High-speed single-breath-hold micro-computed tomography of thoracic and abdominal structures in mice using a simplified method for intubation

Macrophage ablation significantly reduces uptake of imaging probe into organs of the reticuloendothelial system

BACKGROUND

Macrophages engulf particulate contrast media, which is pivotal for biomedical imaging.

PURPOSE

To introduce a macrophage ablation animal model by showing its power to manipulate the kinetics of imaging probes.

MATERIAL AND METHODS

The kinetics of a particulate computed tomography (CT) contrast media was compared in macrophage ablative mice and normal mice. Liposomes (size 220 µg), loaded with clodronate, were injected into the peritoneum of three C57BL/6 mice. On the third day, 200 µL of the particulate agent ExiTron nano 6000 were injected into three macrophage-ablative mice and three control mice. CT scans were acquired before and 3 min, 1 h, 6 h, and 24 h after the ExiTron application. The animals were sacrificed, and their spleens and livers removed. Relative CT values (CTV) were measured and analyzed.

RESULTS

Liver and spleen enhancement of treated mice and controls were increasing over time. The median peak values were different with 225 CTV for treated mice and 582 CTV for controls in the liver (P = 0.032) and 431 CTV for treated and 974 CTV in controls in the spleen (P = 0.016).

CONCLUSION

Macrophage ablation leads to a decrease of enhancement in organs containing high numbers of macrophages, but only marginal changes in macrophage-poor organs. Macrophage ablation can influence the phagocytic activity and thus opens new potentials to investigate and manipulate the uptake of imaging probes.

Orthotopic Human Metastatic Uveal Melanoma Xenograft Mouse Models: Applications for Understanding the Pathophysiology and Therapeutic Management of Metastatic Uveal Melanoma

The propensity of uveal melanoma to metastasize to the liver hinders the accrual of micro-metastatic and end-stage disease tissue samples and restricts the investigation of metastatic uveal melanoma (MUM). Pre-clinical experimental animal models of MUM can help elucidate the pathophysiology of metastatic lesions and provide a tool for designing new therapeutic approaches for MUM. Here, we present an advanced model of hepatic metastases that enables quantitatively visualizing the development of individual hepatic tumor clones and estimating their growth kinetics and colonization efficiency. Similar to clinically observed liver metastases, these models enable the assessment of growth kinetics of the liver micro-metastases and the testing of therapeutic approaches for the treatment of MUM. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Experimental patient-derived xenograft mouse model of metastatic uveal melanoma Basic Protocol 2: Experimental liver micro-metastatic mouse model using splenic injection of metastatic uveal melanoma cells.

Development of Limited-Angle Iterative Reconstruction Algorithms with Context Encoder-Based Sinogram Completion for Micro-CT Applications

Limited-angle iterative reconstruction (LAIR) reduces the radiation dose required for computed tomography (CT) imaging by decreasing the range of the projection angle. We developed an image-quality-based stopping-criteria method with a flexible and innovative instrument design that, when combined with LAIR, provides the image quality of a conventional CT system. This study describes the construction of different scan acquisition protocols for micro-CT system applications. Fully-sampled Feldkamp (FDK)-reconstructed images were used as references for comparison to assess the image quality produced by these tested protocols. The insufficient portions of a sinogram were inpainted by applying a context encoder (CE), a type of generative adversarial network, to the LAIR process. The context image was passed through an encoder to identify features that were connected to the decoder using a channel-wise fully-connected layer. Our results evidence the excellent performance of this novel approach. Even when we reduce the radiation dose by 1/4, the iterative-based LAIR improved the full-width half-maximum, contrast-to-noise and signal-to-noise ratios by 20% to 40% compared to a fully-sampled FDK-based reconstruction. Our data support that this CE-based sinogram completion method enhances the efficacy and efficiency of LAIR and that would allow feasibility of limited angle reconstruction.

