Diagnostic Performance of 18F-FDG PET/CT in Infectious and Inflammatory Diseases according to Published Meta-Analyses. Contrast Media Mol Imaging. 2019;2019:3018349. [PMID: 31427907 PMCID: PMC6683817 DOI: 10.1155/2019/3018349]

99mTc-DTPA-Collagen Radiotracer for the Noninvasive Detection of Infective Endocarditis

Infective endocarditis (IE) represents a significant concern among hospital-acquired infections, frequently caused by the Gram-positive bacterium Staphylococcus aureus. Nuclear imaging is emerging as a noninvasive and precise diagnostic tool. However, the gold standard radiotracer [18F]-FDG cannot distinguish between infection and inflammation, resulting in false positives. Based on the presence of collagen-binding proteins in the cell wall of S. aureus, we propose the radiolabeling of collagen for its evaluation in IE animal models by single-photon emission computed tomography (SPECT) imaging. We radiolabeled rat tail collagen I using DTPA chelator and [99mTc]NaTcO4. Selectivity was evaluated in vitro using 3 Gram-positive bacteria, 1 Gram-negative bacteria and 1 yeast. In vivo SPECT/computed tomography (CT) imaging was conducted on 8 SD rat models of IE and 8 sterile sham model as controls. Ex vivo biodistribution and autoradiography were performed following imaging. Diagnosis of IE was confirmed through microbiological studies and H&E histopathology. [99mTc]-DTPA-Collagen was synthesized successfully with a yield of 42.86 ± 6.35%, a purity of 95.84 ± 1.85% and a stability higher than 90% after 50 h postincubation. In vitro uptake demonstrated the selectivity for Gram-positive bacteria (63.85 ± 15.15%). Ex vivo analysis confirmed hepato-splenic excretion. In vivo SPECT/CT imaging revealed highly localized uptake within the aortic valve with a sensitivity of 62.5% and specificity of 87.5%. We successfully synthesized and characterized a new SPECT radiotracer based on [99mTc]Tc-radiolabeled collagen. In vitro studies demonstrated the selectivity of the radiotracer for Gram-positive bacteria. In vivo SPECT/CT-based assessment in an IE model confirmed the potential of this approach to detect active IE.

Changes in cerebral glucose metabolism among mild long COVID patients: an [18F]FDG PET/CT study

COVID-19, caused by SARS-CoV-2, presents diverse symptoms, including neurological manifestations. This study investigated COVID-19's neurological sequelae, focusing on the central nervous system's involvement through cerebral glycolytic metabolism assessed via PET/CT. Twenty-two patients with mild long COVID cognitive symptoms and 20 healthy volunteers without cognitive, psychiatric, or neurological impairments and no history of COVID-19 infection underwent cerebral PET/CT scans using [18F]FDG to assess cerebral metabolism. The study meticulously evaluated the uptake of [18F]FDG in various brain regions, employing the CortexID Suite software for quantitative analysis. The analysis focused on identifying areas of hypometabolism and hypermetabolism, indicative of altered glucose metabolism possibly related to COVID-19's neurological impact. No statistically significant differences were found between the mild COVID and healthy groups. Although our sample was too small to generate a statistical difference between groups, future studies should explore some findings, such as hypometabolism in 15 regions and hypermetabolism in 11 regions in the mild COVID group. These changes, especially in areas linked to executive functions, sensory perception, and emotional regulation, suggest nuanced alterations in brain function. Our study did not find significant glycolytic metabolic changes in patients with mild long COVID. However, areas of glycolytic hypometabolism and hypermetabolism found in some patients showed biological plausibility with the cognitive and affective symptoms they presented. Future investigations with a larger sample size should be correlated with neuropsychological and neuropsychiatric examinations to confirm this relationship.

Evidence-Based Data on the Diagnostic Role and Clinical Usefulness of [18F]FDG PET/CT in Endocarditis and Cardiac Device Infections

Infective endocarditis and infection of cardiac devices are conditions characterized by high morbidity and mortality, thus requiring a prompt diagnosis. Advanced imaging modalities are often required in the management of infectious endocarditis according to guidelines. The aim of this review is to collect and describe evidence-based knowledge about the diagnostic role and clinical usefulness of [18F]FDG PET/CT in endocarditis and cardiac device infections based on published systematic reviews and meta-analyses on this topic and on recent guidelines. [18F]FDG PET/CT is recommended only in selected cases. This imaging method has good diagnostic accuracy in detecting prosthetic valve endocarditis and cardiac device infection. Furthermore, it can identify extra-cardiac infectious foci changing the clinical management in a significant percentage of cases.

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.

[18F]FDG PET/CT Imaging Is Associated with Lower In-Hospital Mortality in Patients with Pyogenic Spondylodiscitis-A Registry-Based Analysis of 29,362 Cases

BACKGROUND

While MRI is the primary diagnostic tool for the diagnosis of spondylodiscitis, the role of [18F]-fluorodeoxyglucose ([18F]FDG) PET/CT is gaining prominence. This study aimed to determine the frequency of [18F]FDG PET/CT usage and its impact on the in-hospital mortality rate in patients with spondylodiscitis, particularly in the geriatric population.

METHODS

We conducted a Germany-wide cross-sectional study from 2019 to 2021 using an open-access, Germany-wide database, analyzing cases with ICD-10 codes M46.2-, M46.3-, and M46.4- ('Osteomyelitis of vertebrae', 'Infection of intervertebral disc (pyogenic)', and 'Discitis unspecified'). Diagnostic modalities were compared for their association with in-hospital mortality, with a focus on [18F]FDG PET/CT.

RESULTS

In total, 29,362 hospital admissions from 2019 to 2021 were analyzed. Of these, 60.1% were male and 39.9% were female, and 71.8% of the patients were aged 65 years and above. The overall in-hospital mortality rate was 6.5% for the entire cohort and 8.2% for the geriatric subgroup (p < 0.001). Contrast-enhanced (ce) MRI (48.1%) and native CT (39.4%) of the spine were the most frequently conducted diagnostic modalities. [18F]FDG PET/CT was performed in 2.7% of cases. CeCT was associated with increased in-hospital mortality (OR = 2.03, 95% CI: 1.90-2.17, p < 0.001). Cases with documented [18F]FDG PET/CT showed a lower frequency of in-hospital deaths (OR = 0.58, 95% CI: 0.18-0.50; p = 0.002). This finding was more pronounced in patients aged 65 and above (OR = 0.42, 95% CI: 0.27-0.65, p = 0.001).

CONCLUSIONS

Despite its infrequent use, [18F]FDG PET/CT was associated with a lower in-hospital mortality rate in patients with spondylodiscitis, particularly in the geriatric cohort. This study is limited by only considering data on hospitalized patients and relying on the assumption of error-free coding. Further research is needed to optimize diagnostic approaches for spondylodiscitis.

Diagnostic Performance of 18 F-FDG Positron Emission Tomography/Computed Tomography and Blood Test Parameters for Pulmonary Inflammatory Pseudotumor

PURPOSE

Pulmonary inflammatory pseudotumor (PIP) is an inflammatory proliferative tumor-like lesion that frequently exhibits hypermetabolism on 18 F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography imaging (PET/CT) and is readily misdiagnosed as a malignant tumor. The purpose of this study was to identify PIP by combining PET/computed tomography metabolic and blood test characteristics with machine learning.

