Cellular Magnetic Resonance Imaging Research Articles

Magnetic Resonance Imaging of Mammalian Cells Individually Expressing Membrane-Associated Magnetosome Proteins I, L, B, and E

The magnetosome, a membrane-bound iron biomineral formed within magnetotactic bacteria, is a unique model for a magnetic resonance imaging (MRI) reporter gene contrast agent. We are translating this technology to mammalian cells by expressing essential magnetosome genes mamI, mamL, mamB, and mamE into MDA-MB-435 human melanoma cells. Currently, these genes are individually expressed in the cell although the future goal is to express all four genes together. We examined the influence of these genes on cellular MRI relaxation rates by culturing cells in the presence and absence of iron-supplemented medium and scanning them at 3 Tesla using a gelatin phantom. Total cellular iron was measured by inductively-coupled plasma mass spectrometry and correlated with relaxation rates obtained from phantom experiments. Apart from mamE, magnetosome genes that are individually expressed in mammalian cells grown in iron supplement significantly affected cellular transverse relaxation rates compared to cells grown without iron supplement. Interestingly, mamI, mamL, mamB, and mamE (even though the latter had no effect on relaxation rate) significantly affected cellular iron content. This developing gene-based contrast agent will equip MRI with improvement to imaging sensitivity and the technology to track cellular activities long term.

Monocyte MRI Relaxation Rates Are Regulated by Extracellular Iron and Hepcidin.

Many chronic inflammatory conditions are mediated by an increase in the number of monocytes in peripheral circulation, differentiation of monocytes to macrophages, and different macrophage subpopulations during pro- and anti-inflammatory stages of tissue injury. When hepcidin secretion is stimulated during inflammation, the iron export protein ferroportin is targeted for degradation on a limited number of cell types, including monocytes and macrophages. Such changes in monocyte iron metabolism raise the possibility of non-invasively tracking the activity of these immune cells using magnetic resonance imaging (MRI). We hypothesized that hepcidin-mediated changes in monocyte iron regulation influence both cellular iron content and MRI relaxation rates. In response to varying conditions of extracellular iron supplementation, ferroportin protein levels in human THP-1 monocytes decreased two- to eightfold, consistent with paracrine/autocrine regulation of iron export. Following hepcidin treatment, ferroportin protein levels further decreased two- to fourfold. This was accompanied by an approximately twofold increase in total transverse relaxation rate, R2*, compared to non-supplemented cells. A positive correlation between total cellular iron content and R2* improved from moderate to strong in the presence of hepcidin. These findings suggest that hepcidin-mediated changes detected in monocytes using MRI could be valuable for in vivo cell tracking of inflammatory responses.

Inhibition of triple negative breast cancer-associated inflammation and progression by N- acylethanolamine acid amide hydrolase (NAAA)

Triple-negative breast cancer (TNBC) is associated with high mortality due to the high expression of pro-inflammatory cytokines and lack of targeted therapies. N-acylethanolamine acid amidase (NAAA) is an N-terminal cysteine hydrolase that promotes inflammatory responses through the deactivation of Palmitoylethanolamide (PEA), an endogenous bioactive lipid mediator. Here, we examined NAAA expression in TNBC cells (MDA-MB-231 and MDA-MB-BrM2 cells) and the effects of NAAA inhibition on TNBC tumor growth, using a selective NAAA inhibitor AM11095 (IC50 = 20 nM). TNBC cells expressed elevated levels of full-length and splice mRNAs naaa variants. TNBC cells also express the N-acyl ethanol amides and elevated levels of the two fatty acid cores arachidonic (AA) and docosahexaenoic (DHA). PEA or AM11095 inhibited the secretion of IL-6 and IL-8, reduced the activation of the NF-kB pathway, decreased the expression of VEGF and Placental growth factor (PLGF) in TNBCs, and inhibited tumor cell migration in vitro. Using cellular magnetic resonance imaging (MRI), body images of mice administered with human MDA-MB-BrM2 cells treated with AM11095 showed a significant decrease in tumor numbers with a lower volume of tumors and increased mice survival. Mice untreated or treated with vehicle control showed a high number of tumors with high volumes in multiple organs. Thus, NAAA inhibition may constitute a potential therapeutic approach in the management of TNBC-associated inflammation and tumor growth.

