PET/CT in nononcological lung diseases: current applications and future perspectives

Biomarkers in idiopathic pulmonary fibrosis: Current insight and future direction

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive interstitial lung disease with a dismal prognosis. Early diagnosis, accurate prognosis, and personalized therapeutic interventions are essential for improving patient outcomes. Biomarkers, as measurable indicators of biological processes or disease states, hold significant promise in IPF management. In recent years, there has been a growing interest in identifying and validating biomarkers for IPF, encompassing various molecular, imaging, and clinical approaches. This review provides an in-depth examination of the current landscape of IPF biomarker research, highlighting their potential applications in disease diagnosis, prognosis, and treatment response. Additionally, the challenges and future perspectives of biomarker integration into clinical practice for precision medicine in IPF are discussed.

Rabbit systemic glucose metabolism map by total-body dynamic PET/CT technology

BACKGROUND

This study evaluated total-body glucose metabolism in a preclinical lab animal, the rabbit, by employing a dynamic glucose metabolic image obtained with total-body fluorine-18 fluorodeoxyglucose ( 18 F-FDG) PET/computed tomography (PET/CT).

METHODS

The dynamic total-body PET/CT system was used to obtain glucose metabolic imaging from 10 sedated body-matched rabbits. The standard uptake value (SUV) of 18 F-FDG was used to evaluate glucose metabolism. In addition, the correlation between glucose metabolism and sexes was assessed, as well as metabolic differences between left- and right sides.

RESULTS

We found significant distribution heterogeneity of glucose in several organs across the entire body. There were no significant metabolic differences between sexes and between bilateral sides in the 10 rabbits. Thereafter, we assayed the major organ SUV changes by dynamic PET/CT of the major organs. The heart, liver, and urinary system showed more 18 F-FDG, whereas the skeletal muscle, brain, spinal cord, and lungs incorporated less 18 F-FDG. The phenotype of 18 F-FDG uptake was highly correlated with the physiological functions. The 18 F-FDG accumulation in urinary system were observed which could reflect the renal parenchyma glucose metabolism indirectly. However, the low 18 F-FDG uptake in the brain and spinal cord was due to sedation.

CONCLUSION

The total-body glucose metabolic atlas depicted with 18 F-FDG dynamic PET/CT may be used as a reference for assessing pathological 18 F-FDG uptake. Furthermore, this study could be a reference for preclinical research involving abnormality of glucose metabolism.

Assessing the feasibility of SUVindex (a metric derived from FDG PET/CT) for the diagnosis of polymyalgia rheumatica

AIM

To evaluate the feasibility of standard uptake value (SUV) index (ratio lesional maximum SUV [SUVmax] to liver mean SUV [SUVmean]) as a metabolic parameter for diagnosing polymyalgia rheumatica (PMR).

MATERIALS AND METHODS

A retrospective group of patients with PMR and controls with symptoms similar to PMR but diagnosed with other diseases. Semiquantitative and qualitative analysis of 2-[18F]-fluoro-2-deoxy-d-glucose (18F-FDG) uptake at 18 sites was undertaken for all patients. The diagnostic value of positron-emission tomography/computed tomography (PET/CT) for PMR was assessed by R software using logistic regression and a generalised additive model (GAM). All images were examined independently by two nuclear medicine physicians with extensive work experience.

RESULTS

The characteristic sites of PMR were the ischial tuberosity, interspinous bursa, periarticular hip, and symphysis pubis enthesis. The area under the curve (AUC) of the characteristic site SUV index was 0.930, and the best cut-off value was 1.685 with a sensitivity of 84.6% and a specificity of 92.6%. After adjusting for potential confounders, the probability of PMR diagnosis increased as the characteristic site SUV index increased and there was a nonlinear correlation between the two. When the characteristic site SUV index was ≥2.56, the probability of PMR gradually reached the threshold effect, which was as high as 90% or more.

CONCLUSION

The characteristic site SUV index is an independent factor for diagnosing PMR, and PMR should be highly suspected when it is ≥ 1.685. Nonetheless, it is important to note that these findings are based on an initial retrospective single-centre study and require external validation and further prospective evaluation before being translated into clinical practice.

2-deoxy-2-[18F]fluoro-D-glucose Positron Emission Tomography to Monitor Lung Inflammation and Therapeutic Response to Dexamethasone in a Murine Model of Acute Lung Injury

PURPOSE

To image inflammation and monitor therapeutic response to anti-inflammatory intervention using 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) positron emission tomography (PET) in a preclinical model of acute lung injury (ALI).

PROCEDURES

Mice were intratracheally administered lipopolysaccharide (LPS, 2.5 mg/kg) to induce ALI or phosphate-buffered saline as the vehicle control. A subset of mice in the ALI group received two intraperitoneal doses of dexamethasone 1 and 24 h after LPS. [18F]FDG PET/CT was performed 2 days after the induction of ALI. [18F]FDG uptake in the lungs was quantified by PET (%ID/mLmean and standardized uptake value (SUVmean)) and ex vivo γ-counting (%ID/g). The severity of lung inflammation was determined by quantifying the protein level of inflammatory cytokines/chemokines and the activity of neutrophil elastase and glycolytic enzymes. In separate groups of mice, flow cytometry was performed to estimate the contribution of individual immune cell types to the total pulmonary inflammatory cell burden under different treatment conditions.

RESULTS

Lung uptake of [18F]FDG was significantly increased during LPS-induced ALI, and a decreased [18F]FDG uptake was observed following dexamethasone treatment to an intermediate level between that of LPS-treated and control mice. Protein expression of inflammatory biomarkers and the activity of neutrophil elastase and glycolytic enzymes were increased in the lungs of LPS-treated mice versus those of control mice, and correlated with [18F]FDG uptake. Furthermore, dexamethasone-induced decreases in cytokine/chemokine protein levels and enzyme activities correlated with [18F]FDG uptake. Neutrophils were the most abundant cells in LPS-induced ALI, and the pattern of total cell burden during ALI with or without dexamethasone therapy mirrored that of [18F]FDG uptake.

CONCLUSIONS

[18F]FDG PET noninvasively detects lung inflammation in ALI and its response to anti-inflammatory therapy in a preclinical model. However, high [18F]FDG uptake by bone, brown fat, and myocardium remains a technical limitation for quantification of [18F]FDG in the lungs.

Pharyngeal Inflammation on Positron Emission Tomography/Magnetic Resonance Imaging Before and After Obstructive Sleep Apnea Treatment

Rationale: There is upper airway inflammation in patients with obstructive sleep apnea (OSA), which reduces with continuous positive airway pressure (CPAP) therapy. Objectives: Validate the use of positron emission tomography (PET)/magnetic resonance imaging (MRI) to quantify metabolic activity within the pharyngeal mucosa of patients with OSA against nasal lavage proteomics and assess the impact of CPAP therapy. Methods: Adults with OSA underwent [18F]-Fluoro-2-deoxy-D-glucose PET/MRI of the neck before and 3 months after initiating CPAP. Nasal lavage samples were collected. Inflammatory protein expression from samples was analyzed using the Olink platform. Upper airway imaging segmentation was performed. Target-to-background ratio (TBRmax) was calculated from target pharyngeal maximum standard uptake values (SUV) and personalized background mean SUV. Most-diseased segment TBRmax was identified per participant at locations with the highest PET avidity. Correlation analysis was performed between baseline TBRmax and nasal lavage proteomics. TBRmax was compared before and after CPAP using linear mixed-effect models. Results: Among 38 participants, the baseline mean age was 46.3 years (standard deviation [SD], 12.5), 21% were female, the mean body mass index was 30.9 kg/m2 (SD, 4.6), and the mean respiratory disturbance index measured by peripheral arterial tonometry was 31 events/h (SD, 16.4). There was a significant positive correlation between pharyngeal mucosa most-diseased segment TBRmax and nasal lavage proteomic inflammation (r = 0.41 [P < 0.001, false discovery rate = 0.002]). Primary analysis revealed a reduction in the most-diseased segment TBRmax after a median of 2.91 months of CPAP therapy (-0.86 [standard error (SE) ± 0.30; P = 0.007]). Stratified analysis by smoking status revealed a significantly decreased most-diseased segment TBRmax after CPAP therapy among never-smokers but not among ever-smokers (-1.01 [SE ± 0.39; P = 0.015] vs. -0.64 [SE ± 0.49; P = 0.201]). Conclusions: CPAP therapy reduces metabolic activity measured by PET/MRI within the upper airway of adults with OSA. Furthermore, PET/MRI measures of upper airway metabolic activity correlate with a noninvasive marker of inflammation (i.e., nasal lavage inflammatory protein expression).

