A review on the clinical uses of SPECT/CT. Eur J Nucl Med Mol Imaging. 2010;37:1959-1985. [PMID: 20182712 DOI: 10.1007/s00259-010-1390-8]

CIRF: Coupled Image Reconstruction and Fusion Strategy for Deep Learning Based Multi-Modal Image Fusion

Multi-modal medical image fusion (MMIF) is crucial for disease diagnosis and treatment because the images reconstructed from signals collected by different sensors can provide complementary information. In recent years, deep learning (DL) based methods have been widely used in MMIF. However, these methods often adopt a serial fusion strategy without feature decomposition, causing error accumulation and confusion of characteristics across different scales. To address these issues, we have proposed the Coupled Image Reconstruction and Fusion (CIRF) strategy. Our method parallels the image fusion and reconstruction branches which are linked by a common encoder. Firstly, CIRF uses the lightweight encoder to extract base and detail features, respectively, through the Vision Transformer (ViT) and the Convolutional Neural Network (CNN) branches, where the two branches interact to supplement information. Then, two types of features are fused separately via different blocks and finally decoded into fusion results. In the loss function, both the supervised loss from the reconstruction branch and the unsupervised loss from the fusion branch are included. As a whole, CIRF increases its expressivity by adding multi-task learning and feature decomposition. Additionally, we have also explored the impact of image masking on the network's feature extraction ability and validated the generalization capability of the model. Through experiments on three datasets, it has been demonstrated both subjectively and objectively, that the images fused by CIRF exhibit appropriate brightness and smooth edge transition with more competitive evaluation metrics than those fused by several other traditional and DL-based methods.

Polymeric Nanoparticles for Drug Delivery

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

Activity-Based Fluorescence Diagnostics for Cancer

Fluorescence imaging is one of the most promising approaches to achieve intraoperative assessment of the tumor/normal tissue margins during cancer surgery. This is critical to improve the patients' prognosis, and therefore various molecular fluorescence imaging probes have been developed for the identification of cancer lesions during surgery. Among them, "activatable" fluorescence probes that react with cancer-specific biomarker enzymes to generate fluorescence signals have great potential for high-contrast cancer imaging due to their low background fluorescence and high signal amplification by enzymatic turnover. Over the past two decades, activatable fluorescence probes employing various fluorescence control mechanisms have been developed worldwide for this purpose. Furthermore, new biomarker enzymatic activities for specific types of cancers have been identified, enabling visualization of various types of cancers with high sensitivity and specificity. This Review focuses on recent advances in the design, function and characteristics of activatable fluorescence probes that target cancer-specific enzymatic activities for cancer imaging and also discusses future prospects in the field of activity-based diagnostics for cancer.

Reductive prodrug and AIE copolymer nanoparticle for monitoring and chemotherapy

Polymeric micelle systems for drug delivery, monitor and chemotherapy have gained significant attention, and reductive polymeric micelle systems have become particularly attractive due to their controlled release behavior without additional assistance. However, there are challenges in accurately controlling drug and probe release from the nanoparticles and determining the loading content of drug and probe. To address these issues, we have developed a reduction-responsive Pt(IV) prodrug-based polymeric delivery system that can be dynamically monitored using aggregation-induced emission luminogens (AIE) based bioprobes. These polymeric micelle can self-assemble into nanoparticles and release both bio-active Pt(II) drug and bio-probe upon reduction activation. TPE molecules released in the inner endo/lysosomal microenvironment aggregate and fluoresce upon irradiation, thus allowing real-time tracking of drug biodistribution without additional contrast agents. Advantages of this system include position-specific chemical bond cleavage, control of platinum content, and monitoring of drug reduction and biodistribution.

Assessment of unilateral condylar hyperplasia with quantitative SPECT/CT

Purpose

The current study aimedto assess condylar activityin patients with unilateral condylar hyperplasia (UCH) with quantitative SPECT/CT.

Patients and methods

This retrospective study included patients with UCH who underwent quantitative SPECT/CT. SPECT analysis and quantification of SPECT/CT were performed, and the maximum count per pixel and SUVmax of either side of the condyles were calculated.

Results

39 patients were included in the analysisand classified into three subgroups according to the percentile differential right-left ratio: inactive group, left active (LA) group, and right active (RA) group. Totally, the SUVmax of the affected side is significantly higher than the unaffected side (active:5.93 ± 2.43 vs inactive:3.62 ± 1.76, P < 0.001), SUVmax-based ratios correlated well with the ratios based on maximum count (R = 0.944, P < 0.001). ROC analysis showed poorSUVmaxperformance in differentiation between theactive condyles and the inactive condyles due to the lower area under the curve (AUC) (0.588). In subgroup analysis, the affected side is significantly higher than the unaffected side in active groups with SUVmax, no significant difference was found between the active sides or the inactive sides of active groups. Interestingly, the SUVmax of the left side was statistically higher than that of the right sidein the inactive group (P = 0.01),while the left side of the right active group has significantlylower activitythan that in the inactive group, meanwhile,the right side showed no significant difference. Furthermore, each side showed no significant difference between the left active group and the inactive group.

Conclusions

SUVmax is not an optimal measurement effectively used to evaluate active condyles. However, SUV ratios correlated well with the count ratios, and the left side of condyles showed a peculiar feature in condyle growth status reflected in radioactivity quantified with SPECT/CT, which needs further study to determine the role in the development of the UCH.

Intranasal Radioiodinated Ferulic Acid Polymeric Micelles as the First Nuclear Medicine Imaging Probe for ETRA Brain Receptor

INTRODUCTION

The aim of this work was to prepare a selective nuclear medicine imaging probe for the Endothelin 1 receptor A in the brain.

MATERIAL AND METHODS

Ferulic acid (an ETRA antagonist) was radiolabeled using 131I by direct electrophilic substitution method. The radiolabeled ferulic acid was formulated as polymeric micelles to allow intranasal brain delivery. Biodistribution was studied in Swiss albino mice by comparing brain uptake of 131I-ferulic acid after IN administration of 131I-ferulic acid polymeric micelles, IN administration of 131I-ferulic acid solution and IV administration of 131I-ferulic acid solution.

RESULTS

Successful radiolabeling was achieved with an RCY of 98 % using 200 μg of ferulic acid and 60 μg of CAT as oxidizing agents at pH 6, room temperature and 30 min reaction time. 131I-ferulic acid polymeric micelles were successfully formulated with the particle size of 21.63 nm and polydispersity index of 0.168. Radioactivity uptake in the brain and brain/blood uptake ratio for I.N 131I-ferulic acid polymeric micelles were greater than the two other routes at all periods.

CONCLUSION

Our results provide 131I-ferulic acid polymeric micelles as a hopeful nuclear medicine tracer for ETRA brain receptor.

Receptor for advanced glycation end-products: Biological significance and imaging applications

The receptor for advanced glycation end-products (RAGE or AGER) is a transmembrane, immunoglobulin-like receptor that, due to its multiple isoform structures, binds to a diverse range of endo- and exogenous ligands. RAGE activation caused by the ligand binding initiates a cascade of complex pathways associated with producing free radicals, such as reactive nitric oxide and oxygen species, cell proliferation, and immunoinflammatory processes. The involvement of RAGE in the pathogenesis of disorders such as diabetes, inflammation, tumor progression, and endothelial dysfunction is dictated by the accumulation of advanced glycation end-products (AGEs) at pathologic states leading to sustained RAGE upregulation. The involvement of RAGE and its ligands in numerous pathologies and diseases makes RAGE an interesting target for therapy focused on the modulation of both RAGE expression or activation and the production or exogenous administration of AGEs. Despite the known role that the RAGE/AGE axis plays in multiple disease states, there remains an urgent need to develop noninvasive, molecular imaging approaches that can accurately quantify RAGE levels in vivo that will aid in the validation of RAGE and its ligands as biomarkers and therapeutic targets. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Diagnostic Tools > Biosensing.