Regulation of MRI contrast and cellular retention time by cellular interfacial distribution of Gd agents: Implications for stem cell tracking

Human mesenchymal stem cells (hMSCs) were labeled with Dotarem or (Gd-DOTA)2- EM7 (EM7Gd2) via electroporation (EP). Cellular transmission electron microscopy (TEM) reveals free distribution of Gd agents and formation of EM7Gd2 clusters in the cytosol. Cellular magnetic resonance imaging (MRI) reveals that the free Gd agents induce MRI signal enhancement effect due to its fast exocytosis and subsequent interaction with intercellular water molecules. The EM7Gd2 clusters exhibits a longer intracellular retention time and induce a persistent MRI signal reduction effect. The cellular MRI results are interpreted by taking into account both T1 and T2 relaxation rates and their correlation with cellular binding structures of Dotarem and EM7Gd2.

Specific Targeting MRI of Chitosan Oligosaccharide Modified Fe3O4 Nanoprobe on Macrophage and the Inhibition of Macrophage Foaming Induced by ox-LDL

Atherosclerosis (AS) is a primary cause of morbidity and mortality all over the world. Molecular imaging techniques can enable early localization and diagnosis of atherosclerosis plaques. Recent newly developed chitooligosaccharides (CSO) is considered to be capable of target mannose receptors on the surface of macrophages and to inhibit foam cell formation. Here we present a targeting magnetic resonance imaging (MRI) nanoprobe, which was successfully constructed with polyacrylic acid (PAA) modified nanometer iron oxide (Fe3O4) as the core, and coating with CSO molecules, possessing the abilities of targeted MRI and specifically inhibition of the formation of foamy macrophages in the atherosclerotic process. The experimental results showed that the distributions of PAA-Fe3O4 and CSO-PAA-Fe3O4 were uniform and the corresponding sizes were about 5.93 nm and 8.15 nm, respectively. The Fourier transform infrared spectra (FTIR) testified the CSO was coupled with PAA-Fe3O4 successfully. After coupled with CSO, the r1 of PAA-Fe3O4 was increased from 5.317 mM s-1 to 6.147 mM s-1, indicating their potential as MRI contrast agent. Oil Red O staining and total cholesterols (TC) determination showed that CSO-PAA-Fe3O4 could significantly inhibit the foaming process of RAW264.7 cells induced by oxidatively modified low density lipoprotein (ox-LDL). In vitro cellular MRI displayed that, compared with PAA-Fe3O4,CSO-PAA-Fe3O4 could lower the T1 relaxation time of RAW264.7 cells better. In summary, construction of CSO-PAA-Fe3O4 nanoprobe in this study could realize the targeted MRI of macrophages and inhibition of ox-LDL induced macrophage foaming process. This will provide a new avenue in the diagnosis and treatment of AS.

Biocompatible Nanomotors as Active Diagnostic Imaging Agents for Enhanced Magnetic Resonance Imaging of Tumor Tissues In Vivo

AbstractThe limited penetration of imaging agents in solid tumor tissue and cells remains a great challenge to achieve ideal visibility in cancer diagnosis. Herein, a near infrared (NIR) light‐driven Janus mesoporous silica nanomotor (JMS nanomotor) to promote magnetic resonance (MR) imaging in vivo is developed. The JMS nanomotors are prepared by depositing Au on the half‐sphere surface of gadolinium‐doped mesoporous silica nanoparticles. Under NIR irradiation, the nanomotors achieve efficient propulsion through thermophoresis in biological media. To prove the ability of nanomotors as active diagnostic imaging agents, both in vitro and in vivo experiments are carried out. In vitro studies confirm that NIR light can actively propel the JMS nanomotors to effectively seek, adhere to, and mechanically perforate the tumor cells to enhance the cellular uptake and MR imaging. To move a step further, in vivo investigations show that the JMS nanomotors also exhibit improved accumulation and deep penetration in the solid tumor model when exposed to NIR laser, where the MR imaging contrast is significantly enhanced in the majority of tumor tissue. Such JMS nanomotors provide new insight in precise cancer diagnosis and meanwhile MR imaging offers a new tool for real‐time tracking of nanomotors in vivo.

