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

Antibiotic-Derived Radiotracers for Positron Emission Tomography: Nuclear or "Unclear" Infection Imaging?

The excellent features of non-invasive molecular imaging, its progressive technology (real-time, whole-body imaging and quantification), and global impact by a growing infrastructure for positron emission tomography (PET) scanners are encouraging prospects to investigate new concepts, which could transform clinical care of complex infectious diseases. Researchers are aiming towards the extension beyond the routinely available radiopharmaceuticals and are looking for more effective tools that interact directly with causative pathogens. We reviewed and critically evaluated (challenges or pitfalls) antibiotic-derived PET radiopharmaceutical development efforts aimed at infection imaging. We considered both radiotracer development for infection imaging and radio-antibiotic PET imaging supplementing other tools for pharmacologic drug characterization; overall, a total of 20 original PET radiotracers derived from eleven approved antibiotics.

A Case of Clinical Uncertainty Solved: Giant Cell Arteritis with Polymyalgia Rheumatica Swiftly Diagnosed with Long Axial Field of View PET

The clinical presentation of giant cell arteritis (GCA) is often nonspecific. Differentiating GCA from infectious, malignant, or other autoimmune pathology based on signs, symptoms, and laboratory parameters may therefore be difficult. Fluorine-18-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) imaging is an established tool in the diagnostic workup of GCA. An advantage of ¹⁸F-FDG-PET/CT is its ability to assist in the differential diagnosis by being able to demonstrate infection, inflammation, and malignancy when used in conjunction with clinical and laboratory data. Downsides to the use of ¹⁸F-FDG-PET/CT include its relatively low spatial resolution, associated radiation exposure, and the relatively long duration of imaging, causing limited availability and patient inconvenience. The advent of long axial field-of-view (LAFOV) PET/CT systems allows for PET imaging at a reduced imaging time or reduced tracer dose while maintaining high image quality. Here, we provide the first reported case of a patient with GCA and polymyalgia rheumatica (PMR) diagnosed using LAFOV PET/CT imaging. The patient presented in this case report had already been experiencing nonspecific symptoms for several years for which no cause was found. Lab investigations showed increased inflammatory parameters as well as persistent anemia. ¹⁸F-FDG LAFOV PET/CT attained high-quality images with clear signs of GCA and PMR even at 1 min of scan duration.

The Role of Deep Learning in Advancing Breast Cancer Detection Using Different Imaging Modalities: A Systematic Review

Breast cancer is among the most common and fatal diseases for women, and no permanent treatment has been discovered. Thus, early detection is a crucial step to control and cure breast cancer that can save the lives of millions of women. For example, in 2020, more than 65% of breast cancer patients were diagnosed in an early stage of cancer, from which all survived. Although early detection is the most effective approach for cancer treatment, breast cancer screening conducted by radiologists is very expensive and time-consuming. More importantly, conventional methods of analyzing breast cancer images suffer from high false-detection rates. Different breast cancer imaging modalities are used to extract and analyze the key features affecting the diagnosis and treatment of breast cancer. These imaging modalities can be divided into subgroups such as mammograms, ultrasound, magnetic resonance imaging, histopathological images, or any combination of them. Radiologists or pathologists analyze images produced by these methods manually, which leads to an increase in the risk of wrong decisions for cancer detection. Thus, the utilization of new automatic methods to analyze all kinds of breast screening images to assist radiologists to interpret images is required. Recently, artificial intelligence (AI) has been widely utilized to automatically improve the early detection and treatment of different types of cancer, specifically breast cancer, thereby enhancing the survival chance of patients. Advances in AI algorithms, such as deep learning, and the availability of datasets obtained from various imaging modalities have opened an opportunity to surpass the limitations of current breast cancer analysis methods. In this article, we first review breast cancer imaging modalities, and their strengths and limitations. Then, we explore and summarize the most recent studies that employed AI in breast cancer detection using various breast imaging modalities. In addition, we report available datasets on the breast-cancer imaging modalities which are important in developing AI-based algorithms and training deep learning models. In conclusion, this review paper tries to provide a comprehensive resource to help researchers working in breast cancer imaging analysis.