Engineered aptamers for molecular imaging

Molecular imaging, including quantification and molecular interaction studies, plays a crucial role in visualizing and analysing molecular events occurring within cells or organisms, thus facilitating the understanding of biological processes. Moreover, molecular imaging offers promising applications for early disease diagnosis and therapeutic evaluation. Aptamers are oligonucleotides that can recognize targets with a high affinity and specificity by folding themselves into various three-dimensional structures, thus serving as ideal molecular recognition elements in molecular imaging. This review summarizes the commonly employed aptamers in molecular imaging and outlines the prevalent design approaches for their applications. Furthermore, it highlights the successful application of aptamers to a wide range of targets and imaging modalities. Finally, the review concludes with a forward-looking perspective on future advancements in aptamer-based molecular imaging.

Effect of Gaussian Smoothing Filter Size for CT-Based Attenuation Correction on Quantitative Assessment of Bone SPECT/CT: A Phantom Study

This study aims to determine the effect of Gaussian filter size for CT-based attenuation correction (CTAC) on the quantitative assessment of bone SPECT. An experiment was performed using a cylindrical phantom containing six rods, of which one was filled with water and five were filled with various concentrations of K2HPO4 solution (120-960 mg/cm3) to simulate different bone densities. 99mTc-solution of 207 kBq/ml was also included within the rods. SPECT data were acquired at 120 views for 30 s/view. CT for attenuation correction were obtained at 120 kVp and 100 mA. Sixteen different CTAC maps processed with different Gaussian filter sizes (ranging from 0 to 30 mm in 2 mm increments) were generated. SPECT images were reconstructed for each of the 16 CTAC maps. Attenuation coefficients and radioactivity concentrations in the rods were compared with those in the water-filled rod without K2HPO4 solution as a reference. Gaussian filter sizes below 14-16 mm resulted in an overestimation of radioactivity concentrations for rods with high concentrations of K2HPO4 (≥ 666 mg/cm3). The overestimation of radioactivity concentration measurement was 3.8% and 5.5% for 666 mg/cm3 and 960 mg/cm3 K2HPO4 solutions, respectively. The difference in radioactivity concentration between the water rod and the K2HPO4 rods was minimal at 18-22 mm. The use of Gaussian filter sizes smaller than 14-16 mm caused an overestimation of radioactivity concentration in regions of high CT values. Setting the Gaussian filter size to 18-22 mm enables radioactivity concentration to be measured with the least influence on bone density.

Nitrogen-15 dynamic nuclear polarization of nicotinamide derivatives in biocompatible solutions

Dissolution dynamic nuclear polarization (dDNP) increases the sensitivity of magnetic resonance imaging by more than 10,000 times, enabling in vivo metabolic imaging to be performed noninvasively in real time. Here, we are developing a group of dDNP polarized tracers based on nicotinamide (NAM). We synthesized 1-15N-NAM and 1-15N nicotinic acid and hyperpolarized them with dDNP, reaching (13.0 ± 1.9)% 15N polarization. We found that the lifetime of hyperpolarized 1-15N-NAM is strongly field- and pH-dependent, with T1 being as long as 41 s at a pH of 12 and 1 T while as short as a few seconds at neutral pH and fields below 1 T. The remarkably short 1-15N lifetime at low magnetic fields and neutral pH drove us to establish a unique pH neutralization procedure. Using 15N dDNP and an inexpensive rodent imaging probe designed in-house, we acquired a 15N MRI of 1-15N-NAM (previously hyperpolarized for more than an hour) in less than 1 s.

Rare Solid Pancreatic Lesions on Cross-Sectional Imaging

Several solid lesions can be found within the pancreas mainly arising from the exocrine and endocrine pancreatic tissue. Among all pancreatic malignancies, the most common subtype is pancreatic ductal adenocarcinoma (PDAC), to a point that pancreatic cancer and PDAC are used interchangeably. But, in addition to PDAC, and to the other most common and well-known solid lesions, either related to benign conditions, such as pancreatitis, or not so benign, such as pancreatic neuroendocrine neoplasms (pNENs), there are solid pancreatic lesions considered rare due to their low incidence. These lesions may originate from a cell line with a differentiation other than exocrine/endocrine, such as from the nerve sheath as for pancreatic schwannoma or from mesenchymal cells as for solitary fibrous tumour. These rare solid pancreatic lesions may show a behaviour that ranges in a benign to highly aggressive malignant spectrum. This review includes cases of an intrapancreatic accessory spleen, pancreatic tuberculosis, solid serous cystadenoma, solid pseudopapillary tumour, pancreatic schwannoma, purely intraductal neuroendocrine tumour, pancreatic fibrous solitary tumour, acinar cell carcinoma, undifferentiated carcinoma with osteoclastic-like giant cells, adenosquamous carcinoma, colloid carcinoma of the pancreas, primary leiomyosarcoma of the pancreas, primary and secondary pancreatic lymphoma and metastases within the pancreas. Therefore, it is important to determine the correct diagnosis to ensure optimal patient management. Because of their rarity, their existence is less well known and, when depicted, in most cases incidentally, the correct diagnosis remains challenging. However, there are some typical imaging features present on cross-sectional imaging modalities that, taken into account with the clinical and biological context, contribute substantially to achieve the correct diagnosis.

Implementation of xSPECT, xSPECT bone and Broadquant from literature, clinical survey and innovative phantom study with task-based image quality assessment

OBJECTIVE

From patient and phantom studies, we aimed to highlight an original implementation process and share a two-years experience clinical feedback on xSPECT (xS), xSPECT Bone (xB) and Broadquant quantification (Siemens) for 99mTc-bone and 177Lu-NET (neuroendocrine tumors) imaging.

METHODS

Firstly, we checked the relevance of implemented protocols and Broadquant module on the basis of literature and with a homogeneous phantom study respectively. Then, we described xS and xB behaviours with reconstruction parameters (10i-0mm to 40i-20mm) and optimized the protocols through a blinded survey (7 physicians). Finally, the preferred 99mTc-bone reconstruction was assessed through an IEC NEMA phantom including liquid bone spheres. Conventional SNR, CNR, spatial resolution, Q.%error, and recovery curves; and innovative NPS, TTF and detectability score d' were performed (ImQuest software). We also sought to review the adoption of these tools in clinical routine and showed the potential of quantitative xB in the context of theranostics (Xofigo®).

RESULTS

We showed the need of optimization of implemented reconstruction algorithms and pointed out a decay correction particularity with Broadquant. Preferred parameters were 1s-25i-8mm and 1s-25i-5mm for xS/xB-bone and xS-NET imaging respectively. The phantom study highlighted the different image quality especially for the enhanced spatial resolution xB algorithm (1/TTF10%=2.1 mm) and showed F3D and xB shared the best performances in terms of image quality and quantification. xS was generally less efficient.

CONCLUSIONS

Qualitative F3D still remains the clinical standard, xB and Broadquant offer challenging perspectives in theranostics. We introduced the potential of innovative metrics for image quality analysis and showed how CT tools should be adapted to fit nuclear medicine imaging.

