Positron Emission Tomography Molecular Imaging Research Articles

Bone Metastases.

Bone metastases occur frequently in common malignancies such as breast and prostate cancer. They are responsible for considerable morbidity and skeletal-related events. Fortunately, there are now several systemic, focal, and targeted therapies that can improve quality and length of life, including radionuclide therapies. It is therefore important that bone metastases can be detected as early as possible and that treatment can be accurately and sensitively monitored. Several bone-specific and tumor-specific single-photon emission computed tomography and positron emission tomography molecular imaging agents are available, for detection and monitoring response to systemic therapeutics, as well as theranostic agents to confirm target expression and predict response to radionuclide therapies.

Developing Low Molecular Weight PET and SPECT Imaging Agents.

Imaging agents for positron emission tomography (PET) and single-photon emission computerized tomography (SPECT) have shown their utility in many situations, answering clinical questions related to drug development and medical considerations. The discovery and development of imaging agents follow a well-understood process, with variations related to available starting points and to the envisaged imaging application. This article describes the general development path leading from the expression of an imaging need and project initiation to a clinically usable imaging agent. The definition of the project rationale, the design and optimization of early leads, and the assessment of the imaging potential of an imaging agent candidate are followed by preclinical and clinical development activities that differ from those required for therapeutic agents. These include radiolabeling with a positron emitter and first-in-human clinical studies, to rapidly evaluate the ability of a new imaging agent to address the questions it was designed to answer.

Positron emission tomography and its role in the assessment of vulnerable plaques in comparison to other imaging modalities.

The diagnosis and management of vulnerable plaques are topics of high interest in the cardiovascular field. Although imaging techniques like computed tomography angiography (MCTA) and ultrasonography (USG) can structurally evaluate atherosclerotic plaques, they are limited in examining internal cellular processes. Positron emission tomography (PET) molecular imaging, on the other hand, can highlight these cellular processes, including inflammation, angiogenesis, and lipid oxidation. Magnetic resonance imaging (MRI) is also a valuable non-invasive imaging technique that can provide detailed anatomical and functional information on the cardiovascular system. In this review, we compare the advantages and drawbacks of MCTA, USG and MRI imaging techniques with PET molecular imaging in evaluating vulnerable plaques. PET imaging allows physicians to measure different pathophysiological events within the plaque using intravenous radiotracers, of which 18F-fluorodeoxyglucose (18F-FDG) is the most validated one. By using 18F-FDG, physicians can understand the formation of the plaque, assess the accumulation of macrophages, and predict major cardiovascular events. However, some limitations exist in using 18F-FDG, including myocardial uptake and low sensitivity in imaging coronary arteries. We also mention other radiotracers that can help in evaluating vulnerable plaques, including 18F-NaF. Although PET imaging is still challenging, it has shown promise in evaluating vulnerable plaques and could be used to intervene in high-risk patients before major cardiovascular events occur.

Positron Emission Tomography Molecular Imaging of the Major Neurodegenerative Disorders: Overview and Pictorial Essay, from a Nuclear Medicine Center's Perspective.

Computed tomography (CT) and magnetic resonance imaging (MRI) provide key structural information on brain pathophysiology. Positron emission tomography (PET) measures metabolism in the living brain; it plays an important role in molecular neuroimaging and is rapidly expanding its field of application to the study of neurodegenerative diseases. Different PET radiopharmaceuticals allow in vivo characterization and quantization of biological processes at the molecular and cellular levels, from which many neurodegenerative diseases develop. In addition, hybrid imaging tools such as PET/CT and PET/MRI support the utility of PET, enabling the anatomical mapping of functional data. In this overview, we describe the most commonly used PET tracers in the diagnostic work-up of patients with Alzheimer's disease, Parkinson's disease, and other neurodegenerative diseases. We also briefly discuss the pathophysiological processes of tracer uptake in the brain, detailing their specific cellular pathways in clinical cases. This overview is limited to imaging agents already applied in human subjects, with particular emphasis on those tracers used in our department.

Challenges and innovations in brain PET analysis of neurodegenerative disorders: a mini-review on partial volume effects, small brain region studies, and reference region selection.

