and reduced left ventricular ejection fraction (LVEF) (OR = .25 (.08-.84), P = .02) were independently associated with significant stenosis, whereas the association with aTPD (OR10% increase = 1.14 (.98-1.32), P = .08) was modest.

CONCLUSIONS

In the presence of an absolute perfusion deficit (aTPD of ≥3%), rTPD may improve the prediction of significant stenosis in a heterogeneous population of patients examined with [15O]H2O PET. Furthermore, previous CABG and reduced LVEF are associated with nonstenotic perfusion deficiencies, suggesting caution when interpreting myocardial perfusion imaging in such patients.

Resident and recruited macrophages differentially contribute to cardiac healing after myocardial ischemia

Cardiac macrophages are heterogenous in phenotype and functions, which has been associated with differences in their ontogeny. Despite extensive research, our understanding of the precise role of different subsets of macrophages in ischemia/reperfusion (I/R) injury remains incomplete. We here investigated macrophage lineages and ablated tissue macrophages in homeostasis and after I/R injury in a CSF1R-dependent manner. Genomic deletion of a fms-intronic regulatory element (FIRE) in the Csf1r locus resulted in specific absence of resident homeostatic and antigen-presenting macrophages, without affecting the recruitment of monocyte-derived macrophages to the infarcted heart. Specific absence of homeostatic, monocyte-independent macrophages altered the immune cell crosstalk in response to injury and induced proinflammatory neutrophil polarization, resulting in impaired cardiac remodeling without influencing infarct size. In contrast, continuous CSF1R inhibition led to depletion of both resident and recruited macrophage populations. This augmented adverse remodeling after I/R and led to an increased infarct size and deterioration of cardiac function. In summary, resident macrophages orchestrate inflammatory responses improving cardiac remodeling, while recruited macrophages determine infarct size after I/R injury. These findings attribute distinct beneficial effects to different macrophage populations in the context of myocardial infarction.

Quantitative myocardial perfusion SPECT/CT for the assessment of myocardial tracer uptake in patients with three-vessel coronary artery disease: Initial experiences and results

BACKGROUND

To evaluate quantitative myocardial perfusion SPECT/CT datasets for routine clinical reporting and the assessment of myocardial tracer uptake in patients with severe TVCAD.

METHODS

MPS scans were reconstructed as quantitative SPECT datasets using CTs from internal (SPECT/CT, Q_INT) and external (PET/CT, Q_EXT) sources for attenuation correction. TPD was calculated and compared to the TPD from non-quantitative SPECT datasets of the same patients. SUVmax, SUVpeak, and SUVmean were compared between Q_INT and Q_EXT SPECT datasets. Global SUVmax and SUVpeak were compared between patients with and without TVCAD.

RESULTS

Quantitative reconstruction was feasible. TPD showed an excellent correlation between quantitative and non-quantitative SPECT datasets. SUVmax, SUVpeak, and SUVmean showed an excellent correlation between Q_INT and Q_EXT SPECT datasets, though mean SUVmean differed significantly between the two groups. Global SUVmax and SUVpeak were significantly reduced in patients with TVCAD.

CONCLUSIONS

Absolute quantification of myocardial tracer uptake is feasible. The method seems to be robust and principally suitable for routine clinical reporting. Quantitative SPECT might become a valuable tool for the assessment of severe coronary artery disease in a setting of balanced ischemia, where potentially life-threatening conditions might otherwise go undetected.

Prone Myocardial Perfusion Imaging and Breast Attenuation: A Phantom Study

Background:

Soft tissue attenuation artifacts are the most common cause of misinterpretation in myocardial perfusion Imaging (MPI). Few studies assessing the value of prone imaging in women have been published. Breast attenuation artifacts can be present in up to 40% of the MPI studies in women.

Objectives:

This study aimed at evaluating the potential impact of prone MPI on breast attenuation, with a critical analysis of activity optimization and breast size influence.

Methods:

MPI of an Anthropomorphic Torso Phantom with silicone breast prostheses and equivalent adipose tissue was compared to a standard MPI database.

Results:

A medical qualitative and semiquantitative analysis demonstrated higher uptake in the LV anterior segments in the prone position for all injected activities. An artificial myocardium lesion was diagnosable in the right segment in all images, which shows that prone positioning would not mask a true lesion and it assists the cardiologist with a more accurate analysis. These results showed that it is possible to optimize the activity to be injected by up to 55.6% when using combined supine-prone images.

Conclusion:

Prone position has a high impact on the interpretation of MPI in female patients since it reduces the breast attenuation artifacts, and optimizes the radiation protection of the patient and all staff involved in the procedure, making it more cost-effective.

