In-vivo high-resolution X-ray microtomography for liver and spleen tumor assessment in mice

Contrast-enhanced photon-counting micro-CT of tumor xenograft models

Objective. Photon-counting micro-computed tomography (micro-CT) is a major advance in small animal preclinical imaging. Small molecule- and nanoparticle-based contrast agents have been widely used to enable the differentiation of liver tumors from surrounding tissues using photon-counting micro-CT. However, there is a notable gap in the application of these market-available agents to the imaging of breast and ovarian tumors using photon-counting micro-CT. Herein, we have used photon-counting micro-CT to determine the effectiveness of these contrast agents in differentiating ovarian and breast tumor xenografts in live, intact mice.Approach. Nude mice carrying different types of breast and ovarian tumor xenografts (AU565, MDA-MB-231 and SKOV-3 human cancer cells) were injected with ISOVUE-370 (a small molecule-based agent) or Exitron Nano 12000 (a nanoparticle-based agent) and subjected to photon-counting micro-CT. To improve tumor visualization using photon-counting micro-CT, we developed a novel color visualization method, which changes color tones to highlight contrast media distribution, offering a robust alternative to traditional material decomposition methods with less computational demand.Main results. Ourin vivoexperiments confirm the effectiveness of this color visualization approach, showing distinct enhancement characteristics for each contrast agent. Qualitative and quantitative analyses suggest that Exitron Nano 12000 provides superior vasculature enhancement and better quantitative consistency across scans, while ISOVUE-370 delivers a more comprehensive tumor enhancement but with significant variance between scans due to its short blood half-time. Further, a paired t-test on mean and standard deviation values within tumor volumes showed significant differences between the AU565 and SKOV-3 tumor models with the nanoparticle-based contrast agent (p-values < 0.02), attributable to their distinct vascularity, as confirmed by immunohistochemical analysis.Significance. These findings underscore the utility of photon-counting micro-CT in non-invasively assessing the morphology and anatomy of different tumor xenografts, which is crucial for tumor characterization and longitudinal monitoring of tumor progression and response to treatments.

Contrast-enhanced photon-counting micro-CT of tumor xenograft models

Photon-counting micro computed tomography (micro-CT) offers new potential in preclinical imaging, particularly in distinguishing materials. It becomes especially helpful when combined with contrast agents, enabling the differentiation of tumors from surrounding tissues. There are mainly two types of contrast agents in the market for micro-CT: small molecule-based and nanoparticle-based. However, despite their widespread use in liver tumor studies, there is a notable gap in research on the application of these commercially available agents for photon-counting micro-CT in breast and ovarian tumors. Herein, we explored the effectiveness of these agents in differentiating tumor xenografts from various origins (AU565, MDA-MB-231, and SKOV-3) in nude mice, using photon-counting micro-CT. Specifically, ISOVUE-370 (a small molecule-based agent) and Exitrone Nano 12000 (a nanoparticle-based agent) were investigated in this context. To improve tumor visualization, we proposed a novel color visualization method for photon-counting micro-CT, which changes color tones to highlight contrast media distribution, offering a robust alternative to traditional material decomposition methods with less computational demand. Our in vivo experiments confirm its effectiveness, showing distinct enhancement characteristics for each contrast agent. Qualitative and quantitative analyses suggested that Exitrone Nano 12000 provides superior vasculature enhancement and better quantitative consistency across scans, while ISOVUE-370 gives more comprehensive tumor enhancement but with a significant variance between scans due to its short blood half-time. This variability leads to high sensitivity to timing and individual differences among mice. Further, a paired t-test on mean and standard deviation values within tumor volumes showed significant differences between the AU565 and SKOV-3 tumor models with the nanoparticle-based (p-values < 0.02), attributable to their distinct vascularity, as confirmed by immunohistochemistry. These findings underscore the utility of photon-counting micro-CT in non-invasively assessing the morphology and anatomy of different tumor xenografts, which is crucial for tumor characterization and longitudinal monitoring of tumor development and response to treatments.

