Nuclear medicine and molecular imaging advances in the 21st century

FAP-Targeted Nanoparticle-based Imaging in Cancer: A Systematic Review

Background

Fibroblast Activation Protein (FAP)-targeted nanoparticles (NPs) are designed to accumulate in cancerous stroma. These NPs hold promise for imaging applications in cancer therapy.

Objective

This systematic review aimed to comprehensively explore the use of FAP-targeting NPs for cancer diagnosis through different imaging modalities.

Material and Methods

This systematic review followed the framework proposed by O'Malley and Arksey. Peer-reviewed studies were searched in the Scopus, Science Direct, PubMed, and Google Scholar databases. Eligible studies were selected, and data were extracted to investigate the FAP-targeting NPs in imaging. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline was also utilized to present the results.

Results

Five studies met the specified inclusion criteria and were finally selected for analysis. The extracted data was classified into two categories: general and specific data. The general group indicated that most studies have been conducted in Mexico and have increased since 2022, and the specific group showed that colorectal cancer and Nude mice have received the most research attention. Furthermore, FAP-targeted NPs have demonstrated superior diagnostic imaging capabilities, even compared to specific methods for each cancer type. Also, they have been safe, with no toxicity.

Conclusion

FAP-targeted NPs using different ligands, such as Fibroblast Activation Protein Inhibitor (FAPI), can accurately detect tumors and metastases, and outperform specific cancer peptides like PSMA in cancer diagnosis. They are also non-toxic and do not cause radiation damage to tissues. Therefore, FAP-targeted NPs have the potential to serve as a viable alternative to FAP-targeted radionuclides for cancer diagnosis.

Diagnostic Performances of PET/CT Using Fibroblast Activation Protein Inhibitors in Patients with Primary and Metastatic Liver Tumors: A Comprehensive Literature Review

PET/CT using radiolabeled fibroblast activation protein inhibitors (FAPIs) is a promising diagnostic tool in oncology, especially when non-increased and/or physiologically high [18F]FDG uptake (as in liver parenchyma) is observed. We aimed to review the role of PET/CT using radiolabeled FAPIs in primary and/or metastatic liver lesions, and to compare their performances with more "conventional" radiopharmaceuticals. A search algorithm based on the terms "FAPI" AND ("hepatic" OR "liver") was applied, with the last update on 1st January 2024. Out of 177 articles retrieved, 76 studies reporting on the diagnostic application of radiolabeled FAPI PET/CT in at least one patient harboring primary or metastatic liver lesion(s) were fully analyzed. Although there was some heterogeneity in clinical conditions and/or study methodology, PET/CT with radiolabeled FAPIs showed an excellent performance in common primary liver malignancies (hepatocarcinoma, intrahepatic cholangiocarcinoma) and liver metastases (mostly from the gastrointestinal tract and lungs). A higher tumor-to-background ratio for FAPIs than for [18F]FDG was found in primary and metastatic liver lesions, due to lower background activity. Despite limited clinical evidence, radiolabeled FAPIs may be used to assess the suitability and effectiveness of FAPI-derived therapeutic agents such as [177Lu]Lu-FAPI. However, future prospective research on a wider population is needed to confirm the excellent performance.

Insights into the development of 99mTc-radioligands for serotonergic receptors imaging: Synthesis, labeling, In vitro, and In vivo studies

Serotonergic (5-hydroxytryptamine; 5-HT) receptors play critical roles in neurological and psychological disorders such as schizophrenia, anxiety, depression, and Alzheimer's diseases. Therefore, it is particularly important to develop novel radioligands or modify the existing ones to identify the serotonergic receptors involved in psychiatric disorders. Among the 16 subtypes of serotonergic systems, only technetium-99m based radiopharmaceuticals have been evaluated for serotonin-1A (5-HT1A), serotonin-2A (5-HT2A), 5-HT1A/7 heterodimers and serotonin receptor neurotransmitter (SERT). This review focuses on recent efforts in the design, synthesis and evaluation of 99mTc-radioligands used for single photon emission computerized tomography (SPECT) imaging of serotonergic (5-HT) receptors. Additionally, the discussion will cover aspects such as chemical structure, in vitro/vivo stability, affinity toward serotonin receptors, blood-brain barrier permeation (BBB), and biodistribution study.

Development of radiotracers for riboflavin transporter 3 imaging in diseases-A brief overview

Riboflavin (RF, vitamin B2) plays a key role in metabolic oxidation-reduction reactions, especially in the mitochondrial reprogramming of energy metabolism. Riboflavin transporter 3 (RFVT3) is a vital section of the mitochondrial network and involved in riboflavin homeostasis and production of adenosine triphosphate (ATP). The abnormal expression of RFVT3 is closely associated with the occurrence and progression of multiple diseases. Therefore, it is vital to understand the riboflavin internalization pathway under pathological conditions by addressing the abnormal expression of RFVT3, which could be a highly valuable biomarker for the early diagnosis and effective therapy of various diseases.

