New insight of functional molecular imaging into the atheroma biology: 18F-NaF and 18F-FDG in symptomatic and asymptomatic carotid plaques after recent CVA. Preliminary results

Bilateral Carotid Artery Molecular Calcification Assessed by [18F] Fluoride PET/CT: Correlation with Cardiovascular and Thromboembolic Risk Factors

Atherosclerosis, a leading cause of mortality and morbidity worldwide, involves inflammatory processes that result in plaque formation and calcification. The early detection of the molecular changes underlying these processes is crucial for effective disease management. This study utilized positron emission tomography/computed tomography (PET/CT) with [18F] sodium fluoride (NaF) as a tracer to visualize active calcification and inflammation at the molecular level. Our aim was to investigate the association between cardiovascular risk factors and [18F] NaF uptake in the left and right common carotid arteries (LCC and RCC). A cohort of 102 subjects, comprising both at-risk individuals and healthy controls, underwent [18F] NaF PET/CT imaging. The results revealed significant correlations between [18F] NaF uptake and cardiovascular risk factors such as age (β = 0.005, 95% CI 0.003-0.008, p < 0.01 in LCC and β = 0.006, 95% CI 0.004-0.009, p < 0.01 in RCC), male gender (β = -0.08, 95% CI -0.173--0.002, p = 0.04 in LCC and β = -0.13, 95% CI -0.21--0.06, p < 0.01 in RCC), BMI (β = 0.02, 95% CI 0.01-0.03, p < 0.01 in LCC and β = 0.02, 95% CI 0.01-0.03, p < 0.01 in RCC), fibrinogen (β = 0.006, 95% CI 0.0009-0.01, p = 0.02 in LCC and β = 0.005, 95% CI 0.001-0.01, p = 0.01), HDL cholesterol (β = 0.13, 95% CI 0.04-0.21, p < 0.01 in RCC only), and CRP (β = -0.01, 95% CI -0.02-0.001, p = 0.03 in RCC only). Subjects at risk showed a higher [18F] NaF uptake compared to healthy controls (one-way ANOVA; p = 0.02 in LCC and p = 0.04 in RCC), and uptake increased with estimated cardiovascular risk (one-way ANOVA, p < 0.01 in LCC only). These findings underscore the potential of [18F] NaF PET/CT as a sensitive tool for the early detection of atherosclerotic plaque, assessment of cardiovascular risk, and monitoring of disease progression. Further research is needed to validate the technique's predictive value and its potential impact on clinical outcomes.

Sodium fluoride in cardiovascular disorders: A systematic review

BACKGROUND

18-Fluorine sodium fluoride is a well-known radiotracer used for bone metastasis diagnosis. Its uptake correlation with cardiovascular (CV) risk was primarily suggested in oncological patients. Moreover, as a specific marker of microcalcification, it seems to correlate with CV disease progression and plaque instability.

METHODS AND RESULTS

Our purpose was to systematically review clinical studies that characterized the use of this marker in CV conditions. In atherosclerosis, most studies report a positive correlation with the burden of CV risk factors and vascular calcification. A higher uptake was found in culprit plaques/rupture sites in coronary and carotid arteries and it was also linked to high-risk features in histology and intravascular imaging analysis of the plaques. In aortic stenosis, this tracer displayed an increasing uptake with disease severity.

CONCLUSIONS

Sodium fluoride positron emission tomography is a promising non-invasive technique to identify high-risk plaques, which sets ground to a potential use of this tracer in evaluating atherosclerotic disease progression and degenerative changes in aortic valve stenosis. Nevertheless, there is a need for further prospective evidence that demonstrates this technique's value in predicting clinical events, adjusting treatment strategies, and improving patient outcomes.

18Fluorodeoxyglucose uptake in relation to fat fraction and R2* in atherosclerotic plaques, using PET/MRI: a pilot study

Inflammation inside Atherosclerotic plaques represents a major pathophysiological process driving plaques towards rupture. Pre-clinical studies suggest a relationship between lipid rich necrotic core, intraplaque hemorrhage and inflammation, not previously explored in patients. Therefore, we designed a pilot study to investigate the feasibility of assessing the relationship between these plaque features in a quantitative manner using PET/MRI. In 12 patients with high-grade carotid stenosis the extent of lipid rich necrotic core and intraplaque hemorrhage was quantified from fat and R2* maps acquired with a previously validated 4-point Dixon MRI sequence in a stand-alone MRI. PET/MRI was used to measure ¹⁸F-FDG uptake. T1-weighted images from both scanners were used for registration of the quantitative Dixon data with the PET images. The plaques were heterogenous with respect to their volumes and composition. The mean values for the group were as follows: fat fraction (FF) 0.17% (± 0.07), R2* 47.6 s⁻¹ (± 10.9) and target-to-blood pool ratio (TBR) 1.49 (± 0.48). At group level the correlation between TBR and FF_mean was − 0.406, p 0.19 and for TBR and R2*_mean 0.259, p 0.42. The lack of correlation persisted when analysed on a patient-by-patient basis but the study was not powered to draw definitive conclusions. We show the feasibility of analysing the quantitative relationship between lipid rich necrotic cores, intraplaque haemorrhage and plaque inflammation. The ¹⁸F-FDG uptake for most patients was low. This may reflect the biological complexity of the plaques and technical aspects inherent to ¹⁸F-FDG measurements.

