Anesthesia condition for 18F-FDG imaging of lung metastasis tumors using small animal PET

Automatic Quantitative Assessment for Diagnostic and Therapeutic Response in Rodent Myocardial Infarct Model

The purpose of this study was to investigate the most appropriate methodological approach for the automatic measurement of rodent myocardial infarct polar map using histogram-based thresholding and unsupervised deep learning (DL)-based segmentation. A rat myocardial infarction model was induced by ligation of the left coronary artery. Positron emission tomography (PET) was performed 60 min after the administration of 18F-fluoro-deoxy-glucose (18F-FDG), and PET was performed after injecting 64Cu-pyruvaldehyde-bis(N4-methylthiosemicarbazone). Single photon emission computed tomography was performed 60 min after injection of 99mTc-hexakis-2-methoxyisobutylisonitrile and 201Tl. Delayed contrast-enhanced magnetic resonance imaging was performed after injecting Gd-DTPA-BMA. Three types of thresholding methods (naive thresholding, Otsu's algorithm, and multi-Gaussian mixture model (MGMM)) were used. DL segmentation methods were based on a convolution neural network and trained with constraints on feature similarity and spatial continuity of the response map extracted from images by the network. The relative infarct sizes measured by histology and estimated R2 for 18F-FDG were 0.8477, 0.7084, 0.8353, and 0.9024 for naïve thresholding, Otsu's algorithm, MGMM, and DL segmentation, respectively. DL-based method improved the accuracy of MI size assessment.

A guideline proposal for mice preparation and care in 18F-FDG PET imaging

The experimental outcomes of small-animal positron emission tomography (PET) imaging with ¹⁸F-labelled fluorodeoxyglucose (¹⁸F-FDG) can be particularly compromised by animal preparation and care. Several works intend to improve research reporting and amplify the quality and reliability of published research. Though these works provide valuable information to plan and conduct animal studies, manuscripts describe different methodologies—standardization does not exist. Consequently, the variation in details reported can explain the difference in the experimental results found in the literature. Additionally, the resources and guidelines defining protocols for small-animal imaging are scarce, making it difficult for researchers to obtain and compare accurate and reproducible data. Considering the selection of suitable procedures key to ensure animal welfare and research improvement, this paper aims to prepare the way for a future guideline on mice preparation and care for PET imaging with ¹⁸F-FDG. For this purpose, a global standard protocol was created based on recommendations and good practices described in relevant literature.

Quantifying the effects of anesthesia on intracellular oxygen via low-cost portable microscopy using dual-emissive nanoparticles

Intracellular oxygenation is an important parameter for numerous biological studies. While there are a variety of methods available for acquiring in vivo measurements of oxygenation in animal models, most are dependent on indirect oxygen measurements, restraints, or anesthetization. A portable microscope system using a Raspberry Pi computer and Pi Camera was developed for attaching to murine dorsal window chambers. Dual-emissive boron nanoparticles were used as an oxygen-sensing probe while mice were imaged in awake and anesthetized states. The portable microscope system avoids altered in vivo measurements due to anesthesia or restraints while enabling increased continual acquisition durations.

A Brief History of Nuclear Medicine Physics, Instrumentation, and Data Sciences in Korea

We review the history of nuclear medicine physics, instrumentation, and data sciences in Korea to commemorate the 60^th anniversary of the Korean Society of Nuclear Medicine. In the 1970s and 1980s, the development of SPECT, nuclear stethoscope, and bone densitometry systems, as well as kidney and cardiac image analysis technology, marked the beginning of nuclear medicine physics and engineering in Korea. With the introduction of PET and cyclotron in Korea in 1994, nuclear medicine imaging research was further activated. With the support of large-scale government projects, the development of gamma camera, SPECT, and PET systems was carried out. Exploiting the use of PET scanners in conjunction with cyclotrons, extensive studies on myocardial blood flow quantification and brain image analysis were also actively pursued. In 2005, Korea's first domestic cyclotron succeeded in producing radioactive isotopes, and the cyclotron was provided to six universities and university hospitals, thereby facilitating the nationwide supply of PET radiopharmaceuticals. Since the late 2000s, research on PET/MRI has been actively conducted, and the advanced research results of Korean scientists in the fields of silicon photomultiplier PET and simultaneous PET/MRI have attracted significant attention from the academic community. Currently, Korean researchers are actively involved in endeavors to solve a variety of complex problems in nuclear medicine using artificial intelligence and deep learning technologies.

Delayed effects of a single-dose whole-brain radiation therapy on glucose metabolism and myelin density: a longitudinal PET study

PURPOSE

Radiotherapy is an important treatment option for brain tumors, but the unavoidable irradiation of normal brain tissue can lead to delayed cognitive impairment. The mechanisms involved are still not well explained and, therefore, new tools to investigate the processes leading to the delayed symptoms of brain irradiation are warranted. In this study, positron emission tomography (PET) is used to explore delayed functional changes induced by brain irradiation.

