Feasibility of Coronary 18F-Sodium Fluoride Positron-Emission Tomography Assessment With the Utilization of Previously Acquired Computed Tomography Angiography

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.

Increased Subclinical Coronary Artery Pathology in Type 2 Diabetes With Albuminuria

Diabetes affects the kidneys, and the presence of albuminuria reflects widespread vascular damage and is a risk factor for cardiovascular disease (CVD). Still, the pathophysiological association between albuminuria and CVD remains incompletely understood. Recent advances in noninvasive imaging enable functional assessment of coronary artery pathology and present an opportunity to explore the association between albuminuria and CVD. In this cross-sectional study, we evaluated the presence of subclinical coronary artery pathology in people with type 2 diabetes, free of overt CVD. Using multimodal imaging, we assessed the coronary microcalcification activity (18F-sodium fluoride positron emission tomography/computed tomography [PET/CT], plaque inflammation [64Cu-DOTATATE PET/CT], and myocardial flow reserve [82Rb PET/CT]). The study population consisted of 90 participants, stratified by albuminuria; 60 had historic or current albuminuria (urine albumin-to-creatinine ratio [UACR] ≥30 mg/g]), and 30 had normoalbuminuria (UACR <30 mg/g). We demonstrated that any albuminuria (historic or current) was associated with a more severe phenotype, in particular, higher levels of microcalcifications and impaired myocardial microvascular function; however, coronary inflammation activity was similar in people with and without albuminuria. Our findings establish a potential underlying mechanism connecting cardiovascular and kidney diseases and could indicate the initial stages of the cardiorenal syndrome.

ARTICLE HIGHLIGHTS

Coronary Atherosclerotic Plaque Activity and Future Coronary Events

Importance

Recurrent coronary events in patients with recent myocardial infarction remain a major clinical problem. Noninvasive measures of coronary atherosclerotic disease activity have the potential to identify individuals at greatest risk.

Objective

To assess whether coronary atherosclerotic plaque activity as assessed by noninvasive imaging is associated with recurrent coronary events in patients with myocardial infarction.

Design, Setting, and Participants

This prospective, longitudinal, international multicenter cohort study recruited participants aged 50 years or older with multivessel coronary artery disease and recent (within 21 days) myocardial infarction between September 2015 and February 2020, with a minimum 2 years' follow-up.

Intervention

Coronary 18F-sodium fluoride positron emission tomography and coronary computed tomography angiography.

Main Outcomes and Measures

Total coronary atherosclerotic plaque activity was assessed by 18F-sodium fluoride uptake. The primary end point was cardiac death or nonfatal myocardial infarction but was expanded during study conduct to include unscheduled coronary revascularization due to lower than anticipated primary event rates.

Results

Among 2684 patients screened, 995 were eligible, 712 attended for imaging, and 704 completed an interpretable scan and comprised the study population. The mean (SD) age of participants was 63.8 (8.2) years, and most were male (601 [85%]). Total coronary atherosclerotic plaque activity was identified in 421 participants (60%). After a median follow-up of 4 years (IQR, 3-5 years), 141 participants (20%) experienced the primary end point: 9 had cardiac death, 49 had nonfatal myocardial infarction, and 83 had unscheduled coronary revascularizations. Increased coronary plaque activity was not associated with the primary end point (hazard ratio [HR], 1.25; 95% CI, 0.89-1.76; P = .20) or unscheduled revascularization (HR, 0.98; 95% CI, 0.64-1.49; P = .91) but was associated with the secondary end point of cardiac death or nonfatal myocardial infarction (47 of 421 patients with high plaque activity [11.2%] vs 19 of 283 with low plaque activity [6.7%]; HR, 1.82; 95% CI, 1.07-3.10; P = .03) and all-cause mortality (30 of 421 patients with high plaque activity [7.1%] vs 9 of 283 with low plaque activity [3.2%]; HR, 2.43; 95% CI, 1.15-5.12; P = .02). After adjustment for differences in baseline clinical characteristics, coronary angiography findings, and Global Registry of Acute Coronary Events score, high coronary plaque activity was associated with cardiac death or nonfatal myocardial infarction (HR, 1.76; 95% CI, 1.00-3.10; P = .05) but not with all-cause mortality (HR, 2.01; 95% CI, 0.90-4.49; P = .09).

