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.

Novel technique of detecting inflammatory and osseous changes in the glenohumeral joint associated with patient age and weight using FDG- and NaF-PET imaging

OBJECTIVE

The glenohumeral (GH) joint is a classic ball-and-socket joint of the shoulder subject to various pathologies including osteoarthritis (OA). Degenerative changes of the OA evident on traditional imaging are proceeded by molecular changes, which if detected early could enhance disease prevention and treatment. In this study, we use 18F-FluoroDeoxyGlucose (FDG) and 18F-sodium-fluoride (NaF)-PET/CT to investigate the effects limb laterality, age, and BMI on the inflammation and bone turnover of the GH shoulder joint.

METHODS

FDG and NaF-PET/CT scans of 41 females (mean age of 43.9 ± 14.2 years) and 45 males (mean age of 44.5 ± 13.8 years) were analyzed with a semi-quantitative technique based on predefined region of interest.

RESULTS

There was greater FDG uptake in the left side of the GH joint compared to the right in both females (left: 0.79 ± 0.17, right: 0.71 ± 0.2; P < 0.0001) and males (left: 0.76 ± 0.19, right: 0.57 ± 0.18; P < 0.0001). We also observed a strong positive association between BMI and FDG uptakes in females (left: P < 0.0001, r = 0.71, right: P < 0.0001, r = 0.58) and males (left: P < 0.0001, r = 0.56, right: P < 0.0001, r = 0.64). Association between BMI and NaF uptake were found in males as well (left: P = 0.004, r = 0.42, right: P = 0.02, r = 0.35).

CONCLUSION

Our study demonstrates the varying effect of limb laterality and BMI on FDG and NaF uptake at the GH joint. Adoption of molecular imaging will require future studies that correlate tracer uptake with relevant medical and illness history as well as degenerative change evident on traditional imaging.

18F-FDG and 18F-NaF PET/CT Global Assessment of Large Joint Inflammation and Bone Turnover in Rheumatoid Arthritis

Rheumatoid arthritis (RA) involves chronic inflammation of synovial joints, causing pain, stiffness, and limited mobility. ¹⁸F-sodium fluoride (NaF) is a PET tracer whose uptake reflects bone turnover, while ¹⁸F-fludeoxyglucose (FDG) shows glucose metabolism and can serve as a marker for inflammation. The aim of this study is to determine the feasibility of calculating the FDG and NaF mean standardized uptake value (SUVmean) in the knee joint, hip joint, and sacroiliac (SI) joint of RA patients and to determine their association with patient characteristics. Prospective FDG-PET/CT as well as NaF-PET/CT imaging was performed on 18 RA patients. The global SUVmean was calculated on FDG-PET/CT and NaF-PET/CT images using a semiautomated CT-based method of segmentation. FDG and NaF uptake were found to be significantly correlated in the knee (r = 0.77, p < 0.001), but not in the hip and SI joints. In the knee, both NaF SUVmean and FDG SUVmean were significantly correlated with body weight, BMI, leptin, and sclerostin levels (p < 0.05). NaF SUVmean was significantly positively correlated with BMI and leptin for both the hip and SI joints (p < 0.05). No significant correlation was observed between either PET parameter and age, height, erythrocyte sedimentation rate (ESR), and interleukins 1 and 6 (IL-1 and IL-6); however, FDG was correlated with inflammatory markers such as C-reactive protein (CRP) and patient global visual analogue scale (VAS-PtGlobal) in some joints. In this study, both FDG and NaF uptake were quantified in large joints of patients with RA using CT segmentation. NaF and FDG SUVmean were correlated with clinical variables related to body weight and adiposity, suggesting that degenerative joint disease may play a larger role in influencing the uptake of these tracers in large joints than RA disease activity. FDG and its correlation with markers of inflammation such as CRP and VAS-PtGlobal suggests that this tracer may serve as a more specific marker for RA disease activity than NaF. Larger prospective and longitudinal data are necessary to gain a better understanding of the roles of FDG and NaF in evaluating RA joint activity in these joints.