Trial registration: ISRCTN, ISRCTN30673005. Registered 05 January 2021, retrospectively registered.

Procedural recommendations of cardiac PET/CT imaging: standardization in inflammatory-, infective-, infiltrative-, and innervation- (4Is) related cardiovascular diseases: a joint collaboration of the EACVI and the EANM: summary

With this summarized document we share the standard for positron emission tomography (PET)/(diagnostic)computed tomography (CT) imaging procedures in cardiovascular diseases that are inflammatory, infective, infiltrative, or associated with dysfunctional innervation (4Is) as recently published in the European Journal of Nuclear Medicine and Molecular Imaging. This standard should be applied in clinical practice and integrated in clinical (multicentre) trials for optimal standardization of the procedurals and interpretations. A major focus is put on procedures using [¹⁸F]-2-fluoro-2-deoxyglucose ([¹⁸F]FDG), but 4Is PET radiopharmaceuticals beyond [¹⁸F]FDG are also described in this summarized document. Whilst these novel tracers are currently mainly applied in early clinical trials, some multicentre trials are underway and we foresee in the near future their use in clinical care and inclusion in the clinical guidelines. Diagnosis and management of 4Is related cardiovascular diseases are generally complex and often require a multidisciplinary approach by a team of experts. The new standards described herein should be applied when using PET/CT and PET/magnetic resonance, within a multimodality imaging framework both in clinical practice and in clinical trials for 4Is cardiovascular indications.

Carotid artery molecular calcification assessed by [18F]fluoride PET/CT: correlation with cardiovascular and thromboembolic risk factors

OBJECTIVES

There is growing evidence that sodium fluoride ([¹⁸F]fluoride) PET/CT can detect active arterial calcifications at the molecular stage. We investigated the relationship between arterial mineralization in the left common carotid artery (LCC) assessed by [¹⁸F]fluoride PET/CT and cardiovascular/thromboembolic risk.

METHODS

In total, 128 subjects (mean age 48 ± 14 years, 51% males) were included. [¹⁸F]fluoride uptake in the LCC was quantitatively assessed by measuring the blood-pool-corrected maximum standardized uptake value (SUVmax) on each axial slice. Average SUVmax (aSUVmax) was calculated over all slices and correlated with 10-year risk of cardiovascular events estimated by the Framingham model, CHA2DS2-VASc score, and level of physical activity (LPA).

RESULTS

The aSUVmax was significantly higher in patients with increased risk of cardiovascular (one-way ANOVA, p < 0.01) and thromboembolic (one-way ANOVA, p < 0.01) events, and it was significantly lower in patients with greater LPA (one-way ANOVA, p = 0.02). On multivariable linear regression analysis, age ( = 0.07, 95% CI 0.05 - 0.10, p < 0.01), body mass index ( = 0.02, 95% CI 0.01 - 0.03, p < 0.01), arterial hypertension ( = 0.15, 95% CI 0.08 - 0.23, p < 0.01), and LPA ( = -0.10, 95% CI -0.19 to -0.02, p=0.02) were independent associations of aSUVmax.

CONCLUSIONS

Carotid [¹⁸F]fluoride uptake is significantly increased in patients with unfavorable cardiovascular and thromboembolic risk profiles. [¹⁸F]fluoride PET/CT could become a valuable tool to estimate subjects' risk of future cardiovascular events although still major trials are needed to further evaluate the associations found in this study and their potential clinical usefulness.

KEY POINTS

• Sodium fluoride ([¹⁸F]fluoride) PET/CT imaging identifies patients with early-stage atherosclerosis. • Carotid [¹⁸F]fluoride uptake is significantly higher in patients with increased risk of cardiovascular and thromboembolic events and inversely correlated with the level of physical activity. • Early detection of arterial mineralization at a molecular level could help guide clinical decisions in the context of cardiovascular risk assessment.

Procedural recommendations of cardiac PET/CT imaging: standardization in inflammatory-, infective-, infiltrative-, and innervation (4Is)-related cardiovascular diseases: a joint collaboration of the EACVI and the EANM

With this document, we provide a standard for PET/(diagnostic) CT imaging procedures in cardiovascular diseases that are inflammatory, infective, infiltrative, or associated with dysfunctional innervation (4Is). This standard should be applied in clinical practice and integrated in clinical (multicenter) trials for optimal procedural standardization. A major focus is put on procedures using [¹⁸F]FDG, but 4Is PET radiopharmaceuticals beyond [¹⁸F]FDG are also described in this document. Whilst these novel tracers are currently mainly applied in early clinical trials, some multicenter trials are underway and we foresee in the near future their use in clinical care and inclusion in the clinical guidelines. Finally, PET/MR applications in 4Is cardiovascular diseases are also briefly described. Diagnosis and management of 4Is-related cardiovascular diseases are generally complex and often require a multidisciplinary approach by a team of experts. The new standards described herein should be applied when using PET/CT and PET/MR, within a multimodality imaging framework both in clinical practice and in clinical trials for 4Is cardiovascular indications.

