FDG PET of infection and inflammation

Glucose metabolism and radiodensity of abdominal adipose tissue: A 5-year longitudinal study in a large PET cohort

OBJECTIVE

18F-Fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) allows noninvasive assessment of glucose metabolism and radiodensity in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT). We aimed to address the effects of ageing and metabolic factors on abdominal adipose tissue.

DESIGN, PATIENTS AND MEASUREMENTS

We retrospectively analyzed data from 435 healthy men (mean 42.8 years) who underwent a health check-up programme twice, at baseline and the 5-year follow-up. The mean standardized uptake value (SUV) was measured using SAT and VAT and divided by the liver SUV. The mean Hounsfield units (HU) of the SAT and VAT were measured from the CT scans. The effects of clinical variable clusters on SUVR were investigated using Bayesian hierarchical modelling; metabolic cluster (BMI, waist-to-hip ratio, fat percentage, muscle percentage*-1, HOMA-IR), blood pressure (systolic, diastolic), glucose (fasting plasma glucose level, HbA1c) and C-reactive protein.

RESULTS

All the clinical variables changed during the 5-year follow-up period. The SUVR and HU of the VAT increased during follow-up; however, those of the SAT did not change. SUVR and HU were positively correlated with both VAT and SAT. SAT and VAT SUVR were negatively associated with metabolic clusters.

CONCLUSIONS

Ageing led to increased glucose metabolism and radiodensity in VAT, but not in SAT. VAT may reflect the ageing process more directly than SAT. Glucose metabolism was higher and radiodensity was lower in VAT than in SAT, probably owing to differences in gene expression and lipid density. Both glucose metabolism and radiodensity of VAT and SAT reflect metabolic status.

Focal incidental colorectal fluorodeoxyglucose uptake: Should it be spotlighted?

Fluorine-18 fluorodeoxyglucose (F-18 FDG) positron emission tomography/computed tomography (PET/CT) has emerged as a cornerstone in cancer evaluation imaging, with a well-established history spanning several years. This imaging modality, encompassing the examination of the body from the base of the skull to the upper thighs, comprehensively covers the chest and abdominopelvic regions in a singular scan, allowing for a holistic assessment of nearly the entire body, including areas of marginal interest. The inherent advantage of this expansive scan range lies in its potential to unveil unexpected incidental abnormal hypermetabolic areas. The identification of incidental focal FDG uptake within colorectal regions during PET/CT scans is not an uncommon occurrence, albeit fraught with challenges associated with non-specific FDG uptake. The presence of benign colorectal lesions or physiological uptake poses a particular obstacle, as these may manifest with FDG uptake levels that mimic malignancy. Consequently, physicians are confronted with a diagnostic dilemma when encountering abnormal FDG uptake in unexpected colorectal areas. Existing studies have presented divergent results concerning these uptakes. Standardized uptake value and its derivatives have served as pivotal metrics in quantifying FDG uptake in PET images. In this article, we aim to succinctly explore the distinctive characteristics of FDG, delve into imaging findings, and elucidate the clinical significance of incidental focal colorectal uptake. This discussion aims to contribute valuable insights into the nuanced interpretation of such findings, fostering a comprehensive understanding.

Unexpected focal fluorodeoxyglucose uptake in main organs; pass through or pass by?

Since the inception of fluorine-18 fluorodeoxyglucose (F-18 FDG), positron emission tomography/computed tomography (PET/CT) utilizing F-18 FDG has become widely accepted as a valuable imaging modality in the field of oncology, with global prevalence in clinical practice. Given that a single Torso PET/CT scan encompasses the anatomical region from the skull base to the upper thigh, the detection of incidental abnormal focal hypermetabolism in areas of limited clinical interest is both feasible and not uncommon. Numerous investigations have been undertaken to delineate the distinctive features of these findings, yet the outcomes have proven inconclusive. The incongruent results of these studies present a challenge for physicians, leaving them uncertain about the appropriate course of action. This article provides a succinct overview of the characteristics of fluorodeoxyglucose, followed by a comprehensive discussion of the imaging findings and clinical significance associated with incidental focal abnormal F-18 FDG activity in several representative organs. In conclusion, while the prevalence of unrecognized malignancy varies across organs, malignancies account for a substantial proportion, ranging from approximately one-third to over half, of incidental focal uptake. In light of these rates, physicians are urged to exercise vigilance in not disregarding unexpected uptake, facilitating more assured clinical decisions, and advocating for further active evaluation.

18F-FDG PET/CT in left ventricular assist device infections: In-depth characterization and clinical implications

BACKGROUND

Previous retrospective studies suggest a good diagnostic performance of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET)/computed tomography (CT) in left ventricular assist device (LVAD) infections. Our aim was to prospectively evaluate the role of PET/CT in the characterization and impact on clinical management of LVAD infections.

METHODS

A total of 40 patients (aged 58 [53-62] years) with suspected LVAD infection and 5 controls (aged 69 [64-71] years) underwent 18F-FDG-PET/CT. Four LVAD components were evaluated: exit site and subcutaneous driveline (peripheral), pump pocket, and outflow graft. The location with maximal uptake was considered the presumed site of infection. Infection was confirmed by positive culture (exit site or blood) and/or surgical findings.

RESULTS

Visual uptake was present in 40 patients (100%) in the infection group vs 4 (80%) control subjects. For each individual component, the presence of uptake was more frequent in the infection than in the control group. The location of maximal uptake was most frequently the pump pocket (48%) in the infection group and the peripheral components (75%) in the control group. Maximum standard uptake values (SUVmax) were higher in the infection than in the control group: SUVmax (average all components): 6.9 (5.1-8.5) vs 3.8 (3.7-4.3), p = 0.002; SUVmax (location of maximal uptake): 10.6 ± 4.0 vs 5.4 ± 1.9, p = 0.01. Pump pocket infections were more frequent in patients with bacteremia than without bacteremia (79% vs 31%, p = 0.011). Pseudomonas (32%) and methicillin-susceptible Staphylococcus aureus (29%) were the most frequent pathogens and were associated with pump pocket infections, while Staphylococcus epidermis (11%) was associated with peripheral infections. PET/CT affected the clinical management of 83% of patients with infection, resulting in surgical debridement (8%), pump exchange (13%), and upgrade in the transplant listing status (10%), leading to 8% of urgent transplants.

CONCLUSIONS

18F-FDG-PET/CT enables the diagnosis and characterization of the extent of LVAD infections, which can significantly affect the clinical management of these patients.

18F-FDG PET-CT Scans in Oncology Patients Treated with Hyaluronic Acid Filler: Not Always a Pitfall

The use of hyaluronic acid (HA) fillers in oncology patients undergoing PET-CT scans is a topic of debate due to potential interference with imaging accuracy. A 54-year-old female, postmelanoma metastasectomy in the parotid region with subsequent facial nerve palsy (FNP), received HA filler injections for facial symmetry and functional restoration. Follow-up PET-CT scans showed no interference or artifacts attributable to HA injection, allowing for accurate imaging results. This case suggests that HA fillers administered in oncology patients may not universally pose challenges or disrupt PET-CT imaging interpretation. Due to the possible false positives induced by fillers, the inclusion of aesthetic treatments in patients' anamnesis is a crucial step to accurately interpret PET-CT images. Although maintaining high level of caution in interpreting PET-CT results after filler injection is essential, our case emphasizes the safety of this procedure in oncology patients undergoing follow-up PET-CT scans.

Development of Oxadiazolone Activity-Based Probes Targeting FphE for Specific Detection of Staphylococcus aureus Infections

Staphylococcus aureus (S. aureus) is a major human pathogen that is responsible for a wide range of systemic infections. Since its propensity to form biofilms in vivo poses formidable challenges for both detection and treatment, tools that can be used to specifically image S. aureus biofilms are highly valuable for clinical management. Here, we describe the development of oxadiazolone-based activity-based probes to target the S. aureus-specific serine hydrolase FphE. Because this enzyme lacks homologues in other bacteria, it is an ideal target for selective imaging of S. aureus infections. Using X-ray crystallography, direct cell labeling, and mouse models of infection, we demonstrate that oxadiazolone-based probes enable specific labeling of S. aureus bacteria through the direct covalent modification of the FphE active site serine. These results demonstrate the utility of the oxadizolone electrophile for activity-based probes and validate FphE as a target for the development of imaging contrast agents for the rapid detection of S. aureus infections.