Predicting the Efficacy of SBRT for Lung Cancer with 18F-FDG PET/CT Radiogenomics

Purpose: to develop a radiogenomic model on the basis of 18F-FDG PET/CT radiomics and clinical-parameter EGFR for predicting PFS stratification in lung-cancer patients after SBRT treatment. Methods: A total of 123 patients with lung cancer who had undergone 18F-FDG PET/CT examination before SBRT from September 2014 to December 2021 were retrospectively analyzed. All patients’ PET/CT images were manually segmented, and the radiomic features were extracted. LASSO regression was used to select radiomic features. Logistic regression analysis was used to screen clinical features to establish the clinical EGFR model, and a radiogenomic model was constructed by combining radiomics and clinical EGFR. We used the receiver operating characteristic curve and calibration curve to assess the efficacy of the models. The decision curve and influence curve analysis were used to evaluate the clinical value of the models. The bootstrap method was used to validate the radiogenomic model, and the mean AUC was calculated to assess the model. Results: A total of 2042 radiomics features were extracted. Five radiomic features were related to the PFS stratification of lung-cancer patients with SBRT. T-stage and overall stages (TNM) were independent factors for predicting PFS stratification. AUCs under the ROC curve of the radiomics, clinical EGFR, and radiogenomic models were 0.84, 0.67, and 0.86, respectively. The calibration curve shows that the predicted value of the radiogenomic model was in good agreement with the actual value. The decision and influence curve showed that the model had high clinical application values. After Bootstrap validation, the mean AUC of the radiogenomic model was 0.850(95%CI 0.849–0.851). Conclusions: The radiogenomic model based on 18F-FDG PET/CT radiomics and clinical EGFR has good application value in predicting the PFS stratification of lung-cancer patients after SBRT treatment.

The Utility of 18F-NaF-PET/CT in Measuring the Metabolic Activity of Aging Spine: Implications for Osteoporosis

STUDY DESIGN

Cross-sectional; observational.

OBJECTIVES

To determine whether NaF-PET/CT can be used to monitor decreased bone turnover with aging in the spine.

BACKGROUND

Osteoporosis is characterized by structural changes in the bone such as decreased bone mineral density leading to increased risk for fractures. An imaging modality capable of identifying molecular changes that precede these structural changes could be critical for the early diagnosis and monitoring of osteoporosis and other metabolic bone disorders.

METHODS

The potential of 18F-sodium fluoride (NaF)-PET/CT in detecting changes in bone turnover associated with aging was examined in the lumbar spine of 88 healthy volunteers (43 females, 45 males; mean age 44.6 y). Regions of interest equal to the trabecular body of the L1-L4 vertebrae were used to calculate the mean standardized uptake value (SUVmean) and average Hounsfield unit (HU) values. Receiver-operating characteristic (ROC) curve analysis with area under the curve (AUC) using the Wilson/Brown method were generated to assess the value of NaF uptake (SUVmean) in predicting osteoporosis as defined by HU-threshold values. To determine the correlation among global SUVmean, mean HU values, and age, Spearman correlation test was performed on images acquired at 90-minutes post injection.

RESULTS

There was a significant negative correlation between NaF SUVmean and age in females (P < 0.0001, r=-0.59), and a weaker, but also significant correlation in males (P=0.03, r=-0.32). In females only, there was a significant correlation between NaF uptake and age at all acquisition time points. Measured NaF uptake increased by 10-15% with acquisition time in both sexes, from 45 to 90 min and from 90 to 180 min.

CONCLUSION

NaF-PET/CT detects decreased vertebral bone turnover with aging particularly in females. Measured NaF uptake increased with PET acquisition time after tracer injection, which must be considered in follow-up studies monitoring disease development and treatment effects.

Is Imaging Bacteria with PET a Realistic Option or an Illusion?

The application of [¹⁸F]-fluorodeoxyglucose ([¹⁸F]FDG) as a radiotracer to detect sites of inflammation (either due to bacterial infection or primary inflammation) has led to exploring the role of PET in visualizing bacteria directly at sites of infection. However, the results from such efforts are controversial and inconclusive so far. We aimed to assess the limitations of PET as an effective modality in the diagnosis of bacterial infections. Inflammation due to bacterial infections can be visualized by using [¹⁸F]FDG-PET. However, the non-specificity of [¹⁸F]FDG makes it undesirable to visualize bacteria as the underlying cause of inflammation. Hence, more specific radiotracers that possibly bind to or accumulate in bacteria-specific receptors or enzymes are being explored. Several radiotracers, including 2-deoxy-2-[¹⁸F]fluorosorbitol ([¹⁸F]FDS), 6-[¹⁸F]-fluoromaltose, [¹¹C]para-aminobenzoic acid ([¹¹C]PABA), radiolabeled trimethoprim (¹¹C-TMP) and its analog fluoropropyl-trimethoprim (¹⁸F-FPTMP), other radiolabeled sugars, and antimicrobial drugs have been used to image microorganisms. Unfortunately, no progress has been made in translating the results to routine human use; feasibility and other factors have constrained their success in clinical settings. In the current article, we discuss the limitations of direct bacterial visualization with PET tracers, but emphasize the important role of [¹⁸F]FDG-PET as the only option for detecting evidence of infection.

