Noninvasive imaging in cardiovascular therapy: the promise of coronary arterial ¹⁸F-sodium fluoride uptake as a marker of plaque biology

Assessment of atherosclerosis in multiple myeloma and smoldering myeloma patients using 18F- sodium fluoride PET/CT

BACKGROUND

To compare the NaF uptake in the thoracic aorta and whole heart, as an early indicator of atherosclerosis, in multiple myeloma (MM) and smoldering multiple myeloma (SMM) patients with a healthy control (HC) group.

METHODS

Forty-four untreated myeloma patients (35 MM and nine SMM) and twenty-six age and gender-matched HC subjects were collected. Each individual's NaF uptake in three parts of the aorta (AA: ascending aorta, AR: aortic arch, DA: descending aorta) and the whole heart was segmented. Average global standardized uptake value means were derived by sum of the product of each slice area divided by the sum of those slice areas. Results were reported as target to background ratio (TBR).

RESULTS

There was a significant difference between the NaF uptake in the thoracic aorta of myeloma and HC groups [AA (myeloma = 1.82 ± 0.21, HC = 1.24 ± 0.02), AR (myeloma = 1.71 ± 0.19, HC = 1.28 ± 0.03) and DA (myeloma = 1.96 ± 0.28, HC = 1.38 ± 0.03); P-values < 0.001]. The difference in the whole heart NaF uptake between two groups was also significant (P < 0.001).

CONCLUSIONS

We observed a higher uptake of NaF in the thoracic aorta and whole heart of myeloma patients in comparison to the matched control group.

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.

18F-NaF and 18F-FDG as molecular probes in the evaluation of atherosclerosis

The early detection of atherosclerotic disease is vital to the effective prevention and management of life-threatening cardiovascular events such as myocardial infarctions and cerebrovascular accidents. Given the potential for positron emission tomography (PET) to visualize atherosclerosis earlier in the disease process than anatomic imaging modalities such as computed tomography (CT), this application of PET imaging has been the focus of intense scientific inquiry. Although ¹⁸F-FDG has historically been the most widely studied PET radiotracer in this domain, there is a growing body of evidence that ¹⁸F-NaF holds significant diagnostic and prognostic value as well. In this article, we review the existing literature on the application of ¹⁸F-FDG and ¹⁸F-NaF as PET probes in atherosclerosis and present the findings of original animal and human studies that have examined how well ¹⁸F-NaF uptake correlates with vascular calcification and cardiovascular risk.

Coronary fluorine-18-sodium fluoride uptake is increased in healthy adults with an unfavorable cardiovascular risk profile: results from the CAMONA study

OBJECTIVE

Coronary artery fluorine-18-sodium fluoride (F-NaF) uptake reflects coronary artery calcification metabolism and is considered to be an early prognostic marker of coronary heart disease. This study evaluated the relationship between coronary artery F-NaF uptake and cardiovascular risk in healthy adults at low cardiovascular risk.

PARTICIPANTS AND METHODS

Study participants underwent blood pressure measurements, blood analyses, and coronary artery F-NaF PET/CT imaging. In addition, the 10-year risk for the development of cardiovascular disease, on the basis of the Framingham Risk Score, was estimated. Multivariable linear regression evaluated the dependence of coronary artery F-NaF uptake on cardiovascular risk factors.

RESULTS

We recruited 89 (47 men, 42 women) healthy adults aged 21-75 years. Female sex (0.34 kBq/ml; P=0.009), age (0.16 kBq/ml per SD; P=0.002), and BMI (0.42 kBq/ml per SD; P<0.001) were independent determinants of increased coronary artery F-NaF uptake (adjusted R=0.21; P<0.001). Coronary artery F-NaF uptake increased linearly according to the number of cardiovascular risk factors present (P<0.001 for a linear trend). The estimated 10-year risk for the development of cardiovascular disease was on average 2.4 times higher in adults with coronary artery F-NaF uptake in the highest quartile compared with those in the lowest quartile of the distribution (8.0 vs. 3.3%, P<0.001).

CONCLUSION

Our findings indicate that coronary artery F-NaF PET/CT imaging is feasible in healthy adults at low cardiovascular risk and that an unfavorable cardiovascular risk profile is associated with a marked increase in coronary artery F-NaF uptake.