Usefulness of microfocus computed tomography in life science research: preliminary study using murine micro-hepatic tumor models

PURPOSE

Microfocus computed tomography (micro-CT) has not been widely used at high radiation intensity (industrial micro-CT) in life science fields. In this preliminary study, we investigated its potential value in the detection of micro-hepatic tumors in a mouse model.

METHODS

The liver with micro-hepatic tumors was surgically resected en-bloc from mice, and examined with industrial micro-CT and lower intensity micro-CT (small animal micro-CT). The number of hepatic tumors was manually counted on serial images. Then, the accuracy of each technique was determined by preparing matching liver sections and comparing the number of tumors identified in a conventional pathological examination.

RESULTS

The number of hepatic tumors evaluated with industrial micro-CT showed high concordance with the results of the pathological examinations (intraclass correlation coefficient [ICC]: 0.984; 95% confidence interval [CI] 0.959-0.994). On the other hand, the number of hepatic tumors evaluated with the small animal micro-CT showed low concordance with the number identified in the pathological examinations (ICC: 0.533; 95% CI 0.181-0.815).

CONCLUSION

Industrial micro-CT improved the detection of small structures in resected specimens, and might be a promising solution for life science research.

Evaluation of Effects of TGF-β1 Inhibition on Gastric Cancer in Nude Mice by Diffusion Kurtosis Imaging and In-Line X-ray Phase Contrast Imaging With Sequential Histology

Background

Accurate and complete response evaluation after treatment is important to implement individualized therapy for gastric cancer.

Purpose

To investigate the effectiveness of diffusion kurtosis imaging (DKI) and in‐line X‐ray phase contrast imaging (ILXPCI) in the assessment of the therapeutic efficacy by transforming growth factor beta 1 (TGF‐β1) inhibition.

Study Type

Prospective animal study.

Animal Model

Thirty nude mice subcutaneous xenotransplantation tumor model of gastric cancer for DKI and 10 peritoneal metastasis nude mice model for ILXPCI.

Field Strength/Sequence

Examinations before and serially at 7, 14, 21, and 28 days after TGF‐β1 inhibition treatment were performed at 3T MRI including T₂‐weighted imaging (T₂WI) and DKI with five b values of 0, 500, 1000, 1500, 2000 s/mm²; ILXPCI examinations were performed at 14 days after treatment.

Assessment

DKI parameters (apparent diffusion coefficient [ADC], diffusivity [D] and kurtosis [K]) were calculated by two experienced radiologists after postprocessing.

Statistical Tests

For the differences in all the parameters between the baseline and each timepoint for both the treated and the control mice, the Mann–Whitney test was used. The Spearman correlation test was used to evaluate correlations among the DKI parameters and corresponding pathologic necrosis fraction (NF).

Results

ADC, D, and K values were significantly different between the two groups after treatment (P < 0.05). Serial measurements in the treated group showed that the ADC, D, and K values were significantly different at 7, 14, 21, and 28 days compared with baseline (P < 0.05). There were significant correlations between DKI parameters and NF (ADC, r = 0.865, P < 0.001; D, r = 0.802, P < 0.001; K, r = –0.944, P < 0.001). The ILXPCI results in the treated group showed a stronger absorption area than the control group.

Data Conclusion

DKI may be used to evaluate the complete course therapeutic effects of gastric cancer induced by TGF‐β1 inhibition, and the ILXPCI technique will improve the tumor microstructure resolution.

Level of Evidence: 1

Technical Efficacy: Stage 4

J. Magn. Reson. Imaging 2019;49:1553–1564.

Early clinical applications for imaging at microscopic detail: microfocus computed tomography (micro-CT)

Microfocus CT (micro-CT) has traditionally been used in industry and preclinical studies, although it may find new applicability in the routine clinical setting. It can provide high-resolution three-dimensional digital imaging data sets to the same level of detail as microscopic examination without the need for tissue dissection. Micro-CT is already enabling non-invasive detailed internal assessment of various tissue specimens, particularly in breast imaging and early gestational fetal autopsy, not previously possible from more conventional modalities such as MRI or CT. In this review, we discuss the technical aspects behind micro-CT image acquisition, how early work with small animal studies have informed our knowledge of human disease and the imaging performed so far on human tissue specimens. We conclude with potential future clinical applications of this novel and emerging technique.

