Negative Contrast Enhancement Research Articles

Design and Synthesis of Polymer-Functionalized NIR Fluorescent Dyes–Magnetic Nanoparticles for Bioimaging

The fluorescent probes having complete spectral separation between absorption and emission spectra (large Stokes shift) are highly useful for solar concentrators and bioimaging. In bioimaging application, NIR fluorescent dyes have a greater advantage in tissue penetration depth compared to visible-emitting organic dyes or inorganic quantum dots. Here we report the design, synthesis, and characterization of an amphiphilic polymer, poly(isobutylene-alt-maleic anhyride)-functionalized near-infrared (NIR) IR-820 dye and its conjugates with iron oxide (Fe3O4) magnetic nanoparticles (MNPs) for optical and magnetic resonance (MR) imaging. Our results demonstrate that the Stokes shift of unmodified dye can be tuned (from ~106 to 208 nm) by the functionalization of the dye with polymer and MNPs. The fabrication of bimodal probes involves (i) the synthesis of NIR fluorescent dye (IR-820 cyanine) functionalized with ethylenediamine linker in high yield, >90%, (ii) polymer conjugation to the functionalized NIR fluorescent dye, and (iii) grafting the polymer-conjugated dyes on iron oxide MNPs. The resulting uniform, small-sized (ca. 6 nm) NIR fluorescent dye-magnetic hybrid nanoparticles (NPs) exhibit a wider emissive range (800-1000 nm) and minimal cytotoxicity. Our preliminary studies demonstrate the potential utility of these NPs in bioimaging by means of direct labeling of cancerous HeLa cells via NIR fluorescence microscopy and good negative contrast enhancement in T2-weighted MR imaging of a murine model.

Hybrid iron oxide-copolymer micelles and vesicles as contrast agents for MRI: impact of the nanostructure on the relaxometric properties

Magnetic resonance imaging (MRI) is at the forefront of non-invasive medical imaging techniques. It provides good spatial and temporal resolution that can be further improved by the use of contrast agents (CAs), providing a valuable tool for diagnostic purposes. Ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles are attractive MRI contrast agents due to their negative (T2) contrast enhancement capability and biocompatibility. Clusters of USPIOs with polymer material are of particular interest since they can sustain additional functionalities like drug delivery and targeting. Aiming to establish a relationship between the morphology of the clusters and their efficacy as MRI contrast agents (relaxometric properties), we prepared - using three different maghemite (γ-Fe2O3) USPIO diameters - a series of hybrid copolymer/iron oxide CAs presenting two different geometries (micellar or vesicular). The NMR relaxometry profiles confirmed the nature of the physical mechanisms inducing the increase of nuclear relaxation rates at low (magnetic anisotropy) and high (Curie relaxation) magnetic fields. A heuristic model, first proposed by Roch, Muller, Gillis, and Brooks, allowed the fitting of the whole longitudinal relaxivity r1(ν) profile, for samples with different magnetic core sizes. We show that both types of clusters exhibit transverse relaxivity (r2) values comparable to or higher than those of common contrast agents, over the whole tested frequency range. Moreover, in-depth analysis revealed substantially a linear relationship between r2 and the number of encapsulated USPIOs divided by the diameter of the clusters (NUSPIO/DH), for each USPIO size. The cluster structure (i.e. micelle or vesicle) appeared to have a mild influence on the transverse relaxivity value. Indeed, the r2 value was mainly governed by the individual size of the USPIOs, correlated with both the cluster external diameter and the magnetic material volume fraction.

Long-term investigation on the phase stability, magnetic behavior, toxicity, and MRI characteristics of superparamagnetic Fe/Fe-oxide core/shell nanoparticles

To efficiently enhance the contrast obtaining from magnetic resonance imaging (MRI), pharmaceutical grade colloidal dispersions of PEG coated iron-based nanoparticles were prepared and compared to conventional pure iron oxide contrast agent. In this study, we synthesized ~14 nm iron nanoparticles via NaBH(4) reduction of iron(III) chloride in an aqueous medium. The resulting nanoparticles were further oxidized by two different methods via (CH(3))(3)NO oxygen transferring agent and exposure to oxygen flow. XRD and electron microscopy analyses confirmed the formation of a second layer on the surface of α-Fe core. As magnetic measurements and Mössbauer spectra of 4-months post prepared nanoparticles showed, 2.3±0.5 nm amorphous oxide shell produced in oxygen flow could not protect the inner metallic iron from oxidation and resulting sample suffered from drastic change in its characteristics. However, (CH(3))(3)NO yielded nanoparticles with 3.6±0.4 and 4.5±0.7 nm crystalline oxide shells that retained their key properties even in long-term examinations. In addition, no significant difference was detected in cytotoxicity results of MTT assay test up to 4-months for core/shell nanoparticles, in comparison with pure iron oxide sample, and all fall below 50% viability in the iron concentration of 400 μg. In vitro MR signal reduction and corresponding relaxometry parameters, especially r(2)/r(1)>2, assure that all nanoparticles can be administrated for negative contrast enhancement. Accumulation of core/shell nanoparticles in axillary and brachial lymph nodes of examined rats and minimum contrast enhancement of 20% regarding to pure iron oxide implies the efficiency of these materials as potential contrast agent.