Emerging PET Tracers in Cardiac Molecular Imaging

¹⁸F-fluorodeoxyglucose (FDG) and ¹⁸F-sodium fluoride (NaF) represent emerging PET tracers used to assess atherosclerosis-related inflammation and molecular calcification, respectively. By localizing to sites with high glucose utilization, FDG has been used to assess myocardial viability for decades, and its role in evaluating cardiac sarcoidosis has come to represent a major application. In addition to determining late-stage changes such as loss of perfusion or viability, by targeting mechanisms present in atherosclerosis, PET-based techniques have the ability to characterize atherogenesis in the early stages to guide intervention. Although it was once thought that FDG would be a reliable indicator of ongoing plaque formation, micro-calcification as portrayed by NaF-PET/CT appears to be a superior method of monitoring disease progression. PET imaging with NaF has the additional advantage of being able to determine abnormal uptake due to coronary artery disease, which is obscured by physiologic myocardial activity on FDG-PET/CT. In this review, we discuss the evolving roles of FDG, NaF, and other PET tracers in cardiac molecular imaging.

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.

Efficacy and Failure Patterns of Early SBRT to the Primary Tumor in Advanced EGFR-Mutation-Positive Lung Cancer with EFGR-TKI Treatment: A Prospective, Single Arm, Phase II Study

Early stereotactic body radiation therapy (SBRT) to the primary tumor combined with epidermal growth factor receptor tyrosine kinase inhibitor (EFGR-TKI) treatment may increase progression-free survival (PFS) by delaying resistance in patients with advanced EGFR-mutant non-small cell lung cancer (NSCLC). In this prospective, single arm, phase II study, patients with advanced NSCLC were treated with EGFR-TKI (icotinib 125 mg tid or gefitinib 250 mg qd) for one month followed by SBRT (40-60 Gy/5-8 F/5-10 d) to the primary tumor with concurrent EGFR-TKI until disease progression. The primary endpoint was PFS and the patterns of failure. Overall survival (OS) and adverse effects (AEs) were secondary endpoints. Overall, 41 advanced NSCLC patients with EGFR mutations received treatment with 24.42 months of median follow-up time. On average, SBRT was initiated 1.49 months after EGFR-TKI administration. Tumors were found to have an average shrinkage rate of 42.50%. Median PFS was 15.23 months (95% CI 13.10-17.36), while median OS was 27.57 months (95% CI 23.05-32.09). Thirty-three patients were found to have disease progression, of which new site failure (NF) (22 patients, 66.66%) was the most common pattern, followed by original site failure (OF) (7 patients, 21.21%) and simultaneous OF/NF (ONF) (4 patients, 12.12%). There were no Aes equal to or greater than grade 3, with the most frequent AE being radiation pneumonitis. Therefore, administering therapy targeted at the primary tumor using early SBRT after EGFR-TKI initiation is a new potentially safe and effective approach to treat EGFR-mutant advanced NSCLC.

The effects of limb laterality and age on the inflammation and bone turnover of the acromioclavicular shoulder joint: 18 F-fluorodeoxyglucose and 18 F-sodium-fluoride-PET/computed tomography study

PURPOSE

The acromioclavicular (AC) joint is a common site of injury and degenerative changes such as osteoarthritis (OA) of the shoulder. Physical manifestations of OA are preceded by molecular changes, detection of which may enhance early prophylaxis and monitoring of disease progression. In this study, we investigate the use of 18 F-FDG and 18 F-NaF-PET/CT to assess the effects of limb laterality and age on the inflammation and bone turnover of the AC shoulder joint.

METHODS

We analyzed FDG and NaF-PET/CT scans of 41 females (mean age of 43.9 ± 14.2 years) and 45 males (mean age of 44.5 ± 13.8 years) using a semiquantitative technique based on predefined ROI.

RESULTS

There was a greater NaF uptake in the right side of the AC joint compared with the left in both females (left: 2.22 ± 1.00; right: 3.08 ± 1.18; P < 0.0001) and males (left: 2.57 ± 1.49; right: 2.99 ± 1.40; P = 0.003). No consistent correlation between age and NaF or FDG uptakes were found in both females and males. There was also a positive correlation between FDG and NaF uptakes in both left ( P = 0.01; r = 0.37) and right ( P = 0.0006; r = 0.53) AC joints of male subjects.

CONCLUSION

Our study is the first to reveal the varying effect of right-left limb laterality and aging on FDG and NaF uptake at the AC joint. Future studies correlating the history of shoulder trauma, pain, and degenerative change with FDG and NaF-PET/CT findings will be critical in the adoption of molecular imaging in the clinical setting.

