PET/MRI in large-vessel vasculitis: clinical value for diagnosis and assessment of disease activity

FDG PET/CT in large vessel vasculitis

Large vessel vasculitides (LVV) such as giant cell arteritis, Takayasu arteritis and aortitis/periaortitis are characterised by immune-mediated inflammation of medium to large arteries. Clinical disease manifestations can be non-specific and diagnostic imaging plays an important role in the diagnostic pathway. In recent years, FDG PET/CT has proven to be a powerful metabolic tool that can provide a wholed body, non-invasive assessment of vascular inflammation. This review outlines the clinical features of large vessel vasculitis and the closely related entity of polymyalgia rheumatica, summarises the evidence for FDG PET/CT in the assessment of these conditions, and provides guidance for patient preparation, image acquisition and interpretation.

Imaging Challenges and Developments in Large-vessel Vasculitis

Vascular imaging is an integral part of large-vessel vasculitis (LVV) evaluation and management. Several imaging modalities are currently employed in clinical practice including vascular ultrasound, computed tomography angiography, MRI and magnetic resonance angiography, and 18F-fluorodeoxyglucose PET. Well-established roles for imaging in LVV include disease diagnosis and assessment of luminal lesions reflecting vascular damage. The ability of imaging to determine treatment response, monitor disease activity, and predict future arterial damage is an area of active research.

Hybrid PET/MRI of large vessel vasculitis : Radiation dose compared to PET/CT with view on cumulative effective dose

BACKGROUND

The diagnosis of large vessel vasculitis (LVV) is often challenging due to the various clinical appearances and the low prevalence. Hybrid imaging by positron emission tomography and computed tomography (PET/CT) is a highly relevant imaging modality for diagnostics and disease surveillance but may be associated with a significant amount of radiation dose especially in patients with complications.

OBJECTIVE

The aim of this retrospective analysis was to compare the image quality and impact of hybrid imaging methods PET/CT and PET/MRI on the potential for dose reduction.

METHODS

This retrospective single-center study included a cohort of 32 patients who were referred to PET/MRI for the evaluation of LVV, including graft infections and fever of unknown origin. This cohort was compared to a similar cohort of 37 patients who were examined with PET/CT in the same period. Mean radiation dose as well as image quality to establish a diagnosis were compared between the groups.

RESULTS

The mean radiation dose applied in PET/MRI was significantly lower when compared to PET/CT (mean 6.6 mSV vs. 31.7 mSV; p < 0.001). This effect was based on the partially multiphasic CT protocols. At the same time, diagnostic image quality using a 4-point scale showed similar results for both imaging modalities in the work-up of LVV.

CONCLUSION

With PET/MRI, the radiation exposure can be significantly reduced with similar image quality and diagnostic impact. Patients with LVV have a higher risk of receiving a clinically relevant cumulative effective dose (CED) and PET/MRI should be made available to them.

What is new in imaging to assist in the diagnosis of giant cell arteritis and Takayasu's arteritis since the EULAR and ACR/VF recommendations?

Over the past decades, fundamental insights have been gained to establish the pivotal role of imaging in the diagnosis of large-vessel vasculitis, including giant cell arteritis (GCA) and Takayasu's arteritis (TAK). A deeper comprehension of imaging modalities has prompted earlier diagnosis leading to expedited treatment for better prognosis. The European Alliance of Associations in Rheumatology (EULAR) recommended in 2023 that ultrasound should be the initial imaging test in suspected GCA, and Magnetic Resonance Imaging (MRI) remains the first-line imaging modality in suspected TAK. We summarize the recent advances in diagnostic imaging in large vessel vasculitis, highlighting use of combination imaging modalities, and discuss progress in newer imaging techniques such as contrast-enhanced ultrasound, shear wave elastography, ocular ultrasound, ultrasound biomicroscopy, integration of Positron Emission Tomography (PET) with MRI, novel tracer in PET, black blood MRI, orbital MRI, and implementation of artificial intelligence (AI) to existing imaging modalities. Our aim is to offer a perspective on ongoing advancements in imaging for the diagnosis of GCA and TAK, particularly innovative technology, which could potentially boost diagnostic precision.

An overview of 18F-fluorodeoxyglucose positron emission tomography/computed tomography in giant cell arteritis

PET/CT is an imaging modality that is increasingly being used to diagnose large-vessel vasculitis. In the case of giant cell arteritis, it was first used to demonstrate inflammation of the walls of large arterial trunks such as the aorta and its main branches, showing that aortic involvement is common in this vasculitis and associated with the occurrence of aortic complications such as aneurysms. More recently, with the advent of digital PET/CT, study of the cranial arteries (i.e., temporal, occipital, maxillary and vertebral arteries) has become possible, further increasing the diagnostic interest of this examination for the diagnosis of GCA. Despite these advantages, there are still limitations and questions regarding the use of PET/CT for the diagnosis and especially the follow-up of GCA. The aim of this review is to take stock of currently available data on the use of PET/CT for GCA diagnosis and follow-up.

Update on Rheumatic Diseases in Clinical Practice: Recent Concepts and Developments

Diagnostic imaging is essential in the diagnostic process of rheumatic diseases. Given the heterogeneity of this group of diseases and the tremendous impact of novel therapeutic options, guidelines and recommendations regarding the optimal choice of the most appropriate technique/s are continuously revised and radiologists should always be up-to-date. Last, because of the continuous technological innovations, we will assist to the progressive application of advanced techniques and tools in rheumatology.