Current Status and Future Perspective on Molecular Imaging and Treatment of Neuroblastoma

Neuroblastoma is the most common extracranial solid tumor in children and arises from anywhere along the sympathetic nervous system. It is a highly heterogeneous disease with a wide range of prognosis, from spontaneous regression or maturing to highly aggressive. About half of pediatric neuroblastoma patients develop the metastatic disease at diagnosis, which carries a poor prognosis. Nuclear medicine plays a pivotal role in the diagnosis, staging, response assessment, and long-term follow-up of neuroblastoma. And it has also played a prominent role in the treatment of neuroblastoma. Because the structure of metaiodobenzylguanidine (MIBG) is similar to that of norepinephrine, 90% of neuroblastomas are MIBG-avid. 123I-MIBG whole-body scintigraphy is the standard nuclear imaging technique for neuroblastoma, usually in combination with SPECT/CT. However, approximately 10% of neuroblastomas are MIBG nonavid. PET imaging has many technical advantages over SPECT imaging, such as higher spatial and temporal resolution, higher sensitivity, superior quantitative capability, and whole-body tomographic imaging. In recent years, various tracers have been used for imaging neuroblastoma with PET. The importance of patient-specific targeted radionuclide therapy for neuroblastoma therapy has also increased. 131I-MIBG therapy is part of the front-line treatment for children with high-risk neuroblastoma. And peptide receptor radionuclide therapy with radionuclide-labeled somatostatin analogues has been successfully used in the therapy of neuroblastoma. Moreover, radioimmunoimaging has important applications in the diagnosis of neuroblastoma, and radioimmunotherapy may provide a novel treatment modality against neuroblastoma. This review discusses the use of current and novel radiopharmaceuticals in nuclear medicine imaging and therapy of neuroblastoma.

Label-Free Optical Metabolic Imaging in Cells and Tissues

Over the last half century, the autofluorescence of the metabolic cofactors NADH (reduced nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) has been quantified in a variety of cell types and disease states. With the spread of nonlinear optical microscopy techniques in biomedical research, NADH and FAD imaging has offered an attractive solution to noninvasively monitor cell and tissue status and elucidate dynamic changes in cell or tissue metabolism. Various tools and methods to measure the temporal, spectral, and spatial properties of NADH and FAD autofluorescence have been developed. Specifically, an optical redox ratio of cofactor fluorescence intensities and NADH fluorescence lifetime parameters have been used in numerous applications, but significant work remains to mature this technology for understanding dynamic changes in metabolism. This article describes the current understanding of our optical sensitivity to different metabolic pathways and highlights current challenges in the field. Recent progress in addressing these challenges and acquiring more quantitative information in faster and more metabolically relevant formats is also discussed.

Synthesis, Characterization, and Biological Evaluation of Radiolabeled Glutamine Conjugated Polymeric Nanoparticles: A Simple Approach for Tumor Imaging

Application of nanoradiopharmaceuticals for molecular imaging has gained worldwide importance for their multifaceted potentials focusing on providing a safe and cost-effective approach. Biodistribution studies on such species are capable of bringing nanomedicine to patients. Current therapeutically available labeling strategies suffer from different limitations, including off-target cytotoxicity and radiolabel release over time. Poly(lactic-co-glycolic acid)(PLGA) nanoparticles are biodegradable carriers for a variety of contrast agents that can be employed in medicine with high loading capacity for multimodal imaging agents. Here, glutamine-conjugated PLGA polymers were used to construct polymeric nanoparticles (G-PNP) similar to unconjugated PLGA nanoparticles (PNP)s formulated for ex vivo cell labeling and in vivo tumor scintigraphy studies. G-PNP/PNP, characterized by Fourier-transform infrared, atomic-force-microscopy, particle-size, and zeta-potential studies, were biocompatible as evaluated by MTT assay. G-PNPs were radiolabeled with ^99mtechnetium (^99mTc) by borohydrite reduction. G-PNPs demonstrated higher cellular uptake than PNPs, with no major cytotoxicity. Radiochemical purity indicated that ^99mTc labeled G-PNP (^99mTc-G-PNP) can form a stable complex with substantial stability in serum with respect to time. Imaging studies showed that ^99mTc-G-PNP significantly accumulated at the C6 glioma cell induced tumor-site in rats. Thus, ^99mTc-G-PNP demonstrated favorable characteristics and imaging potential which may make it a promising tumor imaging nanoprobe as a nanoradiopharmaceutical.

Visual Scoring of Sacroiliac Joint/Sacrum Ratios of Single-Photon Emission Computed Tomography/Computed Tomography Images Affords High Sensitivity and Negative Predictive Value in Axial Spondyloarthritis

Spondyloarthritis (SpA) is characterized by inflammatory back pain. Magnetic resonance imaging (MRI) was the earlier gold standard technique for detecting early inflammatory change. We reassessed the diagnostic utility of sacroiliac joint/sacrum (SIS) ratios of single-photon emission computed tomography/computed tomography (SPECT/CT) for identifying sacroiliitis. We aimed to investigate of SPECT/CT in diagnosing SpA using a rheumatologist's visual scoring of SIS ratios assessment. We conducted a single-center, medical records review study of patients with lower back pain who underwent bone SPECT/CT from August 2016 to April 2020. We employed semiquantitative visual bone scoring methods of SIS ratio. The uptake of each sacroiliac joint was compared to that of the sacrum (0-2). A score of 2 for the sacroiliac joint of either side was considered diagnostic of sacroiliitis. Of the 443 patients assessed, 40 had axial SpA (axSpA), 24 being radiographic axSpA and 16 being nonradiographic axSpA. The sensitivity, specificity, and positive and negative predictive values of SIS ratio of SPECT/CT for axSpA were 87.5%, 56.5%, 16.6%, and 97.8%, respectively. In receiver operating curve analysis, MRI better diagnosed axSpA than did SIS ratio of SPECT/CT. Although the diagnostic utility of SIS ratio of SPECT/CT was inferior to MRI, visual scoring of SPECT/CT affords high sensitivity and negative predictive value in axSpA. When MRI is inappropriate for certain patients, SIS ratio of SPECT/CT is an alternative tool for identifying axSpA in real practice.

Quantitative liver SPECT/CT is a novel tool to assess liver function, prognosis, and response to treatment in cirrhosis

Background

Functional liver reserve is an important determinant of survival in cirrhosis. The traditional indocyanine green test (ICG) is cumbersome. Hence, we developed and validated a novel liver imaging, a hybrid of SPECT and CT (Q-SPECT/CT), for evaluating disease severity, outcomes, and response to treatment in decompensated cirrhosis (DC).

Methods

We recruited a cohort of DC patients at a tertiary institute between 2016-2019. First, we standardized the Q-SPECT/CT across a predefined range of volumes through phantom experiments. Then we performed clinical and laboratory evaluations, ICG test (retention at 15 min), and Q-SPECT/CT at baseline and 12 months of granulocyte colony-stimulating factor (G-CSF) and standard medical treatment (SMT).

Results

In 109 DC patients, 87.1% males, aged 51 ± 10 years, MELD: 14 (7-21), the percent quantitative liver uptake (%QLU) on Q-SPECT/CT exhibited a strong correlation with CTP (r = -0.728, p < 0.001), MELD (r = -0.743; p < 0.001) and ICG-R-15 (r = -0.720, p < 0.001) at baseline. %QLU had the maximum discrimination (AUC: 0.890-0.920), sensitivity (88.9-90.3%), specificity (81.2-90.7%), and accuracy (85.8-89.4%) than liver volumes on Q-SPECT/CT or ICG test for classifying patients in CTP/MELD based prognostic categories. A significant increase in %QLU (26.09 ± 10.06 to 31.2 ± 12.19, p = 0.001) and improvement in CTP/MELD correlated with better survival of G-CSF treated DC patients (p < 0.05). SMT did not show any improvement in Q-SPECT/CT or clinical severity scores (p > 0.05). %QLU > 25 (adj.H.R.: 0.234, p = 0.003) and G-CSF treatment (adj.H.R.: 0.414, p = 0.009) were independent predictors of better 12-months survival in DC.