Bones on fire: illuminating osteomyelitis through the radiant lens of 18F-FDG PET/CT

Osteomyelitis is an inflammatory process that is caused by an infecting microorganism and leads to progressive bone destruction and loss. Osteomyelitis can occur at any age and can involve any bone. The infection can be limited to a single portion of the bone or can involve several regions, such as marrow, cortex, periosteum, and the surrounding soft tissue. Early and accurate diagnosis plays a crucial role in reducing unnecessary treatment measures, improving the patient's prognosis, and minimizing time and financial costs. In recent years, the use of functional metabolic imaging has become increasingly widespread. Among them, 18F-FDG PET/CT has emerged as a cutting-edge imaging modality that combines anatomical and functional metabolic information. It has seen rapid development in the field of infectious diseases. 18F-FDG PET/CT has been demonstrated to yield acceptable diagnostic accuracy in a number of infectious and inflammatory diseases. This review aims to provide information about the 18F-FDGPET/CT in the use of chronic osteomyelitis,osteomyelitis secondary to a contiguous focus of infection and osteomyelitis associated with peripheral vascular disease.

Deep convolutional neural network for differentiating between sarcoidosis and lymphoma based on [18F]FDG maximum-intensity projection images

OBJECTIVES

To compare the [18F]FDG PET/CT findings of untreated sarcoidosis and malignant lymphoma (ML) and develop convolutional neural network (CNN) models to differentiate between these diseases using maximum intensity projection (MIP) [18F]FDG PET images.

METHODS

We retrospectively collected data on consecutive patients newly diagnosed with sarcoidosis and ML who underwent [18F]FDG PET/CT before treatment. Two nuclear radiologists reviewed the images. CNN models were created using MIP PET images and evaluated with k-fold cross-validation. The points of interest were visualized using gradient-weighted class activation mapping (Grad-CAM).

RESULTS

A total of 56 patients with sarcoidosis and 62 patients with ML were included. Patients with sarcoidosis had more prominent FDG accumulation in the mediastinal lymph nodes and lung lesions, while those with ML had more prominent accumulation in the cervical lymph nodes (all p < 0.001). For the mediastinal lymph nodes, sarcoidosis patients had significant FDG accumulation in the level 2, 4, 7, and 10 lymph nodes (all p < 0.01). Otherwise, the accumulation in ML patients tended to be in the level 1 lymph nodes (p = 0.08). The CNN model using frontal and lateral MIP images achieved an average accuracy of 0.890 (95% CI: 0.804-0.977), a sensitivity of 0.898 (95% CI: 0.782-1.000), a specificity of 0.907 (95% CI: 0.799-1.000), and an area under the curve of 0.963 (95% CI: 0.899-1.000). Grad-CAM showed that the model focused on the sites of abnormal FDG accumulation.

CONCLUSIONS

CNN models based on differences in FDG accumulation sites archive high performance in differentiating between sarcoidosis and ML.

CLINICAL RELEVANCE STATEMENT

We developed a CNN model using MIP images of [18F]FDG PET/CT to distinguish between sarcoidosis and malignant lymphoma. It achieved high performance and could be useful in diagnosing diseases with involvement across organs and lymph nodes.

KEY POINTS

• There are differences in FDG distribution when comparing whole-body [18F]FDG PET/CT findings in patients with sarcoidosis and malignant lymphoma before treatment. • Convolutional neural networks, a type of deep learning technique, trained with maximum-intensity projection PET images from two angles showed high performance. • A deep learning model that utilizes differences in FDG distribution may be helpful in differentiating between diseases with lesions that are characteristically widespread among organs and lymph nodes.

Update on Pediatric Nuclear Medicine in Acute Care

Various radiopharmaceuticals are available for imaging pediatric patients in the acute care setting. This article focuses on the common applications used on a pediatric patient in acute care. To confirm the clinical diagnosis of brain death, brain scintigraphy is considered accurate and has been favorably compared with other methods of detecting the presence or absence of cerebral blood flow. Ventilation-perfusion lung scans are easy and safe to perform with less radiation exposure than computed tomography pulmonary angiography and remain an appropriate procedure to perform on children with suspected pulmonary embolism as a first imaging test in a hemodynamically stable patient with no history of lung disease and normal chest radiograph. 99mTc-pertechnetate scintigraphy (Meckel's scan) is the best noninvasive procedure to establish the diagnosis of ectopic gastric mucosa in Meckel's diverticulum. 99mTcred blood cell scintigraphy generally is useful for assessing lower GI bleeding in patients from any cause. Hepatobiliary scintigraphy is the most accurate diagnostic imaging modality for acute cholecystitis. 99mTc-dimercaptosuccinic acid scintigraphy is the simplest, and the most reliable and sensitive method for the early diagnosis of focal or diffuse functional cortical damage. 99mTcmercaptoacetyltriglycine scintigraphy is used to evaluate for early and late complications of renal transplantation. Bone scintigraphy is a sensitive and noninvasive technique for diagnosis of bone disorders such as osteomyelitis and fracture. 18F-fluorodeoxyglucose-positron emission tomography could be valuable in the evaluation of fever of unknown origin in pediatric patients, with better sensitivity and significantly less radiation exposure than a gallium scan. Moving forward, further refinement of pediatric radiopharmaceutical administered activities, including dose reduction, greater radiopharmaceutical applications, and updated consensus guidelines is warranted, with the use of radionuclide imaging likely to increase.

Metabolic Positron Emission Tomography in Breast Cancer

Metabolic PET, most commonly 18F-fluorodeoxyglucose (FDG) PET/computed tomography (CT), has had a major impact on the imaging of breast cancer and can have important clinical applications in appropriate patients. While limited for screening, FDG PET/CT outperforms conventional imaging in locally advanced breast cancer. FDG PET/CT is more sensitive than conventional imaging in assessing treatment response, accurately predicting complete response or nonresponse in early-stage cases. It also aids in determining disease extent and treatment response in the metastatic setting. Further research, including randomized controlled trials with FDG and other metabolic agents such as fluciclovine, is needed for optimal breast cancer imaging.

[From conventional to cutting edge imaging in rheumatology]

Imaging instruments, such as conventional X‑ray, ultrasound and magnetic resonance imaging (MRI) are now fully established and highly valued in the care of rheumatology patients. However, the information provided by these imaging modalities in their current form is of limited utility for the prognostic prediction of individual patient outcomes. This article illuminates an important part of the development of imaging and shows that the vision of personalized medicine is becoming increasingly more tangible due to the further development of high-resolution imaging techniques, molecular imaging and artificial intelligence.

Imaging in inflammatory arthritis: progress towards precision medicine

Imaging techniques such as ultrasonography and MRI have gained ground in the diagnosis and management of inflammatory arthritis, as these imaging modalities allow a sensitive assessment of musculoskeletal inflammation and damage. However, these techniques cannot discriminate between disease subsets and are currently unable to deliver an accurate prediction of disease progression and therapeutic response in individual patients. This major shortcoming of today's technology hinders a targeted and personalized patient management approach. Technological advances in the areas of high-resolution imaging (for example, high-resolution peripheral quantitative computed tomography and ultra-high field MRI), functional and molecular-based imaging (such as chemical exchange saturation transfer MRI, positron emission tomography, fluorescence optical imaging, optoacoustic imaging and contrast-enhanced ultrasonography) and artificial intelligence-based data analysis could help to tackle these challenges. These new imaging approaches offer detailed anatomical delineation and an in vivo and non-invasive evaluation of the immunometabolic status of inflammatory reactions, thereby facilitating an in-depth characterization of inflammation. By means of these developments, the aim of earlier diagnosis, enhanced monitoring and, ultimately, a personalized treatment strategy looms closer.

