Evaluation of the spline reconstruction technique for preclinical PET imaging

BACKGROUND AND OBJECTIVE

The Spline Reconstruction Technique (SRT) is a fast algorithm based on a novel numerical implementation of an analytic representation of the inverse Radon transform. The purpose of this study is to provide a comparison between SRT, Filtered Back-Projection (FBP), Ordered Subset Expectation Maximization 2D (2D-OSEM), and the Tera-Tomo 3D algorithm, using phantom data at various acquisition durations as well as small-animal data obtained from the Mediso nanoScan® PET/CT scanner.

METHODS

For this purpose, the "NEMA NU 4-2008 standards" protocol was employed at five different realizations and acquisition durations. In addition to the image quality metrics described by the NEMA protocol, Cold Region Contrast was also considered as a figure-of-merit. Furthermore, Cold Region Contrast was measured in the myocardial infarction region of six male Wistar rats. The volumetric defect quantification was assessed with dedicated computer software. Lastly, plots of Recovery Coefficient and Spill-Over Ratio as a function of the Percentage Standard Deviation were generated, after smoothing the phantom reconstructions with four different Gaussian filters. Statistical significance was determined by employing the Kruskal-Wallis test or One-way Analysis of Variance depending on the normality of the variable's distribution.

RESULTS

The present study revealed that, at the expense of slightly increased noise in the reconstructed images, SRT resulted in higher Recovery Coefficient values for small hot regions of interest, when compared with FBP and 2D-OSEM at all acquisition durations. Furthermore, SRT reconstructed images exhibit higher Recovery Coefficient values, for all hot regions of interest, when compared to the other 2D algorithms at short acquisition durations. In both phantom and animal studies, SRT achieved a significant improvement over 2D-OSEM for the Spill-Over Ratio and the Cold Region Contrast. These advantages were maintained even after comparing the algorithms at equal noise levels. The Tera-Tomo 3D algorithm (4 subsets, iterations≥ 13) performed significantly better compared to the other algorithms for all figures-of-merit. No statistically significant differences regarding the myocardial defect size were observed between the algorithms investigated.

CONCLUSIONS

Overall, SRT appears that could be useful for the quantification of small hot regions of interest, cold regions of interest, as well as in low-count imaging applications.

Radiomics/Radiogenomics in Lung Cancer: Basic Principles and Initial Clinical Results

Simple Summary

Radiogenomics is a promising new approach in cancer assessment, providing an evaluation of the molecular basis of imaging phenotypes after establishing associations between radiological features and molecular features at the genomic–transcriptomic–proteomic level. This review focuses on describing key aspects of radiogenomics while discussing limitations of translatability to the clinic and possible solutions to these challenges, providing the clinician with an up-to-date handbook on how to use this new tool.

Abstract

Lung cancer is the leading cause of cancer-related deaths worldwide, and elucidation of its complicated pathobiology has been traditionally targeted by studies incorporating genomic as well other high-throughput approaches. Recently, a collection of methods used for cancer imaging, supplemented by quantitative aspects leading towards imaging biomarker assessment termed “radiomics”, has introduced a novel dimension in cancer research. Integration of genomics and radiomics approaches, where identifying the biological basis of imaging phenotypes is feasible due to the establishment of associations between molecular features at the genomic–transcriptomic–proteomic level and radiological features, has recently emerged termed radiogenomics. This review article aims to briefly describe the main aspects of radiogenomics, while discussing its basic limitations related to lung cancer clinical applications for clinicians, researchers and patients.

