Abdominal magnetic resonance imaging in small rodents using a clinical 1.5 T MR scanner

Radiomics and visual analysis for predicting success of transplantation of heterotopic glioblastoma in mice with MRI

BACKGROUND

Quantifying tumor growth and treatment response noninvasively poses a challenge to all experimental tumor models. The aim of our study was, to assess the value of quantitative and visual examination and radiomic feature analysis of high-resolution MR images of heterotopic glioblastoma xenografts in mice to determine tumor cell proliferation (TCP).

METHODS

Human glioblastoma cells were injected subcutaneously into both flanks of immunodeficient mice and followed up on a 3 T MR scanner. Volumes and signal intensities were calculated. Visual assessment of the internal tumor structure was based on a scoring system. Radiomic feature analysis was performed using MaZda software. The results were correlated with histopathology and immunochemistry.

RESULTS

21 tumors in 14 animals were analyzed. The volumes of xenografts with high TCP (H-TCP) increased, whereas those with low TCP (L-TCP) or no TCP (N-TCP) continued to decrease over time (p < 0.05). A low intensity rim (rim sign) on unenhanced T1-weighted images provided the highest diagnostic accuracy at visual analysis for assessing H-TCP (p < 0.05). Applying radiomic feature analysis, wavelet transform parameters were best for distinguishing between H-TCP and L-TCP / N-TCP (p < 0.05).

CONCLUSION

Visual and radiomic feature analysis of the internal structure of heterotopically implanted glioblastomas provide reproducible and quantifiable results to predict the success of transplantation.

Sex Determination in Two Species of Anuran Amphibians by Magnetic Resonance Imaging and Ultrasound Techniques

The objective of the present study was to evaluate whether gender determination in two amphibian species (Kaloula pulchra and Xenopus laevis) can be reliably carried out by means of magnetic resonance imaging (benchtop magnetic resonance imaging; BT-MRI) or ultrasound (high-resolution ultrasound; HR-US) techniques. Two species of healthy, sexually mature anurans have been used in the present study. Eight Kaloula (blind study) and six Xenopus were used as controls. Magnetic resonance imaging experiments were carried out on a low-field (1 Tesla) benchtop-MRI (BT-MRI) system. HR-US examination was performed with high-resolution equipment. Low-field BT-MRI images provided a clear and quantifiable identification of all the sexual organs present in both genders and species. The HR-US also allowed the identification of testes and ovaries in both species. Results indicate that BT-MRI allowed a very precise sex identification in both anuran species, although its use is limited by the cost of the equipment and the need for anesthesia. HR-US allowed an accurate identification of ovaries of both species whereas a precise identification of testes is limited by the ultrasonographer experience. The main advantages of this technique are the possibility of performing it without anesthesia and the higher availability of equipment in veterinary and zoo institutions.

Pre-clinical imaging of transgenic mouse models of neuroblastoma using a dedicated 3-element solenoid coil on a clinical 3T platform

BACKGROUND

The use of clinical MRI scanners to conduct pre-clinical research facilitates comparisons with clinical studies. Here the utility and sensitivity of anatomical and functional MRI data/biomarkers acquired from transgenic mouse models of neuroblastoma using a dedicated radiofrequency (RF) coil on a clinical 3T scanner was evaluated.

METHODS

Multiparametric MRI of transgenic mice bearing abdominal neuroblastomas was performed at 3T, and data cross-referenced to that acquired from the same mice on a pre-clinical 7T MRI system. T2-weighted imaging, quantitation of the native longitudinal relaxation time (T1) and the transverse relaxation rate (R2*), and dynamic contrast-enhanced (DCE)-MRI, was used to assess tumour volume, phenotype and response to cyclophosphamide or cabozantinib.