Modified signal-to-noise ratio in the liver using the background-to-lung activity ratio to assess image quality of whole-body 18F-fluorodeoxyglucose positron emission tomography

The signal-to-noise ratio in the liver (SNR liver) is commonly used to assess the quality of positron emission tomography (PET) images; however, it is weakly correlated with visual assessments. Conversely, the noise equivalent count (NEC) density showed a strong correlation with visual assessment but did not consider the effects of image reconstruction conditions. Therefore, we propose a new indicator, the modified SNR liver, and plan to verify its usefulness by comparing it with conventional indicators. We retrospectively analyzed 103 patients who underwent whole-body PET/computed tomography (CT). Approximately 60 min after the intravenous injection of ¹⁸F-fluorodeoxyglucose (FDG), the participants were scanned for 2 min/bed. The SNR liver and NEC density were calculated according to the Japanese guidelines for oncology FDG-PET/CT. The modified SNR live was calculated by multiplying the background-to-lung activity ratio by the SNR liver. Patients were classified into groups based on body mass index (BMI) and visual scores. Subsequently, the relationships between these physical indicators, BMI, and visual scores were evaluated. Although the relationship between the modified SNR liver and BMI was inferior to that of NEC density and BMI, the modified SNR liver distinguished the BMI groups more clearly than the conventional SNR liver. Additionally, the modified SNR liver distinguished low visual scores from high scores more accurately than the conventional SNR liver and NEC density. Whether the modified SNR liver is more suitable than the NEC density remains equivocal; however, the modified SNR liver may be superior to the conventional SNR liver for image-quality assessment.

Imaging drug delivery to the lungs: Methods and applications in oncology

Direct delivery to the lung via inhalation is arguably one of the most logical approaches to treat lung cancer using drugs. However, despite significant efforts and investment in this area, this strategy has not progressed in clinical trials. Imaging drug delivery is a powerful tool to understand and develop novel drug delivery strategies. In this review we focus on imaging studies of drug delivery by the inhalation route, to provide a broad overview of the field to date and attempt to better understand the complexities of this route of administration and the significant barriers that it faces, as well as its advantages. We start with a discussion of the specific challenges for drug delivery to the lung via inhalation. We focus on the barriers that have prevented progress of this approach in oncology, as well as the most recent developments in this area. This is followed by a comprehensive overview of the different imaging modalities that are relevant to lung drug delivery, including nuclear imaging, X-ray imaging, magnetic resonance imaging, optical imaging and mass spectrometry imaging. For each of these modalities, examples from the literature where these techniques have been explored are provided. Finally the different applications of these technologies in oncology are discussed, focusing separately on small molecules and nanomedicines. We hope that this comprehensive review will be informative to the field and will guide the future preclinical and clinical development of this promising drug delivery strategy to maximise its therapeutic potential.

TPGS-based and S-thanatin functionalized nanorods for overcoming drug resistance in Klebsiella pneumonia

Tigecycline is regarded as the last line of defense to combat multidrug-resistant Klebsiella pneumoniae. However, increasing utilization has led to rising drug resistance and treatment failure. Here, we design a D-alpha tocopheryl polyethylene glycol succinate-modified and S-thanatin peptide-functionalized nanorods based on calcium phosphate nanoparticles for tigecycline delivery and pneumonia therapy caused by tigecycline-resistant Klebsiella pneumoniae. After incubation with bacteria, the fabricated nanorods can enhance tigecycline accumulation in bacteria via the inhibitory effect on efflux pumps exerted by D-alpha tocopheryl polyethylene glycol succinate and the targeting capacity of S-thanatin to bacteria. The synergistic antibacterial capacity between S-thanatin and tigecycline further enhances the antibacterial activity of nanorods, thus overcoming the tigecycline resistance of Klebsiella pneumoniae. After intravenous injection, nanorods significantly reduces the counts of white blood cells and neutrophils, decreases bacterial colonies, and ameliorates neutrophil infiltration events, thereby largely increasing the survival rate of mice with pneumonia. These findings may provide a therapeutic strategy for infections caused by drug-resistant bacteria.

Overproduction of efflux pumps represents an important mechanism of Klebsiella pneumonia resistance to tigecycline. Here, the authors design TPGS- and S-thanatin functionalized nanorods loaded with tigecycline to increase drug accumulation inside bacteria and overcome bacterial resistance.

PET/CT and inflammatory mediators in systemic sclerosis-associated interstitial lung disease

Objective:

To investigate the correlation of HRCT findings with pulmonary metabolic activity in the corresponding regions using ¹⁸F-FDG PET/CT and inflammatory markers in patients with systemic sclerosis (SSc)-associated interstitial lung disease (ILD).

Methods:

This was a cross-sectional study involving 23 adult patients with SSc-associated ILD without other connective tissue diseases. The study also involved ¹⁸F-FDG PET/CT, HRCT, determination of serum chemokine levels, clinical data, and pulmonary function testing.

Results:

In this cohort of patients with long-term disease (disease duration, 11.8 ± 8.7 years), a nonspecific interstitial pneumonia pattern was found in 19 (82.6%). Honeycombing areas had higher median standardized uptake values (1.95; p = 0.85). Serum levels of soluble tumor necrosis factor receptor 1, soluble tumor necrosis factor receptor 2, C-C motif chemokine ligand 2 (CCL2), and C-X-C motif chemokine ligand 10 were higher in SSc patients than in controls. Serum levels of CCL2-a marker of fibroblast activity-were correlated with pure ground-glass opacity (GGO) areas on HRCT scans (p = 0.007). ¹⁸F-FDG PET/CT showed significant metabolic activity for all HRCT patterns. The correlation between serum CCL2 levels and GGO on HRCT scans suggests a central role of fibroblasts in these areas, adding new information towards the understanding of the mechanisms surrounding cellular and molecular elements and their expression on HRCT scans in patients with SSc-associated ILD.

Conclusions:

¹⁸F-FDG PET/CT appears to be unable to differentiate the intensity of metabolic activity across HRCT patterns in chronic SSc patients. The association between CCL2 and GGO might be related to fibroblast activity in these areas; however, upregulated CCL2 expression in the lung tissue of SSc patients should be investigated in order to gain a better understanding of this association.

Development of a PET/CT molecular radiomics-clinical model to predict thoracic lymph node metastasis of invasive lung adenocarcinoma ≤ 3 cm in diameter

Background

To investigate the value of ¹⁸F-FDG PET/CT molecular radiomics combined with a clinical model in predicting thoracic lymph node metastasis (LNM) in invasive lung adenocarcinoma (≤ 3 cm).

Methods

A total of 528 lung adenocarcinoma patients were enrolled in this retrospective study. Five models were developed for the prediction of thoracic LNM, including PET radiomics, CT radiomics, PET/CT radiomics, clinical and integrated PET/CT radiomics-clinical models. Ten PET/CT radiomics features and two clinical characteristics were selected for the construction of the integrated PET/CT radiomics-clinical model. The predictive performance of all models was examined by receiver operating characteristic (ROC) curve analysis, and clinical utility was validated by nomogram analysis and decision curve analysis (DCA).

Results

According to ROC curve analysis, the integrated PET/CT molecular radiomics-clinical model outperformed the clinical model and the three other radiomics models, and the area under the curve (AUC) values of the integrated model were 0.95 (95% CI: 0.93–0.97) in the training group and 0.94 (95% CI: 0.89–0.97) in the test group. The nomogram analysis and DCA confirmed the clinical application value of this integrated model in predicting thoracic LNM.

Conclusions

The integrated PET/CT molecular radiomics-clinical model proposed in this study can ensure a higher level of accuracy in predicting the thoracic LNM of clinical invasive lung adenocarcinoma (≤ 3 cm) compared with the radiomics model or clinical model alone.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-022-00895-x.

[18F]FDG PET/CT in Short-Term Complications of COVID-19: Metabolic Markers of Persistent Inflammation and Impaired Respiratory Function

SARS-CoV-2 virus infects organs other than the lung, such as mediastinal lymph nodes, spleen, and liver, but, to date, metabolic imaging studies obtained in short-term follow-ups of patients hospitalized with severe COVID-19 infection are rare. Our objective was to evaluate the usefulness of [¹⁸F]FDG-PET/CT in the short-term follow-up of patients admitted for COVID-19 pneumonia and to explore the association of the findings with clinical prognostic markers. The prospective study included 20 patients with COVID-19 pneumonia (November 2020–March 2021). Clinical and laboratory test findings were gathered at admission, 48–72 h post-admission, and 2–3 months post-discharge, when [¹⁸F]FDG-PET/CT and respiratory function tests were performed. Lung volumes, spirometry, lung diffusion capacity for carbon monoxide (DLCO), and respiratory muscle strength were measured. Volumetric [¹⁸F]FDG-PET/CT results were correlated with laboratory and respiratory parameters. Eleven [¹⁸F]FDG-PET/CT (55%) were positive, with hypermetabolic mediastinal lymphadenopathy in 90.9%. Mediastinal lesion’s SUVpeak was correlated with white cells’ count. Eleven (55%) patients had impaired respiratory function, including reduced DLCO (35%). SUVpeak was correlated with %predicted-DLCO. TLG was negatively correlated with %predicted-DLCO and TLC. In the short-term follow-up of patients hospitalized for COVID-19 pneumonia, [¹⁸F]FDG-PET/CT findings revealed significant detectable inflammation in lungs and mediastinal lymph nodes that correlated with pulmonary function impairment in more than half of the patients.