Prognostic significance of conventional and volumetric PET parameters with and without partial volume correction in the assessment of head and neck squamous cell carcinoma

BACKGROUND

The optimal quantification of PET in assessment of head and neck squamous cell carcinoma (HNSCC) is still under development. The effect of partial volume correction (PVC) on the evaluation of survival in the HNSCC patients has not been investigated yet.

METHODOLOGY

Pretreatment 18F-FDG-PET/CT scans of a selected group of 57 patients with advanced stage HNSCC were collected. Conventional (SUVmean and SUVmax) and volumetric [total lesion glycolysis (TLG) and metabolic tumor volume (MTV)] PET metrics were calculated. The ROVER software (ABX GmbH, Radeberg, Germany) automatically applied PVC to the PET metrics. Cox proportional hazards regression model calculated hazard ratio (HR) for assessment of predictive parameters of progression-free survival (PFS).

RESULTS

In multivariate Cox regression analysis, including age, gender, race, human papillomavirus status, and stage, the only significant predictors of PFS were the volumetric PET parameters (TLG: HR, 1.003; 95% CI, 1.001-1.005; P = 0.02), pvcTLG (HR, 1.002; 95% CI, 1.001-1.004; P = 0.01) and MTV (HR, 1.050; 95% CI, 1.024-1.077; P < 0.01). The partial volume-corrected values were significantly higher than the noncorrected values (Wilcoxon sign test; P < 0.05). However, there was not a statistically significant difference between the nonpartial volume corrected and partial volume-corrected PET metrics for assessment of PFS.

CONCLUSION

Volumetric PET metrics were predictors of PFS in Cox regression analysis. Applying PVC could not significantly improve the accuracy of PET metrics for assessment of PFS.

Role of Molecular Imaging with PET/MR Imaging in the Diagnosis and Management of Brain Tumors

Gliomas are the most common primary brain tumors. Hybrid PET/MR imaging has revolutionized brain tumor imaging, allowing for noninvasive, simultaneous assessment of morphologic, functional, metabolic, and molecular parameters within the brain. Molecular information obtained from PET imaging may aid in the detection, classification, prognostication, and therapeutic decision making for gliomas. ¹⁸F-fluorodeoxyglucose (FDG) has been widely used in the setting of brain tumor imaging, and multiple techniques may be employed to optimize this methodology. More recently, a number of non-¹⁸F-FDG-PET radiotracers have been applied toward brain tumor imaging and are used in clinical practice.

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.

A Critical Review of PET Tracers Used for Brain Tumor Imaging

The brain is a common site for metastases as well as primary tumors. Although evaluation of these malignancies with contrast-enhanced MR imaging defines current clinical practice, ¹⁸F-fluorodeoxyglucose (FDG)-PET has shown considerable utility in this area. In addition, many other tracers targeting various aspects of tumor biology have been developed and tested. This article discusses recent developments in PET imaging and the anticipated role of FDG and other tracers in the assessment of brain tumors.

An understanding of the atherosclerotic molecular calcific heterogeneity between coronary, upper limb, abdominal, and lower extremity arteries as assessed by NaF PET/CT

We aimed to quantify the heterogeneity of atherosclerosis in upper and lower limb vessels using ¹⁸F-NaF-PET/CT and compare calcification in coronary arteries to peripheral arteries. 68 healthy controls (42±13.5 years, 35 females, 33 males) and 40 patients at-risk for cardiovascular disease (55±11.9 years, 22 females, 18 males) underwent PET/CT imaging 90 minutes after the injection of ¹⁸F-NaF (2.2 Mbq/Kg). The following arteries were examined: coronary artery (CA), ascending aorta (AS), arch of aorta (AR), descending aorta (DA), abdominal aorta (AA), common iliac artery (CIA), external iliac artery (EIA), femoral artery (FA), popliteal artery (PA). Average SUVmean (aSUVmean) was calculated for each arterial segment. A paired t-test compared the aSUVmean between CA vs. AS, AR, DA, AA, CIA, EIA, FA, and PA. CA aSUVmean in the at-risk group was higher than the healthy control group (0.74±0.04 vs. 0.67±0.04, P=0.03). Furthermore, the ¹⁸F-NaF uptake in the CA was lower than in AS, AR, DA, AA, CIA, EIA, FA, and PA in both healthy (all P≤0.0001) and at-risk (all P≤0.0001). Higher ¹⁸F-NaF uptake in non-cardiac arteries in both healthy controls and patients at-risk suggests CA calcification is a late manifestation of atherosclerosis. This differential expression of atherosclerosis is likely due to interaction of hemodynamic parameters specific to the vascular bed and systemic factors related to the development of atherosclerosis.