In vivo small animal micro-CT using nanoparticle contrast agents

Computed tomography (CT) is one of the most valuable modalities for in vivo imaging because it is fast, high-resolution, cost-effective, and non-invasive. Moreover, CT is heavily used not only in the clinic (for both diagnostics and treatment planning) but also in preclinical research as micro-CT. Although CT is inherently effective for lung and bone imaging, soft tissue imaging requires the use of contrast agents. For small animal micro-CT, nanoparticle contrast agents are used in order to avoid rapid renal clearance. A variety of nanoparticles have been used for micro-CT imaging, but the majority of research has focused on the use of iodine-containing nanoparticles and gold nanoparticles. Both nanoparticle types can act as highly effective blood pool contrast agents or can be targeted using a wide variety of targeting mechanisms. CT imaging can be further enhanced by adding spectral capabilities to separate multiple co-injected nanoparticles in vivo. Spectral CT, using both energy-integrating and energy-resolving detectors, has been used with multiple contrast agents to enable functional and molecular imaging. This review focuses on new developments for in vivo small animal micro-CT using novel nanoparticle probes applied in preclinical research.

Time course of contrast enhancement by micro-CT with dedicated contrast agents in normal mice and mice with hepatocellular carcinoma: comparison of one iodinated and two nanoparticle-based agents

RATIONALE AND OBJECTIVES

The aim of the present study was to characterize the kinetics of two nanoparticle-based contrast agents for preclinical imaging, Exitron nano 6000 and Exitron nano 12000, and the iodinated agent eXIA 160 in both healthy mice and in a mouse model of hepatocellular carcinoma (HCC). Semiautomatic segmentation of liver lesions for estimation of total tumor load of the liver was evaluated in HCC mice.

MATERIALS AND METHODS

The normal time course of contrast enhancement was assessed in 15 healthy C57BL/6 mice. Imaging of tumor spread in the liver was evaluated in 15 mice harboring a transgenic HCC model (ASV-B mice). Automatic segmentation of liver lesions for determination of total tumor burden of the liver was tested in three additional ASV-B mice before and after an experimental therapy.

RESULTS

In healthy mice, clearance of the contrast agent from blood was completed within 3-4 hours for eXIA 160 and Exitron nano 6000, whereas complete blood clearance of Exitron nano 12000 required about 24 hours. eXIA 160 provided maximum liver contrast at 1 hour post injection (p.i.) followed by a continuous decline. Enhancement of liver contrast with Exitron nano 6000 and Exitron nano 12000 reached a plateau at about 4 hours p.i., which lasted until the end of the measurements at 96 hours p.i. Maximum contrast enhancement of the liver was not statistically different between Exitron nano 6000 and Exitron nano 12000, but was about three times lower for eXIA 160 (P < .05). Visually Exitron nano 12000 provided the best liver-to-tumor contrast. Semiautomatic liver and tumor segmentation was feasible after the administration of Exitron nano 12000 but did not work properly for the other two contrast agents.

CONCLUSIONS

Both nanoparticle-based contrast agents provided stronger and longer lasting contrast enhancement of healthy liver parenchyma. Exitron nano 12000 allowed automatic segmentation of tumor lesions for estimation of the total tumor load in the liver.

