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Boswinkel M, Franssen GM, Heskamp S. Radiolabeled Antibodies for Immune Checkpoint PET in Preclinical Research. Methods Mol Biol 2024; 2729:143-158. [PMID: 38006495 DOI: 10.1007/978-1-0716-3499-8_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2023]
Abstract
Antibodies that block immune checkpoints, also called immune checkpoint inhibitors (ICI), have demonstrated impressive anti-tumor efficacy. The success of ICIs results from a complex interplay between cancer cells and their immune microenvironment. One of the predictors for ICI efficacy is the expression of the targeted immune checkpoint, such as programmed death ligand 1 (PD-L1). Immune checkpoints can be expressed on tumor cells and/or subsets of immune cells. PET imaging offers unique possibilities to study the dynamics of immune checkpoint expression in tumor and normal tissues in a longitudinal manner. In this chapter, we describe the methodology to use zirconium-89-labeled antibodies to assess the expression of immune checkpoint molecules in syngeneic murine tumor models by PET imaging.
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Affiliation(s)
- Milou Boswinkel
- Department of Medical Imaging, Nuclear Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Gerben M Franssen
- Department of Medical Imaging, Nuclear Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Sandra Heskamp
- Department of Medical Imaging, Nuclear Medicine, Radboud University Medical Center, Nijmegen, The Netherlands.
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Desmonts C, Lasnon C, Jaudet C, Aide N. PET imaging and quantification of small animals using a clinical SiPM-based camera. EJNMMI Phys 2023; 10:61. [PMID: 37804338 PMCID: PMC10560240 DOI: 10.1186/s40658-023-00583-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Accepted: 09/29/2023] [Indexed: 10/09/2023] Open
Abstract
BACKGROUND Small-animal PET imaging is an important tool in preclinical oncology. This study evaluated the ability of a clinical SiPM-PET camera to image several rats simultaneously and to perform quantification data analysis. METHODS Intrinsic spatial resolution was measured using 18F line sources, and image quality was assessed using a NEMA NU 4-2018 phantom. Quantification was evaluated using a fillable micro-hollow sphere phantom containing 4 spheres of different sizes (ranging from 3.95 to 7.86 mm). Recovery coefficients were computed for the maximum (Amax) and the mean (A50) pixel values measured on a 50% isocontour drawn on each sphere. Measurements were performed first with the phantom placed in the centre of the field of view and then in the off-centre position with the presence of three scattering sources to simulate the acquisition of four animals simultaneously. Quantification accuracy was finally validated using four 3D-printed phantoms mimicking rats with four subcutaneous tumours each. All experiments were performed for both 18F and 68Ga radionuclides. RESULTS Radial spatial resolutions measured using the PSF reconstruction algorithm were 1.80 mm and 1.78 mm for centred and off-centred acquisitions, respectively. Spill-overs in air and water and uniformity computed with the NEMA phantom centred in the FOV were 0.05, 0.1 and 5.55% for 18F and 0.08, 0.12 and 2.81% for 68Ga, respectively. Recovery coefficients calculated with the 18F-filled micro-hollow sphere phantom for each sphere varied from 0.51 to 1.43 for Amax and from 0.40 to 1.01 for A50. These values decreased from 0.28 to 0.92 for Amax and from 0.22 to 0.66 for A50 for 68 Ga acquisition. The results were not significantly different when imaging phantoms in the off-centre position with 3 scattering sources. Measurements performed with the four 3D-printed phantoms showed a good correlation between theoretical and measured activity in simulated tumours, with r2 values of 0.99 and 0.97 obtained for 18F and 68Ga, respectively. CONCLUSION We found that the clinical SiPM-based PET system was close to that obtained with a dedicated small-animal PET device. This study showed the ability of such a system to image four rats simultaneously and to perform quantification analysis for radionuclides commonly used in oncology.
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Affiliation(s)
- Cédric Desmonts
- Nuclear Medicine Department, University Hospital of Caen, Avenue de La Côte de Nacre, 14033, Caen Cedex 9, France.
- Normandy University, UNICAEN, INSERM 1086 ANTICIPE, Caen, France.
| | - Charline Lasnon
- Normandy University, UNICAEN, INSERM 1086 ANTICIPE, Caen, France
- Nuclear Medicine Department, UNICANCER, Comprehensive Cancer Centre F. Baclesse, Caen, France
| | - Cyril Jaudet
- Radiophysics Department, UNICANCER, Comprehensive Cancer Centre F. Baclesse, Caen, France
| | - Nicolas Aide
- Normandy University, UNICAEN, INSERM 1086 ANTICIPE, Caen, France
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Bouillot C, Daligault S, Bolbos R, Costes N, Zimmer L. 3D-printed dual holder system for simultaneous rat PET scanning: design and influence on quantification. EJNMMI Res 2023; 13:80. [PMID: 37676475 PMCID: PMC10485197 DOI: 10.1186/s13550-023-01027-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Accepted: 08/09/2023] [Indexed: 09/08/2023] Open
Abstract
BACKGROUND The low throughout of small animal positron emission tomography (PET) images acquisitions represents a substantial limitation. The aims of this study were (i) to design a low-cost support for simultaneous dynamic PET scanning of two lying rats and (ii) to study its impact on brain image quantification. RESULTS Accuracy of concentration measurement was 5.5% for one phantom in the field of view, and 5.7% for two phantoms measured simultaneously. Ratio concentration between phantoms showed an error of 6.7% ± 5.1% for Solo upper position, 6.7% ± 3.7% for Solo lower position, 5.9% ± 4.3% for Duo upper position, and 7.4% ± 6% for Duo lower position 6.7% for separated measures, and 6.6% for simultaneous measures. In vivo distribution profiles showed no difference between solo and duo uptakes. Region of Interest quantification in the whole brain showed 4.4% variability solo and 3.5% duo. The quantified test-retest bias was 8% in solo and 5% in duo, and the Intraclass Correlation Coefficient was comparable in solo and duo (0.969 vs. 0.966). CONCLUSIONS Our results showed that simultaneous scans of two rats in INVEON do not affect quantification. The dual support system will allow us to reduce protocol costs and duration.