Multiplex Ultrasound Imaging of Perfluorocarbon Nanodroplets Enabled by Decomposition of Postvaporization Dynamics

Despite the real-time, nonionizing, and cost-effective nature of ultrasound imaging, there is a dearth of methods to visualize two or more populations of contrast agents simultaneously─a technique known as multiplex imaging. Here, we present a new approach to multiplex ultrasound imaging using perfluorocarbon (PFC) nanodroplets. The nanodroplets, which undergo a liquid-to-gas phase transition in response to an acoustic trigger, act as activatable contrast agents. This work characterized the dynamic responses of two PFC nanodroplets with boiling points of 28 and 56 °C. These characteristic responses were then used to demonstrate that the relative concentrations of the two populations of PFC nanodroplets could be accurately measured in the same imaging volume within an average error of 1.1%. Overall, the findings indicate the potential of this approach for multiplex ultrasound imaging, allowing for the simultaneous visualization of multiple molecular targets simultaneously.

Radiopharmaceuticals: navigating the frontier of precision medicine and therapeutic innovation

This review article explores the dynamic field of radiopharmaceuticals, where innovative developments arise from combining radioisotopes and pharmaceuticals, opening up exciting therapeutic possibilities. The in-depth exploration covers targeted drug delivery, delving into passive targeting through enhanced permeability and retention, as well as active targeting using ligand-receptor strategies. The article also discusses stimulus-responsive release systems, which orchestrate controlled release, enhancing precision and therapeutic effectiveness. A significant focus is placed on the crucial role of radiopharmaceuticals in medical imaging and theranostics, highlighting their contribution to diagnostic accuracy and image-guided curative interventions. The review emphasizes safety considerations and strategies for mitigating side effects, providing valuable insights into addressing challenges and achieving precise drug delivery. Looking ahead, the article discusses nanoparticle formulations as cutting-edge innovations in next-generation radiopharmaceuticals, showcasing their potential applications. Real-world examples are presented through case studies, including the use of radiolabelled antibodies for solid tumors, peptide receptor radionuclide therapy for neuroendocrine tumors, and the intricate management of bone metastases. The concluding perspective envisions the future trajectory of radiopharmaceuticals, anticipating a harmonious integration of precision medicine and artificial intelligence. This vision foresees an era where therapeutic precision aligns seamlessly with scientific advancements, ushering in a new epoch marked by the fusion of therapeutic resonance and visionary progress.

CycloSiFA: The Next Generation of Silicon-Based Fluoride Acceptors for Positron Emission Tomography (PET)

The ring-opening Si-fluorination of a variety of azasilole derivatives cyclo-1-(iPr2 Si)-4-X-C6 H3 -2-CH2 NR (4: R=2,6-iPr2 C6 H3 , X=H; 4 a: R=2,4,6-Me3 C6 H2 , X=H; 9: R=2,6-iPr2 C6 H3 , X=tBuMe2 SiO; 10: R=2,6-iPr2 C6 H3 , X=OH; 13: R=2,6-iPr2 C6 H3 , X=HCCCH2 O; 22: R=2,6-iPr2 C6 H3 , X=tBuMe2 SiCH2 O) with different 19 F-fluoride sources was studied, optimized and the experience gained was used in a translational approach to create a straightforward 18 F-labelling protocol for the azasilole derivatives [18 F]6 and [18 F]14. The latter constitutes a potential clickable CycloSiFA prosthetic group which might be used in PET tracer development using Cu-catalysed triazole formation. Based on our findings, CycloSiFA has the potential to become a new entry into non-canonical labelling methodologies for radioactive PET tracer development.

The Role of the Biosafety Cabinet in Preventing Infection in the Clinical Laboratory

Clinical laboratories are essential in healthcare to better diagnose, treat, and track medical diseases. However, handling infectious organisms and possibly infectious materials in these laboratories puts the safety of laboratory workers and the general public at risk. By controlling the distribution of infectious substances and stopping the spread of diseases, biosafety cabinets (BSCs) have become crucial tools in guaranteeing laboratory safety. The prevention of infections is most important in medical and laboratory settings. In clinical laboratories, biological and infectious agents are handled, posing threats to healthcare workers and the general public. To avoid infections, proper training of the BSC is essential. Laboratory employees are instructed in aseptic procedures, proper hand posture, and efficient personal protection when working in the cabinet. These instructions decrease the chance of contaminating the surrounding area. Additionally, user ergonomics are taken into account while designing BSC, reducing operator fatigue, and guaranteeing that staff can execute tasks precisely for extended periods. This review highlights the importance of biosafety cabinets in maintaining a secure laboratory environment and explains their crucial function in infection control.