Conclusions and Relevance

In this cohort study of patients with recent myocardial infarction, coronary atherosclerotic plaque activity was not associated with the primary composite end point. The findings suggest that risk of cardiovascular death or myocardial infarction in patients with elevated plaque activity warrants further research to explore its incremental prognostic implications.

Latent Coronary Plaque Morphology From Computed Tomography Angiography, Molecular Disease Activity on Positron Emission Tomography, and Clinical Outcomes

BACKGROUND

Assessments of coronary disease activity with 18F-sodium fluoride positron emission tomography and radiomics-based precision coronary plaque phenotyping derived from coronary computed tomography angiography may enhance risk stratification in patients with coronary artery disease. We sought to investigate whether the prognostic information provided by these 2 approaches is complementary in the prediction of myocardial infarction.

METHODS

Patients with known coronary artery disease underwent coronary 18F-sodium fluoride positron emission tomography and coronary computed tomography angiography on a hybrid positron emission tomography/computed tomography scanner. Coronary 18F-NaF uptake was determined by the coronary microcalcification activity. We performed quantitative plaque analysis of coronary computed tomography angiography datasets and extracted 1103 radiomic features for each plaque. Using weighted correlation network analysis, we derived latent morphological features of coronary lesions which were aggregated to patient-level radiomics nomograms to predict myocardial infarction.

RESULTS

Among 260 patients with established coronary artery disease (age, 65±9 years; 83% men), 179 (69%) participants showed increased coronary 18F-NaF activity (coronary microcalcification activity>0). Over 53 (40-59) months of follow-up, 18 patients had a myocardial infarction. Using weighted correlation network analysis, we derived 15 distinct eigen radiomic features representing latent morphological coronary plaque patterns in an unsupervised fashion. Following adjustments for calcified, noncalcified, and low-density noncalcified plaque volumes and 18F-NaF coronary microcalcification activity, 4 radiomic features remained independent predictors of myocardial infarction (hazard ratio, 1.46 [95% CI, 1.03-2.08]; P=0.03; hazard ratio, 1.62 [95% CI, 1.04-2.54]; P=0.02; hazard ratio, 1.49 [95% CI, 1.07-2.06]; P=0.01; and hazard ratio, 1.50 (95% CI, 1.05-2.13); P=0.02).

CONCLUSIONS

In patients with established coronary artery disease, latent coronary plaque morphological features, quantitative plaque volumes, and disease activity on 18F-sodium fluoride positron emission tomography are additive predictors of myocardial infarction.

The Role of Positron Emission Tomography in Advancing the Understanding of the Pathogenesis of Heart and Vascular Diseases

Cardiovascular disease remains the leading cause of morbidity and mortality worldwide. For developing new therapies, a better understanding of the underlying pathology is required. Historically, such insights have been primarily derived from pathological studies. In the 21st century, thanks to the advent of cardiovascular positron emission tomography (PET), which depicts the presence and activity of pathophysiological processes, it is now feasible to assess disease activity in vivo. By targeting distinct biological pathways, PET elucidates the activity of the processes which drive disease progression, adverse outcomes or, on the contrary, those that can be considered as a healing response. Given the insights provided by PET, this non-invasive imaging technology lends itself to the development of new therapies, providing a hope for the emergence of strategies that could have a profound impact on patient outcomes. In this narrative review, we discuss recent advances in cardiovascular PET imaging which have greatly advanced our understanding of atherosclerosis, ischemia, infection, adverse myocardial remodeling and degenerative valvular heart disease.

Advanced Cardiac Imaging in the Assessment of Aortic Stenosis

Aortic stenosis is the most common form of valve disease in the Western world and a major healthcare burden. Although echocardiography remains the central modality for the diagnosis and assessment of aortic stenosis, recently, advanced cardiac imaging with cardiovascular magnetic resonance, computed tomography, and positron emission tomography have provided invaluable pathological insights that may guide the personalized management of the disease. In this review, we discuss applications of these novel non-invasive imaging modalities for establishing the diagnosis, monitoring disease progression, and eventually planning the invasive treatment of aortic stenosis.

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.