Disease severity and status in Stevens–Johnson syndrome and toxic epidermal necrolysis: Key knowledge gaps and research needs

Stevens–Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) are on a spectrum of cutaneous drug reactions characterized by pan-epidermal necrosis with SJS affecting < 10% of body surface area (BSA), TEN > 30%, and SJS/TEN overlap between 10 and 30%. Severity-of-illness score for toxic epidermal necrolysis (SCORTEN) is a validated tool to predict mortality rates based on age, heart rate, BSA, malignancy and serum urea, bicarbonate, and glucose. Despite improved understanding, SJS/TEN mortality remains constant and therapeutic interventions are not universally accepted for a number of reasons, including rarity of SJS/TEN; inconsistent definition of cases, disease severity, and endpoints in studies; low efficacy of interventions; and variations in treatment protocols. Apart from mortality, none of the other endpoints used to evaluate interventions, including duration of hospitalization, is sufficiently standardized to be reproducible across cases and treatment centers. Some of the gaps in SJS/TEN research can be narrowed through international collaboration to harmonize research endpoints. A case is made for an urgent international collaborative effort to develop consensus on definitions of endpoints such as disease status, progression, cessation, and complete re-epithelialization in interventional studies. The deficiencies of using BSA as the sole determinant of SJS/TEN severity, excluding internal organ involvement and extension of skin necrosis beyond the epidermis, are discussed and the role these factors play on time to healing and mortality beyond the acute stage is highlighted. The potential role of artificial intelligence, biomarkers, and PET/CT scan with radiolabeled glucose as markers of disease status, activity, and therapeutic response is also discussed.

FDG PET/CT in a Patient With Syphilis Suspected of Having Penile Cancer

ABSTRACT

A 58-year-old man with large penile wound and enlarged regional lymph node was suspected of having disseminated penile cancer. FDG PET/CT for primary staging showed high FDG uptake on penis and in several enlarged lymph nodes. However, biopsies revealed no signs of malignancy, but ulceration, inflammation, fibrosis, and spirochetes. Furthermore, Wassermann test was positive. The patient was then treated for syphilis. To our knowledge, this is the first report on FDG PET/CT in a patient suspected of having penile cancer that turned out to be syphilis. Thus, syphilis can be added to the list of benign pitfalls in FDG PET/CT.

A Role of Non-FDG Tracers in Lung Cancer?

Since the introduction of PET/CT hybrid imaging about two decades ago the landscape of oncological imaging has fundamentally changed, opening a new era of molecular imaging with emphasis on functional characterization of biological processes such as metabolism, cellular proliferation, hypoxia, apoptosis, angiogenesis and immune response. The most commonly assessed functional hallmark of cancer is the increased metabolism in tumor cells due to well-known Warburg effect, because of which FDG has been the most employed radiotracer, the so-called pan-cancer agent, in oncological imaging. However, several limitations such as low specificity and low sensitivity for several histopathological forms of lung cancer as well as high background uptake in the normal tissue of FDG imaging lead to numerous serious pitfalls. This restricts its utilization and diagnostic value in lung cancer imaging, even though this is currently considered to be the method of choice in pulmonary cancer imaging. Accurate initial tumor staging and therapy response monitoring with respect to the TNM criteria plays a crucial role in therapy planning and management in patients with lung cancer. To this end, many efforts have been made for decades to develop novel PET radiopharmaceuticals with innovative approaches that go beyond the assessment of increased glycolytic activity alone. Radiopharmaceuticals targeting DNA synthesis, amino acid metabolism, angiogenesis, or hypoxia have been extensively studied, leading to the emergence of indications for specific clinical questions or as a complementary imaging tool alongside existing conventional or FDG imaging. Nevertheless, despite some initial encouraging results, these tracers couldn't gain a widespread use and acceptance in clinical routine. However, given its mechanism of action and some initial pilot studies regarding lung cancer imaging, FAPI has emerged as a very promising alternative tool that could provide superior or comparable diagnostic performance to FDG imaging in lung cancer entities. Thus, in this review article, we summarized the current PET radiopharmaceuticals, different imaging approaches and discussed the potential benefits and clinical applications of these agents in lung cancer imaging.