RESULTS

Excellent T2-weighted image contrast enabled clear tumour delineation at 3T. Significant correlations of tumour volume (R=0.98, P<0.0001) and R2* (R=0.87, P<0.002) measured at 3 and 7T were established. Mice with neuroblastomas harbouring the anaplastic lymphoma kinase mutation exhibited a significantly slower R2* (P<0.001), consistent with impaired tumour perfusion. DCE-MRI was performed simultaneously on three transgenic mice, yielding estimates of Ktrans for each tumour (median Ktrans values of 0.202, 0.168 and 0.114 min-1). Cyclophosphamide elicited a significant reduction in both tumour burden (P<0.002) and native T1 (P<0.01), whereas cabozantinib induced significant (P<0.01) tumour growth delay.

CONCLUSIONS

Simultaneous multiparametric MRI of multiple tumour-bearing animals using this coil arrangement at 3T can provide high efficiency/throughput for both phenotypic characterisation and evaluation of novel therapeutics, and facilitate the introduction of functional MRI biomarkers into aligned imaging-embedded clinical trials.

Magnetic resonance imaging of metastases in xenograft mouse models of cancer

Magnetic resonance imaging (MRI) of small animals has emerged as a valuable tool to noninvasively monitor tumor growth in mouse models of cancer. However, imaging of metastases in mouse models is difficult due to the need for high spatial resolution. We have demonstrated MRI of metastases in the liver, brain, adrenal glands, and lymph nodes in different xenograft mouse models of cancer. MRI of mice was performed with a clinical 3.0 T magnetic resonance scanner and a commercially available small-animal receiver coil. The imaging protocol consisted of T1- and T2-weighted fat-saturated spin echo sequences with a spatial resolution of 200 μm × 200 μm × 500 μm. Total acquisition time was 30 min per mouse. The technique allowed for repetitive examinations of larger animal cohorts to observe the development of metastases.

Endoluminal ultrasound biomicroscopy as a reliable tool for in vivo assessment of colonic inflammation in rats

PURPOSE

Endoscopic ultrasound (EUS) imaging of the colon is an important diagnostic tool for early neoplasia, although usually restricted to the rectum in inflammatory bowel disease (IBD). This study aimed to evaluate the ability of an endoluminal ultrasound biomicroscopic (eUBM) system to detect and characterize lesions simulating Crohn's disease in the colon of rats in vivo.

METHODS

Colitis was induced with trinitrobenzene sulfonic acid instillated in the distal colon. Eighteen Wistar rats were submitted to eUBM in three time points: week 1 group (18 animals examined on day 3 after colitis induction), week 2 group (12 animals on days 3 and 10), and week 3 group (7 animals on days 3, 10, and 17). This design yielded distinct inflammation intensities. Three untreated rats were used for acquisition of control images. Scores were used for comparison with histology.

RESULTS

Scores for eUBM and histology in the different moments of examination achieved a Spearman's rank correlation coefficient of 0.87 (p < 0.001). Findings of wall thickening presented positive predictive value (PPV) and sensitivity of 94 and of 100 %, respectively. Superficial and deep ulcers presented a PPV of 89 and 80 %, respectively, and negative predictive values of 100 and 85 %, respectively.

CONCLUSION

Accurate detection and analysis of the lesions was achieved. The model is essential for the clinical development of the technique and a reproducible method for the evaluation of experimental colitis. eUBM might be applicable in different segments of the gut, developing into a novel adjunct method for IBD evaluation.

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.

Features of in vitro ultrasound biomicroscopic imaging and colonoscopy for detection of colon tumor in mice

The present work tested the capability of ultrasound biomicroscopy (UBM), at 45 MHz, to provide cross-sectional images with appropriate resolution and contrast to detect tumors and determine their penetration depths on the colon of mice, Mus musculus (Linnaeus 1758), treated with carcinogen for colon tumor induction. B-mode images were obtained, in vitro, from each animal (13 treated and 4 untreated) colon opened longitudinally and immersed in saline solution at room temperature. Prior to UBM inspection, all animals were also examined by colonoscopy. The layers of normal colon identified by UBM are: mucosa (hyperechoic), muscularis mucosae (hypoechoic), submucosa (hyperechoic) and muscularis externa (hypoechoic). UBM images of colon lesions presented structures corresponding to tumors (hyperechoic), lymphoid hyperplasia (hypoechoic) and polypoid tumors (hyperechoic). Additionally, tumoral lesion invasion through the colon was also identified. When compared with histopathologic analysis, all colon lesions detected by UBM were confirmed, while colonoscopic findings had two false negatives.