Contrast agents for preclinical targeted X-ray imaging

Micro-computed tomography (micro-CT) is an X-ray based instrument that it is specifically designed for biomedical research at a preclinical stage for live imaging of small animals. This imaging modality is cost-effective, fast, and produces remarkable high-resolution images of X-ray opaque skeleton. Administration of biocompatible X-ray opaque contrast agent allows delineation of the blood vessels, and internal organs and even detection of tumor metastases as small as 300 μm. However, the main limitation of micro-CT lies in the poor efficacy or toxicity of the contrast agents. Moreover, contrast agents for micro-CT have to be stealth nanoparticulate systems, i.e. preventing their rapid renal clearance. The chemical composition and physicochemical properties will condition their uptake and elimination pathways, and therefore all the biological fluids, organs, and tissues trough this elimination route of the nanoparticles will be contrasted. Furthermore, several technologies playing on the nanoparticle properties, aim to influence these biological pathways in order to induce their accumulation onto given targeted sites, organs of tumors. In function of the methodologies carried out, taking benefit or not of the action of immune system, of the natural response of the organism like hepatocyte uptake or enhanced permeation and retention effect, or even accumulation due to ligand/receptor interactions, the technologies are called passive or active targeted imaging. The present review presents the most recent advances in the development of specific contrast agents for targeted X-ray imaging micro-CT, discussing the recent advance of in vivo targeting of nanoparticulate contrast agents, and the influence of the formulations, nature of the nanocarrier, nature and concentration of the X-ray contrasting materials, effect of the surface properties, functionalization and bioconjugation. The pharmacokinetic and versatility of nanometric systems appear particularly advantageous for addressing the versatile biomedical research needs. State of the art investigations are on going to propose contrast agents with tumor accumulating properties and will contribute for development of safer cancer medicine having detection and therapeutic modalities.

Micro-CT of rodents: state-of-the-art and future perspectives

Micron-scale computed tomography (micro-CT) is an essential tool for phenotyping and for elucidating diseases and their therapies. This work is focused on preclinical micro-CT imaging, reviewing relevant principles, technologies, and applications. Commonly, micro-CT provides high-resolution anatomic information, either on its own or in conjunction with lower-resolution functional imaging modalities such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). More recently, however, advanced applications of micro-CT produce functional information by translating clinical applications to model systems (e.g., measuring cardiac functional metrics) and by pioneering new ones (e.g. measuring tumor vascular permeability with nanoparticle contrast agents). The primary limitations of micro-CT imaging are the associated radiation dose and relatively poor soft tissue contrast. We review several image reconstruction strategies based on iterative, statistical, and gradient sparsity regularization, demonstrating that high image quality is achievable with low radiation dose given ever more powerful computational resources. We also review two contrast mechanisms under intense development. The first is spectral contrast for quantitative material discrimination in combination with passive or actively targeted nanoparticle contrast agents. The second is phase contrast which measures refraction in biological tissues for improved contrast and potentially reduced radiation dose relative to standard absorption imaging. These technological advancements promise to develop micro-CT into a commonplace, functional and even molecular imaging modality.

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.

Contrast-enhanced small-animal PET/CT in cancer research: strong improvement of diagnostic accuracy without significant alteration of quantitative accuracy and NEMA NU 4-2008 image quality parameters

Background

The use of iodinated contrast media in small-animal positron emission tomography (PET)/computed tomography (CT) could improve anatomic referencing and tumor delineation but may introduce inaccuracies in the attenuation correction of the PET images. This study evaluated the diagnostic performance and accuracy of quantitative values in contrast-enhanced small-animal PET/CT (_CEPET/CT) as compared to unenhanced small animal PET/CT (_UEPET/CT).

Methods

Firstly, a NEMA NU 4–2008 phantom (filled with ¹⁸F-FDG or ¹⁸F-FDG plus contrast media) and a homemade phantom, mimicking an abdominal tumor surrounded by water or contrast media, were used to evaluate the impact of iodinated contrast media on the image quality parameters and accuracy of quantitative values for a pertinent-sized target. Secondly, two studies in 22 abdominal tumor-bearing mice and rats were performed. The first animal experiment studied the impact of a dual-contrast media protocol, comprising the intravenous injection of a long-lasting contrast agent mixed with ¹⁸F-FDG and the intraperitoneal injection of contrast media, on tumor delineation and the accuracy of quantitative values. The second animal experiment compared the diagnostic performance and quantitative values of _CEPET/CT versus _UEPET/CT by sacrificing the animals after the tracer uptake period and imaging them before and after intraperitoneal injection of contrast media.