Noninvasive assessment of metabolic turnover during inflammation by in vivo deuterium magnetic resonance spectroscopy

Background

Inflammation and metabolism exhibit a complex interplay, where inflammation influences metabolic pathways, and in turn, metabolism shapes the quality of immune responses. Here, glucose turnover is of special interest, as proinflammatory immune cells mainly utilize glycolysis to meet their energy needs. Noninvasive approaches to monitor both processes would help elucidate this interwoven relationship to identify new therapeutic targets and diagnostic opportunities.

Methods

For induction of defined inflammatory hotspots, LPS-doped Matrigel plugs were implanted into the neck of C57BL/6J mice. Subsequently, 1H/19F magnetic resonance imaging (MRI) was used to track the recruitment of 19F-loaded immune cells to the inflammatory focus and deuterium (2H) magnetic resonance spectroscopy (MRS) was used to monitor the metabolic fate of [6,6-2H2]glucose within the affected tissue. Histology and flow cytometry were used to validate the in vivo data.

Results

After plug implantation and intravenous administration of the 19F-containing contrast agent, 1H/19F MRI confirmed the infiltration of 19F-labeled immune cells into LPS-doped plugs while no 19F signal was observed in PBS-containing control plugs. Identification of the inflammatory focus was followed by i.p. bolus injection of deuterated glucose and continuous 2H MRS. Inflammation-induced alterations in metabolic fluxes could be tracked with an excellent temporal resolution of 2 min up to approximately 60 min after injection and demonstrated a more anaerobic glucose utilization in the initial phase of immune cell recruitment.

Conclusion

1H/2H/19F MRI/MRS was successfully employed for noninvasive monitoring of metabolic alterations in an inflammatory environment, paving the way for simultaneous in vivo registration of immunometabolic data in basic research and patients.

Semiquantitative evaluation of 68Ga-DOTANOC uptake in the normal myocardium: establishment of reference values

BACKGROUND

To ascertain presence of physiological uptake and derive standardized uptake values (SUV) of 68Ga-DOTANOC in normal myocardium and establish reference values.

METHODS AND RESULTS

Dedicated cardiac 68Ga-DOTANOC PET/CT studies of patients referred for evaluation of cardiac sarcoidosis (CS) or myocarditis and found to be normal on visual assessment and on cardiac MRI were analyzed semiquantitatively. The studies were acquired 45-60 minutes after intravenous injection of 111-185 MBq of 68Ga-DOTANOC. Myocardial SUVmax normalized to lean body mass (SUVmax_lbm) values for septum, anterior wall, proximal lateral wall, distal lateral wall, inferior wall, and apical region were 1.12 ± .39, 1.09 ± .42, 1.26 ± .49, 1.16 ± .40, 1.23 ± .39, and 1.05 ± .40, respectively. Myocardial SUVmax_lbm-to-blood pool SUVmean_lbm ratios were calculated for each region and 95th percentile values of these ratios were considered the upper limit of normal. 95th percentile values of myocardial SUVmax_lbm-to-blood pool SUVmean_lbm ratio for the corresponding regions were 1.70, 1.70, 2.00 1.95, 2.05, and 1.70, respectively.

CONCLUSION

There can be physiological uptake of 68Ga-DOTANOC in normal myocardium and the reference values of semiquantitative parameters established in this study may be employed as a corroborative tool for visual assessment in patients undergoing 68Ga-DOTANOC PET/CT for suspected CS or myocarditis.

Preclinical evaluation of 2-[18F]fluorodeoxysorbitol as a tracer for targeted imaging of Enterobacterales infection

Fluorine-18-fluorodeoxyglucose ([¹⁸F]FDG) positron emission tomography (¹⁸F-FDG-PET) is widely used for the detection of inflammatory and infectious diseases. Although this modality has proven to be a useful diagnostic tool, reliable distinction of bacterial infection from sterile inflammation or even from a malignancy remains challenging. Therefore, there is a need for bacteria-specific tracers for PET imaging that facilitate a reliable distinction of bacterial infection from other pathology. The present study was aimed at exploring the potential of 2-[¹⁸F]-fluorodeoxysorbitol ([¹⁸F]FDS) as a tracer for detection of Enterobacterales infections. Sorbitol is a sugar alcohol that is commonly metabolized by bacteria of the Enterobacterales order, but not by mammalian cells, which makes it an attractive candidate for targeted bacterial imaging. The latter is important in view of the serious clinical implications of infections caused by Enterobacterales. Here we demonstrate that sorbitol-based PET can be applied to detect a broad range of clinical bacterial isolates not only in vitro, but also in blood and ascites samples from patients suffering from Enterobacterales infections. Notably, the possible application of [¹⁸F]FDS is not limited to Enterobacterales since Pseudomonas aeruginosa and Corynebacterium jeikeium also showed substantial uptake of this tracer. We conclude that [¹⁸F]FDS is a promising tracer for PET-imaging of infections caused by a group of bacteria that can cause serious invasive disease.

Implant Imaging: Perspectives of Nuclear Imaging in Implant, Biomaterial, and Stem Cell Research

Until now, very few efforts have been made to specifically trace, monitor, and visualize implantations, artificial organs, and bioengineered scaffolds for tissue engineering in vivo. While mainly X-Ray, CT, and MRI methods have been used for this purpose, the applications of more sensitive, quantitative, specific, radiotracer-based nuclear imaging techniques remain a challenge. As the need for biomaterials increases, so does the need for research tools to evaluate host responses. PET (positron emission tomography) and SPECT (single photon emission computer tomography) techniques are promising tools for the clinical translation of such regenerative medicine and tissue engineering efforts. These tracer-based methods offer unique and inevitable support, providing specific, quantitative, visual, non-invasive feedback on implanted biomaterials, devices, or transplanted cells. PET and SPECT can improve and accelerate these studies through biocompatibility, inertivity, and immune-response evaluations over long investigational periods at high sensitivities with low limits of detection. The wide range of radiopharmaceuticals, the newly developed specific bacteria, and the inflammation of specific or fibrosis-specific tracers as well as labeled individual nanomaterials can represent new, valuable tools for implant research. This review aims to summarize the opportunities of nuclear-imaging-supported implant research, including bone, fibrosis, bacteria, nanoparticle, and cell imaging, as well as the latest cutting-edge pretargeting methods.

Imaging of Endocarditis and Cardiac Device-Related Infections: An Update

IE is a deadly disease requiring prompt diagnosis for adequate patient's management. The diagnosis requires the integration of clinical signs, microbiology data and imaging data and proper discussion within a multidisciplinary team, the endocarditis team. Since the introduction of ¹⁸F-FDG-PET/CT and WBC SPECT/CT in the diagnostic algorithm of PVE the nuclear medicine imaging specialists is active part of the Endocarditis Team, requiring proper knowledge of dedicated imaging acquisition protocols, expertise for imaging reading and interpretations to select the best test or combination of tests for each specific clinical situation. In this manuscript, we will review the main technical aspects of each imaging procedure, the most recent literature with specific regards to special challenging populations and provide clinical examples.

Evaluation of L-Alanine Metabolism in Bacteria and Whole-Body Distribution with Bacterial Infection Model Mice

The World Health Organization has cautioned that antimicrobial resistance (AMR) will be responsible for an estimated 10 million deaths annually by 2050. To facilitate prompt and accurate diagnosis and treatment of infectious disease, we investigated the potential of amino acids for use as indicators of bacterial growth activity by clarifying which amino acids are taken up by bacteria during the various growth phases. In addition, we examined the amino acid transport mechanisms that are employed by bacteria based on the accumulation of labeled amino acids, Na⁺ dependence, and inhibitory effects using a specific inhibitor of system A. We found that ³H-L-Ala accurately reflects the proliferative activity of Escherichia coli K-12 and pathogenic EC-14 in vitro. This accumulation in E. coli could be attributed to the amino acid transport systems being different from those found in human tumor cells. Moreover, biological distribution assessed in infection model mice with EC-14 using ³H-L-Ala showed that the ratio of ³H-L-Ala accumulated in infected muscle to that in control muscle was 1.20. By detecting the growth activity of bacteria in the body that occurs during the early stages of infection by nuclear imaging, such detection methods may result in expeditious diagnostic treatments for infectious diseases.

