Imaging giant cell arteritis and Aortitis in contrast enhanced 18F-FDG PET/CT: Which imaging score correlates best with laboratory inflammation markers?

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.

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.

ACR Appropriateness Criteria® Noncerebral Vasculitis

Noncerebral vasculitis is a wide-range noninfectious inflammatory disorder affecting the vessels. Vasculitides have been categorized based on the vessel size, such as large-vessel vasculitis, medium-vessel vasculitis, and small-vessel vasculitis. In this document, we cover large-vessel vasculitis and medium-vessel vasculitis. Due to the challenges of vessel biopsy, imaging plays a crucial role in diagnosing this entity. While CTA and MRA can both provide anatomical details of the vessel wall, including wall thickness and enhancement in large-vessel vasculitis, FDG-PET/CT can show functional assessment based on the glycolytic activity of inflammatory cells in the inflamed vessels. Given the size of the vessel in medium-vessel vasculitis, invasive arteriography is still a choice for imaging. However, high-resolution CTA images can depict small-caliber aneurysms, and thus can be utilized in the diagnosis of medium-vessel vasculitis. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Imaging of nonatheromatous carotid artery disease

Imaging diagnosis of nonatheromatous carotid artery disease is challenging due to its low prevalence in contrast to that of atheromatous disease. Congenital anomalies are frequently discovered incidentally, as the chronicity of these conditions allows for compensatory flow development. The inflammatory conditions typically present with nonspecific courses, and a high clinical suspicion along with timely imaging evaluation can guide the diagnosis. Carotid dissection is the result of a partial disruption of the arterial wall and can be seen in previously healthy patients, in patients with underlying noninflammatory arteriopathies or trauma. Traumatic injuries to the carotid artery may occur under many different conditions and mechanisms and timely recognition of high-risk patients improves patient outcomes. Although free-floating thrombi (FFT) formation is typically seen with atherosclerotic plaque rupture, different conditions may also predispose to FFT. In this review article, we study the different imaging features of nonatheromatous carotid artery disease using ultrasonography, computed tomography angiography, magnetic resonance angiography, and digital subtraction angiogram.

Large vessel vasculitis: imaging standards of 18F-FDG PET/CT

Improvements in positron emission tomography (PET) technology have contributed to increased diagnostic accuracy in patients with large-vessel vasculitis (LVV) over the last decades. Many systematic reviews and meta-analyses were conducted, and earlier diagnosis by ¹⁸F-FDG PET can be made in patients suspected of having LVV. Two subtypes, Takayasu arteritis and giant cell arteritis, will progress when poorly responding to corticosteroids and augmented immunosuppression. In most patients, disease activity cannot be monitored by laboratory tests alone; therefore, glucose metabolism may be a source for possible biomarkers. In this review, we present current concepts regarding ¹⁸F-FDG PET/CT imaging standards.

CT texture analysis compared to Positron Emission Tomography (PET) and mutational status in resected melanoma metastases

PURPOSE

To evaluate the potential of CT texture analysis parameters and metabolic characteristics of melanoma metastases in ¹⁸F- FDG PET/CT to predict relevant mutations of tumour cells for targeted therapy in metastatic melanoma patients in correlation with histopathologic specimen.

MATERIAL AND METHODS

66 melanoma patients, examined with contrast-enhanced ¹⁸F-FDG PET/CT before scheduled metastasectomy without any prior systemic therapy, were included in this single-centre retrospective analysis under IRB waiver. The largest, resected metastasis in each patient was assessed with CT texture analysis and semiquantitative ¹⁸F-FDG PET parameters. Correlation between imaging parameters and histopathological mutations (BRAF- and NRAS- genes) were calculated.

RESULTS

Attenuation standard deviation (SD) within target lesion indicated a weak correlation with its SUV_peak (rho -0.292, p 0.017). However, no correlation between CT texture analysis, metabolic ¹⁸F-FDG PET parameters and tumour cell mutation could be established.

CONCLUSION

CT texture parameters cannot replace the diagnostic value of ¹⁸F- FDG PET/CT for metabolic information in melanoma patients. Discrimination between BRAF- and NRAS mutation status was not feasible with CT texture analysis in this exploratory study.

[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.

Long-term treatment with tocilizumab in giant cell arteritis: efficacy and safety in a monocentric cohort of patients

Objective

The efficacy of tocilizumab (TCZ) in GCA is supported by two randomized controlled studies, in which TCZ allowed remission to be achieved after 52 weeks of treatment. However, after discontinuation of treatment, half of the patients relapsed. The aim of this study was to analyse the efficacy and safety of long-term treatment with TCZ and the role of fluorodeoxyglucose (FDG)-PET/CT scanning in the follow-up of these patients.

Methods

We collected the clinical data of a monocentric cohort of GCA patients retrospectively.

Results

Thirty-two patients were treated with TCZ [25 males and 7 females; age = 74 (59–81) years]. Most of them achieved and maintained clinical remission (1 month: 69%; 3 months: 91%; 6 months: 96%; 12 months: 100%), with serological and FDG-PET/CT scan improvement and a reduction of concomitant glucocorticoid therapy. Nineteen patients were treated for >52 weeks, and in 13 of them a dose tapering was performed, whereas in 2 cases TCZ was suspended for disease remission. Only two patients relapsed: one during TCZ tapering and one after TCZ discontinuation. Ten cases of mild infections and a case of urinary sepsis were reported; in patients treated for >1 year there was no increase in the incidence of side effects compared with patients treated for <12 months.