MATERIALS AND METHODS

Male Wistar rats were subjected to a single 25-Gy dose of whole brain X-ray irradiation, or sham-irradiation. To investigate delayed effects of radiation on cerebral glucose metabolism and myelin density, ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET scans were performed at baseline and on day 64 and 94, whereas N-¹¹C-methyl-4,4'-diaminostilbene (¹¹C-MeDAS) PET scans were performed at baseline and on day 60 and 90 post-irradiation. In addition, the open field test (OFT) and novel spatial recognition (NSR) test were performed at baseline and on days 59 and 89 to investigate whether whole brain irradiation induces behavioral changes.

RESULTS

Whole-brain irradiation caused loss of bodyweight and delayed cerebral hypometabolism, with ¹⁸F-FDG uptake in all brain regions being significantly decreased in irradiated rat on day 64 while it remained unchanged in control animals. Only amygdala and cortical brain regions of irradiated rats still showed reduced ¹⁸F-FDG uptake on day 94. ¹¹C-MeDAS uptake in control animals was significantly lower on days 60 and 90 than at the baseline, suggesting a reduction in myelin density in young adults. In irradiated animals, ¹¹C-MeDAS uptake was similarly reduced on day 60, but on day 90 tracer uptake was somewhat increased and not significantly different from baseline anymore. Behavioral tests showed a similar pattern in control and irradiated animals. In both groups, the OFT showed significantly reduced mobility on days 59 and 89, whereas the NSR did not reveal any significant changes in spatial memory over time. Interestingly, a positive correlation between the NSR and ¹¹C-MeDAS uptake was observed in irradiated rats.

CONCLUSIONS

Whole-brain irradiation causes delayed brain hypometabolism, which is not accompanied by white matter loss. Irradiated animals showed similar behavioral changes over time as control animals and, therefore, cerebral hypometabolism could not be linked to behavioral abnormalities. However, spatial memory seems to be associated with myelin density in irradiated rats.

Effects of a Ketogenic Diet on [18F]FDG-PET Imaging in a Mouse Model of Lung Cancer

PURPOSE

Myocardial uptake can hamper visualization of lung tumors, atherosclerotic plaques, and inflammatory diseases in 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) studies because it leads to spillover in adjacent structures. Several preparatory pre-imaging protocols (including dietary restrictions and drugs) have been proposed to decrease physiological [¹⁸F]FDG uptake by the heart, although their effect on tumor glucose metabolism remains largely unknown. The objective of this study was to assess the effects of a ketogenic diet (as an alternative protocol to fasting) on tumor glucose metabolism assessed by [¹⁸F]FDG positron emission tomography (PET) in a mouse model of lung cancer.

PROCEDURES

PET scans were performed 60 min after injection of 18.5 MBq of [¹⁸F]FDG. PET data were collected for 45 min, and an x-ray computed tomograph (CT) image was acquired after the PET scan. A PET/CT study was obtained for each mouse after fasting and after the ketogenic diet. Quantitative data were obtained from regions of interest in the left ventricular myocardium and lung tumor.

RESULTS

Three days on a ketogenic diet decreased mean standard uptake value (SUVmean) in the myocardium (SUVmean 0.95 ± 0.36) more than one night of fasting (SUVmean 1.64 ± 0.93). Tumor uptake did not change under either dietary condition.

CONCLUSIONS

These results show that 3 days on high-fat diets prior to [¹⁸F]FDG-PET imaging does not change tumor glucose metabolism compared with one night of fasting, although high-fat diets suppress myocardial [¹⁸F]FDG uptake better than fasting.

Standardization of Small Animal Imaging-Current Status and Future Prospects

The benefit of small animal imaging is directly linked to the validity and reliability of the collected data. If the data (regardless of the modality used) are not reproducible and/or reliable, then the outcome of the data is rather questionable. Therefore, standardization of the use of small animal imaging equipment, as well as of animal handling in general, is of paramount importance. In a recent paper, guidance for efficient small animal imaging quality control was offered and discussed, among others, the use of phantoms in setting up a quality control program (Osborne et al. 2016). The same phantoms can be used to standardize image quality parameters for multi-center studies or multi-scanners within center studies. In animal experiments, the additional complexity due to animal handling needs to be addressed to ensure standardized imaging procedures. In this review, we will address the current status of standardization in preclinical imaging, as well as potential benefits from increased levels of standardization.