Chelator-Free/Chelator-Mediated Radiolabeling of Colloidally Stabilized Iron Oxide Nanoparticles for Biomedical Imaging

The aim of this study was to develop a bioimaging probe based on magnetic iron oxide nanoparticles (MIONs) surface functionalized with the copolymer (p(MAA-g-EGMA)), which were radiolabeled with the positron emitter Gallium-68. The synthesis of the hybrid MIONs was realized by hydrolytic condensation of a single ferrous precursor in the presence of the copolymer. The synthesized MagP MIONs displayed an average D_h of 87 nm, suitable for passive targeting of cancerous tissues through the enhanced permeation and retention (EPR) effect after intravenous administration, while their particularly high magnetic content ascribes strong magnetic properties to the colloids. Two different approaches were explored to develop MIONs radiolabeled with ⁶⁸Ga: the chelator-mediated approach, where the chelating agent NODAGA-NHS was conjugated onto the MIONs (MagP-NODAGA) to form a chelate complex with ⁶⁸Ga, and the chelator-free approach, where ⁶⁸Ga was directly incorporated onto the MIONs (MagP). Both groups of NPs showed highly efficient radiolabeling with ⁶⁸Ga, forming constructs which were stable with time, and in the presence of PBS and human serum. Ex vivo biodistribution studies of [⁶⁸Ga]Ga- MIONs showed high accumulation in the mononuclear phagocyte system (MPS) organs and satisfactory blood retention with time. In vivo PET imaging with [⁶⁸Ga]Ga-MagP MIONs was in accordance with the ex vivo biodistribution results. Finally, the MIONs showed low toxicity against 4T1 breast cancer cells. These detailed studies established that [⁶⁸Ga]Ga- MIONs exhibit potential for application as tracers for early cancer detection.

Lymphoma Severity and Type Are Associated With Aortic FDG Uptake by 18F-FDG PET/CT Imaging

Background

There is evidence that metabolic disease burden in lymphoma influences patient outcome. However, the impact of disease severity on the cardiovascular system is unknown.

Objectives

The aim of this study was to examine whether lymphoma is associated with arterial inflammation by investigating the relationship between disease metabolic burden and arterial fluorodeoxyglucose (FDG) uptake.

Methods

Sixty-two chemotherapy-naïve patients with active Hodgkin’s or non-Hodgkin’s lymphoma were matched (2:1) to individual control groups of lymphoma patients previously treated and free of active disease. All groups underwent ¹⁸F-FDG position emission tomography–computed tomography imaging. Disease severity was quantified by metabolic tumor volume (MTV) and total lesion glycolysis corresponding to standardized uptake values (SUVs) ≥41% or ≥2.5 of the maximum SUV within lymphoma regions, and aortic FDG uptake was quantified through the target-to-background ratio (TBR). Inflammatory and disease severity biomarkers were also measured.

Results

MTV and total lesion glycolysis measurements were significantly correlated with inflammatory and disease biomarkers. Aortic TBR was higher in patients with active non-Hodgkin’s lymphoma compared with control subjects (median difference 0.51; 95% confidence interval [CI]: 0.28 to 0.78; p < 0.001). Similarly, patients with active Hodgkin’s lymphoma had higher values of aortic TBR compared with control subjects (median difference 0.31; 95% CI: 0.15 to 0.49; p < 0.001). In addition, aortic TBR was modestly increased in patients with stage III to IV disease compared with those with stage I to II disease (median aortic TBR: 2.23 [interquartile range: 2.01 to 2.54] vs. 2.06 [interquartile range: 1.83 to 2.27; p = 0.050). In multivariable analysis, aortic FDG uptake and MTV_≥2.5 values were independently associated (β = 0.425; 95% CI: 0.189 to 0.662; p = 0.001; R² = 0.208), as were aortic FDG uptake and MTV_≥41% (β = 0.407; 95% CI: 0.167 to 0.649, p = 0.001; R² = 0.191).

Conclusions

Aortic wall FDG uptake is related with disease severity indicative of a possible vascular effect of lymphoma. This work highlights a new potential role of molecular imaging in cardio-oncology for evaluating disease severity and its consequences on the vasculature.