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Affiliation(s)
| | | | - Radu Bolbos
- CERMEP-Imagerie du Vivant, 69 boulevard Pinel, 69003, Lyon, France
| | - Nicolas Costes
- CERMEP-Imagerie du Vivant, 69 boulevard Pinel, 69003, Lyon, France
- Lyon Neuroscience Research Center (CRNL), INSERM, Université Claude Bernard, Lyon, France
| | - Luc Zimmer
- CERMEP-Imagerie du Vivant, 69 boulevard Pinel, 69003, Lyon, France
- Lyon Neuroscience Research Center (CRNL), INSERM, Université Claude Bernard, Lyon, France
- Hospices Civils de Lyon, Lyon, France
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Kumar M, Salem K, Jeffery JJ, Fowler AM. PET Imaging of Estrogen Receptors Using 18F-Based Radioligands. METHODS IN MOLECULAR BIOLOGY (CLIFTON, N.J.) 2022; 2418:129-151. [PMID: 35119664 DOI: 10.1007/978-1-0716-1920-9_9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
In vivo molecular imaging of estrogen receptor alpha (ER) can be performed via positron emission tomography (PET) using ER-specific radioligands, such as 16α-[18F]fluoro-17β-estradiol (18F-FES). 18F-FES is a radiopharmaceutical recently approved by the United States Food and Drug Administration for use with PET imaging to detect ER+ lesions in patients with recurrent or metastatic breast cancer as an adjunct to biopsy. 18F-FES PET imaging has been used in clinical studies and preclinical research to assess whole-body ER protein expression and ligand binding function across multiple metastatic sites, to demonstrate inter-tumoral and temporal heterogeneity of ER expression, to quantify the pharmacodynamic effects of ER antagonist treatment, and to predict endocrine therapy response. 18F-FES PET has also been studied for imaging ER in endometrial and ovarian cancer. This chapter details the experimental protocol for 18F-FES PET imaging of ER in preclinical tumor xenograft models. Consistent adherence to key methodologic details will facilitate obtaining meaningful and reproducible 18F-FES PET preclinical imaging results, which could yield additional insight for clinical trials regarding imaging biomarkers and oncologic therapy.
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Affiliation(s)
- Manoj Kumar
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
- Department of Radiology, Canary Center at Stanford for Cancer Early Detection, Stanford School of Medicine, Palo Alto, CA, USA
| | - Kelley Salem
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | | | - Amy M Fowler
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
- University of Wisconsin Carbone Cancer Center, Madison, WI, USA.
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
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Development of a new advanced animal cradle for small animal multiple imaging modalities: acquisition and evaluation of high-throughput multiple-mouse imaging. Phys Eng Sci Med 2021; 44:1367-1376. [PMID: 34724162 DOI: 10.1007/s13246-021-01065-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 10/12/2021] [Indexed: 10/20/2022]
Abstract
The physiological conditions of small animals are an essential component to be considered when acquiring images for pre-clinical studies, and they play a vital role in the overall results of a study. However, several previous studies did not consider these conditions. In this study, a new animal cradle that can be modified and adjusted to suit multiple imaging modalities such as positron emission tomography (PET)/computed tomography (CT) and magnetic resonance imaging (MRI) was developed. Unlike previous cradles where only one mouse can be imaged at a time, a total of four mice can be imaged simultaneously using this new cradle. Additionally, fusion images with high-throughput multiple-mouse imaging (MMI) of PET/MRI and PET/CT images can be acquired using this newly developed cradle. The dynamic brain images were also acquired simultaneously by applying PET dynamic imaging technology to high-throughput MMI methods. The results of this study suggest that the newly developed small animal cradle can be widely used in pre-clinical studies.
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3D-printed multisampling holder for microcomputed tomography applied to life and materials science research. Micron 2021; 150:103142. [PMID: 34509886 DOI: 10.1016/j.micron.2021.103142] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Revised: 08/15/2021] [Accepted: 08/22/2021] [Indexed: 11/21/2022]
Abstract
The aim of this work was to design, fabricate, test and validate a 3D-printed multisampling holder for multi-analysis by microcomputed tomography. Different raw materials were scanned by microcomputed tomography. The raw material chosen was used to fabricate the holder by 3D printing. To validate the multisampling holder, five teeth were filled with a high density-material and scanned in two ways: a single and a multisampling scan mode. For each tooth, the root canal filling volume, porosity volume, closed pore volume, and open pore volume were calculated and compared when the same tooth was scanned in the two sampling scan mode. ABSplus P430™ allowed a high transmission value (84.3 %), and then it was the polymeric material selected to fabricate the holder. In a single sampling scan mode, the scan duration for scanning five teeth was 87.42 min, contrasting with 21.51 min for a multisampling scan mode, which scanned five teeth at the same time. The scan duration time and the cost using a multisampling holder represented a reduction of 75 % and the data volume generated represented a reduction of 60 %. Comparing the two scan modes, the results also showed that the difference of root canal filling volume, porosity volume, closed pore volume, and open pore volume was not statistically significant (p > .05). The multisampling holder was validated to do multi-analysis by microcomputed tomography without significant loss of quantitative accuracy data, allowing a reduction in scan duration time, imaging cost, and data storage.