Micron-sized iron oxide particles for both MRI cell tracking and magnetic fluid hyperthermia treatment

Iron oxide particles (IOP) are commonly used for Cellular Magnetic Resonance Imaging (MRI) and in combination with several treatments, like Magnetic Fluid Hyperthermia (MFH), due to the rise in temperature they provoke under an Alternating Magnetic Field (AMF). Micrometric IOP have a high sensitivity of detection. Nevertheless, little is known about their internalization processes or their potential heat power. Two micrometric commercial IOP (from Bangs Laboratories and Chemicell) were characterized by Transmission Electron Microscopy (TEM) and their endocytic pathways into glioma cells were analyzed. Their Specific Absorption Rate (SAR) and cytotoxicity were evaluated using a commercial AMF inductor. T2-weighted imaging was used to monitor tumor growth in vivo after MFH treatment in mice. The two micron-sized IOP had similar structures and r2 relaxivities (100 mM−1 s−1) but involved different endocytic pathways. Only ScreenMAG particles generated a significant rise in temperature following AMF (SAR = 113 W g−1 Fe). After 1 h of AMF exposure, 60% of ScreenMAG-labeled cells died. Translated to a glioma model, 89% of mice responded to the treatment with smaller tumor volume 42 days post-implantation. Micrometric particles were investigated from their characterization to their intracellular internalization pathways and applied in one in vivo cancer treatment, i.e. MFH.

Black titanium dioxide@manganese dioxide for glutathione-responsive MR imaging and enhanced photothermal therapy.

Multifunctional nanoprobes with tumor microenvironment response are playing important roles in highly efficient theranostics of cancers. Herein, a kind of theranostic nanoprobe was synthesized by coating manganese dioxide (MnO2) on the surface of black commercial P25 titanium dioxide (b-P25). The resultant nanoprobe (b-P25@MnO2) possessed glutathione (GSH)-responsive magnetic resonance (MR) imaging and enhanced photothermal therapy (PTT). In tumor microenvironments, the excessive GSH was consumed by reacting with MnO2 to generate Mn2+ for GSH-responsive MR imaging, in which the longitudinal relaxation rate of b-P25@MnO2 was up to 30.44 mM-1 s-1, showing excellent cellular and intratumoral MR imaging. Moreover, the prepared b-P25@MnO2 exhibited stable and strong photothermal conversion capability with a high photothermal conversion efficiency of 30.67%, by which the 4T1 tumors disappeared completely, indicating safe and highly efficient PTT performance. The current work developed GSH-responsive b-P25@MnO2 nanoprobes, demonstrated for MR imaging and enhanced PTT in cancers.

A Perspective on Cell Tracking with Magnetic Particle Imaging.

Many labs have been developing cellular magnetic resonance imaging (MRI), using both superparamagnetic iron oxide nanoparticles (SPIONs) and fluorine-19 (19F)-based cell labels, to track immune and stem cells used for cellular therapies. Although SPION-based MRI cell tracking has very high sensitivity for cell detection, SPIONs are indirectly detected owing to relaxation effects on protons, producing negative magnetic resonance contrast with low signal specificity. Therefore, it is not possible to reliably quantify the local tissue concentration of SPION particles, and cell number cannot be determined. 19F-based cell tracking has high specificity for perfluorocarbon-labeled cells, and 19F signal is directly related to cell number. However, 19F MRI has low sensitivity. Magnetic particle imaging (MPI) is a new imaging modality that directly detects SPIONs. SPION-based cell tracking using MPI displays great potential for overcoming the challenges of MRI-based cell tracking, allowing for both high cellular sensitivity and specificity, and quantification of SPION-labeled cell number. Here we describe nanoparticle and MPI system factors that influence MPI sensitivity and resolution, quantification methods, and give our perspective on testing and applying MPI for cell tracking.