Applications of machine learning and deep learning in SPECT and PET imaging: General overview, challenges and future prospects

The integration of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging techniques with machine learning (ML) algorithms, including deep learning (DL) models, is a promising approach. This integration enhances the precision and efficiency of current diagnostic and treatment strategies while offering invaluable insights into disease mechanisms. In this comprehensive review, we delve into the transformative impact of ML and DL in this domain. Firstly, a brief analysis is provided of how these algorithms have evolved and which are the most widely applied in this domain. Their different potential applications in nuclear imaging are then discussed, such as optimization of image adquisition or reconstruction, biomarkers identification, multimodal fusion and the development of diagnostic, prognostic, and disease progression evaluation systems. This is because they are able to analyse complex patterns and relationships within imaging data, as well as extracting quantitative and objective measures. Furthermore, we discuss the challenges in implementation, such as data standardization and limited sample sizes, and explore the clinical opportunities and future horizons, including data augmentation and explainable AI. Together, these factors are propelling the continuous advancement of more robust, transparent, and reliable systems.

A translational blueprint for developing intraoperative imaging agents via radiopharmaceutical-guided drug design

Cancer imaging is a rapidly evolving field due to the discovery of novel molecular targets and the availability of corresponding techniques to detect them with high precision, accuracy, and sensitivity. Nuclear medicine is the most widely used molecular imaging modality and has a growing toolkit of clinically used radiopharmaceuticals that enable whole-body tumor visualization, staging, and treatment monitoring for a variety of tumors in a non-invasive manner. The need for similar imaging capabilities in the operating room has led to the emergence of fluorescence-guided surgery (FGS) as a powerful technique that gives surgeons unprecedented ability to distinguish tumors from healthy tissues. While a variety of strategies have been used to develop contrast agents for FGS, the use of radiopharmaceuticals as models brings exceptional translational potential and has increasingly been explored. Here, we review strategies used to convert clinically used radiopharmaceuticals into fluorescent and multimodal counterparts. Unique preclinical and clinical capabilities stemming from radiopharmaceutical-based agent design are also discussed to illustrate the advantages of this approach.

Performance study of a 360° CZT camera for monitoring 177Lu-PSMA treatment

BACKGROUND

The aim of this study was to investigate the quantification performance of a 360° CZT camera for 177Lu-based treatment monitoring.

METHODS

Three phantoms with known 177Lu activity concentrations were acquired: (1) a uniform cylindrical phantom for calibration, (2) a NEMA IEC body phantom for analysis of different-sized spheres to optimise quantification parameters and (3) a phantom containing two large vials simulating organs at risk for tests. Four sets of reconstruction parameters were tested: (1) Scatter, (2) Scatter and Point Spread Function Recovery (PSFR), (3) PSFR only and (4) Penalised likelihood option and Scatter, varying the number of updates (iterations × subsets) with CT-based attenuation correction only. For each, activity concentration (ARC) and contrast recovery coefficients (CRC) were estimated as well as root mean square. Visualisation and quantification parameters were applied to reconstructed patient image data.

RESULTS

Optimised quantification parameters were determined to be: CT-based attenuation correction, scatter correction, 12 iterations, 8 subsets and no filter. ARC, CRC and RMS results were dependant on the methodology used for calculations. Two different reconstruction parameters were recommended for visualisation and for quantification. 3D whole-body SPECT images were acquired and reconstructed for 177Lu-PSMA patients in 2-3 times faster than the time taken for a conventional gamma camera.

CONCLUSION

Quantification of whole-body 3D images of patients treated with 177Lu-PSMA is feasible and an optimised set of parameters has been determined. This camera greatly reduces procedure time for whole-body SPECT.

Radiolabeled NGR-Based Heterodimers for Angiogenesis Imaging: A Review of Preclinical Studies

Since angiogenesis/neoangiogenesis has a major role in tumor development, progression and metastatic spread, the establishment of angiogenesis-targeting imaging and therapeutic vectors is of utmost significance. Aminopeptidase N (APN/CD13) is a pivotal biomarker of angiogenic processes abundantly expressed on the cell surface of active vascular endothelial and various neoplastic cells, constituting a valuable target for cancer diagnostics and therapy. Since the asparagine-glycine-arginine (NGR) sequence has been shown to colocalize with APN/CD13, the research interest in NGR-peptide-mediated vascular targeting is steadily growing. Earlier preclinical experiments have already demonstrated the imaging and therapeutic feasibility of NGR-based probes labeled with different positron emission tomography (PET) and single-photon emission computed tomography (SPECT) radionuclides, including Gallium-68 (68Ga), Copper-64 (64Cu), Technetium-99m (99mTc), Lutetium-177 (177Lu), Rhenium-188 (188Re) or Bismuth-213 (213Bi). To improve the tumor binding affinity and the retention time of single-receptor targeting peptides, NGR motifs containing heterodimers have been introduced to identify multi-receptor overexpressing malignancies. Preclinical studies with various tumor-bearing experimental animals provide useful tools for the investigation of the in vivo imaging behavior of NGR-based heterobivalent ligands. Herein, we review the reported preclinical achievements on NGR heterodimers that could be highly relevant for the development of further target-specific multivalent compounds in diagnostic and therapeutic settings.

