In search of the vulnerable patient or the vulnerable plaque: 18F-sodium fluoride positron emission tomography for cardiovascular risk stratification

Rosuvastatin effect on atherosclerotic plaque metabolism: A subclinical atherosclerosis imaging study with 18F-NaF PET-CT

BACKGROUND AND AIMS

Atherosclerotic plaque fluorine-18 sodium fluoride (18F-NaF) uptake on positron emission tomography with computed tomography (PET-CT) identifies active microcalcification and has been shown to correlate with clinical instability in patients with cardiovascular (CV) disease. Statin therapy promotes coronary macrocalcification over time. Our aim was to investigate rosuvastatin effect on atheroma 18F-NaF uptake.

METHODS

Subjects with high CV risk but without CV events underwent 18F-NaF-PET-CT in a single-centre. Those with subclinical atherosclerosis and significant 18F-NaF plaque uptake were included in a single-arm clinical trial, treated with rosuvastatin 20 mg/daily for six months, and re-evaluated by 18F-NaF-PET-CT. Primary endpoint was reduction in maximum atheroma 18F-NaF uptake in the coronary, aortic or carotid arteries, assessed by the tissue-to-background ratio (TBR). The secondary endpoint was corrected uptake per lesion (CUL) variation.

RESULTS

Forty individuals were enrolled and 38 included in the pharmacological trial; mean age was 64 years, two-thirds were male and most were diabetic. The 10-year expected CV risk was 9.5% (6.0-15.3) for SCORE2 and 31.7 ± 18.7% for ASCVD systems. After six months of rosuvastatin treatment (n = 34), low-density lipoprotein cholesterol lowered from 133.6 ± 33.8 to 58.8 ± 20.7 mg dL-1 (60% relative reduction, p < 0.01). There was a significant 19% reduction in maximum plaque 18F-NaF uptake after treatment, from 1.96 (1.78-2.22) to 1.53 (1.40-2.10), p < 0.001 (primary endpoint analysis). The secondary endpoint CUL was reduced by 23% (p = 0.003).

CONCLUSION

In a single-centre non-randomized clinical trial of high CV risk individuals with subclinical atherosclerosis, the maximum atherosclerotic plaque 18F-NaF uptake was significantly reduced after six months of high-intensity statin.

Role of 18F-sodium fluoride positron emission tomography in imaging atherosclerosis

Atherosclerosis involving vascular beds across the human body remains the leading cause of death worldwide. Coronary and peripheral artery disease, which are almost universally a result of atherosclerotic plaque, can manifest clinically as myocardial infarctions, ischemic stroke, or acute lower-limb ischemia. Beyond imaging myocardial perfusion and blood-flow, nuclear imaging has the potential to depict the activity of the processes that are directly implicated in the atherosclerotic plaque progression and rupture. Out of several tested tracers to date, the literature is most advanced for 18F-sodium fluoride positron emission tomography. In this review, we present the latest data in the field of atherosclerotic 18F-sodium fluoride positron emission tomography imaging, discuss the advantages and limitation of the techniques, and highlight the aspects that require further research in the future.

Automated nonlinear registration of coronary PET to CT angiography using pseudo-CT generated from PET with generative adversarial networks

BACKGROUND

Coronary 18F-sodium-fluoride (18F-NaF) positron emission tomography (PET) showed promise in imaging coronary artery disease activity. Currently image processing remains subjective due to the need for manual registration of PET and computed tomography (CT) angiography data. We aimed to develop a novel fully automated method to register coronary 18F-NaF PET to CT angiography using pseudo-CT generated by generative adversarial networks (GAN).

METHODS

A total of 169 patients, 139 in the training and 30 in the testing sets were considered for generation of pseudo-CT from non-attenuation corrected (NAC) PET using GAN. Non-rigid registration was used to register pseudo-CT to CT angiography and the resulting transformation was used to align PET with CT angiography. We compared translations, maximal standard uptake value (SUVmax) and target to background ratio (TBRmax) at the location of plaques, obtained after observer and automated alignment.