Advances in the Assessment of Coronary Artery Disease Activity with PET/CT and CTA

Non-invasive testing plays a pivotal role in the diagnosis, assessment of progression, response to therapy, and risk stratification of coronary artery disease. Although anatomical plaque imaging by computed tomography angiography (CTA) and ischemia detection with myocardial perfusion imaging studies are current standards of care, there is a growing body of evidence that imaging of the processes which drive atherosclerotic plaque progression and rupture has the potential to further enhance risk stratification. In particular, non-invasive imaging of coronary plaque inflammation and active calcification has shown promise in this regard. Positron emission tomography (PET) with newly-adopted radiotracers provides unique insights into atheroma activity acting as a powerful independent predictor of myocardial infarctions. Similarly, by providing a quantitative measure of coronary inflammation, the pericoronary adipose tissue density (PCAT) derived from standard coronary CTA enhances cardiac risk prediction and allows re-stratification over and above current state-of-the-art assessments. In this review, we shall discuss the recent advances in the non-invasive methods of assessment of disease activity by PET and CTA, highlighting how these methods could improve risk stratification and ultimately benefit patients with coronary artery disease.

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.

Anatomical validation of automatic respiratory motion correction for coronary 18F-sodium fluoride positron emission tomography by expert measurements from four-dimensional computed tomography

BACKGROUND

Respiratory motion correction is of importance in studies of coronary plaques employing ¹⁸ F-NaF; however, the validation of motion correction techniques mainly relies on indirect measures such as test-retest repeatability assessments. In this study, we aim to compare and, thus, validate the respiratory motion vector fields obtained from the positron emission tomography (PET) images directly to the respiratory motion observed during four-dimensional cine-computed tomography (CT) by an expert observer.

PURPOSE

To investigate the accuracy of the motion correction employed in a software (FusionQuant) used for evaluation of ¹⁸ F-NaF PET studies by comparing the respiratory motion of the coronary plaques observed in PET to the respiratory motion observed in 4D cine-CT images.

METHODS

This study included 23 patients who undertook thoracic PET scans for the assessment of coronary plaques using ¹⁸ F-sodium fluoride (¹⁸ F-NaF). All patients underwent a 5-s cine-CT (4D-CT), a coronary CT angiography (CTA), and ¹⁸ F-NaF PET. The 4D-CT and PET scan were reconstructed into 10 phases. Respiratory motion was estimated for the non-contrast visible coronary plaques using diffeomorphic registrations (PET) and compared to respiratory motion observed on 4D-CT. We report the PET motion vector fields obtained in the three principal axes in addition to the 3D motion. Statistical differences were examined using paired t-tests. Signal-to-noise ratios (SNR) are reported for the single-phase images (end-expiratory phase) and for the motion-corrected image-series (employing the motion vector fields extracted during the diffeomorphic registrations).

RESULTS

In total, 19 coronary plaques were identified in 16 patients. No statistical differences were observed for the maximum respiratory motion observed in x, y, and the 3D motion fields (magnitude and direction) between the CT and PET (X direction: 4D CT = 2.5 ± 1.5 mm, PET = 2.4 ± 3.2 mm; Y direction: 4D CT = 2.3 ± 1.9 mm, PET = 0.7 ± 2.9 mm, 3D motion: 4D CT = 6.6 ± 3.1 mm, PET = 5.7 ± 2.6 mm, all p ≥ 0.05). Significant differences in respiratory motion were observed in the systems' Z direction: 4D CT = 4.9 ± 3.4 mm, PET = 2.3 ± 3.2 mm, p = 0.04. Significantly improved SNR is reported for the motion corrected images compared to the end-expiratory phase images (end-expiratory phase = 6.8±4.8, motion corrected = 12.2±4.5, p = 0.001).

CONCLUSION

Similar respiratory motion was observed in two directions and 3D for coronary plaques on 4D CT as detected by automatic respiratory motion correction of coronary PET using FusionQuant. The respiratory motion correction technique significantly improved the SNR in the images.

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.

Bypass Grafting and Native Coronary Artery Disease Activity

OBJECTIVES

The aim of this study was to describe the potential of 18F-sodium fluoride (18F-NaF) positron emission tomography (PET) to identify graft vasculopathy and to investigate the influence of coronary artery bypass graft (CABG) surgery on native coronary artery disease activity and progression.

BACKGROUND

As well as developing graft vasculopathy, CABGs have been proposed to accelerate native coronary atherosclerosis.

METHODS

Patients with established coronary artery disease underwent baseline 18F-NaF PET, coronary artery calcium scoring, coronary computed tomographic angiography, and 1-year repeat coronary artery calcium scoring. Whole-vessel coronary microcalcification activity (CMA) on 18F-NaF PET and change in calcium scores were quantified in patients with and without CABG surgery.