Advances in PET Imaging of Large Vessel Vasculitis: An Update and Future Trends

Systemic vasculitides are autoimmune diseases characterized by inflammation of blood vessels. They are categorized based on the size of the preferentially affected blood vessels: large-, medium-, and small-vessel vasculitides. The main forms of large-vessel vasculitis include giant cell arteritis (GCA) and Takayasu arteritis (TAK). Depending on the location of the affected vessels, various imaging modalities can be employed for diagnosis of large vessel vasculitis: ultrasonography (US), magnetic resonance angiography (MRA), computed tomography angiography (CTA), and [18F]-fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (FDG-PET/CT). These imaging tools offer complementary information about vascular changes occurring in vasculitis. Recent advances in PET imaging in large vessel vasculitis include the introduction of digital long axial field-of-view PET/CT, dedicated acquisition, quantitative methodologies, and the availability of novel radiopharmaceuticals. This review aims to provide an update on the current status of PET imaging in large vessel vasculitis and to share the latest developments on imaging vasculitides.

18F-FDG-PET/MR imaging to monitor disease activity in large vessel vasculitis

Disease-monitoring in large vessel vasculitis (LVV) is challenging. Simultaneous 18F-fluorodeoxyglucose positron emission tomography with magnetic resonance imaging (PET/MRI) provides functional assessment of vascular inflammation alongside high-definition structural imaging with a relatively low burden of radiation exposure. Here, we investigate the ability of PET/MRI to monitor LVV disease activity longitudinally in a prospective cohort of patients with active LVV. We demonstrate that both the PET and MRI components of the scan can distinguish active from inactive disease using established quantification methods. Using logistic-regression modelling of PET/MRI metrics, we devise a novel PET/MRI-specific Vasculitis Activity using MR PET (VAMP) score which is able to distinguish active from inactive disease with more accuracy than established methods and detects changes in disease activity longitudinally. These findings are evaluated in an independent validation cohort. Finally, PET/MRI improves clinicians' assessment of LVV disease activity and confidence in disease management, as assessed via clinician survey. In summary, PET/MRI may be useful in tracking disease activity and assessing treatment-response in LVV. Based on our findings, larger, prospective studies assessing PET/MRI in LVV are now warranted.

Multimodality imaging to assess diagnosis and evaluate complications of large vesselarteritis

Different types of vasculitis can be distinguished according to the blood vessel's size that is preferentially affected: large-vessel, medium-vessel, and small-vessel vasculitides. Giant cell arteritis (GCA) and Takayasu's arteritis (TAK) are the main forms of large-vessel vasculitis, and may lead to lumen narrowing. Clinical manifestations of arterial narrowing on the short- and long term include vision loss, stroke, limb ischemia, and heart failure. Imaging tools are well established diagnostic tests for large-vessel vasculitis and may aid therapy monitoring in selected cases while providing important information regarding the occurrence of vascular damage, tissue and organ complications. This review aims to provide the current status of multimodality imaging for the diagnosis and identification of vascular complications in the field of large vessel vasculitis.

Molecular imaging of large vessel vasculitis

Large vessel vasculitis (LVV) affects mainly large arteries with giant cell arteritis (GCA) and Takayasu arteritis (TAK) being the two most frequent forms. Clinical symptoms can be non-specific, including headache, fatigue, weight loss, and change in vision. Untreated, LVV may also lead to serious complications such as blindness, aortic aneurysm and dissection. Therefore, rapid recognition of the disease leading to accurate diagnosis and appropriate treatment is essential. FDG-PET/CT imaging has emerged as a sensitive marker of active vascular inflammation and its use in the management of LVV is now integrated in guidelines. In this article, we will discuss the role of FDG-PET/CT for the diagnosis of LVV and monitoring of therapy, as well as review technical and interpretation parameters.

EULAR recommendations for the use of imaging in large vessel vasculitis in clinical practice: 2023 update

OBJECTIVES

To update the EULAR recommendations for the use of imaging modalities in primary large vessel vasculitis (LVV).

METHODS

A systematic literature review update was performed to retrieve new evidence on ultrasound, MRI, CT and [18F]-fluorodeoxyglucose positron emission tomography (FDG-PET) for diagnosis, monitoring and outcome prediction in LVV. The task force consisted of 24 physicians, health professionals and patients from 14 countries. The recommendations were updated based on evidence and expert opinion, iterating until voting indicated consensus. The level of agreement was determined by anonymous votes.

RESULTS

Three overarching principles and eight recommendations were agreed. Compared to the 2018 version, ultrasound is now recommended as first-line imaging test in all patients with suspected giant cell arteritis, and axillary arteries should be included in the standard examination. As an alternative to ultrasound, cranial and extracranial arteries can be examined by FDG-PET or MRI. For Takayasu arteritis, MRI is the preferred imaging modality; FDG-PET, CT or ultrasound are alternatives. Although imaging is not routinely recommended for follow-up, ultrasound, FDG-PET or MRI may be used for assessing vessel abnormalities in LVV patients with suspected relapse, particularly when laboratory markers of inflammation are unreliable. MR-angiography, CT-angiography or ultrasound may be used for long-term monitoring of structural damage, particularly at sites of preceding vascular inflammation.

CONCLUSIONS

The 2023 EULAR recommendations provide up-to-date guidance for the role of imaging in the diagnosis and assessment of patients with LVV.