MRI/PET multimodal imaging of the innate immune response in skeletal muscle and draining lymph node post vaccination in rats

The goal of this study was to utilize a multimodal magnetic resonance imaging (MRI) and positron emission tomography (PET) imaging approach to assess the local innate immune response in skeletal muscle and draining lymph node following vaccination in rats using two different vaccine platforms (AS01 adjuvanted protein and lipid nanoparticle (LNP) encapsulated Self-Amplifying mRNA (SAM)). MRI and ¹⁸FDG PET imaging were performed temporally at baseline, 4, 24, 48, and 72 hr post Prime and Prime-Boost vaccination in hindlimb with Cytomegalovirus (CMV) gB and pentamer proteins formulated with AS01, LNP encapsulated CMV gB protein-encoding SAM (CMV SAM), AS01 or with LNP carrier controls. Both CMV AS01 and CMV SAM resulted in a rapid MRI and PET signal enhancement in hindlimb muscles and draining popliteal lymph node reflecting innate and possibly adaptive immune response. MRI signal enhancement and total ¹⁸FDG uptake observed in the hindlimb was greater in the CMV SAM vs CMV AS01 group (↑2.3 - 4.3-fold in AUC) and the MRI signal enhancement peak and duration were temporally shifted right in the CMV SAM group following both Prime and Prime-Boost administration. While cytokine profiles were similar among groups, there was good temporal correlation only between IL-6, IL-13, and MRI/PET endpoints. Imaging mass cytometry was performed on lymph node sections at 72 hr post Prime and Prime-Boost vaccination to characterize the innate and adaptive immune cell signatures. Cell proximity analysis indicated that each follicular dendritic cell interacted with more follicular B cells in the CMV AS01 than in the CMV SAM group, supporting the stronger humoral immune response observed in the CMV AS01 group. A strong correlation between lymph node MRI T2 value and nearest-neighbor analysis of follicular dendritic cell and follicular B cells was observed (r=0.808, P<0.01). These data suggest that spatiotemporal imaging data together with AI/ML approaches may help establish whether in vivo imaging biomarkers can predict local and systemic immune responses following vaccination.

Reversal of spatial memory impairment by phosphodiesterase 3 inhibitor cilostazol is associated with reduced neuroinflammation and increased cerebral glucose uptake in aged male mice

The nucleotide second messenger 3', 5'-cyclic adenosine monophosphate (cAMP) and 3', 5'-cyclic guanosine monophosphate (cGMP) mediate fundamental functions of the brain, including learning and memory. Phosphodiesterase 3 (PDE3) can hydrolyze both cAMP and cGMP and appears to be involved in the regulation of their contents in cells. We previously demonstrated that long-term administration of cilostazol, a PDE3 inhibitor, maintained good memory performance in aging mice. Here, we report on studies aimed at determining whether cilostazol also reverses already-impaired memory in aged male mice. One month of oral 1.5% cilostazol administration in 22-month-old mice reversed age-related declines in hippocampus-dependent memory tasks, including the object recognition and the Morris water maze. Furthermore, cilostazol reduced neuroinflammation, as evidenced by immunohistochemical staining, and increased glucose uptake in the brain, as evidence by positron emission tomography (PET) with 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG). These results suggest that already-expressed memory impairment in aged male mice that depend on cyclic nucleotide signaling can be reversed by inhibition of PDE3. The reversal of age-related memory impairments may occur in the central nervous system, either through cilostazol-enhanced recall or strengthening of weak memories that otherwise may be resistant to recall.

Dynamic FDG-PET imaging for differentiating metastatic from non-metastatic lymph nodes of lung cancer

OBJECTIVES

18F-fluorodeoxyglucose (FDG) PET/CT has been widely used in tumor diagnosis, staging, and response evaluation. To determine an optimal therapeutic strategy for lung cancer patients, accurate staging is essential. Semi-quantitative standardized uptake value (SUV) is known to be affected by multiple factors and may fail to differentiate between benign and malignant lesions. Lymph nodes (LNs) in the mediastinal and pulmonary hilar regions with high FDG uptake due to granulomatous lesions such as tuberculosis, which has a high prevalence in China, pose a diagnostic challenge. This study aims to evaluate the diagnostic value of the quantitative metabolic parameters derived from dynamic 18F-FDG PET/CT in differentiating metastatic and non-metastatic LNs in lung cancer.

METHODS

One hundred and eight patients with pulmonary nodules were enrolled to perform 18F-FDG PET/CT dynamic + static imaging with informed consent. One hundred and thirty-five LNs in 29 lung cancer patients were confirmed by pathology. Static image analysis parameters including LN-SUVmax, LN-SUVmax/primary tumor SUVmax (LN-SUVmax/PT-SUVmax), mediastinal blood pool SUVmax (MBP-SUVmax), LN-SUVmax/MBP-SUVmax, and LN-SUVmax/short diameter. Quantitative parameters including K1, k2, k3 and Ki and of each LN were obtained by applying the irreversible two-tissue compartment model using in-house Matlab software. Ki/K1 was computed subsequently as a separate marker. We further divided the LNs into mediastinal LNs (N=82) and pulmonary hilar LNs (N=53). Wilcoxon rank-sum test or Independent-samples T-test and receiver-operating characteristic (ROC) analysis was performed on each parameter to compare the diagnostic efficacy in differentiating lymph node metastases from inflammatory uptake. P<0.05 were considered statistically significant.

RESULTS

Among the 135 FDG-avid LNs confirmed by pathology, 49 LNs were non-metastatic, and 86 LNs were metastatic. LN-SUVmax, MBP-SUVmax, LN-SUVmax/MBP-SUVmax, and LN-SUVmax/short diameter couldn't well differentiate metastatic from non-metastatic LNs (P>0.05). However, LN-SUVmax/PT-SUVmax have good performance in the differential diagnosis of non-metastatic and metastatic LNs (P=0.039). Dynamic metabolic parameters in addition to k3, the parameters including K1, k2, Ki, and Ki/K1, on the other hand, have good performance in the differential diagnosis of metastatic and non-metastatic LNs (P=0.045, P=0.001, P=0.001, P=0.001, respectively). For ROC analysis, the metabolic parameters Ki (AUC of 0.672 [0.579-0.765], sensitivity 0.395, specificity 0.918) and Ki/K1 (AUC of 0.673 [0.580-0.767], sensitivity 0.570, specificity 0.776) have good performance in the differential diagnosis of metastatic from non-metastatic LNs than SUVmax (AUC of 0.596 [0.498-0.696], sensitivity 0.826, specificity 0.388), included the mediastinal region and pulmonary hilar region.

CONCLUSION

Compared with SUVmax, quantitative parameters such as K1, k2, Ki and Ki/K1 showed promising results for differentiation of metastatic and non-metastatic LNs with high uptake. The Ki and Ki/K1 had a high differential diagnostic value both in the mediastinal region and pulmonary hilar region.

Tailoring Materials for Epilepsy Imaging: From Biomarkers to Imaging Probes

Excising epileptic foci (EF) is the most efficient approach for treating drug-resistant epilepsy (DRE). However, owing to the vast heterogeneity of epilepsies, EF in one-third of patients cannot be accurately located, even after exhausting all current diagnostic strategies. Therefore, identifying biomarkers that truly represent the status of epilepsy and fabricating probes with high targeting specificity are prerequisites for identifying the "concealed" EF. However, no systematic summary of this topic has been published. Herein, the potential biomarkers of EF are first summarized and classified into three categories: functional, molecular, and structural aberrances during epileptogenesis, a procedure of nonepileptic brain biasing toward epileptic tissue. The materials used to fabricate these imaging probes and their performance in defining the EF in preclinical and clinical studies are highlighted. Finally, perspectives for developing the next generation of probes and their challenges in clinical translation are discussed. In general, this review can be helpful in guiding the development of imaging probes defining EF with improved accuracy and holds promise for increasing the number of DRE patients who are eligible for surgical intervention.