A20 modulates lipid metabolism and energy production to promote liver regeneration

Background

Liver Regeneration is clinically of major importance in the setting of liver injury, resection or transplantation. We have demonstrated that the NF-κB inhibitory protein A20 significantly improves recovery of liver function and mass following extended liver resection (LR) in mice. In this study, we explored the Systems Biology modulated by A20 following extended LR in mice.

Methodology and Principal Findings

We performed transcriptional profiling using Affymetrix-Mouse 430.2 arrays on liver mRNA retrieved from recombinant adenovirus A20 (rAd.A20) and rAd.βgalactosidase treated livers, before and 24 hours after 78% LR. A20 overexpression impacted 1595 genes that were enriched for biological processes related to inflammatory and immune responses, cellular proliferation, energy production, oxidoreductase activity, and lipid and fatty acid metabolism. These pathways were modulated by A20 in a manner that favored decreased inflammation, heightened proliferation, and optimized metabolic control and energy production. Promoter analysis identified several transcriptional factors that implemented the effects of A20, including NF-κB, CEBPA, OCT-1, OCT-4 and EGR1. Interactive scale-free network analysis captured the key genes that delivered the specific functions of A20. Most of these genes were affected at basal level and after resection. We validated a number of A20's target genes by real-time PCR, including p21, the mitochondrial solute carriers SLC25a10 and SLC25a13, and the fatty acid metabolism regulator, peroxisome proliferator activated receptor alpha. This resulted in greater energy production in A20-expressing livers following LR, as demonstrated by increased enzymatic activity of cytochrome c oxidase, or mitochondrial complex IV.

Conclusion

This Systems Biology-based analysis unravels novel mechanisms supporting the pro-regenerative function of A20 in the liver, by optimizing energy production through improved lipid/fatty acid metabolism, and down-regulated inflammation. These findings support pursuit of A20-based therapies to improve patients’ outcomes in the context of extreme liver injury and extensive LR for tumor treatment or donation.

Cancer models-multiparametric applications of clinical MRI in rodent hepatic tumor model

Small animal imaging has been a major player in an increasing amount of oncological experiments wherein magnetic resonance imaging (MRI) has become a favorite choice of measures for in vivo small animal imaging due to its advantages of excellent resolution and innocuousness. Based on a clinical MRI scanner, we propose a protocol of multiparametric MRI for noninvasive characterization and therapeutic evaluation of a rat model with implanted liver tumors. This protocol contains six sequences, namely, T (1)-weighted image (T1WI), T (2)-weighted image (T2WI), diffusion-weighed imaging (DWI), T (1)-weighted dynamic contrast-enhanced MRI (DCE-MRI), T (2)-weighted dynamic susceptibility contrast-enhanced MRI (DSC-MRI), and contrast-enhanced T1WI (CE-T1WI), for acquiring anatomic, diffusion, and perfusion information of tumor models. In this chapter, the details about this complete MRI protocol and the rodent liver tumor model are described in order to facilitate the readers to perform their own translational animal imaging research.

Multishot PROPELLER for high-field preclinical MRI

With the development of numerous mouse models of cancer, there is a tremendous need for an appropriate imaging technique to study the disease evolution. High-field T(2)-weighted imaging using PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) MRI meets this need. The two-shot PROPELLER technique presented here provides (a) high spatial resolution, (b) high contrast resolution, and (c) rapid and noninvasive imaging, which enables high-throughput, longitudinal studies in free-breathing mice. Unique data collection and reconstruction makes this method robust against motion artifacts. The two-shot modification introduced here retains more high-frequency information and provides higher signal-to-noise ratio than conventional single-shot PROPELLER, making this sequence feasible at high fields, where signal loss is rapid. Results are shown in a liver metastases model to demonstrate the utility of this technique in one of the more challenging regions of the mouse, which is the abdomen.