Results

There was minimal impact on IQ parameters (%SD_unif and spillover ratios in air and water) when the NEMA NU 4–2008 phantom was filled with ¹⁸F-FDG plus contrast media. In the homemade phantom, measured activity was similar to true activity (−0.02%) and overestimated by 10.30% when vials were surrounded by water or by an iodine solution, respectively. The first animal experiment showed excellent tumor delineation and a good correlation between small-animal (SA)-PET and ex vivo quantification (r² = 0.87, P < 0.0001). The second animal experiment showed a good correlation between _CEPET/CT and _UEPET/CT quantitative values (r² = 0.99, P < 0.0001). Receiver operating characteristic analysis demonstrated better diagnostic accuracy of _CEPET/CT versus _UEPET/CT (senior researcher, area under the curve (AUC) 0.96 versus 0.77, P = 0.004; junior researcher, AUC 0.78 versus 0.58, P = 0.004).

Conclusions

The use of iodinated contrast media for small-animal PET imaging significantly improves tumor delineation and diagnostic performance, without significant alteration of SA-PET quantitative accuracy and NEMA NU 4–2008 IQ parameters.

Iodinated α-tocopherol nano-emulsions as non-toxic contrast agents for preclinical X-ray imaging

Micro-computed tomography (micro-CT) is an emerging imaging modality, due to the low cost of the imagers as well as their efficiency in establishing high-resolution (1-100 μm) three-dimensional images of small laboratory animals and facilitating rapid, structural and functional in vivo visualization. However use of a contrast agent is absolutely necessary when imaging soft tissues. The main limitation of micro-CT is the low efficiency and toxicity of the commercially available blood pool contrast agents. This study proposes new, efficient and non-toxic contrast agents for micro-CT imaging. This formulation consists of iodinated vitamin E (α-tocopheryl 2,3,5-triiodobenzoate) as an oily phase, formulated as liquid nano-emulsion droplets (by low-energy nano-emulsification), surrounded by a hairy PEG layer to confer stealth properties. The originality and strength of these new contrast agents lie not only in their outstanding contrasting properties, biocompatibility and low toxicity, but also in the simplicity of their fabrication: one-step synthesis of highly iodinated oil (iodine constitutes 41.7% of the oil molecule weight) and its spontaneous emulsification. After i.v. administration in mice (8.5% of blood volume), the product shows stealth properties towards the immune system and thus acts as an efficient blood pool contrast agent (t(1/2) = 9.0 h), exhibiting blood clearance following mono-exponential decay. A gradual accumulation predominantly due to hepatocyte uptake is observed and measured in the liver, establishing a strong hepatic contrast, persistent for more than four months. To summarize, in the current range of available or developed contrast agents for preclinical X-ray imaging, this agent appears to be one of the most efficient.

Using X-ray in-line phase-contrast imaging for the investigation of nude mouse hepatic tumors