Novel Musculoskeletal and Orthopedic Applications of 18F-Sodium Fluoride PET

PET imaging with ¹⁸F-sodium fluoride (NaF), combined with computed tomography or magnetic resonance, is a sensitive method of assessing bone turnover. Although NaF-PET is gaining popularity in detecting prostate cancer metastases to bone marrow, osseous changes represent secondary effects of cancer cell growth. PET tracers more appropriate for assessing prostate cancer metastases directly portray malignant activity and include ¹⁸F-fluciclovine and prostatic specific membrane antigen ligands. Recent studies investigating NaF-PET suggest utility in the assessment of benign musculoskeletal disorders. Emerging applications in assessing traumatic injuries, joint disease, back pain, orthopedic complications, and metabolic bone disease are discussed.

Total-Body PET Imaging of Musculoskeletal Disorders

Imaging of musculoskeletal disorders, including arthritis, infection, osteoporosis, sarcopenia, and malignancies, is often limited when using conventional modalities such as radiography, computed tomography (CT), and MR imaging. As a result of recent advances in Positron Emission Tomography (PET) instrumentation, total-body PET/CT offers a longer axial field-of-view, higher geometric sensitivity, and higher spatial resolution compared with standard PET systems. This article discusses the potential applications of total-body PET/CT imaging in the assessment of musculoskeletal disorders.

Utilization of NaF-PET/CT in assessing global cardiovascular calcification using CHADS2 and CHADS2-VASc scoring systems in high risk individuals for cardiovascular disease

CHADS₂ and CHA₂DS₂-VASc scores are used to estimate the risk of strokes in patients with atrial fibrillation. We sought to determine the global quantification of cardiovascular molecular calcification in high risk individuals by NaF-PET/CT and compare it with CHADS₂ and CHA₂DS₂-VASc scores. We identified 40 high risk individuals for cardiovascular disease from the Cardiovascular Molecular Calcification Assessed by ¹⁸F-NaF PET CT (CAMONA) trial and calculated CHADS₂ and CHADS₂-VASc scores for each. Ninety minutes after NaF injection (2.2 Mbq/kg), PET/CT imaging was performed. CT imaging was done for attenuation correction and anatomic correlation. The global cardiac uptake was calculated from regions of interest manually drawn on axial PET/CT images made in OsirixMD. Global cardiac average SUVmean (aSUVmean) values were calculated, and linear regression analysis was employed for statistical purposes. Subjects had mean age of 55 ± 11.9 SD years, (Range: 23-73 years), female 55%. The sample consisted of subjects with a mean aSUVmax of 2.9 ± 1.4, aSUVmean was 0.8 ± 0.2, CHADS₂ 0.9 ± 0.6 (Range: 0-3), CHA₂DS₂-VASc 1.8 ± 1.3 (Range: 0-5). Based on the linear regression models, we found a direct correlation between global cardiac aSUVmean and CHADS₂ score (r=0.58, P≤0.0001) and also between global cardiac aSUVmean and CHA₂DS₂-VASc (r=0.37, P=0.01). Based on the results of our study we conclude that patients with a higher CHADS₂ and CHA₂DS₂-VASc scores had a higher atherosclerotic burden and could be at greater risk of cardiovascular events. These scoring systems can help with risk stratification for predicting future adverse atherosclerotic events.

Correlation of whole-bone marrow dual-time-point 18F-FDG, as measured by a CT-based method of PET/CT quantification, with response to treatment in newly diagnosed multiple myeloma patients

The practical application of dual-time-point-imaging (DTPI) technique still remains controversial. One of the issues is that current parameters of DTPI quantification suffer from some deficiencies, mainly limited sampling of the diseased sites by confining measurements to specific locations. We aimed to examine the correlation between the percent change from early to delayed scans in whole-bone marrow (WBM) ¹⁸F-FDG uptake, as measured by a CT-based method of PET/CT quantification, and response to treatment in multiple myeloma (MM) patients. Pre-treatment ¹⁸F-FDG-PET/CT scans of 36 newly diagnosed MM patients were collected in a prospective study at 1 h and 3 h post tracer injection (NCT02187731). A threshold algorithm based on bone Hounsfield units on CT was applied to segment and quantify WBM ¹⁸F-FDG uptake. Patients were separated into two treatment groups: high-dose therapy with autologous stem cell transplant (HDT) and non-high dose therapy (non-HDT). The International Response Criteria for MM patients was used to determine each patient's response to treatment. In the HDT group, WBM ¹⁸F-FDG uptake increased significantly in patients that had a poor response to treatment, from a median of 1.31 (IQR: 1.13-1.64) at 1 h to a median of 1.85 (1.45-2.10) at 3 h. The median percent change was 37.77% (IQR: 23.47-46.4), with a range of 6.10-50.73 (P = 0.003). However, no significant change in uptake was observed in patients with a complete response (P = 0.24). The same trend was observed for the non-HDT group. WBM uptake of ¹⁸F-FDG assessed with dual-time-point imaging may have a role in predicting treatment response in MM.