Novel PET Imaging of Inflammatory Targets and Cells for the Diagnosis and Monitoring of Giant Cell Arteritis and Polymyalgia Rheumatica

Giant cell arteritis (GCA) and polymyalgia rheumatica (PMR) are two interrelated inflammatory diseases affecting patients above 50 years of age. Patients with GCA suffer from granulomatous inflammation of medium- to large-sized arteries. This inflammation can lead to severe ischemic complications (e.g., irreversible vision loss and stroke) and aneurysm-related complications (such as aortic dissection). On the other hand, patients suffering from PMR present with proximal stiffness and pain due to inflammation of the shoulder and pelvic girdles. PMR is observed in 40-60% of patients with GCA, while up to 21% of patients suffering from PMR are also affected by GCA. Due to the risk of ischemic complications, GCA has to be promptly treated upon clinical suspicion. The treatment of both GCA and PMR still heavily relies on glucocorticoids (GCs), although novel targeted therapies are emerging. Imaging has a central position in the diagnosis of GCA and PMR. While [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) has proven to be a valuable tool for diagnosis of GCA and PMR, it possesses major drawbacks such as unspecific uptake in cells with high glucose metabolism, high background activity in several non-target organs and a decrease of diagnostic accuracy already after a short course of GC treatment. In recent years, our understanding of the immunopathogenesis of GCA and, to some extent, PMR has advanced. In this review, we summarize the current knowledge on the cellular heterogeneity in the immunopathology of GCA/PMR and discuss how recent advances in specific tissue infiltrating leukocyte and stromal cell profiles may be exploited as a source of novel targets for imaging. Finally, we discuss prospective novel PET radiotracers that may be useful for the diagnosis and treatment monitoring in GCA and PMR.

Evaluation of an ImmunoPET Tracer for IL-12 in a Preclinical Model of Inflammatory Immune Responses

The immune cytokine interleukin-12 (IL-12) is involved in cancer initiation and progression, autoimmunity, as well as graft versus host disease. The ability to monitor IL-12 via imaging may provide insight into various immune processes, including levels of antitumor immunity, inflammation, and infection due to its functions in immune signaling. Here, we report the development and preclinical evaluation of an antibody-based IL-12-specific positron emission tomography (PET) tracer. To mimic localized infection and stimulate IL-12 production, BALB/c mice were administered lipopolysaccharide (LPS) intramuscularly. [⁸⁹Zr]Zr-DFO-αIL12 tracer was given one hour post LPS administration and PET images were taken after 5, 24, 48, and 72 hours. We observed significantly higher uptake in LPS-treated mice as compared to controls. Biodistribution of the tracer was evaluated in a separate cohort of mice, where tracer uptake was elevated in muscle, spleen, lymph nodes, and intestines after LPS administration. To evaluate the utility of [⁸⁹Zr]Zr-DFO-αIL12 as an indicator of antigen presenting cell activation after cancer immunotherapy, we compared PET imaging with and without intratumoral delivery of oncolytic adenovirus expressing granulocyte-macrophage colony-stimulating factor (Adv/GM-CSF), which we have shown promotes anti-tumor immunity. BALB/c mice were inoculated orthotopically with the mouse mammary carcinoma line TUBO. Once TUBO tumors reached a volume of ~50 mm³, mice were treated with either three intratumoral injections of 10⁸ PFU Adv/GM-CSF or vehicle control, given every other day. Upon the last dose, [⁸⁹Zr]Zr-DFO-αIL12 was injected intravenously and 72 hours later all mice were imaged via PET. Tumor-specific uptake of [⁸⁹Zr]Zr-DFO-αIL12 was higher in Adv/GM-CSF treated mice versus controls. Tissues were harvested after imaging, and elevated levels of macrophages and CD8⁺ T_c cells were detected in Adv/GM-CSF treated tumors by immunohistochemistry. We validated that IL-12 expression was induced after Adv/GM-CSF by qRT-PCR. Importantly, expression of genes activated by IL-12 (IFNγ, TNFα, and IL-18) were unaffected after IL-12 imaging relative to mice receiving an IgG control tracer, suggesting the tracer antibody does not significantly disrupt signaling. Our results indicate that targeting soluble cytokines such as IL-12 by PET imaging with antibody tracers may serve as a noninvasive method to evaluate the function of the immune milieu in situ.