RESULTS

Automatic end-to-end registration was performed for 30 patients with 88 coronary vessels and took 27.5 seconds per patient. Difference in displacement motion vectors between GAN-based and observer-based registration in the x-, y-, and z-directions was 0.8 ± 3.0, 0.7 ± 3.0, and 1.7 ± 3.9 mm, respectively. TBRmax had a coefficient of repeatability (CR) of 0.31, mean bias of 0.03 and narrow limits of agreement (LOA) (95% LOA: - 0.29 to 0.33). SUVmax had CR of 0.26, mean bias of 0 and narrow LOA (95% LOA: - 0.26 to 0.26).

CONCLUSION

Pseudo-CT generated by GAN are perfectly registered to PET can be used to facilitate quick and fully automated registration of PET and CT angiography.

Novel PET Applications and Radiotracers for Imaging Cardiovascular Pathophysiology

PET allows the assessment of cardiovascular pathophysiology across a wide range of cardiovascular conditions. By imaging processes directly involved in disease progression and adverse events, such as inflammation and developing calcifications (microcalcifications), PET can not only enhance our understanding of cardiovascular disease, but also, as shown for 18F-sodium fluoride, has the potential to predict hard endpoints. In this review, the recent advances in disease activity assessment with cardiovascular PET, which provide hope that this promising technology could be leveraged in the clinical setting, shall be discussed.

Unravelling the role of macrophages in cardiovascular inflammation through imaging: a state-of-the-art review

Cardiovascular disease remains the leading cause of death and disability for patients across the world. Our understanding of atherosclerosis as a primary cholesterol issue has diversified, with a significant dysregulated inflammatory component that largely remains untreated and continues to drive persistent cardiovascular risk. Macrophages are central to atherosclerotic inflammation, and they exist along a functional spectrum between pro-inflammatory and anti-inflammatory extremes. Recent clinical trials have demonstrated a reduction in major cardiovascular events with some, but not all, anti-inflammatory therapies. The recent addition of colchicine to societal guidelines for the prevention of recurrent cardiovascular events in high-risk patients with chronic coronary syndromes highlights the real-world utility of this class of therapies. A highly targeted approach to modification of interleukin-1-dependent pathways shows promise with several novel agents in development, although excessive immunosuppression and resulting serious infection have proven a barrier to implementation into clinical practice. Current risk stratification tools to identify high-risk patients for secondary prevention are either inadequately robust or prohibitively expensive and invasive. A non-invasive and relatively inexpensive method to identify patients who will benefit most from novel anti-inflammatory therapies is required, a role likely to be fulfilled by functional imaging methods. This review article outlines our current understanding of the inflammatory biology of atherosclerosis, upcoming therapies and recent landmark clinical trials, imaging modalities (both invasive and non-invasive) and the current landscape surrounding functional imaging including through targeted nuclear and nanobody tracer development and their application.

The effect of Vitamin-K1 and Colchicine on Vascular Calcification Activity in subjects with Diabetes Mellitus (ViKCoVaC): A double-blind 2x2 factorial randomized controlled trial

BACKGROUND

There is currently no treatment for attenuating progression of arterial calcification. 18F-sodium fluoride positron emission tomography (18F-NaF PET) locates regions of calcification activity. We tested whether vitamin-K1 or colchicine affected arterial calcification activity.

METHODS

154 patients with diabetes mellitus and coronary calcification, as detected using computed tomography (CT), were randomized to one of four treatment groups (placebo/placebo, vitamin-K1 [10 mg/day]/placebo, colchicine [0.5 mg/day]/placebo, vitamin-K1 [10 mg/day]/ colchicine [0.5 mg/day]) in a double-blind, placebo-controlled 2x2 factorial trial of three months duration. Change in coronary calcification activity was estimated as a change in coronary maximum tissue-to-background ratio (TBRmax) on 18F-NaF PET.

RESULTS

149 subjects completed follow-up (vitamin-K1: placebo = 73:76 and colchicine: placebo = 73:76). Neither vitamin-K1 nor colchicine had a statistically significant effect on the coronary TBRmax compared with placebo (mean difference for treatment groups 0·00 ± 0·16 and 0·01 ± 0·17, respectively, p > 0.05). There were no serious adverse effects reported with colchicine or vitamin-K1.

