2-Deoxy-2-[F-18]fluoro-D-glucose joint uptake on positron emission tomography images: rheumatoid arthritis versus osteoarthritis

Case series of rhomboid ligament degeneration, mimicking a supraclavicular adenopathy

A case series of 3 different patients showing very rare costoclavicular ligament increased SUV uptake on PET\CT with history of different types of cancer. This finding has not been described before especially that it corresponds to benign degenerative rather than sinister process. This is supported by low SUV and stability over months of follow up. Furthermore, even in degenerative joint diseases we have found very rare cases of such uptake. Experienced radiologists need to be always involved in the multidisciplinary team approach and be very cautious when approaching such findings to avoid any unnecessary medical interventions.

CD64 as novel molecular imaging marker for the characterization of synovitis in rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is one of the most prevalent and debilitating joint diseases worldwide. RA is characterized by synovial inflammation (synovitis), which is linked to the development of joint destruction. Magnetic resonance imaging and ultrasonography are widely being used to detect the presence and extent of synovitis. However, these techniques do not reveal the activation status of inflammatory cells such as macrophages that play a crucial role in synovitis and express CD64 (Fc gamma receptor (FcγR)I) which is considered as macrophage activation marker.

OBJECTIVES

We aimed to investigate CD64 expression and its correlation with pro-inflammatory cytokines and pro-damaging factors in human-derived RA synovium. Furthermore, we aimed to set up a molecular imaging modality using a radiolabeled CD64-specific antibody as a novel imaging tracer that could be used to determine the extent and phenotype of synovitis using optical and nuclear imaging.

METHODS

First, we investigated CD64 expression in synovium of early- and late-stage RA patients and studied its correlation with the expression of pro-inflammatory and tissue-damaging factors. Next, we conjugated an anti-CD64 antibody with IRDye 800CW and diethylenetriamine penta-acetic acid (DTPA; used for 111In labeling) and tested its binding on cultured THP1 cells, ex vivo RA synovium explants and its imaging potential in SCID mice implanted with human RA synovium explants obtained from RA patients who underwent total joint replacement.

RESULTS

We showed that CD64 is expressed in synovium of early and late-stage RA patients and that FCGR1A/CD64 expression is strongly correlated with factors known to be involved in RA progression. Combined, this makes CD64 a useful marker for imaging the extent and phenotype of synovitis. We reported higher binding of the [111In]In-DTPA-IRDye 800CW anti-CD64 antibody to in vitro cultured THP1 monocytes and ex vivo RA synovium compared to isotype control. In human RA synovial explants implanted in SCID mice, the ratio of uptake of the antibody in synovium over blood was significantly higher when injected with anti-CD64 compared to isotype and injecting an excess of unlabeled antibody significantly reduced the antibody-binding associated signal, both indicating specific receptor binding.

CONCLUSION

Taken together, we successfully developed an optical and nuclear imaging modality to detect CD64 in human RA synovium in vivo.

Label-free, multi-parametric assessments of cell metabolism and matrix remodeling within human and early-stage murine osteoarthritic articular cartilage

Osteoarthritis (OA) is characterized by the progressive deterioration of articular cartilage, involving complicated cell-matrix interactions. Systematic investigations of dynamic cellular and matrix changes during OA progression are lacking. In this study, we use label-free two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) imaging to assess cellular and extracellular matrix features of murine articular cartilage during several time points at early stages of OA development following destabilization of medial meniscus surgery. We detect significant changes in the organization of collagen fibers and crosslink-associated fluorescence of the superficial zone as early as one week following surgery. Such changes become significant within the deeper transitional and radial zones at later time-points, highlighting the importance of high spatial resolution. Cellular metabolic changes exhibit a highly dynamic behavior, and indicate metabolic reprogramming from enhanced oxidative phosphorylation to enhanced glycolysis or fatty acid oxidation over the ten-week observation period. The optical metabolic and matrix changes detected within this mouse model are consistent with differences identified in excised human cartilage specimens from OA and healthy cartilage specimens. Thus, our studies reveal important cell-matrix interactions at the onset of OA that may enable improved understanding of OA development and identification of new potential treatment targets.

Clinical features of atlantoaxial involvement in patients with rheumatoid arthritis using 18F-fluorodeoxyglucose-positron emission tomography with computed tomography

INTRODUCTION/OBJECTIVES

Cervical spine involvement is one of the most serious complications in rheumatoid arthritis (RA). The study aim was to assess the clinical significance of atlantoaxial (AA) joint involvement detected by ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) with computed tomography (CT) in patients with RA.

METHOD

A prospective cross-sectional study was conducted to evaluate AA joint involvement detected by FDG-PET/CT in consecutive RA patients from December 2017 to February 2022. We investigated the relationship between AA joint involvement and clinical data, including disease activity and patients' cervical symptoms.

RESULTS

Among 48 patients enrolled, abnormal FDG uptake at AA joint was detected in 13 (27%). Rheumatoid factor titre, initial disease activity score 28-erythrocyte sedimentation rate and total standardized uptake value were significantly higher in the 13 patients than in the others (P = 0.004, P < 0.001 and P = 0.001, respectively). All patients with abnormal FDG uptake at AA joint had some cervical symptoms regardless of cervical spine X-ray abnormalities. Neck pain on movement and at rest were more frequent in the 13 patients than in the others (P = 0.001 and P = 0.004, respectively). The most sensitive symptom associated with AA joint involvement was neck pain on movement (sensitivity, 69%), and the most specific symptom was neck pain at rest (specificity, 100%).

CONCLUSIONS

AA joint involvement was commonly observed by FDG-PET/CT in patients with active RA, independent of radiographic findings. Specific cervical symptoms can be important surrogate markers for detection of potential AA synovitis associated with active RA. Key Points • AA joint involvement was frequently seen in RA with high disease activity independent of radiographic findings. • Neck pain was a hallmark of AA joint involvement reflecting disease activity, and resting pain was highly specific.

Update on Imaging of Inflammatory Arthritis and Related Disorders

Arthritis and other rheumatic disorders are very frequent in the general population and responsible for a huge physical and disability burden to affected patients as well as a major cost to the society. Precise evaluation often relies on clinical data only but additional imaging may be required i) for a more objective assessment of the disease status, such as in rheumatoid arthritis (RA) or ankylosing spondyloarthritis (AS), ii) for providing prognostic information and evaluating response to treatment or iii) for establishing diagnosis, in patients with unclear clinical picture, such as polymyalgia rheumatica (PMR) and large-vessel vasculitis (LVV). Besides radiological techniques (x-rays, ultrasound, and MRI), functional and molecular imaging has emerged as a valid tool for this purpose in several disorders. Bone scanning has long been a method of choice but is now more used as a triage tool in patients with unclear complaints, including degenerative disorders (eg osteoarthritis). ¹⁸F-FDG-PET/CT (FDG) proved efficient in assessing the extent of the disease and response to treatment in RA and related disorders, and to provide accurate diagnosis in some systemic disorders, including PMR and LVV. Based on glucose metabolism, FDG-PET/CT is able to show increased metabolism in peripheral cells involved in inflammation (eg neutrophils, lymphocytes or monocytes/macrophages) but also in fibroblasts that proliferate in the pannus. The lack of specificity of FDG is a limitation and many alternative tracers were developed at the preclinical stage or applied in the clinics, especially within clinical trials. They include imaging of macrophages using translocator protein (TSPO), folate-receptors or other targets on activated cells. These new tools will undoubtedly become more and more available in the everyday clinical workup of patients with rheumatisms. Finally, it should be kept in mind that a very simple tracer, ¹⁸F-fluoride is widely more performant in AS than FDG.

Preclinical evaluation and pilot clinical study of [18F]AlF-NOTA-FAPI-04 for PET imaging of rheumatoid arthritis

PURPOSE

Fibroblast-like synoviocytes (FLSs) are key effector cells in the inflamed joints of patients with rheumatoid arthritis (RA). Previous studies have suggested that fibroblast activation protein (FAP) is highly expressed in RA-derived FLSs and is a specific marker of activated RA FLSs. In this study, we developed aluminum-[¹⁸F]-labeled 1,4,7-triazacyclononane-N,N',N″-triacetic acid-conjugated FAP inhibitor 04 ([¹⁸F]AlF-NOTA-FAPI-04) to image RA-FLSs in vitro and arthritic joints in collagen-induced arthritis (CIA) mice and RA patients.