Reference values for fluorine-18-fluorodeoxyglucose and fluorine-18-sodium fluoride uptake in human arteries: a prospective evaluation of 89 healthy adults

OBJECTIVE

Reference values of fluorine-18-fluorodeoxyglucose (F-FDG) and fluorine-18-sodium fluoride (F-NaF) uptake in human arteries are unknown. The aim of this study was to determine age-specific and sex-specific reference values of arterial F-FDG and F-NaF uptake.

PARTICIPANTS AND METHODS

Uptake of F-FDG and F-NaF was determined in the ascending aorta, aortic arch, and descending thoracic aorta. In addition, F-FDG uptake was determined in the carotid arteries and F-NaF uptake was determined in the coronary arteries. Arterial F-FDG and F-NaF uptake were quantified as the blood pool subtracted maximum activity concentration in kBq/ml (BS F-FDGmax and BS F-NaFmax, respectively). In addition to determining reference values, we evaluated the influence of age and sex on BS F-FDGmax and BS F-NaFmax.

RESULTS

Arterial F-FDG and F-NaF uptake was assessed in 89 healthy adults aged 21-75 years (mean age: 44±14 years, 53% men). Both BS F-FDGmax and BS F-NaFmax increased with age. BS F-FDGmax increased with age in the descending aorta (β=0.28; P=0.003), whereas BS F-NaFmax increased with age in the ascending aorta (β=0.18; P<0.001), aortic arch (β=0.19; P=0.006), descending aorta (β=0.33; P<0.001), and coronary arteries (β=0.20; P=0.009), respectively. BS F-FDGmax and BS F-NaFmax were not influenced by sex, except for BS F-FDGmax in the ascending aorta.

CONCLUSION

Prospective evaluation of 89 healthy adults generated age-specific and sex-specific reference values of arterial F-FDG and F-NaF uptake. Our findings indicate that arterial F-FDG and F-NaF uptake tend to increase with age.

Positron emission tomography imaging of coronary atherosclerosis

Inflammation has a central role in the progression of coronary atherosclerosis. Recent developments in cardiovascular imaging with the advent of hybrid positron emission tomography have provided a window into the molecular pathophysiology underlying coronary plaque inflammation. Using novel radiotracers targeted at specific cellular pathways, the potential exists to observe inflammation, apoptosis, cellular hypoxia, microcalcification and angiogenesis in vivo. Several clinical studies are now underway assessing the ability of this hybrid imaging modality to inform about atherosclerotic disease activity and the prediction of future cardiovascular risk. A better understanding of the molecular mechanisms governing coronary atherosclerosis may be the first step toward offering patients a more stratified, personalized approach to treatment.

Imaging of coronary atherosclerosis - evolution towards new treatment strategies

Coronary atherosclerosis and the precipitation of acute myocardial infarction are highly complex processes, which makes accurate risk prediction challenging. Rapid developments in invasive and noninvasive imaging technologies now provide us with detailed, exquisite images of the coronary vasculature that allow direct investigation of a wide range of these processes. These modalities include sophisticated assessments of luminal stenoses and myocardial perfusion, complemented by novel measures of the atherosclerotic plaque burden, adverse plaque characteristics, and disease activity. Together, they can provide comprehensive, individualized assessments of coronary atherosclerosis as it occurs in patients. Not only can this information provide important pathological insights, but it can also potentially be used to guide personalized treatment decisions. In this Review, we describe the latest advances in both established and emerging imaging techniques, focusing on the strengths and weakness of each approach. Moreover, we discuss how these technological advances might be translated from attractive images into novel imaging strategies and definite improvements in clinical risk prediction and patient outcomes. This process will not be easy, and the many potential barriers and difficulties are also reviewed.

Newer PET application with an old tracer: role of 18F-NaF skeletal PET/CT in oncologic practice