68Ga-WRWWWW Is a Potential Positron Emission Tomography Probe for Imaging Inflammatory Diseases by Targeting Formyl Peptide Receptor 2

Inflammation plays a significant role in many physiological and pathological processes. Molecular imaging could provide functional as well as anatomical information for visualizing various inflammatory diseases. Advancements in imaging tracers for inflammation would improve the accuracy of diagnosis and monitoring, thus facilitating patient care. The positron emission tomography (PET) imaging tracer, ⁶⁸Ga-labeled antagonist peptide Trp-Arg-Trp-Trp-Trp-Trp (WRWWWW, WRW⁴), targets formyl peptide receptor 2 (FPR2), which is in turn widely distributed in a variety of tissues and is associated with many inflammatory diseases. In the current study, we aimed to investigate the potential of ⁶⁸Ga-WRW⁴ for detecting and monitoring inflammatory lesions in mice. We established an inflammation mouse model by the intramuscular injection of turpentine oil into the left thigh. WRW⁴ was labeled with ⁶⁸Ga with an overall radiochemical yield >90% and radiochemical purity >99%. ⁶⁸Ga-WRW⁴ uptake in inflamed muscle peaked on day 2 (1.14 ± 0.01 percentage of the injected dose per gram of tissue (%ID/g)) and the uptake ratio of inflammatory/normal muscle also reached a maximum (12.36 ± 2.35). Strong PET signals were detected in the left thigh at 60 min after the injection of ⁶⁸Ga-WRW⁴ in experimental mice, but weak or no signals were detected in mice in the blocking and control groups. ⁶⁸Ga-WRW⁴ uptake was in agreement with the dynamics of immune cell infiltration during the inflammatory reaction. These results suggest that ⁶⁸Ga-WRW⁴ is a promising PET tracer suitable for the noninvasive detection of FPR2 expression and for monitoring inflammatory activity in inflammation-bearing mice.

Brain Inflammation and Intracellular α-Synuclein Aggregates in Macaques after SARS-CoV-2 Infection

SARS-CoV-2 causes acute respiratory disease, but many patients also experience neurological complications. Neuropathological changes with pronounced neuroinflammation have been described in individuals after lethal COVID-19, as well as in the CSF of hospitalized patients with neurological complications. To assess whether neuropathological changes can occur after a SARS-CoV-2 infection, leading to mild-to-moderate disease, we investigated the brains of four rhesus and four cynomolgus macaques after pulmonary disease and without overt clinical symptoms. Postmortem analysis demonstrated the infiltration of T-cells and activated microglia in the parenchyma of all infected animals, even in the absence of viral antigen or RNA. Moreover, intracellular α-synuclein aggregates were found in the brains of both macaque species. The heterogeneity of these manifestations in the brains indicates the virus' neuropathological potential and should be considered a warning for long-term health risks, following SARS-CoV-2 infection.

Tumor glycolytic heterogeneity improves detection of regional nodal metastasis in patients with lung adenocarcinoma

OBJECTIVE

The diagnostic performance of ¹⁸F-FDG PET for detecting regional lymph node metastasis in resectable lung cancer is variable, and its sensitivity for adenocarcinoma is even lower. We aimed to evaluate the value of ¹⁸F-FDG PET-derived features in predicting pathological lymph node metastasis in patients with lung adenocarcinoma.

