The Changing Face of Nuclear Cardiology: Guiding Cardiovascular Care Toward Molecular Medicine

Molecular Imaging of Heart Failure: An Update and Future Trends

Molecular imaging can detect and quantify pathophysiological processes underlying heart failure, complementing evaluation of cardiac structure and function with other imaging modalities. Targeted tracers have enabled assessment of various cellular and subcellular mechanisms of heart failure aiming for improved phenotyping, risk stratification, and personalized therapy. This review outlines the current status of molecular imaging in heart failure, accompanied with discussion on novel developments. The focus is on radionuclide methods with data from clinical studies. Imaging of myocardial metabolism can identify left ventricle dysfunction caused by myocardial ischemia that may be reversible after revascularization in the presence of viable myocardium. In vivo imaging of active inflammation and amyloid deposition have an established role in the detection of cardiac sarcoidosis and transthyretin amyloidosis. Innervation imaging has well documented prognostic value in predicting heart failure progression and arrhythmias. Tracers specific for inflammation, angiogenesis and myocardial fibrotic activity are in earlier stages of development, but have demonstrated potential value in early characterization of the response to myocardial injury and prediction of cardiac function over time. Early detection of disease activity is a key for transition from medical treatment of clinically overt heart failure towards a personalized approach aimed at supporting repair and preventing progressive cardiac dysfunction.

FAPI-PET in Cardiovascular Disease

PET probes targeting fibroblasts are frequently used for varying applications in oncology. In recent years, the clinical spectrum has been expanded towards cardiovascular medicine, e.g., after myocardial infarction, in aortic stenosis or as a non-invasive read-out of atherosclerosis. We herein provide a brief overview of the current status of this PET radiotracer in the context of cardiovascular disease, including translational and clinical evidence. In addition, we will also briefly discuss future applications, e.g., the use of fibroblast-targeting PET to investigate bilateral organ function along the cardiorenal axis.

Multimodality Cardiac Imaging and the Imaging Workforce in the United States: Diversity, Disparities, and Future Directions

Innovations in cardiac imaging have fundamentally advanced the understanding and treatment of cardiovascular disease. These advances in noninvasive cardiac imaging have also expanded the role of the cardiac imager and dramatically increased the demand for imagers who are cross-trained in multiple modalities. However, we hypothesize that there is significant variation in the availability of cardiac imaging expertise and a disparity in the adoption of advanced imaging technologies across the United States. To evaluate this, we have brought together the leaders of cardiovascular imaging societies, imaging trainees, as well as collaborated with national imaging accreditation commissions and imaging certification boards to assess the state of cardiac imaging and the diversity of the imaging workforce in the United States. Aggregate data confirm the presence of critical gaps, such as limited access to imaging and imaging expertise in rural communities, as well as disparities in the imaging workforce, notably among women and underrepresented minorities. Based on these results, we have proposed solutions to promote and maintain a robust and diverse community of cardiac imagers and improve equity and accessibility for cardiac imaging technologies.

Phenotyping heart failure by nuclear imaging of myocardial perfusion, metabolism, and molecular targets

Nuclear imaging techniques can detect and quantify pathophysiological processes underlying heart failure, complementing evaluation of cardiac structure and function with other imaging modalities. Combined imaging of myocardial perfusion and metabolism can identify left ventricle dysfunction caused by myocardial ischaemia that may be reversible after revascularization in the presence of viable myocardium. High sensitivity of nuclear imaging to detect targeted tracers has enabled assessment of various cellular and subcellular mechanisms of heart failure. Nuclear imaging of active inflammation and amyloid deposition is incorporated into clinical management algorithms of cardiac sarcoidosis and amyloidosis. Innervation imaging has well-documented prognostic value with respect to heart failure progression and arrhythmias. Emerging tracers specific for inflammation and myocardial fibrotic activity are in earlier stages of development but have demonstrated potential value in early characterization of the response to myocardial injury and prediction of adverse left ventricular remodelling. Early detection of disease activity is a key for transition from broad medical treatment of clinically overt heart failure towards a personalized approach aimed at supporting repair and preventing progressive failure. This review outlines the current status of nuclear imaging in phenotyping heart failure and combines it with discussion on novel developments.