An Update on [18F]Fluoride PET Imaging for Atherosclerotic Disease

Atherosclerosis is the leading cause of life-threatening morbidity and mortality, as the rupture of atherosclerotic plaques leads to critical atherothrombotic events such as myocardial infarction and ischemic stroke, which are the 2 most common causes of death worldwide. Vascular calcification is a complicated pathological process involved in atherosclerosis, and microcalcifications are presumed to increase the likelihood of plaque rupture. Despite many efforts to develop novel non-invasive diagnostic modalities, diagnostic techniques are still limited, especially before symptomatic presentation. From this point of view, vulnerable plaques are a direct target of atherosclerosis imaging. Anatomic imaging modalities have the limitation of only visualizing macroscopic structural changes, which occurs in later stages of disease, while molecular imaging modalities are able to detect microscopic processes and microcalcifications, which occur early in the disease process. Na[¹⁸F]-fluoride positron emission tomography/computed tomography could allow the early detection of plaque instability, which is deemed to be a primary goal in the prevention of cardiac or brain ischemic events, by quantifying the microcalcifications within vulnerable plaques and evaluating the atherosclerotic disease burden.

18F-Sodium Fluoride (18F-NaF) for Imaging Microcalcification Activity in the Cardiovascular System

Accumulating preclinical and clinical evidence suggests that calcification is one of the body's primary responses to injury and a key pathological feature of cardiovascular disease. Calcification activity can now be imaged using 18F-sodium fluoride (18F-NaF) positron emission tomography (PET) in combination with either computed tomography or magnetic resonance. These techniques allow visualization of calcification activity and, therefore, provide different information to the established macroscopic calcium imaged with computed tomography. Indeed, 18F-NaF PET has been used to investigate a wide range of valvular conditions, including aortic stenosis, mitral annular calcification, and bioprosthetic valve disease, as well as vascular conditions, including abdominal aortic aneurysm disease, coronary, and carotid atherosclerosis, peripheral vascular disease, and erectile dysfunction. In this brief review, we will focus on how 18F-NaF PET has improved our pathophysiological understanding of cardiovascular calcification and how it can be used as a marker of vascular calcification, providing a useful tool that can be utilized in clinical trials investigating the prediction of both disease progression and clinical events. Finally, we will discuss how 18F-NaF might be employed clinically to improve patient assessment and to guide decision-making.

Role of 18F-FDG positron emission tomography in carotid atherosclerotic plaque imaging: A systematic review

Stroke and other thromboembolic events in the brain are often due to carotid artery atherosclerosis, and atherosclerotic plaques with inflammation are considered particularly vulnerable, with an increased risk of becoming symptomatic. Positron emission tomography (PET) with 2-deoxy-2-[Fluorine-18] fluoro-D-glucose (¹⁸F-FDG) provides valuable metabolic information regarding arteriosclerotic lesions and may be applied for the detection of vulnerable plaque. At present, however, patients are selected for carotid surgical intervention on the basis of the degree of stenosis alone, and not the vulnerability or inflammation of the lesion. During the past decade, research using PET with the glucose analog tracer ¹⁸F-fluor-deoxy-glucose, has been implemented for identifying increased tracer uptake in symptomatic carotid plaques, and tracer uptake has been shown to correlate with plaque inflammation and vulnerability. These findings imply that ¹⁸F-FDG PET might hold the promise for a new and better diagnostic test to identify patients eligible for carotid endarterectomy. The rationale for developing diagnostic tests based on molecular imaging with ¹⁸F-FDG PET, as well as methods for simple clinical PET approaches, are discussed. This is a systematic review, following Preferred Reporting Items for Systematic Reviews guidelines, which interrogated the PUBMED database from January 2001 to November 2019. The search combined the terms, “atherosclerosis,” “inflammation,” “FDG,” and “plaque imaging.” The search criteria included all types of studies, with a primary outcome of the degree of arterial vascular inflammation determined by ¹⁸F-FDG uptake. This review examines the role of ¹⁸F-FDG PET imaging in the characterization of atherosclerotic plaques.

Dual-Tracer Positron-Emission Tomography for Identification of Culprit Carotid Plaques and Pathophysiology In Vivo

BACKGROUND

Inflammation and microcalcification are interrelated processes contributing to atherosclerotic plaque vulnerability. Positron-emission tomography can quantify these processes in vivo. This study investigates (1) ¹⁸F-fluorodeoxyglucose (FDG) and ¹⁸F-sodium fluoride (NaF) uptake in culprit versus nonculprit carotid atheroma, (2) spatial distributions of uptake, and (3) how macrocalcification affects this relationship.

METHODS

Individuals with acute ischemic stroke with ipsilateral carotid stenosis of ≥50% underwent FDG-positron-emission tomography and NaF-positron-emission tomography. Tracer uptake was quantified using maximum tissue-to-background ratios (TBR_max) and macrocalcification quantified using Agatston scoring.