METHODS

We retrospectively analyzed pretreatment ¹⁸F-FDG PET-derived features of 126 lung adenocarcinoma patients who underwent curative surgery. A logistic regression model was used to analyze the association between study variables and pathological regional lymph node status obtained from the curative surgery. Furthermore, Cox regression analysis was used to test the effect of the study variables on survival outcomes, including disease-free survival (DFS) and overall survival (OS).

RESULTS

The primary tumor entropy (OR = 1.7, p = 0.014) and visual interpretation of regional nodes via ¹⁸F-FDG PET (OR = 2.5, p = 0.026) independently predicted pathological regional lymph node metastasis. The areas under the receiver-operating-characteristic curves were 0.631, 0.671, and 0.711 for visual interpretation, primary tumor entropy, and their combination, respectively. Based on visual interpretation, a primary tumor entropy ≥ 3.0 improved the positive predictive value of positive visual interpretation from 51.2% to 63.0%, whereas an entropy < 3.0 improved the negative predictive value of negative visual interpretation from 75.3% to 82.6%. In cases with positive visual interpretation and low entropy, or negative visual interpretation and high entropy, the nodal metastasis rates were approximately 30%. In the survival analyses, the primary tumor entropy was also independently associated with DFS (HR = 2.7, p = 0.001) and OS (HR = 4.8, p = 0.001).

CONCLUSIONS

Our preliminary results show that the primary tumor entropy may improve ¹⁸F-FDG PET visual interpretation in predicting pathological nodal metastasis in lung adenocarcinoma, and may also show a survival prognostic value. This versatile biomarker may facilitate tailored therapeutic strategies for patients with resectable lung adenocarcinoma.

Comparison of 68Ga-DOTANOC and 18F-FDG PET-CT Scans in the Evaluation of Primary Tumors and Lymph Node Metastasis in Patients With Rectal Neuroendocrine Tumors

BACKGROUND

Lymph node metastasis of rectal neuroendocrine tumors (RNETs) predicts poor prognosis. However, the assessment of lymph node metastasis remains a challenge. It has been reported that 68Ga-DOTANOC and 18F-FDG PET-CT scans could be employed in the work-up of rectal neuroendocrine tumors (RNETs). This study aimed to assess both tracers' ability to identify primary tumors and lymph node (LN) metastasis in RNETs.

METHODS

A total of 537 patients with RNETs were enrolled from January 2014 to January 2021. Both 68Ga-DOTANOC and 18F-FDG PET-CT scans were used to evaluate primary tumors and LN group metastasis. PET images were evaluated through visual and semiquantitative assessment. Receiver Operating Characteristics (ROC) curve analysis was used to investigate the performance of SUVmax of 68Ga-DOTANOC and 18F-FDG PET in predicting LN group metastasis.

RESULTS

Fifty-two patients with preoperative 68Ga-DOTANOC with 18F-FDG PET-CT scans underwent endoscopic biopsy or dissection of the primary tumor, while 11 patients underwent rectal surgery together with regional LN dissection. For primary tumors, 68Ga-DOTANOC had a sensitivity of 89.58% and a positive predictive value (PPV) of 95.56% through visual assessment, while 18F-FDG PET-CT showed 77.08% sensitivity and 97.37% PPV. For the prediction of LN group metastasis, 68Ga-DOTANOC PET-CT had 77.78% sensitivity and 91.67% specificity, while 18F-FDG PET-CT had 38.89% sensitivity and 100% specificity according to visual assessment. The area under the ROC curves (AUC) for 68Ga-DOTANOC PET/CT was 0.852 (95%CI:0.723-0.981) with an optimal SUVmax cut-off value of 2.25, while the AUC for 18F-FDG PET were 0.664 (95%CI:0.415-0.799) with an optimal SUVmax cut-off value of 1.05.

CONCLUSIONS

This study showed that 68Ga-DOTANOC PET-CT was a promising tool for detecting LN metastasis in RNETs with high sensitivity and specificity in visual assessment and semiquantitative assessment, which was better than 18F-FDG PET-CT.