Global disease score (GDS) is the name of the game!

Current uses and understanding of PET imaging in cardiac sarcoidosis

Sarcoidosis is a systemic disease with unclear etiology characterized by the accumulation of noncaseating, immune granulomas in affected tissues. In cardiac sarcoidosis (CS), white blood cells build up within the heart muscles, causing cardiac abnormalities. Accurate and early diagnosis of CS proves challenging. However, usage of positron emission tomography (PET) imaging, namely 18F-FDG-PET, has proven successful in diagnosing inflammatory cardiomyopathy. This review seeks to examine the role of PET in managing ventricular tachycardia in cardiac sarcoidosis. PET, in conjunction with cardiac magnetic resonance imaging (CMR) is also endorsed as the premier method for diagnosis and management of arrhythmias associated with CS by The Heart Rhythm Society. After a CS diagnosis, risk stratification of ventricular arrhythmias is a necessity given the potential for sudden cardiac death. 18F-FDG-PET has been successful in monitoring disease advancement and treatment responses in CS patients. Early stages of CS are often treated with immunosuppression drugs if there are additional signs of VT. Currently, corticosteroid and anti-arrhythmia compounds: methotrexate, cyclophosphamide, infliximab, amiodarone, and azathioprine are used to suppress inflammation. 18F-FDG-PET has certainly proven to be an incredibly useful and accurate diagnostic tool of CS. While late gadolinium enhancement by CMR is efficient in detecting myocardial necrosis and/or advanced fibrosis scarring, 18F-FDG portrays the increased uptake level of glucose metabolism. In combination PET/MRI has proven to be more successful in improving the efficacy of both scans, addressing their drawbacks, and highlighting their advantages. Managing CS patients is highly involved in detecting inflammatory regions of the heart. Early recognition prevents cardiac abnormality, mainly VT and VF in CS patients, and extends lifespan.

Role of PET/CT in diagnosing and monitoring disease activity in rheumatoid arthritis: a review

Rheumatoid Arthritis (RA) is a systemic inflammatory disorder that commonly presents with polyarthritis but can have multisystemic involvement and complications, leading to increased morbidity and mortality. The diagnosis of RA continues to be challenging due to its varied clinical presentations. In this review article, we aim to determine the potential of PET/CT to assist in the diagnosis of RA and its complications, evaluate the therapeutic response to treatment, and predict RA remission. PET/CT has increasingly been used in the last decade to diagnose, monitor treatment response, predict remissions, and diagnose subclinical complications in RA. PET imaging with [18F]-fluorodeoxyglucose ([18F]-FDG) is the most commonly applied radiotracer in RA, but other tracers are also being studied. PET/CT with [18F]-FDG, [18F]-NaF, and other tracers might lead to early identification of RA and timely evidence-based clinical management, decreasing morbidity and mortality. Although PET/CT has been evolving as a promising tool for evaluating and managing RA, more evidence is required before incorporating PET/CT in the standard clinical management of RA.

FDG-PET versus Amyloid-PET Imaging for Diagnosis and Response Evaluation in Alzheimer's Disease: Benefits and Pitfalls

In June 2021, the US Federal Drug and Food Administration (FDA) granted accelerated approval for the antibody aducanumab and, in January 2023, also for the antibody lecanemab, based on a perceived drug-induced removal of cerebral amyloid-beta as assessed by amyloid-PET and, in the case of lecanemab, also a presumption of limited clinical efficacy. Approval of the antibody donanemab is awaiting further data. However, published trial data indicate few, small and uncertain clinical benefits, below what is considered "clinically meaningful" and similar to the effect of conventional medication. Furthermore, a therapy-related decrease in the amyloid-PET signal may also reflect increased cell damage rather than simply "amyloid removal". This interpretation is more consistent with increased rates of amyloid-related imaging abnormalities and brain volume loss in treated patients, relative to placebo. We also challenge the current diagnostic criteria for AD based on amyloid-PET imaging biomarkers and recommend that future anti-AD therapy trials apply: (1) diagnosis of AD based on the co-occurrence of cognitive decline and decreased cerebral metabolism assessed by FDA-approved FDG-PET, (2) therapy efficacy determined by favorable effect on cognitive ability, cerebral metabolism by FDG-PET, and brain volumes by MRI, and (3) neuropathologic examination of all deaths occurring in these trials.

Impact of [18F]FDG PET/CT in the Assessment of Immunotherapy-Induced Arterial Wall Inflammation in Melanoma Patients Receiving Immune Checkpoint Inhibitors

We aimed to investigate the role of [¹⁸F]FDG positron emission tomography/computed tomography (PET/CT) in the early detection of arterial wall inflammation (AWI) in melanoma patients receiving immune checkpoint inhibitors (ICIs). Our retrospective study enrolled 95 melanoma patients who had received ICIs. Inclusion criteria were ICI therapy for at least six months and at least three [¹⁸F]FDG PET/CTs, including one pretreatment session plus two scans three and six months after treatment initiation. AWI was assessed using quantitative and qualitative methods in the subclavian artery, thoracic aorta, and abdominal aorta. We found three patients with AWI visual suspicion in the baseline scan, which increased to five in the second and twelve in the third session. Most of these patients' treatments were terminated due to either immune-related adverse events (irAEs) or disease progression. In the overall population, the ratio of arterial-wall maximum standardized uptake value (SUVmax)/liver-SUVmax was significantly higher three months after treatment than the pretreatment scan in the thoracic aorta (0.83 ± 0.12 vs. 0.79 ± 0.10; p-value = 0.01) and subclavian artery (0.67 ± 0.13 vs. 0.63 ± 0.12; p-value = 0.01), and it remained steady in the six-month follow-up. None of our patients were diagnosed with definite clinical vasculitis on the dermatology follow-up reports. To conclude, our study showed [¹⁸F]FDG PET/CT's potential to visualise immunotherapy-induced subclinical inflammation in large vessels. This may lead to more accurate prediction of irAEs and better patient management.

The role of 18F-FDG PET/CT in primary cutaneous lymphoma: an educational review

INTRODUCTION

Primary cutaneous lymphoma (PCL) is a cutaneous non-Hodgkin's lymphoma that originates in the skin and lacks extracutaneous spread upon initial diagnosis. The clinical management of secondary cutaneous lymphomas is different from that of PCLs, and earlier detection is associated with better prognosis. Accurate staging is necessary to determine the extent of disease and to choose the appropriate treatment. The aim of this review is to investigate the current and potential roles of ¹⁸F- fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG PET/CT) in the diagnosis, staging, and monitoring of PCLs.

METHODS

A focused review of the scientific literature was performed using inclusion criteria to filter results pertaining to human clinical studies performed between 2015 and 2021 that analyzed cutaneous PCL lesions on ¹⁸F PET/CT imaging.