PATIENTS AND METHODS

We recruited 27 patients with PIP and 28 patients with lung cancer (LC). The PET metabolic and blood test parameters were collected, and the differences between the groups were evaluated. In addition, we combined the support vector machine (SVM) classifier with the indicators that differed between the groups to classify PIP and LC.

RESULTS

For PET metabolic parameters, our findings showed that, as compared with the LC group, maximal standardized uptake value ( P < 0.001, t = -4.780), Mean standardized uptake value SUV mean , P < 0.001, t = -4.946), and SD40% ( P < 0.001, t = -4.893) were considerably reduced in the PIP group, whereas CV40% ( P = 0.004, t = 3.012) was significantly greater. For blood test parameters, the total white blood cell count ( P < 0.001, t = 6.457) and absolute neutrophil count ( P < 0.001, t = 6.992) were substantially higher in the PIP group than in the LC group. Furthermore, the performance of SVM trained solely on PET metabolic parameters (mean area under the curve [AUC] = 0.84) was comparable to that of SVM trained solely on blood test parameters (mean AUC = 0.86). Surprisingly, utilizing the combined parameters increased SVM performance significantly (mean AUC = 0.98).

CONCLUSION

PET metabolic and blood test parameters differed significantly between the PIP and LC groups, and the SVM paradigm using these significantly different features has the potential to be used to classify PIP and LC, which has important clinical implications.

Visualisation of in vivo protein synthesis during mycobacterial infection through [68Ga]Ga-DOTA-puromycin µPET/MRI

Radiolabelled puromycin analogues will allow the quantification of protein synthesis through nuclear medicine-based imaging. A particularly useful application could be the non-invasive longitudinal visualisation of mycobacterial activity through direct quantification of puromycin binding. This study assesses the value of [68Ga]Ga-DOTA-puromycin in the visualisation of mycobacteria through positron emission tomography combined with magnetic resonance imaging (µPET/MRI). The radiopharmaceutical was produced by previously published and validated methods. [68Ga]Ga-DOTA-Puromycin imaging was performed on severe immunodeficient mice infected with Bacille Calmette-Guérin-derived M. Bovis (BCG). Acute and chronic infection stages were examined by µPET/MRI. A follow-up group of animals acted as controls (animals bearing S. aureus-derived infection and sterile inflammation) to assess tracer selectivity. [68Ga]Ga-DOTA-puromycin-µPET/MRI images revealed the acute, widespread infection within the right upper shoulder and armpit. Also, [68Ga]Ga-DOTA-puromycin signal sensitivity measured after a 12-week period was lower than that of [18F]FDG-PET in the same animals. A suitable correlation between normalised uptake values (NUV) and gold standard histopathological analysis confirms accurate tracer accumulation in viable bacteria. The radiopharmaceutical showed infection selectivity over inflammation but accumulated in both M. Bovis and S. Aureus, lacking pathogen specificity. Overall, [68Ga]Ga-DOTA-puromycin exhibits potential as a tool for non-invasive protein synthesis visualization, albeit without pathogen selectivity.

Performance of [18F]FDG PET/CT in Diagnosing Cyst Infections in Patients with Autosomal Dominant Polycystic Kidney Disease: A Systematic Review and a Bivariate Meta-Analysis

BACKGROUND

Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography ([18F]FDG PET/CT) has been suggested as a useful imaging method for diagnosing cyst infections in patients with autosomal dominant polycystic kidney disease (ADPKD). The aim of this article is to provide evidence-based data in this setting.

METHODS

A systematic literature review (exploring several bibliographic databases) and a bivariate meta-analysis were carried out to calculate the pooled diagnostic performance of [18F]FDG PET/CT in diagnosing probable cyst infection in ADPKD.

RESULTS

Ten studies (282 PET/CT scans and 249 patients) were included in the analysis. The pooled sensitivity and specificity of [18F]FDG PET/CT in this setting were 84.6% (95% confidence interval: 75.4-90.7) and 94.9% (95% confidence interval: 72.6-99.2), respectively, without statistical heterogeneity or significant publication bias. [18F]FDG PET/CT significantly changed patient management in more than half of ADPKD patients with suspected cyst infection.

CONCLUSIONS

[18F]FDG PET/CT has high performance in diagnosing probable cyst infections in ADPKD patients with an impact on management in the majority of patients. Although more studies are warranted, the provided evidence-based data are an important step towards the integration of [18F]FDG PET/CT in clinical and diagnostic guidelines on probable cyst infection in ADPKD patients.

EANM consensus document on the use of [18F]FDG PET/CT in fever and inflammation of unknown origin

PURPOSE

Patients with fever and inflammation of unknown origin (FUO/IUO) are clinically challenging due to variable clinical presentations with nonspecific symptoms and many differential diagnoses. Positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) is increasingly used in FUO and IUO, but the optimal diagnostic strategy remains controversial. This consensus document aims to assist clinicians and nuclear medicine specialists in the appropriate use of [18F]FDG-PET/CT in FUO and IUO based on current evidence.

METHODS

A working group created by the EANM infection and inflammation committee performed a systematic literature search based on PICOs with "patients with FUO/IUO" as population, "[18F]FDG-PET/CT" as intervention, and several outcomes including pre-scan characteristics, scan protocol, diagnostic yield, impact on management, prognosis, and cost-effectiveness.

RESULTS

We included 68 articles published from 2001 to 2023: 9 systematic reviews, 49 original papers on general adult populations, and 10 original papers on specific populations. All papers were analysed and included in the evidence-based recommendations.

CONCLUSION

FUO and IUO remains a clinical challenge and [18F]FDG PET/CT has a definite role in the diagnostic pathway with an overall diagnostic yield or helpfulness in 50-60% of patients. A positive scan is often contributory by directly guiding treatment or subsequent diagnostic procedure. However, a negative scan may be equally important by excluding focal disease and predicting a favorable prognosis. Similar results are obtained in specific populations such as ICU-patients, children and HIV-patients.

The Role of the 18F-FDG PET/CT in the Management of Patients Suspected of Cardiac Implantable Electronic Devices' Infection

Background: Infection of Cardiac Implantable Electronic Devices (CIEDI) is a real public health problem. The main aim of this study was to determine the diagnostic performance of 18F-FDG PET/CT in the diagnosis of CIEDI. Methods: A total of 48 patients, who performed 18F-FDG PET/CT for the clinical suspicion of CIEDI were retrospectively analyzed; all patients were provided with a model with procedural recommendations before the exam. Sensitivity (Se), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV) and diagnostic accuracy (DA) of 18F-FDG PET/CT were calculated; the reproducibility of qualitative analysis was assessed with Cohen's κ test. The semi-quantitative parameters (SUVmax, SQR and TBR) were evaluated in CIEDI+ and CIEDI- patients using the Student' t-test; ROC curves were elaborated to detect cut-off values. The trend of image quality with regards to procedural recommendation adherence was evaluated. Results: Se, Sp, PPV, NPV and DA were respectively 96.2%, 81.8%, 86.2%, 94.7% and 89.6%. The reproducibility of qualitative analysis was excellent (K = 0.89). Semiquantitative parameters resulted statistically different in CIEDI+ and CIEDI- patients. Cut-off values were SUVmax = 2.625, SQR = 3.766 and TBR = 1.29. Trend curves showed increasing image quality due to adherence to procedural recommendations. Conclusions:18F-FDG-PET/CT is a valid tool in the management of patients suspected of CIEDI and adherence to procedural recommendations improves its image quality.