METHODS

RA FLSs and NIH3T3 cells transfected with FAP were used to perform in vitro-binding studies. Biodistribution was conducted in normal DBA1 mice. Collagen-induced arthritis (CIA) models with different arthritis scores were subjected to [¹⁸F]AlF-NOTA-FAPI-04 and ¹⁸F-FDG PET imaging. Histological examinations were performed to evaluate FAP expression and Cy3 dye-labeled FAPI-04(Cy3-FAPI-04) uptake. Blocking studies with excess unlabeled FAPI-04 in CIA mice and NIH3T3 xenografts in immunocompromised mice were used to evaluate the binding specificity of [¹⁸F]AlF-NOTA-FAPI-04. Additionally, [¹⁸F]AlF-NOTA-FAPI-04 PET imaging was performed on two RA patients.

RESULTS

The binding of [¹⁸F]AlF-NOTA-FAPI-04 increased significantly in RA FLSs and NIH3T3 cells overexpressing FAP compared to their parental controls (^FAP-GFP-NIH3T3 vs. ^GFP-NIH3T3, 2.40 ± 0.078 vs. 0.297 ± 0.05% AD/10⁵ cells; RA FLSs vs. OA FLSs, 1.54 ± 0.064 vs. 0.343 ± 0.056% AD/10⁵ cells). Compared to ¹⁸F-FDG imaging, [18F]AlF-NOTA-FAPI-04 showed high uptake in inflamed joints in the early stage of arthritis, which was positively correlated with the arthritic scores (Pearson r=0.834, P<0.001). In addition, the binding of [¹⁸F]AlF-NOTA-FAPI-04 to cells with high FAP expression and the uptake of [¹⁸F]AlF-NOTA-FAPI-04 in arthritic joints both could be blocked by excessive unlabeled FAPI-04. Fluorescent staining showed that the intensity of Cy3-FAPI-04 binding to FAP increased accordingly as the expression of FAP protein increased in cells and tissue sections. Furthermore, the uptake of [¹⁸F]AlF-NOTA-FAPI-04 in ^FAP-GFP-NIH3T3 xenografts was significantly higher than that in ^GFP-NIH3T3 xenograft (35.44 ± 4.27 vs 7.92 ± 1.83% ID/mL). Finally, [¹⁸F]AlF-NOTA-FAPI-04 PET/CT imaging in RA patients revealed nonphysiologically high tracer uptake in the synovium of arthritic joints.

CONCLUSION

[¹⁸F]AlF-NOTA-FAPI-04 is a promising radiotracer for imaging RA FLSs and could potentially complement the current noninvasive diagnostic parameters.

2-deoxy-2[18F]fluoro-D-glucose positron emission tomography-computed tomography in rheumatological diseases

2-deoxy-2[18F]fluoro-D-glucose (FDG) PET-CT has revolutionized oncological imaging. The cellular processes that make cancer cells visible on FDG PET-CT also occur in a number of inflammatory cells. Exploiting this phenomenon has led to a growth of evidence supporting the use of FDG PET-CT in a wide range of infective and inflammatory diseases. Rheumatological diseases can affect multiple sites within the musculoskeletal system alongside multi-organ extra-articular disease manifestations. Inflammation is central to these diseases, making FDG PET-CT a logical choice. In this review article we describe the various applications of FDG PET-CT in rheumatological diseases using illustrative examples to highlight the beneficial role of FDG PET-CT in each case.

Dissociation between 2-[18F]fluoro-2-deoxy-D-glucose positron emission computed tomography, ultrasound and clinical assessments in patients with non-severe rheumatoid arthritis, including remission

Background

Inflammation of patients joints with severe disease activity of rheumatoid arthritis (RA) has already been visualized and quantified by 2-[¹⁸F]fluoro-2-deoxy-D-glucose positron emission computed tomography ([¹⁸F] FDG PET/CT), but little is known about the metabolic status and its relationship with clinical and ultrasonography (US) metrology in patients with low/moderate activity or in remission.

Methods

Clinical assessments [based on 28-joint disease activity score (DAS₂₈-CRP) and Clinical Disease Activity Index (CDAI)], [¹⁸F] FDG PET/CT, US and X-ray were performed on 63 RA patients classified into remission or low/moderate or severe disease activity groups. PET/CT was visually and then semi-quantitatively analysed by determining the standardized uptake value (SUV) of positive joints.

Results

Of the 1764 joints, 21.1% were tender only, 13.7% swollen only, 27.6% tender or swollen, 7.3% tender and swollen, 20.5% PET/CT-positive and 8.6% US-positive. PET and US measurements were correlated, albeit with poor concordance. The positive predictive value of PET/CT for clinical evaluation (tender and/or swollen) was low, whereas its negative predictive value was high. Highly significant differences were found with the number of PET/CT-positive joints and with cumulative SUV between “severe” and “non-severe” patients (including those in remission and those with low/moderate activity) and not between those classified as “remission” and “non-remission” or “remission” and “low/moderate activity”. Moreover, the correlation between PET/CT measurements and clinical activity was positive only in the CDAI severe disease group. In patients in remission or with low/moderate activity, only 20–30% of joints were PET/CT-negative. In remission, PET/CT and US were positive in different joints, and PET/CT-positive but US-negative joints mainly exhibited RA (38.1%) or normal (49.2%) and not osteoarthritic (12.7%) X-ray patterns.

Conclusions

[¹⁸F] FDG PET/CT was effective at distinguishing patients with severely active disease from other patients. In non-severe RA patients, including those in remission, PET/CT results are discordant from US and clinical observations. A longitudinal analysis is needed to explore the clinical relevance of such infra-clinical disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41927-021-00196-1.

Semi-quantitative analysis of 18F fluorodeoxyglucose uptake in the assessment of disease activity and therapeutic response in rheumatoid arthritis: An institutional experience

¹⁸F fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) can be used to image synovial inflammation in patients with rheumatoid arthritis (RA). Recently, clinical application of novel therapies for RA, such as tumor necrosis factor-α (TNF-α) inhibitor and anti-interleukin-6 receptor antibody, has been introduced. The radiological assessment of disease activity changes of patients who underwent these therapies will help the clinicians to obtain more information about the patients and to decide drug withdrawal or change of medication. It is considered that ¹⁸F-FDG PET scan is generally very expensive; however, the information from ¹⁸F-FDG PET about patients during biological treatments helps discontinuation of these treatments with incomplete response despite its high costs and with possible side effects such as malignant lymphoma. In this study, we evaluated if the 18F-FDG uptake of the affected joints represented by standardized uptake value (SUV) correlated with the clinical assessment of patients with RA. In addition, we would like to evaluate if there was a correlation between the difference of SUV and improvement of clinical findings in RA patients undergoing anti TNF therapies. RA patients who underwent anti-TNFα therapies in a tertiary care hospital were assessed using whole-body ¹⁸F-FDG PET/computed tomography (CT). PET assessments were performed on hip joints, knees, shoulders, wrists, ankles, MCP, and PIP for a total of 28 joints in each patient. The ¹⁸F-FDG uptake was then quantified using the maximum SUV (SUVmax) prior to, and 6 months after the initiation of treatment with anti-TNF-α drugs. Disease activity score (DAS28 and DAS28-C-reactive protein [CRP]) were recorded and white blood cell, matrix metalloproteinases (MMP-3) and rheumatoid factor (RF) were examined in all patients. The average of SUV_max among measured joints, or the sum of these joints (total SUV_max), correlated with DAS28 (r = 0.671, P < 0.001), DAS28-CRP (r = 0.623, P < 0.001), ESR (r = 0.542, P < 0.001), CRP (r = 0.411, P = 0.002), MMP-3 (r = 0.399, P = 0.006), and RF (r = 0.447, P = 0.002). There were correlations between ΔSUV and ΔDAS28 (r = 0.651, P < 0.001), ΔSUV and ΔDAS28-CRP (r = 0.682, P < 0.001), ΔSUV and ΔESR (r = 0.449, P = 0.023), and ΔSUV and ΔMMP-3 (r = 0.457, P = 0.027), respectively. The number of PET-positive joints and the cumulative SUV significantly correlated with the DAS₂₈, which is a composite disease activity score (DAS) that combines the swollen and tender joint counts, the erythrocyte sedimentation rate (DAS₂₈-ESR) or CRP serum levels (DAS₂₈ - CRP) or RF (DAS₂₈ - RF) or metalloproteinases-3 (DAS_28-MMP-3). At baseline and at 6 months' post-treatment with anti-TNFα drugs, there was a significant correlation between the PET results, either visual, the cumulative SUVs or the composite SUV index, and the comprehensive clinical assessment (DAS₂₈), the CRP levels and the number of joints positive for RA, and cumulative synovial thickness. By reflecting inflammatory activity, ¹⁸F-FDG PET may enhance the diagnostic performance and expectation of disease prognosis in RA, especially with early synovial inflammation. The intensity of uptake varied from mild to intense (SUV_max values from 3.10 to 6.0). Overall, these values correlated well with the clinical evaluation of involved joints. ¹⁸F-FDG PET imaging data provided a distribution of joint involvement with varying degrees of severity and phase of disease activity (moderate, low, and remission) in the same patient. PET/CT imaging with ¹⁸F-FDG shows better image quality, provides more confirmative diagnostic information, and will be promising imaging modality in diagnosis and management of RA.