RESULTS & CONCLUSION

A review of 9 clinical studies published after 2015 concluded that ¹⁸F-FDG PET/CT is highly sensitive and specific for aggressive PCLs and proved valuable for identifying extracutaneous disease. These studies found ¹⁸F-FDG PET/CT highly useful for guiding lymph node biopsy and that imaging results influenced therapeutic decision in many cases. These studies also predominantly concluded that ¹⁸F-FDG PET/CT is more sensitive than computed tomography (CT) alone for detection of subcutaneous PCL lesions. Routine revision of nonattenuation-corrected (NAC) PET images may improve the sensitivity of ¹⁸F-FDG PET/CT for detection of indolent cutaneous lesions and may expand the potential uses of ¹⁸F-FDG PET/CT in the clinic. Furthermore, calculating a global disease score from ¹⁸F-FDG PET/CT at every follow-up visit may simplify assessment of disease progression in the early clinical stages, as well as predict the prognosis of disease in patients with PCL.

The value of FDG-PET/CT imaging in the assessment, monitoring, and management of COVID-19

The pathogenesis of Coronavirus Disease 2019 (COVID-19) involves cytokine-driven recruitment and accumulation of inflammatory cells at sites of infection. These activated neutrophils, monocytes, and effector T cells are highly glycolytic and thus appear as [18]F-labeled fluorodeoxyglucose (FDG) avid sites on positron emission tomography (PET) imaging. FDG-PET-computed tomography (FDG-PET/CT) is a highly sensitive modality for the detection, monitoring, and assessing response related to COVID-19 disease activity that holds significant clinical relevance. To date, concerns over cost, access, and undue radiation exposure have limited the use of FDG-PET/CT in COVID-19 to a small number of individuals where PET-based interventions were already indicated. In this review, we summarize the existing literature on the use of FDG-PET in the detection and monitoring of COVID-19 with particular focus on several areas of clinical relevance that warrant future research: (1) incidental early detection of subclinical COVID-19 in patients who have undergone FDG-PET for other underlying diseases, (2) standardized quantitative assessment of COVID-19 disease burden at specific points in time, and (3) analysis of FDG-PET/CT data leading to better characterization of COVID-19 pathogenesis. Employing FDG-PET/CT for these purposes may allow for the earliest detection of COVID-19-associated venous thromboembolism (VTE), standardized monitoring of disease progression and response to treatment, and better characterization of the acute and chronic complications of this disease.

Common carotid segmentation in 18 F-sodium fluoride PET/CT scans: Head-to-head comparison of artificial intelligence-based and manual method

BACKGROUND

Carotid atherosclerosis is a major cause of stroke, traditionally diagnosed late. Positron emission tomography/computed tomography (PET/CT) with ¹⁸ F-sodium fluoride (NaF) detects arterial wall micro-calcification long before macro-calcification becomes detectable by ultrasound, CT or magnetic resonance imaging. However, manual PET/CT processing is time-consuming and requires experience. We compared a convolutional neural network (CNN) approach with manual segmentation of the common carotids.

METHODS

Segmentation in NaF-PET/CT scans of 29 healthy volunteers and 20 angina pectoris patients were compared for segmented volume (Vol) and mean, maximal, and total standardized uptake values (SUVmean, SUVmax, and SUVtotal). SUVmean was the average of SUVmeans within the VOI, SUVmax the highest SUV in all voxels in the VOI, and SUVtotal the SUVmean multiplied by the Vol of the VOI. Intra and Interobserver variability with manual segmentation was examined in 25 randomly selected scans.

RESULTS

Bias for Vol, SUVmean, SUVmax, and SUVtotal were 1.33 ± 2.06, -0.01 ± 0.05, 0.09 ± 0.48, and 1.18 ± 1.99 in the left and 1.89 ± 1.5, -0.07 ± 0.12, 0.05 ± 0.47, and 1.61 ± 1.47, respectively, in the right common carotid artery. Manual segmentation lasted typically 20 min versus 1 min with the CNN-based approach. Mean Vol deviation at repeat manual segmentation was 14% and 27% in left and right common carotids.

CONCLUSIONS

CNN-based segmentation was much faster and provided SUVmean values virtually identical to manually obtained ones, suggesting CNN-based analysis as a promising substitute of slow and cumbersome manual processing.

The emerging role of positron emission tomography (PET) in the management of photon radiotherapy-induced vasculitis in head and neck cancer patients

Purpose

While radiotherapy (RT) for head and neck cancer (HNC) has made recent strides, RT-induced vasculitis continues to adversely affect long-term patient outcomes. Guidelines for managing this complication remain scarce, supporting the need for a sensitive imaging modality in post-treatment evaluations. In this review, we discuss the current literature regarding 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and 18F-sodium fluoride (NaF-PET) in evaluating RT-induced vasculitis in HNC patients, highlighting several arenas of evolving clinical significance: (1) early recognition and standardized evaluation of RT-induced vasculitis, and (2) potential for a multifaceted diagnostic tool to stratify cardiovascular risk in HNC patients.

Methods

Numerous databases, including, but not limited to, Google Scholar and PubMed, were utilized to compile a body of literature regarding PET imaging of RT-induced vasculitis in HNC and related malignancies.

Results

Multiple studies have established the clinical capabilities of FDG-PET/computed tomography (FDG-PET/CT) for detection and management of RT-induced vasculitis in HNC patients, while NaF-PET/CT remains under investigation. Inflammatory vascular stages may be best analyzed by FDG-PET/CT, while vascular microcalcification and atherosclerotic disease may be supplementally assessed by the unique properties of NaF-PET/CT. With these modalities detecting primary stages of more detrimental vascular complications, PET imaging may carry several advantages over conventional, structural techniques.

Conclusion

FDG-PET/CT and NaF-PET/CT hold significant potential as preliminary diagnostic tools in monitoring early inflammation and atherosclerotic plaque development, warranting further research and attention. Applying these techniques in this context may foster proactive and consistent assessments of RT-induced vasculitis in HNC patients, mitigating potential cardiovascular risks through better-informed treatment decisions.

"Global" cardiac atherosclerotic burden assessed by artificial intelligence-based versus manual segmentation in 18F-sodium fluoride PET/CT scans: Head-to-head comparison

BACKGROUND

Artificial intelligence (AI) is known to provide effective means to accelerate and facilitate clinical and research processes. So in this study it was aimed to compare a AI-based method for cardiac segmentation in positron emission tomography/computed tomography (PET/CT) scans with manual segmentation to assess global cardiac atherosclerosis burden.

METHODS

A trained convolutional neural network (CNN) was used for cardiac segmentation in 18F-sodium fluoride PET/CT scans of 29 healthy volunteers and 20 angina pectoris patients and compared with manual segmentation. Parameters for segmented volume (Vol) and mean, maximal, and total standardized uptake values (SUVmean, SUVmax, SUVtotal) were analyzed by Bland-Altman Limits of Agreement. Repeatability with AI-based assessment of the same scans is 100%. Repeatability (same conditions, same operator) and reproducibility (same conditions, two different operators) of manual segmentation was examined by re-segmentation in 25 randomly selected scans.