Challenging Axillary Lymph Nodes on PET/CT in Cancer Patients throughout COVID-19 Vaccination Era

BACKGROUND

The unexpected detection of axillary lymphadenopathy (AxL) in cancer patients (pts) represents a real concern during the COVID-19 vaccination era. Benign reactions may take place after vaccine inoculation, which can mislead image interpretation in patients undergoing F-18-FDG, F-18-Choline, and Ga-68-DOTATOC PET/CT. They may also mimic loco-regional metastases or disease. We assessed PET/CT findings after COVID-19 first dose vaccination in cancer patients and the impact on their disease course management.

METHODS

We evaluated 333 patients undergoing PET/CT (257 F-18-FDG, 54 F-18-Choline, and 23 Ga-68 DOTATOC) scans after the first vaccination with mRNA vaccine (Pfizer-BioNTech) (study group; SG). The uptake index (SUVmax) of suspected AxL was defined as significant when the ratio was > 1.5 as compared to the contralateral lymph nodes. Besides, co-registered CT (Co-CT) features of target lymph nodes were evaluated. Nodes with aggregate imaging positivity were further investigated.

RESULTS

Overall, the prevalence of apparently positive lymph nodes on PET scans was 17.1% during the vaccination period. 107 pts of the same setting, who had undergone PET/CT before the COVID-19 pandemic, represented the control group (CG). Only 3 patients of CG showed reactive lymph nodes with a prevalence of 2.8% (p < 0.001 as compared to the vaccination period). 84.2% of SG patients exhibited benign characteristics on co-CT images and only 9 pts needed thorough appraisal.

CONCLUSION

The correct interpretation of images is crucial to avoid unnecessary treatments and invasive procedures in vaccinated cancer pts. A detailed anamnestic interview and the analysis of lymph nodes' CT characteristics, after performing PET/CT, may help to clear any misleading diagnosis.

The systemic impact of different COVID-19 vaccines in 2-[18F] FDG-PET/CT

Austria started its COVID-19-vaccination program in December 2020 with three different vaccines. As the vaccination program continues, we encountered increased 2-[18F] FDG-activity not only in axillary lymph nodes ipsilateral to the injection site but also in other organs. The aim of this retrospective study is to present results of the metabolic activity of ipsilateral axillary lymph nodes, liver, blood pool, spleen, and bone marrow after three different vaccines. To our knowledge, this is the first study to examine systemic response changes in relation to time after COVID-19 vaccination using three different vaccines. The collected data of 220 eligible vaccinated patients (127 with BioNTech/Pfizer BNT162b2, 61 with Moderna, and 32 with AstraZeneca) examined with 2-[18F] FDG-PET/CT were enrolled. The PET/CT examinations were evaluated from day 1 to day 135 (SD: 23.2, median: 26) after different vaccinations. Seventy-one out of these 220 patients underwent a pre-vaccination 2-[18F] FDG -PET/CT. SUVmax of axillary node(s), and blood pool, liver, spleen, and bone marrow as reference organs were calculated. The ratio of SUVmax activity of axillary lymph node to reference organs was also compared in all patients. The tracer activity dynamics were investigated in three different vaccines. After BioNTech/Pfizer vaccination 2-[18F] FDG activity in axillary lymph nodes shows a steady decrease in all patients. Ten days after vaccination the 2-[18F] FDG uptake was at its highest activity. Seventy days after vaccination, tracer activity is not different from the background activity of 2-[18F] FDG in the axillary region. This result also applies to other two vaccines; however, in the 4th week after Moderna vaccination SUVmax in lymph nodes showed the highest peak of tracer activity. With AstraZeneca the highest activity was at the earlier days. There was no significant statistical difference of SUVmax of lymph nodes or its ratios to other reference organs between three groups of vaccines. SUVmax in lymph nodes was statistically significant lower than SUVmax in the liver, spleen, and bone marrow with p-values of < 0.001, 0.044, and 0.001, respectively. In the group of 71 patients with a pre-vaccination PET/CT examination, the median SUVmax of lymph nodes increased significantly after vaccination from 0.82 (IQR 0.59-1.38) to 1.80 (IQR 1.07-3.89)(p < 0.001). In contrast median tracer activity in the liver decreased from 3.37 (IQR 2.83-3.91) to 3.11 (2.56-3.70) (p = 0.032). There was no significant change of tracer activity after vaccination in other reference regions (mediastinum, spleen, and bone marrow). In this group of 71 patients, there was also no significant difference in tracer activity in different types of vaccines. Local site and ipsilateral axillary lymph node activity in 2-[18F] FDG PET/CT after COVID19-vaccination is suggested in many studies. The main challenge is recognizing the changes in lymph nodes during time after vaccination to minimize false interpretation, foremost in patients with oncological diagnoses. Moreover, different vaccines cause different system metabolic changes. The knowledge of vaccine type, the time interval between vaccination and PET/CT scan is essential, especially in therapy evaluation.

The role of 18F-fluorodeoxyglucose PET/computed tomography in the diagnosis and monitoring of large vessel vasculitides - a review article

In the last two decades, advancements in positron emission tomography (PET) technology have increased the diagnostic accuracy of patients with large-vessel vasculitis (LVV). Numerous systematic reviews and meta-analyses have been conducted, and patients suspected of having LVV can be diagnosed earlier with 18F-FDG PET. Two subtypes, giant cell arteritis (GCA) and Takayasu arteritis (TA), will progress when their response to corticosteroids and enhanced immunosuppression is inadequate. In the majority of patients, disease activity cannot be monitored solely through laboratory procedures; consequently, glucose metabolism may be a source of potential biomarkers. In this article, we discuss the current state of 18F-FDG PET/CT imaging standards.

Emerging Technologies in Diagnosing Periprosthetic Joint Infections

Periprosthetic joint infection (PJI) is a well-known serious complication following joint replacement surgeries and is responsible for high failure rates of implanted devices. Any delay in the diagnosis can compromise treatment success, putting a huge burden on the patients' wellness and healthcare systems. Diagnosing PJIs is quite complex as there is still no gold standard test to reach the definitive diagnosis in a timely manner. A number of laboratory tests and radiological imaging inventions have evolved in the past few years, requiring consistent updates of the available guidelines to keep up with the latest advances in the field. This article highlights the recent advances in diagnosing PJIs and discusses their validity for use in clinical practice.

Diagnostic accuracy of fluorine-18 fluorodeoxyglucose positron emission tomography for suspected primary and postoperative pyogenic spondylitis

OBJECTIVE

Fluorine-18 fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) and PET/CT have been suggested for confirming or excluding musculoskeletal infection but the diagnostic value of this tool for pyogenic spondylitis remains to be confirmed. This meta-analysis was performed to verify the accuracy of ¹⁸F-FDG PET and PET/CT in diagnosing suspected pyogenic spondylitis by performing a systematic review and meta-analysis.