The current role of nuclear medicine in breast cancer

Breast cancer is the most common cancer in females worldwide. Nuclear medicine plays an important role in patient management, not only in initial staging, but also during follow-up. Radiopharmaceuticals to study breast cancer have been used for over 50 years, and several of these are still used in clinical practice, according to the most recent guideline recommendations.In this critical review, an overview of nuclear medicine procedures used during the last decades is presented. Current clinical indications of each of the conventional nuclear medicine and PET/CT examinations are the focus of this review, and are objectively provided. Radionuclide therapies are also referred, mainly summarising the methods to palliate metastatic bone pain. Finally, recent developments and future perspectives in the field of nuclear medicine are discussed. In this context, the promising potential of new radiopharmaceuticals not only for diagnosis, but also for therapy, and the use of quantitative imaging features as potential biomarkers, are addressed.Despite the long way nuclear medicine has gone through, it looks like it will continue to benefit clinical practice, paving the way to improve healthcare provided to patients with breast cancer.

The Role of Molecular Imaging in Personalized Medicine

The concept of personalized medicine refers to the tailoring of medical treatment to each patient's unique characteristics. Scientific advancements have led to a better understanding of how a person's unique molecular and genetic profile makes them susceptible to certain diseases. It provides individualized medical treatments that will be safe and effective for each patient. Molecular imaging modalities play an essential role in this aspect. They are used widely in screening, detection and diagnosis, treatment, assessing disease heterogeneity and progression planning, molecular characteristics, and long-term follow-up. In contrast to conventional imaging approaches, molecular imaging techniques approach images as the knowledge that can be processed, allowing for the collection of relevant knowledge in addition to the evaluation of enormous patient groups. This review presents the fundamental role of molecular imaging modalities in personalized medicine.

Recent Advances in Cardiovascular Diseases Research Using Animal Models and PET Radioisotope Tracers

Cardiovascular diseases (CVD) is a collective term describing a range of conditions that affect the heart and blood vessels. Due to the varied nature of the disorders, distinguishing between their causes and monitoring their progress is crucial for finding an effective treatment. Molecular imaging enables non-invasive visualisation and quantification of biological pathways, even at the molecular and subcellular levels, what is essential for understanding the causes and development of CVD. Positron emission tomography imaging is so far recognized as the best method for in vivo studies of the CVD related phenomena. The imaging is based on the use of radioisotope-labelled markers, which have been successfully used in both pre-clinical research and clinical studies. Current research on CVD with the use of such radioconjugates constantly increases our knowledge and understanding of the causes, and brings us closer to effective monitoring and treatment. This review outlines recent advances in the use of the so-far available radioisotope markers in the research on cardiovascular diseases in rodent models, points out the problems and provides a perspective for future applications of PET imaging in CVD studies.

Digital PET/CT with 18F-FACBC in early castration-resistant prostate cancer: our preliminary results

BACKGROUND

We assessed the role of digital PET/CT (dPET/CT) with ¹⁸F-FACBC in patients affected by castration-resistant prostate cancer with PSA levels ≤ 3 ng/mL (early CRPC), no lesions detectable at cross-sectional imaging (CIM) and bone scan (BS).

METHODS

Clinical data of patients submitted to ¹⁸F-FACBC dPET/CT were retrospectively reviewed. PET/CT results were analyzed: lesions' number, location, and, in case of positive lymph nodes, largest node's short axis (i.e. SA) were annotated. According to PET/CT's results, patients with ¹⁸F-FACBC-avid lesions were further stratified into 1) unifocal; 2) oligometastatic (≤ 5 lesions); 3) disseminated (> 6 lesions).

RESULTS

Twenty-four patients were enrolled. ¹⁸F-FACBC dPET/CT was positive in 21 out of 24 patients (87.5%). Thirteen patients (54.1%) showed recurrence in pelvic region, seven of whom with pelvic nodes' involvement, while eight cases (33.3%) presented ¹⁸F-FACBC-avid metastases to extra-pelvic nodes or bone. Average SA of PET-positive nodes resulted in 8.9 ± 3 mm. Patients were categorized as unifocal in four cases (26.6%), oligometastatic in 10 subjects (66.6%) and disseminated in 1 case (0.6%). PET/CT impacted on clinical management in 14 cases (58.3%).