RESULTS

Among 293 participants (mean age 65 ± 9 years, 84% men), 48 (16%) underwent CABG surgery 2.7 years [IQR: 1.4-10.4 years] previously. Although all arterial and the majority (120 of 128 [94%]) of vein grafts showed no 18F-NaF uptake, 8 saphenous vein grafts in 7 subjects had detectable CMA. Bypassed native coronary arteries had 3 times higher CMA values (2.1 [IQR: 0.4-7.5] vs 0.6 [IQR: 0-2.7]; P < 0.001) and greater progression of 1-year calcium scores (118 Agatston unit [IQR: 48-194 Agatston unit] vs 69 [IQR: 21-142 Agatston unit]; P = 0.01) compared with patients who had not undergone CABG, an effect confined largely to native coronary plaques proximal to the graft anastomosis. In sensitivity analysis, bypassed native coronary arteries had higher CMA (2.0 [IQR: 0.4-7.5] vs 0.8 [IQR: 0.3-3.2]; P < 0.001) and faster disease progression (24% [IQR: 16%-43%] vs 8% [IQR: 0%-24%]; P = 0.002) than matched patients (n = 48) with comparable burdens of coronary artery disease and cardiovascular comorbidities in the absence of bypass grafting.

CONCLUSIONS

Native coronary arteries that have been bypassed demonstrate increased disease activity and more rapid disease progression than nonbypassed arteries, an observation that appears independent of baseline atherosclerotic plaque burden. Microcalcification activity is not a dominant feature of graft vasculopathy.

Respiration-averaged CT versus standard CT attenuation map for correction of 18F-sodium fluoride uptake in coronary atherosclerotic lesions on hybrid PET/CT

BACKGROUND

To evaluate the impact of respiratory-averaged computed tomography attenuation correction (RACTAC) compared to standard single-phase computed tomography attenuation correction (CTAC) map, on the quantitative measures of coronary atherosclerotic lesions of 18F-sodium fluoride (18F-NaF) uptake in hybrid positron emission tomography and computed tomography (PET/CT).

METHODS

This study comprised 23 patients who underwent 18F-NaF coronary PET in a hybrid PET/CT system. All patients had a standard single-phase CTAC obtained during free-breathing and a 4D cine-CT scan. From the cine-CT acquisition, RACTAC maps were obtained by averaging all images acquired over 5 seconds. PET reconstructions using either CTAC or RACTAC were compared. The quantitative impact of employing RACTAC was assessed using maximum target-to-background (TBRMAX) and coronary microcalcification activity (CMA). Statistical differences were analyzed using reproducibility coefficients and Bland-Altman plots.

RESULTS

In 23 patients, we evaluated 34 coronary lesions using CTAC and RACTAC reconstructions. There was good agreement between CTAC and RACTAC for TBRMAX (median [Interquartile range]): CTAC = 1.65 [1.23 to 2.38], RACTAC = 1.63 [1.23 to 2.33], p = 0.55), with coefficient of reproducibility of 0.18, and CMA: CTAC = 0.10 [0 to 1.0], RACTAC = 0.15 [0 to 1.03], p = 0.55 with coefficient of reproducibility of 0.17 CONCLUSION: Respiratory-averaged and standard single-phase attenuation correction maps provide similar and reproducible methods of quantifying coronary 18F-NaF uptake on PET/CT.

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.

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.

Native Aortic Valve Disease Progression and Bioprosthetic Valve Degeneration in Patients With Transcatheter Aortic Valve Implantation

Supplemental Digital Content is available in the text.

Background:

Major uncertainties remain regarding disease activity within the retained native aortic valve, and regarding bioprosthetic valve durability, after transcatheter aortic valve implantation (TAVI). We aimed to assess native aortic valve disease activity and bioprosthetic valve durability in patients with TAVI in comparison with subjects with bioprosthetic surgical aortic valve replacement (SAVR).

Methods:

In a multicenter cross-sectional observational cohort study, patients with TAVI or bioprosthetic SAVR underwent baseline echocardiography, computed tomography angiography, and ¹⁸F-sodium fluoride (¹⁸F-NaF) positron emission tomography. Participants (n=47) were imaged once with ¹⁸F-NaF positron emission tomography/computed tomography either at 1 month (n=9, 19%), 2 years (n=22, 47%), or 5 years (16, 34%) after valve implantation. Patients subsequently underwent serial echocardiography to assess for changes in valve hemodynamic performance (change in peak aortic velocity) and evidence of structural valve dysfunction. Comparisons were made with matched patients with bioprosthetic SAVR (n=51) who had undergone the same imaging protocol.