CONCLUSIONS

In patients with type 2 diabetes, neither vitamin-K1 nor colchicine significantly decreases coronary calcification activity, as estimated by 18F-NaF PET, over a period of 3 months.

CLINICAL TRIAL REGISTRATION

ACTRN12616000024448.

Advances in positron emission tomography tracers related to vascular calcification

Microcalcification, a type of vascular calcification, increases the instability of plaque and easily leads to acute clinical events. Positron emission tomography (PET) is a new examination technology with significant advantages in identifying vascular calcification, especially microcalcification. The use of the ¹⁸F-NaF is undoubtedly the benchmark, and other PET tracers related to vascular calcification are also currently in development. Despite all this, a large number of studies are still needed to further clarify the specific mechanisms and characteristics. This review aimed at providing a summary of the application and progress of different PET tracers and also the future development direction.

In Vivo Coronary 18F-Sodium Fluoride Activity: Correlations With Coronary Plaque Histological Vulnerability and Physiological Environment

OBJECTIVES

This prospective study aimed to evaluate the associations between in vivo coronary ¹⁸F-sodium fluoride (¹⁸F-NaF) positron emission tomography (PET)/computed tomography (CT) activity and ex vivo histological characteristics, to determine whether coronary ¹⁸F-NaF activity is a novel biomarker of plaque pathological vulnerability, and to explore the underlying physiological environment of ¹⁸F-NaF adsorption to vascular microcalcification.

BACKGROUND

¹⁸F-NaF PET/CT is a promising new approach for assessing microcalcification in vascular plaque.

METHODS

Patients with coronary artery disease (CAD) underwent coronary computed tomography angiography (CTA) and ¹⁸F-NaF PET/CT. Histological vulnerability and immunohistochemical characteristics were evaluated in coronary endarterectomy (CE) specimens from patients who underwent coronary artery bypass grafting with adjunctive CE. Correlations between in-vivo coronary ¹⁸F-NaF activity with coronary CTA adverse plaque features and with ex vivo CE specimen morphological features, CD68 expression, inflammatory cytokines expression (tumor necrosis factor-α, interleukin-1β), osteogenic differentiation cytokines expression (osteopontin, runt-related transcription factor 2, osteocalcin) were evaluated. High- and low- to medium-risk plaques were defined by standard pathological classification.

RESULTS

A total of 55 specimens were obtained from 42 CAD patients. Coronary ¹⁸F-NaF activity of high-risk specimens was significantly higher than low- to medium-risk specimens (median [25th-75th percentile]: 1.88 [1.41-2.54] vs 1.12 [0.91-1.54]; P < 0.001). Coronary ¹⁸F-NaF activity showed high discriminatory accuracy in identifying high-risk plaque (AUC 0.80). Coronary CTA adverse plaque features (positive remodeling, low-attenuation plaque, remodeling index), histologically vulnerable features (large necrotic core, thin-fibro cap, microcalcification), CD68 expression, tumor necrosis factor-α expression, and interleukin-1β expression correlated with coronary ¹⁸F-NaF activity (all P < 0.05). No significant association between coronary ¹⁸F-NaF activity and osteogenic differentiation cytokines was found (all P > 0.05).

CONCLUSIONS

Coronary ¹⁸F-NaF activity was associated with histological vulnerability, CD68 expression, inflammatory cytokines expression, but not with osteogenic differentiation cytokines expression. ¹⁸F-NaF PET/CT imaging may provide a powerful tool for detecting high-risk coronary plaque and could improve the risk stratification of CAD patients.

18F-NaF PET uptake characteristics of coronary artery culprit lesions in a cohort of patients of acute coronary syndrome with ST-elevation myocardial infarction and chronic stable angina: A hybrid fluoride PET/CTCA study

BACKGROUND

18F-NaF PET/CT identifies high-risk plaques due to active calcification in coronary arteries with potential to characterize plaques in ST-elevation myocardial infarction (MI) and chronic stable angina (CSA) patients.

METHODS

Twenty-four MI and 17 CSA patients were evaluated with 18F-NaF PET/CTCA for SUVmax and TBR values of culprit and non-culprit plaques in both groups (inter-group and intra-group comparison), and pre- and post-interventional MI plaques sub-analysis.