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Harrison NJ, Shumway KL, Hansen SA, Maitz CA, Thombs LA, Flesner BK. A 3D-printed Apparatus for Imaging Multiple Rats Simultaneously. Comp Med 2021; 71:116-122. [PMID: 33706858 DOI: 10.30802/aalas-cm-20-000089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
CT (computerized tomography) is a necessary imaging modality for cancer staging and disease monitoring. Rodent models of cancer are commonly studied prior to human clinical trials, but CT in rodents can be difficult due to their small size and constant movement, which necessitates general anesthesia. Because microCT equipment is not always available, clinical CT may be a viable alternative. Limitations of microCT and clinical CT include biosecurity, anesthesia to limit image distortion due to motion, and cost. To address several of these constraints, we created a 3D-printed apparatus that accommodated simultaneous imaging of as many as 9 rats under gas anesthesia. Rats were anesthetized in series and placed in a 3 × 3 arrangement. To assess differences in attenuation between individual chambers and rows or columns in the device, we first imaged a standardized phantom plug as a control. We hypothesized that attenuation of specific rat organs would not be affected regardless of the location or position in the 3D-printed device. Four organs-liver, kidney, femur, and brain-were evaluated in 9 rats. For both the phantom and kidneys, statistically significant, but clinically negligible, effects on attenuation were noted between rows but not between columns. We attribute this finding to the absence of a top layer of the apparatus, which thus created asymmetric attenuation and beam hardening through the device. This apparatus allowed us to successfully image 9 rats simultaneously in a clinical CT machine, with negligible effects on attenuation. Planned improvements in this apparatus include completely enclosed versions for biosecure imaging.
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Affiliation(s)
- Nicholas J Harrison
- Veterinary Pathobiology, College of Veterinary Medicine, University of Missouri, Columbia, Missouri
| | - Kate L Shumway
- Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, Missouri
| | - Sarah A Hansen
- Office of Animal Resources, University of Missouri, Columbia, Missouri
| | - Charles A Maitz
- Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, Missouri
| | - Lori A Thombs
- Department of Statistics, College of Arts and Science, University of Missouri, Columbia, Missouri
| | - Brian K Flesner
- Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, Missouri;,
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Validation of Image Qualities of a Novel Four-Mice Bed PET System as an Oncological and Neurological Analysis Tool. J Imaging 2021; 7:jimaging7030043. [PMID: 34460699 PMCID: PMC8321312 DOI: 10.3390/jimaging7030043] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Revised: 02/22/2021] [Accepted: 02/24/2021] [Indexed: 11/20/2022] Open
Abstract
Background: Micro-positron emission tomography (micro-PET), a small-animal dedicated PET system, is used in biomedical studies and has the quantitative imaging capabilities of radiotracers. A single-bed system, commonly used in micro-PET, is laborious to use in large-scale studies. Here, we evaluated the image qualities of a multi-bed system. Methods: Phantom imaging studies were performed to assess the recovery coefficients (RCs), uniformity, and spill-over ratios (SORs) in water- and air-filled chambers. 18F-FDG and 18F-FPEB PET images of xenograft and normal mice from the multi-bed and single-bed systems were compared. Results: For small diameters (< 3 mm), the RC values between the two systems differed significantly. However, for large diameters (> 4 mm), there were no differences in RC values between the two systems. Uniformity and SORs of both systems were within the tolerance limit of 15%. In the oncological study, the estimation of 18F-FDG uptake in the tumor was significantly lower in the multi-bed system than that in the single-bed system. However, 18F-FDG PET in xenograft mice with tumor size > 4 mm revealed the variation between subjects within the multi-bed system group to be less than 12%. In the neurological study, SUV for the multi-bed group was 25–26% lower than that for the single-bed group; however, inter-object variations within the multi-bed system were below 7%. Conclusions: Although the multi-bed system showed lower estimation of radiotracer uptake than that of the single-bed system, the inter-subject variations were within acceptable limits. Our results indicate that the multi-bed system can be used in oncological and neurological studies.