METHODS

We conducted a comprehensive literature search of PubMed, Embase and Cochrane Library to retrieve diagnostic accuracy studies in which suspected pyogenic spondylitis was assessed with ¹⁸F-FDG PET or PET/CT. The pooled sensitivity, specificity, likelihood ratios, diagnostic odds ratio (DOR), summarized receiver operating characteristic curve (sROC) and the area under the sROC (AUC) were calculated by using Stata software.

RESULTS

A total of 18 eligible studies (660 patients) with suspected pyogenic spondylitis were included in the quantitative analysis. ¹⁸F-FDG PET and PET/CT illustrated relatively high sensitivity (0.91, 95% CI: 0.84-0.95) and specificity (0.90, 95% CI: 0.79-0.95) for the diagnosis of pyogenic spondylitis. The pooled DOR and AUC were 86.00 (95% CI, 31.00-240.00) and 0.96 (95% CI, 0.94-0.97), respectively. For diagnosing pyogenic spondylitis without previous spine surgery, the pooled sensitivity, specificity, DOR and AUC were 0.93 (95% CI, 0.85-0.97), 0.91 (95% CI, 0.77-0.97), 136 (95% CI, 35-530) and 0.97 (95% CI, 0.95-0.98), respectively. For diagnosing postoperative pyogenic spondylitis, the pooled sensitivity, specificity, DOR and AUC were 0.85 (95% CI, 0.71 to 0.93), 0.87 (95% CI, 0.66 to 0.96), 38 (95% CI, 9 to 167) and 0.92 (95% CI, 0.89 to 0.94), respectively.

CONCLUSION

¹⁸F-FDG PET and PET/CT presented satisfactory accuracy for diagnosing pyogenic spondylitis. The diagnostic effect of this nuclear imaging method for pyogenic spondylitis without previous spine surgery seems to be better than that for the postoperative ones. However, whether ¹⁸F-FDG PET and PET/CT could become a routine in patients with suspected pyogenic spondylitis remains to be confirmed.

LEVEL OF EVIDENCE

Level I evidence, a summary of meta-analysis.

Radiometal chelators for infection diagnostics

Infection of native tissues or implanted devices is common, but clinical diagnosis is frequently difficult and currently available noninvasive tests perform poorly. Immunocompromised individuals (for example transplant recipients, or those with cancer) are at increased risk. No imaging test in clinical use can specifically identify infection, or accurately differentiate bacterial from fungal infections. Commonly used [18F]fluorodeoxyglucose (18FDG) positron emission computed tomography (PET/CT) is sensitive for infection, but limited by poor specificity because increased glucose uptake may also indicate inflammation or malignancy. Furthermore, this tracer provides no indication of the type of infective agent (bacterial, fungal, or parasitic). Imaging tools that directly and specifically target microbial pathogens are highly desirable to improve noninvasive infection diagnosis and localization. A growing field of research is exploring the utility of radiometals and their chelators (siderophores), which are small molecules that bind radiometals and form a stable complex allowing sequestration by microbes. This radiometal-chelator complex can be directed to a specific microbial target in vivo, facilitating anatomical localization by PET or single photon emission computed tomography. Additionally, bifunctional chelators can further conjugate therapeutic molecules (e.g., peptides, antibiotics, antibodies) while still bound to desired radiometals, combining specific imaging with highly targeted antimicrobial therapy. These novel therapeutics may prove a useful complement to the armamentarium in the global fight against antimicrobial resistance. This review will highlight current state of infection imaging diagnostics and their limitations, strategies to develop infection-specific diagnostics, recent advances in radiometal-based chelators for microbial infection imaging, challenges, and future directions to improve targeted diagnostics and/or therapeutics.

Case Report: Culture-negative Prosthetic Valve Endocarditis

BACKGROUND

Prosthetic valve endocarditis can be difficult to diagnose and cause significant morbidity and mortality, especially when no culture data are available to guide therapy. Transthoracic and transesophageal echocardiograms, the studies of choice for initial endocarditis evaluation, can be less reliable due to artifact and post-surgical changes. Some less common forms of endocarditis may be difficult to culture and, due to their fastidious nature, may delay the identification of causative organisms. Given the lack of directed antimicrobial treatment, culturenegative prosthetic valve endocarditis is specifically difficult. A wide differential diagnosis is critical to make a timely diagnosis and initiate treatment.

CASE PRESENTATION

We present a case of a patient presenting with dyspnea which was found to have culture-negative endocarditis requiring mitral and aortic valve replacement that ultimately was complicated with culture-negative prosthetic valve endocarditis. Identifying a culprit organism made appropriate and timely antimicrobial treatment difficult, ultimately resulting in the patient dying from endocarditis complications.

CONCLUSION

A high index of suspicion is needed when managing infective endocarditis, especially when prosthetic valves are involved. Diagnostic accuracy of cultures and echocardiography may be reduced when dealing with prosthetic valve endocarditis; thus, alternative methods of diagnosis may be required to make a timely diagnosis of causative organisms.

A role of FDG PET/CT for Response Assessment in Large Vessel Disease?

Currently, a large amount of evidence-based data clearly demonstrates the usefulness of [¹⁸F]FDG PET/CT in the diagnosis of several infectious and inflammatory diseases, including those related to the large vessels. The aim of this article is to clarify whether, beyond initial diagnosis, [¹⁸F]FDG PET/CT may have a role in treatment response assessment in inflammatory or infectious diseases of the large vessels, including large vessel vasculitis, vascular graft infection, retroperitoneal fibrosis/chronic periaortitis and infective native aortic aneurysms. Rapidly accumulating data suggest that [¹⁸F]FDG PET/CT could be a valuable imaging method for therapy monitoring in some infectious and inflammatory diseases of large vessels. The available data, albeit preliminary, indicate that [¹⁸F]FDG PET/CT could even play a pivotal role in the management of these diseases, leading to better drug dosage, confirmation of the usefulness of the treatment, and early modification of the therapeutic strategy. However, to date, the role of [¹⁸F]FDG PET/CT for treatment assessment in large vessel diseases, in particular large vessel vasculitis, is not clearly defined and well-designed prospective studies are needed to confirm its possible role in treatment monitoring and treatment guidance.

Early and Late Outcomes of Endovascular Aneurysm Repair for Infected Abdominal Aortic and/or Iliac Aneurysms

BACKGROUND

Infected abdominal aortic and/or iliac aneurysm (AAIA) is a rare condition with a high mortality rate when treated with open surgery. In the past decade, the condition has increasingly been treated with endovascular aneurysm repair (EVAR). However, early and late outcomes, including the continued need for antibiotic treatments and predictors of persistent infection, are poorly understood.

METHODS

We evaluated the outcomes of patients who underwent EVAR for infected AAIA from January 2010 to October 2017. We collected data including patient age, gender, clinical presentation, aneurysm location, culture results, intraoperative details, postoperative complications, 30-day mortality, in-hospital mortality, persistent infection, reintervention, and survival.