MÖNCH detector enables fast and low-dose free-propagation phase-contrast computed tomography of in situ mouse lungs

Due to the complexity of the underlying pathomechanism, in vivo mouse lung-disease models continue to be of great importance in preclinical respiratory research. Longitudinal studies following the cause of a disease or evaluating treatment efficacy are of particular interest but challenging due to the small size of the mouse lung and the fast breathing rate. Synchrotron-based in-line phase-contrast computed tomography imaging has been successfully applied in lung research in various applications, but mostly at dose levels that forbid longitudinal in vivo studies. Here, the novel charge-integrating hybrid detector MÖNCH is presented, which enables imaging of mouse lungs at a pixel size of 25 µm, in less than 10 s and with an entrance dose of about 70 mGy, which therefore will allow longitudinal lung disease studies to be performed in mouse models.

Imaging of Orthotopic Glioblastoma Xenografts in Mice Using a Clinical CT Scanner: Comparison with Micro-CT and Histology

Purpose

There is an increasing need for small animal in vivo imaging in murine orthotopic glioma models. Because dedicated small animal scanners are not available ubiquitously, the applicability of a clinical CT scanner for visualization and measurement of intracerebrally growing glioma xenografts in living mice was validated.

Materials and Methods

2.5x10⁶ U87MG cells were orthotopically implanted in NOD/SCID/ᵞc^-/- mice (n = 9). Mice underwent contrast-enhanced (300 μl Iomeprol i.v.) imaging using a micro-CT (80 kV, 75 μAs, 360° rotation, 1,000 projections, scan time 33 s, resolution 40 x 40 x 53 μm) and a clinical CT scanner (4-row multislice detector; 120 kV, 150 mAs, slice thickness 0.5 mm, feed rotation 0.5 mm, resolution 98 x 98 x 500 μm). Mice were sacrificed and the brain was worked up histologically. In all modalities tumor volume was measured by two independent readers. Contrast-to-noise ratio (CNR) and Signal-to-noise ratio (SNR) were measured from reconstructed CT-scans (0.5 mm slice thickness; n = 18).

Results

Tumor volumes (mean±SD mm³) were similar between both CT-modalities (micro-CT: 19.8±19.0, clinical CT: 19.8±18.8; Wilcoxon signed-rank test p = 0.813). Moreover, between reader analyses for each modality showed excellent agreement as demonstrated by correlation analysis (Spearman-Rho >0.9; p<0.01 for all correlations). Histologically measured tumor volumes (11.0±11.2) were significantly smaller due to shrinkage artifacts (p<0.05). CNR and SNR were 2.1±1.0 and 1.1±0.04 for micro-CT and 23.1±24.0 and 1.9±0.7 for the clinical CTscanner, respectively.

Conclusion

Clinical CT scanners may reliably be used for in vivo imaging and volumetric analysis of brain tumor growth in mice.

Radioimmunoimaging of liver metastases with PET using a 64Cu-labeled CEA antibody in transgenic mice

Purpose

Colorectal cancer is one of the most common forms of cancer, and the development of novel tools for detection and efficient treatment of metastases is needed. One promising approach is the use of radiolabeled antibodies for positron emission tomography (PET) imaging and radioimmunotherapy. Since carcinoembryonic antigen (CEA) is an important target in colorectal cancer, the CEA-specific M5A antibody has been extensively studied in subcutaneous xenograft models; however, the M5A antibody has not yet been tested in advanced models of liver metastases. The aim of this study was to investigate the ⁶⁴Cu-DOTA-labeled M5A antibody using PET in mice bearing CEA-positive liver metastases.

Procedures

Mice were injected intrasplenically with CEA-positive C15A.3 or CEA-negative MC38 cells and underwent micro-computed tomography (micro-CT) to monitor the development of liver metastases. After metastases were detected, PET/MRI scans were performed with ⁶⁴Cu-DOTA-labeled M5A antibodies. H&E staining, immunohistology, and autoradiography were performed to confirm the micro-CT and PET/MRI findings.