RESULTS

Mean (± SD) values with manual vs. CNN-based segmentation were Vol 617.65 ± 154.99 mL vs 625.26 ± 153.55 mL (P = .21), SUVmean 0.69 ± 0.15 vs 0.69 ± 0.15 (P = .26), SUVmax 2.68 ± 0.86 vs 2.77 ± 1.05 (P = .34), and SUVtotal 425.51 ± 138.93 vs 427.91 ± 132.68 (P = .62). Limits of agreement were - 89.42 to 74.2, - 0.02 to 0.02, - 1.52 to 1.32, and - 68.02 to 63.21, respectively. Manual segmentation lasted typically 30 minutes vs about one minute with the CNN-based approach. The maximal deviation at manual re-segmentation was for the four parameters 0% to 0.5% with the same and 0% to 1% with different operators.

CONCLUSION

The CNN-based method was faster and provided values for Vol, SUVmean, SUVmax, and SUVtotal comparable to the manually obtained ones. This AI-based segmentation approach appears to offer a more reproducible and much faster substitute for slow and cumbersome manual segmentation of the heart.

FDG-PET/CT imaging parameters for predicting spontaneous regression of methotrexate-associated lymphoproliferative disorder in patients with rheumatoid arthritis

In this study, we investigated the usefulness of FDG-PET/CT for predicting spontaneous regression in methotrexate-associated lymphoproliferative disorder (MTX-LPD). Twenty patients with rheumatoid arthritis who were diagnosed with MTX-LPD were enrolled in the study. These patients were divided into those who showed spontaneous regression (SR group: ten patients) and those who received chemotherapy after discontinuation of MTX (CTx group: ten patients). Between-group differences in potential biomarkers were compared, including clinical markers at the onset of LPD [serum LDH and interleukin 2 receptor (sIL-2R)], change in absolute number of peripheral lymphocytes (ΔALC) over follow-up, and the FDG-PET/CT-derived parameters of maximum standardized uptake value (SUVmax), mean SUV (SUVmean), peak SUV (SUVpeak), sum of the metabolic tumor volume (MTVsum), and sum of total lesion glycolysis (TLGsum). The levels of sIL-2R, MTVsum, and TLGsum were significantly lower in the SR group than in the CTx group. In addition, ΔALC was higher in the SR group. In conclusion, MTV and TLG values measured by FDG-PET/CT may be suitable for use as predictors of SR in patients with MTX-LPD.

Aortic wall segmentation in 18F-sodium fluoride PET/CT scans: Head-to-head comparison of artificial intelligence-based versus manual segmentation

BACKGROUND

We aimed to establish and test an automated AI-based method for rapid segmentation of the aortic wall in positron emission tomography/computed tomography (PET/CT) scans.

METHODS

For segmentation of the wall in three sections: the arch, thoracic, and abdominal aorta, we developed a tool based on a convolutional neural network (CNN), available on the Research Consortium for Medical Image Analysis (RECOMIA) platform, capable of segmenting 100 different labels in CT images. It was tested on 18F-sodium fluoride PET/CT scans of 49 subjects (29 healthy controls and 20 angina pectoris patients) and compared to data obtained by manual segmentation. The following derived parameters were compared using Bland-Altman Limits of Agreement: segmented volume, and maximal, mean, and total standardized uptake values (SUVmax, SUVmean, SUVtotal). The repeatability of the manual method was examined in 25 randomly selected scans.

RESULTS

CNN-derived values for volume, SUVmax, and SUVtotal were all slightly, i.e., 13-17%, lower than the corresponding manually obtained ones, whereas SUVmean values for the three aortic sections were virtually identical for the two methods. Manual segmentation lasted typically 1-2 hours per scan compared to about one minute with the CNN-based approach. The maximal deviation at repeat manual segmentation was 6%.

CONCLUSIONS

The automated CNN-based approach was much faster and provided parameters that were about 15% lower than the manually obtained values, except for SUVmean values, which were comparable. AI-based segmentation of the aorta already now appears as a trustworthy and fast alternative to slow and cumbersome manual segmentation.

Volumetric parameters from [18 F]FDG PET/CT predicts survival in patients with high-grade gastroenteropancreatic neuroendocrine neoplasms

A positive fluorine-18 labelled 2-deoxy-2-fluoroglucose ([¹⁸ F]FDG) positron emission tomography/computed tomography (PET/CT) has been associated with more aggressive disease and less differentiated neuroendocrine neoplasms (NEN). Although a high maximum standardized uptake value (SUV_max ) predicts poor outcome in NEN, volumetric parameters from [¹⁸ F]FDG PET have not been evaluated for prognostication in a pure high-grade gastroenteropancreatic (GEP) NEN cohort. In this retrospective observational study, we evaluated the volumetric PET parameters total metabolic tumour volume (tMTV) and total total lesion glycolysis (tTLG) for independent prognostication of overall survival (OS). High-grade GEP NEN patients with [¹⁸ F]FDG PET/CT examination and biopsy within 90 days were included. Total MTV and tTLG were calculated using an adaptive thresholding software. Patients were dichotomised into low and high metabolic groups based on median tMTV and tTLG. OS was compared using Kaplan-Meier estimator and log-rank test. Uni and multivariable Cox regression was used to estimate effect sizes and adjust for tumour differentiation and SUV_max . Sixty-six patients (median age 64 years) were included with 14 NET G3 and 52 NEC cases after histological re-evaluation. Median tMTV was 208 cm³ and median tTLG 1899 g. Median OS in the low versus high tMTV-group was 21.2 versus 5.7 months (HR 2.53, p = 0.0007) and 22.8 versus 5.7 months (HR 2.42, p = 0.0012) in the tTLG-group. Adjusted for tumour differentiation and SUV_max , tMTV and tTLG still predicted for poor OS, and both tMTV and tTLG were stronger prognostic parameters than SUV_max . Both regression models showed a strong association between volumetric parameters and OS for both neuroendocrine tumours (NET) G3 and neuroendocrine carcinomas (NEC). OS for the tTLG low metabolic NEC was much higher than for the tTLG high metabolic NET G3 (18.3 vs. 5.7 months). High-grade GEP NEN patients with high tMTV or tTLG had a worse OS regardless of tumour differentiation (NET G3 or NEC). Volumetric PET parameters were stronger prognostic parameters than SUV_max .

Molecular imaging in atherosclerosis

Purpose

As atherosclerosis is a  prominent cause of morbidity and mortality, early detection of atherosclerotic plaques is vital to prevent complications. Imaging plays a significant role in this goal. Molecular imaging and structural imaging detect different phases of atherosclerotic progression. In this review, we explain the relation between these types of imaging with the physiopathology of plaques, along with their advantages and disadvantages. We also discuss in detail the most commonly used positron emission tomography (PET) radiotracers for atherosclerosis imaging.

Method

A comprehensive search was conducted to extract articles related to imaging of atherosclerosis in PubMed, Google Scholar, and Web of Science. The obtained papers were reviewed regarding precise relation with our topic. Among the search keywords utilized were "atherosclerosis imaging", "atherosclerosis structural imaging", "atherosclerosis CT scan" "positron emission tomography", "PET imaging", "18F-NaF", "18F-FDG", and "atherosclerosis calcification."