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).

Association of triglyceride to high density lipoprotein ratio with global cardiac microcalcification to evaluate subclinical coronary atherosclerosis in non-diabetic individuals

OBJECTIVE

Triglycerides (TG) to high density lipoprotein (HDL) ratio has been proposed as a marker of insulin resistance and atherosclerosis. We hypothesize that TG/HDL ratio correlates positively with global cardiac microcalcification as assessed by NaF-PET/CT as a surrogate marker for coronary atherosclerosis in healthy non-diabetic individuals.

METHOD

We identified 68 healthy, non-diabetic individuals (age 41.7 ± 13.5 years; 35/33 female/male) from the CAMONA trial. All underwent PET/CT imaging 90 minutes after NaF injection (2.2 Mbq/Kg). Global cardiac average SUVmean (aSUVmean) was calculated by a trained physician for each individual. Fasting plasma lipid profile (total cholesterol (TC), low-density lipoprotein (LDL), HDL, and TG) and fasting plasma glucose were recorded. TG/HDL ratio was calculated for every individual. Univariate and multivariate linear regression models were used to assess the association between TG/HDL ratio and global cardiac aSUVmean.

RESULT

On univariate analysis, there was a positive linear association of TG/HDL ratio and global cardiac aSUVmean (r=0.244, B=0.047, P=0.045). On multivariate analysis adjusted for age, gender, systolic blood pressure, diastolic blood pressure, smoking status, total cholesterol, low-density lipoprotein, and fasting plasma glucose, TG/HDL ratio was found to be independently associated with global cardiac aSUVmean (B=0.060, 95% CI: 0.007-0.114, P=0.027).

CONCLUSION

There was a positive correlation between TG/HDL ratio with global cardiac microcalcification assessed by NaF-PET/CT imaging.

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.

NaF-PET/CT global assessment in detecting and quantifying subclinical cardiac atherosclerosis and its association with blood pressure in non-dyslipidemic individuals

BACKGROUND

We used ¹⁸F-sodium fluoride (NaF) to assess early atherosclerosis in the global heart in asymptomatic individuals with a coronary calcium score of zero and without a formal diagnosis of hypertension. We hypothesized that these individuals might present with subclinical atherosclerosis that correlates with systolic, diastolic and mean arterial pressure (SBP, DBP, and MAP).

METHODS

We identified 20 asymptomatic individuals (41.6 ± 13.8 years, 8 females) from the CAMONA trial with C-reactive protein ≥3 mg/L, no smoking history, diabetes (fasting blood glucose <126 mg/dl) and dyslipidemia per the Adult Treatment Panel III Guidelines: untreated LDL <160 mg/dL, total cholesterol <240 mg/dL, HDL >40 mg/dL. All underwent PET/CT imaging 90 minutes after NaF injection (2.2 Mbq/Kg). The global cardiac average SUVmean (aSUVmean) was calculated for each individual. Correlation coefficients and linear regression models were employed for statistical analysis.

RESULTS

Significant positive correlation was revealed between global cardiac NaF uptake and all blood pressures: SBP (r=0.44, P=0.05), DBP (r=0.64, P=0.002), and MAP (r=0.59, P=0.007). After adjusting for age and gender, DBP and MAP were independent predictors of higher global cardiac NaF uptake.

CONCLUSION

NaF-PET/CT for detecting and quantifying subclinical atherosclerosis in asymptomatic individuals revealed that cardiac NaF uptake correlated independently with DBP and MAP.

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.

Assessing the feasibility of NaF-PET/CT versus FDG-PET/CT to detect abdominal aortic calcification or inflammation in rheumatoid arthritis patients

OBJECTIVE

We aimed to determine whether NaF-PET/CT or FDG-PET/CT can detect abdominal aortic molecular calcification and inflammation in patients with rheumatoid arthritis (RA).

METHODS

In this study, 18 RA patients (4 women, 14 men; mean age 56.0 ± 11.7) and 18 healthy controls (4 women, 14 men; mean age 55.8 ± 11.9) were included. The controls were matched to patients by sex and age (± 4 years). All subjects of this study underwent NaF-PET/CT scanning 90 min following the administration of NaF. FDG-PET/CT imaging was performed 180 min following intravenous FDG injection. Using OsiriX software, the global mean standardized uptake value (global SUVmean) in abdominal aorta was calculated for both FDG and NaF. The NaF SUVmean and FDG SUVmean were divided by the blood pool activity providing target-to-background ratios (TBR) namely, NaF-TBRmean and FDG-TBRmean. The CT calcium volume score was obtained using a growing region algorithm based on Hounsfield units.