Results

PET/MRI showed that M5A uptake was highest in CEA-positive metastases. The %ID/cm³ (16.5%±6.3%) was significantly increased compared to healthy liver tissue (8.6%±0.9%) and to CEA-negative metastases (5.5%±0.6%). The tumor-to-liver ratio of C15A.3 metastases and healthy liver tissue was 1.9±0.7. Autoradiography and immunostaining confirmed the micro-CT and PET/MRI findings.

Conclusion

We show here that the ⁶⁴Cu-DOTA-labeled M5A antibody imaged by PET can detect CEA positive liver metastases and is therefore a potential tool for staging cancer, stratifying the patients or radioimmunotherapy.

Endotracheal intubation in mice via direct laryngoscopy using an otoscope

Mice, both wildtype and transgenic, are the principal mammalian model in biomedical research currently. Intubation and mechanical ventilation are necessary for whole animal experiments that require surgery under deep anesthesia or measurements of lung function. Tracheostomy has been the standard for intubating the airway in these mice to allow mechanical ventilation. Orotracheal intubation has been reported but has not been successfully used in many studies because of the substantial technical difficulty or a requirement for highly specialized and expensive equipment. Here we report a technique of direct laryngoscopy using an otoscope fitted with a 2.0 mm speculum and using a 20 G intravenous catheter as an endotracheal tube. We have used this technique extensively and reliably to intubate and conduct accurate assessments of lung function in mice. This technique has proven safe, with essentially no animal loss in experienced hands. Moreover, this technique can be used for repeated studies of mice in chronic models.

A comparative analysis of water-soluble and blood-pool contrast agents for in vivo vascular imaging with micro-CT

RATIONALE AND OBJECTIVES

In recent years, micro-computed tomography (micro-CT) has emerged as a high-resolution modality for vascular exploration in vivo. Several x-ray contrast agents for in vivo imaging are on the market and are based on different formulations. The objective of this study was to compare contrast-related and pharmacokinetic properties of a water-soluble compound containing iomeprol (Iomeron 400) and blood-pool agents (eXIA160XL, AuroVist 15 nm, and ExiTron nano 12000) for the identification of suitable in vivo vascular imaging applications.

MATERIALS AND METHODS

Forty-four healthy C57BL/6J mice were used in this study. Iomeprol was administered with a continuous infusion protocol; the other agents as a bolus. Anatomical micro-CT was applied at the head, neck, and lower hind limb before (baseline) and immediately after contrast injection, and used to quantify contrast-related properties of the agents. Dynamic micro-CT was applied at the same regions to characterize the agents pharmacokinetics.

RESULTS

All contrast media revealed safe, except for eXIA160XL, which caused death in four of eight tested animals and was therefore excluded early from the study. AuroVist 15 nm provided the highest attenuation (2.33/mm) as compared to iomeprol (1.97/mm) and ExiTron nano 12000 (1.58/mm) and a maximum temporal variation of contrast of 20% after 30 minutes, but the appearance of a dark skin staining did not allow multiple injections of the agent. Iomeprol passively diffused across capillary membranes, and after 30 minutes doubled the tissue contrast with respect to its initial levels. ExiTron nano 12000 revealed temporal variations of contrast below 10% and significantly reduced clearance rates after the third consecutive injection.

CONCLUSION

AuroVist 15 nm is best suited for anatomical investigation of the vascular network, while the high extravasation levels of iomeprol can be exploited for perfusion analysis. ExiTron nano 12000 is indicated for use in longitudinal monitoring with repeated injections.

Comparison of Fenestra LC, ExiTron nano 6000, and ExiTron nano 12000 for micro-CT imaging of liver and spleen in mice

RATIONALE AND OBJECTIVES

The purpose of this study was to compare different contrast agents for longitudinal liver and spleen imaging in a mouse model of liver metastasis.