Result

Although structural imaging such as computed tomography (CT) offers essential information regarding plaque structure and morphologic features, these modalities can only detect macroscopic alterations that occur later in the disease’s progression, when the changes are frequently irreversible. Molecular imaging modalities like PET, on the other hand, have the advantage of detecting microscopic changes and allow us to treat these plaques before irreversible changes occur. The two most commonly used tracers in PET imaging of atherosclerosis are 18F-sodium fluoride (18F-NaF) and 18F-fluorodeoxyglucose (18F-FDG). While there are limitations in the use of 18F-FDG for the detection of atherosclerosis in coronary arteries due to physiological uptake in myocardium and high luminal blood pool activity of 18F-FDG, 18F-NaF PET is less affected and can be utilized to analyze the coronary arteries in addition to the peripheral vasculature.

Conclusion

Molecular imaging with PET/CT has become a useful tool in the early detection of atherosclerosis. 18F-NaF PET/CT shows promise in the early global assessment of atherosclerosis, but further prospective studies are needed to confirm its role in this area.

Potential and Most Relevant Applications of Total Body PET/CT Imaging

ABSTRACT

The introduction of total body (TB) PET/CT instruments over the past 2 years has initiated a new and exciting era in medical imaging. These instruments have substantially higher sensitivity (up to 68 times) than conventional modalities and therefore allow imaging the entire body over a short period. However, we need to further refine the imaging protocols of this instrument for different indications. Total body PET will allow accurate assessment of the extent of disease, particularly, including the entire axial and appendicular skeleton. Furthermore, delayed imaging with this instrument may enhance the sensitivity of PET for some types of cancer. Also, this modality may improve the detection of venous thrombosis, a common complication of cancer and chemotherapy, in the extremities and help prevent pulmonary embolism. Total body PET allows assessment of atherosclerotic plaques throughout the body as a systematic disease. Similarly, patients with widespread musculoskeletal disorders including both oncologic and nononcologic entities, such as degenerative joint disease, rheumatoid arthritis, and osteoporosis, may benefit from the use of TB-PET. Finally, quantitative global disease assessment provided by this approach will be superior to conventional measurements, which do not reflect overall disease activity. In conclusion, TB-PET imaging may have a revolutionary impact on day-to-day practice of medicine and may become the leading imaging modality in the future.

PET-Based Imaging with 18F-FDG and 18F-NaF to Assess Inflammation and Microcalcification in Atherosclerosis and Other Vascular and Thrombotic Disorders

Positron emission tomography (PET) imaging with ¹⁸F-fluorodeoxyglucose (FDG) represents a method of detecting and characterizing arterial wall inflammation, with potential applications in the early assessment of vascular disorders such as atherosclerosis. By portraying early-stage molecular changes, FDG-PET findings have previously been shown to correlate with atherosclerosis progression. In addition, recent studies have suggested that microcalcification revealed by ¹⁸F-sodium fluoride (NaF) may be more sensitive at detecting atherogenic changes compared to FDG-PET. In this review, we summarize the roles of FDG and NaF in the assessment of atherosclerosis and discuss the role of global assessment in quantification of the vascular disease burden. Furthermore, we will review the emerging applications of FDG-PET in various vascular disorders, including pulmonary embolism, as well as inflammatory and infectious vascular diseases.

Artificial Intelligence in Vascular-PET:: Translational and Clinical Applications

Positron emission tomography (PET) offers an incredible wealth of diverse research applications in vascular disease, providing a depth of molecular, functional, structural, and spatial information. Despite this, vascular PET imaging has not yet assumed the same clinical use as vascular ultrasound, CT, and MR imaging which provides information about late-onset, structural tissue changes. The current clinical utility of PET relies heavily on visual inspection and suboptimal parameters such as SUVmax; emerging applications have begun to harness the tool of whole-body PET to better understand the disease. Even still, without automation, this is a time-consuming and variable process. This review summarizes PET applications in vascular disorders, highlights emerging AI methods, and discusses the unlocked potential of AI in the clinical space.

Critical review of PET imaging for detection and characterization of the atherosclerotic plaques with emphasis on limitations of FDG-PET compared to NaF-PET in this setting

Applications of various positron emission tomography (PET) tracers for assessing atherosclerosis have been evolving over the years. ¹⁸F-fluorodeoxyglucose (FDG)-PET was introduced in 2001 as a probe for this purpose. During the past decade, numerous papers have described a major role for sodium ¹⁸F-fluoride (NaF) as another tracer for assessing this vascular disease. We have reviewed the existing data about the merits of both techniques for assessing atherosclerosis. We have to emphasize that our team has been actively involved in conducting research with both tracers over many years. In this review, we have relied upon the data from the CAMONA study which has become a gold standard for defining the role of PET imaging in atherosclerosis. This study was one of the largest of any in recent years and has allowed comprehensive comparison between these two tracers in detecting and quantifying atherosclerosis. Based on what we have learned from this major undertaking, we believe the role of FDG-PET will be limited in assessing atherosclerosis in clinical work-up. This is relevant to both major and coronary arteries. In contrast to NaF-PET, the role of FDG-PET in assessing coronary artery atherosclerosis is almost non-existent. Based on the existing data in this domain, NaF-PET is an ideal imaging modality for both research and clinical assessment of atherosclerosis. The aim of this review is to describe the pros and cons of both approaches based on the existing data in the literature.

Artificial intelligence-based measurements of PET/CT imaging biomarkers are associated with disease-specific survival of high-risk prostate cancer patients

OBJECTIVE

Artificial intelligence (AI) offers new opportunities for objective quantitative measurements of imaging biomarkers from positron-emission tomography/computed tomography (PET/CT). Clinical image reporting relies predominantly on observer-dependent visual assessment and easily accessible measures like SUV_max, representing lesion uptake in a relatively small amount of tissue. Our hypothesis is that measurements of total volume and lesion uptake of the entire tumour would better reflect the disease`s activity with prognostic significance, compared with conventional measurements.

METHODS

An AI-based algorithm was trained to automatically measure the prostate and its tumour content in PET/CT of 145 patients. The algorithm was then tested retrospectively on 285 high-risk patients, who were examined using ¹⁸F-choline PET/CT for primary staging between April 2008 and July 2015. Prostate tumour volume, tumour fraction of the prostate gland, lesion uptake of the entire tumour, and SUV_max were obtained automatically. Associations between these measurements, age, PSA, Gleason score and prostate cancer-specific survival were studied, using a Cox proportional-hazards regression model.

RESULTS

Twenty-three patients died of prostate cancer during follow-up (median survival 3.8 years). Total tumour volume of the prostate (p = 0.008), tumour fraction of the gland (p = 0.005), total lesion uptake of the prostate (p = 0.02), and age (p = 0.01) were significantly associated with disease-specific survival, whereas SUV_max (p = 0.2), PSA (p = 0.2), and Gleason score (p = 0.8) were not.

CONCLUSION

AI-based assessments of total tumour volume and lesion uptake were significantly associated with disease-specific survival in this patient cohort, whereas SUV_max and Gleason scores were not. The AI-based approach appears well-suited for clinically relevant patient stratification and monitoring of individual therapy.