Imaging Cancer Metabolism with Positron Emission Tomography (PET)

Positron emission tomography (PET) enables the noninvasive spatiotemporal analysis of cancer metabolism in vivo. Both natural and nonnatural PET tracers have been developed to assess metabolic pathways during tumorigenesis, cancer progression, and metastasis. Here we describe the dynamic in vivo PET/CT imaging of the glucose analogue [18F]fluoro-2-deoxy-D-glucose (FDG), taking into consideration the methodology for alternative metabolic PET substrates.

Comparison of different quantification methods for 18F-fluorodeoxyglucose-positron emission tomography studies in rat brains

OBJECTIVES

This study aimed to evaluate several methods to estimate glucose consumption in the male Wister rat brain as measured by PET.

METHODS

Fourteen male Wistar normoglycemic rats were studied. The input function consisted of seventeen blood samples drawn manually from the femoral artery. Glucose uptake values were calculated using the input function resulting from the arterial blood samples and the tissue time-activity curve derived from the PET images. The estimated glucose consumption rate (Ki) based on the 2-tissue compartment model (2TCM) served as the standard for comparisons with the values calculated by the Patlak analysis and with the fractional uptake rate (FUR), standardized uptake value (SUV) and glucose corrected SUV (SUVglu).

RESULTS

No significant difference between the standard Ki and the Patlak Ki was observed. The standard Ki was also found to have strong correlations and concordance with the Ki value estimated by the Patlak analysis. The FUR method presented an excellent correlation with the Ki value obtained by the 2TCM/Patlak analyses, in contrast to the SUV or SUVglu.

CONCLUSIONS

From a methodological point of view, the present findings confirm the theoretical limitations of the cerebral SUV and SUVglu as a substitute for Ki in the estimation of glucose consumption in the brain. Our data suggest that the FUR is the surrogate to Ki.

Sensitivity of pretargeted immunoPET using 68Ga-peptide to detect colonic carcinoma liver metastases in a murine xenograft model: Comparison with 18FDG PET-CT

PURPOSE

The aim of this study was to compare the performances pretargeted immunoPET 68Ga-PETimaging (68Ga-pPET) with anti carcino-embryonic antigen (CEA) and anti-histamine-succinyl-glycine (HSG) recombinant humanized bispecific monoclonal antibody (TF2) and 68Ga-labeled HSG peptide (IMP288) to conventional 18FDG-PET in an orthotopic murine model of liver metastases of human colonic cancer.

METHODS

Hepatic tumor burden following intra-portal injection of luciferase-transfected LS174T cells in nude mice was confirmed using bioluminescence. One group of animals was injected intravenously with TF2 and with 68Ga-IMP288 24 hours later (n=8). Another group received 18FDG (n=8), and a third had both imaging modalities (n=7). PET acquisitions started 1 hour after injection of the radioconjugate. Biodistributions in tumors and normal tissues were assessed one hour after imaging.

RESULTS

Tumor/organ ratios were significantly higher with 68Ga-pPET compared to 18FDG-PET (P<0.05) with both imaging and biodistribution data. 68Ga-pPET sensitivity for tumor detection was 67% vs. 31% with 18FDG PET (P=0.049). For tumors less than 200 mg, the sensitivity was 44% with 68Ga-pPET vs. 0% for 18FDG PET (P=0.031). A strong correlation was demonstrated between tumor uptakes measured on PET images and biodistribution analyses (r2=0.85).

CONCLUSION

68Ga-pPET was more sensitive than 18FDG-PET for the detection of human colonic liver metastases in an orthotopic murine xenograft model. Improved tumor/organ ratios support the use of pretargeting method for imaging and therapy of CEA-expressing tumors.

Comparison of Immuno-PET of CD138 and PET imaging with 64CuCl2 and 18F-FDG in a preclinical syngeneic model of multiple myeloma

PURPOSE

Although recent data from the literature suggest that PET imaging with [18]-Fluorodeoxyglucose (18F-FDG) is a promising technique in multiple myeloma (MM), the development of other radiopharmaceuticals seems relevant. CD138 is currently used as a standard marker in many laboratories for the identification and purification of myeloma cells, and could be used in phenotype tumor imaging. In this study, we evaluated a 64Cu-labeled anti-CD138 murine antibody (64Cu-TE2A-9E7.4) and a metabolic tracer (64CuCl2) for PET imaging in a MM syngeneic mouse model.