A positively charged small-molecule T1 magnetic resonance imaging contrast agent for highly efficient labeling and tracking adipose tissue-derived stem cells

Stem cells have great promise in regenerative medicine, and in vivo visualization of transplanted stem cells with noninvasive technique is essential for tracking and monitoring cell behaviors. Herein, a small-molecule T1 contrast agent with positive charge was prepared for efficiently labeling adipose-derived stem cells (ADSCs) in vitro and in vivo. The contrast agent was synthesized by conjugating quaternary ammonium salt onto DO3A (1, 4, 7, 10-tetraazacyclododecane-1, 4, 7-triacetic acid) skeleton via nucleophilic reaction, then chelating gadolinium ion to form Gd-HP-DO3A-TA complex. The Gd-HP-DO3A-TA exhibited a similar longitudinal relaxivity (4.42 mM−1 s−1) as commercial contrast agent (Gd-DTPA), but it can be efficiently internalized by ADSCs, leading to remarkably enhanced cellular magnetic resonance imaging (MRI) signal intensity without negative effects on viability, proliferation and multi-differentiation potential of ADSCs. Moreover, in vivo experiments revealed that Gd-HP-DO3A-TA-labeled ADSCs can home to the injured liver region with enhanced signal contrast and promote to rebuild liver function. Our results indicate that the small-molecule T1 contrast agent with positive charge has great potential for stem cells labeling and MRI tracking.

Comparing the fate of brain metastatic breast cancer cells in different immune compromised mice with cellular magnetic resonance imaging.

Metastasis is the leading cause of mortality in breast cancer patients, with brain metastases becoming increasingly prevalent. Studying this disease is challenging due to the limited experimental models and methods available. Here, we used iron-based cellular MRI to track the fate of a mammary carcinoma cell line (MDA-MB-231-BR) in vivo to characterize the growth of brain metastases in the nude and severely immune-compromised NOD/SCID/ILIIrg-/- (NSG) mouse. Nude and NSG mice received injections of iron-labeled MDA-MB-231-BR cells. Images were acquired with a 3T MR system and assessed for signal voids and metastases. The percentage of signal voids and the number and volume of metastases were quantified. Ex vivo imaging of the liver, histology, and immunofluorescence labeling was performed. Brain metastases grew more rapidly in NSG mice. At day 21 post cell injection, the average number of brain tumors in NSG mice was approximately four times greater than in nude mice. The persistence of iron-labeled cells, visualized as signal voids by MRI, was also examined. The percentage of voids decreased significantly over time for both nude and NSG mice. Body images revealed that the NSG mice also had metastases in the liver, lungs, and lymph nodes while tumors were only detected in the brains of nude mice. This work demonstrates the advantages of using the highly immune-compromised NSG mouse to study breast cancer metastasis, treatments aimed at inhibiting metastasis and outgrowth of breast cancer metastases in multiple organs, and the role that imaging can play toward credentialing these models that cannot be done with other in vitro or histopathologic methods alone.

Assessment of spin-lattice T1 and spin-spin T2 relaxation time measurements in breast cell cultures at 1.5 Tesla as a potential diagnostic tool in vitro

Magnetic resonance imaging (MRI) is a critically important tool in current medicine. This dynamic diagnostic method allows for detailed and accurate imaging of the human body and diagnosis of metabolic changes by magnetic resonance spectroscopy (MRS) assays. Our work presented herein shows measurement of spin-lattice T1 and spin-spin T2 relaxation time as an indicator of changes in cellular morphology. MRI spin-lattice T1 and spin-spin T2 relaxation time measurements are innovative experiments that provide a detailed picture of the biological microenvironment within cell cultures. Here, we used two types of cell cultures: cancerous and healthy breast cells. By measuring spin-lattice T1 and spin-spin T2 relaxation time in cancerous and healthy cell cultures we can detect differences and morphological conditions of both cell lines. A number of observations indicate that MRI can detect differences between cancer and healthy cells. In order to obtain a high density of cells for our cellular MRI study, we grew the cells in 3D geometry. In this paper, we underline the potential of quantitative MRI in vitro for future cellular mapping of drug concentration and drug efficiency in cell culture. We have shown that MRI, which is used often for imaging of anatomy, is also a promising technology for specific morphological measurements of cells.