Results:

In patients with TAVI, native aortic valves demonstrated ¹⁸F-NaF uptake around the outside of the bioprostheses that showed a modest correlation with the time from TAVI (r=0.36, P=0.023). ¹⁸F-NaF uptake in the bioprosthetic leaflets was comparable between the SAVR and TAVI groups (target-to-background ratio, 1.3 [1.2–1.7] versus 1.3 [1.2–1.5], respectively; P=0.27). The frequencies of imaging evidence of bioprosthetic valve degeneration at baseline were similar on echocardiography (6% versus 8%, respectively; P=0.78), computed tomography (15% versus 14%, respectively; P=0.87), and positron emission tomography (15% versus 29%, respectively; P=0.09). Baseline ¹⁸F-NaF uptake was associated with a subsequent change in peak aortic velocity for both TAVI (r=0.7, P<0.001) and SAVR (r=0.7, P<0.001). On multivariable analysis, ¹⁸F-NaF uptake was the only predictor of peak velocity progression (P<0.001).

Conclusions:

In patients with TAVI, native aortic valves demonstrate evidence of ongoing active disease. Across imaging modalities, TAVI degeneration is of similar magnitude to bioprosthetic SAVR, suggesting comparable midterm durability.

Registration:

URL: https://www.clinicaltrials.gov; Unique identifier: NCT02304276.

Pericoronary and periaortic adipose tissue density are associated with inflammatory disease activity in Takayasu arteritis and atherosclerosis

AIMS

To examine pericoronary adipose tissue (PCAT) and periaortic adipose tissue (PAAT) density on coronary computed tomography angiography for assessing arterial inflammation in Takayasu arteritis (TAK) and atherosclerosis.

METHODS AND RESULTS

PCAT and PAAT density was measured in coronary (n = 1016) and aortic (n = 108) segments from 108 subjects [TAK + coronary artery disease (CAD), n = 36; TAK, n = 18; atherosclerotic CAD, n = 32; matched controls, n = 22]. Median PCAT and PAAT densities varied between groups (mPCAT: P < 0.0001; PAAT: P = 0.0002). PCAT density was 7.01 ± standard error of the mean (SEM) 1.78 Hounsfield Unit (HU) higher in coronary segments from TAK + CAD patients than stable CAD patients (P = 0.0002), and 8.20 ± SEM 2.04 HU higher in TAK patients without CAD than controls (P = 0.0001). mPCAT density was correlated with Indian Takayasu Clinical Activity Score (r = 0.43, P = 0.001) and C-reactive protein (r = 0.41, P < 0.0001) and was higher in active vs. inactive TAK (P = 0.002). mPCAT density above -74 HU had 100% sensitivity and 95% specificity for differentiating active TAK from controls [area under the curve = 0.99 (95% confidence interval 0.97-1)]. The association of PCAT density and coronary arterial inflammation measured by 68Ga-DOTATATE positron emission tomography (PET) equated to an increase of 2.44 ± SEM 0.77 HU in PCAT density for each unit increase in 68Ga-DOTATATE maximum tissue-to-blood ratio (P = 0.002). These findings remained in multivariable sensitivity analyses adjusted for potential confounders.

CONCLUSIONS

PCAT and PAAT density are higher in TAK than atherosclerotic CAD or controls and are associated with clinical, biochemical, and PET markers of inflammation. Owing to excellent diagnostic accuracy, PCAT density could be useful as a clinical adjunct for assessing disease activity in TAK.

Clinical implications of 18F-sodium fluoride uptake in subclinical aortic valve calcification: Its relation to coronary atherosclerosis and its predictive value

BACKGROUND

Uptake of 18F-sodium fluoride (18F-NaF) on positron emission tomography (PET) reflects active calcification. Application of this technique in the early phase of aortic valve calcification (AVC) is of clinical interest. We investigated clinical implications of 18F-NaF uptake in subclinical AVC evaluated simultaneously with coronary atherosclerosis, and the utility of 18F-NaF uptake in predicting AVC progression.

METHODS

We studied 25 patients with subclinical AVC and coronary plaques detected on computed tomography (CT) who underwent 18F-NaF PET/CT. AVC score, volume, mean density, and the presence of high-risk coronary plaque were evaluated on CT in each patient. Focal 18F-NaF uptake in AVC and in coronary plaques was quantified with the maximum tissue-to-background ratio (TBRmax).