FDG-PET reveals improved cardiac regeneration and attenuated adverse remodelling following Sitagliptin + G-CSF therapy after acute myocardial infarction

AIMS

Dual therapy comprising G-CSF for mobilization of bone marrow-derived progenitor cells (BMPCs), with simultaneous pharmacological inhibition of dipeptidylpeptidase-IV for enhanced myocardial recruitment of circulating BMPC via the SDF-1α/CXCR4-axis, has been shown to improve survival after acute myocardial infarction (AMI). Using an innovative method to provide non-invasive serial in vivo measurements and information on metabolic processes, we aimed to substantiate the possible effects of this therapeutic concept on cardiac remodelling after AMI using 2-deoxy-2-[18F]fluoro-d-glucose positron emission tomography (FDG-PET).

METHODS AND RESULTS

AMI was induced in C57BL/6 mice by performing surgical ligation of the left anterior descending artery in these mice. Animals were then treated with granulocyte-colony stimulating factor + Sitagliptin (GS) or placebo for a duration of 5 days following AMI. From serial PET scans, we verified that the infarct size in GS-treated mice (n = 13) was significantly reduced at Day 30 after AMI when compared with the mice receiving placebo (n = 10). Analyses showed a normalized FDG uptake on Day 6 in GS-treated mice, indicating an attenuation of the cardiac inflammatory response to AMI in treated animals. Furthermore, flow cytometry showed a significant increase in the anti-inflammatory M2-macrophages subpopulation in GS-treated animals. In comparing GS treated with placebo animals, those receiving GS-therapy showed a reduction in myocardial hypertrophy and left ventricular dilatation, which indicates the beneficial effect of GS treatment on cardiac remodelling. Remarkably, flow cytometry and immunohistochemistry showed an increase of myocardial c-kit positive cells in treated mice (n = 12 in both groups).

CONCLUSION

Using the innovative method of micro-PET for non-invasive serial in vivo measurements of metabolic myocardial processes in mice, we were able to provide mechanistic evidence that GS therapy improves cardiac regeneration and reduces adverse remodelling after AMI.

EANM procedural guidelines for radionuclide myocardial perfusion imaging with SPECT and SPECT/CT: 2015 revision

Since the publication of the European Association of Nuclear Medicine (EANM) procedural guidelines for radionuclide myocardial perfusion imaging (MPI) in 2005, many small and some larger steps of progress have been made, improving MPI procedures. In this paper, the major changes from the updated 2015 procedural guidelines are highlighted, focusing on the important changes related to new instrumentation with improved image information and the possibility to reduce radiation exposure, which is further discussed in relation to the recent developments of new International Commission on Radiological Protection (ICRP) models. Introduction of the selective coronary vasodilator regadenoson and the use of coronary CT-contrast agents for hybrid imaging with SPECT/CT angiography are other important areas for nuclear cardiology that were not included in the previous guidelines. A large number of minor changes have been described in more detail in the fully revised version available at the EANM home page: http://eanm.org/publications/guidelines/2015_07_EANM_FINAL_myocardial_perfusion_guideline.pdf.

Review of cardiovascular imaging in The Journal of Nuclear Cardiology in 2014: Part 1 of 2: Positron emission tomography, computed tomography, and neuronal imaging

The year 2014 has been an exciting year for the cardiovascular imaging community with significant advances in the realm of nuclear and multimodality cardiac imaging. In this new feature of the Journal of Nuclear Cardiology, we will summarize some of the breakthroughs that were published in the Journal in 2014 in 2 sister articles. This first article will concentrate on publications dealing with cardiac positron emission tomography (PET), computed tomography (CT), and neuronal imaging.

In-vivo monitoring of erythropoietin treatment after myocardial infarction in mice with [⁶⁸Ga]Annexin A5 and [¹⁸F]FDG PET

BACKGROUND

Several studies substantiate the cardioprotective effects of erythropoietin (EPO). Our goal was to quantify the effects of EPO treatment on the early expression of the apoptosis marker phosphatidylserine as well as on the left ventricular volumes and function by means of small animal PET.

METHODS AND RESULTS

Myocardial infarction (MI) was induced in C57BL/6 mice. Animals were assigned to saline or EPO groups and underwent Annexin PET (day 2) and gated FDG PET (days 6 and 30). Annexin uptake was significantly higher in the infarction than in remote myocardium, with no differences between treatment groups. Infarct size showed a slight decrease in the EPO group and a slight increase in the controls, which did not reach statistical significance. Follow-up analyses revealed a significant increase of end-diastolic and end-systolic volumes in the EPO group, in which a stable left ventricular ejection fraction (LVEF) was maintained.

CONCLUSION

We find that deleterious effects of EPO can outweigh cardioprotective effects. The present EPO treatment did not significantly reduce apoptosis after MI, but seemingly provoked significant myocardial dilation while maintaining a stable LVEF. Molecular mechanisms of EPO treatment may need further elucidation to optimize therapy regimens.