Targeted MR Imaging Adopting T1-Weighted Ultra-Small Iron Oxide Nanoparticles for Early Hepatocellular Carcinoma: An in vitro and in vivo Study.

Objective The purpose of this study was to produce an arginylglycylaspartic acid (RGD) peptide-modified ultra-small superparamagnetic iron oxide (Fe3O4) nanoparticles (NPs) for targeted magnetic resonance (MR) imaging of hepatocellular carcinoma (HCC) cells and verify its utility as a T1 positive MRI imaging contrast agent in vitroand in vivo.Methods The carboxylated Fe3O4 NPs stabilized with sodium citrate were conjugated with polyethylene glycol (PEG)-linked RGD nanoparticles to form a novel target contrast agent Fe3O4-PEG-RGD NPs. The specificity of Fe3O4-PEG-RGD to bind RGD receptor was investigated in vitro by HepG2 cellular uptake and cell MR imaging, and in vivo by MR imaging of subcutaneous HepG2 tumors of nude mice.Results The formed Fe3O4-PEG-RGD NPs displayed good biocompatibility, and the ultrahigh r1 relaxivity was 1.37 mM -1S -1. The synthesized Fe3O4-PEG-RGD NPs were demonstrated spherical-like with an approximate diameter of 2.7 nm in similar size. The targeting effect to HepG2 cells was confirmed by in vitro cellular uptake and cell MR imaging. The in vivo MR imaging of nude mice demonstrated that the MR signal intensity enhancement of HepG2 tumor in Fe3O4-PEG-RGD NPs treated mice was significantly higher than in mice treated with non-targeted Fe3O4-mPEG NPs at the same post-administration time point. Conclusion The results indicate that the Fe3O4-PEG-RGD particles have potential utility as T1 positive contrast agent in targeted MR imaging.

Tailor-made PEG coated iron oxide nanoparticles as contrast agents for long lasting magnetic resonance molecular imaging of solid cancers.

Magnetic resonance imaging (MRI) is the most powerful technique for non-invasive diagnosis of human diseases and disorders. Properly designed contrast agents can be accumulated in the damaged zone and be internalized by cells, becoming interesting cellular MRI probes for disease tracking and monitoring. However, this approach is sometimes limited by the relaxation rates of contrast agents currently in clinical use, which show neither optimal pharmacokinetic parameters nor toxicity. In this work, a suitable contrast agent candidate, based on iron oxide nanoparticles (IONPs) coated with polyethyleneglycol, was finely designed, prepared and fully characterized under a physical, chemical and biological point of view. To stand out the real potential of our study, all the experiments were performed in comparison with Ferumoxytol, a FDA approved IONPs. IONPs with a core size of 15 nm and coated with polyethyleneglycol of 5 kDa (OD15-P5) resulted the best ones, being able to be uptaken by both tumoral cells and macrophages and showing no toxicity for in vitro and in vivo experiments. In vitro and in vivo MRI results for OD15-P5 showed r2 relaxivity values higher than Ferumoxitol. Furthermore, the injected OD15-P5 were completely retained at the tumor site for up to 24 h showing high potential as MRI contrast agents for real time long-lasting monitoring of the tumor evolution.

Cellular magnetic resonance imaging: in vivo tracking of gastric cancer cells and detecting of lymph node metastases using microparticles of iron oxide in mice.

BackgroundMonitoring the fate of implanted cells over time in an experimental animal may provide a new way to track the metastatic process. Lymph node metastase is of extremely importance for the prognostic prediction of gastric carcinoma. The aim of this study was to assess the feasibility of magnetic resonance imaging (MRI), using micron-sized superparamagnetic iron oxide particles (MPIO), for monitoring of the fate of gastric cancer cells and detecting the migration of gastric cancer cells through the lymphatic system in a mouse model.MethodsSGC-7901 gastric cancer cells were labeled with green fluorescent MPIO. The cells were monitored in vitro at multiple time points by staining for iron-labeled cells and by flow cytometric detection of the fluorescent MPIO. MPIO-labeled cells were implanted subcutaneously into nude mice, and cellular MRI was performed at different time points until 35 days postinjection.ResultsThe potential for retention of the iron particles in vitro was evaluated. Our results showed that the labeling and uptake efficiency of MPIO reached 90.0% after 24 hrs of incubation, and a small percentage of cells that retained MPIO could be examined until 16 days after labeling. In vivo MRI-based tracking over several weeks in mice revealed regions of signal loss in the primary tumors for up to 5 weeks. Furthermore, small regions of signal void were detected in images of the inguinal lymph nodes in three mice at day 28 postinjection or later, and histological assays confirmed the presence of iron-labeled cancer cells.ConclusionThis study supports MPIO-based cell tracking is a useful tool for monitoring the fate of gastric cancer cells in mice over time, which may facilitate progress in understanding the mechanisms of early regional lymph node micrometastases.