RESULTS

There were positive correlations between AVC TBRmax (A-TBRmax) and AVC parameters on CT. The 14 patients with high-risk coronary plaque had significantly higher A-TBRmax than those without such plaque (1.60 ± 0.18 vs 1.42 ± 0.13, respectively; P = 0.012). A-TBRmax positively correlated with maximum TBRmax of coronary plaque per patient (r = 0.55, P = 0.0043). In the 11 patients who underwent follow-up CT scan, A-TBRmax positively correlated with subsequent increase in AVC score (r = 0.74, P = 0.0091).

CONCLUSION

Our 18F-NaF PET- and CT-based data indicate relationships between calcification activity in subclinical AVC and characteristics of coronary atherosclerosis. 18F-NaF PET may provide new information regarding molecular conditions and future progression of subclinical AVC.

Predictors of 18F-sodium fluoride uptake in patients with stable coronary artery disease and adverse plaque features on computed tomography angiography

AIMS

In patients with stable coronary artery disease (CAD) and high-risk plaques (HRPs) on coronary computed tomography angiography (CTA), we sought to define qualitative and quantitative CTA predictors of abnormal coronary 18F-sodium fluoride uptake (18F-NaF) by positron emission tomography (PET).

METHODS AND RESULTS

Patients undergoing coronary CTA were screened for HRP. Those who presented with ≥3 CTA adverse plaque features (APFs) including positive remodelling; low attenuation plaque (LAP, <30 HU), spotty calcification; obstructive coronary stenosis ≥50%; plaque volume >100 mm3 were recruited for 18F-NaF PET. In lesions with stenosis ≥25%, quantitative plaque analysis and maximum 18F-NaF target to background ratios (TBRs) were measured. Of 55 patients, 35 (64%) manifested coronary 18F-NaF uptake. Of 68 high-risk lesions 49 (70%) had increased PET tracer activity. Of the APFs, LAP had the highest sensitivity (39.4%) and specificity (98.3%) for predicting 18F-NaF uptake. TBR values were higher in lesions with LAP compared to those without [1.6 (1.3-1.8) vs. 1.1 (1.0-1.3), P = 0.01]. On adjusted multivariable regression analysis, LAP (both qualitative and quantitative) was independently associated with plaque TBR [LAP qualitative: β = 0.47, 95% confidence interval (CI) 0.30-0.65; P < 0.001] and (LAP volume: β = 0.20 per 10 mm3, 95% CI 0.13-0.27; P < 0.001).

CONCLUSION

In stable CAD patients with HRP, LAP is predictive of 18F-NaF coronary uptake, but 18F-NaF is often seen in the absence of LAP. If 18F-NaF uptake is shown to be associated with adverse outcomes and becomes clinically used, the presence of LAP may define patients who would not benefit from the added testing.

Quantitative clinical nuclear cardiology, part 2: Evolving/emerging applications

Quantitative analysis has been applied extensively to image processing and interpretation in nuclear cardiology to improve disease diagnosis and risk stratification. This is Part 2 of a two-part continuing medical education article, which will review the potential clinical role for emerging quantitative analysis tools. The article will describe advanced methods for quantifying dyssynchrony, ventricular function and perfusion, and hybrid imaging analysis. This article discusses evolving methods to measure myocardial blood flow with positron emission tomography and single-photon emission computed tomography. Novel quantitative assessments of myocardial viability, microcalcification and in patients with cardiac sarcoidosis and cardiac amyloidosis will also be described. Lastly, we will review the potential role for artificial intelligence to improve image analysis, disease diagnosis, and risk prediction. The potential clinical role for all these novel techniques will be highlighted as well as methods to optimize their implementation.

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 Uptake Predicts Outcomes in Patients With Coronary Artery Disease

BACKGROUND

Reliable methods for predicting myocardial infarction in patients with established coronary artery disease are lacking. Coronary ¹⁸F-sodium fluoride (¹⁸F-NaF) positron emission tomography (PET) provides an assessment of atherosclerosis activity.

OBJECTIVES

This study assessed whether ¹⁸F-NaF PET predicts myocardial infarction and provides additional prognostic information to current methods of risk stratification.

METHODS

Patients with known coronary artery disease underwent ¹⁸F-NaF PET computed tomography and were followed up for fatal or nonfatal myocardial infarction over 42 months (interquartile range: 31 to 49 months). Total coronary ¹⁸F-NaF uptake was determined by the coronary microcalcification activity (CMA).