Potential applications of PET/MRI in non-oncologic conditions within the abdomen and pelvis

PET/MRI is a relatively new imaging modality with several advantages over PET/CT that promise to improve imaging of the abdomen and pelvis for specific diagnostic tasks by combining the superior soft tissue characterization of MRI with the functional information acquired from PET. PET/MRI has an established role in staging and response assessment of multiple abdominopelvic malignancies, but the modality is not yet established for non-oncologic conditions of the abdomen and pelvis. In this review, potential applications of PET/MRI for non-oncologic conditions of abdomen and pelvis are outlined, and the available literature is reviewed to highlight promising areas for further research and translation into clinical practice.

The Role of Imaging in Diagnosis and Monitoring of Large Vessel Vasculitis

Technological advances and increased recognition of the prevalence and implications of large vessel vasculitis have led to robust research into various imaging techniques. Although there is still debate about which modality to choose in specific clinical scenarios, Ultrasound, PET/CT, MRI/A, and CT/A offer complementary information regarding diagnosis, disease activity, and vascular complication monitoring. Recognition of the strengths and limitations of each technique is important for appropriate application in clinical practice.

Multi-modality cardiac image computing: A survey

Multi-modality cardiac imaging plays a key role in the management of patients with cardiovascular diseases. It allows a combination of complementary anatomical, morphological and functional information, increases diagnosis accuracy, and improves the efficacy of cardiovascular interventions and clinical outcomes. Fully-automated processing and quantitative analysis of multi-modality cardiac images could have a direct impact on clinical research and evidence-based patient management. However, these require overcoming significant challenges including inter-modality misalignment and finding optimal methods to integrate information from different modalities. This paper aims to provide a comprehensive review of multi-modality imaging in cardiology, the computing methods, the validation strategies, the related clinical workflows and future perspectives. For the computing methodologies, we have a favored focus on the three tasks, i.e., registration, fusion and segmentation, which generally involve multi-modality imaging data, either combining information from different modalities or transferring information across modalities. The review highlights that multi-modality cardiac imaging data has the potential of wide applicability in the clinic, such as trans-aortic valve implantation guidance, myocardial viability assessment, and catheter ablation therapy and its patient selection. Nevertheless, many challenges remain unsolved, such as missing modality, modality selection, combination of imaging and non-imaging data, and uniform analysis and representation of different modalities. There is also work to do in defining how the well-developed techniques fit in clinical workflows and how much additional and relevant information they introduce. These problems are likely to continue to be an active field of research and the questions to be answered in the future.

Refractory Takayasu's Arteritis with Severe Coronary Involvement-Case Report and Literature Review

This report presents the case of a female patient diagnosed with Takayasu arteritis from childhood, with severe, refractory coronary involvement, leading to two acute coronary syndromes and multiple anginous episodes. Consequently, the patient suffered aorto-bicarotid bypass two times, multiple interventional procedures with stent implantation, balloon angioplasty, and up to ten repeated in-stent restenosis that required reinterventions, despite being on maximal immunosuppressive treatment. In recent years, various studies have been reported that aim to best characterize this particular type of vascular damage and to indicate optimal therapeutic options for treatment. The latter should be based on the activity of the underlying disease; however, no reliable markers are available in TA. The management of TA patients with coronary involvement continues to be a challenge and requires both drug and interventional techniques to avoid life-threatening events.

Arterial wall fibrosis in Takayasu arteritis and its potential for therapeutic modulation

Arterial wall damage in Takayasu arteritis (TAK) can progress despite immunosuppressive therapy. Vascular fibrosis is more prominent in TAK than in giant cell arteritis (GCA). The inflamed arterial wall in TAK is infiltrated by M1 macrophages [which secrete interleukin-6 (IL-6)], which transition to M2 macrophages once the inflammation settles. M2 macrophages secrete transforming growth factor beta (TGF-β) and glycoprotein non-metastatic melanoma protein B (GPNMB), both of which can activate fibroblasts in the arterial wall adventitia. Mast cells in the arterial wall of TAK also activate resting adventitial fibroblasts. Th17 lymphocytes play a role in both TAK and GCA. Sub-populations of Th17 lymphocytes, Th17.1 lymphocytes [which secrete interferon gamma (IFN-γ) in addition to interleukin-17 (IL-17)] and programmed cell death 1 (PD1)-expressing Th17 (which secrete TGF-β), have been described in TAK but not in GCA. IL-6 and IL-17 also drive fibroblast activation in the arterial wall. The Th17 and Th1 lymphocytes in TAK demonstrate an activation of mammalian target organ of rapamycin 1 (mTORC1) driven by Notch-1 upregulation. A recent study reported that the enhanced liver fibrosis score (derived from serum hyaluronic acid, tissue inhibitor of metalloproteinase 1, and pro-collagen III amino-terminal pro-peptide) had a moderate-to-strong correlation with clinically assessed and angiographically assessed vascular damage. In vitro experiments suggest the potential to target arterial wall fibrosis in TAK with leflunomide, tofacitinib, baricitinib, or mTORC1 inhibitors. Since arterial wall inflammation is followed by fibrosis, a strategy of combining immunosuppressive agents with drugs that have an antifibrotic effect merits exploration in future clinical trials of TAK.