MATERIALS AND METHODS

Mice developing liver metastases underwent longitudinal micro-computed tomography imaging after injection of Fenestra LC, ExiTron nano 6000, or ExiTron nano 12000. Elimination times and contrast enhancement of liver and spleen were compared.

RESULTS

For all contrast agents, liver contrast peaked at approximately 4 hours and spleen contrast at 48 hours postinjection. A single dose of 100 μL of ExiTron nano 6000 or 12000 resulted in longstanding enhancement of liver and spleen tissue for longer than 3 weeks, whereas repeated injections of 400 μL of Fenestra LC were required to retain contrast at acceptable levels and allowed imaging of the liver/spleen for up to 2 and 9 days, respectively.

CONCLUSION

Both ExiTron nano agents provide longer and stronger contrast enhancement of liver and spleen compared to Fenestra LC, and they do so at a 75% lower injection volume in mice.

Assisted ventilation without endotracheal intubation in rats

This technique was performed to allow for an additional approach to assist in ventilation. A modified ventilation nose cone was placed over the nose, which allowed the animal to not require endotracheal intubation. This method was effective in ventilating the animals during thoracic and abdominal procedures without requiring endotracheal intubation.

Gold nanoparticles as high-resolution X-ray imaging contrast agents for the analysis of tumor-related micro-vasculature

BACKGROUND

Angiogenesis is widely investigated in conjunction with cancer development, in particular because of the possibility of early stage detection and of new therapeutic strategies. However, such studies are negatively affected by the limitations of imaging techniques in the detection of microscopic blood vessels (diameter 3-5 μm) grown under angiogenic stress. We report that synchrotron-based X-ray imaging techniques with very high spatial resolution can overcome this obstacle, provided that suitable contrast agents are used.

RESULTS

We tested different contrast agents based on gold nanoparticles (AuNPs) for the detection of cancer-related angiogenesis by synchrotron microradiology, microtomography and high resolution X-ray microscopy. Among them only bare-AuNPs in conjunction with heparin injection provided sufficient contrast to allow in vivo detection of small capillary species (the smallest measured lumen diameters were 3-5 μm). The detected vessel density was 3-7 times higher than with other nanoparticles. We also found that bare-AuNPs with heparin allows detecting symptoms of local extravascular nanoparticle diffusion in tumor areas where capillary leakage appeared.

CONCLUSIONS

Although high-Z AuNPs are natural candidates as radiology contrast agents, their success is not guaranteed, in particular when targeting very small blood vessels in tumor-related angiography. We found that AuNPs injected with heparin produced the contrast level needed to reveal--for the first time by X-ray imaging--tumor microvessels with 3-5 μm diameter as well as extravascular diffusion due to basal membrane defenestration. These results open the interesting possibility of functional imaging of the tumor microvasculature, of its development and organization, as well as of the effects of anti-angiogenic drugs.

Lung tumour growth kinetics in SPC-c-Raf-1-BB transgenic mice assessed by longitudinal in-vivo micro-CT quantification

Background

SPC-c-Raf-1-BxB transgenic mice develop genetically induced disseminated lung adenocarcinoma allowing examination of carcinogenesis and evaluation of novel treatment strategies. We report on assessment of lung tumour growth kinetics using a semiautomated region growing segmentation algorithm.

Methods

156 non contrast-enhanced respiratory gated micro-CT of the lungs were obtained in 12 SPC-raf transgenic (n = 9) and normal (n = 3) mice at different time points. Region-growing segmentation of the aerated lung areas was obtained as an inverse surrogate for tumour burden. Time course of segmentation volumes was assessed to demonstrate the potential of the method for follow-up studies.

Results

Micro-CT allowed assessment of tumour growth kinetics and semiautomated region growing enabled quantitative analysis. Significant changes of the segmented lung volumes over time could be shown (p = 0.009). Significant group differences could be detected between transgenic and normal animals for time points 8 to 13 months (p = 0.043), when marked tumour progression occurred.

