[68Ga]Ga-FAPI-04 PET/CT on assessing Crohn's disease intestinal lesions

Distinguishing benign from malignant lesions with high [68 Ga]Ga-FAPI-04 uptake in oncology patients: Insights from dynamic total-body [68 Ga]Ga-FAPI-04 PET/CT

BACKGROUND AND PURPOSE

While [68 Ga]Ga-FAPI-04 PET/CT is widely used in various malignant tumors diagnosis, its specificity is challenged by high uptake in benign lesions such as inflammatory lymphadenopathy, bone fractures, and degenerative changes. This study aimed to quantitatively assess and characterize the metabolic heterogeneity of [68 Ga]Ga-FAPI-04 uptake in benign and malignant lesions using dynamic total-body PET/CT.

METHODS

Dynamic total-body [68 Ga]Ga-FAPI-04 PET/CT scans (0-60 min post-injection) were performed on 17 oncology patients. Time-activity curves (TACs) were generated for benign and malignant lesions with high [68 Ga]Ga-FAPI-04 uptake. The reversible two-tissue compartment model (2T4k) was used to derive kinetic metrics, including K1, k2, k3, k4, vB and VT. Receiver operating characteristic (ROC) curve analysis was used to determine the cut-off values for differentiating benign and malignant lesions.

RESULTS

The study included 58 malignant and 55 inflammatory lesions with high [68 Ga]Ga-FAPI-04 uptake. Malignant lesions exhibited higher K1 (0.277 ± 0.217 ml/ccm/min vs. 0.221 ± 0.216 ml/ccm/min, P = 0.011), vB (0.042 ± 0.007 vs. 0.013 ± 0.004, P < 0.001), and lower k3 (0.267 ± 0.041 1/min vs. 0.481 ± 0.085 1/min, P = 0.008) compared to benign lesions. Lesions were classified into low, medium, and high-probability groups for being malignant based on K1, k3 and vB values, with probabilities of 0%, 50.7%, and 92.0%, respectively (P < 0.001).

CONCLUSIONS

Kinetic metrics, particularly K1, k3 and vB values, show promise as imaging biomarkers for distinguishing between benign and malignant lesions with high [68 Ga]Ga-FAPI-04 uptake in oncology patients. These metrics reflect the metabolic heterogeneity of the lesions and may improve diagnostic accuracy in oncological imaging.

Intense fibroblast activation protein inhibitor localization around the site of embolized gastroduodenal artery in a patient with metachronous pancreatic adenocarcinoma: A potential pitfall in positron imaging

68Gallium-Fibroblast activation protein inhibitor (68Ga-FAPI) positron emission tomography/computed tomography (PET/CT) is increasingly used for evaluating various epithelial neoplasms. Despite addressing some pitfalls, many remain unacknowledged. This report details a 77-year-old man with suspected pancreatic malignancy who underwent a 68Ga-FAPI PET/CT scan post-gastroduodenal coil embolization for upper gastrointestinal bleeding. The scan revealed intense 68Ga-FAPI uptake in the pancreatic body and tail malignancy and around the embolized gastroduodenal artery, indicating a healing process. This highlights the importance of understanding FAPI expression in recent surgical sites for accurate radiologic interpretation.

68 Ga-FAPI PET/CT Depicted the Fibrosis of Ischemic Colitis

ABSTRACT

Ischemic colitis is the most common form of ischemic bowel disease; identification of ischemic colitis with PET/CT is rare. We present a case of unexplained ischemic colitis in a 66-year-old man who underwent 18 F-FDG PET/CT to exclude intestinal malignancy and was subsequently recruited in a clinical trial regarding 68 Ga-FAPI. 18 F-FDG PET/CT showed intense activity in the intestinal lumen where mucosa had chronic inflammation. Conversely, 68 Ga-FAPI PET/CT revealed high tracer uptake in the intestinal wall and adjacent mesentery. Our case showed the different distribution pattern of 18 F-FDG and 68 Ga-FAPI in ischemic colitis.