The skeleton is one of the most common sites for metastatic disease, particularly from breast and prostate cancer. Bone metastases are associated with considerable morbidity, and accurate imaging of the skeleton is important in determining the appropriate therapeutic plan. Sodium fluoride labeled with fluorine 18 (sodium fluoride F 18 [(18)F-NaF]) is a positron-emitting radiopharmaceutical first introduced several decades ago for skeletal imaging. (18)F-NaF was approved for clinical use as a positron emission tomographic (PET) agent by the U.S. Food and Drug Administration in 1972. The early use of this agent was limited, given the difficulties of imaging its high-energy photons on the available gamma cameras. For skeletal imaging, it was eventually replaced by technetium 99m ((99m)Tc)-labeled agents because of the technical limitations of (18)F-NaF. During the past several years, the widespread availability and implementation of hybrid PET and computed tomographic (CT) dual-modality systems (PET/CT) have encouraged a renewed interest in (18)F-NaF PET/CT for routine clinical use in bone imaging. Because current PET/CT systems offer high sensitivity and spatial resolution, the use of (18)F-NaF has been reevaluated for the detection of malignant and nonmalignant osseous disease. Growing evidence suggests that (18)F-NaF PET/CT provides increased sensitivity and specificity in the detection of bone metastases. Furthermore, the favorable pharmacokinetics of (18)F-NaF, combined with the superior imaging characteristics of PET/CT, supports the routine clinical use of (18)F-NaF PET/CT for oncologic imaging for skeletal metastases. In this article, a review of the indications, imaging appearances, and utility of (18)F-NaF PET/CT in the evaluation of skeletal disease is provided, with an emphasis on oncologic imaging.

Small entities with large impact: microcalcifications and atherosclerotic plaque vulnerability

PURPOSE OF REVIEW

Atherosclerotic plaque rupture and subsequent acute events, such as myocardial infarction and stroke, contribute to the majority of cardiovascular-related deaths. Calcification has emerged as a significant predictor of cardiovascular morbidity and mortality, challenging previously held notions that calcifications stabilize atherosclerotic plaques. In this review, we address this discrepancy through recent findings that not all calcifications are equivalent in determining plaque stability.

RECENT FINDINGS

The risk associated with calcification is inversely associated with calcification density. As opposed to large calcifications that potentially stabilize the plaque, biomechanical modeling indicates that small microcalcifications within the plaque fibrous cap can lead to sufficient stress accumulation to cause plaque rupture. Microcalcifications appear to derive from matrix vesicles enriched in calcium-binding proteins that are released by cells within the plaque. Clinical detection of microcalcifications has been hampered by the lack of imaging resolution required for in-vivo visualization; however, recent studies have demonstrated promising new techniques to predict the presence of microcalcifications.

SUMMARY

Microcalcifications play a major role in destabilizing atherosclerotic plaques. The identification of critical characteristics that lead to instability along with new imaging modalities to detect their presence in vivo may allow early identification and prevention of acute cardiovascular events.

Delayed sodium 18F-fluoride PET/CT imaging does not improve quantification of vascular calcification metabolism: results from the CAMONA study

BACKGROUND

This study aimed to determine if delayed sodium (18)F-fluoride (Na(18)F) PET/CT imaging improves quantification of vascular calcification metabolism. Blood-pool activity can disturb the arterial Na(18)F signal. With time, blood-pool activity declines. Therefore, delayed imaging can potentially improve quantification of vascular calcification metabolism.

METHODS AND RESULTS

Twenty healthy volunteers and 18 patients with chest pain were prospectively assessed by triple time-point PET/CT imaging at approximately 45, 90, and 180 minutes after Na(18)F administration. For each time point, global uptake of Na(18)F was determined in the coronary arteries and thoracic aorta by calculating the blood-pool-corrected maximum standardized uptake value (cSUV(MAX)). A target-to-background ratio (TBR) was calculated to determine the contrast resolution at 45, 90, and 180 minutes. Furthermore, we assessed whether the acquisition time-point affected the relation between cSUV(MAX) and the estimated 10-year risk for fatal cardiovascular disease (SCORE %). Coronary cSUV(MAX) (P = .533) and aortic cSUV(MAX) (P = .654) remained similar with time, whereas the coronary TBR (P < .0001) and aortic TBR (P < .0001) significantly increased with time. Even though the contrast resolution improved with time, positive correlations between SCORE % and coronary cSUV(MAX) (P < .020) and aortic cSUV(MAX) (P < .005) were observed at all investigated time points.

CONCLUSIONS

Delayed Na(18)F PET/CT imaging does not improve quantification of vascular calcification metabolism. Although contrast resolution improves with time, arterial Na(18)F avidity is invariant to the time between Na(18)F administration and PET/CT acquisition. Therefore, the optimal PET/CT acquisition time-point to quantify vascular calcification metabolism is achieved as early as 45 minutes after Na(18)F administration.