18-Fluorodeoxyglucose positron emission tomography/computed tomography for large vessel vasculitis in clinical practice

Diagnosis, prognostic assessment, and monitoring disease activity in patients with large vessel vasculitis (LVV) can be challenging. Early recognition of LVV and treatment adaptation is essential because vascular complications (aneurysm, dilatations, ischemic complications) or treatment related side effects can occur frequently in these patients. 18-fluorodeoxyglucose positron emission tomography/computed tomography (2-[18F]FDG-PET/CT) is increasingly used to diagnose, follow, and evaluate treatment response in LVV. In this review, we aimed to summarize the current evidence on the value of 2-[18F]FDG-PET/CT for diagnosis, follow, and treatment monitoring in LVV.

Evaluation of Arterial Histopathology and microRNA Expression That Underlie Ultrasonography Findings in Temporal Arteries of Patients with Giant Cell Arteritis

The aim of this study was to assess the interrelation between vascular ultrasonography (US) findings, histopathological data, and the expression of selected dysregulated microRNAs (miRNAs) in giant cell arteritis (GCA). The study included data on the clinical parameters, US measurements, and temporal artery biopsies (TABs) of 46 treatment-naïve patients diagnosed with GCA and 22 age-matched non-GCA patient controls. We performed a comprehensive comparative and correlation analysis along with generation of receiver operating characteristic (ROC) curves to ascertain the diagnostic performance of US examination parameters and selected miRNAs for GCA diagnosis. We showed significant differences in the US-measured intima-media thickness of the temporal arteries, the presence of a halo sign, and the presence of luminal stenosis between GCA-positive/TAB-positive, GCA-positive/TAB-negative, and non-GCA patients. Correlation analysis revealed significant associations between several histopathological parameters, US-measured intima-media thickness, and the halo sign. We found that the significant overexpression of miR-146b-5p, miR-155-5p, miR-511-5p, and miR-21-5p, and the under-expression of the miR-143/145 cluster, miR-30a-5p, and miR-125a-5p, coincides and is associated with the presence of a halo sign in patients with GCA. Notably, we determined a high diagnostic performance of miR-146b-5p, miR-21-3p, and miR-21-5p expression profiles in discriminating GCA patients from non-GCA controls, suggesting their potential utilization as putative biomarkers of GCA. Taken together, our study provides an insight into the US-based diagnostic evaluation of GCA by revealing the complex interrelation of clearly defined image findings with underlying vascular immunopathology and altered arterial tissue-specific miRNA profiles.

Hybrid PET/MRI in Infection and Inflammation: An Update About the Latest Available Literature Evidence

PET/MRI has been reported to be promising in the diagnosis and evaluation of infection and inflammation including brain disorders, bone and soft tissue infections and inflammations, cardiovascular, abdominal, and systemic diseases. However, evidence came out manly from anecdotal cases or small cohorts. The present review aimed to update the latest available evidence about the role of PET/MRI in infection and inflammation. The search (January, 1 2018-July, 8 2022) on PubMed produced 504 results. Sixty-five articles were selected and included in the qualitative synthesis. The number of publications on PET/MRI in the 3 years 2018-2020 was comparable, while it increased in 2021 and 2022 (from 11 to 17 and 15, respectively). [¹⁸F]FDG and ⁶⁸Ga-DOTA-FAPI-04 were the most frequently used (42/65) and innovative radiopharmaceuticals, respectively. [¹⁸F]fluoride (9/65), translocator protein (TSPO)-targeted PET agents (6/65), CXCR4 receptor targeting tracer and β-amyloid plaques binding radiopharmaceuticals (2/65 and 2/65, respectively) were also used. Most PET/MRI studies in the period 2018-2022 focused on inflammation (55/65), and cardiovascular diseases represented the most frequent field of interest (30/65), also when considering each year singularly. An increasing trend in bone and joint publications was observed in the considered period (12/65). Other topics included neurology (11/65), inflammatory bowel disease (8/65), and other (4/65). PET/MRI technology demonstrated to be useful in infection and inflammation, being superior to each single modality and/or facilitating diagnosis in a number of conditions (eg, cardiac sarcoidosis, myocarditis, endocarditis), and/or allowing to provide insightful information about disease biology and apply innovative radiopharmaceuticals (eg, neurology, atherosclerosis). Publications focused on PET/MRI in large vessel vasculitis and aortic diseases include both diagnostic and discovery objectives. The current review corroborates the potential of PET/MRI - combining in a single examination the high soft tissue contrast, high resolution, and functional information of MRI, with molecular data provided by PET technology - to positively impact on the management of infectious diseases and inflammatory conditions.

Outcome Measures and Biomarkers for Disease Assessment in Takayasu Arteritis

Takayasu arteritis (TAK) is a less common large vessel vasculitis where histopathology of involved arteries is difficult to access except during open surgical procedures. Assessment of disease activity in TAK, therefore, relies on surrogate measures. Clinical disease activity measures such as the National Institutes of Health (NIH) score, the Disease Extent Index in TAK (DEI.TAK) and the Indian TAK Clinical Activity Score (ITAS2010) inconsistently associate with acute phase reactants (APRs). Computerized tomographic angiography (CTA), magnetic resonance angiography (MRA), or color Doppler Ultrasound (CDUS) enables anatomical characterization of stenosis, dilatation, and vessel wall characteristics. Vascular wall uptake of 18-fluorodeoxyglucose or other ligands using positron emission tomography computerized tomography (PET-CT) helps assess metabolic activity, which reflects disease activity well in a subset of TAK with normal APRs. Angiographic scoring systems to quantitate the extent of vascular involvement in TAK have been developed recently. Erythrocyte sedimentation rate and C-reactive protein have a moderate performance in distinguishing active TAK. Numerous novel biomarkers are under evaluation in TAK. Limited literature suggests a better assessment of active disease by combining APRs, PET-CT, and circulating biomarkers. Validated damage indices and patient-reported outcome measures specific to TAK are lacking. Few biomarkers have been evaluated to reflect vascular damage in TAK and constitute important research agenda.