Positron emission tomography-magnetic resonance imaging as a research tool in musculoskeletal conditions

Compared to positron emission tomography/computed tomography (PET/CT), the uptake of PET- magnetic resonance imaging (MRI) has been slow, even more so in clinical practice compared to the (pre-)clinical research setting. However, for applications in musculoskeletal (MSK) research, the combination of PET and MRI into a single modality offers attractive advantages over other imaging modalities. Most importantly, MRI has exquisite soft-tissue detail without the use of contrast agents or ionizing radiation, superior bone marrow visualization, and an extensive spectrum of distinct multiparametric assessment methods. In the preclinical setting, the introduction of PET inserts for small-animal MRI machines has proven to be a successful concept in bringing this technology to the lab. Initial hurdles in quantification have been mainly overcome in this setting. In parallel, a promising range of radiochemistry techniques has been developed to create multimodality probes that offer the possibility of simultaneously querying different metabolic pathways. Not only will these applications help in elucidating disease mechanisms, but they can also facilitate drug development. The clinical applications of PET/MRI in MSK are still limited, but encouraging initial results with novel radiotracers suggest a high potential for use in various MSK conditions, including osteoarthritis, rheumatoid arthritis, ankylosing spondylitis and inflammation and infection. Further innovations will be required to bring down the cost of PET/MRI to justify a broader clinical implementation, and remaining issues with quality control and standardization also need to be addressed. Nevertheless, PET/MRI is a powerful platform for MSK research with distinct qualities that are not offered by other techniques.

The imaging quantification of multiple organs by dynamic 18F-FDG PET/CT in discharged COVID-19 patients: A prospective pilot study

Purpose: To early identify abnormal lesions by applying the ¹⁸F-FDG PET dynamic modeling approach for discharged patients recovering from COVID-19. Methods: Seven discharged COVID-19 patients (COVID-19 group), twelve healthy volunteers (control group 1), and eight cancer patients with normal pulmonary function (control group 2) were prospectively enrolled. Control group 1 completed static ¹⁸F-FDG PET/CT only; COVID-19 group and control group 2 completed 60-min dynamic ¹⁸F-FDG PET/CT. Among COVID-19 group and control group 2, the uptake of FDG on the last frame (at 55-60 min) of dynamic scans was used for static analysis. Prior to performing scans, COVID-19 patients provided negative real-time Reverse Transcription-Polymerase Chain Reaction (rRT-PCR) of SARS-CoV-2, normal lung functions test, and normal laboratory test. Organ-to-liver standard uptake ratio (OLR, i.e. SUV_max ^{evaluated organ}/ SUV_max ^liver) from conventional static data and Patlak analysis based on the dynamic modeling to calculate the ¹⁸F-FDG net uptake rate constant (K_i) were performed. Results: Compared to the control groups, COVID-19 patients at two to three months after discharge still maintained significantly higher K_i values in multiple organs (including lung, bone marrow, lymph nodes, myocardium and liver), although results for regular OLR measurements were normal for all discharged COVID-19 patients. Taking the image of lung as an example, the differences of SUV_max images between COVID-19 group and control group were hard to distinguish. In contrast, a high ¹⁸F-FDG signal of the lung among the COVID-19 group was observed for K_i images. Conclusion: The K_i from ¹⁸F-FDG PET/CT dynamic imaging quantification might contribute to identifying residual lesions for COVID-19 survivors. Trial registration: The trial is registered with ClinicalTrials.gov, number NCT04519255 (IRB-approved number, K52-1).

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.

The role of imaging techniques in understanding and evaluating the long-term pulmonary effects of COVID-19

INTRODUCTION

Limited data exist regarding the long-term pulmonary sequelae of COVID-19. Identifying features utilizing multiple imaging modalities engenders a clearer picture of the illness's long-term consequences.

AREAS COVERED

This review encompasses the common pulmonary findings associated with different imaging modalities during acute and late remission stages of COVID-19 pneumonia.

EXPERT OPINION

Chest x-ray, a common preliminary diagnostic imaging technique, is not optimal for extended care due to limited tissue contrast resolution providing suboptimal assessment of pulmonary pathology and subtle interval changes. Ultrasound may be utilized on a case-by-case basis in certain patient populations, or in countries with limited resources. Chest CT's accessibility, high tissue contrast and spatial resolution make it the foremost modality for long-term COVID-19 follow-up. While MRI can viably monitor extrapulmonary disease due to its lack of radiation and high inherent soft-tissue contrast, it has limited pulmonary utility due to motion artifact and alveolar gas decreasing lung signal. Although 18F-FDG-PET/CT is costly and has limited specificity, it can provide molecular level data and inflammation quantification. Lung perfusion scintigraphy may also explain COVID-19 induced thromboembolic events and persistent dyspnea despite normal structural imaging and testing results. Correlating the long-term pulmonary findings of COVID-19 with each imaging modality is essential in elucidating the post-recovery course.

ACR Appropriateness Criteria® Diffuse Lung Disease

Diffuse lung disease, frequently referred to as interstitial lung disease, encompasses numerous disorders affecting the lung parenchyma. The potential etiologies of diffuse lung disease are broad with several hundred established clinical syndromes and pathologies currently identified. Imaging plays a critical role in diagnosis and follow-up of many of these diseases, although multidisciplinary discussion is the current standard for diagnosis of several DLDs. This document aims to establish guidelines for evaluation of diffuse lung diseases for 1) initial imaging of suspected diffuse lung disease, 2) initial imaging of suspected acute exacerbation or acute deterioration in cases of confirmed diffuse lung disease, and 3) clinically indicated routine follow-up of confirmed diffuse lung disease without acute deterioration. 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.

COVID-19 pneumonia: A review of typical radiological characteristics

Coronavirus disease 2019 (COVID-19) was first discovered after unusual cases of severe pneumonia emerged by the end of 2019 in Wuhan (China) and was declared a global public health emergency by the World Health Organization in January 2020. The new pathogen responsible for the infection, genetically similar to the beta-coronavirus family, is known as severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), and the current gold standard diagnostic tool for its detection in respiratory samples is the reverse transcription-polymerase chain reaction test. Imaging findings on COVID-19 have been widely described in studies published throughout last year, 2020. In general, ground-glass opacities and consolidations, with a bilateral and peripheral distribution, are the most typical patterns found in COVID-19 pneumonia. Even though much of the literature focuses on chest computed tomography (CT) and X-ray imaging and their findings, other imaging modalities have also been useful in the assessment of COVID-19 patients. Lung ultrasonography is an emerging technique with a high sensitivity, and thus useful in the initial evaluation of SARS-CoV-2 infection. In addition, combined positron emission tomography-CT enables the identification of affected areas and follow-up treatment responses. This review intends to clarify the role of the imaging modalities available and identify the most common radiological manifestations of COVID-19.

18F-FDG-PET/CT in SARS-CoV-2 infection and its sequelae

In recent months, much of the scientific efforts have focused on research on SARSCoV-2 infection and its consequences in humans. Still, many aspects remain unknown. It is known that the damage caused by SARS-CoV-2 is multifactorial and that its extension goes beyond lung inflammation and the acute phase, with the appearance of numerous complications and sequelae. To date, knowledge about the usefulness of 18F-FDG-PET/CT in the acute phase has been limited to the incidental detection of SARS-CoV-2 unsuspected pneumonia. Recent studies have been appearing collecting the findings of 18F-FDG-PET/CT in long COVID-19 or persistent COVID-19 state as well as the alterations caused after mass vaccination of the population in the metabolic studies. This work aims to review the existing literature focusing on these three issues and to briefly present our own preliminary experience.