Septic Pulmonary Emboli Detected by 18F-FDG PET/CT in a Patient with Central Venous Catheter-Related Staphylococcus aureus Bacteremia

We describe a case of ¹⁸F-FDG PET/CT detecting septic pulmonary emboli in a patient with Staphylococcus aureus catheter-related bloodstream infection (CRBSI). The patient, who had an implantable venous access port for chemotherapy, underwent ¹⁸F-FDG PET/CT to diagnose unsuspected infectious foci. The PET/CT examination made it possible to offer a suggestive diagnosis and yielded metastatic infectious foci.

In vivo Imaging of Cannabinoid Type 2 Receptors: Functional and Structural Alterations in Mouse Model of Cerebral Ischemia by PET and MRI

PURPOSE

Stroke is one of the most prevalent vascular diseases. Non-invasive molecular imaging methods have the potential to provide critical insights into the temporal dynamics and follow alterations of receptor expression and metabolism in ischemic stroke. The aim of this study was to assess the cannabinoid type 2 receptor (CB2R) levels in transient middle cerebral artery occlusion (tMCAO) mouse models at subacute stage using positron emission tomography (PET) with our novel tracer [18F]RoSMA-18-d6 and structural imaging by magnetic resonance imaging (MRI).

PROCEDURES

Our recently developed CB2R PET tracer [18F]RoSMA-18-d6 was used for imaging neuroinflammation at 24 h after reperfusion in tMCAO mice. The RNA expression levels of CB2R and other inflammatory markers were analyzed by quantitative real-time polymerase chain reaction using brain tissues from tMCAO (1 h occlusion) and sham-operated mice. [18F]fluorodeoxyglucose (FDG) was included for evaluation of the cerebral metabolic rate of glucose (CMRglc). In addition, diffusion-weighted imaging and T2-weighted imaging were performed for anatomical reference and delineating the lesion in tMCAO mice.

RESULTS

mRNA expressions of inflammatory markers TNF-α, Iba1, MMP9 and GFAP, CNR2 were increased to 1.3-2.5 fold at 24 h after reperfusion in the ipsilateral compared to contralateral hemisphere of tMCAO mice, while mRNA expression of the neuronal marker MAP-2 was markedly reduced to ca. 50 %. Reduced [18F]FDG uptake was observed in the ischemic striatum of tMCAO mouse brain at 24 h after reperfusion. Although higher activity of [18F]RoSMA-18-d6 in ex vivo biodistribution studies and higher standard uptake value ratio (SUVR) were detected in the ischemic ipsilateral compared to contralateral striatum in tMCAO mice, the in vivo specificity of [18F]RoSMA-18-d6 was confirmed only in the CB2R-rich spleen.

CONCLUSIONS

This study revealed an increased [18F]RoSMA-18-d6 measure of CB2R and a reduced [18F]FDG measure of CMRglc in the ischemic striatum of tMCAO mice at subacute stage. [18F]RoSMA-18-d6 might be a promising PET tracer for detecting CB2R alterations in animal models of neuroinflammation without neuronal loss.

Gut Microbiota Dynamics in Relation to Long-COVID-19 Syndrome: Role of Probiotics to Combat Psychiatric Complications

Increasing numbers of patients who recover from COVID-19 report lasting symptoms, such as fatigue, muscle weakness, dementia, and insomnia, known collectively as post-acute COVID syndrome or long COVID. These lasting symptoms have been examined in different studies and found to influence multiple organs, sometimes resulting in life-threating conditions. In this review, these symptoms are discussed in connection to the COVID-19 and long-COVID-19 immune changes, highlighting oral and psychiatric health, as this work focuses on the gut microbiota’s link to long-COVID-19 manifestations in the liver, heart, kidney, brain, and spleen. A model of this is presented to show the biological and clinical implications of gut microbiota in SARS-CoV-2 infection and how they could possibly affect the therapeutic aspects of the disease. Probiotics can support the body’s systems in fighting viral infections. This review focuses on current knowledge about the use of probiotics as adjuvant therapies for COVID-19 patients that might help to prevent long-COVID-19 complications.

An Ag2S@ZIF-Van nanosystem for NIR-II imaging of bacterial-induced inflammation and treatment of wound bacterial infection

Bacterial diseases pose a serious threat to human health. Continued development of precise diagnostic methods and synergistic therapy techniques for combating bacteria are needed. Herein a hybrid nanosystem (Ag₂S@ZIF-Van NS) was constructed by one-step self-assembly of Zn²⁺, vancomycin (Van) and Ag₂S quantum dots (QDs). The nanosystem possesses excellent second near-infrared transparency window (NIR-II) fluorescence properties (∼1200 nm emission wavelength), good photothermal conversion properties, and biocompatibility. The material system enables precise, targeted NIR-II fluorescent imaging of bacterial inflammation in vivo as well as promoting anti-bacterial and wound healing effects.

Changes in Metabolism as a Diagnostic Tool for Lung Cancer: Systematic Review

Lung cancer is the leading cause of cancer-related mortality worldwide, with five-year survival rates varying from 3–62%. Screening aims at early detection, but half of the patients are diagnosed in advanced stages, limiting therapeutic possibilities. Positron emission tomography-computed tomography (PET-CT) is an essential technique in lung cancer detection and staging, with a sensitivity reaching 96%. However, since elevated 18F-fluorodeoxyglucose (¹⁸F-FDG) uptake is not cancer-specific, PET-CT often fails to discriminate between malignant and non-malignant PET-positive hypermetabolic lesions, with a specificity of only 23%. Furthermore, discrimination between lung cancer types is still impossible without invasive procedures. High mortality and morbidity, low survival rates, and difficulties in early detection, staging, and typing of lung cancer motivate the search for biomarkers to improve the diagnostic process and life expectancy. Metabolomics has emerged as a valuable technique for these pitfalls. Over 150 metabolites have been associated with lung cancer, and several are consistent in their findings of alterations in specific metabolite concentrations. However, there is still more variability than consistency due to the lack of standardized patient cohorts and measurement protocols. This review summarizes the identified metabolic biomarkers for early diagnosis, staging, and typing and reinforces the need for biomarkers to predict disease progression and survival and to support treatment follow-up.

PET/MRI in Pediatric Neuroimaging: Primer for Clinical Practice

Modern pediatric imaging seeks to provide not only exceptional anatomic detail but also physiologic and metabolic information of the pathology in question with as little radiation penalty as possible. Hybrid PET/MR imaging combines exquisite soft-tissue information obtained by MR imaging with functional information provided by PET, including metabolic markers, receptor binding, perfusion, and neurotransmitter release data. In pediatric neuro-oncology, PET/MR imaging is, in many ways, ideal for follow-up compared with PET/CT, given the superiority of MR imaging in neuroimaging compared with CT and the lower radiation dose, which is relevant in serial imaging and long-term follow-up of pediatric patients. In addition, although MR imaging is the main imaging technique for the evaluation of spinal pathology, PET/MR imaging may provide useful information in several clinical scenarios, including tumor staging and follow-up, treatment response assessment of spinal malignancies, and vertebral osteomyelitis. This review article covers neuropediatric applications of PET/MR imaging in addition to considerations regarding radiopharmaceuticals, imaging protocols, and current challenges to clinical implementation.