RESULTS

Among 792 patients diagnosed with AAIA, 64 were diagnosed with primary infected aneurysm, underwent EVAR, and were included in this study (81.3% male; median age, 72 years; range, 18-94 years). The most commonly isolated organisms were Salmonella species (34%), followed by Streptococcus (21%), and Staphylococcus species (21%). Aneurysms were intact in 48 patients (75%) and were ruptured in 16 (25%). The perioperative mortality was 4.7% (3 patients) of whom one was diagnosed with ruptured infected AAIA. Six (9.4%) patients died during hospitalization, 5 of severe sepsis with multiorgan failure and one of myocardial infarction. Among the 58 surviving patients, 34 (58.6%) had persistent infection, of whom 13 (22.4%) required early and late reintervention, including 2 with endograft infection, 8 with primary and secondary aortoenteric fistula, 2 with recurrent new aortic infection, and one with graft limb occlusion. The remaining 24 patients were able to discontinue antibiotics and had no recurrence or need for reintervention. Overall survival rates at 1, 3, and 5 years in the antibiotic-discontinuation group were 91.7%, 87.5%, and 68.0%, respectively, and 82.4%, 52.6%, and 32.9%, respectively, in the persistent-infection group (P = 0.009). In multivariable analysis, primary aortoenteric fistula (Adjusted OR [aOR], 20.469; 95% confidence interval (CI), 1.265-331.320; P = 0.034) and preoperative serum albumin level <3 g/dL (aOR, 7.399; 95% CI, 1.176-46.558; P = 0.033) were preoperative parameter that predicted persistent infection. A C-reactive protein level more than 5 mg/L (aOR, 34.378; 95% CI, 4.888-241.788; P < 0.001) was observed in patients with persistent infection.

CONCLUSIONS

EVAR is a feasible treatment with acceptable perioperative mortality for infected AAIA. Patients able to discontinue antibiotics have better survival and lower reintervention rates than those with persistent infection. A preoperative albumin level below 3 g/dL and primary aortoenteric fistula predicted persistent infection in this population.

Sterile endogenous panophthalmitis with uncontrolled diabetes

A female patient with type 2 diabetes in her 50s presented to casualty with a 1-day history of red, painful right eye. Visual acuity (VA) bilaterally was 6/12, but a right anterior uveitis was noted, with hazy fundal view. She was discharged on topical steroid and mydriatic drops with a 2-day follow-up. VA remained unchanged, but she developed right proptosis, restricted eye movements, lid swelling, relative afferent pupillary defect and an intraocular pressure (IOP) of 39 mm Hg. She was admitted and treated with intravenous and intravitreal antibiotics, intravenous antifungals and IOP-lowering drugs. Blood tests showed raised inflammatory markers and an HbA1c of 127 mmol/mol. Over her admission, right eye vision deteriorated to no light perception. A B-scan ultrasound revealed panophthalmitis and a retinal abscess. All investigations looking for a source were negative. Inflammatory markers settled, but despite aggressive treatment, the panophthalmitis did not improve. She was discharged with a follow-up to consider enucleation.

Positron Emission Tomography Probes for Imaging Cytotoxic Immune Cells

Non-invasive positron emission tomography (PET) imaging of immune cells is a powerful approach for monitoring the dynamics of immune cells in response to immunotherapy. Despite the clinical success of many immunotherapeutic agents, their clinical efficacy is limited to a subgroup of patients. Conventional imaging, as well as analysis of tissue biopsies and blood samples do not reflect the complex interaction between tumour and immune cells. Consequently, PET probes are being developed to capture the dynamics of such interactions, which may improve patient stratification and treatment evaluation. The clinical efficacy of cancer immunotherapy relies on both the infiltration and function of cytotoxic immune cells at the tumour site. Thus, various immune biomarkers have been investigated as potential targets for PET imaging of immune response. Herein, we provide an overview of the most recent developments in PET imaging of immune response, including the radiosynthesis approaches employed in their development.

PET-CT imaging of pulmonary inflammation using [68Ga]Ga-DOTA-TATE

PURPOSE

In the characterization of severe lung diseases, early detection of specific inflammatory cells could help to monitor patients' response to therapy and increase chances of survival. Macrophages contribute to regulating the resolution and termination of inflammation and have increasingly been of interest for targeted therapies. [⁶⁸Ga]Ga-DOTA-TATE is an established clinical radiopharmaceutical targeting somatostatin receptor subtype 2 (SSTR 2). Since activated macrophages (M1) overexpress SSTR 2, the aim of this study was to investigate the applicability of [⁶⁸Ga]Ga-DOTA-TATE for positron emission tomography (PET) imaging of M1 macrophages in pulmonary inflammation.

METHODS

Inflammation in the pig lungs was induced by warm saline lavage followed by injurious ventilation in farm pigs (n = 7). Healthy pigs (n = 3) were used as control. A 60-min dynamic PET scan over the lungs was performed after [⁶⁸Ga]Ga-DOTA-TATE injection and [¹⁸F]FDG scan was executed afterward for comparison. The uptake of both tracers was assessed as mean standardized uptake values (SUV_mean) 30-60-min post-injection. The PET scans were followed by computed tomography (CT) scans, and the Hounsfield units (HU) were quantified of the coronal segments. Basal and apical segments of the lungs were harvested for histology staining. A rat lung inflammation model was also studied for tracer specificity using lipopolysaccharides (LPS) by oropharyngeal aspiration. Organ biodistribution, ex vivo autoradiography (ARG) and histology samples were conducted on LPS treated, octreotide induced blocking and control healthy rats.

RESULTS

The accumulation of [⁶⁸Ga]Ga-DOTA-TATE on pig lavage model was prominent in the more severely injured dorsal segments of the lungs (SUVmean = 0.91 ± 0.56), compared with control animals (SUVmean = 0.27 ± 0.16, p < 0.05). The tracer uptake corresponded to the damaged areas assessed by CT and histology and were in line with HU quantification. The [⁶⁸Ga]Ga-DOTA-TATE uptake in LPS treated rat lungs could be blocked and was significantly higher compared with control group.

CONCLUSION

The feasibility of the noninvasive assessment of tissue macrophages using [⁶⁸Ga]Ga-DOTA-TATE/PET was demonstrated in both porcine and rat lung inflammation models. [⁶⁸Ga]Ga-DOTA-TATE has a great potential to be used to study the role and presence of macrophages in humans in fight against severe lung diseases.

Maladaptive trained immunity and clonal hematopoiesis as potential mechanistic links between periodontitis and inflammatory comorbidities

Periodontitis is bidirectionally associated with systemic inflammatory disorders. The prevalence and severity of this oral disease and linked comorbidities increases with aging. Here, we review two newly emerged concepts, trained innate immunity (TII) and clonal hematopoiesis of indeterminate potential (CHIP), which together support a potential hypothesis on how periodontitis affects and is affected by comorbidities and why the susceptibility to periodontitis and comorbidities increases with aging. Given that chronic diseases are largely triggered by the action of inflammatory immune cells, modulation of their bone marrow precursors, the hematopoietic stem and progenitor cells (HSPCs), may affect multiple disorders that emerge as comorbidities. Such alterations in HSPCs can be mediated by TII and/or CHIP, two non-mutually exclusive processes sharing a bias for enhanced myelopoiesis and production of innate immune cells with heightened proinflammatory potential. TII is a state of elevated immune responsiveness based on innate immune (epigenetic) memory. Systemic inflammation can initiate TII in the bone marrow via sustained rewiring of HSPCs, which thereby display a skewing toward the myeloid lineage, resulting in generation of hyper-reactive or "trained" myeloid cells. CHIP arises from aging-related somatic mutations in HSPCs, which confer a survival and proliferation advantage to the mutant HSPCs and give rise to an outsized fraction of hyper-inflammatory mutant myeloid cells in the circulation and tissues. This review discusses emerging evidence that supports the notion that TII and CHIP may underlie a causal and age-related association between periodontitis and comorbidities. A holistic mechanistic understanding of the periodontitis-systemic disease connection may offer novel diagnostic and therapeutic targets for treating inflammatory comorbidities.