CONCLUSIONS

¹⁸F-FACBC dPET/CT detected M1 status in 33.3% of early CRPC patients, significantly impacting on clinical management.

Optimization of Precursor Synthesis Conditions of (2S,4S)4–[18F]FPArg and Its Application in Glioma Imaging

Although the tracer (2S,4S)4–[¹⁸F]FPArg is expected to provide a powerful imaging method for the diagnosis and treatment of clinical tumors, it has not been realized due to the low yield of chemical synthesis and radiolabeling. A simple synthetic method for the radiolabeled precursor of (2S,4S)4–[¹⁸F]FPArg in stable yield was obtained by adjusting the sequence of the synthetic steps. Furthermore, the biodistribution experiments confirmed that (2S,4S)4–[¹⁸F]FPArg could be cleared out quickly in wild type mouse. Cell uptake experiments and U87MG tumor mouse microPET–CT imaging experiments showed that the tumor had high uptake of (2S,4S)4–[¹⁸F]FPArg and the clearance was slow, but (2S,4S)4–[¹⁸F]FPArg was rapidly cleared in normal brain tissue. MicroPET–CT imaging of nude mice bearing orthotopic HS683–Luc showed that (2S,4S)4–[¹⁸F]FPArg can penetrate blood–brain barrier and image gliomas with a high contrast. Therefore, (2S,4S)4–[¹⁸F]FPArg is expected to be further applied in the diagnosis and efficacy evaluation of clinical glioma.

Dual-Labelling Strategies for Nuclear and Fluorescence Molecular Imaging: Current Status and Future Perspectives

Molecular imaging offers the possibility to investigate biological and biochemical processes non-invasively and to obtain information on both anatomy and dysfunctions. Based on the data obtained, a fundamental understanding of various disease processes can be derived and treatment strategies can be planned. In this context, methods that combine several modalities in one probe are increasingly being used. Due to the comparably high sensitivity and provided complementary information, the combination of nuclear and optical probes has taken on a special significance. In this review article, dual-labelled systems for bimodal nuclear and optical imaging based on both modular ligands and nanomaterials are discussed. Particular attention is paid to radiometal-labelled molecules for single-photon emission computed tomography (SPECT) and positron emission tomography (PET) and metal complexes combined with fluorescent dyes for optical imaging. The clinical potential of such probes, especially for fluorescence-guided surgery, is assessed.

Targeted Dual-Modal PET/SPECT-NIR Imaging: From Building Blocks and Construction Strategies to Applications

Molecular imaging is an emerging non-invasive method to qualitatively and quantitively visualize and characterize biological processes. Among the imaging modalities, PET/SPECT and near-infrared (NIR) imaging provide synergistic properties that result in deep tissue penetration and up to cell-level resolution. Dual-modal PET/SPECT-NIR agents are commonly combined with a targeting ligand (e.g., antibody or small molecule) to engage biomolecules overexpressed in cancer, thereby enabling selective multimodal visualization of primary and metastatic tumors. The use of such agents for (i) preoperative patient selection and surgical planning and (ii) intraoperative FGS could improve surgical workflow and patient outcomes. However, the development of targeted dual-modal agents is a chemical challenge and a topic of ongoing research. In this review, we define key design considerations of targeted dual-modal imaging from a topological perspective, list targeted dual-modal probes disclosed in the last decade, review recent progress in the field of NIR fluorescent probe development, and highlight future directions in this rapidly developing field.

Evaluation of [18F]tetrafluoroborate as a Potential PET Imaging Agent in a Sodium Iodide Symporter-Transfected Cell Line A549 and Endogenous NIS-Expressing Cell Lines MKN45 and K1

[¹⁸F]tetrafluoroborate (TFB) has been introduced as the ¹⁸F-labeled PET imaging probe for the human sodium iodide symporter (NIS). Noninvasive NIS imaging using [¹⁸F]TFB has received much interest in recent years for evaluating various NIS-expressing tumors. Cancers are a global concern with enormous implications; therefore, improving diagnostic methods for accurate detection of cancer is extremely important. Our aim was to investigate the PET imaging capabilities of [¹⁸F]TFB in NIS-transfected lung cell line A549 and endogenous NIS-expressing tumor cells, such as thyroid cancer K1 and gastric cancer MKN45, and broaden its application in the medical field. Western blot and flow cytometry were used to assess the NIS expression level. Radioactivity counts of [¹⁸F]TFB, in vitro, in the three tumor cells were substantially higher than those in the KI inhibition group in the uptake experiment. In vivo PET imaging clearly delineated the three tumors based on the specific accumulation of [¹⁸F]TFB in a mouse model. Ex vivo biodistribution investigation showed high [¹⁸F]TFB absorption in the tumor location, which was consistent with the PET imaging results. These results support the use of NIS-transfected lung cell line A549 and NIS-expressing tumor cells MKN45 and K1, to investigate probing capabilities of [¹⁸F]TFB. We also demonstrate, for the first time, the feasibility of [¹⁸F]TFB in diagnosing stomach cancer. In conclusion, this study illustrates the promising future of [¹⁸F]TFB for tumor diagnosis and NIS reporter imaging.