Head-to-Head Comparison of CZT-SPECT and SPECT/CT Myocardial Perfusion Imaging: Interobserver and Intraobserver Agreement and Diagnostic Performance

BACKGROUND

Myocardial perfusion imaging (MPI) plays a crucial role in diagnosing coronary artery disease (CAD), with single-photon emission computed tomography (SPECT) being a widely accepted method. The accuracy of MPI relies on image quality and the expertise of physicians. While CZT-SPECT cameras offer advantages, they can be susceptible to attenuation artifacts. Therefore, our objective was to evaluate the diagnostic accuracy of CZT-SPECT and SPECT/CT in a clinical setting.

METHOD

We conducted a prospective single-center study involving patients with known or suspected stable ischemic heart disease who underwent SPECT-MPI using CZT-SPECT and SPECT/CT scanners, and the latter was equipped with cardiofocal collimation. Experienced physicians performed analysis and reporting based on automated quantification and visual image interpretation.

RESULTS

A total of 77 patients (32 women (41.6%) and 45 men (58.4%) with an average age of 71.9 ± 8.9 years) were included. The agreement between readers regarding the final conclusion based on imaging reporting using both devices was very high (Kappa 0.87-0.93). Per-vessel analysis revealed a trend suggesting that CZT-SPECT was superior to conventional SPECT/CT in terms of sensitivity, positive predictive value (PPV), negative predictive value (NPV), and accuracy, although the difference did not reach statistical significance.

CONCLUSION

Our study demonstrated that CZT-SPECT imaging offers comparable diagnostic accuracy, improved patient comfort, and eliminates CT-induced radiation compared to SPECT/CT. These findings suggest that cardiac CZT-SPECT imaging has the potential to become a valuable imaging modality in clinical practice.

PET-Derived Increased Inflammation in Large Vessels is linked to Relapse-Free Survival in Patients with Giant Cell Arteritis

BACKGROUND

 Despite anti-inflammatory treatment, patients with giant cell arteritis (GCA) experience relapse. We aimed to determine respective relapse predictors focusing on [18F]fluorodeoxyglucose ([18F]FDG)-PET-based parameters.

MATERIAL AND METHODS

 21 therapy-naïve GCA patients received [18F]FDG-PET/CT. Patients were divided in two groups: those who relapsed during course of disease and those who did not. Median follow up was 15 months. [18F]FDG-PET/CT was analyzed for visual (PET vascular activity score [VAS]) and quantitative parameters, including Target-to-background-Ratio with liver (TBRliver) and jugular vein (TBRjv) serving as reference tissues. In addition, clinical parameters were tested.

RESULTS

 8/21 (38.1 %) had relapse. Clinical parameters could not significantly discriminate between relapse vs no-relapse, including age (p = 0.9) or blood-based inflammatory markers (white blood cell counts [WBC] and c-reactive protein [CRP], p = 0.72, each). PETVAS score could also not differentiate between respective subgroups (p = 0.59). In a quantitative assessment, TBRjv demonstrated a trend towards significance (p = 0.28). TBRliver, however, separated between patients with and without relapse (p = 0.03).

CONCLUSION

 [18F]FDG PET quantification of vessels may be useful to identify GCA patients prone to relapse during follow-up.

Regulatory Agencies and PET/CT Imaging in the Clinic

PURPOSE OF REVIEW

The regulatory steps necessary to bring new PET radiopharmaceuticals to the clinic will be reviewed. The US Food and Drug Administration (FDA) provides approval to manufacture and use diagnostic radiopharmaceuticals, including those for cardiovascular PET/CT. Medicare not only provides insurance reimbursement for imaging procedures for its beneficiaries but also sets an example for third-party insurers to cover these procedures.