RESULTS

Culprit plaques in MI patients had significantly higher SUVmax (1.6; IQR 0.6 vs 1.3; IQR 0.3, P = 0.03) and TBR (1.4; IQR 0.6 vs 1.1; IQR 0.4, P = 0.006) than culprit plaques of CSA. Pre-interventional culprit plaques of MI group (n = 11) revealed higher SUVmax (P = 0.007) and TBR (P = 0.008) values than culprit CSA plaques. Culprit plaques showed significantly higher SUVmax (P = 0.006) and TBR (P = 0.0003) than non-culprit plaques in MI group, but without significant difference between culprit and non-culprit plaques in CSA group. With median TBR cutoff value of 1.4 in MI culprit plaques, 6/7 plaques (85.7%) among the event prone non-culprit lesions had TBR values > 1.4 in CSA group.

CONCLUSION

The study shows higher SUVmax and TBR values in MI culprit plaques and comparable TBR values for event prone plaques of CSA group in identifying high-risk plaques.

Observer repeatability and interscan reproducibility of 18F-sodium fluoride coronary microcalcification activity

BACKGROUND

We aimed to establish the observer repeatability and interscan reproducibility of coronary 18F-sodium-fluoride positron emission tomography (PET) uptake using a novel semi-automated approach, coronary microcalcification activity (CMA).

METHODS

Patients with multivessel coronary artery disease underwent repeated hybrid PET and computed tomography angiography (CTA) imaging (PET/CTA). CMA was defined as the integrated standardized uptake values (SUV) in the entire coronary tree exceeding 2 standard deviations above the background SUV. Coefficients of repeatability between the same observer (intraobserver repeatability), between 2 observers (interobserver repeatability) and coefficient of reproducibility between 2 scans (interscan reproducibility), were determined at vessel and patient level.

RESULTS

In 19 patients, CMA was assessed twice in 43 coronary vessels on two PET/CT scans performed 12 ± 5 days apart. There was excellent intraclass correlation for intraobserver and interobserver repeatability as well as interscan reproducibility (all ≥ 0.991). There was 100% intraobserver, interobserver and interscan agreement for the presence (CMA > 0) or absence (CMA = 0) of coronary18F-NaF uptake. Mean CMA was 3.12 ± 0.62 with coefficients of repeatability of ≤ 10% for all measures: intraobserver 0.24 and 0.22, interobserver 0.30 and 0.29 and interscan 0.33 and 0.32 at a per-vessel and per-patient level, respectively.

CONCLUSIONS

CMA is a repeatable and reproducible global measure of coronary atherosclerotic activity.

Aortic valve imaging using 18F-sodium fluoride: impact of triple motion correction

BACKGROUND

Current 18F-NaF assessments of aortic valve microcalcification using 18F-NaF PET/CT are based on evaluations of end-diastolic or cardiac motion-corrected (ECG-MC) images, which are affected by both patient and respiratory motion. We aimed to test the impact of employing a triple motion correction technique (3 × MC), including cardiorespiratory and gross patient motion, on quantitative and qualitative measurements.

MATERIALS AND METHODS

Fourteen patients with aortic stenosis underwent two repeat 30-min PET aortic valve scans within (29 ± 24) days. We considered three different image reconstruction protocols; an end-diastolic reconstruction protocol (standard) utilizing 25% of the acquired data, an ECG-gated (four ECG gates) reconstruction (ECG-MC), and a triple motion-corrected (3 × MC) dataset which corrects for both cardiorespiratory and patient motion. All datasets were compared to aortic valve calcification scores (AVCS), using the Agatston method, obtained from CT scans using correlation plots. We report SUVmax values measured in the aortic valve and maximum target-to-background ratios (TBRmax) values after correcting for blood pool activity.

RESULTS

Compared to standard and ECG-MC reconstructions, increases in both SUVmax and TBRmax were observed following 3 × MC (SUVmax: Standard = 2.8 ± 0.7, ECG-MC = 2.6 ± 0.6, and 3 × MC = 3.3 ± 0.9; TBRmax: Standard = 2.7 ± 0.7, ECG-MC = 2.5 ± 0.6, and 3 × MC = 3.3 ± 1.2, all p values ≤ 0.05). 3 × MC had improved correlations (R2 value) to the AVCS when compared to the standard methods (SUVmax: Standard = 0.10, ECG-MC = 0.10, and 3 × MC = 0.20; TBRmax: Standard = 0.20, ECG-MC = 0.28, and 3 × MC = 0.46).