Systematic evaluation of imaging techniques and baseline characteristics in patients with suspected vasculitis

Purpose

To assess the diagnostic value of different imaging modalities in distinguishing systemic vasculitis from other internal and immunological diseases.

Methods

This retrospective study included 134 patients with suspected vasculitis who underwent ultrasound, magnetic resonance imaging (MRI), or ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) between 01/2010 and 01/2019, finally consisting of 70 individuals with vasculitis. The main study parameter was the confirmation of the diagnosis using one of the three different imaging modalities, with the adjudicated clinical and histopathological diagnosis as the gold standard. A secondary parameter was the morphological appearance of the vessel affected by vasculitis.

Results

Patients with systemic vasculitis had myriad clinical manifestations with joint pain as the most common symptom. We found significant correlations between different imaging findings suggestive of vasculitis and the final adjudicated clinical diagnosis. In this context, on MRI, vessel wall thickening, edema, and diameter differed significantly between vasculitis and non-vasculitis groups (p < 0.05). Ultrasound revealed different findings that may serve as red flags in identifying patients with vasculitis, such as vascular occlusion or halo sign (p = 0.02 vs. non-vasculitis group). Interestingly, comparing maximal standardized uptake values from PET/CT examinations with vessel wall thickening or vessel diameter did not result in significant differences (p > 0.05).

Conclusions

We observed significant correlations between different imaging findings suggestive of vasculitis on ultrasound or MRI and the final adjudicated diagnosis. While ultrasound and MRI were considered suitable imaging methods for detecting and discriminating typical vascular changes, ¹⁸F-FDG PET/CT requires careful timing and patient selection given its moderate diagnostic accuracy.

Combined modality PET/MR for the detection of severe large vessel vasculitis

Background

Large vessel vasculitis (LVV) can be characterized based on symptom severity, and this characterization helps clinicians decide upon treatment approach. Our aim was to compare the imaging findings of combined modality positron emission tomography/magnetic resonance (PET/MR) and inflammatory markers between severe and non-severe LVV. A retrospective query was performed to identify all patients with LVV who underwent PET/MR at our institution between January 2015 and January 2021.

Results

Eleven patients (nine females; age 62.2 ± 16.4 years) underwent 15 PET/MR scans. Positivity was defined by findings indicative of active LVV on each modality: PET positive if vessel metabolic activity > liver metabolic activity; MR positive if wall thickening or contrast enhancement. When positive PET or positive MR findings were considered a positive scan, LVV patients with severe disease (n = 9 scans) showed a higher number of positive scans (n = 9) compared to the number of positive scans in non-severe patients (n = 3) (p < 0.05). The sensitivity and specificity for the detection of severe LVV were 1.00 and 0.50, respectively. When only the presence of both positive PET and positive MR findings were considered a positive scan, inflammatory marker levels were not significantly different between severe and non-severe LVV groups (severe: erythrocyte sedimentation rate (ESR) = 9.8 ± 10.6 mm/h; C-reactive protein (CRP) = 0.6 ± 0.4 mg/dL) (non-severe: ESR = 14.3 ± 22.4 mm/h; CRP = 0.5 ± 0.6 mg/dL). Blood- and liver-normalized maximum standardized uptake values were not significantly different between severe and non-severe patients (1.4 ± 0.3 vs 1.5 ± 0.4; 1.1 ± 0.4 vs 1.0 ± 0.3, respectively).

Conclusions

Because of the differences observed, PET/MR appears to be better suited to facilitate the characterization of LVV as severe or non-severe compared to inflammatory marker measurements and quantitative measurements of metabolic activity. Qualitative assessment of PET and MR positivity by 18F-fluorodeoxyglucose PET/MR may be able to supplement clinical symptoms-based LVV classification decisions and may be helpful when clinical symptoms overlap with other disease processes.

Advances in Takayasu arteritis: An Asia Pacific perspective

Takayasu Arteritis (TA) is a rare form of chronic granulomatous large vessel vasculitis that is more common in Asia compared to other parts of the world. There have been several developments in the field of Takayasu arteritis in relation to genetics, classification, clinical features, imaging, disease activity assessment and management and much of these works have been done in the Asia Pacific region. We will be discussing selected few in the current review.

Looking ahead: giant-cell arteritis in 10 years time

Although great improvements have been achieved in the fields of diagnosing and treating patients with giant-cell arteritis (GCA) in the last decades, several questions remain unanswered. The progressive increase in the number of older people, together with growing awareness of the disease and use of advanced diagnostic tools by healthcare professionals, foretells a possible increase in both prevalence and number of newly diagnosed patients with GCA in the coming years. A thorough clarification of pathogenetic mechanisms and a better definition of clinical subsets are the first steps toward a better understanding of the disease and, subsequently, toward a better use of existing and future therapeutic options. Examination of the role of different imaging techniques for GCA diagnosing and monitoring, optimization, and personalization of glucocorticoids and other immunosuppressive agents, further development and introduction of novel drugs, identification of prognostic factors for long-term outcomes and management of treatment discontinuation will be the central topics of the research agenda in years to come.