RECENT FINDINGS

FDA provides extensive guidance for performing studies to obtain the safety and efficacy data needed to approve PET radiopharmaceuticals, and the pace of approval has recently increased. There also has been considerable progress in insurance coverage for PET by Medicare. Several promising agents for cardiovascular PET imaging are in the development pipeline. Challenges remain, however, including low levels of reimbursement and the application of appropriate use criteria for imaging procedures. It is important for cardiologists to understand the regulatory steps involved in translating PET radiopharmaceuticals to the clinic. Recent progress in both FDA approvals and Medicare coverage should facilitate the clinical use of new PET agents for molecular imaging of the heart.

Clinical Utility of C-Reactive Protein and White Blood Cell Count for Scheduling an [18F]FDG PET/CT in Patients with Giant Cell Arteritis

OBJECTIVES

2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) PET/CT can be utilized in patients with giant cell arteritis (GCA), but pretest probability of established laboratory marker such as C-reactive protein (CRP) and white blood cell count (WBC) has not been defined yet. We aimed to elucidate the clinical utility of CRP and WBC for scheduling an [¹⁸F]FDG scan.

METHODS

18 treatment-naïve GCA patients and 14 GCA subjects with anti-inflammatory treatment (glucocorticoids or comparable drugs), who underwent [¹⁸F]FDG PET/CT and who had no other inflammatory disease at time of scan, were identified. A semi-quantitative analysis in 11 vessel segments was conducted, with averaged jugular vein, healthy liver and lung tissue (Target-to-background ratio [TBR]_{VJ/liver/lung}) serving as background. Derived TBR were then correlated with CRP and WBC at time of PET using Spearman's correlation.

RESULTS

For all treatment-naïve patients, TBR_VJ was 2.3±1.1 (95%CI, 2.2-2.5), TBR_liver was 1.0±0.5 (95%CI, 0.9-1.0) and average TBR_lung was 6.3±3.6 (95%CI, 5.8-6.8). No significant correlation was noted for either CRP (TBR_VJ: R=-0.19; TBR_liver: R=-0.03; TBR_lung: R=-0.17; each P ≥ 0.44) or for WBC (TBR_VJ: R=-0.40; TBR_liver: R=-0.32; TBR_lung: R=-0.37; each P ≥ 0.10). Similar results were recorded for patients under treatment at time of PET. Again, no significant correlation was reached for either CRP (TBR_VJ: R=-0.17; TBR_liver: R=-0.28; TBR_lung: R=-0.09; each P ≥ 0.32) or WBC (TBR_VJ: R=-0.06; TBR_liver: R=-0.13; TBR_lung: R=0.06; each P ≥ 0.65).

CONCLUSIONS

In GCA patients with and without anti-inflammatory treatment, CRP and WBC did not substantially correlate with TBR at time of scan. Given the rather limited pretest probability of those parameters, such laboratory values may have less diagnostic utility to order an [¹⁸F]FDG PET/CT.

Nuclear Imaging in Pediatric Cardiology: Principles and Applications

Nuclear imaging plays a unique role within diagnostic imaging since it focuses on cellular and molecular processes. Using different radiotracers and detection techniques such as the single photon emission scintigraphy or the positron emission tomography, specific parameters can be assessed: myocardial perfusion and viability, pulmonary perfusion, ventricular function, flow and shunt quantification, and detection of inflammatory processes. In pediatric and congenital cardiology, nuclear imaging can add complementary information compared to other imaging modalities such as echocardiography or magnetic resonance imaging. In this state-of-the-art paper, we appraise the different techniques in pediatric nuclear imaging, evaluate their advantages and disadvantages, and discuss the current clinical applications.