FDG-PET/CT of COVID-19 and Other Lung Infections

While not conventionally used as the first-line modality, [¹⁸F]-2-fluoro-2-deoxy-D-glucose (FDG) - positron emission tomography/computed tomography (PET/CT) can identify infection and inflammation both earlier and with higher sensitivity than anatomic imaging modalities [including chest X-ray (CXR), computed tomography (CT), and magnetic resonance imaging (MRI)]. The extent of inflammation and, conversely, recovery within the lungs, can be roughly quantified on FDG-PET/CT using maximum standardized uptake value (SUVmax) values. The Coronavirus disease 2019 (COVID-19) pandemic has highlighted the value of FDG-PET/CT in diagnosis, elucidation of acute pulmonary and extrapulmonary manifestations, and long-term follow up. Similarly, many other pulmonary infections such as previously documented coronaviruses, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, cryptococcosis, histoplasmosis, mucormycosis, and typical/atypical mycobacterial infections have all been identified and characterized using FDG-PET/CT imaging. The goal of this review is to summarize the actual and potential benefits of FDG-PET/CT in the imaging of COVID-19 and other lung infections. Further research is necessary to determine the best indications and clinical applications of FDG-PET/CT, improve its specificity, and ultimately ascertain how this modality can best be utilized in the diagnostic work up of infectious pathologies.

Diagnostic performance of quantitative and qualitative parameters for the diagnosis of aortic graft infection using [18F]-FDG PET/CT

PURPOSE

The aim of this study was the evaluation of quantitative and qualitative parameters for the diagnosis of aortic graft infection (AGI) using [18F]-FDG PET/CT.

METHODS

PET/CT was performed in 50 patients with clinically suspected AGI. 12 oncological patients with aortic repair but without suspicion of AGI were included in the analysis to serve as control cohort. The [18F]-FDG uptake pattern around the graft was assessed using (a) a five-point visual grading scale (VGS), (b) SUVmax and (c) different graft-to-background ratios (GBRs). The diagnostic performance of VGS, SUVmax and GBRs was assessed and compared by ROC analysis.

RESULTS

28 infected and 34 uninfected grafts were identified by standard of reference. SUVmax and VGS were the most powerful predictors for the diagnosis of AGI according to the area under the curve (AUC 0.988 and 0.983, respectively) without a significant difference compared to GBRs. SUVmax and VGS showed congruent and accurate findings in 54 patients (i.e. either both positive or negative), yielding sensitivity and specificity (100%) in this subgroup of patients.

CONCLUSION

Quantitative analysis by SUVmax and qualitative analysis by VGS are highly effective in the diagnosis of AGI and should be tested as an outcome measure in prospective trials.

Spine Infections: the role of Fluorodeoxyglucose Positron Emission Tomography (FDG PET) in the context of the actual diagnosis guideline

Spondylodiscitis is an infectious process that requires numerous health care professionals to be clearly diagnosed and eventually successfully treated. It implies a variety of microbiological agents and conditions; during the diagnostic workup, it is difficult to correctly identify them, and the clinician has to rapidly choose the correct treatment to avoid permanent injuries to the patient. In this context, we conducted a review to better understand the most suitable use of Positron Emission Tomography with 18-Fluoro-deossi-glucose (FDG PET) in a patient suspected of spondylodiscitis, based on current guidelines and literature.. We wanted to review the role of FDG PET in the spondylodiscitis diagnosis and follow up in the context of the current guidelines.

Medical Imaging in the Diagnosis of Schistosomiasis: A Review

Schistosomiasis is one of the most important parasitic diseases and it is endemic in tropical and subtropical areas. Clinical and laboratory data are fundamental for the diagnosis of schistosomiasis, but diagnostic imaging techniques such as x-rays, ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography/computed tomography (PET/CT) may be helpful in the evaluation of disease severity and complications. In this context, the aim of this review is to explore the actual role of diagnostic imaging in the diagnosis of schistosomiasis, underlining advantages and drawbacks providing information about the utilization of diagnostic imaging techniques in this context. Furthermore, we aim to provide a useful guide regarding imaging features of schistosomiasis for radiology and nuclear medicine physicians of non-endemic countries: in fact, in the last years non-endemic countries have experienced important flows of migrants from endemic areas, therefore it is not uncommon to face cases of this disease in daily practice.

Prevalence and Significance of Hypermetabolic Lymph Nodes Detected by 2-[18F]FDG PET/CT after COVID-19 Vaccination: A Systematic Review and a Meta-Analysis

Recently, several articles reported incidental findings at 2-[¹⁸F]FDG PET/CT in patients who have received COVID-19 vaccinations, including hypermetabolic axillary lymph nodes (HALNs) ipsilateral to the COVID-19 vaccine injection site which may cause diagnostic dilemmas. The aim of our work was to calculate the prevalence of this finding. A comprehensive computer literature search of PubMed/MEDLINE, Embase, and Cochrane library databases was performed to identify recently published articles that investigated the prevalence of HALNs detected by 2-[¹⁸F]FDG PET/CT after COVID-19 vaccination. Pooled prevalence of this finding was calculated through a meta-analytic approach. Nine recently published articles including 2354 patients undergoing 2-[¹⁸F]FDG PET/CT after recent COVID-19 vaccination have been included in the systematic review. Overall, HALNs ipsilateral to the vaccine injection site were frequent findings mainly due to vaccine-related immune response in most of the cases. The pooled prevalence of HALNs after COVID-19 vaccination was 37% (95% confidence interval: 27–47%) but with significant heterogeneity among the included studies. Physicians must be aware and recognize the significant frequency of HALNs at 2-[¹⁸F]FDG PET/CT related to immune response to vaccine injection. Larger studies are needed to confirm the findings of this systematic review and meta-analysis.