Vessel inflammation and morphological changes in patients with large vessel vasculitis: a retrospective study

OBJECTIVE

The aim was to identify any association between imaging signs of vessel wall inflammation (positron emission tomography-CT (PET-CT) score and CT/MR wall thickening) and synchronous and subsequent vascular damage (stenoses/dilations) in patients with large vessel vasculitis (LVV).

METHODS

Consecutive patients with LVV referred to a tertiary centre in 2007-2020 with baseline PET-CT and morphological imaging (CT/MR angiography) performed within 3 months were included. All available PET-CT and CT/MR scans were reviewed to assess PET-CT uptake (4-point semi-quantitative score), wall thickening, stenoses and dilations for 15 vascular segments. The associations of baseline PET score and CT/MR wall thickening with synchronous and incident stenoses/dilations at CT/MR performed 6-30 months from baseline were evaluated in per-segment and per-patient analyses. Respective areas under the receiver operating characteristic curve (AUC) were calculated.

RESULTS

We included 100 patients with LVV (median age: 48 years, 22% males). Baseline PET score and wall thickening were strongly associated (Cuzick non-parametric test for trend across order groups (NPtrend) <0.001). The association with synchronous stenoses/dilations was weak for PET score (NPtrend=0.01) and strong for wall thickening (p<0.001). In per-patient analyses, sensitivity/specificity for ≥1 synchronous stenoses/dilations were 44%/67% for PET score ≥2 and 66.7%/60.5% for wall thickening. Subsequent CTs/MRs were available in 28 patients, with seven incident stenoses/dilations. Baseline PET score was strongly associated with incident stenoses/dilations (p=0.001), while baseline wall thickening was not (p=0.708), with AUCs for incident stenoses/dilations of 0.80 for PET score and 0.52 for wall thickening.

CONCLUSION

PET score and wall thickening are strongly associated, but only baseline PET score is a good predictor of incident vessel wall damage in LVV.

Large-vessel vasculitis

Large-vessel vasculitis (LVV) manifests as inflammation of the aorta and its major branches and is the most common primary vasculitis in adults. LVV comprises two distinct conditions, giant cell arteritis and Takayasu arteritis, although the phenotypic spectrum of primary LVV is complex. Non-specific symptoms often predominate and so patients with LVV present to a range of health-care providers and settings. Rapid diagnosis, specialist referral and early treatment are key to good patient outcomes. Unfortunately, disease relapse remains common and chronic vascular complications are a source of considerable morbidity. Although accurate monitoring of disease activity is challenging, progress in vascular imaging techniques and the measurement of laboratory biomarkers may facilitate better matching of treatment intensity with disease activity. Further, advances in our understanding of disease pathophysiology have paved the way for novel biologic treatments that target important mediators of disease in both giant cell arteritis and Takayasu arteritis. This work has highlighted the substantial heterogeneity present within LVV and the importance of an individualized therapeutic approach. Future work will focus on understanding the mechanisms of persisting vascular inflammation, which will inform the development of increasingly sophisticated imaging technologies. Together, these will enable better disease prognostication, limit treatment-associated adverse effects, and facilitate targeted development and use of novel therapies.

Pediatric cardiothoracic vasculitis: multimodality imaging review

The pediatric vasculitides are a relatively uncommon and heterogeneous group of disorders characterized by vessel inflammation, often with cardiothoracic involvement. Diagnosis and monitoring are often clinically challenging because of the nonspecific symptoms and laboratory markers. Thus, imaging has assumed increasing importance for early detection of disease activity, extent and complications as well as long-term monitoring pre- and post-treatment. Herein, we review the major pediatric vasculitides with frequent chest manifestations, including Takayasu arteritis, Kawasaki disease, granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis, microscopic polyangiitis, Behçet disease and potential mimics. We highlight key clinical features and management considerations, emphasizing the central role of imaging.

Use of Contrast-Enhanced Ultrasound Sonography in Giant Cell Arteritis: A Proof-of-Concept Study

C-Reactive protein and erythrocyte sedimentation rate are crucial parameters used to monitor giant cell arteritis (GCA). Given that tocilizumab is approved for the treatment of GCA, these parameters are less sensitive because of the effects of interleukin-6 receptor blockade. Thus, the optimal method for monitoring GCA patients undergoing tocilizumab therapy, especially patients exhibiting a persistent thickened vessel wall in large vessels, remains unclear. Contrast-enhanced ultrasonography (CEUS) can increase the visibility of tissue perfusion by slow blood flow, which cannot be detected by power color doppler. We used CEUS to investigate patients with active and inactive GCA of the large vessels (active large vessel arteritis [aLVV]/inactive large vessel arteritis [iLVV]) who were not administered tocilizumab in this proof-of-concept study. After injection of the ultrasound contrast agent, the contrasted area (CA) of large vessels in a transverse section was calculated twice: first when the lumen was contrasted completely and once again 4-8 s later. We investigated the value of increase in CA that exhibited the best sensitivity and specificity for aLVV. Twenty-four patients were included in this study: 15 with aLVV and 9 with iLVV. The CA increased from 32.2 ± 16.8 to 52.5 ± 21.3 mm² (p < 0.0001) in aLVV. The mean CA remained unchanged in iLVV. The best cutoff value to differentiate between aLVV and iLVV was a ≥25% increase in CA with a sensitivity and specificity of 91.7% and 100%, respectively. Our study indicates that CEUS can detect aLVV with high sensitivity and specificity. Incorporation of CEUS into routine clinical practice might result in a good method for monitoring disease activity in LVV in GCA patients. The limitation of our study was the small number of patients and the lack of investigator blinding to clinical data.