Conclusion

In our cohort of patients, we confirmed the efficacy of TCZ in the induction and maintenance of remission of GCA, demonstrating an important steroid-sparing effect and a good safety profile. Long-term treatment seems to prevent relapse of the disease, suggesting that TCZ treatment can be continued for >52 weeks with efficacy and safety.

Mechanism and biomarkers in aortitis--a review

Aortitis can be the manifestation of an underlying infectious or noninfectious disease process. An autoimmune cause is suggested in a large proportion of noninfectious causes. Similar to other autoimmune diseases, the pathophysiology of aortitis has been investigated in detail, but the etiology remains unknown. Most cases of aortitis often go undetected for a long time and are often identified at late stages of the disease. Recent advances in imaging techniques have significantly improved the diagnosis of aortitis. However, significant challenges associated with the imaging techniques limit their use. Several routine inflammation-based markers, such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and inflammatory cytokines, are nonspecific and, therefore, have limited use in the diagnosis of aortitis. The search for more specific serum biomarkers, which can facilitate detection and progression is under progress. Several autoantibodies have been identified, but assigning their role in the pathogenesis as well as their specificity remains a challenge. The current review addresses some of these issues in detail. KEY MESSAGES: • Noninfectious aortitis is an autoimmune disease. • Several biomarkers, including cytokines and autoantibodies, are increased in aortitis. • Imaging techniques, commonly used to detect aortitis, are associated with the high cost and technical challenges. • There is a need to develop low-cost biomarker-based detection tools. • The knowledge of biomarkers in aortitis detection is discussed.

Comparative study of 18F-FDG PET/CT and CT angiography in detection of large vessel vasculitis

OBJECTIVE

Compare ¹⁸F-FDG PET/CT and CTangio in the diagnosis of extracraneal large vessel involvement in patients with suspicion of large vessel vasculitis (LVV).

MATERIAL AND METHODS

A retrospective database reviewed 59 patients with clinical suspicion of LVV undergoing ¹⁸F-FDG PET/CT and CTangio. In 55 patients PET/TC and CTangio were done simultaneously in the same machine and in 4 patients with a scan interval of<1 month. PET/CT analyses included qualitatively and quantitative analysis (ratio SUVmax ¹⁸F-FDG vessel/SUVmax liver). CTangio was assessed for concentric mural thickening, contrast wall enhancement and structural vascular changes as potential complications of vasculitis.

RESULTS

¹⁸F-FDG PET/CT and CTangio show high specificity (97.2%) for LVV diagnosis, with an excellent sensitivity for ¹⁸F-FDG PET/CT (95.6%) and lower for CTangio (60.9%), which leads to a high negative predictive value for ¹⁸F-FDG PET/CT (97.2%) and a high false negative rate for CTangio (39.1%). A 70% concordance between ¹⁸F-FDG PET/CT and CTangio was obtained (Kappa index 0.70± 0.095 (P<.001).

CONCLUSION

The results show the greater potential of ¹⁸F-FDG PET/CT for the detection and extension of LVV. Therefore, ¹⁸F-FDG PET/CT should be exploited to the maximum and consider as the first line imaging technique in the extracranial diagnosis of LVV and its possible association with polymyalgia rheumatica. The addition of CTangio could be more indicated in patients with Takayasu arteritis and in long-standing and/or severe vasculitis since it increases the accuracy in the detection of possible vascular complications.

Immuno-Imaging to Predict Treatment Response in Infection, Inflammation and Oncology

Background: Molecular nuclear medicine plays a pivotal role for diagnosis in a preclinical phase, in genetically susceptible patients, for radio-guided surgery, for disease relapse evaluation, and for therapy decision-making and follow-up. This is possible thanks to the development of new radiopharmaceuticals to target specific biomarkers of infection, inflammation and tumour immunology. Methods: In this review, we describe the use of specific radiopharmaceuticals for infectious and inflammatory diseases with the aim of fast and accurate diagnosis and treatment follow-up. Furthermore, we focus on specific oncological indications with an emphasis on tumour immunology and visualizing the tumour environment. Results: Molecular nuclear medicine imaging techniques get a foothold in the diagnosis of a variety of infectious and inflammatory diseases, such as bacterial and fungal infections, rheumatoid arthritis, and large vessel vasculitis, but also for treatment response in cancer immunotherapy. Conclusion: Several specific radiopharmaceuticals can be used to improve diagnosis and staging, but also for therapy decision-making and follow-up in infectious, inflammatory and oncological diseases where immune cells are involved. The identification of these cell subpopulations by nuclear medicine techniques would provide personalized medicine for these patients, avoiding side effects and improving therapeutic approaches.

Diagnosis and management of giant cell arteritis: an Asia-Pacific perspective

Giant cell arteritis is the commonest primary vasculitis of the elderly. However, the prevalence does vary widely between populations with highest incidence amongst Northern Europeans and lowest amongst East Asians. Preliminary studies suggest that clinical manifestations may differ between different populations. Newer diagnostic approaches including ultrasound, MR angiography and PET imaging are under review. While there have been recent advances in the diagnosis of GCA particularly with regard to imaging, there is an urgent need for improvements in methods of diagnosis, treatment and requirement for screening. Glucocorticoid treatment remain the backbone of therapy. However, glucocorticoid therapy is associated with significant adverse effects. Conventional and novel immunosuppressive agents have only demonstrated modest effects in a subgroup of steroid refractory GCA due to the different arms of the immune system at play. However, recently a study of IL-6 blockade demonstrated benefit in GCA. Newer approaches such as fast-track pathways can also result in improvements in consequences of GCA including blindness.