Conclusion

Q-SPECT/CT (%QLU) is a novel non-invasive, diagnostic, prognostic, and theragnostic marker of liver reserve and its functions in cirrhosis patients.

Clinical trial registration

Clinicaltrials.gov, NCT02451033 and NCT03415698.

Biodistribution of Multimodal Gold Nanoclusters Designed for Photoluminescence-SPECT/CT Imaging and Diagnostic

Highly biocompatible nanostructures for multimodality imaging are critical for clinical diagnostics improvements in the future. Combining optical imaging with other techniques may lead to important advances in diagnostics. The purpose of such a system would be to combine the individual advantages of each imaging method to provide reliable and accurate information at the site of the disease bypassing the limitations of each. The aim of the presented study was to evaluate biodistribution of the biocompatible technetium-99m labelled bovine serum albumin-gold nanoclusters (^99mTc-BSA-Au NCs) as photoluminescence-SPECT/CT agent in experimental animals. It was verified spectroscopically that radiolabelling with ^99mTc does not influence the optical properties of BSA-Au NCs within the synthesized ^99mTc-BSA-Au NCs bioconjugates. Biodistribution imaging of the ^99mTc-BSA-Au NCs in Wistar rats was performed using a clinical SPECT/CT system. In vivo imaging of Wistar rats demonstrated intense cardiac blood pool activity, as well as rapid blood clearance and accumulation in the kidneys, liver, and urinary bladder. Confocal images of kidney, liver and spleen tissues revealed no visible uptake indicating that the circulation lifetime of ^99mTc-BSA-Au NCs in the bloodstream might be too short for accumulation in these tissues. The cellular uptake of ^99mTc-BSA-Au NCs in kidney cells was also delayed and substantial accumulation was observed only after 24-h incubation. Based on our experiments, it was concluded that ^99mTc-BSA-Au NCs could be used as a contrast agent and shows promise as potential diagnostic agents for bloodstream imaging of the excretory organs in vivo.

Advanced imaging for risk stratification for ventricular arrhythmias and sudden cardiac death

Sudden cardiac death (SCD) is a leading cause of mortality, comprising approximately half of all deaths from cardiovascular disease. In the US, the majority of SCD (85%) occurs in patients with ischemic cardiomyopathy (ICM) and a subset in patients with non-ischemic cardiomyopathy (NICM), who tend to be younger and whose risk of mortality is less clearly delineated than in ischemic cardiomyopathies. The conventional means of SCD risk stratification has been the determination of the ejection fraction (EF), typically via echocardiography, which is currently a means of determining candidacy for primary prevention in the form of implantable cardiac defibrillators (ICDs). Advanced cardiac imaging methods such as cardiac magnetic resonance imaging (CMR), single-photon emission computerized tomography (SPECT) and positron emission tomography (PET), and computed tomography (CT) have emerged as promising and non-invasive means of risk stratification for sudden death through their characterization of the underlying myocardial substrate that predisposes to SCD. Late gadolinium enhancement (LGE) on CMR detects myocardial scar, which can inform ICD decision-making. Overall scar burden, region-specific scar burden, and scar heterogeneity have all been studied in risk stratification. PET and SPECT are nuclear methods that determine myocardial viability and innervation, as well as inflammation. CT can be used for assessment of myocardial fat and its association with reentrant circuits. Emerging methodologies include the development of "virtual hearts" using complex electrophysiologic modeling derived from CMR to attempt to predict arrhythmic susceptibility. Recent developments have paired novel machine learning (ML) algorithms with established imaging techniques to improve predictive performance. The use of advanced imaging to augment risk stratification for sudden death is increasingly well-established and may soon have an expanded role in clinical decision-making. ML could help shift this paradigm further by advancing variable discovery and data analysis.

Production Review of Accelerator-Based Medical Isotopes

The production of reactor-based medical isotopes is fragile, which has meant supply shortages from time to time. This paper reviews alternative production methods in the form of cyclotrons, linear accelerators and neutron generators. Finally, the status of the production of medical isotopes in China is described.

Radiopharmaceuticals for PET and SPECT Imaging: A Literature Review over the Last Decade

Positron emission tomography (PET) uses radioactive tracers and enables the functional imaging of several metabolic processes, blood flow measurements, regional chemical composition, and/or chemical absorption. Depending on the targeted processes within the living organism, different tracers are used for various medical conditions, such as cancer, particular brain pathologies, cardiac events, and bone lesions, where the most commonly used tracers are radiolabeled with 18F (e.g., [¹⁸F]-FDG and NA [¹⁸F]). Oxygen-15 isotope is mostly involved in blood flow measurements, whereas a wide array of ¹¹C-based compounds have also been developed for neuronal disorders according to the affected neuroreceptors, prostate cancer, and lung carcinomas. In contrast, the single-photon emission computed tomography (SPECT) technique uses gamma-emitting radioisotopes and can be used to diagnose strokes, seizures, bone illnesses, and infections by gauging the blood flow and radio distribution within tissues and organs. The radioisotopes typically used in SPECT imaging are iodine-123, technetium-99m, xenon-133, thallium-201, and indium-111. This systematic review article aims to clarify and disseminate the available scientific literature focused on PET/SPECT radiotracers and to provide an overview of the conducted research within the past decade, with an additional focus on the novel radiopharmaceuticals developed for medical imaging.

Technical note: Partitioning of gated single photon emission computed tomography raw data for protocols optimization

PURPOSE

Methodologies for optimization of SPECT image acquisition can be challenging due to imaging throughput, physiological bias, and patient comfort constraints. We evaluated a vendor-independent method for simulating lower count image acquisitions.

METHODS

We developed an algorithm that recombines the ECG-gated raw data into reduced counting acquisitions. We then tested the algorithm to simulate reduction of counting statistics from phantom SPECT image acquisition, which was synchronized with an ECG simulator. The datasets were reconstructed with a resolution recovery algorithm and the summed stress score (SSS) was assessed by three readers (two experts and one automatic).

RESULTS

The algorithm generated varying counting levels, simulating multiple examinations at the same time. The error between the expected and the simulated countings ranged from approximately 5% to 10% for the ungated simulations and 0% for the gated simulations.

CONCLUSIONS

The vendor-independent algorithm successfully generated lower counting statistics datasets from single-gated SPECT raw data. This method can be readily implemented for optimal SPECT research aiming to lower the injected activity and/ or to shorten the acquisition time.

Prefabricated 3D-Printed Tissue-Engineered Bone for Mandibular Reconstruction: A Preclinical Translational Study in Primate

The advent of three dimensionally (3D) printed customized bone grafts using different biomaterials has enabled repairs of complex bone defects in various in vivo models. However, studies related to their clinical translations are truly limited. Herein, 3D printed poly(lactic-co-glycolic acid)/β-tricalcium phosphate (PLGA/TCP) and TCP scaffolds with or without recombinant bone morphogenetic protein −2 (rhBMP-2) coating were utilized to repair primate’s large-volume mandibular defects and compared efficacy of prefabricated tissue-engineered bone (PTEB) over direct implantation (without prefabrication). ¹⁸F-FDG PET/CT was explored for real-time monitoring of bone regeneration and vascularization. After 3-month’s prefabrication, the original 3D-architecture of the PLGA/TCP-BMP scaffold was found to be completely lost, while it was properly maintained in TCP-BMP scaffolds. Besides, there was a remarkable decrease in the PLGA/TCP-BMP scaffold density and increase in TCP-BMP scaffolds density during ectopic (within latissimus dorsi muscle) and orthotopic (within mandibular defect) implantation, indicating regular bone formation with TCP-BMP scaffolds. Notably, PTEB based on TCP-BMP scaffold was successfully fabricated with pronounced effects on bone regeneration and vascularization based on radiographic, ¹⁸F-FDG PET/CT, and histological evaluation, suggesting a promising approach toward clinical translation.