EXPERIMENTAL DESIGN AND RESULTS

64Cu-TE2A-9E7.4 antibody and 64CuCl2 were evaluated via PET imaging and biodistribution studies in C57BL / KaLwRij mice bearing either 5T33-MM subcutaneous tumors or bone lesions. These results were compared to 18F-FDG-PET imaging. Autoradiography and histology of representative tumors were secondly conducted. In biodistribution and PET studies, 64Cu-TE2A-9E7.4 displayed good tumor uptake of subcutaneous and intra-medullary lesions, greater than that demonstrated with 18F-FDG-PET. In control experiments, only low-level, non-specific uptake of 64Cu-labeled isotype IgG was observed in tumors. Similarly, low activity concentrations of 64CuCl2 were accumulated in MM lesions. Histopathologic analysis of the immuno-PET-positive lesions revealed the presence of plasma cell infiltrates within the bone marrow.

CONCLUSIONS

64Cu-labeled anti-CD138 antibody can detect subcutaneous MM tumors and bone marrow lesions with high sensitivity, outperforming 18F-FDG-PET and 64CuCl2 in this preclinical model. These data support 64Cu-anti-CD138 antibody as a specific and promising new imaging radiopharmaceutical agent in MM.

Gender differences in cerebral metabolism for color processing in mice: A PET/MRI Study

INTRODUCTION

Color processing is a central component of mammalian vision. Gender-related differences of color processing revealed by non-invasive functional transcranial Doppler ultrasound suggested right hemisphere pattern for blue/yellow chromatic opponency by men, and a left hemisphere pattern by women.

MATERIALS AND METHODS

The present study measured the accumulation of [18F]fluorodeoxyglucose ([18F]FDG) in mouse brain using small animal positron emission tomography and magnetic resonance imaging (PET/MRI) with statistical parametric mapping (SPM) during light stimulation with blue and yellow filters compared to darkness condition.

RESULTS

PET revealed a reverse pattern relative to dark condition compared to previous human studies: Male mice presented with left visual cortex dominance for blue through the right eye, while female mice presented with right visual cortex dominance for blue through the left eye. We applied statistical parametric mapping (SPM) to examine gender differences in activated architectonic areas within the orbital and medial prefrontal cortex and related cortical and sub-cortical areas that lead to the striatum, medial thalamus and other brain areas. The metabolic connectivity of the orbital and medial prefrontal cortex evoked by blue stimulation spread through a wide range of brain structures implicated in viscerosensory and visceromotor systems in the left intra-hemispheric regions in male, but in the right-to-left inter-hemispheric regions in female mice. Color functional ocular dominance plasticity was noted in the right eye in male mice but in the left eye in female mice.

CONCLUSIONS

This study of color processing in an animal model could be applied in the study of the role of gender differences in brain disease.

Cardiac Radionuclide Imaging in Rodents: A Review of Methods, Results, and Factors at Play

The interest around small-animal cardiac radionuclide imaging is growing as rodent models can be manipulated to allow the simulation of human diseases. In addition to new radiopharmaceuticals testing, often researchers apply well-established probes to animal models, to follow the evolution of the target disease. This reverse translation of standard radiopharmaceuticals to rodent models is complicated by technical shortcomings and by obvious differences between human and rodent cardiac physiology. In addition, radionuclide studies involving small animals are affected by several extrinsic variables, such as the choice of anesthetic. In this paper, we review the major cardiac features that can be studied with classical single-photon and positron-emitting radiopharmaceuticals, namely, cardiac function, perfusion and metabolism, as well as the results and pitfalls of small-animal radionuclide imaging techniques. In addition, we provide a concise guide to the understanding of the most frequently used anesthetics such as ketamine/xylazine, isoflurane, and pentobarbital. We address in particular their mechanisms of action and the potential effects on radionuclide imaging. Indeed, cardiac function, perfusion, and metabolism can all be significantly affected by varying anesthetics and animal handling conditions.

Molecular and Integrative Physiological Effects of Isoflurane Anesthesia: The Paradigm of Cardiovascular Studies in Rodents using Magnetic Resonance Imaging

To-this-date, the exact molecular, cellular, and integrative physiological mechanisms of anesthesia remain largely unknown. Published evidence indicates that anesthetic effects are multifocal and occur in a time-dependent and coordinated manner, mediated via central, local, and peripheral pathways. Their effects can be modulated by a range of variables, and their elicited end-effect on the integrative physiological response is highly variable. This review summarizes the major cellular and molecular sites of anesthetic action with a focus on the paradigm of isoflurane (ISO) - the most commonly used anesthetic nowadays - and its use in prolonged in vivo rodent studies using imaging modalities, such as magnetic resonance imaging (MRI). It also presents established evidence for normal ranges of global and regional physiological cardiac function under ISO, proposes optimal, practical methodologies relevant to the use of anesthetic protocols for MRI and outlines the beneficial effects of nitrous oxide supplementation.

PET imaging of glucose metabolism, neuroinflammation and demyelination in the lysolecithin rat model for multiple sclerosis

Background:

Injection of lysolecithin in the central nervous system results in demyelination accompanied by local activation of microglia and recruitment of monocytes. Positron-emission tomography (PET) imaging, using specific tracers, may be an adequate technique to monitor these events in vivo and therefore may become a tool for monitoring disease progression in multiple sclerosis (MS) patients.