Fluorodeoxyglucose PET/CT of Arthritis in Rheumatic Diseases: A Pictorial Review

Rheumatic diseases are various painful conditions that affect joints, bones, cartilage, tendons, ligaments, and muscles. Arthritis is a typical condition of rheumatic disease. Although rheumatoid arthritis is a representative rheumatic disease, various diseases other than rheumatoid arthritis can also affect joints, and differential diagnosis of rheumatic diseases is often difficult owing to the similar clinical manifestations. However, accurate diagnosis is crucial for an appropriate treatment strategy. The utility of fluorine 18 fluorodeoxyglucose (FDG) PET/CT has been established, and it is widely used for assessing malignancies. In addition to accumulating in tumor cells, FDG also accumulates in inflammatory tissue, allowing FDG PET/CT to demonstrate arthritis. PET/CT allows evaluation of whole-body articular and extra-articular lesions in one examination, representing a key advantage over US and MRI, which allow assessment of only a few regions because of their limited field of view. Although FDG PET/CT is sensitive for detecting inflammatory lesions, the uptake itself is nonspecific; therefore, knowledge of characteristic uptake patterns is necessary to narrow the differential diagnosis in rheumatic disease. Furthermore, pathognomonic extra-articular findings such as vasculitis, skin lesions, lymphadenopathy, and chondritis play an important role in achieving accurate diagnosis. The authors present the FDG PET/CT appearances of (a) rheumatoid arthritis and allied disorders (polymyalgia rheumatica, remitting seronegative symmetrical synovitis with pitting edema, adult-onset Still disease), (b) spondyloarthritis (ankylosing spondylitis, psoriatic arthritis, reactive arthritis, inflammatory bowel disease arthritis, SAPHO [synovitis, acne, pustulosis, hyperostosis, and osteitis] syndrome, chronic recurrent multifocal osteomyelitis), and (c) miscellaneous systemic disorders with arthropathy (relapsing polychondritis, multicentric reticulohistiocytosis, amyloidosis, sarcoidosis, hemophilia). ^©RSNA, 2020.

Novel positron emission tomography tracers for imaging of rheumatoid arthritis

Positron emission tomography (PET) is a nuclear imaging modality that relies on visualization of molecular targets in tissues, which is nowadays combined with a structural imaging modality such as computed tomography (CT) or Magnetic Resonance Imaging (MRI) and referred to as hybrid PET imaging. This technique allows to image specific immunological targets in rheumatoid arthritis (RA). Moreover, quantification of the PET signal enables highly sensitive monitoring of therapeutic effects on the molecular target. PET may also aid in stratification of the immuno-phenotype at baseline in order to develop personalized therapy. In this systematic review we will provide an overview of novel PET tracers, investigated in the context of RA, either pre-clinically, or clinically, that specifically visualize immune cells or stromal cells, as well as other factors and processes that contribute to pathology. The potential of these tracers in RA diagnosis, disease monitoring, and prediction of treatment outcome will be discussed. In addition, novel PET tracers established within the field of oncology that may be of use in RA will also be reviewed in order to expand the future opportunities of PET imaging in RA.

Utility of 18F-Fluorodeoxyglucose Positron Emission Tomography in Inflammatory Rheumatism, Particularly Polymyalgia Rheumatica: A Retrospective Study of 222 PET/CT

Purpose: The objective of this study was to evaluate periarticular FDG uptake scores from ¹⁸F-FDG-PET/CT to identify polymyalgia rheumatica (PMR) within a population presenting rheumatic diseases.

Methods: A French retrospective study from 2011 to 2015 was conducted. Patients who underwent ¹⁸F-FDG-PET/CT for diagnosis or follow-up of a rheumatism or an unexplained biological inflammatory syndrome were included. Clinical data and final diagnosis were reviewed. Seventeen periarticular sites were sorted by a visual reading enabling us to calculate two scores: mean FDG visual uptake score, number of sites with significant uptake same as that or higher than liver uptake intensity and by a semi-quantitative analysis using mean maximum standardized uptake value (SUVmax). Optimal cutoffs of visual score and SUVmax to diagnose PMR were determined using receiver operating characteristics curves.

Results: Among 222 ¹⁸F-FDG PET/CT selected for 215 patients, 161 ¹⁸F-FDG PET/CT were performed in patients who presented inflammatory rheumatism as a final diagnosis (of whom 57 PMR). The presence of at least three sites with significant uptake identified PMR with a sensitivity of 86% and a specificity of 85.5% (AUC 0.872, 95% CI [0.81–0.93]). The mean FDG visual score cutoff to diagnose a PMR was 0.765 with a sensitivity of 82.5% and a specificity of 75.8% (AUC 0.854; 95% CI [0.80–0.91]). The mean SUVmax cutoff to diagnose PMR was 2.168 with a sensitivity of 77.2% and a specificity of 77.6% (AUC 0.842; 95% CI [0.79–0.89]).

Conclusions: This study suggests that ¹⁸F-FDG PET/CT had good performances to identify PMR within a population presenting rheumatic diseases.

Quantifying disease activity in rheumatoid arthritis with the TSPO PET ligand 18F-GE-180 and comparison with 18F-FDG and DCE-MRI

Purpose

While the aetiology of rheumatoid arthritis (RA) remains unclear, many of the inflammatory components are well characterised. For diagnosis and therapy evaluation, in vivo insight into these processes would be valuable. Various imaging probes have shown value including dynamic contrast-enhanced (DCE) MRI and PET/CT using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) or tracers targeting the translocator protein (TSPO). To evaluate ¹⁸F-GE-180, a novel TSPO PET tracer, for detecting and quantifying disease activity in RA, we compared ¹⁸F-GE-180 uptake with that of ¹⁸F-FDG and DCE-MRI measures of inflammation.

Methods

Eight RA patients with moderate-to-high, stable disease activity and active disease in at least one wrist were included in this study (NCT02350426). Participants underwent PET/CT examinations with ¹⁸F-GE-180 and ¹⁸F-FDG on separate visits, covering the shoulders and from the pelvis to the feet, including hands and wrists. DCE-MRI was performed on one affected hand. Uptake was compared visually between tracers as judged by an experienced radiologist and quantitatively using the maximum standardised uptake value (SUV_max). Uptake for both tracers was correlated with DCE-MRI parameters of inflammation, including the volume transfer coefficient K^trans using Pearson correlation (r).

Results

PET/CT imaging with ¹⁸F-GE-180 in RA patients showed marked extra-synovial uptake around the affected joints. Overall sensitivity for detecting clinically affected joints was low (14%). ¹⁸F-GE-180 uptake did not or only weakly correlate with DCE-MRI parameters in the wrist (r = 0.09–0.31). ¹⁸F-FDG showed higher sensitivity for detecting symptomatic joints (34%), as well as strong positive correlation with DCE-MRI parameters (SUV_max vs. K^trans: r = 0.92 for wrist; r = 0.68 for metacarpophalangeal joints).