RESULTS

In a post hoc analysis of data collected for prospective observational studies, the authors studied 293 study participants (age: 65 ± 9 years; 84% men), of whom 203 (69%) showed increased coronary ¹⁸F-NaF activity (CMA >0). Fatal or nonfatal myocardial infarction occurred only in patients with increased coronary ¹⁸F-NaF activity (20 of 203 with a CMA >0 vs. 0 of 90 with a CMA of 0; p < 0.001). On receiver operator curve analysis, fatal or nonfatal myocardial infarction prediction was highest for ¹⁸F-NaF CMA, outperforming coronary calcium scoring, modified Duke coronary artery disease index and Reduction of Atherothrombosis for Continued Health (REACH) and Secondary Manifestations of Arterial Disease (SMART) risk scores (area under the curve: 0.76 vs. 0.54, 0.62, 0.52, and 0.54, respectively; p < 0.001 for all). Patients with CMA >1.56 had a >7-fold increase in fatal or nonfatal myocardial infarction (hazard ratio: 7.1; 95% confidence interval: 2.2 to 25.1; p = 0.003) independent of age, sex, risk factors, segment involvement and coronary calcium scores, presence of coronary stents, coronary stenosis, REACH and SMART scores, the Duke coronary artery disease index, and recent myocardial infarction.

CONCLUSIONS

In patients with established coronary artery disease, ¹⁸F-NaF PET provides powerful independent prediction of fatal or nonfatal myocardial infarction.

Quantitative clinical nuclear cardiology, part 2: Evolving/emerging applications

Quantitative analysis has been applied extensively to image processing and interpretation in nuclear cardiology to improve disease diagnosis and risk stratification. This is Part 2 of a two-part continuing medical education article, which will review the potential clinical role for emerging quantitative analysis tools. The article will describe advanced methods for quantifying dyssynchrony, ventricular function and perfusion, and hybrid imaging analysis. This article discusses evolving methods to measure myocardial blood flow with positron emission tomography and single-photon emission computed tomography. Novel quantitative assessments of myocardial viability, microcalcification and in patients with cardiac sarcoidosis and cardiac amyloidosis will also be described. Lastly, we will review the potential role for artificial intelligence to improve image analysis, disease diagnosis, and risk prediction. The potential clinical role for all these novel techniques will be highlighted as well as methods to optimize their implementation. (J Nucl Cardiol 2020).

Non-invasive imaging of high-risk coronary plaque: the role of computed tomography and positron emission tomography

Despite recent advances, cardiovascular disease remains the leading cause of death globally. As such, there is a need to optimise our current diagnostic and risk stratification pathways in order to better deliver individualised preventative therapies. Non-invasive imaging of coronary artery plaque can interrogate multiple aspects of coronary atherosclerotic disease, including plaque morphology, anatomy and flow. More recently, disease activity is being assessed to provide mechanistic insights into in vivo atherosclerosis biology. Molecular imaging using positron emission tomography is unique in this field, with the potential to identify specific biological processes using either bespoke or re-purposed radiotracers. This review provides an overview of non-invasive vulnerable plaque detection and molecular imaging of coronary atherosclerosis.

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.

Noninvasive Imaging to Assess Atherosclerotic Plaque Composition and Disease Activity: Coronary and Carotid Applications

Cardiovascular disease is one of the leading causes of mortality and morbidity worldwide. Atherosclerosis imaging has traditionally focused on detection of obstructive luminal stenoses or measurements of plaque burden. However, with advances in imaging technology it has now become possible to noninvasively interrogate plaque composition and disease activity, thereby differentiating stable from unstable patterns of disease and potentially improving risk stratification. This manuscript reviews multimodality imaging in this field, focusing on carotid and coronary atherosclerosis and how these novel techniques have the potential to complement current imaging assessments and improve clinical decision making.

Detecting unstable plaques in humans using cardiac CT: Can it guide treatments?

Advances in imaging technology have driven the rapid expansion in the use of CT in the assessment of coronary atherosclerotic plaque. Based on a rapidly growing evidence base, current guidelines recommend coronary CT angiography as the first-line diagnostic test for patients presenting with stable chest pain. There is a growing need to refine current methods for diagnosis and risk stratification to improve the individualisation of preventative therapies. Imaging assessments of high-risk plaque with CT can be used to differentiate stable from unstable patterns of coronary atherosclerosis and potentially to improve patient risk stratification. This review will focus on coronary imaging with CT with a specific focus on the detection of coronary atherosclerosis, high-risk plaque features, and the implications for patient management.