Cyclotron production and radiochemical purification of terbium-155 for SPECT imaging

Background

Terbium-155 [T_1/2 = 5.32 d, Eγ = 87 keV (32%) 105 keV (25%)] is an interesting radionuclide suitable for single photon emission computed tomography (SPECT) imaging with potential application in the diagnosis of oncological disease. It shows similar decay characteristics to the clinically established indium-111 and would be a useful substitute for the diagnosis and prospective dosimetry with biomolecules that are afterwards labeled with therapeutic radiolanthanides and pseudo-radiolanthanides, such as lutetium-177 and yttrium-90. Moreover, terbium-155 could form part of the perfect “matched pair” with the therapeutic radionuclide terbium-161, making the concept of true radiotheragnostics a reality. The aim of this study was the investigation of the production of terbium-155 via the ¹⁵⁵Gd(p,n)¹⁵⁵Tb and ¹⁵⁶Gd(p,2n)¹⁵⁵Tb nuclear reactions and its subsequent purification, in order to obtain a final product in quantity and quality sufficient for preclinical application. The ¹⁵⁶Gd(p,2n)¹⁵⁵Tb nuclear reaction was performed with 72 MeV protons (degraded to ~ 23 MeV), while the ¹⁵⁵Gd(p,n)¹⁵⁵Tb reaction was degraded further to ~ 10 MeV, as well as performed at an 18 MeV medical cyclotron, to demonstrate its feasibility of production.

Result

The ¹⁵⁶Gd(p,2n)¹⁵⁵Tb nuclear reaction demonstrated higher production yields of up to 1.7 GBq, however, lower radionuclidic purity when compared to the final product (~ 200 MBq) of the ¹⁵⁵Gd(p,n)¹⁵⁵Tb nuclear reaction. In particular, other radioisotopes of terbium were produced as side products. The radiochemical purification of terbium-155 from the target material was developed to provide up to 1.0 GBq product in a small volume (~ 1 mL 0.05 M HCl), suitable for radiolabeling purposes. The high chemical purity of terbium-155 was proven by radiolabeling experiments at molar activities up to 100 MBq/nmol. SPECT/CT experiments were performed in tumor-bearing mice using [¹⁵⁵Tb]Tb-DOTATOC.

Conclusion

This study demonstrated two possible production routes for high activities of terbium-155 using a cyclotron, indicating that the radionuclide is more accessible than the exclusive mass-separated method previously demonstrated. The developed radiochemical purification of terbium-155 from the target material yielded [¹⁵⁵Tb]TbCl₃ in high chemical purity. As a result, initial cell uptake investigations, as well as SPECT/CT in vivo studies with [¹⁵⁵Tb]Tb-DOTATOC, were successfully performed, indicating that the chemical separation produced a product with suitable quality for preclinical studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41181-021-00153-w.

The Evolution and Future of Targeted Cancer Therapy: From Nanoparticles, Oncolytic Viruses, and Oncolytic Bacteria to the Treatment of Solid Tumors

While many classes of chemotherapeutic agents exist to treat solid tumors, few can generate a lasting response without substantial off-target toxicity despite significant scientific advancements and investments. In this review, the paths of development for nanoparticles, oncolytic viruses, and oncolytic bacteria over the last 20 years of research towards clinical translation and acceptance as novel cancer therapeutics are compared. Novel nanoparticle, oncolytic virus, and oncolytic bacteria therapies all start with a common goal of accomplishing therapeutic drug activity or delivery to a specific site while avoiding off-target effects, with overlapping methodology between all three modalities. Indeed, the degree of overlap is substantial enough that breakthroughs in one therapeutic could have considerable implications on the progression of the other two. Each oncotherapeutic modality has accomplished clinical translation, successfully overcoming the potential pitfalls promising therapeutics face. However, once studies enter clinical trials, the data all but disappears, leaving pre-clinical researchers largely in the dark. Overall, the creativity, flexibility, and innovation of these modalities for solid tumor treatments are greatly encouraging, and usher in a new age of pharmaceutical development.

123I-Meta-Iodobenzylguanidine Single-Photon Emission Computerized Tomography/Computerized Tomography Scintigraphy in the Management of Neuroblastoma

Neuroblastoma is the most common pediatric extracranial solid tumor. High-risk neuroblastoma is the most frequent presentation with an overall survival of approximately 50%. ¹²³I-meta-iodobenzylguanidine (¹²³I-mIBG) scintigraphy in the assessment of the primary tumor and its metastases at diagnosis and after chemotherapy is a cornerstone imaging modality. In particular, the bulk of skeletal metastatic disease evaluated with ¹²³I-mIBG at diagnosis and the following chemotherapy has a prognostic value. Currently, single-photon emission computerized tomography/computerised tomography (SPECT/CT) is considered a fundamental part of ¹²³I-mIBG scintigraphy. ¹²³I-mIBG SPECT/CT is a highly specific and sensitive imaging biomarker and it has been the basis of all existing neuroblastoma trials requiring molecular imaging. The introduction of SPECT/CT has shown not only the heterogeneity of the mIBG uptake within the primary tumor but also the presence of completely mIBG nonavid metastatic lesions with mIBG-avid primary neuroblastomas. It is currently possible to semi-quantitatively assess tracer uptake with standardized uptake value, which allows a more precise evaluation of the tracer avidity and can help monitor chemotherapy response. The patchy mIBG uptake has consequences from a theranostic perspective and may partly explain the failure of some neuroblastomas to respond to ¹³¹I-mIBG molecular radiotherapy. Various positron emission tomography tracers, targeting different aspects of neuroblastoma cell biology, are being tested as possible alternatives to ¹²³I-mIBG.

Positron emission tomography and single photon emission computed tomography imaging of tertiary lymphoid structures during the development of lupus nephritis

Lymphoid neogenesis occurs in tissues targeted by chronic inflammatory processes, such as infection and autoimmunity. In systemic lupus erythematosus (SLE), such structures develop within the kidneys of lupus-prone mice ((NZBXNZW)F1) and are observed in kidney biopsies taken from SLE patients with lupus nephritis (LN). The purpose of this prospective longitudinal animal study was to detect early kidney changes and tertiary lymphoid structures (TLS) using in vivo imaging. Positron emission tomography (PET) by tail vein injection of 18-F-fluoro-2-deoxy-D-glucose (¹⁸F-FDG)(PET/FDG) combined with computed tomography (CT) for anatomical localization and single photon emission computed tomography (SPECT) by intraperitoneal injection of ^99mTC labeled Albumin Nanocoll (^99mTC-Nanocoll) were performed on different disease stages of NZB/W mice (n = 40) and on aged matched control mice (BALB/c) (n = 20). By using one-way ANOVA analyses, we compared two different compartmental models for the quantitative measure of ¹⁸F-FDG uptake within the kidneys. Using a new five-compartment model, we observed that glomerular filtration of ^18FFDG in lupus-prone mice decreased significantly by disease progression measured by anti-dsDNA Ab production and before onset of proteinuria. We could not visualize TLS within the kidneys, but we were able to visualize pancreatic TLS using ^99mTC Nanocoll SPECT. Based on our findings, we conclude that the five-compartment model can be used to measure changes of FDG uptake within the kidney. However, new optimal PET/SPECT tracer administration sites together with more specific tracers in combination with magnetic resonance imaging (MRI) may make it possible to detect formation of TLS and LN before clinical manifestations.