Alavi-Carlsen Calcification Score (ACCS): A Simple Measure of Global Cardiac Atherosclerosis Burden

Multislice cardiac CT characterizes late stage macrocalcification in epicardial arteries as opposed to PET/CT, which mirrors early phase arterial wall changes in epicardial and transmural coronary arteries. With regard to tracer, there has been a shift from using mainly ¹⁸F-fluorodeoxyglucose (FDG), indicating inflammation, to applying predominantly ¹⁸F-sodium fluoride (NaF) due to its high affinity for arterial wall microcalcification and more consistent association with cardiovascular risk factors. To make NaF-PET/CT an indispensable adjunct to clinical assessment of cardiac atherosclerosis, the Alavi–Carlsen Calcification Score (ACCS) has been proposed. It constitutes a global assessment of cardiac atherosclerosis burden in the individual patient, supported by an artificial intelligence (AI)-based approach for fast observer-independent segmentation. Common measures for characterizing epicardial coronary atherosclerosis by NaF-PET/CT as the maximum standardized uptake value (SUV) or target-to-background ratio are more versatile, error prone, and less reproducible than the ACCS, which equals the average cardiac SUV. The AI-based approach ensures a quick and easy delineation of the entire heart in 3D to obtain the ACCS expressing ongoing global cardiac atherosclerosis, even before it gives rise to CT-detectable coronary calcification. The quantification of global cardiac atherosclerotic burden by the ACCS is suited for management triage and monitoring of disease progression with and without intervention.

Magnetic resonance imaging-based partial volume-corrected 18F-sodium fluoride positron emission tomography in the femoral neck

OBJECTIVES

18F-sodium fluoride (NaF) is a radiotracer used in PET that reflects calcium metabolism and osteoblastic activity. In this study, we assessed the construct validity of a novel application of global assessment to measure NaF uptake in the femoral neck as a method of evaluating physiologic changes in osteoblastic metabolism with age.

METHODS

Whole-body NaF-PET/computed tomography (CT) images and MRI of 24 male patients with a history of nonmetastatic prostate cancer between the ages of 36 and 82 years (67.8 ± 9.6) were analyzed. A region of interest delineated the entire femoral neck on the PET/CT image to determine the mean standardized uptake value (SUVmean). Correction for the partial volume effect was performed by measuring the volume of inert yellow bone marrow by MRI segmentation. Multiple linear regression was used to assess the relationship of uptake with age and body weight.

RESULTS

The SUVmean with and without partial volume correction decreased with respect to age (P = 0.001 and P = 0.002, respectively). Body weight was not significantly related to any measured PET parameter.

CONCLUSION

Our results support the use of global NaF uptake with magnetic resonance-derived partial volume correction in the femoral neck. Because osteoblastic metabolism is known to decrease with normal aging, the observed decrease in NaF uptake constitutes evidence for convergent validity, indicating that the proposed methodology likely reflects systemic osteoblastic activity. Future studies of this methodology are warranted in other instances of varying osteoblastic activity such as in metabolic bone diseases and for the evaluation of therapy targeting osteoblastic metabolism.

Global brain glucose uptake on 18F-FDG-PET/CT is influenced by chronic cardiovascular risk

PURPOSE

The goal of this study was to assess global cerebral glucose uptake in subjects with known cardiovascular risk factors by employing a quantitative 18F-fluorodeoxyglucose-PET/computed tomography (FDG-PET/CT) technique. We hypothesized that at-risk subjects would demonstrate decreased global brain glucose uptake compared to healthy controls.

METHODS

We compared 35 healthy male controls and 14 male subjects at increased risk for cardiovascular disease (CVD) as assessed by the systematic coronary risk evaluation (SCORE) tool. All subjects were grouped into two age-matched cohorts: younger (<50 years) and older (≥50 years). The global standardized uptake value mean (Avg SUVmean) was measured by mapping regions of interest of the entire brain across the supratentorial structures and cerebellum. Wilcoxon's rank-sum test was used to assess the differences in Avg SUVmean between controls and at-risk subjects.

RESULTS

Younger subjects demonstrated higher brain Avg SUVmean than older subjects. In addition, in both age strata, the 10-year risk for fatal CVD according to the SCORE tool was significantly greater in the at-risk groups than in healthy controls (younger: P = 0.0304; older: P = 0.0436). In the younger cohort, at-risk subjects demonstrated significantly lower brain Avg SUVmean than healthy controls (P = 0.0355). In the older cohort, at-risk subjects similarly had lower Avg SUVmean than controls (P = 0.0343).

CONCLUSIONS

Global brain glucose uptake appears to be influenced by chronic cardiovascular risk factors. Therefore, FDG-PET/CT may play a role in determining the importance of CVD on brain function and has potential for monitoring the efficacy of various therapeutic interventions.

Emerging role of 18F-FDG PET/CT in Castleman disease: a review

Castleman disease (CD) describes a group of rare hematologic conditions involving lymphadenopathy with characteristic histopathology and a spectrum of clinical abnormalities. CD is divided into localized or unicentric CD (UCD) and multicentric CD (MCD) by imaging. MCD is further divided based on etiological driver into human herpesvirus-8-associated MCD, POEMS-associated MCD, and idiopathic MCD. There is notable heterogeneity across MCD, but increased level of pro-inflammatory cytokines, particularly interleukin-6, is an established disease driver in a portion of patients. FDG-PET/CT can help determine UCD versus MCD, evaluate for neoplastic conditions that can mimic MCD clinico-pathologically, and monitor therapy responses. CD requires more robust characterization, earlier diagnosis, and an accurate tool for both monitoring and treatment response evaluation; FDG-PET/CT is particularly suited for this. Moving forward, future prospective studies should further characterize the use of FDG-PET/CT in CD and specifically explore the utility of global disease assessment and dual time point imaging.

Trial registration ClinicalTrials.gov, NCT02817997, Registered 29 June 2016, https://clinicaltrials.gov/ct2/show/NCT02817997

Granulomatous-Lymphocytic Interstitial Lung Disease in Common Variable Immunodeficiency-Features of CT and 18F-FDG Positron Emission Tomography/CT in Clinically Progressive Disease

Common variable immunodeficiency (CVID) is characterized not only by recurrent bacterial infections, but also autoimmune and inflammatory complications including interstitial lung disease (ILD), referred to as granulomatous-lymphocytic interstitial lung disease (GLILD). Some patients with GLILD have waxing and waning radiologic findings, but preserved pulmonary function, while others progress to end-stage respiratory failure. We reviewed 32 patients with radiological features of GLILD from our Norwegian cohort of CVID patients, including four patients with possible monogenic defects. Nineteen had deteriorating lung function over time, and 13 had stable lung function, as determined by pulmonary function testing of forced vital capacity (FVC), and diffusion capacity of carbon monoxide (DLCO). The overall co-existence of other non-infectious complications was high in our cohort, but the prevalence of these was similar in the two groups. Laboratory findings such as immunoglobulin levels and T- and B-cell subpopulations were also similar in the progressive and stable GLILD patients. Thoracic computer tomography (CT) scans were systematically evaluated and scored for radiologic features of GLILD in all pulmonary segments. Pathologic features were seen in all pulmonary segments, with traction bronchiectasis as the most prominent finding. Patients with progressive disease had significantly higher overall score of pathologic features compared to patients with stable disease, most notably traction bronchiectasis and interlobular septal thickening. 18F-2-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) positron emission tomography/CT (PET/CT) was performed in 17 (11 with progressive and six with stable clinical disease) of the 32 patients and analyzed by quantitative evaluation. Patients with progressive disease had significantly higher mean standardized uptake value (SUVmean), metabolic lung volume (MLV) and total lung glycolysis (TLG) as compared to patients with stable disease. Nine patients had received treatment with rituximab for GLILD. There was significant improvement in pathologic features on CT-scans after treatment while there was a variable effect on FVC and DLCO.