[18F-FDG-PET/CT in SARS-CoV-2 infection and its sequelae]

In recent months, much of the scientific efforts have focused on research on SARSCoV-2 infection and its consequences in humans. Still, many aspects remain unknown. It is known that the damage caused by SARS-CoV-2 is multifactorial and that its extension goes beyond lung inflammation and the acute phase, with the appearance of numerous complications and sequelae. To date, knowledge about the usefulness of 18F-FDG-PET/CT in the acute phase has been limited to the incidental detection of SARS-CoV-2 unsuspected pneumonia. Recent studies have been appearing collecting the findings of 18F-FDG- PET/CT in long COVID-19 or persistent COVID-19 state as well as the alterations caused after mass vaccination of the population in the metabolic studies. This work aims to review the existing literature focusing on these three issues and to briefly present our own preliminary experience.

Global research trends in COVID-19 with MRI and PET/CT: a scoping review with bibliometric and network analyses

Objective

To identify and evaluate the indexed studies that allow us to understand the implications of imaging studies in MRI and PET/CT related to COVID-19 research.

Methods

Scoping review. Articles in PubMed, Scopus, and Web of Science (WoS) were scanned from 2019 to 2021 with COVID-19, MRI, and PET-CT as keywords. EndNote software and manual checking removed the duplicated references. Our assessment includes citation, bibliometric, keyword network, and statistical analyses using descriptive statistics and correlations. Highlighted variables were publication year, country, journals, and authorship.

Results

Only 326 papers were included. The most cited article reached 669 cites; this number represented 21.71% of 3081 citations. The top-15 cited authors received 1787 citations, which represented 58% of the total cites. These authors had affiliations from ten countries (Belgium, China, France, Italy, Japan, Spain, Sweden, Turkey, United Kingdom (UK), and the USA). The top-30 journals were cited 2762 times, representing 89.65% of the total cites. Only five journals were cited more than 100 times; Int J Infect Dis had the most significant number of citations (674). Some of the unexpected keywords were encephalitis, stroke, microbleeds, myocarditis.

Conclusion

COVID-19 pandemic is still spreading worldwide, and the knowledge about its different facets continues advancing. MRI and PET/CT are being used in more than 50% of the selected studies; research trends span seven categories, no only the diagnostic but others like socio-economic impact and pathogenesis Developed countries had an advantage by having hospitals with more resources, including MRI and PET/CT facilities in the same institution to supplement basic assessment in patients with COVID-19.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40336-021-00460-x.

Multiple brain abscesses presented with monoparesis in a patient with lung abscess mimicking lung cancer

Multiple brain abscesses associated with the lung mass require differential diagnosis from cancerous diseases. Here, we report a rare case of multiple brain abscesses originating from a lung abscess. A 65-year-old man presented with a 2-day history of motor weakness during antibiotic treatment for pneumonia. Brain magnetic resonance imaging (MRI) revealed multiple enhanced lesions of various sizes in the whole brain. Diffusion-weighted MRI showed high signal intensity in several lesions, and magnetic resonance (MR) spectroscopy showed reduced N-acetyl-aspartate (NAA) and high lactate-lipid complex levels. Positron emission tomography/computed tomography revealed a hypermetabolic mass-like lesion (size: 5 × 3 cm) in the right lower lobe. The patient was diagnosed with organizing pneumonia by bronchoscopy and was successfully treated with empirical antibiotics for multiple brain abscesses and lung abscesses. If new neurological deficits occur during the treatment of inflammatory diseases such as pneumonia, the possibility of brain abscesses and cancerous conditions should be considered. Appropriate diagnosis and antibiotic treatment should be performed to ensure favorable outcomes.

Limitations and Pitfalls of FDG-PET/CT in Infection and Inflammation

White blood cells activated by either a pathogen or as part of a systemic inflammatory disease are characterized by high energy consumption and are therefore taking up the glucose analogue PET tracer FDG avidly. It is therefore not surprising that a steadily growing body of research and clinical reports now supports the use of FDG PET/CT to diagnose a wide range of patients with non-oncological diseases. However, using FDG PET/CT in patients with infectious or inflammatory diseases has some limitations and potential pitfalls that are not necessarily as pronounced in oncology FDG PET/CT. Some of these limitations are of a general nature and related to the laborious acquisition of PET images in patients that are often acutely ill, whereas others are more disease-specific and related to the particular metabolism in some of the organs most commonly affected by infections or inflammatory disease. Both inflammatory and infectious diseases are characterized by a more diffuse and less pathognomonic pattern of FDG uptake than oncology FDG PET/CT and the affected organs also typically have some physiological FDG uptake. In addition, patients referred to PET/CT with suspected infection or inflammation are rarely treatment naïve and may have received varying doses of antibiotics, corticosteroids or other immune-modulating drugs at the time of their examination. Combined, this results in a higher rate of false positive FDG findings and also in some cases a lower sensitivity to detect active disease. In this review, we therefore discuss the limitations and pitfalls of FDG PET/CT to diagnose infections and inflammation taking these issues into consideration. Our review encompasses the most commonly encountered inflammatory and infectious diseases in head and neck, in the cardiovascular system, in the abdominal organs and in the musculoskeletal system. Finally, new developments in the field of PET/CT that may help overcome some of these limitations are briefly highlighted.

Imaging of COVID-19: CT, MRI, and PET

Soon after reports of a novel coronavirus capable of causing severe pneumonia surfaced in late 2019, expeditious global spread of the Severe Acute Respiratory Distress Syndrome Coronavirus 2 (SARS-CoV-2) forced the World Health Organization to declare an international state of emergency. Although best known for causing symptoms of upper respiratory tract infection in mild cases and fulminant pneumonia in severe disease, Coronavirus Disease 2019 (COVID-19) has also been associated with gastrointestinal, neurologic, cardiac, and hematologic presentations. Despite concerns over poor specificity and undue radiation exposure, chest imaging nonetheless remains central to the initial diagnosis and monitoring of COVID-19 progression, as well as to the evaluation of complications. Classic features on chest CT include ground-glass and reticular opacities with or without superimposed consolidations, frequently presenting in a bilateral, peripheral, and posterior distribution. More recently, studies conducted with MRI have shown excellent concordance with chest CT in visualizing typical features of COVID-19 pneumonia. For patients in whom exposure to ionizing radiation should be avoided, particularly pregnant patients and children, pulmonary MRI may represent a suitable alternative to chest CT. Although PET imaging is not typically considered among first-line investigative modalities for the diagnosis of lower respiratory tract infections, numerous reports have noted incidental localization of radiotracer in parenchymal regions of COVID-19-associated pulmonary lesions. These findings are consistent with data from Middle East Respiratory Syndrome-CoV cohorts which suggested an ability for 18F-FDG PET to detect subclinical infection and lymphadenitis in subjects without overt clinical signs of infection. Though highly sensitive, use of PET/CT for primary detection of COVID-19 is constrained by poor specificity, as well as considerations of cost, radiation burden, and prolonged exposure times for imaging staff. Even still, decontamination of scanner bays is a time-consuming process, and proper ventilation of scanner suites may additionally require up to an hour of downtime to allow for sufficient air exchange. Yet, in patients who require nuclear medicine investigations for other clinical indications, PET imaging may yield the earliest detection of nascent infection in otherwise asymptomatic individuals. Especially for patients with concomitant malignancies and other states of immunocompromise, prompt recognition of infection and early initiation of supportive care is crucial to maximizing outcomes and improving survivability.

Relative clinical utility of simultaneous 18F-fluorodeoxyglucose PET/MRI and PET/CT for preoperative cervical cancer diagnosis

Objective

To investigate the utility of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) for the preoperative diagnosis of cervical cancer.

Methods

We retrospectively analyzed 114 patients who were diagnosed with cervical cancer and underwent PET/MRI (n = 59) or PET/computed tomography (PET/CT) (n = 65) before surgery. The maximal standardized uptake value (SUV_max) and mean SUV (SUV_mean) were determined for regions of interest in the resultant radiographic images.

Results

Relative to PET/CT, ¹⁸F-FDG PET/MRI exhibited higher specificity and sensitivity in defining the primary tumor bounds and higher sensitivity for detection of bladder involvement. The SUV_max and SUV_mean of PET/MRI were remarkably higher than those of PET/CT as a means of detecting primary tumors, bladder involvement, and the lymph node status. However, no significant differences in these values were detected when comparing the two imaging approaches as a means of detecting vaginal involvement or para-aortic lymph node metastasis.

Conclusions

These outcomes may demonstrate the capability of ¹⁸F-FDG PET/MRI to clarify preoperative cervical cancer diagnoses in the context of unclear PET/CT findings. However, studies directly comparing SUVs in different lesion types from patients who have undergone both PET/MRI and PET/CT scans are essential to validate and expand upon these findings.