The effects of chemotherapy on arterial inflammation assessed by 18 FDG PET-CT in patients with Lymphoma

Introduction

Anti-cancer treatment can lead to increased cardiovascular morbidity among lymphoma survivors. This may be the result of direct effect of treatment on heart function, or indirect acceleration of atherosclerosis. 18F-fluorodeoxyglucose (FDG) uptake is a sensitive and robust marker for assessment of atherosclerotic inflammation.

Purpose

To investigate the effects of chemotherapy on arterial inflammation using FDG-PET CT in patients with lymphoma.

Methods

Fifty nine (mean age 58±17 years) patients with Hodgkin (n=39) or non-Hodgkin lymphomas (n=20) underwent 18FDG PET-CT imaging at baseline, interim and after completion of chemotherapy as part of their routine protocol. Arterial inflammation was assessed by arterial target to background ratio (TBR) of the aortic wall along the entire aorta. The index vessel TBR (the vessel with the higher value at baseline) was used for assessment of arterial inflammation. Patients with Hodgkin Lymphomas (HL) underwent therapy with Doxorubicin, bleomycin, vinblastine and dacarbazine (ABVD). The interim of their treatment was set at 1 to 3 days prior to initiating the 3rd chemotherapy cycle. Patients with non Hodgkin Lymphomas (NHL) underwent therapy with cyclophosphamide, doxorubicin, vincristine, and prednisone+rituximab (R-CHOP). The interim of their treatment was set at 2 weeks post the 4th chemotherapy cycle. All patients we reassessed 6 weeks after chemotherapy completion.

Results

There were no differences in age and atherosclerotic risk factors (hypertension, diabetes, dyslipidemia and smoking), between the two groups (all P&gt;0.05). Similarly, there were no differences in mean (±SD) index vessel TBR between HL and NHL patients (2.4±0.7 vs 2.7±0.9, respectively, P=0.65). In the whole study population the index vessel TBR progressively decreased after the end of therapy (by 0.53±0.11, from baseline to 6 weeks following the end of therapies) (F=10.94, P&lt;0.001, ANOVA). The index vessel TBR decreased in both HL and NHL patients at 6 weeks after therapy compared to baseline level (all P&lt;0.01, ANOVA, figure). The decrease at the interim scan was more pronounced in NHL compared to HL patients, however at 6 weeks after chemotherapy completion the index vessel TBR decreased further in patients with HL, while it increased slightly compared to interim levels in NHL patients (figure 1).

Conclusion

Arterial inflammation is reduced during and post-chemotherapy in patients with lymphoma. The index vessel TBR changes at the interim phase and 6 weeks after therapy completion indicate a different effect of specific treatment regimes in arterial inflammation between HL and NHL patients.

Figure 1

Funding Acknowledgement

Type of funding source: None

P3363Severity of lymphoma is associated with aortic FDG uptake assessed by FDG PET/CT imaging

Introduction

There is increasing evidence that metabolic disease burden in lymphoma modifies patients' outcome. However, the impact of disease severity on cardiovascular system remains unknown.

Purpose

To investigate whether lymphoma is associated with arterial inflammation by examining the relationship between disease burden and arterial F-18 Fluorodeoxyglucose (FDG) uptake assessed by positron emission tomography/computed tomography (PET/CT) in Hodgkin and non-Hodgkin sub-types.

Methods

Sixty-two patients (43 male, mean age 58±18 years) with Hodgkin (n=29) or non-Hodgkin lymphoma (n=33) underwent FDG PET/CT imaging before chemotherapy. Disease severity was quantified by total metabolic tumor volume (TMTV) that represents the volume exhibiting standard uptake values (SUV) ≥41% or ≥2.5 of maximum SUV within lymphoma regions, while aortic FDG uptake assessment was based on target-to-background ratio (TBR). Serum high sensitivity-C-reactive protein (hs-CRP), white blood count (WBC), ratio of neutrophils to lymphocytes (N/L), albumin and lactic acid dehydrogenase (LDH) values were recorded in all the patients.