Positron Emission Tomography (PET) brain imaging is increasingly utilized in clinical and research settings due to its unique ability to study biological processes and subtle changes in living subjects. However, PET imaging is not without its limitations. Currently, bias introduced by partial volume effect (PVE) and poor signal-to-noise ratios of some radiotracers can hamper accurate quantification. Technological advancements like ultra-high-resolution scanners and improvements in radiochemistry are on the horizon to address these challenges. This will enable the study of smaller brain regions and may require more sophisticated methods (e.g., data-driven approaches like unsupervised clustering) for reference region selection and to improve quantification accuracy. This review delves into some of these critical aspects of PET molecular imaging and offers suggested strategies for improvement. This will be illustrated by showing examples for dopaminergic and cholinergic nerve terminal ligands.

Deoxyfluorination of phenols for chemoselective 18F-labeling of peptides.

The challenge of forming C-18F bonds is often a bottleneck in the development of new 18F-labeled tracer molecules for noninvasive functional imaging studies using positron emission tomography (PET). Nucleophilic aromatic substitution is the most widely employed reaction to functionalize aromatic substrates with the radioactive fluorine-18 but its scope is restricted to arenes containing electron-withdrawing substituents. Furthermore, many protic functional groups are incompatible with basic fluoride anions. Peptide substrates, which are highly desirable targets for PET molecular imaging, are particularly challenging to label with fluorine-18 because they are densely functionalized and sensitive to high temperatures and basic conditions. To expand the utility of nucleophilic aromatic substitution with fluorine-18, we describe two complementary procedures for the radiodeoxyfluorination of bench-stable and easy-to-access phenols that ensure rapid access to densely functionalized electron-rich and electron-poor 18F-aryl fluorides. The first procedure details the synthesis of an 18F-synthon and its subsequent ligation to the cysteine residue of Arg-Gly-Asp-Cys in 10.5 h from commercially available starting materials (189-min radiosynthesis). The second procedure describes the incorporation of commercially available CpRu(Fmoc-tyrosine)OTf into a fully protected peptide Lys-Met-Glu-(CpRu-Tyr)-Leu via solid-phase peptide synthesis and subsequent ruthenium-mediated uronium deoxyfluorination with fluorine-18 followed by deprotection, accomplished within 7 d (116-min radiosynthesis). Both radiolabeling methods are highly chemoselective and have conveniently been automated using commercially available radiosynthesis equipment so that the procedures described can be employed for the synthesis of peptide-based PET probes for in vivo imaging studies according to as low as reasonably achievable (ALARA) principles.

Treating Primary Aldosteronism-Induced Hypertension: Novel Approaches and Future Outlooks.

Primary aldosteronism (PA) is the most common cause of secondary hypertension and is associated with increased morbidity and mortality when compared with blood pressure-matched cases of primary hypertension. Current limitations in patient care stem from delayed recognition of the condition, limited access to key diagnostic procedures, and lack of a definitive therapy option for nonsurgical candidates. However, several recent advances have the potential to address these barriers to optimal care. From a diagnostic perspective, machine-learning algorithms have shown promise in the prediction of PA subtypes, while the development of noninvasive alternatives to adrenal vein sampling (including molecular positron emission tomography imaging) has made accurate localization of functioning adrenal nodules possible. In parallel, more selective approaches to targeting the causative aldosterone-producing adrenal adenoma/nodule (APA/APN) have emerged with the advent of partial adrenalectomy or precision ablation. Additionally, the development of novel pharmacological agents may help to mitigate off-target effects of aldosterone and improve clinical efficacy and outcomes. Here, we consider how each of these innovations might change our approach to the patient with PA, to allow more tailored investigation and treatment plans, with corresponding improvement in clinical outcomes and resource utilization, for this highly prevalent disorder.

Positron emission tomography in oncology

Positron emission tomography (PET) is ahighly sensitive imaging tool that noninvasively characterizes metabolic processes and molecular targets. PET has become an integral part of oncological diagnostics and an increasingly important tool for oncological therapy management. PET assessment, for example, directly influences treatment escalation or de-escalation in context of Hodgkin lymphomas or is, in case of lung cancer, able to reduce unnecessary surgeries. Hence, molecular PET imaging represents an indispensable tool in the development of personalized treatments. Furthermore, the development of new radiotracers for specific cell surface structures offers apromising potential for diagnostics and-combined with therapeutic nuclides-also for therapies. One recent example are radioligands targeting prostate-specific membrane antigen, which are relevant in prostate cancer.