CXCR4-targeted theranostics in oncology

A growing body of literature reports on the upregulation of C-X-C motif chemokine receptor 4 (CXCR4) in a variety of cancer entities, rendering this receptor as suitable target for molecular imaging and endoradiotherapy in a theranostic setting. For instance, the CXCR4-targeting positron emission tomography (PET) agent [⁶⁸ Ga]PentixaFor has been proven useful for a comprehensive assessment of the current status quo of solid tumors, including adrenocortical carcinoma or small-cell lung cancer. In addition, [⁶⁸ Ga]PentixaFor has also provided an excellent readout for hematological malignancies, such as multiple myeloma, marginal zone lymphoma, or mantle cell lymphoma. PET-based quantification of the CXCR4 capacities in vivo allows for selecting candidates that would be suitable for treatment using the theranostic equivalent [¹⁷⁷Lu]/[⁹⁰Y]PentixaTher. This CXCR4-directed theranostic concept has been used as a conditioning regimen prior to hematopoietic stem cell transplantation and to achieve sufficient anti-lymphoma/-tumor activity in particular for malignant tissues that are highly sensitive to radiation, such as the hematological system. Increasing the safety margin, pretherapeutic dosimetry is routinely performed to determine the optimal activity to enhance therapeutic efficacy and to reduce off-target adverse events. The present review will provide an overview of current applications for CXCR4-directed molecular imaging and will introduce the CXCR4-targeted theranostic concept for advanced hematological malignancies.

Associations between Normal Organs and Tumor Burden in Patients Imaged with Fibroblast Activation Protein Inhibitor-Directed Positron Emission Tomography

Simple Summary

Several radiolabeled fibroblast activation protein targeted inhibitors (FAPI) have been developed for molecular imaging and therapy. A potential correlation of radiotracer uptake in normal organs and extent of tumor burden may have consequences for a theranostic approach using ligands structurally associated with [⁶⁸Ga]Ga-FAPI, as one may anticipate decreased doses to normal organs in patients with extensive tumor load. In the present proof-of-concept study investigating patients with solid tumors, we aimed to quantitatively determine the normal organ biodistribution of [⁶⁸Ga]Ga-FAPI-04, depending on the extent of tumor. Except for a trend towards significance in the myocardium, we did not observe any relevant associations between PET-based tumor burden and normal organs. Those preliminary findings may trigger future studies to determine possible implications for theranostic approaches and FAP-directed drugs, as one may expect an unchanged dose for normal organs even in patients with higher tumor load.

Abstract

(1) Background: We aimed to quantitatively investigate [⁶⁸Ga]Ga-FAPI-04 uptake in normal organs and to assess a relationship with the extent of FAPI-avid tumor burden. (2) Methods: In this single-center retrospective analysis, thirty-four patients with solid cancers underwent a total of 40 [⁶⁸Ga]Ga-FAPI-04 PET/CT scans. Mean standardized uptake values (SUV_mean) for normal organs were established by placing volumes of interest (VOIs) in the heart, liver, spleen, pancreas, kidneys, and bone marrow. Total tumor burden was determined by manual segmentation of tumor lesions with increased uptake. For tumor burden, quantitative assessment included maximum SUV (SUV_max), tumor volume (TV), and fractional tumor activity (FTA = TV × SUV_mean). Associations between uptake in normal organs and tumor burden were investigated by applying Spearman’s rank correlation coefficient. (3) Results: Median SUV_mean values were 2.15 in the pancreas (range, 1.05–9.91), 1.42 in the right (range, 0.57–3.06) and 1.41 in the left kidney (range, 0.73–2.97), 1.2 in the heart (range, 0.46–2.59), 0.86 in the spleen (range, 0.55–1.58), 0.65 in the liver (range, 0.31–2.11), and 0.57 in the bone marrow (range, 0.26–0.94). We observed a trend towards significance for uptake in the myocardium and tumor-derived SUV_max (ρ = 0.29, p = 0.07) and TV (ρ = −0.30, p = 0.06). No significant correlation was achieved for any of the other organs: SUV_max (ρ ≤ 0.1, p ≥ 0.42), TV (ρ ≤ 0.11, p ≥ 0.43), and FTA (ρ ≤ 0.14, p ≥ 0.38). In a sub-analysis exclusively investigating patients with high tumor burden, significant correlations of myocardial uptake with tumor SUV_max (ρ = 0.44; p = 0.03) and tumor-derived FTA with liver uptake (ρ = 0.47; p = 0.02) were recorded. (4) Conclusions: In this proof-of-concept study, quantification of [⁶⁸Ga]Ga-FAPI-04 PET showed no significant correlation between normal organs and tumor burden, except for a trend in the myocardium. Those preliminary findings may trigger future studies to determine possible implications for treatment with radioactive FAP-targeted drugs, as higher tumor load or uptake may not lead to decreased doses in the majority of normal organs.