Results

TMTV measurements correlated significantly with hs-CRP, WBC, N/L ratio, albumin and LDH. (Table) Patients with advanced stage disease (III-IV) had higher aortic TBR values compared to those with stage I-II disease (median 2.19 interquartile range (1.96–2.54) vs. 2.04 (1.83–2.15) p=0.046 respectively). Aortic TBR was related with N/L ratio (R=0.370, p=0.009), while no significant correlation was observed with either WBC or hs-CRP values (p=0.930 and p=0.296, respectively). There were significant associations between aortic TBR uptake and TMTV values even after adjustment for age, sex, LDH, albumin, N/L ratio, as well as for the number of cardiovascular risk factors of each patient (β=0.353, p=0.001, adjusted R2=0.318 for TMTV41%, β=0.442, p=0.001, adjusted R2=0.269 for TMTV2.5).

Table 1. Pearson correlation between indices of lymphomas' severity and serum biomarkers PET derived measurements Hs-CRP P-value Neutrophils to lymphocytes ratio P-value MTV41% 0.306 0.016 0.317 0.026 MTV2.5 0.312 0.013 0.389 0.006 Albumin LDH MTV41% −0.281 0.044 0.465 <0.001 MTV2.5 −0.419 0.002 0.616 <0.001

Conclusions

Aortic wall FDG uptake is related with disease severity and subtype of lymphoma indicating a vascular effect of lymphoma, as well as a new potential role of molecular imaging in cardio-oncology by evaluation of disease severity and its consequences to vascular beds with a single examination.

Tumor Targeting via Sialic Acid: [68Ga]DOTA-en-pba as a New Tool for Molecular Imaging of Cancer with PET

PURPOSE

The aim of this study was to demonstrate the potential of Ga-68-labeled macrocycle (DOTA-en-pba) conjugated with phenylboronic vector for tumor recognition by positron emission tomography (PET), based on targeting of the overexpressed sialic acid (Sia).

PROCEDURES

The imaging reporter DOTA-en-pba was synthesized and labeled with Ga-68 at high efficiency. Cell binding assay on Mel-C and B16-F10 melanoma cells was used to evaluate melanin production and Sia overexpression to determine the best model for demonstrating the capability of [⁶⁸Ga]DOTA-en-pba to recognize tumors. The in vivo PET imaging was done with B16-F10 tumor-bearing SCID mice injected with [⁶⁸Ga]DOTA-en-pba intravenously. Tumor, blood, and urine metabolites were assessed to evaluate the presence of a targeting agent.

RESULTS

The affinity of [⁶⁸Ga]DOTA-en-pba to Sia was demonstrated on B16-F10 melanoma cells, after the production of melanin as well as Sia overexpression was proved to be up to four times higher in this cell line compared to that in Mel-C cells. Biodistribution studies in B16-F10 tumor-bearing SCID mice showed blood clearance at the time points studied, while uptake in the tumor peaked at 60 min post-injection (6.36 ± 2.41 % ID/g). The acquired PET images were in accordance with the ex vivo biodistribution results. Metabolite assessment on tumor, blood, and urine samples showed that [⁶⁸Ga]DOTA-en-pba remains unmetabolized up to at least 60 min post-injection.

CONCLUSIONS

Our work is the first attempt for in vivo imaging of cancer by targeting overexpression of sialic acid on cancer cells with a radiotracer in PET.

Investigation of Image Reconstruction Parameters of the Mediso nanoScan PC Small-Animal PET/CT Scanner for Two Different Positron Emitters Under NEMA NU 4-2008 Standards

PURPOSE

The Tera-Tomo 3D image reconstruction algorithm (a version of OSEM), provided with the Mediso nanoScan® PC (PET8/2) small-animal positron emission tomograph (PET)/x-ray computed tomography (CT) scanner, has various parameter options such as total level of regularization, subsets, and iterations. Also, the acquisition time in PET plays an important role. This study aims to assess the performance of this new small-animal PET/CT scanner for different acquisition times and reconstruction parameters, for 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) and Ga-68, under the NEMA NU 4-2008 standards.