Conclusion

Patients with progressive GLILD as defined by deteriorating pulmonary function had significantly greater pathology on pulmonary CT and FDG-PET CT scans as compared to patients with stable disease, with traction bronchiectasis and interlobular septal thickening as prominent features.

Association between atherosclerotic cardiovascular disease risk score estimated by pooled cohort equation and coronary plaque burden as assessed by NaF-PET/CT

Pooled Cohort Equations (PCE) combines metabolic and non-metabolic parameters to predict the 10-year risk of atherosclerotic cardiovascular disease (ASCVD). Therefore, we hypothesize that ASCVD risk score is correlated to global cardiac microcalcification, as assessed by 18F-sodium fluoride-positron emission tomography/computed tomography (NaF-PET/CT). Sixty-one individuals (53.4±8.9 years, 32 females, 100% Caucasian) without known ASCVD underwent NaF-PET/CT imaging. Global cardiac average SUVmean (aSUVmean), also known as the Alavi-Carlsen Calcification Score, was calculated across manually defined regions of interest on each axial slice for each individual. The 10-year ASCVD risk score was determined for each individual using the PCE as per ACC/AHA guidelines, and then individuals were categorized into low-, borderline-, intermediate-, and high-risk groups based on their score. Linear regression analysis was applied to compare each individual's ASCVD score and aSUVmean. Global cardiac aSUVmean stratified by groups estimated by 10-year ASCVD risk score were 0.67±0.09 for low risk (n=32), 0.70±0.11 for borderline risk (n=10), 0.72±0.10 for intermediate risk (n=17), and 0.78±0.10 for high risk (n=2). ASCVD risk score was significantly correlated to aSUVmean (r=0.27, P=0.03). This is among the first studies to compare ASCVD risk scores to cardiac plaque burden as assessed by NaF-PET/CT. Large, prospective studies are needed to further investigate the potential of NaF uptake in ASCVD.

18F-FDG-PET/CT in radiation therapy-induced parotid gland inflammation

Background

¹⁸F-fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) is used in the clinical management of oncologic and inflammatory pathologies. It may have utility in detecting radiotherapy (RT)-induced damage of oral tissues. Thus, the aim of the present study was to use FDG-PET/CT to evaluate parotid gland inflammation following RT in patients with head and neck cancer (HNC).

Methods

This retrospective study included patients with HNC treated with photon, proton, or combined photon/proton RT, in addition to chemotherapy. All patients received FDG-PET/CT imaging pre-treatment and 3 months post-treatment. The average mean standardized uptake value (Avg SUVmean) and the average maximum standardized uptake value (Avg SUVmax) of the left and right parotid glands were determined by global assessment of FDG activity using OsiriX MD software. A two-tailed paired t test was used to compare Avg SUVmean and Avg SUVmax pre- and post-RT.

Results

Forty-seven HNC patients were included in the study. Parotid gland Avg SUVmean was significantly higher at 3 months post-treatment than pre-treatment (p < 0.05) in patients treated with photon RT, but no significant differences were found between pre- and post-treatment Avg SUVmean in patients treated with proton RT or combined photon/proton RT.

Conclusion

Our results suggest that photon RT may cause radiation-induced inflammation of the parotid gland, and that proton RT, which distributes less off-target radiation, is a safer treatment alternative.

Assessment of Total-Body Atherosclerosis by PET/Computed Tomography

Atherosclerotic burden has become the focus of cardiovascular risk assessment. PET/computed tomography (CT) imaging with the tracers 18F-fluorodeoxyglucose and 18F-sodium fluoride shows arterial wall inflammation and microcalcification, respectively. Arterial uptake of both tracers is modestly age dependent. 18F-sodium fluoride uptake is consistently associated with risk factors and more easily measured in the heart. Because of extremely high sensitivity, ultrashort acquisition, and minimal radiation to the patient, total-body PET/CT provides unique opportunities for atherosclerosis imaging: disease screening and delayed and repeat imaging with global disease scoring and parametric imaging to better characterize the atherosclerosis of individual patients.

Atherosclerosis Imaging with 18F-Sodium Fluoride PET

The evidence on atherosclerosis imaging with ¹⁸F-sodium-fluoride (NaF) positron emission tomography (PET) is hotly debated because of the different patient characteristics, methodology, vascular beds, etc. in reported studies. This review is a continuation of a previous review on this topic, which covered the period 2010-2018. The purpose was to examine whether some of the most important questions that the previous review had left open had been elucidated by the most recent literature. Using principles of a systematic review, we ended analyzing 25 articles dealing with the carotids, coronary arteries, aorta, femoral, intracranial, renal, and penile arteries. The knowledge thus far can be summarized as follows: by targeting active arterial microcalcification, NaF uptake is considered a marker of early stage atherosclerosis, is age-dependent, and consistently associated with cardiovascular risk. Longitudinal studies on NaF uptake, conducted in the abdominal aorta only, showed unchanged uptake in postmenopausal women for nearly four years and varying uptake in prostate cancer patients over 1.5 years, despite constant or increasing calcium volume detected by computed tomography (CT). Thus, uncertainty remains about the transition from active arterial wall calcification marked by increased NaF uptake to less active or consolidated calcification detected by CT. The question of whether early-phase atherosclerosis and calcification can be modified remains also unanswered due to lack of intervention studies.

Artificial intelligence-based detection of lymph node metastases by PET/CT predicts prostate cancer-specific survival

INTRODUCTION

Lymph node metastases are a key prognostic factor in prostate cancer (PCa), but detecting lymph node lesions from PET/CT images is a subjective process resulting in inter-reader variability. Artificial intelligence (AI)-based methods can provide an objective image analysis. We aimed at developing and validating an AI-based tool for detection of lymph node lesions.

METHODS

A group of 399 patients with biopsy-proven PCa who had undergone ¹⁸ F-choline PET/CT for staging prior to treatment were used to train (n = 319) and test (n = 80) the AI-based tool. The tool consisted of convolutional neural networks using complete PET/CT scans as inputs. In the test set, the AI-based lymph node detections were compared to those of two independent readers. The association with PCa-specific survival was investigated.