Left ventricular remodelling post-myocardial infarction: pathophysiology, imaging, and novel therapies

Most patients survive acute myocardial infarction (MI). Yet this encouraging development has certain drawbacks: heart failure (HF) prevalence is increasing and patients affected tend to have more comorbidities worsening economic strain on healthcare systems and impeding effective medical management. The heart’s pathological changes in structure and/or function, termed myocardial remodelling, significantly impact on patient outcomes. Risk factors like diabetes, chronic obstructive pulmonary disease, female sex, and others distinctly shape disease progression on the ‘road to HF’. Despite the availability of HF drugs that interact with general pathways involved in myocardial remodelling, targeted drugs remain absent, and patient risk stratification is poor. Hence, in this review, we highlight the pathophysiological basis, current diagnostic methods and available treatments for cardiac remodelling following MI. We further aim to provide a roadmap for developing improved risk stratification and novel medical and interventional therapies.

Therapeutic Effects of Lipid Lowering Medications on Myocardial Blood Flow, Inflammation, and Sympathetic Nerve Activity Using Nuclear Techniques

PURPOSE OF REVIEW

Statins are routinely applied in patients with coronary artery disease, as they allow significantly to reduce blood cholesterol levels. Although those drugs are endorsed by current guidelines and prescribed routinely, a substantial portion of patients are still statin-intolerant and image-piloted strategies may then be helpful to identify patients that need further intensified treatment, e.g., to initiate treatment with proprotein convertase subtilisin / kexin type 9 inhibitors (PCSK9i). In addition, it has also been advocated that statins exhibit nonlipid, cardio-protective effects including improved cardiac nerve integrity, blood flow, and anti-inflammatory effects in congestive heart failure (HF) patients.

RECENT FINDINGS

In subjects after myocardial infarction treated with statins, ^123II-metaiodobenzylguanidine (MIBG) scintigraphy has already revealed enhanced cardiac nerve function relative to patients without statins. In addition, all of those aforementioned statin-targeted pathways in HF can be visualized and monitored using dedicated cardiac radiotracers, e.g., ¹²³I-MIBG or ¹⁸F-AF78 (for cardiac nerve function), ¹⁸F-flurpiridaz (to determine coronary flow) or ⁶⁸Ga-PentixaFor (to detect inflammation). Statins exhibit various cardio-beneficial effects, including improvement of cardiac nerve function, blood flow, and reduction of inflammation, which can all be imaged using dedicated nuclear cardiac radiotracers. This may allow for in vivo monitoring of statin-induced cardioprotection beyond lipid profiling in HF patients.

Molecular imaging of inflammation crosstalk along the cardio-renal axis following acute myocardial infarction

Rationale: Acute myocardial infarction (MI) triggers a systemic inflammatory response including crosstalk along the heart-kidney axis. We employed radionuclide-based inflammation-targeted whole-body molecular imaging to identify potential cardio-renal crosstalk after MI in a translational setup. Methods: Serial whole-body positron emission tomography (PET) with the specific CXCR4 ligand 68Ga-Pentixafor was performed after MI in mice. Tracer retention in kidneys and heart was compared to hematopoietic organs to evaluate systemic inflammation, validated by ex vivo analysis and correlated with progressive contractile dysfunction. Additionally, 96 patients underwent 68Ga-Pentixafor PET within the first week after MI, for systems-based image analysis and to determine prognostic value for adverse renal outcome. Results: In mice, transient myocardial CXCR4 upregulation occurred early after MI. Cardiac and renal PET signal directly correlated over the time course (r = 0.62, p < 0.0001), suggesting an inflammatory link between organs. Ex-vivo autoradiography (r = 0.9, p < 0.01) and CD68 immunostaining indicated signal localization to inflammatory cell content. Renal signal at 7d was inversely proportional to left ventricular ejection fraction at 6 weeks after MI (r = -0.79, p < 0.01). In patients, renal CXCR4 signal also correlated with signal from infarct (r = 0.25, p < 0.05) and remote myocardium (r = 0.39, p < 0.0001). Glomerular filtration rate (GFR) was available in 48/96 (50%) during follow-up. Worsening of renal function (GFR loss >5 mL/min/1.73m2), occurred a mean 80.5 days after MI in 16/48 (33.3%). Kaplan-Meier analysis revealed adverse renal outcome for patients with elevated remote myocardial CXCR4 signal (p < 0.05). Multivariate Cox analysis confirmed an independent predictive value (relative to baseline GFR, LVEF, infarct size; HR, 5.27). Conclusion: Systems-based CXCR4-targeted molecular imaging identifies inflammatory crosstalk along the cardio-renal axis early after MI.