Vulnerable plaque imaging using 18F-sodium fluoride positron emission tomography

Positron emission tomography (PET) with ¹⁸F-sodium fluoride (¹⁸F-NaF) has emerged as a promising non-invasive imaging modality to identify high-risk and ruptured atherosclerotic plaques. By visualizing microcalcification, ¹⁸F-NaF PET holds clinical promise in refining how we evaluate coronary artery disease, shifting our focus from assessing disease burden to atherosclerosis activity. In this review, we provide an overview of studies that have utilized ¹⁸F-NaF PET for imaging atherosclerosis. We discuss the associations between traditional coronary artery disease measures (risk factors) and ¹⁸F-NaF plaque activity. We also present the data on the histological validation as well as show how ¹⁸F-NaF uptake is associated with plaque morphology on intravascular and CT imaging. Finally, we discuss the technical challenges associated with ¹⁸F-NaF coronary PET highlighting recent advances in this area.

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.

Triple-gated motion and blood pool clearance corrections improve reproducibility of coronary 18F-NaF PET

PURPOSE

To improve the test-retest reproducibility of coronary plaque 18F-sodium fluoride (18F-NaF) positron emission tomography (PET) uptake measurements.

METHODS

We recruited 20 patients with coronary artery disease who underwent repeated hybrid PET/CT angiography (CTA) imaging within 3 weeks. All patients had 30-min PET acquisition and CTA during a single imaging session. Five PET image-sets with progressive motion correction were reconstructed: (i) a static dataset (no-MC), (ii) end-diastolic PET (standard), (iii) cardiac motion corrected (MC), (iv) combined cardiac and gross patient motion corrected (2 × MC) and, (v) cardiorespiratory and gross patient motion corrected (3 × MC). In addition to motion correction, all datasets were corrected for variations in the background activities which are introduced by variations in the injection-to-scan delays (background blood pool clearance correction, BC). Test-retest reproducibility of PET target-to-background ratio (TBR) was assessed by Bland-Altman analysis and coefficient of reproducibility.

RESULTS

A total of 47 unique coronary lesions were identified on CTA. Motion correction in combination with BC improved the PET TBR test-retest reproducibility for all lesions (coefficient of reproducibility: standard = 0.437, no-MC = 0.345 (27% improvement), standard + BC = 0.365 (20% improvement), no-MC + BC = 0.341 (27% improvement), MC + BC = 0.288 (52% improvement), 2 × MC + BC = 0.278 (57% improvement) and 3 × C + BC = 0.254 (72% improvement), all p < 0.001). Importantly, in a sub-analysis of 18F-NaF-avid lesions with gross patient motion > 10 mm following corrections, reproducibility was improved by 133% (coefficient of reproducibility: standard = 0.745, 3 × MC = 0.320).

CONCLUSION

Joint corrections for cardiac, respiratory, and gross patient motion in combination with background blood pool corrections markedly improve test-retest reproducibility of coronary 18F-NaF PET.

The clinical utility of hybrid imaging for the identification of vulnerable plaque and vulnerable patients

Despite decades of research and major innovations in technology, cardiovascular disease remains the leading cause of death globally. Our understanding of major cardiovascular events and their prevention is centred around the atherosclerotic plaque and the processes that ultimately lead to acute plaque rupture. Recent advances in hybrid imaging technology allow the combination of high spatial resolution and anatomical detail with molecular assessments of disease activity. This provides the ability to identify vulnerable plaque characteristics and differentiate active and quiescent disease, with the potential to improve patient risk stratification. Combined positron emission tomography and computed tomography is the prototypical non-invasive hybrid imaging technique for coronary artery plaque assessment. In this review we discuss the current state of play in the field of hybrid coronary atherosclerosis imaging.

Gating Approaches in Cardiac PET Imaging

Cardiac PET provides high sensitivity and high negative predictive value in the diagnosis of coronary artery disease and cardiomyopathies. Cardiac, respiratory as well as bulk patient motion have detrimental effects on thoracic PET imaging, in particular on cardiovascular PET imaging where the motion can affect the PET images quantitatively as well as qualitatively. Gating can ameliorate the unfavorable impact of motion additionally enabling evaluation of left ventricular systolic function. In this article, the authors review the recent advances in gating approaches and highlight the advances in data-driven approaches, which hold promise in motion detection without the need for complex hardware setup.