Design, Synthesis, and Utility of Defined Molecular Scaffolds

A growing theme in chemistry is the joining of multiple organic molecular building blocks to create functional molecules. Diverse derivatizable structures—here termed “scaffolds” comprised of “hubs”—provide the foundation for systematic covalent organization of a rich variety of building blocks. This review encompasses 30 tri- or tetra-armed molecular hubs (e.g., triazine, lysine, arenes, dyes) that are used directly or in combination to give linear, cyclic, or branched scaffolds. Each scaffold is categorized by graph theory into one of 31 trees to express the molecular connectivity and overall architecture. Rational chemistry with exacting numbers of derivatizable sites is emphasized. The incorporation of water-solubilization motifs, robust or self-immolative linkers, enzymatically cleavable groups and functional appendages affords immense (and often late-stage) diversification of the scaffolds. Altogether, 107 target molecules are reviewed along with 19 syntheses to illustrate the distinctive chemistries for creating and derivatizing scaffolds. The review covers the history of the field up through 2020, briefly touching on statistically derivatized carriers employed in immunology as counterpoints to the rationally assembled and derivatized scaffolds here, although most citations are from the past two decades. The scaffolds are used widely in fields ranging from pure chemistry to artificial photosynthesis and biomedical sciences.

Osteoid Osteoma: An Updated Review of Epidemiology, Pathogenesis, Clinical Presentation, Radiological Features, and Treatment Option

Osteoid osteoma, the third most common benign bone tumor, usually occurs in the cortex of long bones. It consists of a radiolucent nidus surrounded by reactive osteosclerosis. Generally, osteoid osteoma affects young males. Nocturnal pain that eases with salicylates or nonsteroidal anti-inflammatory drugs (NSAID) is the typical clinical presentation. Sometimes, it remains undiagnosed for a long time. Plain radiography and computed tomography are usually sufficient for the diagnosis of osteoid osteoma. Initial treatment includes salicylates and NSAID because the tumor often regresses spontaneously over 2-6 years. Surgical treatment is indicated in case of unresponsive pain to medical therapy, no tolerance of prolonged NSAID therapy due to side effects, and no willingness to activity limitations. Nowadays, minimally invasive techniques have replaced open surgery and are considered the gold standard of surgical treatment. Although cryoablation seems superior in terms of the nerve damage and immunotherapy effect, radiofrequency ablation is the preferred technique.

Cancer theranostic platforms based on injectable polymer hydrogels

Theranostic platforms that combine therapy with diagnosis not only prevent the undesirable biological responses that may occur when these processes are conducted separately, but also allow individualized therapies for patients. Polymer hydrogels have been employed to provide well-controlled drug release and targeted therapy in theranostics, where injectable hydrogels enable non-invasive treatment and monitoring with a single injection, offering greater patient comfort and efficient therapy. Efforts have been focused on applying injectable polymer hydrogels in theranostic research and clinical use. This review highlights recent progress in the design of injectable polymer hydrogels for cancer theranostics, particularly focusing on the elements/components of theranostic hydrogels, and their cross-linking strategies, structures, and performance with regard to drug delivery/tracking. Therapeutic agents and tracking modalities that are essential components of the theranostic platforms are introduced, and the design strategies, properties and applications of the injectable hydrogels developed via two approaches, namely chemical bonds and physical interactions, are described. The theranostic functions of the platforms are highly dependent on the architecture and components employed for the construction of hydrogels. Challenges currently presented by theranostic platforms based on injectable hydrogels are identified, and prospects of acquiring more comfortable and personalized therapies are proposed.

Endoglin/CD105-Based Imaging of Cancer and Cardiovascular Diseases: A Systematic Review

Molecular imaging of pathologic lesions can improve efficient detection of cancer and cardiovascular diseases. A shared pathophysiological feature is angiogenesis, the formation of new blood vessels. Endoglin (CD105) is a coreceptor for ligands of the Transforming Growth Factor-β (TGF-β) family and is highly expressed on angiogenic endothelial cells. Therefore, endoglin-based imaging has been explored to visualize lesions of the aforementioned diseases. This systematic review highlights the progress in endoglin-based imaging of cancer, atherosclerosis, myocardial infarction, and aortic aneurysm, focusing on positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), near-infrared fluorescence (NIRF) imaging, and ultrasound imaging. PubMed was searched combining the following subjects and their respective synonyms or relevant subterms: “Endoglin”, “Imaging/Image-guided surgery”. In total, 59 papers were found eligible to be included: 58 reporting about preclinical animal or in vitro models and one ex vivo study in human organs. In addition to exact data extraction of imaging modality type, tumor or cardiovascular disease model, and tracer (class), outcomes were described via a narrative synthesis. Collectively, the data identify endoglin as a suitable target for intraoperative and diagnostic imaging of the neovasculature in tumors, whereas for cardiovascular diseases, the evidence remains scarce but promising.

Size-controlled bimodal in vivo nanoprobes as near-infrared phosphors and positive contrast agents for magnetic resonance imaging

Rare-earth-doped nanoparticles (NPs), such as NaGdF₄ nanocrystals doped with light-emitting rare earth ions, are promising bimodal probes that allow the integration of over 1000 nm near-infrared (OTN-NIR; NIR-II/III) fluorescence imaging and magnetic resonance imaging (MRI) of live bodies. A precise control of the particle size is the key factor for achieving a high signal-to-noise ratio in both NIR fluorescence and MR images and for regulating their function in the body. In this study, size-controlled NaGdF₄:Yb³⁺, Er³⁺ NPs prepared by stepwise crystal growth were used for in vivo bimodal imaging. Hexagonal NaGdF₄:Yb³⁺,Er³⁺ NPs coated with poly(ethylene glycol)-poly(acrylic acid) block copolymer, with hydrodynamic diameters of 15 and 45 nm, were prepared and evaluated as bimodal NPs for OTN-NIR fluorescence imaging and MRI. Their longitudinal (T ₁) and transverse (T ₂) relaxation rates at the static magnetic field strength of 1.0 T, as well as their cytotoxicity towards NIH3T3 cell lines, were evaluated and compared to study the effect of size. Using these particles, blood vessel visualization was achieved by MRI, with the highest relaxometric ratio (r ₁/r ₂) of 0.79 reported to date for NaGdF₄-based nanoprobes (r ₁ = 19.78 mM^-1 s^-1), and by OTN-NIR fluorescence imaging. The results clearly demonstrate the potential of the size-controlled PEG-modified NaGdF₄:Yb³⁺,Er³⁺ NPs as powerful 'positive' T ₁-weight contrast MRI agents and OTN-NIR fluorophores.

SPECT/CT Correlation in the Diagnosis of Unilateral Condilar Hyperplasia

Objective: To evaluate the correlation between metabolic bone activity measured by single photon emission computed tomography (SPECT) and the anatomic condylar characteristics acquired by computed tomography (CT), in patients with unilateral condylar hyperplasia (UCH). Method and Materials/Patients: Observational, descriptive study in a group of 71 patients with clinical diagnosis of UCH and indication of SPECT/CT. Bone SPECT images obtained in a gamma-camera GE Infina and processed in a station Xeleris 3 with the program Volumetrix MI Evolution for bone. CT images acquired in a PET/CT Biograph mcT20 equipment (Siemens) processed in a station Osirix V 7.5.1 (Pixmeo, Bomex, Switzerland). Results: The sample included 24 men (33.8%) and 47 women (66.2%). Active state UCH was detected in 40 (56.3%) cases (over 55% uptake in the affected condyle) and 38 (53.5%) presented mandibular deviation to the right side. No significant differences related to sex, age, or mandibular deviation side were found. Mandibular deviation was the only morphologic feature related to active/inactive UCH (p = 0.003). The likelihood of active CH was significantly higher in patients with mandibular deviation higher than 6 mm compared with <6 mm (odds ratio (OR): 3.51, confidence interval (CI) 95%: 1.27–9.72). Conclusion: There is a significant correlation between the magnitude of mandibular deviation quantified on CT and metabolic findings obtained by SPECT in patients with UCH. The risk of active UCH is 3.5 times higher in patients with a mandibular deviation ≥6 mm.