Incidental findings suggestive of COVID-19 pneumonia in oncological patients undergoing 18F-FDG PET/CT studies: association between metabolic and structural lung changes

Although the novel coronavirus disease 2019 (COVID-19) can present as non-specific clinical forms, subclinical cases represent an important route of transmission and a significant source of mortality, mainly in high-risk subpopulations such as cancer patients. A deeper knowledge about the shift in cellular metabolism of Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infected cells could provide new insights about its pathogenic and host response and help to diagnose pulmonary involvement. We explored the association between metabolic and structural changes of lung parenchyma in asymptomatic cancer patients with suspected COVID-19 pneumonia, as a potential added diagnostic value of fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography-computed tomography (PET/CT) scans in this subpopulation. Methods: Within the period of February 19 and May 29, 2020 ¹⁸F-FDG PET/CT studies were reviewed to identify those cancer patients with suggestive incidental findings of COVID-19 pneumonia. PET studies were interpreted through qualitative (visual) and semiquantitative analysis (measurement of maximum standardized uptake value, SUV_max) evaluating lung findings. Several characteristic signs of COVID-19 pneumonia on computed tomography (CT) were described as COVID-19 Reporting and Data System (CO-RADS) categories (1-6). After comparing SUV_max values of pulmonary infiltrates among different CO-RADS categories, we explored the best potential cut-off values of pulmonary SUV_max against CO-RADS categories as "gold standard" result to discard the diagnosis of COVID-19 pneumonia. Results: CT signs classified as CO-RADS category 5 or 6 were found in 16/41 (39%) oncological patients derived to multimodal PET/CT imaging. SUV_max was higher in patients with CO-RADS 5 and 6 vs. 4 (6.17±0.82 vs. 3.78±0.50, P = 0.04) and vs. 2 and 3 categories (3.59±0.41, P = 0.01). A specificity of 93.8% (IC 95%: 71.7-99.7%) and an accuracy of 92.9% were obtained when combining a CO-RADS score 5-6 with a SUV_max of 2.45 in pulmonary infiltrates. Conclusion: In asymptomatic cancer patients, the metabolic activity in lung infiltrates is closely associated with several combined tomographic changes characteristic of COVID-19 pneumonia. Multimodal ¹⁸F-FDG PET/CT imaging could provide additional information during early diagnosis in selected predisposed patients during pandemic. The prognostic implications of simultaneous radiological and molecular findings in cancer and other high-risk subpopulations for COVID-19 pneumonia deserve further evaluation in prospective researches.

Asymptomatic SARS-CoV-2 infection: Incidental findings on FDG PET/CT

RATIONALE AND OBJECTIVES

Identify the incidental findings of Covid-19 pneumonitis on 18F-FDG PET/CT scan in asymptomatic oncologic patients. The goal was to detect clinically unsuspected Covid-19 infections to prevent community spread.

MATERIALS AND METHODS

Retrospective analysis was conducted to recognize the pattern of metabolic and radiographic alterations on 18F-FDG PET/CT scans in Covid-19 patients. 492 18F-FDG PET/CT scans were reviewed for pulmonary and systemic abnormalities.

RESULTS

18F-FDG PET/CT demonstrated new lung infiltrates in 29 asymptomatic patients. 13/29 patients had Covid-19 infection confirmed by nasopharyngeal nucleic acid PCR test. The most common lung abnormality was pure ground-glass opacity (GGO) (90%) in peripheral distribution (100%), involving 1 lobe in four patients (30.8%), 2-3 lobes in four patients, and 4-5 lobes in five patients (38.4%). Mean SUVmax was 4.7 (range 1.3-13.1). Ten patients developed symptoms, mainly fever, fatigue, and dry cough, within 6.4 ± 7.8 days (range 1-24). Of the available laboratory data of 12 patients, eight developed lymphopenia, and five patients had neutrophilia. Five patients required hospitalization, and two died of complications.

CONCLUSION

For a given geographic region in the later stage of a pandemic, such as Covid-19, community spread of the disease is common. Therefore, it is not surprising to find it in asymptomatic being imaged for other indications. Recognition of its manifestation and effectively mounting mitigation protocols is essential to further reduce SARS-CoV-2 spread, especially to susceptible groups, predominantly the elderly and people with comorbidities.

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.

Establishment and verification of a prediction model based on clinical characteristics and positron emission tomography/computed tomography (PET/CT) parameters for distinguishing malignant from benign ground-glass nodules

Background

To develop and verify a prediction model for distinguishing malignant from benign ground-glass nodules (GGNs) combined with clinical characteristics and ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) parameters.

Methods

We retrospectively analyzed 170 patients (56 males and 114 females) with GGNs who underwent PET/CT and high-resolution CT examination in our hospital from November 2011 to December 2019. The clinical and imaging data of all patients were collected, and the nodules were randomly divided into a derivation set and a validation set. For the derivation set, we used multivariate logistic regression to develop a prediction model for distinguishing benign from malignant GGNs. A receiver operating characteristic (ROC) curve was used to evaluate the diagnostic efficacy of the model, and the data in the validation set were used to verify the prediction model.

Results

Among the 170 patients, 197 GGNs were confirmed via postoperative pathological examination or clinical follow-up. There were 21 patients with 27 GGNs in the benign group and 149 patients with 170 GGNs in the adenocarcinoma group. A total of five parameters, including the patient's sex, nodule location, margin, pleural indentation, and standardized uptake value (SUV) index (the ratio of nodule SUVmax to liver SUVmean), were selected to develop a prediction model for distinguishing benign from malignant GGNs. The area under the curve (AUC) of the model was 0.875 in the derivation set, with a sensitivity of 0.702 and a specificity of 0.923. The positive likelihood ratio was 9.131, and the negative likelihood ratio was 0.322. In the validation set, the AUC of the model was 0.874, which was not significantly different from the derivation set (P=0.989).

Conclusions

This study developed and validated a prediction model based on ¹⁸F-FDG PET/CT imaging and clinical characteristics for distinguishing malignant from benign GGNs. The model showed good diagnostic efficacy and high specificity, which can improve the preoperative diagnosis of high-risk GGNs.

Association Between 18F-FDG PET/CT-Based SUV Index and Malignant Status of Persistent Ground-Glass Nodules

To explore the association between ¹⁸F-FDG PET/CT-based SUV index and malignant risk of persistent ground-glass nodules (GGNs). We retrospectively analyzed a total of 166 patients with GGN who underwent PET/CT examination from January 2012 to October 2019. There were 113 women and 53 men, with an average age of 60.8 ± 9.1 years old. A total of 192 GGNs were resected and confirmed by pathology, including 22 in benign group and 170 in adenocarcinoma group. They were divided into three groups according to SUV index tertiles: Tertile 1 (0.14–0.54), Tertile 2 (0.55–1.17), and Tertile 3 (1.19–6.78), with 64 GGNs in each group. The clinical and imaging data of all patients were collected and analyzed. After adjusting for the potential confounding factors, we found that the malignancy risk of GGN significantly decreased as the SUV index increased (OR, 0.245; 95%CI, 0.119–0.504; P <0.001), the average probability of malignant GGN was 89.1% (95% CI, 53.1–98.3%), 80.5% (95% CI, 36.7–96.7%), and 34.3% (95%CI, 9.5–72.2%) for Tertile 1 to Tertile 3. And the increasing trend of SUV index was significantly correlated with the reduction of malignant risk (OR, 0.099; 95%CI, 0.025–0.394; P = 0.001), especially between Tertile 3 versus Tertile 1 (OR, 0.064; 95%CI, 0.012–0.356; P = 0.002). Curve fitting showed that the SUV index was linearly and negatively correlated with the malignant risk of GGN. SUV index is an independent correlation factor for malignancy risk of GGN, the higher the SUV index, the lower the probability of GGN malignancy.

GMP-compliant fully automated radiosynthesis of [18F]FEPPA for PET/MRI imaging of regional brain TSPO expression

Background

Expression of translocator protein (TSPO) on the outer mitochondrial membrane of activated microglia is strongly associated with neuroinflammation. The second-generation PET ligand [¹⁸F]FEPPA specifically binds TSPO to enable in vivo visualization and quantification of neuroinflammation. We optimized a fully automated radiosynthesis method and evaluated the utility of [¹⁸F]FEPPA, the second-generation PET ligand specifically binds TSPO, in a mouse model of systemic LPS challenge to detect TSPO-associated signals of central and peripheral inflammation. In vivo dynamic PET/MR imaging was performed in LPS-induced and control mice after [¹⁸F]FEPPA administration. The relationship between the [¹⁸F]FEPPA signal and the dose of LPS was assessed. The cytokine levels (i.e., TNF-α, Il-1β, Il-6) in LPS-induced mice were measured by RT-PCR. Standard uptake value (SUV), total volume of distribution (VT) and area under the curve (AUC) were determined based on the metabolite-uncorrected plasma input function. Western blotting and immunostaining were used to measure TSPO expression in the brain.