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Gsell W, Molinos C, Correcher C, Belderbos S, Wouters J, Junge S, Heidenreich M, Velde GV, Rezaei A, Nuyts J, Cawthorne C, Cleeren F, Nannan L, Deroose CM, Himmelreich U, Gonzalez AJ. Characterization of a preclinical PET insert in a 7 tesla MRI scanner: beyond NEMA testing. Phys Med Biol 2020; 65:245016. [PMID: 32590380 DOI: 10.1088/1361-6560/aba08c] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
This study evaluates the performance of the Bruker positron emission tomograph (PET) insert combined with a BioSpec 70/30 USR magnetic resonance imaging (MRI) scanner using the manufacturer acceptance protocol and the NEMA NU 4-2008 for small animal PET. The PET insert is made of 3 rings of 8 monolithic LYSO crystals (50 × 50 × 10 mm3) coupled to silicon photomultipliers (SiPM) arrays, conferring an axial and transaxial FOV of 15 cm and 8 cm. The MRI performance was evaluated with and without the insert for the following radiofrequency noise, magnetic field homogeneity and image quality. For the PET performance, we extended the NEMA protocol featuring system sensitivity, count rates, spatial resolution and image quality to homogeneity and accuracy for quantification using several MRI sequences (RARE, FLASH, EPI and UTE). The PET insert does not show any adverse effect on the MRI performances. The MR field homogeneity is well preserved (Diameter Spherical Volume, for 20 mm of 1.98 ± 4.78 without and -0.96 ± 5.16 Hz with the PET insert). The PET insert has no major effect on the radiofrequency field. The signal-to-noise ratio measurements also do not show major differences. Image ghosting is well within the manufacturer specifications (<2.5%) and no RF noise is visible. Maximum sensitivity of the PET insert is 11.0% at the center of the FOV even with simultaneous acquisition of EPI and RARE. PET MLEM resolution is 0.87 mm (FWHM) at 5 mm off-center of the FOV and 0.97 mm at 25 mm radial offset. The peaks for true/noise equivalent count rates are 410/240 and 628/486 kcps for the rat and mouse phantoms, and are reached at 30.34/22.85 and 27.94/22.58 MBq. PET image quality is minimally altered by the different MRI sequences. The Bruker PET insert shows no adverse effect on the MRI performance and demonstrated a high sensitivity, sub-millimeter resolution and good image quality even during simultaneous MRI acquisition.
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Affiliation(s)
- Willy Gsell
- Biomedical MRI, Department of Imaging and Pathology, KU Leuven, Leuven, Belgium
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A novel tracer for in vivo optical imaging of fatty acid metabolism in the heart and brown adipose tissue. Sci Rep 2020; 10:11209. [PMID: 32641756 PMCID: PMC7343860 DOI: 10.1038/s41598-020-68065-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 06/16/2020] [Indexed: 12/04/2022] Open
Abstract
Multiplexed imaging is essential for the evaluation of substrate utilization in metabolically active organs, such as the heart and brown adipose tissue (BAT), where substrate preference changes in pathophysiologic states. Optical imaging provides a useful platform because of its low cost, high throughput and intrinsic ability to perform composite readouts. However, the paucity of probes available for in vivo use has limited optical methods to image substrate metabolism. Here, we present a novel near-infrared (NIR) free fatty acid (FFA) tracer suitable for in vivo imaging of deep tissues such as the heart. Using click chemistry, Alexa Fluor 647 DIBO Alkyne was conjugated to palmitic acid. Mice injected with 0.05 nmol/g bodyweight of the conjugate (AlexaFFA) were subjected to conditions known to increase FFA uptake in the heart (fasting) and BAT [cold exposure and injection with the β3 adrenergic agonist CL 316, 243(CL)]. Organs were subsequently imaged both ex vivo and in vivo to quantify AlexaFFA uptake. The blood kinetics of AlexaFFA followed a two-compartment model with an initial fast compartment half-life of 0.14 h and a subsequent slow compartment half-life of 5.2 h, consistent with reversible protein binding. Ex vivo fluorescence imaging after overnight cold exposure and fasting produced a significant increase in AlexaFFA uptake in the heart (58 ± 12%) and BAT (278 ± 19%) compared to warm/fed animals. In vivo imaging of the heart and BAT after exposure to CL and fasting showed a significant increase in AlexaFFA uptake in the heart (48 ± 20%) and BAT (40 ± 10%) compared to saline-injected/fed mice. We present a novel near-infrared FFA tracer, AlexaFFA, that is suitable for in vivo quantification of FFA metabolism and can be applied in the context of a low cost, high throughput, and multiplexed optical imaging platform.
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Greenwood HE, Nyitrai Z, Mocsai G, Hobor S, Witney TH. High-Throughput PET/CT Imaging Using a Multiple-Mouse Imaging System. J Nucl Med 2019; 61:292-297. [PMID: 31519806 PMCID: PMC7002164 DOI: 10.2967/jnumed.119.228692] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2019] [Accepted: 07/24/2019] [Indexed: 12/25/2022] Open
Abstract
A considerable limitation of current small-animal PET/CT imaging is the low throughput of acquisitions. Consequently, to sufficiently power a study, high costs accumulate. Together with a commercial scanner manufacturer, we developed a 4-bed mouse “hotel” to simultaneously image up to 4 mice, thereby reducing costs and maximizing the efficiency of radiotracer use when compared with scans performed with a single mouse bed. Methods: For physiologic evaluation of the mouse hotel, temperature and anesthesia were tested for uniformity in conjunction with 18F-FDG PET/CT imaging of mini image-quality phantoms designed to fit the new imaging system. After reconstruction, National Electrical Manufacturers Association NU-4 tests examined uniformity, recovery coefficients, and spillover ratios. To evaluate the mouse hotel under standard in vivo imaging conditions, 4 mice were simultaneously scanned by dynamic 18F-FDG PET/CT over 60 min, and quantified images were compared with those acquired using a single mouse bed. Results: The mouse hotel maintained a constant temperature of 36.8°C ± 0.4°C, with anesthesia distributed evenly to each nose cone (2.9 ± 0.1 L/min). The National Electrical Manufacturers Association tests revealed values within tolerable limits for uniformity, for recovery coefficients in rods larger than 2 mm, and for spillover ratios in the nonradioactive water- and air-filled chambers. There was low variability in radiotracer uptake in all major organs for the mouse hotel versus the single mouse bed. Conclusion: Analysis of images acquired using the mouse hotel confirmed its utility to increase the throughput of small-animal PET imaging without considerable loss of image quality or quantitative precision. In comparison to a single mouse bed, the cost and time associated with each scan were substantially reduced.