Fluorine-19 Cellular MRI Detection of In Vivo Dendritic Cell Migration and Subsequent Induction of Tumor Antigen-Specific Immunotherapeutic Response.

A major hurdle in the advancement of cell-based cancer immunotherapies is the inability to track in vivo therapeutic cell migration. With respect to dendritic cell (DC)-based cancer immunotherapies, this lack of knowledge represents an even greater hurdle as the quantity of tumor-antigenspecific DC reaching a secondary lymphoid organ post injection is predictive of the magnitude of the ensuing tumor-specific immune response. We propose fluorine-19 (F-19) cellular magnetic resonance imaging (MRI) as a suitable and non-invasive imaging modality capable of detecting and quantifying DC migration in vivo and thus, serving as a surrogate marker of DC-based immunotherapeutic effectiveness. Murine DC were generated from bone marrow precursors and labeled with a [19F]perfluorocarbon ([19F]PFC)-based cell labeling agent. DC were characterized by viability and phenotyping assessments as well as characterized by ability to induce in vivo tumor-specific immune responses following immunization in a B16-F10 mouse model of melanoma. The in vivo migration of [19F]PFC (PFC)-labeled DC was first compared to control unlabeled DCby microscopyand then measured using F-19 cellular MRI. Culture conditions were optimized such that > 90% of DC labeled with PFC without affecting viability, phenotype, and function. This optimization permitted consistent detection of PFC-labeled DC migration using F-19 cellular MRI and resulted in the first successful comparison of in vivo migration between PFC-labeled and control unlabeled therapeutic cells of the same origin. PFC-labeled DC are migration-competent in vivo in a B16-F10 tumor-bearing mouse model. We report a non-invasive and longitudinal imaging modality capable of detecting and quantifying therapeutic cell migration at both 9.4 and 3Tesla (T) and suitable for therapeutic cell tracking in a tumor-bearing mouse model. F-19 MRI cell tracking is broadly applicable across disease states and is conducive to clinical translation.

Cellular Magnetic Resonance Imaging with Superparamagnetic Iron Oxide: Methods and Applications in Cancer

Superparamagnetic iron oxide (SPIO) has been used as a contrast agent for magnetic resonance imaging (MRI) since the late 20th century. With the development of SPIO, cellular MRI has been recognized as a suitable and highly sensitive noninvasive modality with great potential to benefit translational research. In addition to its traditional diagnostic property, latest advances have conferred SPIO with multifunctionality. Several SPIO-based theranostic probes with targeting, therapeutic and diagnosis components have been successfully developed. The objective of this brief review is to summarize the characteristics, synthesizing methods, labeling approaches and current applications of SPIO-based cellular MRI in oncology. Herein, we first depict the history, classification and advantages of and the differences between T1- and T2/T2*-based SPIO contrast agents for cancer treatment. Second, we outline current coating materials that render SPIO less toxic and more biocompatible to mammalian cells. Finally, the cell labeling techniques and applications of SPIO-based MRI for tracking mesenchymal stem cell tumor–homing in preclinical models are introduced.

Determination of portal vein tumor thrombus blood supply using in vivo cellular magnetic resonance imaging in a rabbit model.