Increased levels of acidic free-N-glycans, including multi-antennary and fucosylated structures, in the urine of cancer patients

We recently reported increased levels of urinary free-glycans in some cancer patients. Here, we focused on cancer related alterations in the levels of high molecular weight free-glycans. The rationale for this study was that branching, elongation, fucosylation and sialylation, which lead to increases in the molecular weight of glycans, are known to be up-regulated in cancer. Urine samples from patients with gastric cancer, pancreatic cancer, cholangiocarcinoma and colorectal cancer and normal controls were analyzed. The extracted free-glycans were fluorescently labeled with 2-aminopyridine and analyzed by multi-step liquid chromatography. Comparison of the glycan profiles revealed increased levels of glycans in some cancer patients. Structural analysis of the glycans was carried out by performing chromatography and mass spectrometry together with enzymatic or chemical treatments. To compare glycan levels between samples with high sensitivity and selectivity, simultaneous measurements by reversed-phase liquid chromatography-selected ion monitoring of mass spectrometry were also performed. As a result, three lactose-core glycans and 78 free-N-glycans (one phosphorylated oligomannose-type, four sialylated hybrid-type and 73 bi-, tri- and tetra-antennary complex-type structures) were identified. Among them, glycans with α1,3-fucosylation ((+/− sialyl) Lewis X), triply α2,6-sialylated tri-antennary structures and/or a (Man3)GlcNAc1-core displayed elevated levels in cancer patients. However, simple α2,3-sialylation and α1,6-core-fucosylation did not appear to contribute to the observed increase in the level of glycans. Interestingly, one tri-antennary free-N-glycan that showed remarkable elevation in some cancer patients contained a unique Glcβ1-4GlcNAc-core instead of the common GlcNAc2-core at the reducing end. This study provides further insights into free-glycans as potential tumor markers and their processing pathways in cancer.

Positron emission tomography/magnetic resonance imaging in musculoskeletal benign conditions

A wide spectrum of benign musculoskeletal (orthopedic and rheumatological) conditions affect the general population. Collectively, these are common, and they can inflict significant morbidity with resultant negative impact on the quality of life of patients. For many of these conditions, there is established evidence for research and clinical use of PETCT and MRI for assessment of disease. Introduction of integrated PET/MRI around a decade ago brought optimism that combining the strength of PET and MRI techniques on a single platform could have synergistic effect to benefit imaging assessment of patients, including in the context of benign musculoskeletal conditions. This review specifically focuses on the progress that has been made. This aims to showcase clinical studies derived primarily from the integrated PET/MRI platforms for the evaluation of common orthopedic and rheumatological conditions. Despite enthusiasm and progress by early adopters of the PET/MRI technology, significant barriers are present for its wider adoption, validation, and translation to routine clinical practice. Attenuation correction is a particular challenge which affects regions close to the skeleton and impacts PET/MRI assessment of musculoskeletal disorders. Continued effort on research and validation, as well as promotion of its multimodal multiparametric capability to clinical and pharmaceutical stakeholders, and increased availability through increased adoption of PET/MRI scanners internationally, may accelerate its translation into routine clinical practice in this domain.

Comparison of L- and D-Amino Acids for Bacterial Imaging in Lung Infection Mouse Model

The effectiveness of L- and D-amino acids for detecting the early stage of infection in bacterial imaging was compared. We evaluated the accumulation of ³H-L-methionine (Met), ³H-D-Met, ³H-L-alanine (Ala), and ³H-D-Ala in E. coli EC-14 and HaCaT cells. Biological distribution was assessed in control and lung-infection-model mice with EC-14 using ³H-L- and D-Met, and ¹⁸F-FDG. A maximum accumulation of ³H-L- and D-Met, and ³H-L- and D-Ala occurred in the growth phase of EC-14 in vitro. The accumulation of ³H-L-Met and L-Ala was greater than that of ³H-D-Met and D-Ala in both EC-14 and HaCaT cells. For all radiotracers, the accumulation was greater in EC-14 than in HaCaT cells at early time points. The accumulation was identified at 5 min after injection in EC-14, whereas the accumulation gradually increased in HaCaT cells over time. There was little difference in biodistribution between ³H-L-and D-Met except in the brain. ³H-L- and D-Met were sensitive for detecting areas of infection after the spread of bacteria throughout the body, whereas ¹⁸F-FDG mainly detected primary infection areas. Therefore, ¹¹C-L- and D-Met, radioisotopes that differ only in terms of ³H labeling, could be superior to ¹⁸F-FDG for detecting bacterial infection in lung-infection-model mice.

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.

Common Skeletal Neoplasms and Nonneoplastic Lesions at 18F-FDG PET/CT

Numerous primary and metastatic osseous lesions and incidental osseous findings are encountered at fluorine 18 (¹⁸F) fluorodeoxyglucose (FDG) PET/CT. These lesions show varying degrees of FDG uptake. Malignancies are generally more FDG avid than are benign lesions, but many exceptions exist. Although aggressive lesions tend to be more FDG avid than nonaggressive lesions, this concept holds true particularly for lesions of the same histologic subtype. In addition, some benign osseous processes such as Paget disease have variable degrees of FDG avidity on the basis of disease metabolic activity. This creates a diagnostic dilemma for radiologists and clinicians, especially in patients with known malignancies, and can result in unnecessary diagnostic imaging or interventions for incidental osseous lesions. Evaluation of morphologic CT characteristics of osseous lesions at FDG PET/CT can be a valuable adjunct to metabolic analysis to further characterize lesions, enhance diagnostic and staging accuracy, and avoid unnecessary invasive biopsy procedures. The authors review the common primary and metastatic bone lesions at FDG PET/CT, with an emphasis on morphologic CT assessment of lesions to help narrow the differential diagnosis. Imaging manifestations of common incidental nonneoplastic bone lesions at FDG PET/CT are discussed to provide information on differentiation of these lesions from osseous neoplasms. The guidelines of the National Comprehensive Cancer Network (NCCN) for common primary osseous malignancies are also summarized. Online supplemental material is available for this article. ^©RSNA, 2021.

18F-Fluciclovine Avid Axillary Lymph Nodes After COVID-19 Vaccination on PET/CT for Suspected Recurrence of Prostate Cancer

Abnormally increased ¹⁸F-FDG avidity of axillary lymph nodes has become a frequent diagnostic dilemma on PET/CT in the current climate of global vaccinations directed against severe acute respiratory syndrome coronavirus 2. This avidity is due to the inflammatory response evoked by vaccines and the nonspecific nature of ¹⁸F-FDG uptake, which is increased in both malignant and inflammatory processes. Similarly, ¹⁸F-fluciclovine, an amino acid analog indicated for the assessment of biochemical recurrence of prostate cancer, may also demonstrate nonspecific inflammatory uptake. We report a case of ¹⁸F-fluciclovine PET/CT obtained for concern about prostate cancer. In this case, isolated avid lymph nodes were seen in the left axilla. A screening questionnaire revealed that the patient had recently received the second dose of the Pfizer-BioNTech coronavirus disease 2019 vaccine in his left shoulder, and hence, the uptake was determined to be reactive.

Dose escalation biodistribution, positron emission tomography/computed tomography imaging and dosimetry of a highly specific radionuclide-labeled non-blocking nanobody

BACKGROUND

Immunotherapy is a valuable option for cancer treatment, and the curative effect of anti-PD-1/PD-L1 therapy correlates closely with PD-L1 expression levels. Positron emission tomography (PET) imaging of PD-L1 expression is feasible using ⁶⁸Ga-NOTA-Nb109 nanobody. ⁶⁸Ga-NOTA-Nb109 was generated by radionuclide (⁶⁸Ga) labeling of Nb109 using a NOTA chelator. To facilitate clinical trials, we explored the optimal dose range of ⁶⁸Ga-NOTA-Nb109 in BALB/c A375-hPD-L1 tumor-burdened nude mice and C57-hPD-L1 transgenic MC38-hPD-L1 tumor-burdened mice by administration of a single intravenous dose of ⁶⁸Ga-NOTA-Nb109 and confirmed the dose in cynomolgus monkeys. The biodistribution data of cynomolgus monkey PET images were extrapolated to estimate the radiation dose for the adult male and female using OLINDA2.1 software.