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Affiliation(s)
- Hannah E Greenwood
- Centre for Advanced Biomedical Imaging, Division of Medicine, University College London, London, United Kingdom.,Department of Imaging Chemistry and Biology, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom; and
| | | | - Gabor Mocsai
- Mediso Medical Imaging Systems, Budapest, Hungary
| | - Sandor Hobor
- Mediso Medical Imaging Systems, Budapest, Hungary
| | - Timothy H Witney
- Department of Imaging Chemistry and Biology, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom; and
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Wardak M, Nguyen PK. The Gift of Light: Using Multiplexed Optical Imaging to Probe Cardiac Metabolism in Health and Disease. Circ Cardiovasc Imaging 2018; 11:e007597. [PMID: 29555838 DOI: 10.1161/circimaging.118.007597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Mirwais Wardak
- From the Department of Radiology (M.W.), Molecular Imaging Program at Stanford (MIPS) (M.W.), Division of Cardiovascular Medicine, Department of Medicine (P.K.N.), and Stanford Cardiovascular Institute (M.W., P.K.N.), Stanford University School of Medicine, CA; and Cardiology Section, Veterans Affairs Palo Alto Health Care Administration, CA (P.K.N.)
| | - Patricia K Nguyen
- From the Department of Radiology (M.W.), Molecular Imaging Program at Stanford (MIPS) (M.W.), Division of Cardiovascular Medicine, Department of Medicine (P.K.N.), and Stanford Cardiovascular Institute (M.W., P.K.N.), Stanford University School of Medicine, CA; and Cardiology Section, Veterans Affairs Palo Alto Health Care Administration, CA (P.K.N.).
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Effects of common anesthetic agents on [ 18F]flumazenil binding to the GABA A receptor. EJNMMI Res 2016; 6:80. [PMID: 27826950 PMCID: PMC5101239 DOI: 10.1186/s13550-016-0235-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Accepted: 10/29/2016] [Indexed: 12/25/2022] Open
Abstract
Background The availability of GABAA receptor binding sites in the brain can be assessed by positron emission tomography (PET) using the radioligand, [18F]flumazenil. However, the brain uptake and binding of this PET radioligand are influenced by anesthetic drugs, which are typically needed in preclinical imaging studies and clinical imaging studies involving patient populations that do not tolerate relatively longer scan times. The objective of this study was to examine the effects of anesthesia on the binding of [18F]flumazenil to GABAA receptors in mice. Methods Brain and whole blood radioactivity concentrations were measured ex vivo by scintillation counting or in vivo by PET in four groups of mice following administration of [18F]flumazenil: awake mice and mice anesthetized with isoflurane, dexmedetomidine, or ketamine/dexmedetomidine. Dynamic PET recordings were obtained for 60 min in mice anesthetized by either isoflurane or ketamine/dexmedetomidine. Static PET recordings were obtained at 25 or 55 min after [18F]flumazenil injection in awake or dexmedetomidine-treated mice acutely anesthetized with isoflurane. The apparent distribution volume (VT*) was calculated for the hippocampus and frontal cortex from either the full dynamic PET scans using an image-derived input function or from a series of ex vivo experiments using whole blood as the input function. Results PET images showed persistence of high [18F]flumazenil uptake (up to 20 % ID/g) in the brains of mice scanned under isoflurane or ketamine/dexmedetomidine anesthesia, whereas uptake was almost indiscernible in late samples or static scans from awake or dexmedetomidine-treated animals. The steady-state VT* was twofold higher in hippocampus of isoflurane-treated mice and dexmedetomidine-treated mice than in awake mice. Conclusions Anesthesia has pronounced effects on the binding and blood-brain distribution of [18F]flumazenil. Consequently, considerable caution must be exercised in the interpretation of preclinical and clinical PET studies of GABAA receptors involving the use of anesthesia.