RESULTS

In 26 individuals, median most diseased segment TBR_max (interquartile range) was higher in culprit than in nonculprit atheroma for both FDG (2.08 [0.52] versus 1.89 [0.40]; P<0.001) and NaF (2.68 [0.63] versus 2.39 [1.02]; P<0.001). However, whole vessel TBR_max was higher in culprit arteries for FDG (1.92 [0.41] versus 1.71 [0.31]; P<0.001) but not NaF (1.85 [0.28] versus 1.79 [0.60]; P=0.10). NaF uptake was concentrated at carotid bifurcations, while FDG was distributed evenly throughout arteries. Correlations between FDG and NaF TBR_max differed between bifurcations with low macrocalcification (r_s=0.38; P<0.001) versus high macrocalcification (r_s=0.59; P<0.001).

CONCLUSIONS

This is the first study to demonstrate increased uptake of both FDG and NaF in culprit carotid plaques, with discrete distributions of pathophysiology influencing vulnerability in vivo. These findings have implications for our understanding of the natural history of the disease and for the clinical assessment and management of carotid atherosclerosis.

Clinical imaging of cardiovascular inflammation

Cardiovascular disease due to atherosclerosis is the number one cause of morbidity and mortality worldwide. In the past twenty years, compelling preclinical and clinical data have indicated that a maladaptive inflammatory response plays a crucial role in the development of atherosclerosis initiation and progression in the vasculature, all the way to the onset of life-threatening cardiovascular events. Furthermore, inflammation is key to heart and brain damage and healing after myocardial infarction or stroke. Recent evidence indicates that this interplay between the vasculature, organs target of ischemia and the immune system is mediated by the activation of hematopoietic organs (bone marrow and spleen). In this evolving landscape, non-invasive imaging is becoming more and more essential to support either mechanistic preclinical studies to investigate the role of inflammation in cardiovascular disease (CVD), or as a translational tool to quantify inflammation in the cardiovascular system and hematopoietic organs in patients. In this review paper, we will describe the clinical applications of non-invasive imaging to quantify inflammation in the vasculature, infarcted heart and brain, and hematopoietic organs in patients with cardiovascular disease, with specific focus on [18F]FDG PET and other novel inflammation-specific radiotracers. Furthermore, we will briefly describe the most recent clinical applications of other imaging techniques such as MRI, SPECT, CT, CEUS and OCT in this arena.

Should vascular wall 18F-FDG uptake be adjusted for the extent of atherosclerotic burden?

Vascular wall ¹⁸F-FDG uptake is often used as a surrogate marker of atherosclerotic plaque inflammation. A potential caveat is that vascular wall ¹⁸F-FDG uptake is higher simply because more atherosclerosis is present. To determine if the degree of inflammation is high or low relative to the extent of atherosclerosis, vascular wall ¹⁸F-FDG uptake may require statistical adjustment for a non-inflammatory marker reflecting the extent of atherosclerosis, e.g. calcification. Adjustments is probably needed if (1) vascular wall ¹⁸F-FDG uptake correlates sufficiently strongly with arterial calcification and (2) adjustment for extent of calcification affects determinants of vascular ¹⁸F-FDG uptake. This study addresses these questions. ¹⁸F-FDG PET/low-dose-CT scans of 99 patients were used. Cardiovascular risk factors were assessed and PET/CT scans were analysed for standardized ¹⁸F-FDG uptake values and calcification. ANOVA was used to establish the association between vascular ¹⁸F-FDG uptake and calcification. Multiple linear regression (with and without calcification as independent variable) was used to show whether determinants of vascular ¹⁸F-FDG uptake were affected by the degree of calcification. ¹⁸F-FDG uptake was related to increased calcification in the aortic arch, descending and abdominal aorta. However, ¹⁸F-FDG uptake showed considerable overlap between categories of calcification. Age and body mass index were main determinants of vascular ¹⁸F-FDG uptake. In multiple regression analyses, most standardized beta coefficients of these determinants were not affected by adjustment for the degree of calcification. Although vascular ¹⁸F-FDG uptake is related to total atherosclerotic burden, as reflected by vascular calcification, the association is weak and unlikely to affect the identification of determinants of atherosclerotic inflammation implicating no need for adjustment in future studies.

Basic Science of PET Imaging for Inflammatory Diseases

FDG-PET/CT has recently emerged as a useful tool for the evaluation of inflammatory diseases too, in addition to that of malignant diseases. The imaging is based on active glucose utilization by inflammatory tissue. Autoradiography studies have demonstrated high FDG uptake in macrophages, granulocytes, fibroblasts, and granulation tissue. Especially, activated macrophages are responsible for the elevated FDG uptake in some types of inflammation. According to one study, after activation by lipopolysaccharide of cultured macrophages, the [¹⁴C]2DG uptake by the cells doubled, reaching the level seen in glioblastoma cells. In activated macrophages, increase in the expression of total GLUT1 and redistributions from the intracellular compartments toward the cell surface have been reported. In one rheumatoid arthritis model, following stimulation by hypoxia or TNF-α, the highest elevation of the [³H]FDG uptake was observed in the fibroblasts, followed by that in macrophages and neutrophils. As the fundamental mechanism of elevated glucose uptake in both cancer cells and inflammatory cells, activation of glucose metabolism as an adaptive response to a hypoxic environment has been reported, with transcription factor HIF-1α playing a key role. Inflammatory cells and cancer cells seem to share the same molecular mechanism of elevated glucose metabolism, lending support to the notion of usefulness of FDGPET/CT for the evaluation of inflammatory diseases, besides cancer.

