Elsevier

Journal of Nuclear Cardiology

Volume 25, Issue 6, December 2018, Pages 1960-1967
Journal of Nuclear Cardiology

Original Article
Dual-time-point FDG PET/CT imaging in prosthetic heart valve endocarditis

https://doi.org/10.1007/s12350-017-0902-3Get rights and content

Abstract

Purpose

FDG PET/CT has been of increasing interest in the diagnostic workup of prosthetic heart valve endocarditis (PVE). Some reports advocate later imaging time points to improve the diagnostic accuracy for PVE. In this study, we compared standard and late FDG PET/CT images in patients with a clinical suspicion of PVE.

Materials and Methods

Fourteen scans in 13 patients referred for FDG PET/CT for suspicion of PVE performed at standard (60 min post injection) and late (150 min post injection) time points were scored based on visual interpretation and semi-quantitatively with SUVmax and target-to-background ratio (TBR, defined as [SUVmax valve/SUVmean blood pool]). Final diagnosis was based on surgical findings in all cases of infection (n = 6) and unremarkable follow-up in all others (n = 8).

Results

Late images were more prone to false positive interpretation for both visual and semi-quantitative analyses. Visual analysis of the standard images yielded 1 false negative and 1 false positive result. On the late images, no scans were false negative but 5 scans were false positive.

Conclusion

Late FDG PET/CT imaging for PVE seems prone to false positive results. Therefore, late imaging should be interpreted with caution.

Introduction

Prosthetic heart valve (PHV) implantation is performed at an increasing rate, due to the prevalence of heart valve disease increasing in tandem with the growing aging population, with over 800,000 annual procedures estimated to be performed worldwide by the year 2050.1 Prosthetic heart valve (PHV) endocarditis (PVE) is a relatively uncommon complication, with an incidence of 0.3-1.0% per patient per year,2 but is associated with an alarmingly high mortality rate, especially when Staphylococcus aureus is the pathogen involved.2,3 PVE can be difficult to diagnose, with echocardiography unable to identify signs of the disease in up to 30% of cases.4,5

Computed tomography angiography (CTA) of the valve area has been shown to be of complementary value to clinical routine workup in suspected PVE,6 although it can be difficult to distinguish between non-infectious postoperative anatomical variation and infectious complications in select cases.

Fluorine-18 fluorodeoxyglucose positron emission tomography with CT-based attenuation correction (FDG PET/CT) is gaining momentum as a tool in the diagnosis of suspected PVE,7, 8, 9, 10 due to its ability to image inflammation activity as opposed to the aforementioned modalities that image anatomy only. Recently, FDG PET/CT was added as a diagnostic modality in the guidelines of the European Society of Cardiology for the diagnosis and management of infectious endocarditis.11

However, the optimal imaging protocol for FDG PET/CT in PVE is still unclear, with preparatory protocols and timing of image acquisition still subjects of debate. In standard oncological FDG PET/CT protocols, images are acquired 60 minutes after injection of the tracer. However, for the detection of infection and inflammation, both earlier and later imaging have been proposed; the former based on the fast influx of glucose into inflammatory cells followed by efflux based on active glucose-6-phosphatase,12 the latter based on persistent influx in inflammation and further clearance of glucose from the blood pool leading to higher contrast between activity in infectious foci and background.13

Based on earlier reports, delayed imaging may be of additional value in diagnosing infection of cardiovascular implants.13,14 We performed both standard and delayed acquisitions of FDG PET/CT images in a number of patients referred for possible PVE under the assumption that the delayed images may improve diagnostic accuracy.

Section snippets

Methods

Based on earlier reports,13,14 we added delayed acquisition at 150 minutes post injection of the radiotracer to our clinical protocol for FDG PET/CT for suspicion of PVE, in keeping with the innovation and development stages as described by the IDEAL framework.15 Thirteen patients with 14 scans referred for FDG PET/CT with suspected PVE in the University Medical Center Utrecht were imaged at standard and late time points after giving informed consent. The local ethical committee waived review

Results

Scans were performed for suspected PVE of one mitral valve replacement, one pulmonic valve replacement, and 11 aortic valve replacements. In two patients, the aortic valve replacement was part of a Bentall graft of the aortic root and ascending aorta. Median time from implantation to FDG PET/CT was 654 days (range 21-4992 days). Two patients were scanned within the first six weeks after implantation. Standard images were acquired at a mean of 65 minutes post injection (range 56-80 minutes), and

Discussion

With the aim to improve our imaging protocol in patients with suspected PVE, according to the IDEAL criteria, we compared standard and late acquisition of FDG PET/CT images in suspected PVE in a small cohort of patients. The most important finding of our study was that delayed images did not compare favorably to standard images, as delayed images were more prone to false positive results. Changes in SUVmax and TBR between standard and late images showed great variation in both the PVE group and

New Knowledge Gained

Based on our current data, we cannot recommend the use of delayed FDG PET/CT imaging in PVE, whether as substitution for or as an adjunct to standard images, as we believe the risk of false positive interpretation is too high in either scenario.

Conclusion

Delayed imaging at 150 minutes post injection does not seem to improve the interpretation of FDG PET/CT in PVE as it seems prone to false positive findings. Imaging at the standard oncology protocol acquisition time outperformed delayed imaging both in visual and semi-quantitative analysis.

Disclosures

R.P.J. Budde has received and L.E. Swart is funded by a research Grant from the Dutch Heart Foundation (DHF 2013T071). A.M. Scholtens, H.J. Verberne, and M.G.E.H. Lam declare no conflict of interest regarding this study.

Ethical Approval

All procedures performed were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Informed Consent

Informed consent was obtained from all individual participants as part of the clinical routine before imaging procedures in our hospital. Due to the retrospective nature of the study, no study-specific informed consent applies.

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