Objectives:

The objective of this paper is to evaluate the potential of PET imaging in monitoring local lesions, using [11C]MeDAS, [11C]PK11195 and [18F]FDG as PET tracers for myelin density, microglia activation and glucose metabolism, respectively.

Methods:

Sprague-Dawley rats were stereotactically injected with either 1% lysolecithin or saline in the corpus callosum and striatum of the right brain hemisphere. PET imaging was performed three days, one week and four weeks after injection. Animals were terminated after PET imaging and the brains were explanted for (immuno)histochemical analysis.

Results:

PET imaging was able to detect local demyelination induced by lysolecithin in the corpus callosum and striatum with [11C]MeDAS and concomitant microglia activation and monocyte recruitment with [11C]PK11195. [18F]FDG imaging demonstrated that glucose metabolism was maintained in the demyelinated lesions.

Conclusion:

PET imaging with multiple tracers allows simultaneous in vivo monitoring of myelin density, neuroinflammation and brain metabolism in small MS-like lesions, indicating its potential to monitor disease progression in MS patients.

RGD peptide-conjugated multimodal NaGdF4:Yb3+/Er3+ nanophosphors for upconversion luminescence, MR, and PET imaging of tumor angiogenesis

Multimodal nanoparticles have been extensively studied for target-specific imaging and therapy of various diseases, including cancer. In this study, radiolabeled arginine-glycine-aspartic acid (RGD)-functionalized Er(3+)/Yb(3+) co-doped NaGdF(4) upconversion nanophosphors (UCNPs) were synthesized and evaluated as a multimodal PET/MR/optical probe with tumor angiogenesis-specific targeting properties.

METHODS

A dimeric cyclic RGDyk ((cRGDyk)(2)) peptide was conjugated to polyacrylic acid-coated NaGdF(4):Yb(3+)/Er(3+) UCNPs along with polyethylene glycol molecules and was consecutively radiolabeled with (124)I. In vitro cytotoxicity testing was performed for 3 d. Upconversion luminescence imaging of (cRGDyk)(2)-UCNP was performed on U87MG cells with a laboratory-made confocal microscope. In vivo small-animal PET and clinical 3-T T1-weighted MR imaging of (124)I-labeled RGD-functionalized UCNPs was acquired with or without blocking of cyclic RGD peptide in a U87MG tumor model. Inductively coupled plasma mass spectrometry and biologic transmission electron microscopy were done to evaluate gadolinium concentration and UCNP localization, respectively.

RESULTS

Polymer-coated UCNPs and dimeric RGD-conjugated UCNPs were monodispersely synthesized, and those of hydrodynamic size were 30 ± 8 nm and 32 ± 9 nm, respectively. (cRGDyk)(2)-UCNPs have a low cytotoxic effect on cells. Upconversion luminescence signals of (cRGDyk)(2)-UCNP were specifically localized on the surface of U87MG cells. (124)I-c(RGDyk)(2)-UCNPs specifically accumulated in U87MG tumors (2.8 ± 0.8 vs. 1.3 ± 0.4 percentage injected dose per gram in the blocking experiment), and T1-weighted MR images showed significant positive contrast enhancement in U87MG tumors. Tumor localization of (124)I-c(RGDyk)(2)-UCNPs was confirmed by inductively coupled plasma mass spectrometry and biologic transmission electron microscopy analysis.

CONCLUSION

These results suggest that (124)I-labeled RGD-functionalized UCNPs have high specificity for α(v)β(3) integrin-expressing U87MG tumor cells and xenografted tumor models. Multimodal UCNPs can be used as a platform nanoparticle with multimodal imaging for cancer-specific diagnoses.

Comparison of cell-labeling methods with ¹²⁴I-FIAU and ⁶⁴Cu-PTSM for cell tracking using chronic myelogenous leukemia cells expressing HSV1-tk and firefly luciferase