Results

The fully automated [¹⁸F]FEPPA radiosynthesis produced an uncorrected radiochemical yield of 30 ± 2% within 80 min, with a radiochemical purity greater than 99% and specific activity of 148.9‒216.8 GBq/µmol. Significant differences were observed in the brain after [¹⁸F]FEPPA administration: SUV, VT and AUC were 1.61 ± 0.1, 1.25 ± 0.12 and 1.58 ± 0.09-fold higher in LPS-injected mice than controls. TNF-α, Il-1β and Il-6 mRNA levels were also elevated in the brains of LPS-injected mice. Western blotting revealed TSPO (p < 0.05) and Iba-1 (p < 0.01) were upregulated in the brain after LPS administration. In LPS-injected mice, TSPO immunoactivity colocalized with Iba-1 in the cerebrum and TSPO was significantly overexpressed in the hippocampus and cerebellum. The peripheral organs (heart, lung) of LPS-injected mice had higher [¹⁸F]FEPPA signal-to-noise ratios than control mice.

Conclusions

Based on the current data on ligand specificity and selectivity in central tissues using 7 T PET/MR imaging, we demonstrate that [¹⁸F]FEPPA accumulations significant increased in the specific brain regions of systemic LPS-induced neuroinflammation (5 mg/kg). Future investigations are needed to determine the sensitivity of [¹⁸F]FEPPA as a biomarker of neuroinflammation as well as the correlation between the PET signal intensity and the expression levels of TSPO.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-021-00768-9.

Mapping of Translocator Protein (18 kDa) in Peripheral Sterile Inflammatory Disease and Cancer through PET Imaging

Positron emission tomography (PET) imaging of the translocator 18 kDa protein (TSPO) with radioligands has become an effective means of research in peripheral inflammatory conditions that occur in many diseases and cancers. The peripheral sterile inflammatory diseases (PSIDs) are associated with a diverse group of disorders that comprises numerous enduring insults including the cardiovascular, respiratory, gastrointestinal, or musculoskeletal system. TSPO has recently been introduced as a potential biomarker for peripheral sterile inflammatory diseases (PSIDs). The major critical issue related to PSIDs is its timely characterization and localization of inflammatory foci for proper therapy of patients. As an alternative to metabolic imaging, protein imaging expressed on immune cells after activation is of great importance. The five transmembrane domain translocator protein-18 kDa (TSPO) is upregulated on the mitochondrial cell surface of macrophages during inflammation, serving as a potential ligand for PET tracers. Additionally, the overexpressed TSPO protein has been positively correlated with various tumor malignancies. In view of the association of escalated TSPO expression in both disease conditions, it is an immensely important biomarker for PET imaging in oncology and PSIDs. In this review, we summarize the most outstanding advances on TSPO-targeted PSIDs and cancer in the development of TSPO ligands as a potential diagnostic tool, specifically discussing the last five years.

Assessment of extra-parenchymal lung involvement in asymptomatic cancer patients with COVID-19 pneumonia detected on 18F-FDG PET-CT studies

BACKGROUND

Lung involvement in patients with coronavirus disease 2019 (COVID-19) undergoing PET-CT has been previously reported. However, FDG uptake outside lung parenchyma was poorly characterized in detail. We evaluated the extra-parenchymal lung involvement in asymptomatic cancer patients with COVID-19 pneumonia through 18F-FDG PET-CT.

METHODS

A total of 1079 oncologic 18F-FDG PET-CT were performed between February 2 and May 18, 2020. Confirmed COVID-19 pneumonia was defined as characteristic ground-glass bilateral CT infiltrates and positive genetic/serologic tests. Nonmetastatic extra-parenchymal lung PET-CT findings were evaluated through qualitative (visual), quantitative (measurements on CT), and semiquantitative (maximum standardized uptake value: SUVmax on PET) interpretation. Clinical data, blood tests, and PET-CT results were compared between patients with and without COVID-19 pneumonia.

RESULTS

A total of 23 18F-FDG PET-CT scans with pulmonary infiltrates suggestive of COVID-19 and available laboratory data were included: 14 positive (cases) and 9 negative (controls) for COVID-19 infection, representing a low prevalence of COVID-19 pneumonia (1.3%). Serum lactate dehydrogenase and D-dimers tended to be increased in COVID-19 cases. Extra-parenchymal lung findings were found in 42.9% of patients with COVID-19, most frequently as mediastinal and hilar nodes with 18F-FDG uptake (35.7%), followed by incidental pulmonary embolism in two patients (14.3%). In the control group, extra-pulmonary findings were observed in a single patient (11.1%) with 18F-FDG uptake located to mediastinal, hilar, and cervical nodes. Nasopharyngeal and hepatic SUVmax were similar in both groups.

CONCLUSION

In cancer patients with asymptomatic COVID-19 pneumonia, 18F-FDG PET-CT findings are more frequently limited to thoracic structures, suggesting that an early and silent distant involvement is very rare. Pulmonary embolism is a frequent and potentially severe finding raising special concern. PET-CT can provide new pathogenic insights about this novel disease.

Quercetin: a savior of alveolar barrier integrity under hypoxic microenvironment

High altitude pulmonary edema (HAPE) is generally characterized by the loss of alveolar epithelial barrier integrity. The current study was undertaken to assess the noninvasive approaches of HAPE diagnosis and to evaluate the prophylactic potential of quercetin in preventing alveolar junction impairments. Male SD rats fed with quercetin 1 h prior to hypoxia (7,620 m, for 6 h) were selected. PET/CT imaging was performed to visualize the lung uptake of ¹⁸F-FDG in animals under hypoxia. Further, oxidant status, catalase activity, hematological & blood gas parameters were evaluated. Moreover, tight junction (TJ) proteins (ZO-1, JAM-C, Claudin-4, and occludin) expression analysis was accomplished using immune-blotting. The structural differences in lung epithelia were noted by TEM imaging. Quercetin prophylaxis has significantly reduced the FDG uptake in rat lungs under hypoxia. It has also dramatically alleviated the protein oxidation followed by an elevation in catalase activity in the lungs under hypoxia. The TJ protein expression in the lungs has also been restored to normal upon quercetin pre-treatment. Concomitantly, the quercetin preconditioning has elicited the stable blood gas and hematological parameters under hypoxia. The observations from TEM imaging have also implicated the normal lung epithelial structures in the quercetin pretreated animals under hypoxia. Quercetin prophylaxis has significantly restored alveolar epithelium integrity by abating oxidative stress in the lungs under hypoxia.Abbreviations: CT- Computed Tomography¹⁸F-FDG- Fluorodeoxyglucose (¹⁸FHAPE- High Altitude Pulmonary EdemaHb- HemoglobinHCT- HematocritHCO₃^- BicarbonateJAM- Junctional Adhesion MoleculeKBq- Killo BecquerelPaO₂- Partial pressure of arterial oxygenPaCO₂- Partial pressure of arterial carbon di-oxidePET- Positron Emission TomographyRBC- Red Blood CorpusclesSD- Sprague DawleyTJ- Tight JunctionsTEM- Transmission Electron MicroscopyWBC- White Blood CorpusclesZO- Zona Occludin.

Inflammatory response in lungs and extrapulmonary sites detected by [18F] fluorodeoxyglucose PET/CT in convalescing COVID-19 patients tested negative for coronavirus

BACKGROUND

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in an ongoing global pandemic of coronavirus disease 2019 (COVID-19). The challenges associated with imaging infected patients have resulted, to date, in a paucity of metabolic imaging studies of patients with severe COVID-19 infection. Furthermore, it remains unclear if any abnormal metabolic events are taking place in patients who have recovered from COVID-19.

PURPOSE

To use [¹⁸F] fluorodeoxyglucose ([¹⁸F] FDG) positron emission tomography/computed tomography (PET/CT) to measure metabolic activity in inflamed organs of patients convalescing post severe COVID-19 infection.

MATERIALS AND METHODS

A prospective study was performed in seven convalescing patients who were recovering from severe COVID-19 infection in February 2020. Prior to [¹⁸F] FDG PET/CT, all patients had received two consecutive negative results of real-time reverse transcriptase polymerase chain reaction (RT-PCR) for SARS-CoV-2 nucleic acid. Clinical intake including symptoms, treatment, laboratory test results, and follow-up was performed. The PET/CT images of COVID-19 patients were compared to a control group of patients that were matched for age and sex.