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Reilhac A, Boisson F, Wimberley C, Parmar A, Zahra D, Hamze H, Davis E, Arthur A, Bouillot C, Charil A, Grégoire MC. Simultaneous scanning of two mice in a small-animal PET scanner: a simulation-based assessment of the signal degradation. Phys Med Biol 2016; 61:1371-88. [PMID: 26797268 DOI: 10.1088/0031-9155/61/3/1371] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In PET imaging, research groups have recently proposed different experimental set ups allowing multiple animals to be simultaneously imaged in a scanner in order to reduce the costs and increase the throughput. In those studies, the technical feasibility was demonstrated and the signal degradation caused by additional mice in the FOV characterized, however, the impact of the signal degradation on the outcome of a PET study has not yet been studied. Here we thoroughly investigated, using Monte Carlo simulated [18F]FDG and [11C]Raclopride PET studies, different experimental designs for whole-body and brain acquisitions of two mice and assessed the actual impact on the detection of biological variations as compared to a single-mouse setting. First, we extended the validation of the PET-SORTEO Monte Carlo simulation platform for the simultaneous simulation of two animals. Then, we designed [18F]FDG and [11C]Raclopride input mouse models for the simulation of realistic whole-body and brain PET studies. Simulated studies allowed us to accurately estimate the differences in detection between single- and dual-mode acquisition settings that are purely the result of having two animals in the FOV. Validation results showed that PET-SORTEO accurately reproduced the spatial resolution and noise degradations that were observed with actual dual phantom experiments. The simulated [18F]FDG whole-body study showed that the resolution loss due to the off-center positioning of the mice was the biggest contributing factor in signal degradation at the pixel level and a minimal inter-animal distance as well as the use of reconstruction methods with resolution modeling should be preferred. Dual mode acquisition did not have a major impact on ROI-based analysis except in situations where uptake values in organs from the same subject were compared. The simulated [11C]Raclopride study however showed that dual-mice imaging strongly reduced the sensitivity to variations when mice were positioned side-by-side while no sensitivity reduction was observed when they were facing each other. This is the first study showing the impact of different experimental designs for whole-body and brain acquisitions of two mice on the quality of the results using Monte Carlo simulated [18F]FDG and [11C]Raclopride PET studies.
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Yang M, Fan Q, Zhang R, Cheng K, Yan J, Pan D, Ma X, Lu A, Cheng Z. Dragon fruit-like biocage as an iron trapping nanoplatform for high efficiency targeted cancer multimodality imaging. Biomaterials 2015; 69:30-7. [PMID: 26275860 DOI: 10.1016/j.biomaterials.2015.08.001] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2015] [Accepted: 08/01/2015] [Indexed: 12/11/2022]
Abstract
Natural biopolymer based multifunctional nanomaterials are perfect candidates for multimodality imaging and therapeutic applications. Conventional methods of building multimodal imaging probe require either cross-linking manners to increase its in vivo stability or attach a target module to realize targeted imaging. In this study, the intrinsic photoacoustic signals and the native strong chelating properties with metal ions of melanin nanoparticle (MNP), and transferrin receptor 1 (TfR1) targeting ability of apoferritin (APF) was employed to construct an efficient nanoplatform (AMF) without tedious assembling process. Smart APF shell significantly increased metal ions loading (molar ratio of 1:800, APF/Fe(3+)) and therefore improved magnetic resonance imaging (MRI) sensitivity. Moreover, synergistic use of Fe(3+) and APF contributed to high photoacounstic imaging (PAI) sensitivity. AMF showed excellent bio-stability and presented good in vivo multimodality imaging (PET/MRI/PAI) properties (good tumor uptake, high specificity and high tumor contrast) in HT29 tumor because of its targeting property combined with the enhanced permeability and retention (EPR) effect, making it promising in theranostics and translational nanomedicine.
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Affiliation(s)
- Min Yang
- Key Laboratory of Nuclear Medicine, Ministry of Health, Jiangsu Key Laboratory of Molecular Nuclear Medicine, Jiangsu Institute of Nuclear Medicine, Wuxi 214063, China; Molecular Imaging Program at Stanford (MIPS), Canary Center at Stanford for Cancer Early Detection, Department of Radiology and Bio-X Program, School of Medicine, Stanford University, CA 94305-5484, USA
| | - Quli Fan
- Molecular Imaging Program at Stanford (MIPS), Canary Center at Stanford for Cancer Early Detection, Department of Radiology and Bio-X Program, School of Medicine, Stanford University, CA 94305-5484, USA
| | - Ruiping Zhang
- Molecular Imaging Program at Stanford (MIPS), Canary Center at Stanford for Cancer Early Detection, Department of Radiology and Bio-X Program, School of Medicine, Stanford University, CA 94305-5484, USA
| | - Kai Cheng
- Molecular Imaging Program at Stanford (MIPS), Canary Center at Stanford for Cancer Early Detection, Department of Radiology and Bio-X Program, School of Medicine, Stanford University, CA 94305-5484, USA
| | - Junjie Yan
- Key Laboratory of Nuclear Medicine, Ministry of Health, Jiangsu Key Laboratory of Molecular Nuclear Medicine, Jiangsu Institute of Nuclear Medicine, Wuxi 214063, China
| | - Donghui Pan
- Key Laboratory of Nuclear Medicine, Ministry of Health, Jiangsu Key Laboratory of Molecular Nuclear Medicine, Jiangsu Institute of Nuclear Medicine, Wuxi 214063, China
| | - Xiaowei Ma
- Molecular Imaging Program at Stanford (MIPS), Canary Center at Stanford for Cancer Early Detection, Department of Radiology and Bio-X Program, School of Medicine, Stanford University, CA 94305-5484, USA
| | - Alex Lu
- Molecular Imaging Program at Stanford (MIPS), Canary Center at Stanford for Cancer Early Detection, Department of Radiology and Bio-X Program, School of Medicine, Stanford University, CA 94305-5484, USA
| | - Zhen Cheng
- Molecular Imaging Program at Stanford (MIPS), Canary Center at Stanford for Cancer Early Detection, Department of Radiology and Bio-X Program, School of Medicine, Stanford University, CA 94305-5484, USA.