Cell-tracking methods with molecular-imaging modality can monitor the biodistribution of cells. In this study, the direct-labeling method with ⁶⁴Cu-pyruvaldehyde-bis(N4-methylthiosemicarbazone) (⁶⁴Cu-PTSM), indirect cell-labeling methods with herpes simplex virus type 1-thymidine kinase (HSV1-tk)-mediated ¹²⁴I-2'-fluoro-2'-deoxy-1-β-D-arabinofuranosyl-5-iodouracil (¹²⁴I-FIAU) were comparatively investigated in vitro and in vivo for tracking of human chronic myelogenous leukemia cells. K562-TL was established by retroviral transduction of the HSV1-tk and firefly luciferase gene in the K562 cell. K562-TL cells were labeled with ⁶⁴Cu-PTSM or ¹²⁴I-FIAU. Cell labeling efficiency, viability, and radiolabels retention were compared in vitro. The biodistribution of radiolabeled K562-TL cells with each radiolabel and small-animal positron emission tomography imaging were performed. Additionally, in vivo and ex vivo bioluminescence imaging (BLI) and tissue reverse transcriptase-polymerase chain reaction (RT-PCR) analysis were used for confirming those results. K562-TL cells were efficiently labeled with both radiolabels. The radiolabel retention (%) of ¹²⁴I-FIAU (95.2%±1.1%) was fourfold higher than ⁶⁴Cu-PTSM (23.6%±0.7%) at 24 hours postlabeling. Viability of radiolabeled cells was statistically nonsignificant between ¹²⁴I-FIAU and ⁶⁴Cu-PTSM. The radioactivity of each radiolabeled cells was predominantly accumulated in the lungs and liver at 2 hours. Both the radioactivity of ⁶⁴Cu-PTSM- and ¹²⁴I-FIAU-labeled cells was highly accumulated in the liver at 24 hours. However, the radioactivity of ¹²⁴I-FIAU-labeled cells was markedly decreased from the body at 24 hours. The K562-TL cells were dominantly localized in the lungs and liver, which also verified by BLI and RT-PCR analysis at 2 and 24 hours postinjection. The ⁶⁴Cu-PTSM-labeled cell-tracking method is more efficient than ¹²⁴I-FIAU-labeled cell tracking, because of markedly decrease of radioactivity and fast efflux of ¹²⁴I-FIAU in vivo. In spite of a high labeling yield and radiolabel retention of ¹²⁴I-FIAU in vitro, the in vivo cell-tracking method using ⁶⁴Cu-PTSM could be a useful method to evaluate the distribution and targeting of various cell types, especially, stem cells and immune cells.

In vivo differentiation of human amniotic epithelial cells into cardiomyocyte-like cells and cell transplantation effect on myocardial infarction in rats: comparison with cord blood and adipose tissue-derived mesenchymal stem cells

Human amniotic epithelial cells (h-AECs), which have various merits as a cell source for cell therapy, are known to differentiate into cardiomyocytes in vitro. However, the ability of h-AECs to differentiate into cardiomyocytes in vivo and their cell transplantation effects on myocardial infarction are still unknown. In this study, we assessed whether h-AECs could differentiate into cardiomyocytes in vivo and whether h-AECs transplantation can decrease infarct size and improve cardiac function, in comparison to transplantation of cord blood-derived mesenchymal stem cells (MSCs) or adipose tissue-derived MSCs. For our study, we injected h-AECs, cord blood-derived MSCs, adipose tissue-derived MSCs, and saline into areas of myocardial infarction in athymic nude rats. After 4 weeks, 3% of the surviving h-AECs expressed myosin heavy chain, a marker specific to the myocardium. Compared with the saline group, all cell-implanted groups showed a higher ejection fraction, lower infarct area by positron emission tomography and histology, and more abundant myocardial gene and protein expression in the infarct area. We showed that h-AECs can differentiate into cardiomyocyte-like cells, decrease infarct size, and improve cardiac function in vivo. The beneficial effects of h-AECs were comparable to those of cord blood and adipose tissue-derived MSCs. These results support the need for further studies of h-AECs as a cell source for myocardial regeneration due to their plentiful availability, low immunity, and lack of ethical issues related to their use.

Impact of inherent variability and experimental parameters on the reliability of small animal PET data

Background

Noninvasive preclinical imaging methodologies such as small animal positron emission tomography (PET) allow the repeated measurement of the same subject which is generally assumed to reduce the variability of the experimental outcome parameter and to produce more robust results. In this study, the variability of tracer uptake in the rodent brain was assessed within and between subjects using the established radiopharmaceuticals ¹⁸F-FDG and ¹⁸F-fallypride. Moreover, experimental factors with potential impact on study outcome were elicited, and the effect of their strict homogenization was assessed.

Methods

Brain standardized uptake values of rodents were compared between three PET scans of the same animal and scans of different individuals. ¹⁸F-FDG ex vivo tissue sampling was performed under variation of the following experimental parameters: gender, age, cage occupancy, anesthetic protocol, environmental temperature during uptake phase, and tracer formulation.

Results

No significant difference of variability in ¹⁸F-FDG or ¹⁸F-fallypride brain or striatal uptake was identified between scans of the same and scans of different animals (COV = 14 ± 7% vs. 21 ± 10% for ¹⁸F-FDG). ¹⁸F-FDG brain uptake was robust regarding a variety of experimental parameters; only anesthetic protocols showed a significant impact. In contrast to a heterogenization approach, homogenization of groups produced more false positive effects in ¹⁸F-FDG organ distribution showing a false positive rate of 9% vs. 6%.