RESULTS

The average NaF-TBRmean score among RA patients was significantly greater than that of healthy controls (median 1.61; IQR 1.49-1.88 and median 1.40; IQR 1.23-1.52, P = 0.002). The average CT calcium volume score among RA patients was also significantly greater than that of healthy controls (median 1.96 cm³; IQR 0.57-5.48 and median 0.004 cm³; IQR 0.04-0.05, P < 0.001). There was no significant difference between the average FDG-TBRmean scores in the RA patients when compared to healthy controls (median 1.29; IQR 1.13-1.52 and median 1.29; IQR 1.13-1.52, respectively, P = 0.98).

CONCLUSION

Quantitative assessment with NaF-PET/CT identifies increased molecular calcification in the wall of the abdominal aorta among patients with RA as compared with healthy controls, while quantitative assessment with FDG-PET/CT did not identify a difference in aortic vessel wall FDG uptake between the RA and healthy control groups.

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.

Comparison of methods of quantifying global synovial metabolic activity with FDG-PET/CT in rheumatoid arthritis

AIM

2-deoxy-2-[¹⁸ F]fluoro-d-glucose positron emission tomography/computed tomography (FDG-PET/CT) can portray increased glycolysis due to inflammation in rheumatoid arthritis (RA). The aim of this study was to evaluate and compare the reliability and construct validity of two methods of quantifying RA disease activity using FDG-PET/CT.

METHOD

Nineteen RA patients and 19 healthy controls matched to sex and age underwent prospective FDG-PET/CT imaging. Metabolic and volumetric metrics were calculated using fixed and adaptive thresholding techniques and partial volume correction. Fixed thresholds segmented regions above average maximum physiological uptake in controls. Differences of means between RA and controls were assessed using t tests, and discrimination was assessed using receiver operating characteristics. Spearman correlation analysis was used to assess associations between FDG-PET/CT measures and clinical assessments of disease activity.

RESULTS

All FDG-PET/CT measures were substantially different and nearly non-overlapping between RA and controls (all P < .001). Area under the curve (AUC) for adaptive threshold parameters ranged from 0.986 to 0.997, and AUC for fixed threshold parameters ranged from 0.898 to 0.945. PET parameters were found to correlate positively with various clinical features, namely C-reactive protein, erythrocyte sedimentation rate, interleukin (IL)-6, IL-1, and swollen joint count.

CONCLUSION

All FDG-PET/CT parameters reflecting global RA disease activity differentiated between RA and controls, indicating high clinical utility to diagnose and assess RA. Adaptive thresholds can be used in a wider setting without control data, but methods utilizing fixed thresholds were more reproducible and more closely associated with indications of inflammation.

Evolving Role of PET-Based Novel Quantitative Techniques in the Management of Hematological Malignancies

"The role of ¹⁸F-fluorodeoxyglucose PET/computed tomography in hematological malignancies continues to expand in disease diagnosis, staging, and management. A key advantage of PET over other imaging modalities is its ability to quantify tracer uptake, which can be used to determine degree of disease activity. Although tracer uptake with PET is conventionally measured in focal lesions, novel quantitative techniques are being investigated that set objective protocols and produce robust parameters that represent total disease activity portrayed by PET. This article discusses recent advances in PET quantification that can improve reliability and accuracy of characterizing hematological malignancies."

Association between age, uptake of 18F-fluorodeoxyglucose and of 18F-sodium fluoride, as cardiovascular risk factors in the abdominal aorta

OBJECTIVE

We aimed to assess the feasibility of quantifying fluorine-18-fluorodexoglucose (¹⁸F-FDG) and ¹⁸F-sodium fluoride (¹⁸F-NaF) uptake in abdominal aorta and examine their association with age and cardiovascular risk factors.

SUBJECTS AND METHODS

Our study comprised 123 subjects (48±14 years of age, 62 men) including 78 healthy volunteers and 45 patients with chest pain syndrome, who originally enrolled in the CAMONA study in Odense, Denmark (NCT01724749). All subjects underwent ¹⁸F-FDG positron emission tomography/computed tomography (PET/CT) and ¹⁸F-NaF PET/CT on separate days, 180min and 90min after administration of tracers, respectively. The global tracer uptake value (GTUV) in the abdominal aorta was determined as sum of the product of each slice area and its corresponding average standardized uptake value (SUV mean), divided by the sum of those slice areas. In addition, for each subject, the 10 years Framingham risk score (FRS) was calculated. The correlations between ¹⁸F-NaF and ¹⁸F-FDG GTUV with age and 10 years FRS were assessed in all, healthy and patient subjects.