Conclusions

The correlations between DCE-MRI parameters and ¹⁸F-FDG uptake support use of this PET tracer for quantification of inflammatory burden in RA. The TSPO tracer ¹⁸F-GE-180, however, has shown limited use for the investigation of RA due to its poor sensitivity and ability to quantify disease activity in RA.

The folate receptor β as a macrophage-mediated imaging and therapeutic target in rheumatoid arthritis

Macrophages play a key role in the pathophysiology of rheumatoid arthritis (RA). Notably, positive correlations have been reported between synovial macrophage infiltration and disease activity as well as therapy outcome in RA patients. Hence, macrophages can serve as an important target for both imaging disease activity and drug delivery in RA. Folate receptor β (FRβ) is a glycosylphosphatidyl (GPI)-anchored plasma membrane protein being expressed on myeloid cells and activated macrophages. FRβ harbors a nanomolar binding affinity for folic acid allowing this receptor to be exploited for RA disease imaging (e.g., folate-conjugated PET tracers) and therapeutic targeting (e.g., folate antagonists and folate-conjugated drugs). This review provides an overview of these emerging applications in RA by summarizing and discussing properties of FRβ, expression of FRβ in relation to macrophage polarization, FRβ-targeted in vivo imaging modalities, and FRβ-directed drug targeting.

Correlation of benign incidental findings seen on whole-body PET-CT with knee MRI: patterns of 18F-FDG avidity, intra-articular pathology, and bone marrow edema lesions

OBJECTIVES

To correlate patterns of ¹⁸F-FDG uptake on whole-body PET-CT with MR findings and compare the degree of FDG activity between symptomatic and asymptomatic knees.

MATERIALS AND METHODS

Retrospective database query was performed using codes for knee MRI as well as whole-body PET-CT. Patients with malignant disease involving the knee or hardware were excluded. Patients who had both studies performed within 1 year between 2012 and 2017 were included for analysis. Knee joint osteoarthrosis, meniscal and ligamentous integrity, presence of joint effusion, and synovitis were assessed and recorded. Bone marrow edema lesions (BMELs) were identified, segmented, and analyzed using volumetric analysis. SUVmax was assessed over the suprapatellar joint space, intercondylar notch and Hoffa's fat pad. Symptomatic and asymptomatic knees were compared in patients with unilateral symptoms.

RESULTS

Twenty-two cases (20 patients) with mean age 63.3 years (range, 36-91 years) were included. Two patients had bilateral pain. The most FDG avid regions in both symptomatic and asymptomatic knees were the intercondylar notch (SUVmax = 1.84 vs. 1.51), followed by suprapatellar pouch (SUVmax = 1.74 vs. 1.29) and Hoffa's fat pad (SUVmax = 1.01 vs. 0.87). SUVmax was significantly associated with cartilage loss (mean modified Outerbridge score) (r = 0.60, p = 0.003) and degree of synovitis (r = 0.48, p = 0023). Overall, mean SUVmax was significantly higher in the presence of a meniscal tear (1.83 ± 0.67 vs. 1.22 ± 0.40, p = 0.030). Nine patients had BMELs (volume: range = 0.6-27.8, mean = 7.79) however there was no significant association between BMEL volume and SUVmax.

CONCLUSIONS

Higher FDG activity correlates with intra-articular derangement and the intercondylar notch represents the most metabolically active region of the knee.

Musculoskeletal Pitfalls on Fluorodeoxyglucose F 18 PET-Computed Tomography: Pictorial Review

A wide range of musculoskeletal processes can demonstrate increased uptake on PET-computed tomography (CT) with fluorodeoxyglucose (FDG) F 18, including reactive, benign neoplastic, inflammatory, traumatic, posttreatment, and arthritic conditions that may mimic malignancy. In addition, physiologic causes of increased FDG uptake such as asymmetric muscle use and presence of brown fat can lead to increased FDG uptake and potential false-positive results. This article presents various case examples of non-malignant musculoskeletal hypermetabolism on 18F-FDG PET-CT and describes useful tools to avoid the potential pitfall of misinterpreting these as malignancy.

The importance of synovial inflammation in osteoarthritis: current evidence from imaging assessments and clinical trials

Synovial abnormalities have been observed at multiple stages of osteoarthritis (OA). Increasing evidence suggests that it may play an important role in the OA pathological process. Many assessment systems using magnetic resonance imaging (MRI) and ultrasound have been established to detect synovial inflammation in OA. These have been used to inform the current investigation of OA disease phenotypes and progression and can be utilised in the future for clinical trials developing potential treatments. This narrative review aims to illustrate the importance of synovial tissue in OA and provide an overview of imaging assessments and possible therapies targeting synovial abnormalities.

Molecular Imaging of Inflammatory Arthritis and Related Disorders

Rheumatic disorders comprise a number of diseases that range from benign, mildly symptomatic degenerative disease to severe systemic disorders such as giant-cell vasculitis with dramatic consequences such as acute blindness. The former is relatively common, whereas the latter is rare. In between, commonly encountered disorders such as rheumatoid arthritis and the various spondyloarthritides, with or without peripheral enthesitis, are daily challenges for the caring physician. Clinical evaluation is of utmost importance and is constantly described under the form of specialist guidelines in all parts of the world. Objective assessment of inflammatory arthritis and related disorders is of interest both for the care of the individual patient and for the assessment of the effects of the many novel experimental therapies proposed in this field, most of them being very expensive. High-resolution ultrasound, CT and spectral CT, MRI using various sequences, and molecular imaging using either gamma camera imaging (including SPECT-CT) or PET-CT are all proposed for a better assessment of these diseases. This review focuses on the several nuclear medicine techniques that are or may become useful to helping provide better patient care in this field and is mainly oriented to inflammatory rheumatic disorders, excluding mechanical degenerative diseases.

PET/MRI of metabolic activity in osteoarthritis: A feasibility study

PURPOSE

To evaluate positron emission tomography / magnetic resonance imaging (PET/MRI) knee imaging to detect and characterize osseous metabolic abnormalities and correlate PET radiotracer uptake with osseous abnormalities and cartilage degeneration observed on MRI.

MATERIALS AND METHODS

Both knees of 22 subjects with knee pain or injury were scanned at one timepoint, without gadolinium, on a hybrid 3.0T PET-MRI system following injection of 18 F-fluoride or 18 F-fluorodeoxyglucose (FDG). A musculoskeletal radiologist identified volumes of interest (VOIs) around bone abnormalities on MR images and scored bone marrow lesions (BMLs) and osteophytes using a MOAKS scoring system. Cartilage appearance adjacent to bone abnormalities was graded with MRI-modified Outerbridge classifications. On PET standardized uptake values (SUV) maps, VOIs with SUV greater than 5 times the SUV in normal-appearing bone were identified as high-uptake VOI (VOIHigh ). Differences in 18 F-fluoride uptake between bone abnormalities, BML, and osteophyte grades and adjacent cartilage grades on MRI were identified using Mann-Whitney U-tests.

RESULTS

SUVmax in all subchondral bone lesions (BML, osteophytes, sclerosis) was significantly higher than that of normal-appearing bone on MRI (P < 0.001 for all). Of the 172 high-uptake regions on 18 F-fluoride PET, 63 (37%) corresponded to normal-appearing subchondral bone on MRI. Furthermore, many small grade 1 osteophytes (40 of 82 [49%]), often described as the earliest signs of osteoarthritis (OA), did not show high uptake. Lastly, PET SUVmax in subchondral bone adjacent to grade 0 cartilage was significantly lower compared to that of grades 1-2 (P < 0.05) and grades 3-4 cartilage (P < 0.001).

CONCLUSION

PET/MRI can simultaneously assess multiple early metabolic and morphologic markers of knee OA across multiple tissues in the joint. Our findings suggest that PET/MR may detect metabolic abnormalities in subchondral bone, which appear normal on MRI.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;45:1736-1745.