CONCLUSION

3 × MC improves the correlation between the AVCS and SUVmax and TBRmax and should be considered in PET studies of aortic valves using 18F-NaF.

The effect of vitamin K1 on arterial calcification activity in subjects with diabetes mellitus: a post hoc analysis of a double-blind, randomized, placebo-controlled trial

BACKGROUND

Coronary and aortic artery calcifications are generally slow to develop, and their burden predicts cardiovascular disease events. In patients with diabetes mellitus, arterial calcification is accelerated and calcification activity can be detected using 18F-sodium fluoride positron emission tomography (18F-NaF PET).

OBJECTIVES

We aimed to determine whether vitamin K1 supplementation inhibits arterial calcification activity in individuals with diabetes mellitus.

METHODS

This was a post hoc analysis of the ViKCoVaC (effect of Vitamin-K1 and Colchicine on Vascular Calcification activity in subjects with Diabetes Mellitus) double-blind randomized controlled trial conducted in Perth, Western Australia. Individuals with diabetes mellitus and established coronary calcification (coronary calcium score > 10), but without clinical coronary artery disease, underwent baseline 18F-NaF PET imaging, followed by oral vitamin K1 supplementation (10 mg/d) or placebo for 3 mo, after which 18F-NaF PET imaging was repeated. We tested whether individuals randomly assigned to vitamin K1 supplementation had reduced development of new 18F-NaF PET positive lesions within the coronary arteries and aorta.

RESULTS

In total, 149 individuals completed baseline and follow-up imaging studies. Vitamin K1 supplementation independently decreased the odds of developing new 18F-NaF PET positive lesions in the coronary arteries (OR: 0.35; 95% CI: 0.16, 0.78; P = 0.010), aorta (OR: 0.27; 95% CI: 0.08, 0.94; P = 0.040), and in both aortic and coronary arteries (OR: 0.28; 95% CI: 0.13, 0.63; P = 0.002).

CONCLUSIONS

In individuals with diabetes mellitus, supplementation with 10 mg vitamin K1/d may prevent the development of newly calcifying lesions within the aorta and the coronary arteries as detected using 18F-NaF PET. Further long-term studies are needed to test this hypothesis.This trial was registered at anzctr.org.au as ACTRN12616000024448.

Determinants of 18F-NaF uptake in femoral arteries in patients with type 2 diabetes mellitus

BACKGROUND

The goal of this study was to investigate the potential determinants of 18F-NaF uptake in femoral arteries as a marker of arterial calcification in patients with type 2 diabetes and a history of arterial disease.

METHODS AND RESULTS

The study consisted of participants of a randomized controlled trial to investigate the effect of vitamin K2 (NCT02839044). In this prespecified analysis, subjects with type 2 diabetes and known arterial disease underwent full body 18F-NaF PET/CT. Target-to-background ratio (TBR) was calculated by dividing the mean SUVmax from both superficial femoral arteries by the SUVmean in the superior vena cava (SVC) and calcium mass was measured on CT. The association between 18F-NaF TBR and cardiovascular risk factors was investigated using uni- and multivariate linear regression corrected for age and sex. In total, 68 patients (mean age: 69 ± 8 years; male: 52) underwent 18F-NaF PET/CT. Higher CT calcium mass, total cholesterol, and HbA1c were associated with higher 18F-NaF TBR after adjusting.

CONCLUSION

This study shows that several modifiable cardiovascular risk factors (total cholesterol, triglycerides, HbA1c) are associated with femoral 18F-NaF tracer uptake in patients with type 2 diabetes.

Iterative reconstruction incorporating background correction improves quantification of [18F]-NaF PET/CT images of patients with abdominal aortic aneurysm

BACKGROUND

A confounding issue in [18F]-NaF PET/CT imaging of abdominal aortic aneurysms (AAA) is the spill in contamination from the bone into the aneurysm. This study investigates and corrects for this spill in contamination using the background correction (BC) technique without the need to manually exclude the part of the AAA region close to the bone.