RESULTS

There was a significant, positive correlation between subjects' age and ¹⁸F-NaF GTUV (r=0.35, P<0.001), but not ¹⁸F-FDG GTUV (r=0.06, P=0.53). Also, there was a significant, positive correlation between 10 years FRS and ¹⁸F-NaF GTUV (r=0.30, P<0.001), but not ¹⁸F-FDG GTUV (r=0.01, P=0.95). Individual differences in ¹⁸F-FDG and 1¹⁸F-NaF uptake were large in both healthy subjects and patients.

CONCLUSION

In this study, the global uptake of ¹⁸F-NaF in abdominal aorta was positively associated with age and 10 years FRS in all subjects, healthy and patient groups, whereas the global uptake of ¹⁸F-FDG was not.

Metastatic Seeding Attacks Bone Marrow, Not Bone: Rectifying Ongoing Misconceptions

Conventional modalities, such as bone scintigraphy, are commonly used to assess osseous abnormalities in skeletal metastasis. Fluorine-18 (¹⁸F)-sodium fluoride (NaF) PET similarly portrays osteoblastic activity but with improved spatial and contrast resolution and more accurate anatomic localization. However, these modalities rely on indirect evidence for tumor activity. PET imaging with ¹⁸F-fluorodeoxyglucose (FDG) and tumor-specific tracers may have an increased role by directly portraying the metabolic activity of cancer cells, which are often seeded in bone marrow and cause osseous disease after initial latency. This article describes the utility and limitations of these modalities in assessing skeletal metastases.

Pre-treatment partial-volume-corrected TLG is the best predictor of overall survival in patients with relapsing/refractory non-hodgkin lymphoma following radioimmunotherapy

The role of fluorodeoxyglucose-positron emission tomography (FDG-PET) has been well established in assessment of lymphoma, including non-Hodgkin lymphoma (NHL). The aim of this study was to compare changes and survival predictive values of various quantification parameters of FDG-PET/CT in patients with relapsing/refractory lymphoma before and after radioimmunotherapy (RIT). Data from 17 patients with relapsing/refractory NHL, treated with targeted RIT after chemotherapy/radiotherapy, were retrospectively collected. FDG-PET/CT scans were performed approximately three months before and six months after RIT. An adaptive contrast-oriented thresholding algorithm was used to segment lesions on the FDG-PET images. Wilcoxon signed-rank tests were used to assess changes in SUVmax, SUVmean, partial volume-corrected SUVmean (pvcSUVmean), total lesion glycolysis (TLG), and pvcTLG before and after treatment. The patients were followed up after completing RIT for up to 10 years. Kaplan-Meier and Cox regression analyses evaluated the association between the quantification parameters and survival data. In the survived group, the decrease in mean percentage of change for TLG and pvcTLG was greater than SUVmax, SUVmean and pvcSUVmean [TLG: 253.9 to 106.9, -81.4%; P = 0.052 and pvcTLG: 368.9 to 153.3, -58.4%; P = 0.04]. In addition, overall survival (OS) was shorter in patients with pre-RIT pvcTLG more than 644 compared to those below this value (log-rank P < 0.01). In univariate Cox regression for OS, a higher baseline pvcTLG was a significant prognostic factor (HR: 6.8, P = 0.02). Our results showed that pre-treatment pvcTLG was the best predictor of OS in patients with relapsing/refractory NHL following RIT.

Diagnosis and Monitoring of Osteoporosis With 18F-Sodium Fluoride PET: An Unavoidable Path for the Foreseeable Future

The prevalence of metabolic bone diseases particularly osteoporosis and its precursor, osteopenia, continue to grow as serious global health issues today. On a worldwide perspective, 200million people suffer from osteoporosis and in 2005, over 2million fracture incidents were estimated due to osteoporosis in the United States. Currently, osteoporosis and other metabolic bone diseases are evaluated primarily through dual energy X-ray absorptiometry, and rarely by bone biopsy with tetracycline labeling or Technetium-99m (^99mTc) based bone scintigraphy. Deficiencies in these methods have prompted the use of more precise methods of assessment. This review highlights the use of ¹⁸F-sodium fluoride (NaF) with PET (NaF-PET), NaF-PET/CT, or NaF-PET/MRI in the evaluation of osteoporosis and osteopenia in the lumbar spine and hip. This imaging modality provides a molecular perspective with respect to the underlying metabolic alterations that lead to osseous disorders by measuring bone turnover through standardized uptake values. Its sensitivity and ability to examine the entire skeletal system make it a more superior imaging modality compared to standard structural imaging techniques. Further research is needed to determine its accuracy in reflecting the efficacy of therapeutic interventions in metabolic bone diseases.