Potential of PET-MRI for imaging of non-oncologic musculoskeletal disease

Early detection of musculoskeletal disease leads to improved therapies and patient outcomes, and would benefit greatly from imaging at the cellular and molecular level. As it becomes clear that assessment of multiple tissues and functional processes are often necessary to study the complex pathogenesis of musculoskeletal disorders, the role of multi-modality molecular imaging becomes increasingly important. New positron emission tomography-magnetic resonance imaging (PET-MRI) systems offer to combine high-resolution MRI with simultaneous molecular information from PET to study the multifaceted processes involved in numerous musculoskeletal disorders. In this article, we aim to outline the potential clinical utility of hybrid PET-MRI to these non-oncologic musculoskeletal diseases. We summarize current applications of PET molecular imaging in osteoarthritis (OA), rheumatoid arthritis (RA), metabolic bone diseases and neuropathic peripheral pain. Advanced MRI approaches that reveal biochemical and functional information offer complementary assessment in soft tissues. Additionally, we discuss technical considerations for hybrid PET-MR imaging including MR attenuation correction, workflow, radiation dose, and quantification.

Diagnosis and management of rheumatoid arthritis; What is the current role of established and new imaging techniques in clinical practice?

Ultrasound and magnetic resonance imaging (MRI) have become established imaging techniques for the management of rheumatoid arthritis. Several publications have pointed out the advantages of these techniques for a more complete evaluation of the inflammation and structural damage at joint level. Recently new imaging techniques as the positron emission tomography (PET) associated with computed tomography (CT) or MRI scan, and the optical imaging have been introduced in the panorama. This article presents the advantages and limitations of each imaging techniques in light with the recent publications.

Pilot study on 18 F-FDG PET/CT for detection of inflammatory changes in blood-induced knee arthropathy in a rabbit model

RATIONALE

¹⁸ F-FDG-PET/CT has a potential role in the early detection of haemophilic arthritis, at a time when treatment may still avoid further joint degeneration. The purposes of this pilot study were to determine the ability of ¹⁸ F-FDG-PET/CT to detect inflammatory changes associated with blood-induced arthropathy in knees of a rabbit model.

METHODS

Ten juvenile rabbits were imaged at baseline and weeks 5 and 17 post intraarticular autologous blood injections (ABI). Five rabbits in group 1 (G1) had ABI into the same knee joint every 2 weeks (total, eight injections). Five rabbits in group 2 (G2) had only two injections into the same knee, at weeks 5 and 17. Images were assessed visually and semi-quantitatively by measuring maximal standardized uptake values (SUVmax) and standardized uptake ratio (SUR = SUVmax in affected knee/SUVmax in non-affected knee).

RESULTS

More rabbits in G1 than G2 presented with positive chronic inflammatory synovial scores at week 17. Mean iron staining scores in injected knees were greater for G1 than for G2 (P = 0.049). No increased uptake was identified in the injected knees in any of the rabbits at baseline or at week 5. At week 17, all G1 rabbits demonstrated increased uptake in their affected knees with higher mean SUVmax (1.5) than normal knees (1.0) (P < 0.02). None of the G2 rabbits showed asymmetric increased uptake. The SUR of G1 was higher at week 17 compared to baseline (P < 0.01) and week 5 (P < 0.01). The SUR at week 17 was higher for G1 than for G2 (1.13) rabbits (P < 0.01).

CONCLUSION

¹⁸ F-FDG-PET is able to detect the inflammatory changes associated with haemophilic arthropathy in this experimental model.

Increased 18F-FDG uptake suggests synovial inflammatory reaction with osteoarthritis: preliminary in-vivo results in humans

OBJECTIVE

The aim of this prospective study was to compare the metabolic activity of the knee joints of a group of patients with painful knees clinically (such as recurrent joint pain, joint instability, and functional limitations) consistent with osteoarthritis and those of another group of patients without such complaints, using [F]-2-fluoro-2-deoxy-D-glucose (F-FDG)-PET imaging.

METHODS

A total of 97 patients who participated in either painful joint prosthesis or diabetic foot research studies involving F-FDG-PET scans were asked to complete a knee pain questionnaire. The patients were asked whether they experienced pain in any joint, and if so, which joints were affected.

RESULTS

A total of 18 knee joints without prosthesis were reported to be painful. The maximum standardized uptake values (SUVmax) of the middle joint space and lateral synovial tissue of these 18 knees were measured and compared with those of a set of patients with control asymptomatic knees. The average SUVmax of the middle part of the joint space in the painful knees was 1.35±0.59 compared with an average SUVmax value of 0.86±0.14 in the control group (P=0.0176). The average SUVmax of the synovium in the lateral part of the painful joints was 1.17±0.49 compared with 0.73±0.31 in the control group (P=0.0161).

CONCLUSION

These data indicate that increased F-FDG uptake is associated with knee pain in osteoarthritis patients and that there is a positive relationship between the two parameters.

High-resolution (18)F-FDG PET/CT for assessing disease activity in rheumatoid and psoriatic arthritis: findings of a prospective pilot study

OBJECTIVE

Rheumatoid arthritis (RA) and psoriatic arthritis (PsA) commonly affect the small joints of the wrist and hand. We evaluated the performance of a new, high-resolution extremity positron emission tomography (PET)/CT scanner for characterizing and quantifying pathologies associated with the two arthritides in the wrist and hand joints.

METHODS

Patients with RA or PsA underwent fluorine-18 fludeoxyglucose ((18)F-FDG) PET/CT wrist and hand imaging, respectively, on the high-resolution scanner. Calibrated CT images and co-registered PET images were reconstructed. PET/CT was derived for the radiocarpal and pisiform-triquetral compartments, joints with erosive changes, sites of synovitis or tenosynovitis and the nail bed and were correlated with clinical and MRI findings.

RESULTS

Significantly elevated (18)F-FDG uptake was measured for the radiocarpal and pisiform-triquetral compartments and at sites of bone erosion, synovitis, pannus and oedema, compared with unaffected joints (p < 0.05) in patients with RA, consistent with their clinical findings. In patients with PsA, significantly elevated (18)F-FDG uptake was measured for joints with synovitis compared with unaffected joints (p < 0.05), with patterns of (18)F-FDG uptake along the tendons, at the enthesis and in the nail bed, consistent with tenosynovitis, enthesitis and nail dystrophy, respectively.

CONCLUSION

High-resolution (18)F-FDG PET/CT imaging of the wrist and hand is feasible in an RA or PsA patient cohort and is capable of providing quantifiable measures of disease activity (synovitis, enthesitis, oedema and bone destruction).

ADVANCES IN KNOWLEDGE

High-resolution PET/CT imaging shows promise as a tool for understanding the pathogenesis of the arthritic process and for non-invasive, objective assessment of RA or PsA severity and therapy selection.

(99m)Tc-MDP bone scintigraphy of the hand: comparing the use of novel cadmium zinc telluride (CZT) and routine NaI(Tl) detectors

Background

Cadmium zinc telluride (CZT) solid-state detectors have been recently introduced in the field of nuclear medicine in cardiology and breast imaging. The aim of the current study was to evaluate the performance of the novel detectors (CZT) compared to that of the routine NaI(Tl) in bone scintigraphy. A dual-headed CZT-based camera dedicated originally to breast imaging has been used, and in view of the limited size of the detectors, the hands were chosen as the organ for assessment. This is a clinical study.

Methods

Fifty-eight consecutive patients (total 116 hands) referred for bone scan for suspected hand pathology gave their informed consent to have two acquisitions, using the routine camera and the CZT-based camera. The latter was divided into full-dose full-acquisition time (FD CZT) and reduced-dose short-acquisition time (RD CZT) on CZT technology, so three image sets were available for analysis. Data analysis included comparing the detection of hot lesions and identification of the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints.

Results

A total of 69 hot lesions were detected on the CZT image sets; of these, 61 were identified as focal sites of uptake on NaI(Tl) data. On FD CZT data, 385 joints were identified compared to 168 on NaI(Tl) data (p < 0.001). There was no statistically significant difference in delineation of joints between FD and RD CZT data as the latter identified 383 joints.

Conclusions

Bone scintigraphy using a CZT-based gamma camera is associated with improved lesion detection and anatomic definition. The superior physical characteristics of this technique raised a potential reduction in administered dose and/or acquisition time without compromising image quality.