RESULTS

⁶⁸Ga-NOTA-Nb109 was stable in physiologic media and human serum. Ex vivo biodistribution studies showed rapid and specific uptake in A375-hPD-L1 or MC38-hPD-L1 tumors. The estimated ED₅₀ was approximately 5.4 µg in humanized mice. The injected mass (0.3-100 µg in nude mice and approximately 1-100 µg in humanized mice) greatly influenced the general biodistribution, with a better tumor-to-background ratio acquired at lower doses of Nb109 (0.3-10 µg in nude mice and approximately 1 µg in humanized mice), indicating maximum uptake in tumors at administered mass doses below the estimated ED_50. Therefore, a single 15-μg/kg dose was adopted for the PET/CT imaging in the cynomolgus monkey. The highest specific and persistent uptake of the tracer was detected in the spleen, except the levels in the kidney and urine bladder, which was related to metabolism and excretion. The spleen-to-muscle ratio of the tracer exceeded 10 from immediately to 4 h after administration, indicating that the dose was appropriate. The estimated effective dose was calculated to yield a radiation dose of 4.1 mSv to a patient after injecting 185 MBq of ⁶⁸Ga-NOTA-Nb109.

CONCLUSION

⁶⁸Ga-NOTA-Nb109 showed specific accumulation in hPD-L1 xenografts in ex vivo biodistribution studies and monkey PET/CT imaging. The dose escalation distribution data provided a recommended dose range for further use, and the safety of the tracer was confirmed in dosimetry studies.

Xanthogranulomatous Pyelonephritis: A Narrative Review with Current Perspectives on Diagnostic Imaging and Management, Including Interventional Radiology Techniques

Xanthogranulomatous Pyelonephritis (XGP) is a rare, chronic granulomatous inflammatory condition thought to arise secondary to a combination of obstruction, recurrent bacterial infection and an incomplete immune response resulting in focal or diffuse renal destruction. This destruction may be profound with the potential to infiltrate surrounding tissues and viscera. The imaging features of XGP can be ambiguous, mimicking malignancy, tuberculosis (TB) and malakoplakia earning the title of "the great imitator". Computed tomography (CT) is the mainstay of XGP diagnosis and staging, accurately quantifying the stone burden and staging the renal destruction, including the extent of extra-renal spread. Although some cases in children have been successfully treated with antibiotics alone, nephrectomy remains the most common treatment for XGP in adults. The specific management strategy needs to be tailored to individual patients given the potential constellation of renal and extrarenal abnormalities. Although XGP has classically required open nephrectomy, laparoscopic nephrectomy has an increasing role to play arising from the advancement in laparoscopic skills, technique and instruments. Nephron-sparing partial nephrectomy may be considered in the focal form. Interventional radiology techniques most often play a supportive role, eg, in the initial drainage of associated abscesses, but have rarely achieved renal salvage. This narrative review seeks to synthesise the existing literature and summarise the radiological approach and interventional radiology management situated in a clinical context.

Leptin resistance before and after obesity: evidence that tissue glucose uptake underlies adipocyte enlargement and liver steatosis/steatohepatitis in Zucker rats from early-life stages

BACKGROUND

Leptin resistance occurs in obese patients, but its independent contribution to adiposity and the accompanying metabolic diseases, i.e., diabetes, liver steatosis, and steatohepatitis, remains to be established. This study was conducted in an extreme model of leptin resistance to investigate mechanisms initiating diabetes, fat expansion, liver steatosis, and inflammatory disease, focusing on the involvement of glucose intolerance and organ-specific glucose uptake in brown and subcutaneous adipose tissues (BAT, SAT) and in the liver.

METHODS

We studied preobese and adult Zucker rats (fa/fa, fa/+ ) during fasting or glucose loading to assess glucose tolerance. Relevant pancreatic and intestinal hormonal levels were measured by Milliplex. Imaging of ¹⁸F-fluorodeoxyglucose by positron emission tomography was used to quantify glucose uptake in SAT, BAT, and liver, and evaluate its relationship with adipocyte size and biopsy-proven nonalcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH).

RESULTS

Preobese fa/fa pups showed impaired glucose tolerance, adipocyte enlargement, hepatic microsteatosis, and lobular inflammation, with elevated hepatic post-glucose load glucose uptake and production. Adult fa/fa rats had more severe glucose intolerance, fasting hyperglycemia, hormonal abnormalities, elevated glucose uptake in SAT and BAT, and more markedly in the liver, together with macrosteatosis, and highly prevalent hepatic inflammation. Organ glucose uptake was proportional to the degree of fat accumulation and tissue inflammation and was able to dissect healthy from NAFLD and NAFLD/NASH livers. Most severe NASH livers showed a decline in glucose uptake and liver enzymes.

CONCLUSIONS

In fa/fa Zucker rats, leptin resistance leads to glucose intolerance, mainly due to hepatic glucose overproduction, preceding obesity, and explaining pancreatic and intestinal hormonal changes and fat accumulation in adipocytes and hepatocytes. Our data support the involvement of liver glucose uptake in the pathogenesis of liver inflammatory disease. Its potential as more generalized biomarker or diagnostic approach remains to be established outside of our leptin-receptor-deficient rat model.

Brain-gut-liver interactions across the spectrum of insulin resistance in metabolic fatty liver disease

Metabolic associated fatty liver disease (MAFLD), formerly named "nonalcoholic fatty liver disease" occurs in about one-third of the general population of developed countries worldwide and behaves as a major morbidity and mortality risk factor for major causes of death, such as cardiovascular, digestive, metabolic, neoplastic and neuro-degenerative diseases. However, progression of MAFLD and its associated systemic complications occur almost invariably in patients who experience the additional burden of intrahepatic and/or systemic inflammation, which acts as disease accelerator. Our review is focused on the new knowledge about the brain-gut-liver axis in the context of metabolic dysregulations associated with fatty liver, where insulin resistance has been assumed to play an important role. Special emphasis has been given to digital imaging studies and in particular to positron emission tomography, as it represents a unique opportunity for the noninvasive in vivo study of tissue metabolism. An exhaustive revision of targeted animal models is also provided in order to clarify what the available preclinical evidence suggests for the causal interactions between fatty liver, dysregulated endogenous glucose production and insulin resistance.

Performance Evaluation of a Deep Learning System for Differential Diagnosis of Lung Cancer With Conventional CT and FDG PET/CT Using Transfer Learning and Metadata

PURPOSE

We aimed to evaluate the performance of a deep learning system for differential diagnosis of lung cancer with conventional CT and FDG PET/CT using transfer learning (TL) and metadata.

METHODS

A total of 359 patients with a lung mass or nodule who underwent noncontrast chest CT and FDG PET/CT prior to treatment were enrolled retrospectively. All pulmonary lesions were classified by pathology (257 malignant, 102 benign). Deep learning classification models based on ResNet-18 were developed using the pretrained weights obtained from ImageNet data set. We propose a deep TL model for differential diagnosis of lung cancer using CT imaging data and metadata with SUVmax and lesion size derived from PET/CT. The area under the receiver operating characteristic curve (AUC) of the deep learning model was measured as a performance metric and verified by 5-fold cross-validation.

RESULTS

The performance metrics of the conventional CT model were generally better than those of the CT of PET/CT model. Introducing metadata with SUVmax and lesion size derived from PET/CT into baseline CT models improved the diagnostic performance of the CT of PET/CT model (AUC = 0.837 vs 0.762) and the conventional CT model (AUC = 0.877 vs 0.817).

CONCLUSIONS

Deep TL models with CT imaging data provide good diagnostic performance for lung cancer, and the conventional CT model showed overall better performance than the CT of PET/CT model. Metadata information derived from PET/CT can improve the performance of deep learning systems.

Pitfalls in interpretation of FDG PET/CT: Septic pulmonary emboli mimicking metastases in a case of gastric carcinoma

Inflammatory lesions may sometimes show intense tracer uptake and mimic neoplastic lesions on (18) F-fluoro-deoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT). We report one such false positive case on FDG PET/CT, where septic pulmonary emboli (SPE) mimicked pulmonary metastases. A 45-year-old man with stomach cancer had an indwelling central venous catheter (CVC) in situ while on neoadjuvant chemotherapy. He underwent FDG PET/CT scan for response assessment and the images revealed multiple, intensely FDG avid, peripheral, lung nodules with feeding vessels, which were suspicious for pulmonary metastases. A day later, the patient developed fever with chills and his blood culture showed bacterial growth (Enterobacter cloacae). A provisional diagnosis of SPE from an infected CVC was made. Chemotherapy was withheld, CVC removed, and the catheter tip was sent for bacterial culture. Following a 4-week course of antibiotic treatment, the patient became afebrile. Culture from the CVC tip grew the same organism, as was seen earlier in the patient's blood culture, thus pin-pointing the source of infection in our case. Diagnosis of SPE was clinched when follow-up CT chest done after completion of antibiotic course showed complete resolution of the lung lesions.