Molecular imaging of carotid artery atherosclerosis with PET: a systematic review

PURPOSE

To conduct a systematic review of articles on PET imaging of carotid atherosclerosis with emphasis on clinical usefulness and comparison with other imaging modalities.

METHODS

Research articles reporting carotid artery PET imaging with different radiotracers until 30 November 2018 were systematically searched for in Medline/PubMed, Scopus, Embase, Google Scholar, and Cochrane Library. Duplicates were removed, and editorials, case studies, and investigations on feasibility or reproducibility of PET imaging and of patients with end-stage diseases or immunosuppressive medications were omitted. After quality assessment of included articles using Joanna Briggs Institute checklists, all eligible articles were reviewed.

RESULTS

Of 1718 primary hits, 53 studies comprising 4472 patients, aged 47-91 years (78.8% males), were included and grouped under the following headlines: diagnostic performance, risk factors, laboratory findings, imaging modalities, and treatment. ¹⁸F-fluorodeoxyglucose (FDG) (49/53) and ¹⁸F-sodium fluoride (NaF) (5/53) were the most utilized tracers to visualize carotid wall inflammation and microcalcification, respectively. Higher carotid FDG uptake was demonstrated in patients with than without symptomatic carotid atherosclerosis. Normal carotid arteries presented with the lowest FDG uptake. In symptomatic atherosclerosis, carotid arteries ipsilateral to a cerebrovascular event had higher FDG uptake than the contralateral carotid artery. FDG uptake was significantly associated with age, male gender, and body mass index in healthy individuals, and in addition with arterial hypertension, hypercholesterolemia, and diabetes mellitus in patients. Histological assessment indicated a strong correlation between microcalcification and NaF uptake in symptomatic patients. Histological evidence of calcification correlated inversely with FDG uptake, which was associated with increased macrophage and CD68 count, both accounting for increased local inflammatory response.

CONCLUSION

FDG-PET visualizes the inflammatory part of carotid atherosclerosis enabling risk stratification to a certain degree, whereas NaF-PET seems to indicate long-term consequences of ongoing inflammation by demonstrating microcalcification allowing discrimination of atherosclerotic from normal arteries and suggesting clinically significant carotid atherosclerosis.

Atherosclerosis imaging with 18F-sodium fluoride PET: state-of-the-art review

Purpose

We examined the literature to elucidate the role of 18F-sodium fluoride (NaF)-PET in atherosclerosis.

Methods

Following a systematic search of PubMed/MEDLINE, Embase, and Cochrane Library included articles underwent subjective quality assessment with categories low, medium, and high. Of 2811 records, 1780 remained after removal of duplicates. Screening by title and abstract left 41 potentially eligible full-text articles, of which 8 (about the aortic valve (n = 1), PET/MRI feasibility (n = 1), aortic aneurysms (n = 1), or quantification methodology (n = 5)) were dismissed, leaving 33 published 2010–2012 (n = 6), 2013–2015 (n = 11), and 2016–2018 (n = 16) for analysis.

Results

They focused on coronary (n = 8), carotid (n = 7), and femoral arteries (n = 1), thoracic aorta (n = 1), and infrarenal aorta (n = 1). The remaining 15 studies examined more than one arterial segment. The literature was heterogeneous: few studies were designed to investigate atherosclerosis, 13 were retrospective, 9 applied both FDG and NaF as tracers, 24 NaF only. Subjective quality was low in one, medium in 13, and high in 19 studies. The literature indicates that NaF is a very specific tracer that mimics active arterial wall microcalcification, which is positively associated with cardiovascular risk. Arterial NaF uptake often presents before CT-calcification, tends to decrease with increasing density of CT-calcification, and appears, rather than FDG-avid foci, to progress to CT-calcification. It is mainly surface localized, increases with age with a wide scatter but without an obvious sex difference. NaF-avid microcalcification can occur in fatty streaks, but the degree of progression to CT-calcification is unknown. It remains unknown whether medical therapy influences microcalcification. The literature held no therapeutic or randomized controlled trials.

Conclusion

The literature was heterogeneous and with few clear cut messages. NaF-PET is a new approach to detect and quantify microcalcification in early-stage atherosclerosis. NaF uptake correlates with cardiovascular risk factors and appears to be a good measure of the body’s atherosclerotic burden, potentially suited also for assessment of anti-atherosclerotic therapy.

Electronic supplementary material

The online version of this article (10.1007/s00259-019-04603-1) contains supplementary material, which is available to authorized users.