Objective: This study aimed to investigate the anatomic configuration of the blood vessels that contribute to portal vein tumor thrombus (PVTT), a common complication of hepatocellular carcinoma, in VX2 rabbits.Materials and methods: Peripheral blood mononuclear cells (MNCs) were isolated and labeled using superparamagnetic iron oxide particles in vitro. Twenty-four rabbits were injected with the VX2 tumor via the portal vein to establish the PVTT model. The rabbits (n=6/treatment group) were randomly assigned into four groups. Rabbits of groups A, B and C received an infusion of iron-labeled MNCs via the hepatic artery, the portal vein or the auricular vein, respectively, whereas rabbits of group D received an injection of normal saline via the auricular vein 7 days after the injection of VX2 tumors. MRI was performed, and the signal intensity (SI) of the PVTTs was measured on T2-weighted images (T2WIs) 1 day after the transfusion of iron-labeled cells.Results: The SI of PVTTs, as measured on T2WIs, in rabbits of groups A, B, C and D was 241.400 (172.350, 364.825), 221.150 (203.775, 318.225), 590.200 (363.325, 728.875) and 568.050 (474.725, 705.150), respectively. Our data showed a significant decrease in the SI of PVTTs in rabbits of groups A and B compared with rabbits of groups C and D (group A vs group C, U=4.000, p=0.025; group A vs group D, U=2.000, p=0.010; group B vs group C, U=4.000, p=0.025; group B vs group D, U=1.000, p=0.006). There was no significant difference in the SI of PVTTs in rabbits of group A and B.Conclusion: Our results indicated that the portal vein and the hepatic artery supplied blood flow to the PVTT in rabbits.

Cellular MRI Reveals Altered Brain Arrest of Genetically Engineered Metastatic Breast Cancer Cells.

Purpose The combined use of anatomical magnetic resonance imaging (MRI), cellular MRI, and bioluminescence imaging (BLI) allows for sensitive and improved monitoring of brain metastasis in preclinical cancer models. By using these complementary technologies, we can acquire measurements of viable single cell arrest in the brain after systemic administration, the clearance and/or retention of these cells thereafter, the growth into overt tumours, and quantification of tumour volume and relative cancer cell viability over time. While BLI is very useful in measuring cell viability, some considerations have been reported using cells engineered with luciferase such as increased tumour volume variation, changes in pattern of metastatic disease, and inhibition of in vivo tumour growth. Procedures Here, we apply cellular and anatomical MRI to evaluate in vivo growth differences between iron oxide labeled naïve (4T1BR5) and luciferase-expressing (4T1BR5-FLuc-GFP) murine brain-seeking breast cancer cells. Balb/C mice received an intracardiac injection of 20,000 cells and were imaged with MRI on days 0 and 14. Mice that received 4T1BR5-FLuc-GFP cells were also imaged with BLI on days 0 and 14. Results The number of signal voids in the brain (representing iron-labeled cancer cells) on day 0 was significantly higher in mice receiving 4T1BR5 cells compared to mice receiving 4T1BR5-FLuc-GFP cells (p < 0.0001). Mice that received 4T1BR5 cells also had significantly higher total brain tumour burden and number of brain metastases than mice that received 4T1BR5-FLuc-GFP cells (p < 0.0001). Conclusions By employing highly sensitive cellular MRI tools, we demonstrate that engineered cells did not form tumours as well as their naïve counterparts, which appear to primarily be due to a reduction in cell arrest. These results indicate that engineering cancer cells with reporter genes may alter their tropism towards particular organs and highlight another important consideration for research groups that use reporter gene imaging to track metastatic cancer cell fate in vivo.

Magnetic Resonance Techniques for Imaging White Matter.

The white matter is a complex network of brain fibers connecting different information processing regions in the brain. In recent years, the investigation of white matter in humans and in animal models has greatly benefitted from the introduction of in vivo noninvasive magnetic resonance imaging (MRI) techniques. MRI allows for multiple in vivo time-point whole-brain acquisition in the same subject, thus it can be used longitudinally to monitor white matter brain change, intervention effects, as well as disease progression. However, MRI has low spatial resolution compared to gold standard cellular techniques and MRI measures are sensitive to a number of tissue properties resulting in a lack of specificity.The following chapter describes in simple technical terms to non-imaging experts some common MRI techniques that can be used to investigate white matter structure noninvasively, covering some of the advantages and pitfalls of each technique.