Development of a bespoke phantom to optimize molecular PET imaging of pituitary tumors

BackgroundImage optimization is a key step in clinical nuclear medicine, and phantoms play an essential role in this process. However, most phantoms do not accurately reflect the complexity of human anatomy, and this presents a particular challenge when imaging endocrine glands to detect small (often subcentimeter) tumors. To address this, we developed a novel phantom for optimization of positron emission tomography (PET) imaging of the human pituitary gland. Using radioactive 3D printing, phantoms were created which mimicked the distribution of 11C-methionine in normal pituitary tissue and in a small tumor embedded in the gland (i.e., with no inactive boundary, thereby reproducing the in vivo situation). In addition, an anatomical phantom, replicating key surrounding structures [based on computed tomography (CT) images from an actual patient], was created using material extrusion 3D printing with specialized filaments that approximated the attenuation properties of bone and soft tissue.ResultsThe phantom enabled us to replicate pituitary glands harboring tumors of varying sizes (2, 4 and 6 mm diameters) and differing radioactive concentrations (2 ×, 5 × and 8 × the normal gland). The anatomical phantom successfully approximated the attenuation properties of surrounding bone and soft tissue. Two iterative reconstruction algorithms [ordered subset expectation maximization (OSEM); Bayesian penalized likelihood (BPL)] with a range of reconstruction parameters (e.g., 3, 5, 7 and 9 OSEM iterations with 24 subsets; BPL regularization parameter (β) from 50 to 1000) were tested. Images were analyzed quantitatively and qualitatively by eight expert readers. Quantitatively, signal was the highest using BPL with β = 50; noise was the lowest using BPL with β = 1000; contrast was the highest using BPL with β = 100. The qualitative review found that accuracy and confidence were the highest when using BPL with β = 400.ConclusionsThe development of a bespoke phantom has allowed the identification of optimal parameters for molecular pituitary imaging: BPL reconstruction with TOF, PSF correction and a β value of 400; in addition, for small (< 4 mm) tumors with low contrast (2:1 or 5:1), sensitivity may be improved using a β value of 100. Together, these findings should increase tumor detection and confidence in reporting scans.

The MAPT p.P301L mutation presents as a rare early-onset corticobasal syndrome: A case report

Corticobasal syndrome (CBS) is an uncommon movement disorder with a heterogeneous clinical presentation. CBS is generally recognized as a sporadic disorder, although rare familial and isolated genetic cases have been reported among Westerners. We describe a 49-year-old Taiwanese woman that presented with a three-year history of progressive right-hand dystonia, akinetic-rigidity, ideomotor apraxia, and slowness of gait. Her family history included autosomal-dominant parkinsonism with cognitive decline. A genetic analysis revealed a pathogenic heterozygous missense variant, c.902C&gt;T (p.P301L), on exon 10 of the MAPT gene. The antemortem diagnosis of CBS was supported by clinical, structural, brain glucose metabolism, and tau protein molecular positron emission tomography imaging data. These findings expanded the phenotypic spectrum of the MAPT p.P301L mutation. A literature review illustrated the genetic pleiotropy of MAPT mutations in tau-related neurodegenerative disorders. This study was the first to describe a patient in an Asian family with a MAPT mutation that presented as young-onset CBS. Our findings demonstrated the heterogenous phenotypic spectrum of this rare genetic variant. MAPT mutations should be considered in patients with early-onset or familial CBS in the Asian population.