Experimental evaluation of the GE NM/CT 870 CZT clinical SPECT system equipped with WEHR and MEHRS collimator

Purpose

A high‐energy‐resolution whole‐body SPECT‐CT device (NM/CT 870 CZT; C‐SPECT) equipped with a CZT detector has been developed and is being used clinically. A MEHRS collimator has also been developed recently, with an expected improvement in imaging accuracy using medium‐energy radionuclides. The objective of this study was to compare and analyze the accuracies of the following devices: a WEHR collimator and the MEHRS collimator installed on a C‐SPECT, and a NaI scintillation detector‐equipped Anger‐type SPECT (A‐SPECT) scanner, with a LEHR and LMEGP.

Methods

A line phantom was used to measure the energy resolutions including collimator characteristics in the planar acquisition of each device using ^99mTc and ¹²³I. We also measured the system's sensitivity and high‐contrast resolution using a lead bar phantom. We evaluated SPECT spatial resolution, high‐contrast resolution, radioactivity concentration linearity, and homogeneity, using a basic performance evaluation phantom. In addition, the effect of scatter correction was evaluated by varying the sub window (SW) employed for scattering correction.

Results

The energy resolution with ^99mTc was 5.6% in C‐SPECT with WEHR and 9.9% in A‐SPECT with LEHR. Using 123I, the results were 9.1% in C‐SPECT with WEHR, 5.5% in C‐SPECT with MEHRS, and 10.4% in A‐SPECT with LMEGP. The planar spatial resolution was similar under all conditions, but C‐SPECT performed better in SPECT acquisition. High‐contrast resolution was improved in C‐SPECT under planar condition and SPECT. The sensitivity and homogeneity were improved by setting the SW for scattering correction to 3% of the main peak in C‐SPECT.

Conclusion

C‐SPECT demonstrates excellent energy resolution and improved high‐contrast resolution for each radionuclide. In addition, when using 123I, careful attention should be paid to SW for scatter correction. By setting the appropriate SW, C‐SPECT with MEHRS has an excellent scattered ray removal effect, and highly homogenous imaging is possible while maintaining the high‐contrast resolution.

Nuclear Medicine in Times of COVID-19: How Radiopharmaceuticals Could Help to Fight the Current and Future Pandemics

The emergence and global spread of COVID-19, an infectious disease caused by the novel coronavirus SARS-CoV-2, has resulted in a continuing pandemic threat to global health. Nuclear medicine techniques can be used for functional imaging of (patho)physiological processes at the cellular or molecular level and for treatment approaches based on targeted delivery of therapeutic radionuclides. Ongoing development of radiolabeling methods has significantly improved the accessibility of radiopharmaceuticals for in vivo molecular imaging or targeted radionuclide therapy, but their use for biosafety threats such as SARS-CoV-2 is restricted by the contagious nature of these agents. Here, we highlight several potential uses of nuclear medicine in the context of SARS-CoV-2 and COVID-19, many of which could also be performed in laboratories without dedicated containment measures. In addition, we provide a broad overview of experimental or repurposed SARS-CoV-2-targeting drugs and describe how radiolabeled analogs of these compounds could facilitate antiviral drug development and translation to the clinic, reduce the incidence of late-stage failures and possibly provide the basis for radionuclide-based treatment strategies. Based on the continuing threat by emerging coronaviruses and other pathogens, it is anticipated that these applications of nuclear medicine will become a more important part of future antiviral drug development and treatment.

Is 67gallium dead? A retrospective review of 67gallium imaging in a single tertiary referral centre

BACKGROUND

[67Ga]Ga-citrate scanning has been used to investigate patients with known or suspected infection for over 50 years, continuing to maintain a clinical niche in many centres. The introduction of single photon emission tomography/computed tomography (SPECT/CT) in addition to planar imaging has improved the specificity of diagnosis.

AIM

To examine the experience of modern [67Ga]Ga-citrate scanning in a single tertiary referral centre, considering the diagnostic yield of the study.

METHODS

A retrospective audit was undertaken of 100 consecutive [67Ga]Ga-citrate scans at Royal North Shore Hospital, Sydney. Recorded information included patient demographics, clinical information/history, and primary and secondary diagnoses. Subgroup analyses included patients with a confirmed diagnosis of infection or a suspected diagnosis of infection.

RESULTS

The median age of patients was 68.5 years. Totally, 39/100 patients undergoing [67Ga]Ga-citrate scanning presented with a confirmed site of infection, with 2/6 patients with infective endocarditis and 5/12 patients with bacteraemia diagnosed with an additional, previously unknown, site of active infection (compared to 1/21 patients without documented bacteraemia). 61/100 patients did not have a confirmed site of infection before [67Ga]Ga-citrate scan (as per clinical history). 34/61 of these patients had a positive scan result for active infection/inflammation. Of 20 patients with a positive blood culture but no suspected site of infection, the source was identified in 9.

CONCLUSION

[67Ga]Ga-citrate has diagnostic value in the evaluation of complex patients with high-risk infection. High diagnostic yield is demonstrated in patients with bacteraemia with or without a confirmed site of infection, particularly when combined with SPECT/CT.

Handling of Doubtful WBC Scintigraphies in Patients with Suspected Prosthetic Joint Infections

Despite the application of EANM recommendations for radiolabelled white-blood-cells (WBC) scintigraphy, some cases still remain doubtful based only on visual analysis. The aim of this study was to investigate the role of semi-quantitative analysis and bone marrow scan (BMS) in solving doubtful cases. We retrospectively evaluated all [^99mTc]HMPAO-WBC scintigraphies performed, in the last 7 years, for a suspected monolateral prosthetic joint infection (PJI). In doubtful cases, we used five different thresholds of increase of target-to-background (T/B) ratio, between delayed and late images, as criteria of positivity (5%, 10%, 15%, 20% and 30%). BMS were also analysed and sensitivity, specificity and accuracy of different methods were calculated according to final diagnosis. The sensitivity, specificity and accuracy were, respectively, 77.8%, 43.8% and 53.0% for the cut-off at 5%; 72.2%, 66.7% and 68.2% for the cut-off at 10%; 66.7%, 75.0% and 72.7% for the cut-off at 15%; 66.7%, 85.4% and 80.3% for the cut-off at 20%; 33.3%, 93.8% and 77.3% for the cut-off at 30%. BMS provided a significantly higher diagnostic performance than 5%, 10% and 15% thresholds. Conversely, we did not observe any statistically significant difference between BMS and the cut-off of more than 20%. Therefore, doubtful cases should be analysed semi-quantitatively. An increase in T/B ratio of more than 20% between delayed and late images, should be considered as a criterion of positivity, thus avoiding BMS.

Advances in the In Vivo Molecular Imaging of Invasive Aspergillosis

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

Utility of Single-Photon Emission Computed Tomography/Computed Tomography in Suspected Unilateral Condylar Hyperplasia: A Histopathologic Validation Study

PURPOSE

The purpose of this study is to evaluate the utility of hybrid single-photon emission computed tomography (SPECT) and computed tomography (CT) with technetium-99m methylene diphosphonate in patients with suspected active unilateral condylar hyperplasia (UCH) using histopathology as the reference standard.

METHODS

Twenty-four patients with suspected active UCH prospectively underwent technetium-99m methylene diphosphonate planar bone scintigraphy with SPECT/CT of the mandible. Qualitative and quantitative readings for growth activity were performed by 3 nuclear medicine physicians and the final diagnosis was derived from postoperative histopathological examination. Readings were reported as positive, equivocal, or negative. Total, maximum, and mean counts were recorded for each condyle on SPECT/CT images. The uptake of the index (suspected) condyle was expressed as a count ratio (R_total, R_mean, R_max), a percentage uptake (P_total, P_mean, P_max), background-corrected counts (B_total, B_mean, B_max), as well as CT-based condylar diameters (R_CT,P_CT) relative to the contralateral condyle.