RESULTS

Residual pulmonary lesions were present in all patients and maximum standard uptake value (SUVmax), average standard uptake value (SUVavg), maximum CT intensity (CTmax), and average CT intensity (CTavg) were all significantly greater than in the control group (p < 0.01 for all). In addition, SUVmax and SUVavg were significantly greater in the mediastinal lymph node and liver, and SUVmax was significantly greater in the spleen, of COVID-19 patients compared with controls (p < 0.05 for all). For the spleen, SUVmax (r² = 0.863, p = 0.003) and SUVavg (r² = 0.797, p = 0.007) were significantly correlated with blood lymphocyte count, and which was below the normal range in five of the seven (71.4%) patients convalescing post severe COVID-19 infection.

CONCLUSION

[¹⁸F] FDG PET/CT quantitative analysis has shown that significant inflammation remained in lungs, mediastinal lymph nodes, spleen, and liver after two consecutive negative RT-PCR tests in patients convalescing post severe COVID-19 infection.

Mapping COVID-19 functional sequelae: the perspective of nuclear medicine

Severe acute respiratory syndrome coronavirus 2 infection is capable of affecting several organs. Direct viral toxicity, pro-inflammatory and pro-thrombotic induction, endothelial damage, immune imbalance, and dysregulation of the renin-angiotensin-aldosterone system are the mechanisms underlying the viral potential of multiple organ damage. The impairment of four organs stands out among severe patients: lung, heart, kidney, and endothelium. The nuclear medicine field holds accurate and safe exam techniques, such as positron emission tomography-computed tomography and scintigraphy, that allow the anatomophysiological study of the majority of human organ systems. By choosing the most appropriate method and radiopharmaceutical, analyzing the presence of inflammation, fibrosis, changes in perfusion, and function of desired organs is possible. Therefore, its use in the monitoring of patients with coronavirus disease 2019 becomes relevant, especially for monitoring sequelae. In this review, we discuss the use of Nuclear Medicine in the detection, monitoring, and therapeutic evaluation of pulmonary and extrapulmonary sequelae by coronavirus disease 2019.

Advances in the In Vivo Molecular Imaging of Invasive Aspergillosis

Invasive pulmonary aspergillosis (IPA) is a life-threatening infection of immunocompromised patients with Aspergillus fumigatus, a ubiquitous environmental mould. While there are numerous functioning antifungal therapies, their high cost, substantial side effects and fear of overt resistance development preclude permanent prophylactic medication of risk-patients. Hence, a fast and definitive diagnosis of IPA is desirable, to quickly identify those patients that really require aggressive antimycotic treatment and to follow the course of the therapeutic intervention. However, despite decades of research into this issue, such a diagnostic procedure is still not available. Here, we discuss the array of currently available methods for IPA detection and their limits. We then show that molecular imaging using positron emission tomography (PET) combined with morphological computed tomography or magnetic imaging is highly promising to become a future non-invasive approach for IPA diagnosis and therapy monitoring, albeit still requiring thorough validation and relying on further acceptance and dissemination of the approach. Thereby, our approach using the A. fumigatus-specific humanized monoclonal antibody hJF5 labelled with ⁶⁴Cu as PET-tracer has proven highly effective in pre-clinical models and hence bears high potential for human application.

Clinical features and radiological manifestations of COVID-19 disease

Coronavirus disease 2019 (COVID-19) was discovered after unusual cases of severe pneumonia emerged in December 2019 in Wuhan Province (China). Coronavirus is a family of single-stranded RNA viruses. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is transmitted from person to person. Although asymptomatic individuals can transmit the virus, symptomatic patients are more contagious. The incubation period ranges from 3-7 d and symptoms are mainly respiratory, including pneumonia or pulmonary embolism in severe cases. Elevated serum levels of interleukins (IL)-2, IL-6, IL-7 indicate the presence of cytokine release syndrome, which is associated with disease severity. The disease has three main phases: Viral infection, pulmonary involvement, and hyperinflammation. To date, no treatment has proved to be safe or effective. Chest X-ray and computed tomography (CT) are the primary imaging tests for diagnosis of SARS-CoV-2 pneumonia, follow-up, and detection of complications. The main radiological findings are ground-glass opacification and areas of consolidation. The long-term clinical course is unknown, although some patients may develop pulmonary fibrosis. Positron emission tomography-computed tomography (PET-CT) is useful to assess pulmonary involvement, to define the affected areas, and to assess treatment response. The pathophysiology and clinical course of COVID-19 infection remain poorly understood. However, patterns detected on CT and PET-CT may help to diagnose and guide treatment. In this mini review, we analyze the clinical manifestations and radiological findings of COVID-19 infection.

Physiologically variable ventilation reduces regional lung inflammation in a pediatric model of acute respiratory distress syndrome

BACKGROUND

Benefits of variable mechanical ventilation based on the physiological breathing pattern have been observed both in healthy and injured lungs. These benefits have not been characterized in pediatric models and the effect of this ventilation mode on regional distribution of lung inflammation also remains controversial. Here, we compare structural, molecular and functional outcomes reflecting regional inflammation between PVV and conventional pressure-controlled ventilation (PCV) in a pediatric model of healthy lungs and acute respiratory distress syndrome (ARDS).

METHODS

New-Zealand White rabbit pups (n = 36, 670 ± 20 g [half-width 95% confidence interval]), with healthy lungs or after induction of ARDS, were randomized to five hours of mechanical ventilation with PCV or PVV. Regional lung aeration, inflammation and perfusion were assessed using x-ray computed tomography, positron-emission tomography and single-photon emission computed tomography, respectively. Ventilation parameters, blood gases and respiratory tissue elastance were recorded hourly.

RESULTS

Mechanical ventilation worsened respiratory elastance in healthy and ARDS animals ventilated with PCV (11 ± 8%, 6 ± 3%, p < 0.04), however, this trend was improved by PVV (1 ± 4%, - 6 ± 2%). Animals receiving PVV presented reduced inflammation as assessed by lung normalized [¹⁸F]fluorodeoxyglucose uptake in healthy (1.49 ± 0.62 standardized uptake value, SUV) and ARDS animals (1.86 ± 0.47 SUV) compared to PCV (2.33 ± 0.775 and 2.28 ± 0.3 SUV, respectively, p < 0.05), particularly in the well and poorly aerated lung zones. No benefit of PVV could be detected on regional blood perfusion or blood gas parameters.

CONCLUSIONS

Variable ventilation based on a physiological respiratory pattern, compared to conventional pressure-controlled ventilation, reduced global and regional inflammation in both healthy and injured lungs of juvenile rabbits.

Imaging Diagnostics and Pathology in SARS-CoV-2-Related Diseases

In December 2019, physicians reported numerous patients showing pneumonia of unknown origin in the Chinese region of Wuhan. Following the spreading of the infection over the world, The World Health Organization (WHO) on 11 March 2020 declared the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) outbreak a global pandemic. The scientific community is exerting an extraordinary effort to elucidate all aspects related to SARS-CoV-2, such as the structure, ultrastructure, invasion mechanisms, replication mechanisms, or drugs for treatment, mainly through in vitro studies. Thus, the clinical in vivo data can provide a test bench for new discoveries in the field of SARS-CoV-2, finding new solutions to fight the current pandemic. During this dramatic situation, the normal scientific protocols for the development of new diagnostic procedures or drugs are frequently not completely applied in order to speed up these processes. In this context, interdisciplinarity is fundamental. Specifically, a great contribution can be provided by the association and interpretation of data derived from medical disciplines based on the study of images, such as radiology, nuclear medicine, and pathology. Therefore, here, we highlighted the most recent histopathological and imaging data concerning the SARS-CoV-2 infection in lung and other human organs such as the kidney, heart, and vascular system. In addition, we evaluated the possible matches among data of radiology, nuclear medicine, and pathology departments in order to support the intense scientific work to address the SARS-CoV-2 pandemic. In this regard, the development of artificial intelligence algorithms that are capable of correlating these clinical data with the new scientific discoveries concerning SARS-CoV-2 might be the keystone to get out of the pandemic.

Diagnostic Value of Imaging Modalities for COVID-19: Scoping Review

BACKGROUND

Coronavirus disease (COVID-19) is a serious infectious disease that causes severe respiratory illness. This pandemic represents a serious public health risk. Therefore, early and accurate diagnosis is essential to control disease progression. Radiological examination plays a crucial role in the early identification and management of infected patients.

OBJECTIVE

The aim of this review was to identify the diagnostic value of different imaging modalities used for diagnosis of COVID-19.