The fibroblast activation protein alpha as a biomarker of pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a rare, chronic, and progressive interstitial lung disease with an average survival of approximately 3 years. The evolution of IPF is unpredictable, with some patients presenting a relatively stable condition with limited progression over time, whereas others deteriorate rapidly. In addition to IPF, other interstitial lung diseases can lead to pulmonary fibrosis, and up to a third have a progressive phenotype with the same prognosis as IPF. Clinical, biological, and radiological risk factors of progression were identified, but no specific biomarkers of fibrogenesis are currently available. A recent interest in the fibroblast activation protein alpha (FAPα) has emerged. FAPα is a transmembrane serine protease with extracellular activity. It can also be found in a soluble form, also named anti-plasmin cleaving enzyme (APCE). FAPα is specifically expressed by activated fibroblasts, and quinoline-based specific inhibitors (FAPI) were developed, allowing us to visualize its distribution in vivo by imaging techniques. In this review, we discuss the use of FAPα as a useful biomarker for the progression of lung fibrosis, by both its assessment in human fluids and/or its detection by imaging techniques and immunohistochemistry.

Role of artificial intelligence in Crohn's disease intestinal strictures and fibrosis

Crohn's disease (CD) is a chronic inflammatory disorder of the gastrointestinal tract. Intestinal fibrosis or stricture is one of the most prevalent complications in CD with a high recurrence rate. Manual examination of intestinal fibrosis or stricture by physicians may be biased or inefficient. A rapid development of artificial intelligence (AI) technique in recent years facilitates the detection of existing or possible intestinal fibrosis and stricture in CD through various modalities, including endoscopy, imaging examination, and serological biomarkers. We reviewed the articles on AI application in diagnosing intestinal fibrosis and stricture in CD during the past decade and categorized them into three aspects based on the detection methods, and found that AI helps accurate and expedient identification and prediction of intestinal fibrosis and stenosis in CD.

The Role of Fibroblast Activation Protein Inhibitor Positron Emission Tomography in Inflammatory and Infectious Diseases: An Updated Systematic Review

The role of fibroblast activation protein inhibitor (FAPI) positron emission tomography/computed tomography (PET/CT) is emerging for the assessment of non-oncological diseases, such as inflammatory and infectious diseases, even if the evidence in the literature is still in its initial phases. We conducted a systematic search of Scopus, PubMed/MEDLINE, Embase, and Cochrane library databases for studies published before 31 December 2023 reporting infectious and inflammatory disease imaging with FAPI PET/CT. We included twenty-one studies for a total of 1046 patients. The most frequent disease studied was lung interstitial disease, investigated in six studies for a total of 200 patients, followed by bone and joint diseases in two studies and 185 patients, IgG4-related disease in 53 patients, and Crohn's disease in 30 patients. Despite the heterogeneity of studies in terms of study design and technical features, FAPI PET/CT showed a high detection rate and diagnostic role. Moreover, when compared with 2-[18F]FDG PET/CT (n = 7 studies), FAPI PET/CT seems to have better diagnostic performances. The presence of chronic inflammation and tissue remodeling, typical of immune-mediated inflammatory conditions, may be the underlying mechanism of FAPI uptake.

Fibroblast Activation Protein Inhibitor Tracers and Their Preclinical, Translational, and Clinical Status in China

Quinoline-based fibroblast activation protein (FAP) inhibitors (FAPIs) have recently emerged as a focal point in global nuclear medicine, underscored by their promising applications in cancer theranostics and the diagnosis of various nononcological conditions. This review offers an in-depth summary of the existing literature on the evolution and use of FAPI tracers in China, tracing their journey from preclinical to clinical research. Moreover, this review also assesses the diagnostic accuracy of FAPI PET for the most common cancers in China, analyzes its impact on oncologic management paradigms, and investigates the potential of FAP-targeted radionuclide therapy in patients with advanced or metastatic cancer. This review also summarizes studies using FAPI PET for nononcologic disorders in China. Thus, this qualitative overview presents a snapshot of China's engagement with FAPI tracers, aiming to guide future research endeavors.

Application Value of 68 Ga-FAPI PET/CT in the Evaluation of Myelofibrotic Diseases

PURPOSE

Fibroblast activation protein is highly expressed in neoplastic lesions and various fibrotic tissues, making it an attractive target for disease evaluation. 68 Ga-labeled fibroblast activation protein inhibitor (FAPI), a new tumor interstitial imaging agent, holds promise for evaluating myelofibrosis. Therefore, this study aimed to use 68 Ga-FAPI PET/CT for the noninvasive visualization and quantification of the extent of myelofibrosis.

PATIENTS AND METHODS

This was a prospective clinical study involving 22 patients with myelofibrosis who underwent 68 Ga-FAPI PET/CT. The uptake of 68 Ga-FAPI was measured in their respective bone marrow and spleen, and the obtained imaging findings were compared with laboratory, cytogenetic, and histopathological data.