METHODS

Seventy-two (72) datasets of patients with AAA were reconstructed with the standard ordered subset expectation maximization (OSEM) algorithm incorporating point spread function (PSF) modelling. The spill in effect in the aneurysm was investigated using two target regions of interest (ROIs): one covering the entire aneurysm (AAA), and the other covering the aneurysm but excluding the part close to the bone (AAAexc). ROI analysis was performed by comparing the maximum SUV in the target ROI (SUVmax(T)), the corrected cSUVmax (SUVmax(T) - SUVmean(B)) and the target-to-blood ratio (TBR = SUVmax(T)/SUVmean(B)) with respect to the mean SUV in the right atrium region.

RESULTS

There is a statistically significant higher [18F]-NaF uptake in the aneurysm than normal aorta and this is not correlated with the aneurysm size. There is also a significant difference in aneurysm uptake for OSEM and OSEM + PSF (but not OSEM + PSF + BC) when quantifying with AAA and AAAexc due to the spill in from the bone. This spill in effect depends on proximity of the aneurysms to the bone as close aneurysms suffer more from spill in than farther ones.

CONCLUSION

The background correction (OSEM + PSF + BC) technique provided more robust AAA quantitative assessments regardless of the AAA ROI delineation method, and thus it can be considered as an effective spill in correction method for [18F]-NaF AAA studies.

Advances in Quantitative Analysis of 18F-Sodium Fluoride Coronary Imaging

¹⁸F-sodium fluoride (¹⁸F-NaF) positron emission tomography (PET) has emerged as a promising noninvasive imaging tool for the assessment of active calcification processes in coronary artery disease. ¹⁸F-NaF uptake colocalizes to high-risk and ruptured atherosclerotic plaques. Most recently, ¹⁸F-NaF coronary uptake was shown to be a robust and independent predictor of myocardial infarction in patients with advanced coronary artery disease. In this review, we provide an overview of the advances in coronary ¹⁸F-NaF imaging. In particular, we discuss the recently developed and validated motion correction techniques which address heart contractions, tidal breathing, and patient repositioning during the prolonged PET acquisitions. Additionally, we discuss a novel quantification approach—the coronary microcalcification activity (which has been inspired by the widely employed method in oncology total active tumor volume measurement). This new method provides a single number encompassing ¹⁸F-NaF activity within the entire coronary vasculature rather than just information regarding a single area of most intense tracer uptake.

Coronary 18F-sodium fluoride PET detects high-risk plaque features on optical coherence tomography and CT-angiography in patients with acute coronary syndrome

BACKGROUND AND AIMS

¹⁸F-Sodium Fluoride Positron Emission Tomography (¹⁸F-NaF PET) non-invasively detects micro-calcification activity, the earliest stage of atherosclerotic arterial calcification. We studied the association between coronary ¹⁸F-NaF uptake and high-risk plaque features on intra-coronary optical coherence tomography (OCT) and CT-angiography (CTCA) and the potential application to patient-level risk stratification.

METHODS

Sixty-two prospectively recruited patients with acute coronary syndrome (ACS) underwent multi-vessel OCT, ¹⁸F-NaF PET and CTCA. The maximum tissue to background ratio (TBRmax = standardised uptake value (SUV)max/SUVbloodpool) was measured in each coronary segment on ¹⁸F-NaF PET scans. High-risk plaque features on OCT and CTCA were compared in matched coronary segments. The number of patients testing positive (>2SD above the normal range) for micro-calcification activity was determined.

RESULTS

In 62 patients (age, mean ± standard deviation (SD) = 61 ± 9 years, 85% male) the coronary segments with elevated ¹⁸F-NaF uptake had higher lipid arc (LA) (median [25th-75th centile]: 74° [35°-117°] versus 48° [15°-83°], p=0.021), higher prevalence of macrophages [n(%): 37 (62%) versus 89 (39%), p=0.008] and lower plaque free wall (PFW) (50° [7°-110°] versus 94° [34°-180°], p=0.027) on OCT, and a higher total plaque burden (p=0.011) and higher dense calcified plaque burden (p= 0.001) on CTCA, when compared with ¹⁸F-NaF negative segments. Patients grouped by increasing number of coronary lesions positive for microcalcification activity (0,1, ≥2) showed decreasing plaque free wall, increasing calcification and increasing macrophages on OCT (respectively p=0.008, p < 0.001 and p=0.028).