Conclusions

Repeated measurements of the same animal may not reduce data variability compared with measurements on different animals. Controlled heterogenization of test groups with regard to experimental parameters is advisable as it decreases the generation of false positive results and thus increases external validity of study outcome.

PET/CT imaging in mouse models of myocardial ischemia

Different species have been used to reproduce myocardial infarction models but in the last years mice became the animals of choice for the analysis of several diseases, due to their short life cycle and the possibility of genetic manipulation. Many techniques are currently used for cardiovascular imaging in mice, including X-ray computed tomography (CT), high-resolution ultrasound, magnetic resonance imaging, and nuclear medicine procedures. Cardiac positron emission tomography (PET) allows to examine noninvasively, on a molecular level and with high sensitivity, regional changes in myocardial perfusion, metabolism, apoptosis, inflammation, and gene expression or to measure changes in anatomical and functional parameters in heart diseases. Currently hybrid PET/CT scanners for small laboratory animals are available, where CT adds high-resolution anatomical information. This paper reviews mouse models of myocardial infarction and discusses the applications of dedicated PET/CT systems technology, including animal preparation, anesthesia, radiotracers, and images postprocessing.

124I-HuCC49deltaCH2 for TAG-72 antigen-directed positron emission tomography (PET) imaging of LS174T colon adenocarcinoma tumor implants in xenograft mice: preliminary results

Background

¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG-PET) is widely used in diagnostic cancer imaging. However, the use of ¹⁸F-FDG in PET-based imaging is limited by its specificity and sensitivity. In contrast, anti-TAG (tumor associated glycoprotein)-72 monoclonal antibodies are highly specific for binding to a variety of adenocarcinomas, including colorectal cancer. The aim of this preliminary study was to evaluate a complimentary determining region (CDR)-grafted humanized C_H2-domain-deleted anti-TAG-72 monoclonal antibody (HuCC49deltaC_H2), radiolabeled with iodine-124 (¹²⁴I), as an antigen-directed and cancer-specific targeting agent for PET-based imaging.

Methods

HuCC49deltaC_H2 was radiolabeled with ¹²⁴I. Subcutaneous tumor implants of LS174T colon adenocarcinoma cells, which express TAG-72 antigen, were grown on athymic Nu/Nu nude mice as the xenograft model. Intravascular (i.v.) and intraperitoneal (i.p.) administration of ¹²⁴I-HuCC49deltaC_H2 was then evaluated in this xenograft mouse model at various time points from approximately 1 hour to 24 hours after injection using microPET imaging. This was compared to i.v. injection of ¹⁸F-FDG in the same xenograft mouse model using microPET imaging at 50 minutes after injection.

Results

At approximately 1 hour after i.v. injection, ¹²⁴I-HuCC49deltaC_H2 was distributed within the systemic circulation, while at approximately 1 hour after i.p. injection, ¹²⁴I-HuCC49deltaC_H2 was distributed within the peritoneal cavity. At time points from 18 hours to 24 hours after i.v. and i.p. injection, ¹²⁴I-HuCC49deltaC_H2 demonstrated a significantly increased level of specific localization to LS174T tumor implants (p = 0.001) when compared to the 1 hour images. In contrast, approximately 50 minutes after i.v. injection, ¹⁸F-FDG failed to demonstrate any increased level of specific localization to a LS174T tumor implant, but showed the propensity toward more nonspecific uptake within the heart, Harderian glands of the bony orbits of the eyes, brown fat of the posterior neck, kidneys, and bladder.

Conclusions

On microPET imaging, ¹²⁴I-HuCC49deltaC_H2 demonstrates an increased level of specific localization to tumor implants of LS174T colon adenocarcinoma cells in the xenograft mouse model on delayed imaging, while ¹⁸F-FDG failed to demonstrate this. The antigen-directed and cancer-specific ¹²⁴I-radiolabled anti-TAG-72 monoclonal antibody conjugate, ¹²⁴I-HuCC49deltaC_H2, holds future potential for use in human clinical trials for preoperative, intraoperative, and postoperative PET-based imaging strategies, including fused-modality PET-based imaging platforms.

Small-animal PET/CT for monitoring the development and response to chemotherapy of thymic lymphoma in Trp53-/- mice

Transgenic mouse models of human cancers represent one of the most promising approaches to elucidate clinically relevant mechanisms of action and provide insights into the treatment efficacy of new antitumor drugs. The use of Trp53 transgenic mice (Trp53 knockout [Trp53(-/-)] mice) for these kinds of studies is, so far, restricted by limitations in detecting developing tumors and the lack of noninvasive tools for monitoring tumor growth, progression, and treatment response.