Association between carotid 18F-NaF and 18F-FDG uptake on PET/CT with ischemic vascular brain disease on MRI in patients with carotid artery disease

OBJECTIVE

Atherosclerosis is a dynamic and complex process characterized by the formation and progression of plaque mediated by various pathophysiologic steps including inflammation and calcification. The present study aimed to evaluate the association between carotid ¹⁸F-sodium fluoride (NaF) and ¹⁸F-fluorodeoxyglucose (FDG) uptake with the severity of ischemic vascular brain disease on MRI in patients with carotid artery disease.

METHODS

A total of 28 patients who were scheduled to undergo clinically indicated carotid endarterectomy or stenting for carotid artery disease were examined with ¹⁸F-NaF and ¹⁸F-FDG PET/CT and brain MRI. The PET/CT images were evaluated by qualitative and semiquantitative analyses. The maximum standardized uptake value (SUV) for the plaque and the average of mean SUV within the lumen of both internal jugular veins was calculated, and the target-to-blood pool ratio (TBR) was determined. The ischemic vascular brain disease on MRI was graded separately in the bilateral hemisphere as 0, 1, 2, and 3, with 0 being absent and 3 being the most severe.

RESULTS

In two patients, only a unilateral carotid artery was analyzed because of previous indwelling stent. ¹⁸F-NaF focal uptake was observed in 50 carotid arteries. ¹⁸F-FDG focal uptake was observed in 47 carotid arteries. The mean (± SD) ¹⁸F-NaF TBR (2.93 ± 0.89) was significantly higher than the mean (± SD) ¹⁸F-FDG TBR (2.41 ± 0.84) (p < 0.001). The mean (± SD) values of ¹⁸F-NaF TBR were 2.63 ± 0.76 in grade 1, 2.90 ± 0.91 in grade 2, and 3.81 ± 0.60 in grade 3. Significant differences in ¹⁸F-NaF TBR were observed between grades 1 and 3 (p < 0.001) and grades 2 and 3 (p = 0.02). The mean (± SD) values of ¹⁸F-FDG TBR were 2.35 ± 0.77 in grade 1, 2.23 ± 0.48 in grade 2, and 2.87 ± 1.32 in grade 3. No significant differences in ¹⁸F-FDG TBR were noted between any of the ischemic vascular brain disease grades.

CONCLUSIONS

These preliminary results suggest that carotid ¹⁸F-NaF uptake in patients with carotid artery disease may be associated with the severity of the ischemic vascular brain disease observed on MRI.

18F-sodium fluoride positron emission tomography assessed microcalcifications in culprit and non-culprit human carotid plaques

BACKGROUND

18F-NaF positron emission tomography (PET) targets microcalcifications. We compared in vitro microPET assessed 18F-NaF uptake between culprit and non-culprit human carotid plaques. Furthermore, we compared 18F-NaF uptake with calcification visualized on microcomputed tomography (microCT).

METHODS

Carotid plaques from stroke patients undergoing surgery were incubated in 18F-NaF and scanned using a microPET and a microCT scan. The average PET assessed 18F-NaF uptake was expressed as percentage of the incubation dose per gram (%Inc/g). 18F-NaF PET volume of interest (VOI) was compared with CT calcification VOI.

RESULTS

23 carotid plaques (17 culprit, 6 non-culprit) were included. The average 18F-NaF uptake in culprit carotid plaques was comparable with the uptake in non-culprit carotid plaques (median 2.32 %Inc/g [IQR 1.98 to 2.81] vs. median 2.35 %Inc/g [IQR 1.77 to 3.00], P = 0.916). Only a median of 10% (IQR 4 to 25) of CT calcification VOI showed increased 18F-NaF uptake, while merely a median of 35% (IQR 6 to 42) of 18F-NaF PET VOI showed calcification on CT.

CONCLUSIONS

18F-NaF PET represents a different stage in the calcification process than CT. We observed a similar PET assessed 18F-NaF uptake and pattern in culprit and non-culprit plaques of high-risk patients, indicating that this method may be of more value in early atherosclerotic stenosis development.

Carotid Plaque Positron Emission Tomography Imaging and Cerebral Ischemic Disease