Aortic Fistulas: Pathophysiologic Features, Imaging Findings, and Diagnostic Pitfalls

Fistulas between the aorta and surrounding organs are extremely rare but can be fatal if they are not identified and treated promptly. Most of these fistulas are associated with a history of trauma or vascular intervention. However, spontaneous aortic fistulas (AoFs) can develop in patients with weakened vasculature, which can be due to advanced atherosclerotic disease, collagen-vascular disease, vasculitides, and/or hematogenous infections. The clinical features of AoFs are often nonspecific, with patients presenting with bleeding manifestations, back or abdominal pain, fever, and shock. Confirmation with invasive endoscopy is often impractical in the acute setting. Imaging plays an important role in the management of AoFs, and multiphasic multidetector CT angiography is the initial imaging examination of choice. Obvious signs of AoF include intravenous contrast material extravasation into the fistulizing hollow organ, tract visualization, and aortic graft migration into the adjacent structure. However, nonspecific indirect signs such as loss of fat planes and ectopic foci of gas are seen more commonly. These indirect signs can be confused with other entities such as infection and postoperative changes. Management may involve complex and staged surgical procedures, depending on the patient's clinical status, site of the fistula, presence of infection, and anticipated tissue friability. As endovascular interventions become more common, radiologists will need to have a high index of suspicion for this entity in patients who have a history of aneurysms, vascular repair, or trauma and present with bleeding. Online supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article. ^©RSNA, 2021.

Correlation Between 18F-FDG Uptake and Immune Cell Infiltration in Metastatic Brain Lesions

Background

The purpose of this study was to investigate the correlation between ¹⁸F-fluorodeoxyglucose (FDG) uptake and infiltrating immune cells in metastatic brain lesions.

Methods

This retrospective study included 34 patients with metastatic brain lesions who underwent brain ¹⁸F-FDG positron emission tomography (PET)/computed tomography (CT) followed by surgery. ¹⁸F-FDG uptake ratio was calculated by dividing the standardized uptake value (SUV) of the metastatic brain lesion by the contralateral normal white matter uptake value. We investigated the clinicopathological characteristics of the patients and analyzed the correlation between ¹⁸F-FDG uptake and infiltration of various immune cells. In addition, we evaluated immune-expression levels of glucose transporter 1 (GLUT1), hexokinase 2 (HK2), and Ki-67 in metastatic brain lesions.

Results

The degree of ¹⁸F-FDG uptake of metastatic brain lesions was not significantly correlated with clinical parameters. There was no significant relationship between the ¹⁸F-FDG uptake and degree of immune cell infiltration in brain metastasis. Furthermore, other markers, such as GLUT1, HK2, and Ki-67, were not correlated with degree of ¹⁸F-FDG uptake. In metastatic brain lesions that originated from breast cancer, a higher degree of ¹⁸F-FDG uptake was observed in those with high expression of CD68.

Conclusions

In metastatic brain lesions, the degree of ¹⁸F-FDG uptake was not significantly associated with infiltration of immune cells. The ¹⁸F-FDG uptake of metastatic brain lesions from breast cancer, however, might be associated with macrophage activity.

Highlighting COVID-19: What the imaging exams show about the disease

Coronavirus disease 2019 (COVID-19), a global emergency, is caused by severe acute respiratory syndrome coronavirus 2. The gold standard for its diagnosis is the reverse transcription polymerase chain reaction, but considering the high number of infected people, the low availability of this diagnostic tool in some contexts, and the limitations of the test, other tools that aid in the identification of the disease are necessary. In this scenario, imaging exams such as chest X-ray (CXR) and computed tomography (CT) have played important roles. CXR is useful for assessing disease progression because it allows the detection of extensive consolidations, besides being a fast and cheap method. On the other hand, CT is more sensitive for detecting lung changes in the early stages of the disease and is also useful for assessing disease progression. Of note, ground-glass opacities are the main COVID-19-related CT findings. Positron emission tomography combined with CT can be used to evaluate chronic and substantial damage to the lungs and other organs; however, it is an expensive test. Lung ultrasound (LUS) has been shown to be a promising technique in that context as well, being useful in the screening and monitoring of patients, disease classification, and management related to mechanical ventilation. Moreover, LUS is an inexpensive alternative available at the bedside. Finally, magnetic resonance imaging, although not usually requested, allows the detection of pulmonary, cardiovascular, and neurological abnormalities associated with COVID-19. Furthermore, it is important to consider the challenges faced in the radiology field in the adoption of control measures to prevent infection and in the follow-up of post-COVID-19 patients.

Radionuclide Imaging of Fungal Infections and Correlation with the Host Defense Response

The human response to invading fungi includes a series of events that detect, kill, or clear the fungi. If the metabolic host response is unable to eliminate the fungi, an infection ensues. Some of the host response’s metabolic events to fungi can be imaged with molecules labelled with radionuclides. Several important clinical applications have been found with radiolabelled biomolecules of inflammation. ¹⁸F-fluorodeoxyglucose is the tracer that has been most widely investigated in the host defence of fungi. This tracer has added value in the early detection of infection, in staging and visualising dissemination of infection, and in monitoring antifungal treatment. Radiolabelled antimicrobial peptides showed promising results, but large prospective studies in fungal infection are lacking. Other tracers have also been used in imaging events of the host response, such as the migration of white blood cells at sites of infection, nutritional immunity in iron metabolism, and radiolabelled monoclonal antibodies. Many tracers are still at the preclinical stage. Some tracers require further studies before translation into clinical use. The application of therapeutic radionuclides offers a very promising clinical application of these tracers in managing drug-resistant fungi.

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.

FDG-PET/CT in intensive care patients with bloodstream infection

Background

2-Deoxy-2-[18F]fluoro-D-glucose (FDG) positron emission tomography (PET)/computed tomography (CT) is an advanced imaging technique that can be used to examine the whole body for an infection focus in a single examination in patients with bloodstream infection (BSI) of unknown origin. However, literature on the use of this technique in intensive care patients is scarce. The purpose of this study was to evaluate the diagnostic yield of FDG-PET/CT in intensive care patients with BSI.

Methods

In this retrospective cohort study, all intensive care patients from our Dutch university medical center who had culture-proven BSI between 2010 and 2020 and underwent FDG-PET/CT to find the focus of infection were included. Diagnostic performance was calculated and logistic regression analysis was performed to evaluate the association between FDG-PET/CT outcome and C-reactive protein level (CRP), leukocyte count, duration of antibiotic treatment, duration of ICU stay, quality of FDG-PET/CT, and dependency on mechanical ventilation. In addition, the impact of FDG-PET/CT on clinical treatment was evaluated.

Results

30 intensive care patients with BSI were included. In 21 patients, an infection focus was found on FDG-PET/CT which led to changes in clinical management in 14 patients. FDG-PET/CT achieved a sensitivity of 90.9% and specificity of 87.5% for identifying the focus of infection. Poor quality of the FDG-PET images significantly decreased the likelihood of finding an infection focus as compared to reasonable or good image quality (OR 0.16, P = 0.034). No other variables were significantly associated with FDG-PET/CT outcome. No adverse events during the FDG-PET/CT procedure were reported.

Conclusion

FDG-PET/CT has a high diagnostic yield for detecting the infection focus in patients with BSI admitted to intensive care. Poor PET image quality was significantly associated with a decreased likelihood of finding the infection focus in patients with BSI. This could be improved by adequate dietary preparation and cessation of intravenous glucose and glucose-regulating drugs. Recent advances in PET/CT technology enable higher image quality with shorter imaging time and may contribute to routinely performing FDG-PET/CT in intensive care patients with BSI of unknown origin.