CONCLUSIONS

¹⁸F-NaF uptake is associated with high-risk plaque features on OCT and CTCA in a per-segment and per-patient analysis in subjects hospitalized for ACS.

18F-Sodium Fluoride Positron Emission Tomography Activity Predicts the Development of New Coronary Artery Calcifications

OBJECTIVE

The coronary calcium score (CCS) predicts cardiovascular disease risk in individuals with diabetes, and rate of progression of CCS is an additional and incremental marker of risk. ¹⁸F-sodium fluoride positron emission tomography (¹⁸F-NaF PET) detects early and active calcifications within the vasculature. We aimed to ascertain the relationship between ¹⁸F-NaF PET activity and CCS progression in patients with diabetes. Approach and Results: We identified individuals between 50 and 80 years with diabetes and no history of clinical coronary artery disease. Those with a CCS ≥10 were invited to undergo ¹⁸F-NaF PET scanning and then repeat CCS >2 years later. ¹⁸F-NaF PET and CCS analysis were performed on a per-coronary and a per-patient level. We compared the proportion of CCS progressors in ¹⁸F-NaF PET-positive versus ¹⁸F-NaF PET-negative coronary arteries. Forty-one participants with 163 coronary arteries underwent follow-up CCS 2.8±0.5 years later. ¹⁸F-NaF PET-positive coronary arteries (n=52) were more likely to be CCS progressors, compared with negative coronary arteries (n=111; 86.5% versus 52.3%, P<0.001). Adjusting for baseline CCS, ¹⁸F-NaF PET-positive disease was an independent predictor of subsequent CCS progression (odds ratio, 2.92 [95% CI, 1.32-6.45], P=0.008). All subjects (100%, 15/15) with ≥2 ¹⁸F-NaF-positive coronary arteries progressed in CCS.

CONCLUSIONS

In subjects with diabetes, ¹⁸F-NaF PET positivity at baseline, independently predicted the progression of calcifications within the coronary arteries 2.8 years later. These findings suggest ¹⁸F-NaF PET may be a promising technique for earlier identification of patients at higher risk of cardiovascular events.

Whole-vessel coronary 18F-sodium fluoride PET for assessment of the global coronary microcalcification burden

PURPOSE

18F-sodium fluoride (18F-NaF) has shown promise in assessing disease activity in coronary arteries, but currently used measures of activity - such as maximum target to background ratio (TBRmax) - are defined by single pixel count values. We aimed to develop a novel coronary-specific measure of 18F-NaF PET reflecting activity throughout the entire coronary vasculature (coronary microcalcification activity [CMA]).

METHODS

Patients with recent myocardial infarction and multi-vessel coronary artery disease underwent 18F-NaF PET and coronary CT angiography. We assessed the association between coronary 18F-NaF uptake (both TBRmax and CMA) and coronary artery calcium scores (CACS) as well as low attenuation plaque (LAP, attenuation < 30 Hounsfield units) volume.

RESULTS

In 50 patients (64% males, 63 ± 7 years), CMA and TBRmax were higher in vessels with LAP compared to those without LAP (1.09 [0.02, 2.34] versus 0.0 [0.0, 0.0], p < 0.001 and 1.23 [1.16, 1.37] versus 1.04 [0.93, 1.11], p < 0.001). Compared to a TBRmax threshold of 1.25, CMA > 0 had a higher diagnostic accuracy for detection of LAP: sensitivity of 93.1 (83.3-98.1)% versus 58.6 (44.9-71.4)% and a specificity of 95.7 (88.0-99.1)% versus 80.0 (68.7-88.6)% (both p < 0.001). 18F-NaF uptake assessed by CMA correlated more closely with LAP (r = 0.86, p < 0.001) than the CT calcium score (r = 0.39, p < 0.001), with these associations outperforming those observed for TBRmax values (LAP r = 0.63, p < 0.001; CT calcium score r = 0.30, p < 0.001).