Current advances in giant cell arteritis

PURPOSE OF REVIEW

The aim of this study was to present the latest advances in giant cell arteritis (GCA) care, and recent national and international rheumatology societies guidance which influences clinical practice.

RECENT FINDINGS

Cranial ultrasound reduces diagnostic delay and improves clinical outcomes. Immediate high dose glucocorticoids remain the standard treatment for GCA. Controlled trial evidence using Tocilizumab, an interleukin-6 receptor antagonist, shows good clinical efficacy with steroid-sparing effects.

SUMMARY

Improved patient outcomes require formalizing pathways to diagnosis and closer liaison with rheumatology for long-term management with second-line therapies.

State of the art of 18F-FDG PET/CT application in inflammation and infection: a guide for image acquisition and interpretation

AIM

The diagnosis, severity and extent of a sterile inflammation or a septic infection could be challenging since there is not one single test able to achieve an accurate diagnosis. The clinical use of 18F-fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) imaging in the assessment of inflammation and infection is increasing worldwide. The purpose of this paper is to achieve an Italian consensus document on [18F]FDG PET/CT or PET/MRI in inflammatory and infectious diseases, such as osteomyelitis (OM), prosthetic joint infections (PJI), infective endocarditis (IE), prosthetic valve endocarditis (PVE), cardiac implantable electronic device infections (CIEDI), systemic and cardiac sarcoidosis (SS/CS), diabetic foot (DF), fungal infections (FI), tuberculosis (TBC), fever and inflammation of unknown origin (FUO/IUO), pediatric infections (PI), inflammatory bowel diseases (IBD), spine infections (SI), vascular graft infections (VGI), large vessel vasculitis (LVV), retroperitoneal fibrosis (RF) and COVID-19 infections.

METHODS

In September 2020, the inflammatory and infectious diseases focus group (IIFG) of the Italian Association of Nuclear Medicine (AIMN) proposed to realize a procedural paper about the clinical applications of [18F]FDG PET/CT or PET/MRI in inflammatory and infectious diseases. The project was carried out thanks to the collaboration of 13 Italian nuclear medicine centers, with a consolidate experience in this field. With the endorsement of AIMN, IIFG contacted each center, and the pediatric diseases focus group (PDFC). IIFG provided for each team involved, a draft with essential information regarding the execution of [18F]FDG PET/CT or PET/MRI scan (i.e., indications, patient preparation, standard or specific acquisition modalities, interpretation criteria, reporting methods, pitfalls and artifacts), by limiting the literature research to the last 20 years. Moreover, some clinical cases were required from each center, to underline the teaching points. Time for the collection of each report was from October to December 2020.

RESULTS

Overall, we summarized 291 scientific papers and guidelines published between 1998 and 2021. Papers were divided in several sub-topics and summarized in the following paragraphs: clinical indications, image interpretation criteria, future perspectivess and new trends (for each single disease), while patient preparation, image acquisition, possible pitfalls and reporting modalities were described afterwards. Moreover, a specific section was dedicated to pediatric and PET/MRI indications. A collection of images was described for each indication.

CONCLUSIONS

Currently, [18F]FDG PET/CT in oncology is globally accepted and standardized in main diagnostic algorithms for neoplasms. In recent years, the ever-closer collaboration among different European associations has tried to overcome the absence of a standardization also in the field of inflammation and infections. The collaboration of several nuclear medicine centers with a long experience in this field, as well as among different AIMN focus groups represents a further attempt in this direction. We hope that this document will be the basis for a "common nuclear physicians' language" throughout all the country.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40336-021-00445-w.

Identify. Quantify. Predict. Why Immunologists Should Widely Use Molecular Imaging for Coronavirus Disease 2019

Molecular imaging using PET/CT or PET/MRI has evolved from an experimental imaging modality at its inception in 1972 to an integral component of diagnostic procedures in oncology, and, to lesser extent, in cardiology and neurology, by successfully offering in-vivo imaging and quantitation of key pathophysiological targets or molecular signatures, such as glucose metabolism in cancerous disease. Apart from metabolism probes, novel radiolabeled peptide and antibody PET tracers, including radiolabeled monoclonal antibodies (mAbs) have entered the clinical arena, providing the in-vivo capability to collect target-specific quantitative in-vivo data on cellular and molecular pathomechanisms on a whole-body scale, and eventually, extract imaging biomarkers possibly serving as prognostic indicators. The success of molecular imaging in mapping disease severity on a whole-body scale, and directing targeted therapies in oncology possibly could translate to the management of Coronavirus Disease 2019 (COVID-19), by identifying, localizing, and quantifying involvement of different immune mediated responses to the infection with SARS-COV2 during the course of acute infection and possible, chronic courses with long-term effects on specific organs. The authors summarize current knowledge for medical imaging in COVID-19 in general with a focus on molecular imaging technology and provide a perspective for immunologists interested in molecular imaging research using validated and immediately available molecular probes, as well as possible future targets, highlighting key targets for tailored treatment approaches as brought up by key opinion leaders.

Systemic vasculitides and the role of multitechnique imaging in the diagnosis

Vasculitis, a systemic disease characterised by inflammation of the blood vessels, remains challenging to diagnose and manage. Vessel size has been the basis for classifying systemic vasculitides. Imaging plays a vital role in diagnosing this challenging disease. This review article aims (a) to summarise up-to-date literature in this field, as well as include classification updates and (b) to review available imaging techniques, recent advances, and emphasis on imaging findings to diagnose large vessel vasculitides.