Clinical value of whole-body PET/CT in patients with active rheumatic diseases

Advanced imaging techniques may enable early diagnosis and monitoring of therapy in various rheumatic diseases. To prevent irreversible tissue damage, inflammatory rheumatic disease must be diagnosed and treated in pre-clinical stages, requiring highly sensitive detection techniques. Positron emission tomography (PET) provides highly sensitive, quantitative imaging at a molecular level, revealing the important pathophysiological processes underlying inflammation. This review provides an overview of the current utility of ¹⁸ F-fluorodeoxyglucose (FDG)-PET/computed tomography (CT) in patients with active rheumatic diseases such as rheumatoid arthritis, spondyloarthritis, polymyalgia rheumatica, adult-onset Still’s disease, relapsing polychondritis, immunoglobulin G4-related disease, large-vessel vasculitis, Wegener’s granulomatosis, polymyositis, and dermatomyositis. We also discuss the role of FDG-PET/CT in the diagnosis and monitoring of these diseases.

(18)F-FDG and (18)F-NaF PET/CT demonstrate coupling of inflammation and accelerated bone turnover in rheumatoid arthritis

OBJECTIVE

To compare the findings in rheumatoid arthritis (RA)-affected joints between (18)F-fluorodeoxyglucose (FDG) and (18)F-fluoride (NaF) positron emission tomography (PET)/computed tomography (CT).

METHODS

We enrolled twelve RA patients who started a new biologic agent (naïve 9 and switch 3). At entry, both hands were examined by (18)F-FDG PET/CT, (18)F-NaF PET/CT, and X-ray. Intensity of PET signals was determined by standardized uptake value max (SUVmax) in metacarpophalangeal (MCP), proximal interphalangeal (PIP), and ulnar, medial, and radial regions of the wrists. Hand X-rays were evaluated according to the Genant-modified Sharp score at baseline and 6 months.

RESULTS

Both (18)F-FDG and (18)F-NaF accumulated in RA-affected joints. The SUVmax of (18)F-FDG correlated with that of (18)F-NaF in individual joints (r = 0.65), though detail distribution was different between two tracers. (18)F-NaF and (18)F-FDG signals were mainly located in the bone and the surrounding soft tissues, respectively. The sum of SUVmax of (18)F-NaF correlated with disease activity score in 28 joint (DAS28), modified health assessment questionnaire (MHAQ), and radiographic progression. (18)F-FDG and (18)F-NaF signals were associated with the presence of erosions, particularly progressive ones.

CONCLUSION

Our data show that both (18)F-FDG and (18)F-NaF PET signals were associated with RA-affected joints, especially those with ongoing erosive changes.

Use of 18F-fluoride positron emission tomography as a predictor of the hip osteoarthritis progression

OBJECTIVE

The prediction of hip osteoarthritis (OA) progression is still a difficult issue. We have adopted (18)F-fluoride positron emission tomography (PET) for the evaluation of hip osteoarthritis, and investigated the prediction utility of (18)F-fluoride PET for both pain worsening and OA progression using a logistic regression model.

MATERIALS AND METHODS

A total of 57 hip joints were analyzed for progression risk factors for pain worsening and minimum joint space (MJS) narrowing by logistic regression analysis. Sex, age, BMI, existence of pain, the PET maximum standardized uptake value (SUV(max)), Kellgren and Lawrence grade, MJS, and follow-up period were used as explanatory variables. Receiver operating characteristic analysis was performed to calculate the cutoff value of the SUV(max).

RESULTS

Multivariate logistic regression analysis revealed significant differences only in the SUV(max) values for pain worsening and MJS narrowing. The odds ratio of the SUV(max) for pain worsening was 1.89, and for MJS narrowing it was 11.02. The SUV(max) cutoff value was 7.2 (sensitivity: 1.00, specificity: 0.84) for pain worsening and 6.4 (sensitivity: 0.92, specificity: 0.83) for MJS narrowing.

CONCLUSIONS

Our results indicate that the PET SUV(max) is a best predictor of pain worsening and MJS narrowing. This imaging modality has a great potential for the prediction of OA progression.

Sustained macrophage infiltration upon multiple intra-articular injections: an improved rat model of rheumatoid arthritis for PET guided therapy evaluation

To widen the therapeutic window for PET guided evaluation of novel anti-RA agents, modifications were made in a rat model of rheumatoid arthritis (RA). Arthritis was induced in the right knee of Wistar rats with repeated boosting to prolong articular inflammation. The contralateral knee served as control. After immunization with methylated bovine serum albumin (mBSA) in complete Freund's adjuvant and custom Bordetella pertussis antigen, one or more intra-articular (i.a.) mBSA injections were given over time in the right knee. Serum anti-mBSA antibodies, DTH response, knee thickness, motion, and synovial macrophages were analyzed and [18F]FDG(-general inflammation) and (R)-[11C]PK11195 (macrophages-)PET was performed followed by ex vivo tissue distribution. Significant anti-mBSA levels, DTH, swelling of arthritic knee, and sustained and prolonged macrophage infiltration in synovial tissue were found, especially using multiple i.a. injections. Increased [18F]FDG and (R)-[11C]PK11195 accumulation was demonstrated in arthritic knees as compared to contralateral knees, which was confirmed in ex vivo tissue distribution studies. Boosting proved advantageous for achieving a chronic model without remission. The model will offer excellent opportunities for repeated PET studies to monitor progression of disease and efficacy of novel therapeutic agents for RA in the same animal.

[Positron emission tomography with (18)F-FDG in the evaluation of patients with rheumatoid arthritis--a systematic review]

INTRODUCTION

Rheumatoid arthritis (RA) is a disease characterized by inflammation of the synovial membrane. Several authors have investigated the role of positron emission tomography (PET) with fluorine-18 fluorodeoxyglucose ((18)F-FDG) in RA.

OBJECTIVES

To systematically review the current literature on the role of (18)F-FDG PET in the diagnosis, determination of disease activity and assessment of treatment response in patients with RA.

METHODS

Searches were conducted in Medline, Cochrane Library, Lilacs, Pubmed and Scopus in Portuguese, English and Spanish languages, using the keywords "rheumatoid arthritis", "synovitis", "FDG", "PET", "glycolytic metabolism" and "disease activity".

RESULTS

142o articles were initially identified, of which only 40 were related directly to the subject. Twelve original articles and three case reports that met the inclusion criteria were selected.

DISCUSSION

The presence of activated macrophages and fibroblasts in pannus are responsible for the intense periarticular uptake of (18)F-FDG. The uptake patterns do not allow the differential diagnosis with other arthritides. The uptake intensity and the number of joints involved are metabolic parameters of disease activity that correlate well with the composite indices. Longitudinal studies of PET have proven useful in assessing the response to treatment with anti-TNF. When performed early, PET can predict the therapeutic response.

CONCLUSION

Although the actual role of this new technique for the investigation of RA is not yet established, (18)F-FDG PET is a promising tool in determining the activity and prediction of response to treatment of patients with RA.

Quantifying synovial inflammation: Emerging imaging techniques

Imaging techniques to assess synovial inflammation includes radiography, ultrasound, computed tomography, magnetic resonance imaging (MRI) and recently positron emission tomography. The ideal objective of imaging approaches are to quantify synovial inflammation by capturing features such as synovial hyperplasia, neo-angiogenesis and infiltration of immune cells in the synovium. This may enable clinicians to estimate response to therapy by measuring the improvement in the inflammatory signals at the level of synovium. Ultrasound can provide information regarding thickening of the synovial membrane and can reveal increased synovial blood flow using power Doppler technique. Bone marrow edema and synovial membrane thickness on MRI scan may serve as indicators for arthritis progression. Enhancement of the synovium on dynamic contrast MRI may closely mirror the inflammatory activity in the synovium. Diffusion tensor imaging is an advance MRI approach that evaluates the inflammation related to cell infiltration or aggregation in an inflamed synovium. In this review, we summarize the newer imaging techniques and their developments to evaluate synovial inflammation.

Imaging of non-osteochondral tissues in osteoarthritis

OBJECTIVE

The aim of this review is to describe imaging techniques for evaluation of non-osteochondral structures such as the synovium, menisci in the knee, labrum in the hip, ligaments and muscles and to review the literature from recent clinical and epidemiological studies of OA.

METHODS

This is a non-systematic narrative review of published literature on imaging of non-osteochondral tissues in OA. PubMed and MEDLINE search for articles published up to 2014, using the keywords osteoarthritis, synovitis, meniscus, labrum, ligaments, plica, muscles, magnetic resonance imaging (MRI), ultrasound, computed tomography (CT), scintigraphy, and positron emission tomography (PET).