Experimental Nuclear Medicine Meets Tumor Biology

Personalized treatment of cancer patients demands specific and validated biomarkers for tumor diagnosis and therapy. The development and validation of such require translational preclinical models that recapitulate human diseases as accurately as possible. Moreover, there is a need for convergence of different (pre)clinical disciplines that openly share their knowledge and methodologies. This review sheds light on the differential perception of biomarkers and gives an overview of currently used models in tracer development and approaches for biomarker discovery.

Tumor-Specificity Growth Factor Combined with Tumor Markers in Nuclear Medicine Imaging to Identify Prostate Cancer Osteonosus

Objective

This study has explored the application value of malignant tumor SPE growth factor (TSGF) combined with tumor markers (TM) (TSGF + TM) in nuclear medicine imaging to identify prostate cancer osteonosus (PCO).

Methods

A retrospective analysis for 70 patients with prostate cancer and bone disease admitted to our hospital was performed, 30 healthy persons in the same period were selected as the control group, and the advantages and disadvantages of various examinations were analyzed. All patients were diagnosed with PET whole body bone imaging. Suspicious lesions could be examined by MRI or CT. According to the results of imaging examination, patients were divided into 40 cases of malignant prostate cancer and 30 cases of benign prostate cancer. All the patients underwent 18F-FDG-PET imaging, alpha-fetoprotein (AFP), and TSGF + TM determination. The case diagnosis results were compared and analyzed, and the sensitivity (SEN), specificity (SPE), and accuracy (ACC) of various detection methods were calculated. The SEN, SPE, and ACC of positron emission tomography (PET) were 90.9%, 57.8%, and 81.2%, respectively; those of TM were 79.2%, 94.6%, and 69.8%, respectively; and those of TSGF + TM were 95.9%, 100%, and 97.3%, respectively. The accuracy of combined diagnosis of tumors can reach 100%. The AFP and TSGF levels of serum TM were compared and analyzed, and it was found that the benign lesion group and the malignant lesion group showed significant increases compared with the control group, and the difference between the malignant lesion group and the control group was obvious (P < 0.05). SGF combined with TM could obtain a more definite diagnosis in PCO.

Conclusion

TSGF + TM combined with 18F-FDG-PET imaging showed important clinical value to diagnose the PCO. The imaging accuracy of TSGF + TM combined with 18F-FDG-PET is 97.3%, and the specificity of tumor diagnosis is 100%. Therefore, the TSGF + TM applied in medical imaging and identification of PCO was worthy of clinical promotion.

Gallium-68 Labeling of the Cyclin-Dependent Kinase 4/6 Inhibitors as Positron Emission Tomography Radiotracers for Tumor Imaging

Cyclin-dependent kinase 4 and 6 (CDK4/6) have emerged as interesting therapeutic drug targets with many potential applications in anti-tumors, especially in breast cancer. A novel CDK4/6 kinase-derived positron emission tomography (PET) imaging agent was designed based on palbociclib modified with a chelator DOTA. This new compound with a chelator DOTA-palbociclib was radiolabeled with gallium 68 (⁶⁸Ga). After labeling, the purity and stability were evaluated, and the blood pharmacokinetics were carried out in normal healthy mice. Human breast cancer MCF-7 (ER+/HER2-) cells were used for in vitro cell uptake tests. PET imaging and ex vivo biodistribution were conducted in MCF-7 tumor-bearing mice. Specific binding of tumors was evaluated by the blocking assay. Furthermore, the uptake of ⁶⁸Ga-DOTA-palbociclib in tumors was studied by autoradiography of tissue sections followed by immunofluorescence evaluation of CDK4 and CDK6. ⁶⁸Ga-DOTA-palbociclib was synthesized very simply in a high labeling rate and radiochemical purity in 10 min. The labeling compound showed excellent stability both in vitro and in vivo and exhibited good pharmacokinetics, making it suitable for in vivo imaging. Cell uptake studies display that co-incubation with palbociclib can inhibit cellular uptake of ⁶⁸Ga-DOTA-palbociclib. In vivo imaging and ex vivo biodistribution in mice bearing MCF-7 tumors both showed obvious radioactive uptake in the tumor and higher tumor-to-muscle ratios, while the tumor radioactivity accumulation was significantly decreased when prior administered with an excess of cold palbociclib, confirming CDK4/6 specific binding of ⁶⁸Ga-DOTA-palbociclib in vivo. Autoradiography of the avid tumor section showed a high correlation between immunofluorescence with the CDK4/6 positive areas of the tumor, further demonstrating that ⁶⁸Ga-DOTA-palbociclib specifically targeted CDK4/6 positive tumors. We synthesized ⁶⁸Ga-DOTA-palbociclib, a new CDK4/6 kinase PET imaging agent, and validated its excellent stability, pharmacokinetics, and specific tumor binding. Based on our primary results, ⁶⁸Ga-DOTA-palbociclib is a promising imaging agent with the potential to tailor a precise treatment program for CDK4/6 inhibitors.