PROCEDURES

Various image quality metrics were calculated for different realizations of [¹⁸F]FDG and Ga-68 filled image quality (IQ) phantoms.

RESULTS

[¹⁸F]FDG imaging produced improved images over Ga-68. The best compromise for the optimization of all image quality factors is achieved for at least 30 min acquisition and image reconstruction with 52 iteration updates combined with a high regularization level.

CONCLUSION

A high regularization level at 52 iteration updates and 30 min acquisition time were found to optimize most of the figures of merit investigated.

68Ga-radiolabeled AGuIX nanoparticles as dual-modality imaging agents for PET/MRI-guided radiation therapy

Aim: The aim of this study was to develop a dual-modality positron emission tomography/magnetic resonance (PET/MR) imaging probe by radiolabeling gadolinium-containing AGuIX derivatives with the positron-emitter Gallium-68 (68Ga). Materials & methods: AGuIX@NODAGA nanoparticles were labeled with 68Ga at high efficiency. Tumor accumulation in an appropriate disease model was assessed by ex vivo biodistribution and in vivo PET/MR imaging. Results: 68Ga-AGuIX@NODAGA was proven to passively accumulate in U87MG human glioblastoma tumor xenografts. Metabolite assessment in serum, urine and tumor samples showed that 68Ga-AGuIX@NODAGA remains unmetabolized up to at least 60 min postinjection. Conclusion: This study demonstrates that 68Ga-AGuIX@NODAGA can be used as a dual-modality PET/MR imaging agent with passive accumulation in the diseased area, thus showing great potential for PET/MR image-guided radiation therapy.

Intratumoral accumulation of podoplanin-expressing lymph node stromal cells promote tumor growth through elimination of CD4+ tumor-infiltrating lymphocytes

The beneficial effects of checkpoint blockade in tumor immunotherapy are limited to patients with increased tumor-infiltrating lymphocytes (TILs). Delineation of the regulatory networks that orchestrate the presence of TILs holds great promise for the design of effective immunotherapies. Podoplanin/gp38 (PDPN)-expressing lymph node stromal cells (LNSCs) are present in tumor stroma; however, their effect in the regulation of TILs remains elusive. Herein we demonstrate that intratumor injection of ex-vivo-isolated PDPN⁺ LNSCs into melanoma-bearing mice induces elimination of TILs and promotes tumor growth. In support, PDPN⁺ LNSCs exert their function through direct inhibition of CD4⁺ T cell proliferation in a cell-to-cell contact independent fashion. Mechanistically, we demonstrate that PDPN⁺ LNSCs mediate T cell growth arrest and induction of apoptosis to activated CD69⁺CD4⁺ T cells. Importantly, LTbR-Ig-mediated blockade of PDPN⁺ LNSCs expansion and function significantly attenuates melanoma tumor growth and enhances the infiltration and proliferation of CD4⁺ TILs. Overall, our findings decipher a novel role of PDPN-expressing LNSCs in the elimination of CD4⁺ TILs and propose a new target for tumor immunotherapy.

Studying the properties of the updating coefficients in the OSEM algorithm for iterative image reconstruction in PET

We have studied the properties of the pixel updating coefficients in the 2D ordered subsets expectation maximization (OSEM) algorithm for iterative image reconstruction in positron emission tomography, in order to address the problem of image quality degradation-a known property of the technique after a number of iterations. The behavior of the updating coefficients has been extensively analyzed on synthetic coincidence data, using the necessary software tools. The experiments showed that the statistical properties of these coefficients can be correlated with the quality of the reconstructed images as a function of the activity distribution in the source and the number of subsets used. Considering the fact that these properties can be quantified during the reconstruction process of data from real scans where the activity distribution in the source is unknown the results of this study might be useful for the development of a stopping criterion for the OSEM algorithm.