Molecular Imaging Using Cardiac PET/CT: Opportunities to Harmonize Diagnosis and Therapy

PURPOSE OF REVIEW

Current therapeutic strategies to mitigate heart failure progression after myocardial infarction involve support of endogenous repair through molecular targets. The capacity for repair varies greatly between individuals. In this review, we will assess how cardiac PET/CT enables precise characterization of early pathogenetic processes which govern ventricle remodeling and progression to heart failure.

RECENT FINDINGS

Inflammation in the first days after myocardial infarction predicts subsequent functional decline and can influence therapy decisions. The expansion of anti-inflammatory approaches to improve outcomes after myocardial infarction may benefit from noninvasive characterization using imaging. Novel probes also allow visualization of fibroblast transdifferentiation and activation, as a precursor to ventricle remodeling. The expanding arsenal of molecular imaging agents in parallel with new treatment options provides opportunity to harmonize diagnostic imaging with precision therapy.

Vessel Wall Inflammatory Activity as Determined by F-18 Fluorodeoxyglucose PET in Large Vessel Vasculitis Is Attenuated by Immunomodulatory Drugs

F-18 fluorodeoxyglucose (F-18 FDG) PET/CT plays an increasing role in the diagnostic workup of large vessel vasculitis (LVV); however, information on the relationship between immunosuppressive drugs and vessel wall uptake is limited. In 94 patients with a confirmed diagnosis of LVV, the vessel wall-to-liver ratio (VLR) was assessed in eight vessel segments. Patients were grouped according to intake of immunomodulatory drugs (Group 1, prednisone; Group 2, prednisone + methotrexate; and Group 3, prednisone + others) and compared to treatment-naïve individuals. A total of 54/94 (57.4%) were treated with immunomodulatory drugs (Group 1, 29/49 (53.7%); Group 2, 9/54 (16.7%); Group 3, 11/54 (20.4%); and Group 4, 5/54 (9.3%)), whereas the remainder received no therapy (40/94 (42.6%)). The mean VLR of the arterial segments correlated significantly with the hematopoietic organs (r ≥ 0.22, p ≤ 0.05), c-reactive protein (r ≥ 0.25, p ≤ 0.05), and prednisone dosage (r ≥ −0.4, p ≤ 0.05). Relative to treatment-naïve patients, a significantly lower VLR was recorded in 5/8 (62.5%) of the investigated vessel segments in Group 1 (p ≤ 0.02), in 6/8 of the vessel segments in Group 2 (75.0%, p ≤ 0.006), and in 7/8 of the segments in Group 3 (87.5%, p ≤ 0.05). In LVV, the F-18 FDG uptake in vessel wall as a marker of inflammatory activity was attenuated by immunomodulatory drugs, which provides a foundation for future serial monitoring of treatment efficacy.

A radioiodinated FR-β-targeted tracer with improved pharmacokinetics through modification with an albumin binder for imaging of macrophages in AS and NAFL

PURPOSE

The formation of advanced plaques, which is characterized by the uninterrupted aggregation of macrophages with high expression of folate receptor-β (FR-β), is observed in several concomitant metabolic syndromes. The objective of this study was to develop a novel FR-β-targeted single-photon emission computed tomography (SPECT) radiotracer and validate its application to the noninvasive detection of atherosclerosis (AS) plaque and non-alcoholic fatty liver (NAFL).