Background and Purpose- The clinical utility of positron emission tomography (PET) imaging in evaluating carotid artery plaque vulnerability remains unclear. Two tracers of recent interest for carotid plaque imaging are ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) and ¹⁸F-sodium fluoride (¹⁸F-NaF). We performed a systematic review and meta-analysis evaluating the association between carotid artery ¹⁸F-FDG or ¹⁸F-NaF uptake and recent or future cerebral ischemic events. Methods- A systematic review of Ovid MEDLINE, Ovid EMBASE, and the Cochrane library was conducted from inception to December 2017 for articles evaluating PET tracer uptake in recently symptomatic versus asymptomatic carotid arteries, and articles evaluating carotid uptake in relation to future ischemic events. Cerebral ischemic events were defined as ipsilateral strokes, transient ischemic attacks, or amaurosis fugax. We quantitatively pooled studies by a random-effects model when 3 or more studies were amenable for analysis. We assessed the standardized mean difference between tracer uptake in the symptomatic versus asymptomatic carotid artery using Cohen's d metric. Results- After screening 4144 unique articles, 13 prospective cohort studies assessing carotid artery ¹⁸F-FDG uptake in patients with recent cerebral ischemia were eligible for review. Eleven cohorts of 290 subjects scanned with ¹⁸F-FDG were eligible for meta-analysis. We found that carotid arteries ipsilateral to recent ischemic events had significantly higher ¹⁸F-FDG uptake than asymptomatic arteries (Cohen's d =0.492; CI=0.130-0.855; P=0.008) as well as significant heterogeneity (Cochran's Q =31.5; P=0.0005; I²=68.3%). Meta-regression was not performed due to the limited number of studies in the analysis. Only 2 studies investigating ¹⁸F-NaF PET imaging, and another 2 articles investigating ischemic event recurrence were found. Conclusions- Recent ipsilateral cerebral ischemia may be associated with increased carotid ¹⁸F-FDG uptake on PET imaging regardless of degree of carotid stenosis, although significant heterogeneity was found, and these results should be interpreted with caution. Emerging evidence suggests a similar association may be present with ¹⁸F-NaF plaque uptake. More studies are warranted to provide definitive conclusions on the utility of ¹⁸F-FDG or ¹⁸F-NaF in carotid plaque evaluation before investigating carotid PET as a diagnostic tool for cerebral ischemic events.

Mannose impairs tumour growth and enhances chemotherapy

It is now well established that tumours undergo changes in cellular metabolism1. As this can reveal tumour cell vulnerabilities and because many tumours exhibit enhanced glucose uptake2, we have been interested in how tumour cells respond to different forms of sugar. Here we report that the monosaccharide mannose causes growth retardation in several tumour types in vitro, and enhances cell death in response to major forms of chemotherapy. We then show that these effects also occur in vivo in mice following the oral administration of mannose, without significantly affecting the weight and health of the animals. Mechanistically, mannose is taken up by the same transporter(s) as glucose3 but accumulates as mannose-6-phosphate in cells, and this impairs the further metabolism of glucose in glycolysis, the tricarboxylic acid cycle, the pentose phosphate pathway and glycan synthesis. As a result, the administration of mannose in combination with conventional chemotherapy affects levels of anti-apoptotic proteins of the Bcl-2 family, leading to sensitization to cell death. Finally we show that susceptibility to mannose is dependent on the levels of phosphomannose isomerase (PMI). Cells with low levels of PMI are sensitive to mannose, whereas cells with high levels are resistant, but can be made sensitive by RNA-interference-mediated depletion of the enzyme. In addition, we use tissue microarrays to show that PMI levels also vary greatly between different patients and different tumour types, indicating that PMI levels could be used as a biomarker to direct the successful administration of mannose. We consider that the administration of mannose could be a simple, safe and selective therapy in the treatment of cancer, and could be applicable to multiple tumour types.

18F-FDG Uptake on PET/CT in Symptomatic versus Asymptomatic Carotid Disease: a Meta-Analysis

INTRODUCTION

The role of positron emission tomography (PET)/computed tomography (CT) in the determination of inflammation in arterial disease is not well defined. This can provide information about arterial wall inflammation in atherosclerotic disease, and may give insight into plaque stability. The aim of this review was to perform a meta-analysis of PET/CT with ¹⁸F-FDG (fluorodeoxyglucose) uptake in symptomatic and asymptomatic carotid artery disease.

METHODS

This was a systematic review, following PRISMA guidelines, which interrogated the MEDLINE database from January 2001 to May 2017. The search combined the terms, "inflammation", "FDG", and "stroke". The search criteria included all types of studies, with a primary outcome of the degree of arterial vascular inflammation determined by ¹⁸F-FDG uptake. Analysis involved an inverse weighted variance estimate of pooled data, using a random effects model.

RESULTS

A total of 14 articles (539 patients) were included in the meta-analysis. Comparing carotid artery ¹⁸F-FDG uptake in symptomatic versus asymptomatic disease yielded a standard mean difference of 0.94 (95% CI 0.58-1.130; p < .0001; I² = 65%).

CONCLUSIONS

PET/CT using ¹⁸F-FDG can demonstrate carotid plaque inflammation, and is a marker of symptomatic disease. Further studies are required to understand the clinical implication of PET/CT as a risk prediction tool.

Noninvasive Assessment of Carotid Plaques Calcification by 18F-Sodium Fluoride Accumulation: Correlation with Pathology

BACKGROUD

Vascular calcification is currently recognized as an important pathobiological process in atherosclerosis, but the mechanism remains elusive. Given the similarities in vascular calcification and bone formation, ¹⁸F-sodium fluoride (¹⁸F-NaF) is now considered a novel marker of vascular calcification. This study aimed to correlate ¹⁸F-NaF accumulation with the histological characterization of vascular calcification in carotid plaques.

METHODS

A total of 8 patients who were undergoing carotid endarterectomy (CEA) for carotid artery stenosis were recruited. Before CEA, ¹⁸F-NaF positron emission tomography and computed tomography (PET-CT) studies were conducted. ¹⁸F-NaF uptake was measured by the maximum standardized uptake value and the target-to-background ratio. The Hounsfield unit (HU) value was also measured. Postoperative carotid plaques were investigated by hematoxylin and eosin staining, alizarin red staining, and immunohistochemistry (alpha-smooth muscle actin and CD68).