Positronenemissionstomographie in der Onkologie

Positron emission tomography (PET) is a highly sensitive imaging tool that noninvasively characterizes metabolic processes and molecular targets. PET has become an integral part of oncological diagnostics and an increasingly important tool for oncological therapy management. PET assessment, for example, directly influences treatment escalation or de-escalation in context of Hodgkin lymphomas or is, in case of lung cancer, able to reduce unnecessary surgeries. Hence, molecular PET imaging represents an indispensable tool in the development of personalized treatments. Furthermore, the development of new radiotracers for specific cell surface structures offers a promising potential for diagnostics and—combined with therapeutic nuclides—also for therapies. One recent example are radioligands targeting prostate-specific membrane antigen, which are relevant in prostate cancer.

PET Molecular Imaging in Drug Development: The Imaging and Chemistry Perspective.

Positron emission tomography with selective radioligands advances the drug discovery and development process by revealing information about target engagement, proof of mechanism, pharmacokinetic and pharmacodynamic profiles. Positron emission tomography (PET) is an essential and highly significant tool to study therapeutic drug development, dose regimen, and the drug plasma concentrations of new drug candidates. Selective radioligands bring up target-specific information in several disease states including cancer, cardiovascular, and neurological conditions by quantifying various rates of biological processes with PET, which are associated with its physiological changes in living subjects, thus it reveals disease progression and also advances the clinical investigation. This study explores the major roles, applications, and advances of PET molecular imaging in drug discovery and development process with a wide range of radiochemistry as well as clinical outcomes of positron-emitting carbon-11 and fluorine-18 radiotracers.

Positron Emission Tomography Molecular Imaging for Phenotyping and Management of Lymphoma.

Positron emission tomography (PET) represents molecular imaging for non-invasive phenotyping of physiological and biochemical processes in various oncological diseases. PET imaging with 18F-fluorodeoxyglucose (18F-FDG) for glucose metabolism evaluation is the standard imaging modality for the clinical management of lymphoma. One of the 18F-FDG PET applications is the detection and pre-treatment staging of lymphoma, which is highly sensitive. 18F-FDG PET is also applied during treatment to evaluate the individual chemo-sensitivity and accordingly guide the response-adapted therapy. At the end of the therapy regiment, a negative PET scan is indicative of a good prognosis in patients with advanced Hodgkin's lymphoma and diffuse large B-cell lymphoma. Thus, adjuvant radiotherapy may be alleviated. Future PET studies using non-18F-FDG radiotracers, such as 68Ga-labeled pentixafor (a cyclic pentapeptide that enables sensitive and high-contrast imaging of C-X-C motif chemokine receptor 4), 68Ga-labeled fibroblast activation protein inhibitor (FAPI) that reflects the tumor microenvironment, and 89Zr-labeled atezolizumab that targets the programmed cell death-ligand 1 (PD-L1), may complement 18F-FDG and offer essential tools to decode lymphoma phenotypes further and identify the mechanisms of lymphoma therapy.

Imaging High-Risk Atherothrombosis Using a Novel Fibrin-Binding Positron Emission Tomography Probe.

High-risk atherosclerosis is an underlying cause of cardiovascular events, yet identifying the specific patient population at immediate risk is still challenging. Here, we used a rabbit model of atherosclerotic plaque rupture and human carotid endarterectomy specimens to describe the potential of molecular fibrin imaging as a tool to identify thrombotic plaques. Atherosclerotic plaques in rabbits were induced using a high-cholesterol diet and aortic balloon injury (N=13). Pharmacological triggering was used in a group of rabbits (n=9) to induce plaque disruption. Animals were grouped into thrombotic and nonthrombotic plaque groups based on gross pathology (gold standard). All animals were injected with a novel fibrin-specific probe 68Ga-CM246 followed by positron emission tomography (PET)/magnetic resonance imaging 90 minutes later. 68Ga-CM246 was quantified on the PET images using tissue-to-background (back muscle) ratios and standardized uptake value. Both tissue-to-background (back muscle) ratios and standardized uptake value were significantly higher in the thrombotic versus nonthrombotic group (P<0.05). Ex vivo PET and autoradiography of the abdominal aorta correlated positively with in vivo PET measurements. Plaque disruption identified by 68Ga-CM246 PET agreed with gross pathology assessment (85%). In ex vivo surgical specimens obtained from patients undergoing elective carotid endarterectomy (N=12), 68Ga-CM246 showed significantly higher binding to carotid plaques compared to a D-cysteine nonbinding control probe. We demonstrated that molecular fibrin PET imaging using 68Ga-CM246 could be a useful tool to diagnose experimental and clinical atherothrombosis. Based on our initial results using human carotid plaque specimens, in vivo molecular imaging studies are warranted to test 68Ga-CM246 PET as a tool to stratify risk in atherosclerotic patients.