RESULTS

Published literature showed imaging of non-osteochondral tissues in OA relies primarily on MRI and ultrasound. The use of semiquantitative and quantitative imaging biomarkers of non-osteochondral tissues in clinical and epidemiological OA studies is reported. We highlight studies that have compared both imaging methodologies directly, and those that have established a relationship between imaging biomarkers and clinical outcomes. We provide recommendations as to which imaging protocols should be used to assess disease-specific changes regarding synovium, meniscus in the knee, labrum in the hip, and ligaments, and highlight potential pitfalls in their usage.

CONCLUSION

MRI and ultrasound are currently the most useful imaging modalities for evaluation of non-osteochondral tissues in OA. MRI evaluation of any tissue needs to be performed using appropriate MR pulse sequences. Ultrasound may be particularly useful for evaluation of small joints of the hand. Nuclear medicine and CT play a limited role in imaging of non-osteochondral tissues in OA.

18F-FDG PET of the hands with a dedicated high-resolution PEM system (arthro-PET): correlation with PET/CT, radiography and clinical parameters

PURPOSE

The aim of this study was to prospectively determine the feasibility and compare the novel use of a positron emission mammography (PEM) scanner with standard PET/CT for evaluating hand osteoarthritis (OA) with (18)F-FDG.

METHODS

Institutional review board approval and written informed consent were obtained for this HIPAA-compliant prospective study in which 14 adults referred for oncological (18)F-FDG PET/CT underwent dedicated hand PET/CT followed by arthro-PET using the PEM device. Hand radiographs were obtained and scored for the presence and severity of OA. Summed qualitative and quantitative joint glycolytic scores for each modality were compared with the findings on plain radiography and clinical features.

RESULTS

Eight patients with clinical and/or radiographic evidence of OA comprised the OA group (mean age 73 ± 7.7 years). Six patients served as the control group (53.7 ± 9.3 years). Arthro-PET quantitative and qualitative joint glycolytic scores were highly correlated with PET/CT findings in the OA patients (r = 0.86. p = 0.007; r = 0.94, p = 0.001). Qualitative arthro-PET and PET/CT joint scores were significantly higher in the OA patients than in controls (38.7 ± 6.6 vs. 32.2 ± 0.4, p = 0.02; 37.5 ± 5.4 vs. 32.2 ± 0.4, p = 0.03, respectively). Quantitative arthro-PET and PET/CT maximum SUV-lean joint scores were higher in the OA patients, although they did not reach statistical significance (20.8 ± 4.2 vs. 18 ± 1.8, p = 0.13; 22.8 ± 5.38 vs. 20.1 ± 1.54, p = 0.21). By definition, OA patients had higher radiographic joint scores than controls (30.9 ± 31.3 vs. 0, p = 0.03).

CONCLUSION

Hand imaging using a small field of view PEM system (arthro-PET) with FDG is feasible, performing comparably to PET/CT in assessing metabolic joint activity. Arthro-PET and PET/CT showed higher joint FDG uptake in OA. Further exploration of arthro-PET in arthritis management is warranted.

Molecular imaging of rheumatoid arthritis: emerging markers, tools, and techniques

Early diagnosis and effective monitoring of rheumatoid arthritis (RA) are important for a positive outcome. Instant treatment often results in faster reduction of inflammation and, as a consequence, less structural damage. Anatomical imaging techniques have been in use for a long time, facilitating diagnosis and monitoring of RA. However, mere imaging of anatomical structures provides little information on the processes preceding changes in synovial tissue, cartilage, and bone. Molecular imaging might facilitate more effective diagnosis and monitoring in addition to providing new information on the disease pathogenesis. A limiting factor in the development of new molecular imaging techniques is the availability of suitable probes. Here, we review which cells and molecules can be targeted in the RA joint and discuss the advances that have been made in imaging of arthritis with a focus on such molecular targets as folate receptor, F4/80, macrophage mannose receptor, E-selectin, intercellular adhesion molecule-1, phosphatidylserine, and matrix metalloproteinases. In addition, we discuss a new tool that is being introduced in the field, namely the use of nanobodies as tracers. Finally, we describe additional molecules displaying specific features in joint inflammation and propose these as potential new molecular imaging targets, more specifically receptor activator of nuclear factor κB and its ligand, chemokine receptors, vascular cell adhesion molecule-1, αVβ₃ integrin, P2X7 receptor, suppression of tumorigenicity 2, dendritic cell-specific transmembrane protein, and osteoclast-stimulatory transmembrane protein.

Promising potential of new generation translocator protein tracers providing enhanced contrast of arthritis imaging by positron emission tomography in a rat model of arthritis

Introduction

Early diagnosis of and subsequent monitoring of therapy for rheumatoid arthritis (RA) could benefit from detection of (sub)clinical synovitis. Imaging of (sub)clinical arthritis by targeting the translocator protein (TSPO) on activated macrophages is feasible using (R)-[¹¹C] PK11195-based positron emission tomography (PET), but clinical applications are limited by background uptake in peri-articular bone/bone marrow. The purpose of the present study was to evaluate two other TSPO ligands with potentially lower background uptake in neurological studies, [¹¹C]DPA-713 and [¹⁸F]DPA-714, in a rat model of arthritis.

Methods

TSPO binding of DPA-713, DPA-714 and PK11195 were assessed by in vitro competition studies with [³H]DPA-713 using human macrophage THP-1 cells and CD14⁺ monocytes from healthy volunteers. In vivo studies were performed in rats with methylated bovine serum albumin-induced knee arthritis. Immunohistochemistry with anti-TSPO antibody was performed on paraffin-embedded sections. Rats were imaged with [¹¹C]DPA-713 or [¹⁸F]DPA-714 PET, followed by ex vivo tissue distribution studies. Results were compared with those obtained with the tracer (R)-[¹¹C]PK11195, the established ligand for TSPO.

Results

In THP-1 cells, relative TSPO binding of DPA-713 and DPA-714 were 7-fold and 25-fold higher, respectively, than in PK11195. Comparable results were observed in CD14⁺ monocytes from healthy volunteers. In the arthritis rat model, immunohistochemistry confirmed the presence of TSPO-positive inflammatory cells in the arthritic knee. PET images showed that uptake of [¹¹C]DPA-713 and [¹⁸F]DPA-714 in arthritic knees was significantly increased compared with contralateral knees and knees of normal rats. Uptake in arthritic knees could be largely blocked by an excess of PK11195. [¹¹C]DPA-713 and [¹⁸F]DPA-714 provided improved contrast compared with (R)-[¹¹C]PK11195, as was shown by significantly higher arthritic knee-to-bone ratios of [¹¹C]DPA-713 (1.60 ± 0.31) and [¹⁸F]DPA-714 (1.55 ± 0.10) compared with (R)-[¹¹C]PK11195 (1.14 ± 0.19).

Conclusions

[¹¹C]DPA-713 and [¹⁸F]DPA-714 clearly visualized arthritis and exhibited lower (peri-articular) bone/bone marrow uptake than (R)-[¹¹C]PK11195. These features merit further investigation of these tracers for early diagnosis and therapy monitoring of RA in a clinical setting.

Metabolic patterns of the shoulder joint on (18)F-fluorodeoxyglucose positron emission tomography/computed tomography in adhesive capsulitis

OBJECTIVE

The purpose of our study was to demonstrate metabolic patterns on (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) in patients with adhesive capsulitis (AC).

METHODS

We retrospectively reviewed (18)F-FDG PET/CT performed on 22 shoulders of 21 patients diagnosed with AC: 2 shoulders with stage I, 14 with stage II, and 6 with stage III. A clinical diagnosis of AC was retrospectively made based on clinical examination, clinical course, and imaging. The pattern of radiotracer uptake was analyzed. Standardized uptake values in rotator interval (RI), anterior joint capsule (AJC), axillary recess (AR), and greater tuberosity were measured and compared to those of the contralateral side and the control group consisting of 40 shoulders in 20 subjects without shoulder pain.