RESULTS

¹⁸F-NaF uptake was observed in the bilateral carotid bifurcation of all patients. Compared with the pathology results, there was a significant correlation between tracer activity in the carotid plaques and the calcification in the corresponding histological sections (integrated optical density [IOD]: r = .781, P = .022; positive area: r = .765, P = .027). A negative correlation was observed between ¹⁸F-NaF uptake and smooth muscle cell staining (IOD: r = -.710, P = .049). ¹⁸F-NaF uptake did not correlate with carotid artery stenosis, HU value, or inflammation.

CONCLUSIONS

¹⁸F-NaF PET-CT is a noninvasive imaging method for the assessment of calcification in human carotid atherosclerotic plaques and a promising approach to studying calcification in atherosclerotic lesions.

18F-Fluoride and 18F-Fluorodeoxyglucose Positron Emission Tomography After Transient Ischemic Attack or Minor Ischemic Stroke: Case-Control Study

Supplemental Digital Content is available in the text.

Background—

Combined positron emission tomography (PET) and computed tomography (CT) can assess both anatomy and biology of carotid atherosclerosis. We sought to assess whether ¹⁸F-fluoride or ¹⁸F-fluorodeoxyglucose can identify culprit and high-risk carotid plaque.

Methods and Results—

We performed ¹⁸F-fluoride and ¹⁸F-fluorodeoxyglucose PET/CT in 26 patients after recent transient ischemic attack or minor ischemic stroke: 18 patients with culprit carotid stenosis awaiting carotid endarterectomy and 8 controls without culprit carotid atheroma. We compared standardized uptake values in the clinically adjudicated culprit to the contralateral asymptomatic artery, and assessed the relationship between radiotracer uptake and plaque phenotype or predicted cardiovascular risk (ASSIGN score [Assessing Cardiovascular Risk Using SIGN Guidelines to Assign Preventive Treatment]). We also performed micro PET/CT and histological analysis of excised plaque. On histological and micro PET/CT analysis, ¹⁸F-fluoride selectively highlighted microcalcification. Carotid ¹⁸F-fluoride uptake was increased in clinically adjudicated culprit plaques compared with asymptomatic contralateral plaques (log₁₀standardized uptake value_mean 0.29±0.10 versus 0.23±0.11, P=0.001) and compared with control patients (log₁₀standardized uptake value_mean 0.29±0.10 versus 0.12±0.11, P=0.001). ¹⁸F-Fluoride uptake correlated with high-risk plaque features (remodeling index [r=0.53, P=0.003], plaque burden [r=0.51, P=0.004]), and predicted cardiovascular risk [r=0.65, P=0.002]). Carotid ¹⁸F-fluorodeoxyglucose uptake appeared to be increased in 7 of 16 culprit plaques, but no overall differences in uptake were observed in culprit versus contralateral plaques or control patients. However, ¹⁸F-fluorodeoxyglucose did correlate with predicted cardiovascular risk (r=0.53, P=0.019), but not with plaque phenotype.

Conclusions—

¹⁸F-Fluoride PET/CT highlights culprit and phenotypically high-risk carotid plaque. This has the potential to improve risk stratification and selection of patients who may benefit from intervention.

Nε-(carboxymethyl)lysine Concentration in Debris from Carotid Artery Stenting Correlates Independently with Signal Intensity on T1-Weighted Black-Blood Magnetic Resonance Images

BACKGROUND AND PURPOSE

Because magnetic resonance imaging (MRI) focuses on the morphological characteristics of carotid artery plaques, its diagnostic value with respect to plaque vulnerability is limited. We examined the correlation between N^ε-(carboxymethyl)lysine (CML), a main chemical structure of advanced glycation end-products, and the vulnerability of plaques visualized on MRI scans.

MATERIALS AND METHODS

We enrolled 43 patients who had undergone carotid artery stenting (CAS) for carotid artery stenosis; all underwent MRI studies, including black-blood MRI and diffusion-weighted imaging (DWI). The signal intensity ratio (SIR) of plaques to adjacent sternocleidomastoid muscle (P/M) on T1- and T2-weighted images (T1WI, T2WI) was calculated. Protein samples were extracted from debris trapped by a filter device. The concentrations of CML and myeloperoxidase (MPO) were measured by solid-phase enzyme-linked immunosorbent assay.

RESULTS

The patients were classified into 2 groups based on their SIR-P/M on T1WI and T2WI scans. We observed a higher incidence of post-CAS DWI lesions in patients with a higher than a lower SIR-P/M on T1WI; the CML and MPO concentrations in their CAS debris were also higher. No such differences were seen in patients with a higher or lower SIR-P/M on T2WI scans. The concentration of CML in CAS debris correlated independently with the SIR-P/M on T1WI of the carotid plaques, and was related to the concentration of MPO in CAS debris.

CONCLUSIONS

Our findings suggest CML as a candidate molecular imaging probe for the identification of vulnerable plaques.