METHODS

We hypothesized that quantitative small-animal PET with (18)F-FDG was able to detect the onset and location of tumor development, follow tumor progression, and monitor response to chemotherapy. To test these hypotheses, C57BL/6J Trp53(-/-) mice underwent longitudinal small-animal PET during lymphoma development and gemcitabine treatment. Trp53 wild-type (Trp53(+/+)) mice were used as controls, and histology after full necropsy served as the gold standard.

RESULTS

In Trp53(+/+) mice, the thymic standardized uptake value (SUV) did not exceed 1.0 g/mL, with decreasing (18)F-FDG uptake over time. Conversely, all Trp53(-/-) mice that developed thymic lymphoma showed increasing thymic glucose metabolism, with a mean SUV doubling time of 9.0 wk (range, 6.0-17.5 wk). Using an SUV of 3.0 g/mL as a criterion provided a sensitivity of 78% and a specificity of 100% for the detection of thymic lymphoma. Treatment monitoring with (18)F-FDG PET correctly identified all histologic responses and relapses to gemcitabine.

CONCLUSION

(18)F-FDG small-animal PET can be used to visualize onset and progression of thymic lymphomas in Trp53(-/-) mice and monitor response to chemotherapy. Thus, (18)F-FDG small-animal PET provides an in vivo means to assess intervention studies in the Trp53 transgenic mouse model.

Effects of anesthetic protocol on normal canine brain uptake of 18F-FDG assessed by PET/CT

The purpose of this study was to assess the effects of four anesthetic protocols on normal canine brain uptake of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) using positron emission tomography/computed tomography (PET/CT). Five clinically normal beagle dogs were anesthetized with (1) propofol/isoflurane, (2) medetomidine/pentobarbital, (3) xylazine/ketamine, and (4) medetomidine/tiletamine-zolazepam in a randomized cross-over design. The standard uptake value (SUV) of FDG was obtained in the frontal, parietal, temporal and occipital lobes, cerebellum, brainstem and whole brain, and compared within and between anesthetic protocols using the Friedman test with significance set at P < 0.05. Significant differences in SUVs were observed in various part of the brain associated with each anesthetic protocol. The SUV for the frontal and occipital lobes was significantly higher than in the brainstem in all dogs. Dogs receiving medetomidine/tiletamine-zolazepam also had significantly higher whole brain SUVs than the propofol/isoflurane group. We concluded that each anesthetic protocol exerted a different regional brain glucose uptake pattern. As a result, when comparing brain glucose uptake using PET/CT, one should consider the effects of anesthetic protocols on different regions of the glucose uptake in the dog's brain.

Feasibility of template-guided attenuation correction in cat brain PET imaging

PURPOSE

Attenuation correction (AC) is important in quantitative positron emission tomography (PET) imaging of medium-sized animals such as the cat. However, additional time for transmission (TX) scanning and tracer uptake is required in PET studies with animal-dedicated PET scanners because post-injection TX scanning is not available in these systems. The aim of this study was to validate a template-guided AC (TGAC) method that does not require TX PET data for AC in cat 2-deoxy-2-[F-(18)fluoro-D-glucose (FDG) brain PET imaging.

METHODS

PET scans were acquired using a microPET Focus 120 scanner. TX data were obtained using a (68)Ge point source before the injection of FDG. To generate the attention map (mu-map) template for the TGAC, a target image of emission (EM) PET was selected, and spatial normalization parameters of individual EM data onto the target were reapplied to the corresponding mu-maps. The inverse transformations of the mu-map template into the individual spaces were performed, and the transformed template was forward projected to generate the AC factor. The TGAC method was compared with measured AC (MAC) and calculated AC (CAC) methods using region of interest (ROI) and SPM analyses.

RESULTS

The ROI analysis showed that the activity of the TGAC EM PET images strongly correlated with those of the MAC data (y = 0.98x + 0.01, R(2) = 0.96). In addition, no significant difference was observed in the SPM analysis. By contrast, the CAC showed a significantly higher uptake in the deep gray regions compared to the MAC (corrected P < 0.05). The ROI correlation with MAC was worse than with the TGAC (R(2) = 0.84). In SPM analysis for the voxel-wise group comparisons between before and after the induction of deafness, only the TGAC showed equivalent results with the MAC.

CONCLUSIONS

The TGAC was reliable in cat FDG brain PET studies in terms of compatibility with the MAC method. The TGAC might be a useful option for increasing study throughput and decreasing the probability of subject movement. In addition, it might reduce the possible biological effects of long-term anesthesia on the cat brain in investigations using animal-dedicated PET scanners.