RESULTS

The AI-based tool detected more lymph node lesions than Reader B (98 vs. 87/117; p = .045) using Reader A as reference. AI-based tool and Reader A showed similar performance (90 vs. 87/111; p = .63) using Reader B as reference. The number of lymph node lesions detected by the AI-based tool, PSA, and curative treatment was significantly associated with PCa-specific survival.

CONCLUSION

This study shows the feasibility of using an AI-based tool for automated and objective interpretation of PET/CT images that can provide assessments of lymph node lesions comparable with that of experienced readers and prognostic information in PCa patients.

Reinventing Molecular Imaging with Total-Body PET, Part II: Clinical Applications

Total-body PET scans will initiate a new era for the PET clinic. The benefits of 40-fold effective sensitivity improvement provide new capabilities to image with lower radiation dose, perform delayed imaging, and achieve improved temporal resolution. These technical features are detailed in the first of this 2-part series. In this part, the clinical impacts of the novel features of total-body PET scans are further explored. Applications of total-body PET scans focus on the real-time interrogation of systemic disease manifestations in a variety of practical clinical contexts. Total-body PET scans make clinical systems biology imaging a reality.

Prognostic significance of 18F-sodium fluoride in newly diagnosed multiple myeloma patients

Focal bone lesions and fractures due to weakened bone are associated with higher morbidity and mortality of multiple myeloma (MM) patients. ¹⁸F-sodium fluoride (¹⁸F-NaF) is a sensitive PET radiotracer for detection of abnormal bone metabolism and, therefore, is particularly suited to assess the degree of bone involvement in MM patients. We aimed to investigate the prognostic significance of metabolic active volume (MAV) of ¹⁸F-NaF-avid lesions in MM patients. In addition to MAV, conventional methods of PET quantification, namely SUVmean and SUVmax, were measured in each patient for the purpose of comparison. Thirty-seven newly diagnosed MM patients were included. PET imaging was performed after intravenous administration of 200 MBq NaF. Active bone lesions and fractures on whole-body ¹⁸F-NaF-PET/CT scans were identified. An adaptive thresholding algorithm automatically calculated the total MAV, SUVmean and SUVmax for each patient (ROVER, ABX, Radeberg, Germany). The patients were followed for a median of 39.8 months after treatment (range: 17.8-55.4). The overall survival (OS) of patients with ¹⁸F-NaF-MAV value > 38.65 (36.36% [N of Events/Total N: 4/11]) was significantly shorter than that of patients with ¹⁸F-NaF-MAV value < 38.65 (3.85% [1/26]; P = 0.002). In multivariate forward stepwise (conditional LR) Cox regression analysis of prognostic factors of OS (including ¹⁸F-NaF-MAV (> 38.65 or < 38.65), age, gender, beta-2 microglobulin, and revised international staging system), ¹⁸F-NaF-MAV remained the only significant factor (HR: 14.39, P = 0.02). The results for PFS were not significant. Moreover, Kaplan-Meier analyses of conventional methods of PET quantification did not reveal any statistically significant log-rank p-values. MM patients with high ¹⁸F-NaF-MAV had shorter overall survival, compared to those with low ¹⁸F-NaF-MAV levels (NCT02187731).

Diagnosis and Monitoring of Osteoporosis with Total-Body 18F-Sodium Fluoride-PET/CT

In recent years, ¹⁸F-Sodium Fluoride (NaF)-PET/CT has seen its role in the detection and management of osteoporosis increase. This article reviews the extent of this application in the literature, its efficacy compared with other comparable imaging tools, and how total-body PET/CT combined with global disease assessment can revolutionize measurement of total osteoporotic disease activity. NaF-PET/CT eventually can be the modality of choice for metabolic bone disorders, especially with these advances in technology and computation.

Hepatic alveolar echinococcosis: correlation between computed tomography morphology and inflammatory activity in positron emission tomography

Positron emission tomography-computed tomography (PET-CT) with 18F-fluorodesoxyglucose (FDG) is the imaging modality of choice for assessing inflammation surrounding hepatic alveolar echinococcosis (AE) lesions. This study is the first to evaluate FDG uptake in hepatic AE (n = 51) based on the standardized uptake value (SUV) and to correlate the SUVs with primary morphology and calcification patterns, based on the Echinococcus multilocularis Ulm Classification for Computed-Tomography (EMUC-CT). Our results show that the SUVs were increased for lesions with EMUC-CT types I-IV primary morphology, compared to the surrounding healthy liver tissue (SUV = 2.5 ± 0.4; p < 0.05). Type IV lesions included, by far, the highest number of PET-negative lesions. A comparison of lesions with different primary morphologies showed clear differences. The highest SUVs were found for types I and III, and the lowest was found for type IV. Type IV lesions (SUV, 3.8 ± 1.5) showed significantly lower uptake compared to type I (SUV, 6.9 ± 3.5; p = 0.030) and type III (SUV, 7.4 ± 3.9; p = 0.031) lesions. For type II lesions, the results showed only a statistical trend (SUV, 6.1 ± 3.1; p = 0.073). Due to the small number of cases, an evaluation of type V (n = 1) lesions was not possible. The different SUVs of lesions with different primary morphologies, particularly the lower FDG uptake observed in type IV lesions, suggested that these SUVs might reflect different stages of the disease.

Assessing the effects of body weight on subchondral bone formation with quantitative 18F-sodium fluoride PET

OBJECTIVES

The aim of this study was to quantify subchondral bone remodeling in the elbows, hands, knees, and feet using volumetric and metabolic parameters derived from ¹⁸F-sodium fluoride positron emission tomography (NaF-PET) and to assess the convergent validity of these parameters as an index of joint degeneration and preclinical osteoarthritis.

METHODS

A retrospective analysis was conducted in 34 subjects (32 males, 2 females) with metastatic bone disease who underwent full-body NaF-PET/CT scans. An adaptive contrast-oriented thresholding algorithm was applied to segment NaF-avid regions in the bilateral elbows, hands, knees, and feet of each subject, and metabolically active volume (MAV), maximum standardized uptake value (SUVmax), mean metabolic volumetric product (MVPmean), and partial volume-corrected MVPmean (cMVPmean) of the segmented regions were calculated. Global parameters for MAV, SUVmax, MVPmean, and cMVPmean were defined as the sum of the corresponding values in all the joints of a subject. Inter-rater reliability was determined with Lin's concordance correlation, and associations of global values with subject body weight and age were assessed with Pearson correlation and Spearman correlation analyses.

RESULTS

Inter-rater reliability was observed to be the highest in SUVmax (ρc = 0.99), followed by MVPmean (ρc = 0.96), cMVPmean (ρc = 0.93), and MAV (ρc = 0.93). MAV, MVPmean, and cMVPmean were observed to significantly increase with weight (all p < 0.0001) determined by Pearson correlation. In addition, Spearman rank-order analysis demonstrated a significant correlation between SUVmax and weight in addition to MAV, MVPmean, and cMVPmean and weight (all p < 0.01). No significant association between age and any PET parameter was observed.