METHODS

A comprehensive literature search was conducted using the PubMed, Scopus, Web of Science, and Google Scholar databases. The keywords diagnostic imaging, radiology, respiratory infection, pneumonia, coronavirus infection and COVID-19 were used to identify radiology articles focusing on the diagnosis of COVID-19 and to determine the diagnostic value of various imaging modalities, including x-ray, computed tomography (CT), ultrasound, and nuclear medicine for identification and management of infected patients.

RESULTS

We identified 50 articles in the literature search. Studies that investigated the diagnostic roles and imaging features of patients with COVID-19, using either chest CT, lung ultrasound, chest x-ray, or positron emission topography/computed tomography (PET/CT) scan, were discussed. Of these imaging modalities, chest x-ray and CT scan are the most commonly used for diagnosis and management of COVID-19 patients, with chest CT scan being more accurate and sensitive in identifying COVID-19 at early stages. Only a few studies have investigated the roles of ultrasound and PET/CT scan in diagnosing COVID-19.

CONCLUSIONS

Chest CT scan remains the most sensitive imaging modality in initial diagnosis and management of suspected and confirmed patients with COVID-19. Other diagnostic imaging modalities could add value in evaluating disease progression and monitoring critically ill patients with COVID-19.

Incidental COVID-19 Pneumonia on 18F-Fluorocholine PET/CT

We present the case of a patient who underwent ¹⁸F-fluorocholine PET/CT for biochemical recurrence of prostate cancer in which bilateral pneumonia was diagnosed. In the current state of COVID-19 pandemic, a high prevalence of incidental pneumonia may be expected, even with previous clinical triage, explained by a nondefined number of patients who were asymptomatic or minimally symptomatic for infectious process. Therefore, nuclear medicine physicians should be prepared to recognize and diagnose incidental COVID-19 pneumonia manifestation on ¹⁸F-fluorocholine PET/CT, due to the crucial epidemiological implications.

18F-FDG PET/CT Metabolic Behavior of COVID-19 Pneumonia: A Series of 4 Patients With RT-PCR Confirmation

Between March 26 and April 6, among 80 patients who underwent F-FDG PET/CT in our department (Brescia, Italy), 4 showed the presence of an interstitial pneumonia suspected for COVID-19 with reverse transcriptase polymerase chain reaction confirmation. All patients except one had bilateral ground-glass opacities and/or lung consolidations in at least 2 pulmonary lobes. Inferior lobes and basal segments were the most frequent site of disease. All lung lesions had an increased FDG uptake corresponding to the interstitial pneumonia, and in one case, mediastinal nodal involvement was registered.

Noninvasive methods for detection of chronic lung allograft dysfunction in lung transplantation

Lung transplantation (LTx) is the only therapeutic option for end-stage lung diseases. Chronic lung allograft dysfunction (CLAD), which manifests as airflow restriction and/or obstruction, is the primary factor limiting the long-term survival of patients after surgery. According to histopathological and radiographic findings, CLAD comprises two phenotypes, bronchiolitis obliterans syndrome and restrictive allograft syndrome. Half of all lung recipients will develop CLAD in 5 years, and this rate may increase up to 75% 10 years after surgery owing to the paucity in accurate and effective early detection and treatment methods. Recently, many studies have presented noninvasive methods for detecting CLAD and improving diagnosis and intervention. However, the significance of accurately detecting CLAD remains controversial. We reviewed published studies that have presented noninvasive methods for detecting CLAD to highlight the current knowledge on clinical symptoms, spirometry, imaging examinations, and other methods to detect the disease.

World Trade Center-Cardiorespiratory and Vascular Dysfunction: Assessing the Phenotype and Metabolome of a Murine Particulate Matter Exposure Model

Vascular changes occur early in the development of obstructive airways disease. However, the vascular remodeling and dysfunction due to World Trade Center-Particulate Matter (WTC-PM) exposure are not well described and are therefore the focus of this investigation. C57Bl/6 female mice oropharyngeally aspirated 200 µg of WTC-PM₅₃ or phosphate-buffered saline (PBS) (controls). 24-hours (24-hrs) and 1-Month (1-M) after exposure, echocardiography, micro-positron emission tomography(µ-PET), collagen quantification, lung metabolomics, assessment of antioxidant potential and soluble-receptor for advanced glycation end products (sRAGE) in bronchoalveolar lavage(BAL) and plasma were performed. 24-hrs post-exposure, there was a significant reduction in (1) Pulmonary artery(PA) flow-velocity and pulmonary ejection time(PET) (2) Pulmonary acceleration time(PAT) and PAT/PET, while (3) Aortic ejection time(AET) and velocity time integral(VTI) were increased, and (4) Aortic acceleration time (AAT)/AET, cardiac output and stroke volume were decreased compared to controls. 1-M post-exposure, there was also significant reduction of right ventricular diameter as right ventricle free wall thickness was increased and an increase in tricuspid E, A peaks and an elevated E/A. The pulmonary and cardiac standard uptake value and volume 1-M post-exposure was significantly elevated after PM-exposure. Similarly, α-smooth muscle actin(α-SMA) expression, aortic collagen deposition was elevated 1-M after PM exposure. In assessment of the metabolome, prominent subpathways included advanced glycation end products (AGEs), phosphatidylcholines, sphingolipids, saturated/unsaturated fatty acids, eicosanoids, and phospholipids. BAL superoxide dismutase(SOD), plasma total-antioxidant capacity activity, and sRAGE (BAL and plasma) were elevated after 24-hrs. PM exposure and associated vascular disease are a global health burden. Our study shows persistent WTC-Cardiorespiratory and Vascular Dysfunction (WTC-CaRVD), inflammatory changes and attenuation of antioxidant potential after PM exposure. Early detection of vascular disease is crucial to preventing cardiovascular deaths and future work will focus on further identification of bioactive therapeutic targets.

Interstitial Lung Disease in Systemic Sclerosis: Focus on Early Detection and Intervention

Systemic sclerosis (SSc) is a progressive and often devastating disease characterized by autoimmune dysfunction, vasculopathy, and fibrosis. Interstitial lung disease (ILD) is identified in the majority of patients with SSc and is the leading cause of SSc-related mortality. Although clinical manifestations and ILD severity vary among patients, lung function typically declines to the greatest extent during the first 3-4 years after disease onset. We aim to provide an overview of SSc-associated ILD (SSc-ILD) with a focus on current and emerging tools for early diagnosis of ILD and current and novel treatments under investigation. Early detection of ILD provides the opportunity for early therapeutic intervention, which could improve patient outcomes. Thoracic high-resolution computed tomography is the most effective method of identifying ILD in patients with SSc; it enables detection of mild lung abnormalities and plays an important role in monitoring disease progression. Cyclophosphamide and mycophenolate mofetil are the most commonly prescribed treatments for SSc-ILD. Recently, nintedanib (an antifibrotic) was approved by the Food and Drug Administration for patients with SSc-ILD; it is indicated for slowing the rate of decline in pulmonary function. However, there is a need for additional effective and well-tolerated disease-modifying therapy. Ongoing studies are evaluating other antifibrotics and novel agents. We envision that early detection of lung involvement, combined with the emergence and integration of novel therapies, will lead to improved outcomes in patients with SSc-ILD.

Small pulmonary granuloma is often misdiagnosed as lung cancer by positron emission tomography/computer tomography in diabetic patients

OBJECTIVES

A small pulmonary granuloma (SPG) is often misdiagnosed as lung cancer in diabetic patients by positron emission tomography/computed tomography (PET/CT). The present study was conducted to investigate whether diabetes is the influencing factor and to determine other related factors that have an impact on the diagnostic results following PET/CT examination.

METHODS

All clinical, imaging and pathological data of patients diagnosed with pulmonary nodules by PET/CT from January 2004 to December 2017 in our department were collected. Patients with an SPG who were wrongly diagnosed with lung cancer by PET/CT were enrolled (n = 79). The propensity score matching method was used to create a comparable control adenocarcinoma group (n = 395). Maximum standard uptake values, diabetes and fasting blood-glucose (FBG) were determined and analysed.

RESULTS

The average maximum standard uptake values in the 2 groups were comparable (P = 0.801). Maximum standard uptake values in 5 subsections were not significantly different between the 2 groups (P = 0.135). The odds ratio (OR) of 3.326 [95% confidence interval (CI) 1.671-6.623] for diabetes favoured misdiagnosis and was statistically significant (P < 0.001). Furthermore, in patients with high FBG levels (≥7.0 mmol/l), the risk of misdiagnosis of SPG increased significantly compared with normal FBG level (OR 2.601, 95% CI 1.174-5.761; P = 0.015).

CONCLUSIONS

Diabetes and high FBG level were the influencing factors in the false-positive results of lung cancer by PET/CT examination.