Comparison of 18 F-FDG PET/CT and 68 Ga-DOTATATE PET/CT in the Targeted Imaging of Culprit Tumors Causing Osteomalacia

Objective

To assess and compare the performance of fluorine‐18‐labeled fluorodeoxyglucose positron emission tomography (¹⁸F‐FDG‐PET/ CT) and gallium‐68‐labeled tetraazacyclododecanetetraacetic acid‐DPhe1‐Tyr3‐octreotate (⁶⁸Ga‐ DOTATATE) PET/CT in the targeted imaging of culprit tumors causing osteomalacia.

Methods

This was a clinical retrospective analysis. We analyzed 13 patients (five men, eight women; mean age, 49 years; range, 19–55 years) with suspicion of tumor‐induced osteomalacia (TIO) between March 2017 and October 2019. All patients underwent two functional imaging methods to locate the culprittumors. Studies were performed on a PET/CT scanner. The injection doses of ¹⁸F‐ FDG and ⁶⁸Ga‐DOTATATE were 0.5mCi/kg and approximately 5.0mCi, respectively. In the two scans, the whole body was captured from head to toe 45 to 60 min after intravenous tracer injection. ⁶⁸Ga‐DOTATATE PET/CT and ¹⁸F‐FDG PET/CT imaging results locate culprit tumors according to the following criteria: (i) abnormal foci uptake concentration was observed locally, and the uptake level was higher than the background level of the right lobe of the liver; (ii) combined CT showed or did not have obvious abnormal density changes; and (iii) non‐specific ingestion lesions due to fracture, arthritis, necrosis of femoral head are excluded. Compared with the results of pathological examination and clinical follow‐up, the sensitivity, specificity and accuracy of ⁶⁸Ga‐DOTATATE PET/CT imaging and ¹⁸F‐FDG PET/CT imaging for TIO were analyzed.

Results

All patients had symptoms of osteomalacia and hypophosphatemia. The lag time (symptoms to PET diagnosis) ranged from 2 to 12 years. There were eight cases of TIO patients and five cases of non‐TIO patients confirmed by surgery, pathology and follow‐up. Among the eight TIO patients, there were six cases (75.0%) of PMTs, one case (12.5%) of giant cell tumor, one case (12.5%) of hemangiopericutoma. Most (n = 6, 75.0%) of the confirmed tumors in our patient population were in the lower extremities, followed by craniofacial regions (n = 1, 12.5%), and torso (n = 1, 12.5%), respectively. Among the five non‐TIO patients, there were two cases of Fanconi syndrome, one case of rickets, and two cases of sporadic osteomalacia hypophosphorus. The culprit tumors could be located either in the bone (n = 5, 62.5%) or the soft tissue (n = 3, 37.5%). ¹⁸F‐FDG PET/CT was able to localize the tumor in six (6/13, 46.1%) patients. ⁶⁸Ga‐DOTATATE PET/CT detected tumor in 8 (83.3%) of 13 patients. The sensitivity of ⁶⁸Ga‐DOTATATE PET/CT imaging and ¹⁸F‐FDG PET/CT imaging in the evaluation of TIO in our patient population were 100% (8/8) vs 75% (6/8). The specificity of the two different methods was 80% (4/5). The overall accuracy was 92.3% (12/13) vs 76.9% (10/13).

Conclusions

⁶⁸Ga‐DOTATATE PET/CT is very effective in assessing hypophosphatemia patients with TIO typical symptoms compared with ¹⁸F‐FDG. Therefore, in clinically suspected cases of hypophosphatemic osteomalacia, ⁶⁸Ga‐DOTATATE PET/CT should be preferred as an imaging modality investigation to avoid delay in the treatment of this disease.

Long COVID hallmarks on [18F]FDG-PET/CT: a case-control study

Purpose

The present study hypothesised that whole-body [18F]FDG-PET/CT might provide insight into the pathophysiology of long COVID.

Methods

We prospectively enrolled 13 adult long COVID patients who complained for at least one persistent symptom for >30 days after infection recovery. A group of 26 melanoma patients with negative PET/CT matched for sex/age was used as controls (2:1 control to case ratio). Qualitative and semi-quantitative analysis of whole-body images was performed. Fisher exact and Mann-Whitney tests were applied to test differences between the two groups. Voxel-based analysis was performed to compare brain metabolism in cases and controls. Cases were further grouped according to prevalent symptoms and analysed accordingly.

Results

In 4/13 long COVID patients, CT images showed lung abnormalities presenting mild [18F]FDG uptake. Many healthy organs/parenchyma SUVs and SUV ratios significantly differed between the two groups (p ≤ 0.05). Long COVID patients exhibited brain hypometabolism in the right parahippocampal gyrus and thalamus (uncorrected p < 0.001 at voxel level). Specific area(s) of hypometabolism characterised patients with persistent anosmia/ageusia, fatigue, and vascular uptake (uncorrected p < 0.005 at voxel level).

Conclusion

[18F]FDG PET/CT acknowledged the multi-organ nature of long COVID, supporting the hypothesis of underlying systemic inflammation. Whole-body images showed increased [18F]FDG uptake in several “target” and “non-target” tissues. We found a typical pattern of brain hypometabolism associated with persistent complaints at the PET time, suggesting a different temporal sequence for brain and whole-body inflammatory changes. This evidence underlined the potential value of whole-body [18F]FDG PET in disclosing the pathophysiology of long COVID.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05294-3.

Coronavirus Disease 2019 (COVID-19) in Molecular Imaging: A Systematic Review of Incidental Detection of SARS-CoV-2 Pneumonia on PET Studies

There have been several reports of the incidental detection of severe acute respiratory syndrome coronavirus 2 pneumonia on positron emission tomography/computed tomography (PET/CT) studies, which represent the potential role of molecular imaging in the detection and management of coronavirus disease 2019. Here, we systematically review the value of PET/CT in this setting. We conducted a systematic search on June 23, 2020, for PET studies with findings suggestive of coronavirus disease 2019. Web of Science, PubMed, Scopus, EMBASE, and Google Scholar databases were used. Patients with at least one PET/CT imaging evaluation were included in the study. Fifty-two patients in 30 publications with a mean age of 60 ± 12.74 (age range; 27-87) were included in this study, of which 28 (53.8%) were male, and 19 (36.5%) were female. In 5 (9.7%) patients, gender was not reported. PET/CT was performed with 18F-fluorodeoxyglucose for 48 (92.3%), 18F-choline for 3 (5.8%), and 68Ga-PSMA for 1 (1.9%) patients. The mean SUV max of pulmonary lesions with 18F-fluorodeoxyglucose uptake was 4.9 ± 2.3. Moreover, 39 (75%) cases had an underlying malignancy, including 18 different type of primary cancers and 6 (11.5%) patients with metastatic disease. The most common pulmonary findings in PET/CT were bilateral hypermetabolic ground-glass opacities in 39 (75%), consolidation in 18 (34.6%), and interlobular thickening in 4 (7.6%). In addition, mediastinal 14 (27%) and hilar 10 (19.2%) lymph node involvement with increased metabolic activity was frequently identified. Early diagnosis of severe acute respiratory syndrome coronavirus 2 pneumonia is not only crucial for both appropriate patient management but also helps to ensure appropriate postexposure precautions are implemented for the department and hospital staff and those who have been in contact with the patient.