Deep Learning-Based Positron Emission Tomography Molecular Imaging in the Assessment of Cognitive Dysfunction in Patients with Epilepsy

This work aimed to investigate the application of positron emission tomography (PET) molecular imaging based on the deep learning algorithm in the assessment of cognitive dysfunction in patients with epilepsy. In this study, 52 hospitalized patients with epilepsy were selected as the epilepsy group and treated with different kinds of antiepileptic drugs, and 52 volunteers were selected as the control group. A U-net optimized network structure algorithm based on deep learning was proposed in this study and compared with a fully convolutional neural network (FCNN). Besides, it was applied in the PET molecular imaging of patients with epilepsy, and the segmentation effect of the U-net optimized network structure was good. According to event-related potential examinations, the proportion of patients with cognitive dysfunction in the epilepsy group (74.19%) was higher than the proportion of the control group (7.46%) ( P &lt; 0.05 ). The patients with cognitive dysfunction (57.89%) who took one antiepileptic drug were lower than those with two antiepileptic drugs (84.61%) ( P &lt; 0.05 ). The difference was statistically obvious in the overall quality of life of patients with epilepsy ( P &lt; 0.05 ). The occurrence of cognitive dysfunction in patients with epilepsy was related to the type of seizures. In addition, the quality of life of patients who suffered from cognitive dysfunction was low.

Investigation of using positronium and its annihilation for hypoxia PET imaging

Positron emission tomography (PET) is widely used for medical imaging to investigate the spatial distribution of pharmaceuticals labelled with positron emitters in patients. This study investigated the potential to perform three gamma (3γ) imaging based on ortho-positronium annihilation for assessment of tumour hypoxia. Evaluation of Oxygen deficiency is necessary to assure successful treatment. It was reported that PET imaging with a radioisotope could be used as molecular markers to detect tumour hypoxia. This method is based on the physics of 2γ annihilation. However, the 3γ annihilation yield is governed by the positronium formation as well as in quenching rates which could be used as a new PET molecular imaging modality. This study provides a method for the preparation of biological samples with different oxygen concentrations as well as developing a configuration system for the determination of the 3γ yield using high-purity germanium (HPGe) detectors to investigate the measurement of 3γ imaging. This study compares the decay rates in oxygen and nitrogen saturated samples of water and serum, the results show that 3γ annihilation with different oxygen concentrations could illustrate the oxygenation in biological models. Even though many diverse disciplines are involved in this work, the advantages and disadvantages of each possible technique have yet to be concisely summarized. This study sets out the background to the clinical applications of the 3γ PET technique and compares this non-invasive method with existing oxygen measurement devices.

Phase III randomized trial of PSMA PET prior to definitive radiation therapy for unfavorable intermediate-risk or high-risk prostate cancer [PSMA dRT]: Study protocol NCT04457245.