Patterns and trends of population radiation exposure and projected the risk of exposure-induced death from gamma camera examinations in Yazd Province

INTRODUCTION

The use of nuclear medicine examinations as imaging modalities has recently increased. This study aimed to assess the radiation dose delivered to patients from common diagnostic nuclear medicine examinations and estimate the risk of exposure-induced death (REID). In addition, the frequency of nuclear medicine procedures were evaluated from 2015-2018.

MATERIALS AND METHODS

The data were collected from adult patients who had undergone cardiac, skeletal, renal, lacrimal, and thyroid imaging. For each patient, the effective dose was calculated using dose conversion factors, and REID was estimated using PCXMC. The frequency of examinations between 2015 and 2018 was obtained from the hospital information system (HIS).

RESULTS

The highest estimated effective dose was attributed to the scans of myocardial stress (8.09 ± 1.28 mSv), myocardial rest (5.59 ± 1.27 mSv), and thyroid imaging (3.93 ± 0.55 mSv). In addition, cardiac stress examination had the highest REID values for solid cancers (212.5 ± 67.5) and bone scans had the highest REID values for leukemia (11.5 ± 2.5). A large increase in the number of myocardial perfusion scans was a significant contributor to an increase in collective effective dose from 23.37 man-Sv in 2015 to 49.47 man-Sv in 2018, a compound annual growth rate (CAGR) of 26%.

CONCLUSION

Although the annual frequency and per capita effective dose of nuclear medicine procedures in Yazd Province increased continuously, they were comparably lower than those reported for other countries. Despite this, the cancer risks of nuclear medicine scans at the individual level are negligible (around 0.01% excess fatal cancer risk), yet the increasing tendency for these examinations could be of concern.

Head-to-Head Comparison of Fibroblast Activation Protein Inhibitors (FAPI) Radiotracers versus [18F]F-FDG in Oncology: A Systematic Review

Several recent studies comparing radiolabeled fibroblast activation protein inhibitors (FAPI) and fluorine-18 fluorodeoxyglucose ([18F]F-FDG) as positron emission tomography (PET) radiotracers in oncology have been published. The aim of this systematic review is to perform an updated evidence-based summary about the comparison of these PET radiotracers in oncology to better address further research in this setting. Studies or subsets of studies comparing radiolabeled FAPI and [18F]F-FDG as PET radiotracers in oncology were eligible for inclusion in this systematic review. A systematic literature search of PubMed/MEDLINE and Cochrane library databases was performed until August 2021. Literature data about the comparison of [18F]F-FDG and radiolabeled FAPI are rapidly increasing. Overall, taking into account radiotracer uptake and tumor-to-background uptake ratio, compared to [18F]F-FDG PET, an equal or higher detection of primary tumors and/or metastatic lesions was usually demonstrated by using radiolabeled FAPI PET. In particular, the cancer entities with better detection rate of tumor lesions by using radiolabeled FAPI PET, compared to [18F]F-FDG PET, were gastrointestinal tumors, liver tumors, breast cancer and nasopharyngeal carcinoma. Further comparison studies are needed to better evaluate the best field of application of radiolabeled FAPI PET.

Diagnostic performance of [124I]m-iodobenzylguanidine PET/CT in patients with pheochromocytoma