Procedural recommendations of cardiac PET/CT imaging: standardization in inflammatory-, infective-, infiltrative-, and innervation (4Is)-related cardiovascular diseases: a joint collaboration of the EACVI and the EANM

With this document, we provide a standard for PET/(diagnostic) CT imaging procedures in cardiovascular diseases that are inflammatory, infective, infiltrative, or associated with dysfunctional innervation (4Is). This standard should be applied in clinical practice and integrated in clinical (multicenter) trials for optimal procedural standardization. A major focus is put on procedures using [¹⁸F]FDG, but 4Is PET radiopharmaceuticals beyond [¹⁸F]FDG are also described in this document. Whilst these novel tracers are currently mainly applied in early clinical trials, some multicenter trials are underway and we foresee in the near future their use in clinical care and inclusion in the clinical guidelines. Finally, PET/MR applications in 4Is cardiovascular diseases are also briefly described. Diagnosis and management of 4Is-related cardiovascular diseases are generally complex and often require a multidisciplinary approach by a team of experts. The new standards described herein should be applied when using PET/CT and PET/MR, within a multimodality imaging framework both in clinical practice and in clinical trials for 4Is cardiovascular indications.

Imaging for Diagnosis, Monitoring, and Outcome Prediction of Large Vessel Vasculitides

Purpose of Review

To discuss and summarize the latest evidence on imaging techniques in giant cell arteritis (GCA) and Takayasu arteritis (TAK). This is a report on the performance of ultrasound (US), magnetic resonance imaging (MRI), computed tomography (CT), 18F-fluorodeoxyglucose positron emission tomography (18-FDG-PET), and other emerging imaging techniques in diagnosis, outcome prediction, and monitoring of disease activity.

Recent Findings

Imaging techniques have gained an important role for diagnosis of large vessel vasculitides (LVV). As signs of vasculitis, US, MRI, and CT show a homogeneous arterial wall thickening, which is mostly concentric. PET displays increased FDG uptake in inflamed artery walls. US is recommended as the initial imaging modality in GCA. MRI and PET/CT may also detect vasculitis of temporal arteries. For TAK, MRI is recommended as the first imaging modality as it provides a good overview without radiation. Extracranial LVV can be confirmed by all four modalities. In addition, MRI and PET/CT provide consistent examination of the aorta and its branches. New techniques such as contrast-enhanced ultrasound, PET/MRI, and auxiliary methods such as “computer-assisted quantitative analysis” have emerged and need to be further validated.

Summary

Imaging has partly replaced histology for confirming LVV. Provided experience and adequate training, US, MRI, CT, or PET provide excellent diagnostic accuracy. Imaging results need to complement history and clinical examination. Ongoing studies are evaluating the role of imaging for monitoring and outcome measurement.

Potential Applications of PET Scans, CT Scans, and MR Imaging in Inflammatory Diseases: Part II: Cardiopulmonary and Vascular Inflammation

Detecting inflammation is among the most important aims of medical imaging. Inflammatory process involves immune system activity and local tissue response. The role of PET with fludeoxyglucose F 18 has been expanded. Systemic vasculitides and cardiopulmonary inflammatory disorders constitute a wide range of diseases with multisystemic manifestations. PET with fludeoxyglucose F 18 is useful in their diagnosis, assessment, and follow-up. This article provides an overview of the current status and potentials of hybrid molecular imaging in evaluating cardiopulmonary and vascular inflammatory diseases focusing on the potential for PET with fludeoxyglucose F 18/MR imaging and PET/CT scans.

[The current place of non-invasive large-vessel imaging in the diagnosis and follow-up of giant cell arteritis]

Large vessel involvement in giant cell arteritis has long been described, although its right frequency and potential prognostic value have only been highlighted for two decades. Large vessel involvement not only is associated with a high incidence of late aortic aneurysms, but also might cause greater resistance to glucocorticoids and longer treatment duration, as well as worse late cardiovascular outcomes. These data were brought to our attention, thanks to substantial progress recently made in large vessel imaging. This relies on four single, often complementary, approaches of varying availability: colour Doppler ultrasound, contrast-enhanced computed tomography with angiography and, magnetic resonance imaging, which all demonstrate homogeneous circumferential wall thickening and describe structural changes; 18F-fluorodeoxyglucose positron emission tomography-computed tomography (PET/CT), which depicts wall inflammation and assesses many vascular territories in the same examination. In addition, integrated head-and-neck PET/CT can accurately and reliably diagnose cranial arteritis. All four procedures exhibit high diagnostic performance for a large vessel arteritis diagnosis so that the choice is left to the physician, depending on local practices and accessibility; the most important is to carry out the chosen modality without delay to avoid false or equivocal results, due to early vascular oedema changes as a result of high dose glucocorticoid treatment. Yet, ultrasound study of the superficial cranial and subclavian/axillary arteries remains a first line assessment aimed at strengthening and expediting the clinical diagnosis as well as raising suspicion of large-vessel involvement. In treated patients, vascular imaging results are poorly correlated with clinical-biological controlled disease so that it is strongly recommended not to renew imaging studies unless a large vessel relapse or complication is suspected. On the other hand, a structural monitoring of aorta following giant cell arteritis is mandatory, but uncertainties remain regarding the best procedural approach, timing of first control and spacing between controls. Individuals at greater risk of developing aortic complication, e.g. those with classic risk factors for aneurysm and/or visualised aortitis, should be monitored more closely.