Conclusion

The presented region-growing segmentation algorithm allows in-vivo quantification of multifocal lung adenocarcinoma in SPC-raf transgenic mice. This enables the assessment of tumour load and progress for the study of carcinogenesis and the evaluation of novel treatment strategies.

Three-dimensional in vivo imaging of the murine liver: a micro-computed tomography-based anatomical study

Various murine models are currently used to study acute and chronic pathological processes of the liver, and the efficacy of novel therapeutic regimens. The increasing availability of high-resolution small animal imaging modalities presents researchers with the opportunity to precisely identify and describe pathological processes of the liver. To meet the demands, the objective of this study was to provide a three-dimensional illustration of the macroscopic anatomical location of the murine liver lobes and hepatic vessels using small animal imaging modalities. We analysed micro-CT images of the murine liver by integrating additional information from the published literature to develop comprehensive illustrations of the macroscopic anatomical features of the murine liver and hepatic vasculature. As a result, we provide updated three-dimensional illustrations of the macroscopic anatomy of the murine liver and hepatic vessels using micro-CT. The information presented here provides researchers working in the field of experimental liver disease with a comprehensive, easily accessable overview of the macroscopic anatomy of the murine liver.

Micro-CT based experimental liver imaging using a nanoparticulate contrast agent: a longitudinal study in mice

Background

Micro-CT imaging of liver disease in mice relies on high soft tissue contrast to detect small lesions like liver metastases. Purpose of this study was to characterize the localization and time course of contrast enhancement of a nanoparticular alkaline earth metal-based contrast agent (VISCOVER ExiTron nano) developed for small animal liver CT imaging.

Methodology

ExiTron nano 6000 and ExiTron nano 12000, formulated for liver/spleen imaging and angiography, respectively, were intravenously injected in C57BL/6J-mice. The distribution and time course of contrast enhancement were analysed by repeated micro-CT up to 6 months. Finally, mice developing liver metastases after intrasplenic injection of colon carcinoma cells underwent longitudinal micro-CT imaging after a single injection of ExiTron nano.

Principal Findings

After a single injection of ExiTron nano the contrast of liver and spleen peaked after 4–8 hours, lasted up to several months and was tolerated well by all mice. In addition, strong contrast enhancement of abdominal and mediastinal lymph nodes and the adrenal glands was observed. Within the first two hours after injection, particularly ExiTron nano 12000 provided pronounced contrast for imaging of vascular structures. ExiTron nano facilitated detection of liver metastases and provided sufficient contrast for longitudinal observation of tumor development over weeks.

Conclusions

The nanoparticulate contrast agents ExiTron nano 6000 and 12000 provide strong contrast of the liver, spleen, lymph nodes and adrenal glands up to weeks, hereby allowing longitudinal monitoring of pathological processes of these organs in small animals, with ExiTron nano 12000 being particularly optimized for angiography due to its very high initial vessel contrast.

Evaluation of a continuous-rotation, high-speed scanning protocol for micro-computed tomography

OBJECTIVE

Micro-computed tomography is used frequently in preclinical in vivo research. Limiting factors are radiation dose and long scan times. The purpose of the study was to compare a standard step-and-shoot to a continuous-rotation, high-speed scanning protocol.

METHODS

Micro-computed tomography of a lead grid phantom and a rat femur was performed using a step-and-shoot and a continuous-rotation protocol. Detail discriminability and image quality were assessed by 3 radiologists. The signal-to-noise ratio and the modulation transfer function were calculated, and volumetric analyses of the femur were performed. The radiation dose of the scan protocols was measured using thermoluminescence dosimeters.

RESULTS

The 40-second continuous-rotation protocol allowed a detail discriminability comparable to the step-and-shoot protocol at significantly lower radiation doses. No marked differences in volumetric or qualitative analyses were observed.

CONCLUSIONS

Continuous-rotation micro-computed tomography significantly reduces scanning time and radiation dose without relevantly reducing image quality compared with a normal step-and-shoot protocol.