Correlation of 18F-FDG PET/CT uptake with severity of MRI findings and epidural steroid injection sites in patients with symptomatic degenerative disease of the lumbar spine: a retrospective study

PURPOSE

We aimed to retrospectively correlate 18F-fluorodeoxyglucose (18F-FDG) metabolic activity with lumbar spine magnetic resonance imaging (MRI) findings and epidural steroid injection sites in patients with symptomatic degenerative disease of the lumbar spine.

METHODS

A database search was conducted for patients receiving epidural injections <12 months after a positron emission tomography/computed tomography (PET/CT). Maximum standard uptake values (SUVmax) were measured at the facet joints, neural foramina, and spinal canal. Severity of facet arthrosis, disc degeneration, neuroforaminal, and canal stenosis was determined on MRI using previously described grading scales. Spearman rank coefficient assessed association between PET/CT FDG uptake and severity of MRI findings. The SUVmax was also compared with injection sites.

RESULTS

Twenty-five patients were included, comprising MRI (n=19) and injection (n=22 patients; 18 interlaminar, 8 transforaminal) groups. Injections were performed an average of 2.6 months after PET/CT. The greatest SUVmax occurred at the L5-S1 spinal canal (mean SUVmax = 2.25). A statistically significant, positive correlation between uptake and grade of spinal canal stenosis was seen only at L4-L5 (r=0.60, p = 0.007). No other significant association was found with spinal canal or neuroforaminal stenosis, or grade of facet joint or disc degeneration. All patients reported symptomatic improvement after injections with mean pain score improvement of 4.4 on a 10-point scale (SD, 2.9). There was moderate agreement between sites of epidural injection and highest SUVmax (κ= 0.591, p < 0.001).

CONCLUSION

18F-FDG metabolic activity on PET/CT corresponds with MRI findings about the lumbar spinal column, but there is no significant correlation between severity of MRI findings and radiotracer uptake. Given the moderate agreement between metabolic activity and levels of symptomatic spinal stenosis, further studies are warranted to fully evaluate the diagnostic potential of FDG PET/CT as a surrogate for guiding epidural injections.

Discovery of potential imaging and therapeutic targets for severe inflammation in COVID-19 patients

The Coronavirus disease 2019 (COVID-19) has been spreading worldwide with rapidly increased number of deaths. Hyperinflammation mediated by dysregulated monocyte/macrophage function is considered to be the key factor that triggers severe illness in COVID-19. However, no specific targeting molecule has been identified for detecting or treating hyperinflammation related to dysregulated macrophages in severe COVID-19. In this study, previously published single-cell RNA-sequencing data of bronchoalveolar lavage fluid cells from thirteen COVID-19 patients were analyzed with publicly available databases for surface and imageable targets. Immune cell composition according to the severity was estimated with the clustering of gene expression data. Expression levels of imaging target molecules for inflammation were evaluated in macrophage clusters from single-cell RNA-sequencing data. In addition, candidate targetable molecules enriched in severe COVID-19 associated with hyperinflammation were filtered. We found that expression of SLC2A3, which can be imaged by [¹⁸F]fluorodeoxyglucose, was higher in macrophages from severe COVID-19 patients. Furthermore, by integrating the surface target and drug-target binding databases with RNA-sequencing data of severe COVID-19, we identified candidate surface and druggable targets including CCR1 and FPR1 for drug delivery as well as molecular imaging. Our results provide a resource in the development of specific imaging and therapy for COVID-19-related hyperinflammation.

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.

PET/CT Variants and Pitfalls in Breast Cancers

There are a number of normal variants and pitfalls which are important to consider when evaluating F-18 Fluorodeoxyglucose (FDG) with Positron Emission Tomography (PET) in breast cancer patients. Although FDG-PET is not indicated for the initial diagnosis of breast cancer, focally increased glucose metabolism within breast tissue represents a high likelihood for a neoplastic process and requires further evaluation. Focally increased glucose metabolism is not unique to breast cancer. Other malignancies such as lymphoma, metastases from solid tumors as well as inflammatory changes also may demonstrate increased glucose metabolism either within the breast or at other sites throughout the body. Importantly, benign breast disease may also exhibit increased glucose metabolism, limiting the specificity of FDG-PET. Breast cancer has a wide range of metabolic activity attributed to tumor heterogeneity and breast cancer subtype. Intracellular signaling pathways regulating tumor glucose utilization contribute to these pitfalls of PET/CT in breast cancer. The evaluation of axillary lymph nodes by FDG-PET is less accurate than sentinel lymph node procedure, however is very accurate in identifying level II and III axillary lymph node metastases or retropectoral metastases. It is important to note that non-malignant inflammation in lymph nodes are often detected by modern PET/CT technology. Therefore, particular consideration should be given to recent vaccinations, particularly to COVID-19, which can commonly result in increased metabolic activity of axillary nodes. Whole body FDG-PET for staging of breast cancer requires specific attention to physiologic variants of FDG distribution and a careful comparison with co-registered anatomical imaging. The most important pitfalls are related to inflammatory changes including sarcoidosis, sarcoid like reactions, and other granulomatous diseases as well as secondary neoplastic processes.

Role of 18F-FDG PET/CT in the Assessment of Response to Antitubercular Chemotherapy and Identification of Treatment Endpoint in Patients With Tuberculosis of the Joints: A Pilot Study

AIMS

The aim of this study was to explore the utility of 18F-FDG PET/CT in the assessment of response to antitubercular treatment (ATT) and identification of treatment endpoint.

PATIENTS AND METHODS

Forty patients (mean age, 35.3 years; 27 men) with clinically, radiologically, and histopathologically proven joint tuberculosis prospectively underwent clinical, biochemical, and PET/CT evaluation at baseline and after ~6, 12, and 18 months of ATT. Two patients were lost to follow-up, and 1 defaulted treatment. The remaining 37 were followed up until complete response (CR) was achieved. Images were visually and quantitatively (SUVmax ratio and metabolically active disease volume [MV]) evaluated by 2 experienced nuclear medicine physicians.

RESULTS

Knee (n = 18) and ankle (n = 7) were the most frequently involved sites. The median MV and SUVmax ratio at baseline were 85.10 mL and 7.21, respectively. Five patients had noncontiguous vertebral involvement, 12 had pulmonary lesions, 2 had abscesses, 6 had mediastinal, and 30 had local lymph nodal involvement. Complete response was seen in 1/39, 11/37, and 30/37 patients after 6, 12, and 18 months of ATT. Significant reductions in visual analog scale score, tenderness, joint swelling, SUVmax ratios, and MVs (Friedman test, P < 0.001) were seen after each follow-up. The median time-to-CR in skeletal lesions was significantly longer than extraskeletal lesions (591 vs 409 days; Wilcoxon signed-rank test, P < 0.001). Time-to-CR in joint lesions positively correlated with MV at first follow-up (Pearson = 0.452, P = 0.005) and negatively correlated with percentage change in MV (first follow-up from baseline) (Pearson = -0.620, P < 0.001). ROC analysis yielded a cutoff of ≤71% reduction in MV at first follow-up (80.8% sensitivity, 81.8% specificity) to predict extension of ATT beyond 12 months. Using ROC analysis at second follow-up, a cutoff of ≤12.67 mL (for CR) was derived and was validated in patients at the third follow-up, with an accuracy of 84.4%. Patients with CR in PET/CT maintained disease-free state during a mean follow-up of 271 days.

CONCLUSIONS

18F-FDG PET/CT is an excellent tool in estimating total disease burden, assessing response to ATT and identification of treatment endpoint in joint tuberculosis.