RESULTS

Four patterns of uptake were noted: (1) glenoid type I (n = 16), with uptake in RI, AJC, and AR; (2) glenoid type II (n = 2),with uptake in AJC and AR; (3) glenoid type III (n = 2), with uptake in RI and AJC; (4) focal type (n = 2), with uptake in RI or AR. Affected side SUVmax for RI, AJC, and AR was significantly higher compared with the unaffected side and the control group. Two shoulders with stage I AC had patterns similar to the ones with stage II or III.

CONCLUSION

Specific patterns of (18)F-FDG uptake with dominant uptake in RI, AJC, or AR may be related to AC.

Nuclear imaging of rheumatic diseases

Advanced imaging techniques are promising tools to assist in the early diagnosis and monitoring of therapy in various rheumatic diseases. As there is now increasing emphasis on diagnosing inflammatory rheumatic disease in the pre-clinical stages, so that treatment may be instituted early and ideally prevent irreversible tissue damage, highly sensitive techniques are needed to detect subclinical inflammation. Moreover, there is an increasing need to develop individualised treatment protocols at reasonable cost and with optimal therapeutic effect. Tools are required that can image the therapeutic target and sensitively trace changes in disease activity. Nuclear imaging techniques have the potential to fulfil these clinical needs. Positron emission tomography is emerging as an important modality as it provides highly sensitive, quantitative imaging at a molecular level, to reveal the important pathophysiological processes underlying inflammation. This chapter provides an overview of currently available nuclear imaging techniques, including recent technical developments, and discusses their role in the diagnosis and monitoring of rheumatic disease.

Assessment of collagen-induced arthritis using cyanine 5.5 conjugated with hydrophobically modified glycol chitosan nanoparticles: correlation with 18F-fluorodeoxyglucose positron emission tomography data

OBJECTIVE

To evaluate the potential and correlation between near-infrared fluorescence (NIRF) imaging using cyanine 5.5 conjugated with hydrophobically modified glycol chitosan nanoparticles (HGC-Cy5.5) and (18)F-fluorodeoxyglucose-positron emission tomography ((18)F-FDG-PET) imaging of collagen-induced arthritis (CIA).

MATERIALS AND METHODS

We used 10 CIA and 3 normal mice. Nine days after the injecting collagen twice, microPET imaging was performed 40 minutes after the intravenous injection of 9.3 MBq (18)F-FDG in 200 µL PBS. One day later, NIRF imaging was performed two hours after the intravenous injection of HGC-cy5.5 (5 mg/kg). We assessed the correlation between these two modalities in the knees and ankles of CIA mice.

RESULTS

The mean standardized uptake values of (18)F-FDG for knees and ankles were 1.68 ± 0.76 and 0.79 ± 0.71, respectively, for CIA mice; and 0.57 ± 0.17 and 0.54 ± 0.20 respectively for control mice. From the NIRF images, the total photon counts per 30 mm(2) for knees and ankles were 2.32 ± 1.54 × 10(5) and 2.75 ± 1.51 × 10(5), respectively, for CIA mice, and 1.22 ± 0.27 × 10(5) and 0.88 ± 0.24 × 10(5), respectively, for control mice. These two modalities showed a moderate correlation for knees (r = 0.604, p = 0.005) and ankles (r = 0.464, p = 0.039). Moreover, both HGC-Cy5.5 (p = 0.002) and (18)F-FDG-PET (p = 0.005) imaging also showed statistically significant differences between CIA and normal mice.

CONCLUSION

NIRF imaging using HGC-Cy5.5 was moderately correlated with (18)F-FDG-PET imaging in the CIA model. As such, HGC-Cy5.5 imaging can be used for the early detection of rheumatoid arthritis.

Bone formation rather than inflammation reflects ankylosing spondylitis activity on PET-CT: a pilot study

Introduction

Positron Emission Tomography - Computer Tomography (PET-CT) is an interesting imaging technique to visualize Ankylosing Spondylitis (AS) activity using specific PET tracers. Previous studies have shown that the PET tracers [¹⁸F]FDG and [¹¹C](R)PK11195 can target inflammation (synovitis) in rheumatoid arthritis (RA) and may therefore be useful in AS. Another interesting tracer for AS is [¹⁸F]Fluoride, which targets bone formation. In a pilot setting, the potential of PET-CT in imaging AS activity was tested using different tracers, with Magnetic Resonance Imaging (MRI) and conventional radiographs as reference.

Methods

In a stepwise approach different PET tracers were investigated. First, whole body [¹⁸F]FDG and [¹¹C](R)PK11195 PET-CT scans were obtained of ten AS patients fulfilling the modified New York criteria. According to the BASDAI five of these patients had low and five had high disease activity. Secondly, an extra PET-CT scan using [¹⁸F]Fluoride was made of two additional AS patients with high disease activity. MRI scans of the total spine and sacroiliac joints were performed, and conventional radiographs of the total spine and sacroiliac joints were available for all patients. Scans and radiographs were visually scored by two observers blinded for clinical data.

Results

No increased [¹⁸F]FDG and [¹¹C](R)PK11195 uptake was noticed on PET-CT scans of the first 10 patients. In contrast, MRI demonstrated a total of five bone edema lesions in three out of 10 patients. In the two additional AS patients scanned with [¹⁸F]Fluoride PET-CT, [¹⁸F]Fluoride depicted 17 regions with increased uptake in both vertebral column and sacroiliac joints. In contrast, [¹⁸F]FDG depicted only three lesions, with an uptake of five times lower compared to [¹⁸F]Fluoride, and again no [¹¹C](R)PK11195 positive lesions were found. In these two patients, MRI detected nine lesions and six out of nine matched with the anatomical position of [¹⁸F]Fluoride uptake. Conventional radiographs showed structural bony changes in 11 out of 17 [¹⁸F]Fluoride PET positive lesions.

Conclusions

Our PET-CT data suggest that AS activity is reflected by bone activity (formation) rather than inflammation. The results also show the potential value of PET-CT for imaging AS activity using the bone tracer [¹⁸F]Fluoride. In contrast to active RA, inflammation tracers [¹⁸F]FDG and [¹¹C](R)PK11195 appeared to be less useful for AS imaging.

Imaging in arthritis: quantifying effects of therapeutic intervention using MRI and molecular imaging

Modern imaging techniques are becoming increasingly important in assessing the course of arthritis and in permitting measurement of response to treatment as part of the follow-up of patients. They include ultrasonography (US), MRI, PET/CT, and biofluorescence. In patients with rheumatoid arthritis, clinical evaluation is significantly less sensitive than either US or MRI in detecting synovitis. As a result, imaging is a useful alternative to achieving proper assessment of disease activity. The different areas in which the new imaging techniques could help practicing rheumatologists and internal physicians include the following: early and differential diagnosis of arthritis, evaluation of disease activity, prognosis, assessment of treatment efficacy, assessment of remission, and evaluation of subclinical disease. MRI is probably the best imaging method to study disease activity in RA, because it can study all the joints with similar efficacy, has been sufficiently standardised, and yields data on inflammation that can be quantified. Different methods, developed to score synovitis activity, are increasingly used in clinical trials. The main application of PET/CT in rheumatology is the diagnosis and follow-up of large vessel vasculitis. More recently, also RA disease activity has been evaluated, allowing a panoramic view of the patient. Molecular imaging studies molecular and cellular processes in intact living organisms in a non-invasive fashion. In fluorescence, dyes, that emit light upon excitation by a light source and are read by a camera, can be used to show inflamed areas where neoangiogenesis, vasodilatation, and increased vessel permeability are present. These dyes can be coupled with different compounds including antibodies and drugs.

Future and upcoming non-neoplastic applications of PET/CT imaging

The role of fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) in the diagnosis, staging, and monitoring of neoplastic conditions is well established. The clinical utility of PET/CT has now expanded to the diagnosis of autoimmune, inflammatory, infectious, as well as non-neoplastic conditions, such as the vasculitides, atherosclerosis, and granulomatous conditions, including sarcoidosis and inflammatory bowel disease, in addition to a variety of neurologic disorders. The availability of new PET radiotracers is expected to expand PET/CT applications to a variety of other clinical domains. New radioligands for studying inflammation and neurodegenerative processes are under development. Here, we discuss the evolving potential role of PET imaging for the evaluation and monitoring of miscellaneous conditions, including osteoarthritis, interstitial lung disease, vascular thromboses, and osteoporosis.