RESULTS

Interobserver agreement was 0.79 and 0.83 for planar bone scintigraphy and SPECT/CT, respectively, with a total of 5 and 1 equivocal readings from the respective modalities. Surgery was performed in 22 patients; all of them had pathologically proven UCH. SPECT/CT was slightly more sensitive than planar bone scintigraphy (91 vs 78%) with identical specificity (96%). R_total, R_mean, P_total, and P_mean demonstrated area under the curve between 84% and 86%. Metrics based on CT diameters and background-corrected counts were not associated with UCH diagnosis.

CONCLUSIONS

Quantitative approaches based on total or mean count ratio or relative count percentage were equally predictive for UCH diagnosis; however, they were slightly less sensitive compared with qualitative technetium-99m methylene diphosphonate SPECT/CT evaluation. SPECT/CT evaluation has the potential to decrease the equivocal readings.

The Role of Imaging Techniques to Define a Peri-Prosthetic Hip and Knee Joint Infection: Multidisciplinary Consensus Statements

Diagnosing a peri-prosthetic joint infection (PJI) remains challenging despite the availability of a variety of clinical signs, serum and synovial markers, imaging techniques, microbiological and histological findings. Moreover, the one and only true definition of PJI does not exist, which is reflected by the existence of at least six different definitions by independent societies. These definitions are composed of major and minor criteria for defining a PJI, but most of them do not include imaging techniques. This paper highlights the pros and cons of available imaging techniques—X-ray, ultrasound, computed tomography (CT), Magnetic Resonance Imaging (MRI), bone scintigraphy, white blood cell scintigraphy (WBC), anti-granulocyte scintigraphy, and fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT), discusses the added value of hybrid camera systems—single photon emission tomography/computed tomography (SPECT/CT), PET/CT and PET/MRI and reports consensus answers on important clinical questions that were discussed during the Third European Congress on Inflammation/Infection Imaging in Rome, December 2019.

The diagnostic value of SPECT/CT in predicting the occurrence of osteonecrosis following femoral neck fracture: a prospective cohort study

Backgrounds

One of the most significant complications after a femoral neck fracture is osteonecrosis of the femoral head (ONFH). The concomitant use of single-photon emission computed tomography (SPECT) with computed tomography (CT) increases the sensitivity for detecting the anatomic location and severity of ONFH. In this study, we evaluated the diagnostic value of SPECT/CT for the occurrence of ONFH by quantifying the perfusion status of the femoral head.

Methods

A total of 30 patients who had multiple pinnings for femur neck fractures were included in this study. We classified the perfusion status into three groups: normal perfusion, decreased perfusion, and avascular groups, and compared the occurrence of femoral head necrosis between them. For quantitative analysis, we evaluated the uptake ratio of both femur heads (head-to-head uptake ratio). If the patient’s contralateral hip was incomparable, we measured the uptake ratio from the superior dome of the ipsilateral acetabulum (head-to-acetabulum uptake ratio).

Results

Twenty-four patients out of 30 achieved bone union, whereas the others developed ONFH. When the population was divided into intact and defective perfusion groups on scintigraphy, the sensitivity, specificity, and accuracy of the test were 83.3, 75.0, and 76.7%, respectively. The mean head-to-head uptake ratio value with a 95% confidence interval (CI) was 1.10 (95% CI: 0.85–1.36). In the osteonecrosis group, the mean value of the head-to-head uptake ratio was 0.33 (95% CI: 0.28–0.38). In contrast, the ratio was 1.30 (95% CI: 1.03–1.57) in the non-osteonecrosis group, demonstrating a significant difference in the uptake ratio (P < 0.001). When the cutoff value of the uptake ratio was set to 0.5, both the sensitivity and specificity were 100%. There was also a significant difference in the head-to-acetabulum uptake ratio between the two groups (P <  0.001).

Conclusions

SPECT/CT was useful in evaluating the perfusion status of the femoral head, showing high accuracy in predicting the occurrence of avascular necrosis. To demonstrate the reliability and validity of SPECT/CT, further prospective studies on a larger scale are warranted.

Exploiting proteases for cancer theranostic through molecular imaging and drug delivery

The measurement of biological processes at a molecular and cellular level serves as a basis for molecular imaging. As compared with traditional imaging approaches, molecular imaging functions to probe molecular anomalies that are the basis of a disease rather than the evaluation of end results of these molecular changes. Proteases play central role in tumor invasion, angiogenesis and metastasis thus can be exploited as a target for imaging probes in early diagnosis and treatment of tumors. Molecular imaging of protease has undergone tremendous breakthroughs in the field of diagnosis. It allows the clinicians not only to see the tumor location but also provides an insight into the expression and activity of different types of markers associated with the tumor microenvironment. These imaging techniques are expected to have a huge impact on early cancer detection and personalized cancer treatment. Effective development of protease imaging probes with the highest in vivo biocompatibility, stability and most appropriate pharmacokinetics for clinical translation will upsurge the success level of early cancer detection and treatment.

Abdominal splenosis and its differential diagnoses: What the radiologist needs to know

Splenosis is a benign acquired condition characterized by the presence of heterotopic viable splenic tissue in other organs or within cavities such as peritoneum, retroperitoneum, or thorax after splenic trauma or surgery. Abdominal splenosis is often an incidental finding and computed tomography and magnetic resonance usually allow a confident diagnosis. The typical enhancement that parallels the spleen is a useful hallmark of splenosis. Splenic implants lack contrast uptake in the hepatobiliary phase and show high signal at high b-values on diffusion-weighted images. In some cases splenosis may mimic malignant and benign conditions in the peritoneum as well as in hollow and parenchymal abdominal organs and further investigations - including scintigraphy with Tc99m-labelled heat-denatured red blood cells or biopsy - are sometimes required in challenging cases. This pictorial essay reviews the imaging presentation and potential differential diagnosis of splenosis according to the site of implantation. A prompt and accurate radiological diagnosis of splenosis can avoid unnecessary biopsy or surgery.

Technetium-Radiolabeled Mannose-Functionalized Gold Nanoparticles as Nanoprobes for Sentinel Lymph Node Detection

Gold nanoparticles (AuNPs) are considered valuable nanomaterials for the design of radiolabeled nanoprobes for single-photon emission computed tomography (SPECT) imaging. Radiolabeled and functionalized AuNPs could improve lymphatic mapping by enhancing the radioactive signaling of individual particles in the sentinel node. In this study, an alternative method for functionalizing commercial AuNps with mannose is described. The chemical derivatization and biofunctionalization of AuNPs were performed with lipoic acid and mannose, respectively. Several levels of mannose were tested; the thiolate hydrazinonicotinamide-glycine-glycine-cysteine (HYNIC) molecule was also used for ^99mTc radiolabeling. Physicochemical characterization of this system includes U-V spectroscopy, dynamic light scattering, Fourier-transform infrared spectroscopy, and transmission electron microscopy. The most stable nanoprobe, in terms of the aggregation, radiolabeling efficiency, and purity, was tested in a sentinel lymph node model in a rat by microSPECT/computed tomography (CT) imaging. The SPECT images revealed that ^99mTc-radiolabeled AuNPs functionalized with mannose can track and accumulate in lymph nodes in a similar way to the commercial ^99mTc-Sulfur colloid, commonly used in clinical practice for sentinel lymph node detection. These promising results support the idea that ^99mTc-AuNPs-mannose could be used as a SPECT contrast agent for lymphatic mapping.