CONCLUSIONS

These preliminary data demonstrate the feasibility and reliability of assessing bone turnover at the joints using quantitative NaF-PET. Our findings corroborate the fact that biomechanical factors including mechanical loading and weight-bearing are contributors to osteoarthritis disease progression.

Potential Applications of PET-Based Novel Quantitative Techniques in Pediatric Diseases and Disorders

The progress made in hybrid PET imaging during the past decades has significantly expanded the role of this modality in both clinical and research applications. Semi-quantitative PET/CT has been the workhorse of clinical PET/CT due to its simplicity and availability. In addition to semi-quantitative PET/CT, volumetric PET and global metabolic activity have recently shown promise in a more accurate assessment of various diseases. PET/CT has been widely used in pediatric oncologic and non-oncologic diseases. Here we have highlighted few of the pitfalls in the quantitative PET/CT and their potential remedies which have potential in PET/CT evaluation of pediatric diseases.

18F-FDG PET Assessment of Malignant Pleural Mesothelioma: Total Lesion Volume and Total Lesion Glycolysis-The Central Role of Volume

Cancer survival is related to tumor volume. ¹⁸F-FDG PET measurement of tumor volume holds promise but is not yet a clinical tool. Measurements come in 2 forms: the first is total lesion volume (TLV) based on the number of voxels in the tumor, and the second is total lesion glycolysis (TLG), which is the TLV multiplied by the average SUL (i.e., SUV normalized for lean mass) of the tumor (SUL_average). In this study, we measured tumor volume in patients with malignant pleural mesothelioma (MPM). Methods: A threshold-based program in Interactive Data Language was developed to measure tumor volume in ¹⁸F-FDG PET images. Nineteen patients with MPM were studied before and after 2 cycles (6 wk) of chemoimmunotherapy. Measurements included TLV, TLG, the sum of the SULs in the tumor (SUL_total, a measure of total ¹⁸F-FDG uptake), and SUL_average Results: Baseline TLV ranged from 11 to 2,610 cm³ TLG ranged from 32 to 8,552 cm³ g/mL and correlated strongly with TLV. Although tumor volumes ranged over 3 orders of magnitude, SUL_average stayed within a narrow range of 2.4-5.3 units. Thus, TLV was the major component of TLG, whereas SUL_average was a minor component and was essentially constant. Further evaluation of SUL_average showed that in this cohort its 2 components, SUL_total and TLV, changed in parallel and were strongly correlated (r = 0.99, P < 0.01). Thus, whether the tumors were large or small, ¹⁸F-FDG uptake as measured by SUL_total was proportional to the TLV. Conclusion: TLG equals TLV multiplied by SUL_average, essentially TLV multiplied by a constant. Thus TLG, commonly considered a measure of metabolic activity in tumors, is also in this cohort a measure of tumor volume. The constancy of SUL_average is due to the fact that ¹⁸F-FDG uptake is proportional to tumor volume. Thus, in this study, ¹⁸F-FDG uptake was also a measure of volume.

Role of 18F-NaF-PET in assessing aortic valve calcification with age

Aortic valve calcification is a slow and progressive pathological process that can manifest in various degrees from mild thickening of the valve known as aortic sclerosis to severe calcification that hinders the leaflet motion, known as aortic stenosis. The evolving concept of aortic calcification is thought to result from infiltration of macrophages and T-lymphocytes. Moreover, the incidence of aortic valve calcification increases with age, in particular over the age of 50. In this study, we aimed to assess ¹⁸F-sodium fluoride (¹⁸F-NaF) uptake by the aortic valve on PET/CT scans performed in two age groups; 25-35 and 50-75 years of age. We hypothesized that patients aged 50-75, comprising of both healthy and high risk for cardiovascular disease (CVD), would have higher uptake of ¹⁸F-NaF than patients aged 25-35 and further that in the former group those who were at high risk for CVD had also higher ¹⁸F-NaF uptake. The 25-35-year group comprised of 6 males and 6 females, mean age 30 ± 3.5 years, while the 50-75-year group included 18 males and 20 females, mean age 61 ± 6.2 years. All underwent PET/CT imaging 90 minutes following the injection of 2.2 MBq of ¹⁸F-NaF per kg body weight. Aortic valve analysis was performed on axial sections using standard guided computer software (OsiriX MD software, version 9.0.02). The average aortic valve SUVmean was calculated for each patient. Univariate regression models stratified by age group were employed to determine the association of SUVmean with age. In the 50-75-year group, explanatory multivariable regression modeling was applied using available demographic and baseline information. SUVmean was found to be higher in the 50-75 age group than in the 25-35 age group: 0.91 ± 0.25 and 0.86 ± 0.26, respectively. The association of SUVmean with age was much stronger in individuals aged 50-75 years (r = 0.64, P<0.001) than individuals aged 25-35 years (r = 0.20, P = 0.53). In addition, in the 50-75 age group the association was much stronger in subjects with a high risk of CVD than in individuals without: r = 0.68, P = 0.001 versus r = 0.48, P = 0.042. Furthermore, the SUVmean was found to be higher in the high-risk group aged 50-75 than in the low-risk healthy group aged 50-75: 0.98 ± 0.32 and 0.83 ± 0.13. Aortic valve ¹⁸F-NaF uptake was higher in patients belonging to the age group of 50-75 years and correlated positively with age and high risk of CVD. These data provide evidence for a potential role of ¹⁸F-NaF PET/CT in identifying calcific changes in the aortic valve and may help direct therapeutic intervention prior to the development of symptomatic valvular disease.

18F-FDG-PET/CT in the quantification of photon radiation therapy-induced vasculitis

Radiation therapy (RT) is an important component of care for head and neck cancers (HNC). Photon RT vasculitis is a complication of incidental dose delivery to nearby vascular structures. However, optimal methods for early diagnosis are not clearly established. The aim of this study was to evaluate ¹⁸F-FDG-PET/CT in detecting radiation-induced vasculitis of the left common carotid (LCC) and the arch of the aorta (AoA) in patients treated for HNC. ¹⁸F-FDG-PET/CT scans obtained before RT (Pre-RT) and 3 months after RT (Post-RT) were retrospectively reviewed in 30 HNC patients (25 males, 5 females; average age 57.9±8.1 years) treated with photon RT. All subjects underwent ¹⁸F-FDG-PET/CT imaging 60 minutes after 5.0 MBq/kg ¹⁸F-FDG injection. Average standard uptake values (Avg SUVmean) of the LCC and AoA were obtained by global assessment. A two-tailed paired t-test was used to assess the difference in Avg SUVmean between pre- and post-RT imaging. Subjects demonstrated significant increased Avg SUVmean within the LCC post-RT (pre = 1.42, post = 1.65, P<0.001), with a mean increase of 0.23 SUV. Similarly, subjects exhibited higher ¹⁸F-FDG uptake in the AoA post-RT (pre = 1.44, post = 1.69, P<0.01), with a mean increase of 0.23 SUV. ¹⁸F-FDG-PET/CT may be used to detect and quantify photon RT vasculitis in HNC patients. Further investigation is warranted to evaluate the clinical implications of this pathology and the role for alternative treatment strategies in minimizing tissue toxicity.

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.