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The relationship between serial [(18) F]PBR06 PET imaging of microglial activation and motor function following stroke in mice. Mol Imaging Biol 2015; 16:821-9. [PMID: 24865401 DOI: 10.1007/s11307-014-0745-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
PURPOSE Using [(18) F]PBR06 positron emission tomography (PET) to characterize the time course of stroke-associated neuroinflammation (SAN) in mice, to evaluate whether brain microglia influences motor function after stroke, and to demonstrate the use of [(18) F]PBR06 PET as a therapeutic assessment tool. PROCEDURES Stroke was induced by transient middle cerebral artery occlusion (MCAO) in Balb/c mice (control, stroke, and stroke with poststroke minocycline treatment). [18 F]PBR06 PET/CT imaging, rotarod tests, and immunohistochemistry (IHC) were performed 3, 11, and 22 days poststroke induction (PSI). RESULTS The stroke group exhibited significantly increased microglial activation, and impaired motor function. Peak microglial activation was 11 days PSI. There was a strong association between microglial activation, motor function, and microglial protein expression on IHC. Minocycline significantly reduced microglial activation and improved motor function by day 22 PSI. CONCLUSION [18 F]PBR06 PET imaging noninvasively characterizes the time course of SAN, and shows increased microglial activation is associated with decreased motor function.
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Palner M, Shen B, Jeon J, Lin J, Chin FT, Rao J. Preclinical Kinetic Analysis of the Caspase-3/7 PET Tracer 18F-C-SNAT: Quantifying the Changes in Blood Flow and Tumor Retention After Chemotherapy. J Nucl Med 2015; 56:1415-21. [PMID: 26045308 DOI: 10.2967/jnumed.115.155259] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Accepted: 04/13/2015] [Indexed: 12/13/2022] Open
Abstract
UNLABELLED Early detection of tumor response to therapy is crucial to the timely identification of the most efficacious treatments. We recently developed a novel apoptosis imaging tracer, (18)F-C-SNAT (C-SNAT is caspase-sensitive nanoaggregation tracer), that undergoes an intramolecular cyclization reaction after cleavage by caspase-3/7, a biomarker of apoptosis. This caspase-3/7-dependent reaction leads to an enhanced accumulation and retention of (18)F activity in apoptotic tumors. This study aimed to fully examine in vivo pharmacokinetics of the tracer through PET imaging and kinetic modeling in a preclinical mouse model of tumor response to systemic anticancer chemotherapy. METHODS Tumor-bearing nude mice were treated 3 times with intravenous injections of doxorubicin before undergoing a 120-min dynamic (18)F-C-SNAT PET/CT scan. Time-activity curves were extracted from the tumor and selected organs. A 2-tissue-compartment model was fitted to the time-activity curves from tumor and muscle, using the left ventricle of the heart as input function, and the pharmacokinetic rate constants were calculated. RESULTS Both tumor uptake (percentage injected dose per gram) and the tumor-to-muscle activity ratio were significantly higher in the treated mice than untreated mice. Pharmacokinetic rate constants calculated by the 2-tissue-compartment model showed a significant increase in delivery and accumulation of the tracer after the systemic chemotherapeutic treatment. Delivery of (18)F-C-SNAT to the tumor tissue, quantified as K1, increased from 0.31 g⋅(mL⋅min)(-1) in untreated mice to 1.03 g⋅(mL⋅min)(-1) in treated mice, a measurement closely related to changes in blood flow. Accumulation of (18)F-C-SNAT, quantified as k3, increased from 0.03 to 0.12 min(-1), proving a higher retention of (18)F-C-SNAT in treated tumors independent from changes in blood flow. An increase in delivery was also found in the muscular tissue of treated mice without increasing accumulation. CONCLUSION (18)F-C-SNAT has significantly increased tumor uptake and significantly increased tumor-to-muscle ratio in a preclinical mouse model of tumor therapy. Furthermore, our kinetic modeling of (18)F-C-SNAT shows that chemotherapeutic treatment increased accumulation (k3) in the treated tumors, independent of increased delivery (K1).