RESULTS

68 Ga-FAPI uptake in the bone marrow was significantly and positively correlated with the myelofibrosis grade ( r > 0.8, P < 0.001). 68 Ga-FAPI PET/CT showed visually negative results in patients with grades 0-1 myelofibrosis and positive in those with grades 2-3, but the level of involvement varied. 68 Ga-FAPI PET/CT provides a noninvasive means of visualizing the extent of systemic bone marrow involvement and differentiation between the early and advanced stages of fibrosis.

CONCLUSIONS

68 Ga-FAPI PET/CT shows promise as a method for visualizing and quantifying myelofibrosis, providing suitable sites for bone marrow biopsy. The extent of 68 Ga-FAPI uptake by bone marrow increases with the progression of myelofibrosis, thus it is a simple and noninvasive measurement that can be used to evaluate the progression of myelofibrosis. Nevertheless, although 68 Ga-FAPI PET/CT has demonstrated a potential value in prognostic assessment, further confirmation is needed.

Contemporary Imaging Assessment of Strictures and Fibrosis in Crohn Disease, With Focus on Quantitative Biomarkers: From the AJR Special Series on Imaging of Fibrosis

Patients with Crohn disease commonly have bowel strictures develop, which exhibit varying degrees of inflammation and fibrosis. Differentiation of the distinct inflammatory and fibrotic components of strictures is key for the optimization of therapeutic management and for the development of antifibrotic drugs. Cross-sectional imaging techniques, including ultrasound, CT, and MRI, allow evaluation of the full thickness of the bowel wall as well as extramural complications and associated mesenteric abnormalities. Although promising data have been reported for a range of novel imaging biomarkers for detection of fibrosis and quantification of the degree of fibrosis, these biomarkers lack sufficient validation and standardization for clinical use. Additional methods, including PET with emerging radiotracers, artificial intelligence, and radiomics, are also under investigation for stricture characterization. In this review, we highlight the clinical relevance of identifying fibrosis in Crohn disease, review the histopathologic aspects of strictures in Crohn disease, summarize the morphologic imaging findings of strictures, and explore contemporary developments in the use of cross-sectional imaging techniques for detecting and characterizing intestinal strictures, with attention given to emerging quantitative biomarkers.

Tissue fibrosis induced by radiotherapy: current understanding of the molecular mechanisms, diagnosis and therapeutic advances

Cancer remains the leading cause of death around the world. In cancer treatment, over 50% of cancer patients receive radiotherapy alone or in multimodal combinations with other therapies. One of the adverse consequences after radiation exposure is the occurrence of radiation-induced tissue fibrosis (RIF), which is characterized by the abnormal activation of myofibroblasts and the excessive accumulation of extracellular matrix. This phenotype can manifest in multiple organs, such as lung, skin, liver and kidney. In-depth studies on the mechanisms of radiation-induced fibrosis have shown that a variety of extracellular signals such as immune cells and abnormal release of cytokines, and intracellular signals such as cGAS/STING, oxidative stress response, metabolic reprogramming and proteasome pathway activation are involved in the activation of myofibroblasts. Tissue fibrosis is extremely harmful to patients' health and requires early diagnosis. In addition to traditional serum markers, histologic and imaging tests, the diagnostic potential of nuclear medicine techniques is emerging. Anti-inflammatory and antioxidant therapies are the traditional treatments for radiation-induced fibrosis. Recently, some promising therapeutic strategies have emerged, such as stem cell therapy and targeted therapies. However, incomplete knowledge of the mechanisms hinders the treatment of this disease. Here, we also highlight the potential mechanistic, diagnostic and therapeutic directions of radiation-induced fibrosis.

FAPI PET/CT Imaging-An Updated Review

Despite revolutionizing the field of oncological imaging, Positron Emission Tomography (PET) with [18F]Fluorodeoxyglucose (FDG) as its workhorse is limited by a lack of specificity and low sensitivity in certain tumor subtypes. Fibroblast activation protein (FAP), a type II transmembrane glycoprotein, is expressed by cancer-associated fibroblasts (CAFs) that form a major component of the tumor stroma. FAP holds the promise to be a pan-cancer target, owing to its selective over-expression in a vast majority of neoplasms, particularly epithelial cancers. Several radiolabeled FAP inhibitors (FAPI) have been developed for molecular imaging and potential theranostic applications. Preliminary data on FAPI PET/CT remains encouraging, with extensive multi-disciplinary clinical research currently underway. This review summarizes the existing literature on FAPI PET/CT imaging with an emphasis on diagnostic applications, comparison with FDG, pitfalls, and future directions.