TPS172 Background: Definitive radiation therapy (dRT) is an effective initial treatment of intermediate-risk (IR) and high-risk (HR) prostate cancer (PCa). Positron emission tomography (PET) using small molecule probes targeting prostate-specific membrane antigen (PSMA PET) is superior to standard of care imaging (CT, MRI, bone scan) for detecting regional and distant metastatic PCa. PSMA PET thus has the potential to guide primary radiotherapy planning in patients and improve outcomes. The purpose of the present randomized trial is to evaluate the success rate of dRT for IR or HR PCa with and without planning based on PSMA PET. Methods: We will randomize 312 patients to proceed with standard dRT (control Arm 1, n=150), or undergo a PSMA PET scan prior to dRT planning (intervention arm 2, n = 162). In the control arm, dRT will be performed as routinely planned in accordance with initial stratification. In the intervention arm, the treating radiation oncologist can incorporate PSMA PET findings into the RT planning. We assume that approximately 8% of subjects randomized to arm 2 will be found to have M1 disease and thus will be more appropriate candidates for long-term systemic or multimodal therapy, rather than curative intent dRT. PET M1 patients will thus not be included in the analysis of the primary endpoint. The primary endpoint is the success rate of dRT measured as PFS after initiation of dRT. Progression is defined as (whichever occurs first): biochemical recurrence defined as a rise by 2 ng/mL or more above the nadir PSA (defined as the lowest PSA achieved) after radiotherapy with or without short-term hormonal therapy; appearance of metastasis or loco-regional recurrence (diagnosed by any imaging or biopsy); initiation of any new salvage therapy, or death from any cause. Discussion: This is the first randomized phase 3 prospective trial designed to determine whether PSMA PET molecular imaging can improve outcomes in patients with PCa who receive dRT. In this trial the incorporation of PSMA PET may improve the success rate of curative intent radiotherapy in two ways: to optimize patient selection and to personalizes the radiotherapy plan. Clinical trial registration: IND#147591, UCLA IRB #20-000378, ClinicalTrials.gov Identifier NCT04457245. Clinical trial information: NCT04457245.

Carbon-11: Radiochemistry and Target-Based PET Molecular Imaging Applications in Oncology, Cardiology, and Neurology.

The positron emission tomography (PET) molecular imaging technique has gained its universal value as a remarkable tool for medical diagnosis and biomedical research. Carbon-11 is one of the promising radiotracers that can report target-specific information related to its pharmacology and physiology to understand the disease status. Currently, many of the available carbon-11 (t1/2 = 20.4 min) PET radiotracers are heterocyclic derivatives that have been synthesized using carbon-11 inserted different functional groups obtained from primary and secondary carbon-11 precursors. A spectrum of carbon-11 PET radiotracers has been developed against many of the upregulated and emerging targets for the diagnosis, prognosis, prediction, and therapy in the fields of oncology, cardiology, and neurology. This review focuses on the carbon-11 radiochemistry and various target-specific PET molecular imaging agents used in tumor, heart, brain, and neuroinflammatory disease imaging along with its associated pathology.

Current and future perspectives on functional molecular imaging in nephro-urology: theranostics on the horizon.

In recent years, a paradigm shift from single-photon-emitting radionuclide radiotracers toward positron-emission tomography (PET) radiotracers has occurred in nuclear oncology. Although PET-based molecular imaging of the kidneys is still in its infancy, such a trend has emerged in the field of functional renal radionuclide imaging. Potentially allowing for precise and thorough evaluation of renal radiotracer urodynamics, PET radionuclide imaging has numerous advantages including precise anatomical co-registration with CT images and dynamic three-dimensional imaging capability. In addition, relative to scintigraphic approaches, PET can allow for significantly reduced scan time enabling high-throughput in a busy PET practice and further reduces radiation exposure, which may have a clinical impact in pediatric populations. In recent years, multiple renal PET radiotracers labeled with 11C, 68Ga, and 18F have been utilized in clinical studies. Beyond providing a precise non-invasive read-out of renal function, such radiotracers may also be used to assess renal inflammation. This manuscript will provide an overview of renal molecular PET imaging and will highlight the transformation of conventional scintigraphy of the kidneys toward novel, high-resolution PET imaging for assessing renal function. In addition, future applications will be introduced, e.g. by transferring the concept of molecular image-guided diagnostics and therapy (theranostics) to the field of nephrology.

Tri-functional platform for construction of modular antibody fragments for in vivo 18F-PET or NIRF molecular imaging.

Positron emission tomography (PET) molecular imaging is a powerful tool for interrogating physiological and biochemical processes to understand the biology of disease and advance therapeutic developments. Near-infrared fluorescence (NIRF) optical imaging has become increasingly popular for intraoperative staging to enable cellular resolution imaging of tumor margins during surgical resection. In addition, engineered antibody fragments have emerged as promising molecular imaging agents given their exquisite target selectivity, rapid systemic clearance and site-selective chemical modification. We report a tri-functional platform for construction of a modular antibody fragment that can rapidly be labeled with radionuclides or fluorophores for PET or NIRF molecular imaging of prostate stem cell antigen (PSCA).