The purpose of this paper is to report the noninvasive imaging of hepatic tumors without contrast agents. Both normal tissues and tumor tissues can be detected, and tumor tissues in different stages can be classified quantitatively. We implanted BEL-7402 human hepatocellular carcinoma cells into the livers of nude mice and then imaged the livers using X-ray in-line phase-contrast imaging (ILPCI). The projection images' texture feature based on gray level co-occurrence matrix (GLCM) and dual-tree complex wavelet transforms (DTCWT) were extracted to discriminate normal tissues and tumor tissues. Different stages of hepatic tumors were classified using support vector machines (SVM). Images of livers from nude mice sacrificed 6 days after inoculation with cancer cells show diffuse distribution of the tumor tissue, but images of livers from nude mice sacrificed 9, 12, or 15 days after inoculation with cancer cells show necrotic lumps in the tumor tissue. The results of the principal component analysis (PCA) of the texture features based on GLCM of normal regions were positive, but those of tumor regions were negative. The results of PCA of the texture features based on DTCWT of normal regions were greater than those of tumor regions. The values of the texture features in low-frequency coefficient images increased monotonically with the growth of the tumors. Different stages of liver tumors can be classified using SVM, and the accuracy is 83.33%. Noninvasive and micron-scale imaging can be achieved by X-ray ILPCI. We can observe hepatic tumors and small vessels from the phase-contrast images. This new imaging approach for hepatic cancer is effective and has potential use in the early detection and classification of hepatic tumors.

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.

PET/CT imaging of c-Myc transgenic mice identifies the genotoxic N-nitroso-diethylamine as carcinogen in a short-term cancer bioassay

BACKGROUND

More than 100,000 chemicals are in use but have not been tested for their safety. To overcome limitations in the cancer bioassay several alternative testing strategies are explored. The inability to monitor non-invasively onset and progression of disease limits, however, the value of current testing strategies. Here, we report the application of in vivo imaging to a c-Myc transgenic mouse model of liver cancer for the development of a short-term cancer bioassay.

METHODOLOGY/PRINCIPAL FINDINGS

μCT and ¹⁸F-FDG μPET were used to detect and quantify tumor lesions after treatment with the genotoxic carcinogen NDEA, the tumor promoting agent BHT or the hepatotoxin paracetamol. Tumor growth was investigated between the ages of 4 to 8.5 months and contrast-enhanced μCT imaging detected liver lesions as well as metastatic spread with high sensitivity and accuracy as confirmed by histopathology. Significant differences in the onset of tumor growth, tumor load and glucose metabolism were observed when the NDEA treatment group was compared with any of the other treatment groups. NDEA treatment of c-Myc transgenic mice significantly accelerated tumor growth and caused metastatic spread of HCC in to lung but this treatment also induced primary lung cancer growth. In contrast, BHT and paracetamol did not promote hepatocarcinogenesis.

CONCLUSIONS/SIGNIFICANCE

The present study evidences the accuracy of in vivo imaging in defining tumor growth, tumor load, lesion number and metastatic spread. Consequently, the application of in vivo imaging techniques to transgenic animal models may possibly enable short-term cancer bioassays to significantly improve hazard identification and follow-up examinations of different organs by non-invasive methods.

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.

[Contribution of microCT structural imaging to preclinical evaluation of hepatocellular carcinoma chemotherapeutics on orthotopic graft in ACI rats]

Animal experimentation is a prerequisite for preclinical evaluation of treatments such as chemotherapy. It's strictly regulated with the purpose of reducing the number of experimental animal as well as their pain. Small animal imaging should provide a painless longitudinal follow up of tumor progression on a single animal. The aim of the study is to validate small animal imaging by microscanner (μscan) in longitudinal follow up of a hepatocellular carcinoma (HCC) and to demonstrate its interest for in vivo evaluation of tumor response to different therapeutics. An HCC model achieved by orthotopic graft of the MH3924A cell line in ACI rats was followed using a Imtek/Siemens microscanner (μscan) with contrast agents (Fenestra(®) LC/VC). The procedures giving the optimal enhancement of the liver as well as a reliable determination of tumor volumes by μscan were validated. Three protocols for therapeutic assessment through μscan longitudinal follow up were performed. Each consisted in three groups testing a chemotherapy (gemcitabine, gemcitabine-oxaliplatine or sorafenib) versus two control groups (placebo and doxorubicine). Comparison was done on tumor volumes, median and actual survivals. There was a significant correlation between tumor volumes measured by μscan and autopsy. Treatment by sorafenib, at the contrary of gemcitabine alone or with oxaliplatine, resulted in a significant reduction in tumor volumes and prolongation of actuarial survival. These results are consistent with available clinical data for these diverse therapeutics. In conclusion, small animal imaging with μscan is a non-invasive, reliable, and reproducible method for preclinical evaluation of antitumor agents.