CONCLUSIONS

Automated assessment of disease activity across the entire coronary vasculature is feasible using 18F-NaF CMA, providing a single measurement that has closer agreement with CT markers of plaque vulnerability than more traditional measures of plaque activity.

Coronary artery 18F-NaF PET analysis with the use of an elastic motion correction software

INTRODUCTION

18F-Sodium Fluoride Positron Emission Tomography (18F-NaF PET) is a novel molecular imaging modality with promise for use as a risk stratification tool in cardiovascular disease. There are limitations in the analysis of small and rapidly moving coronary arteries using traditional PET technology. We aimed to validate the use of a motion correction algorithm (eMoco) on coronary 18F-NaF PET outcome parameters.

METHODS

Patients admitted with an acute coronary syndrome underwent 18F-NaF PET and computed tomography coronary angiography. 18F-NaF PET data were analyzed using a diastolic reconstruction, an ungated reconstruction and the eMoco reconstruction.

RESULTS

Twenty patients underwent 18F-NaF PET imaging and 17 patients had at least one positive lesion that could be used to compare PET reconstruction datasets. eMoco improved noise (the coefficient of variation of the blood pool radiotracer activity) compared to the diastolic dataset (0.09 [0.07 to 0.12] vs 0.14[0.11 to 0.17], p < .001) and marginally improved coronary lesion maximum tissue-to-background ratios compared to the ungated dataset (1.33 [1.05 to 1.48]vs 1.29 [1.04 to 1.40], p = .011).

CONCLUSION

In this pilot dataset, the eMoco reconstruction algorithm for motion correction appears to have potential in improving coronary analysis of 18F-NaF PET by reducing noise and increasing maximum counts. Further testing in a larger patient dataset is warranted.

Analytical quantification of aortic valve 18F-sodium fluoride PET uptake

BACKGROUND

Challenges to cardiac PET-CT include patient motion, prolonged image acquisition and a reduction of counts due to gating. We compared two analytical tools, FusionQuant and OsiriX, for quantification of gated cardiac 18F-sodium fluoride (18F-fluoride) PET-CT imaging.

METHODS

Twenty-seven patients with aortic stenosis were included, 15 of whom underwent repeated imaging 4 weeks apart. Agreement between analytical tools and scan-rescan reproducibility was determined using the Bland-Altman method and Lin's concordance correlation coefficients (CCC).

RESULTS

Image analysis was faster with FusionQuant [median time (IQR) 7:10 (6:40-8:20) minutes] compared with OsiriX [8:30 (8:00-10:10) minutes, p = .002]. Agreement of uptake measurements between programs was excellent, CCC = 0.972 (95% CI 0.949-0.995) for mean tissue-to-background ratio (TBRmean) and 0.981 (95% CI 0.965-0.997) for maximum tissue-to-background ratio (TBRmax). Mean noise decreased from 11.7% in the diastolic gate to 6.7% in motion-corrected images (p = .002); SNR increased from 25.41 to 41.13 (p = .0001). Aortic valve scan-rescan reproducibility for TBRmax was improved with FusionQuant using motion correction compared to OsiriX (error ± 36% vs ± 13%, p < .001) while reproducibility for TBRmean was similar (± 10% vs ± 8% p = .252).

CONCLUSION

18F-fluoride PET quantification with FusionQuant and OsiriX is comparable. FusionQuant with motion correction offers advantages with respect to analysis time and reproducibility of TBRmax values.

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.

Selection of abstracts from the scientific sessions of The Society Of Nuclear Medicine and Molecular Imaging annual meeting Anaheim CA

This mini-review highlights cardiovascular studies that were presented during the Society of Nuclear Medicine and Molecular Imaging (SNMMI) 2019 annual meeting in Anaheim, California. The aim is to provide the readers insight to noteworthy studies related to the fields of nuclear cardiology presented during the conference. Although cardiovascular applications of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are not the primary focus of the SNMMI, several scientific teams working in this field presented their latest findings in Anaheim. While this review is directed to the benefit of those who were not able to attend the annual meeting, we believe that a general overview may also be useful for those who did attend as it is often difficult to get exposure to all the high-quality abstracts presented at this large conference.