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Affiliation(s)
- Mikael Palner
- Department of Radiology, Molecular Imaging Program at Stanford, Stanford University School of Medicine, Stanford, California; and
| | - Bin Shen
- Department of Radiology, Molecular Imaging Program at Stanford, Stanford University School of Medicine, Stanford, California; and
| | - Jongho Jeon
- Department of Radiology, Molecular Imaging Program at Stanford, Stanford University School of Medicine, Stanford, California; and
| | - Jianguo Lin
- Department of Radiology, Molecular Imaging Program at Stanford, Stanford University School of Medicine, Stanford, California; and Key Laboratory of Nuclear Medicine, Jiangsu Institute of Nuclear Medicine, Wuxi, China
| | - Frederick T Chin
- Department of Radiology, Molecular Imaging Program at Stanford, Stanford University School of Medicine, Stanford, California; and
| | - Jianghong Rao
- Department of Radiology, Molecular Imaging Program at Stanford, Stanford University School of Medicine, Stanford, California; and
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Atashroo DA, Paik KJ, Chung MT, McArdle A, Senarath-Yapa K, Zielins ER, Tevlin R, Duldulao CR, Walmsley GG, Wearda T, Marecic O, Longaker MT, Wan DC. Assessment of viability of human fat injection into nude mice with micro-computed tomography. J Vis Exp 2015:e52217. [PMID: 25590561 DOI: 10.3791/52217] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Lipotransfer is a vital tool in the surgeon's armamentarium for the treatment of soft tissue deficits of throughout the body. Fat is the ideal soft tissue filler as it is readily available, easily obtained, inexpensive, and inherently biocompatible.(1) However, despite its burgeoning popularity, fat grafting is hampered by unpredictable results and variable graft survival, with published retention rates ranging anywhere from 10-80%. (1-3) To facilitate investigations on fat grafting, we have therefore developed an animal model that allows for real-time analysis of injected fat volume retention. Briefly, a small cut is made in the scalp of a CD-1 nude mouse and 200-400 µl of processed lipoaspirate is placed over the skull. The scalp is chosen as the recipient site because of its absence of native subcutaneous fat, and because of the excellent background contrast provided by the calvarium, which aids in the analysis process. Micro-computed tomography (micro-CT) is used to scan the graft at baseline and every two weeks thereafter. The CT images are reconstructed, and an imaging software is used to quantify graft volumes. Traditionally, techniques to assess fat graft volume have necessitated euthanizing the study animal to provide just a single assessment of graft weight and volume by physical measurement ex vivo. Biochemical and histological comparisons have likewise required the study animal to be euthanized. This described imaging technique offers the advantage of visualizing and objectively quantifying volume at multiple time points after initial grafting without having to sacrifice the study animal. The technique is limited by the size of the graft able to be injected as larger grafts risk skin and fat necrosis. This method has utility for all studies evaluating fat graft viability and volume retention. It is particularly well-suited to providing a visual representation of fat grafts and following changes in volume over time.
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Affiliation(s)
- David A Atashroo
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Kevin J Paik
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Michael T Chung
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Adrian McArdle
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Kshemendra Senarath-Yapa
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Elizabeth R Zielins
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Ruth Tevlin
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Christopher R Duldulao
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Graham G Walmsley
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Taylor Wearda
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Owen Marecic
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine
| | - Michael T Longaker
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine; Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine
| | - Derrick C Wan
- Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine; Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine;
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Seidel J, Bernardo ML, Wong KJ, Xu B, Williams MR, Kuo F, Jagoda EM, Basuli F, Li C, Griffiths GL, Green MV, Choyke PL. Simultaneous ECG-gated PET imaging of multiple mice. Nucl Med Biol 2014; 41:582-6. [PMID: 24909865 PMCID: PMC4104247 DOI: 10.1016/j.nucmedbio.2014.03.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Revised: 02/11/2014] [Accepted: 03/04/2014] [Indexed: 10/25/2022]
Abstract
INTRODUCTION We describe and illustrate a method for creating ECG-gated PET images of the heart for each of several mice imaged at the same time. The method is intended to increase "throughput" in PET research studies of cardiac dynamics or to obtain information derived from such studies, e.g. tracer concentration in end-diastolic left ventricular blood. METHODS An imaging bed with provisions for warming, anesthetic delivery, etc., was fabricated by 3D printing to allow simultaneous PET imaging of two side-by-side mice. After electrode attachment, tracer injection and placement of the animals in the scanner field of view, ECG signals from each animal were continuously analyzed and independent trigger markers generated whenever an R-wave was detected in each signal. PET image data were acquired in "list" mode and these trigger markers were inserted into this list along with the image data. Since each mouse is in a different spatial location in the FOV, sorting of these data using trigger markers first from one animal and then the other yields two independent and correctly formed ECG-gated image sequences that reflect the dynamical properties of the heart during an "average" cardiac cycle. RESULTS The described method yields two independent ECG-gated image sequences that exhibit the expected properties in each animal, e.g. variation of the ventricular cavity volumes from maximum to minimum and back during the cardiac cycle in the processed animal with little or no variation in these volumes during the cardiac cycle in the unprocessed animal. CONCLUSION ECG-gated image sequences for each of several animals can be created from a single list mode data collection using the described method. In principle, this method can be extended to more than two mice (or other animals) and to other forms of physiological gating, e.g. respiratory gating, when several subjects are imaged at the same time.
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Affiliation(s)
- Jurgen Seidel
- Molecular Imaging Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA; Contractor to Leidos Biomedical Research, Inc., Frederick, MD, USA.
| | - Marcelino L Bernardo
- Molecular Imaging Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA; Leidos Biomedical Research, Inc., Frederick, MD, USA
| | - Karen J Wong
- Molecular Imaging Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - Biying Xu
- Imaging Probe Development Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA; Kelly Services Inc., Troy, MI, USA
| | - Mark R Williams
- Molecular Imaging Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA; Leidos Biomedical Research, Inc., Frederick, MD, USA
| | - Frank Kuo
- Molecular Imaging Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA; Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD, USA
| | - Elaine M Jagoda
- Molecular Imaging Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - Falguni Basuli
- Imaging Probe Development Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA; Kelly Services Inc., Troy, MI, USA
| | - Changhui Li
- Imaging Probe Development Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA; Kelly Services Inc., Troy, MI, USA
| | - Gary L Griffiths
- Molecular Imaging Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA; Clinical Research Directorate/CMRP, Leidos Biomedical Research, Inc. (formerly SAIC-Frederick, Inc.) Frederick National Laboratory for Cancer Research, Frederick, MD, USA
| | - Michael V Green
- Molecular Imaging Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA; Contractor to Leidos Biomedical Research, Inc., Frederick, MD, USA
| | - Peter L Choyke
- Molecular Imaging Program, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
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