Time-course of contrast enhancement in spleen and liver with Exia 160, Fenestra LC, and VC

OBJECTIVE

The purpose of this study was to compare the time-course of contrast-enhancement in spleen and liver using Exia 160 in comparison with Fenestra LC and VC in healthy mice.

PROCEDURES

Healthy C57bl/6 mice were used in this study. Fenestra LC and VC was administered intravenously at a dose of 0.1 ml/20 g or 0.2 ml/20 g. Exia 160 at a dose of 0.05 ml/20 g or 0.1 ml/20 g. Each animal underwent a micro-CT scan before contrast injection (baseline) and immediately after contrast injection. Additional scans were performed at 1, 2, 3, 4, 24, and 48 h after contrast administration. The mice who received Exia 160 were also scanned after 15, 30, and 45 min.

RESULTS

The peak enhancement of Exia 160 occurred after 15 min for the spleen and after 30 min for the liver.

CONCLUSIONS

Exia 160 allows rapid spleen and liver enhancement. The high iodine content results in small injection volumes.

In vivo small-animal imaging using micro-CT and digital subtraction angiography

Small-animal imaging has a critical role in phenotyping, drug discovery and in providing a basic understanding of mechanisms of disease. Translating imaging methods from humans to small animals is not an easy task. The purpose of this work is to review in vivo x-ray based small-animal imaging, with a focus on in vivo micro-computed tomography (micro-CT) and digital subtraction angiography (DSA). We present the principles, technologies, image quality parameters and types of applications. We show that both methods can be used not only to provide morphological, but also functional information, such as cardiac function estimation or perfusion. Compared to other modalities, x-ray based imaging is usually regarded as being able to provide higher throughput at lower cost and adequate resolution. The limitations are usually associated with the relatively poor contrast mechanisms and potential radiation damage due to ionizing radiation, although the use of contrast agents and careful design of studies can address these limitations. We hope that the information will effectively address how x-ray based imaging can be exploited for successful in vivo preclinical imaging.

Micro-CT imaging with a hepatocyte-selective contrast agent for detecting liver metastasis in living mice

RATIONALE AND OBJECTIVES

Micro-computed tomography (CT) is a important tool for longitudinal imaging of tumor development. The detection and monitoring of tumors in the liver in live animals using micro-CT is challenging. We evaluated the feasibility of high-resolution micro-CT enhanced with a hepatocyte-selective contrast agent for detecting liver metastases in a live murine model.

MATERIALS AND METHODS

Hepatic metastases were induced in 10 BALB/C mice. Two mice each were randomly selected on days 3, 5, 7, 10, and 13 after CT26 colon adenocarcinoma cells were injected into the portal vein; micro-CT imaging was performed at 10 minutes and 4 hours after intravenous administration of a hepatocyte-selective contrast agent at a dose of 0.4 mL/mouse. The attenuation values of the normal liver and the tumors were obtained. The number of metastases was counted and their sizes were measured on the micro-CT images. Gross or histopathologic evaluation was performed for correlating the liver tumors with the micro-CT images.

RESULTS

A total of 74 separate tumor sites larger than 300 microm in diameter were detected on pathologic examination of the mice that were sacrificed 7 days after cell injection. On micro-CT, 66 of 74 tumors were detected (83.8%). The smallest tumor detected on micro-CT was 300 microm. There were eight false-negative readings on micro-CT. The sizes of the individual liver metastases measured by micro-CT and on the excised specimen were highly correlated (P < .001). The correlation between the CT scan measurement and the actual measurement was r = 0.8354 (P < .0001).

CONCLUSIONS

High-resolution micro-CT enhanced with a hepatocyte-selective contrast agent can be a promising tool for detecting liver metastases in a live murine model.