METHODS

Two radioiodinated probes, [¹³¹I]IPBF and [¹³¹I]IBF, were developed, and cell uptake studies were used to identify their specific targets for activated macrophages. Biodistribution in normal mice was performed to obtain the pharmacokinetic information of the probes. Apolipoprotein E knockout (ApoE^-/-) mice with atherosclerotic aortas were induced by a high-fat and high-cholesterol (HFHC) diet. To investigate the affinity of radiotracers to FR-β, K_d values were determined using in vitro assays. In addition, the assessments of the aorta in the ApoE^-/- mice at different stages were performed using in vivo SPECT/CT imaging, and the findings were compared by histology.

RESULTS

Both [¹³¹I]IPBF and [¹³¹I]IBF were synthesized with > 95% radiochemical purity and up to 3 MBq/nmol molar activity. In vitro assay of [¹³¹I]IPBF showed a moderate binding affinity to plasma proteins and specific uptake in activated macrophages. The prolonged blood elimination half-life (t_1/2z) of [¹³¹I]IPBF (8.14 h) was observed in a pharmacokinetic study of normal mice, which was significantly longer than that of [¹³¹I]IBF (t_1/2z = 2.95 h). As expected, the K_d values of [¹³¹I]IPBF and [¹³¹I]IBF in the Raw 264.7 cells were 43.94 ± 9.83 nM and 61.69 ± 15.19 nM, respectively. SPECT imaging with [¹³¹I]IPBF showed a high uptake in advanced plaques and NAFL. Radioactivity in excised aortas examined by ex vivo autoradiography further confirmed the specific uptake of [¹³¹I]IPBF in high-risk AS plaques.

CONCLUSIONS

In summary, we reported a proof-of-concept study of an albumin-binding folate derivative for macrophage imaging. The FR-β-targeted probe, [¹³¹I]IPBF, significantly prolongs the plasma elimination half-life and has the potential for the monitoring of AS plaques and concomitant fatty liver.

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.

CXCR4-Directed PET/CT in Patients with Newly Diagnosed Neuroendocrine Carcinomas

We aimed to elucidate the diagnostic potential of the C-X-C motif chemokine receptor 4 (CXCR4)-directed positron emission tomography (PET) tracer ⁶⁸Ga-Pentixafor in patients with poorly differentiated neuroendocrine carcinomas (NEC), relative to the established reference standard ¹⁸F-FDG PET/computed tomography (CT). In our database, we retrospectively identified 11 treatment-naïve patients with histologically proven NEC, who underwent ¹⁸F-FDG and CXCR4-directed PET/CT for staging and therapy planning. The images were analyzed on a per-patient and per-lesion basis and compared to immunohistochemical staining (IHC) of CXCR4 from PET-guided biopsies. ⁶⁸Ga-Pentixafor visualized tumor lesions in 10/11 subjects, while¹⁸F-FDG revealed sites of disease in all 11 patients. Although weak to moderate CXCR4 expression could be corroborated by IHC in 10/11 cases, ¹⁸F-FDG PET/CT detected significantly more tumor lesions (102 vs. 42; total lesions, n = 107; p < 0.001). Semi-quantitative analysis revealed markedly higher ¹⁸F-FDG uptake as compared to ⁶⁸Ga-Pentixafor (maximum and mean standardized uptake values (SUV) and tumor-to-background ratios (TBR) of cancerous lesions, SUV_max: 12.8 ± 9.8 vs. 5.2 ± 3.7; SUV_mean: 7.4 ± 5.4 vs. 3.1 ± 3.2, p < 0.001; and, TBR 7.2 ± 7.9 vs. 3.4 ± 3.0, p < 0.001). Non-invasive imaging of CXCR4 expression in NEC is inferior to the reference standard ¹⁸F-FDG PET/CT.