^123/131I-MIBG scintigraphy has shown a high specificity for imaging pheochromocytoma and paraganglioma however with low sensitivity due to low spatial resolution. ¹²⁴I-MIBG PET may overcome this limitation to improve the staging of patients with (suspected) pheochromocytoma. Methods: We analyzed the sensitivity, specificity, positive and negative predictive values (PPV, NPV) of ¹²⁴I-MIBG PET in 43 consecutive patients with suspected (recurrence of) pheochromocytoma using histopathological (n = 25) and clinical validation (n = 18) as standard of truth. Furthermore, we compared ¹²⁴I-MIBG PET versus contrast enhanced CT (CE-CT) per-patient and per-lesion detection rate of ¹²⁴I-MIBG PET in 13 additional patients with known metastatic malignant pheochromocytoma (MMP). Results: ¹²⁴I-MIBG PET/CT was positive in 19/43 (44%) patients with suspected pheochromocytoma. Presence of pheochromocytoma was confirmed in 22/43 (51%). ¹²⁴I-MIBG PET/CT sensitivity, specificity, PPV, NPV were 86%, 100%, 100%, 88%, respectively. ¹²⁴I-MIBG PET was positive in 11/13 (85%) MMP patients. Combined ¹²⁴I-MIBG PET and CE-CT detected 173 lesions, of which 166 (96%) and 118 (68%) were visible on ¹²⁴I-MIBG PET and CE-CT, respectively. Discussion: ¹²⁴I-MIBG PET detects pheochromocytoma with high accuracy at initial staging and high detection rate at re-staging. Superior diagnostic performance aids guidance of surgical and medical management including personalized ¹³¹I-MIBG therapy.

Microfluidics-Coupled Radioluminescence Microscopy for In Vitro Radiotracer Kinetic Studies

Integrated bioassay systems that combine microfluidics and radiation detectors can deliver medical radiopharmaceuticals to live cells with precise timing, while minimizing radiation dose and sample volume. However, the spatial resolution of many radiation imaging systems is limited to bulk cell populations. Here, we demonstrate microfluidics-coupled radioluminescence microscopy (μF-RLM), a new integrated system that can image radiotracer uptake in live adherent cells growing inside microincubators with spatial resolution better than 30 μm. Our method enables on-chip radionuclide imaging by incorporating an inorganic scintillator plate (CdWO4) into a microfluidic chip. We apply this approach to investigate the factors that influence the dynamic uptake of [18F]fluorodeoxyglucose (FDG) by cancer cells. In the first experiment, we measured the effect of flow on FDG uptake of cells and found that a continuous flow of the radiotracer led to fourfold higher uptake than static incubation, suggesting that convective replenishment enhances molecular radiotracer transport into cells. In the second set of experiments, we applied pharmacokinetic modeling to show that lactic acidosis inhibits FDG uptake by cancer cells in vitro and that this decrease is primarily due to downregulation of FDG transport into the cells. The other two rate constants, which represent FDG export and FDG metabolism, were relatively unaffected by lactic acidosis. Lactic acidosis is common in solid tumors because of the dysregulated metabolism and inefficient vasculature. In conclusion, μF-RLM is a simple and practical approach for integrating high-resolution radionuclide imaging within standard microfluidics devices, thus potentially opening venues for investigating the efficacy of radiopharmaceuticals in in vitro cancer models.

Computational Analysis of Clinical and Molecular Markers and New Theranostic Possibilities in Primary Open-Angle Glaucoma

Primary open-angle glaucoma (POAG) is a paramount cause of irreversible visual disability worldwide. We focus on identifying clinical and molecular facts that may help elucidating the pathogenic mechanisms of the disease. By using ophthalmological approaches (biomicroscopy, ocular fundus, optical coherence tomography, and perimetry) and experimental tests (enzyme-linked immunosorbent assay (ELISA), high performance liquid chromatography (HPLC), and Western blot/immunoblotting) directed to evaluate the oxidative stress, inflammation, apoptosis, and neurodegeneration processes, we gather information to build a network of data to perform a computational bioinformatics analysis. Our results showed strong interaction of the above players and its downstream effectors in POAG pathogenesis. In conclusion, specific risk factors were identified, and molecules involved in multiple pathways were found in relation to anterior and posterior eye segment glaucoma changes, pointing to new theranostic challenges for better managing POAG progression.

A Systematic Review of Molecular Imaging Agents Targeting Bradykinin B1 and B2 Receptors

Kinins, bradykinin and kallidin are vasoactive peptides that signal through the bradykinin B1 and B2 receptors (B1R and B2R). B2R is constitutively expressed in healthy tissues and mediates responses such as vasodilation, fluid balance and retention, smooth muscle contraction, and algesia, while B1R is absent in normal tissues and is induced by tissue trauma or inflammation. B2R is activated by kinins, while B1R is activated by kinins that lack the C-terminal arginine residue. Perturbations of the kinin system have been implicated in inflammation, chronic pain, vasculopathy, neuropathy, obesity, diabetes, and cancer. In general, excess activation and signaling of the kinin system lead to a pro-inflammatory state. Depending on the disease context, agonism or antagonism of the bradykinin receptors have been considered as therapeutic options. In this review, we summarize molecular imaging agents targeting these G protein-coupled receptors, including optical and radioactive probes that have been used to interrogate B1R/B2R expression at the cellular and anatomical levels, respectively. Several of these preclinical agents, described herein, have the potential to guide therapeutic interventions for these receptors.