Methotrexate-conjugated magnetic nanoparticles for thermochemotherapy and magnetic resonance imaging of tumor

There is significant interest in recent years in developing magnetic nanoparticles (MNPs) having multifunctional characteristics with complimentary roles. In this study, methotrexate (MTX) was conjugated on the iron oxide magnetic nanoparticles surface via a poly(ethyleneimine) self-assembled monolayer (MTX–MNPs). The novel platform combined cancer chemotherapy, hyperthermia and potential monitoring of the progression of disease through magnetic resonance imaging (MRI). The conjugation of MTX on the magnetite surface was confirmed by Fourier transform infrared spectroscopy and change of zeta potential. Transmission electron microscope (TEM) showed that MTX–MNPs were morphologically spherical. The average diameter of MTX–MNPs was 30.1 ± 5.2 nm determined by dynamic light scattering. Magnetic measurements revealed that the saturation magnetization of MTX–MNPs reached 68.8 emu/g and the nanoparticles were superparamagnetic. The MTX–MNPs had good heating properties in an alternating magnetic field. TEM results showed that a larger number of MTX–MNPs were internalized into the MCF-7 cellular cytoplasm compared with the MNPs. The MTX–MNPs demonstrated highly synergistic antiproliferative effects of simultaneous chemotherapy and hyperthermia in MCF-7 breast cancer cells. A significant negative contrast enhancement was observed with magnetic resonance phantom imaging for MCF-7 cells over L929cells, when both were cultured with the nanoconjugate. The MTX–MNPs with combined characteristics of thermochemotherapy and MRI could be of high clinical significance in the treatment of tumor.

Imaging Brain Neuronal Activity Using Functionalized Magnetonanoparticles and MRI

This study explored the use of non-radioactive 2-deoxy glucose (2DG)-labeled magnetonanoparticles (MNP) and magnetic resonance imaging (MRI) to detect functional activity during rest, peripheral stimulation, and epileptic seizures, in animal models. Non-radioactive 2DG was covalently attached to magnetonanoparticles composed of iron oxide and dextran and intravenous (tail) injections were performed. 2DG-MNP was injected in resting and stimulated naïve rodents and the subsequent MRI was compared to published (14)C-2DG autoradiography data. Reproducibility and statistical significance was established in one studied model. Negative contrast enhancement (NCE) in acute seizures and chronic models of epilepsy were investigated. MRI NCE due to 2DG-MNP particles was compared to that of plain (unconjugated) MNP in one animal. NCE due to 2DG-MNP particles at 3T, which is approved for human use, was also investigated. Histology showed presence of MNP (following intravenous injection) in the brain tissues of resting naïve animal. 2DG-MNP intraparenchymal uptake was visible on MRI and histology. The locations of NCE agreed with published results of 2DG autoradiography in resting and stimulated animals and epileptic rats. Localization of epileptogenicity was confirmed by subsequent depth-electrode EEG (iEEG). Non-radioactive 2DG-MNP can cross the blood-brain barrier (BBB) and may accurately localize areas of increased activity. Although, this proof-of-principle study involves only a limited number of animals, and much more research and quantification are necessary to demonstrate that 2DG-MNP, or MNPs conjugated with other ligands, could eventually be used to image localized cerebral function with MRI in humans, this MNP-MRI approach is potentially applicable to the use of many bioactive molecules as ligands for imaging normal and abnormal localized cerebral functions.

Paramagnetic dysprosium oxide nanoparticles and dysprosium hydroxide nanorods as T2 MRI contrast agents

We report here paramagnetic dysprosium nanomaterial-based T2 MRI contrast agents. A large r2 and a negligible r1 is an ideal condition for T2 MR imaging. At this condition, protons are strongly and nearly exclusively induced for T2 MR imaging. The dysprosium nanomaterials fairly satisfy this because they are found to possess a decent r2 but a negligible r1 arising from L + S state 4f-electrons in Dy(III) ion (6H15/2). Their r2 will also further increase with increasing applied field because of unsaturated magnetization at room temperature. Therefore, MR imaging and various physical properties of the synthesized d-glucuronic acid coated ultrasmall dysprosium oxide nanoparticles (davg = 3.2 nm) and dysprosium hydroxide nanorods (20 × 300 nm) are investigated. These include hydrodynamic diameters, magnetic properties, MR relaxivities, cytotoxicities, and 3 tesla in vivo T2 MR images. Here, MR imaging properties of dysprosium hydroxide nanorods have not been reported so far. These two samples show r2s of 65.04 and 181.57 s−1mM−1, respectively, with negligible r1s at 1.5 tesla and at room temperature, no in vitro cytotoxicity up to 100 μM Dy, and clear negative contrast enhancements in 3 tesla in vivo T2 MR images of a mouse liver, which will be even more improved at higher MR fields. Therefore, d-glucuronic acid coated ultrasmall dysprosium oxide nanoparticles with renal excretion can be a potential candidate as a sensitive T2 MRI contrast agent at MR field greater than 3 tesla.

A T1, T2 magnetic resonance imaging (MRI)-fluorescent imaging (FI) by using ultrasmall mixed gadolinium–europium oxide nanoparticles

Multiple molecular imaging is a challenging subject. Water-soluble and biocompatible lactobionic acid coated ultrasmall mixed gadolinium–europium oxide nanoparticles with an average particle diameter of 1.75 nm and an average hydrodynamic diameter of 4.16 nm were synthesized and applied for T1, T2 MRI-FI in vitro and in vivo. They had r1 and r2 values of 11.9 and 38.7 s−1 mM−1, respectively, and showed clear dose-dependent contrast changes in both R1 and R2 map images. In addition, they showed both positive and negative contrast enhancements in 3 tesla T1 and T2 MR images in a mouse, respectively, and fluorescent confocal images in both DU145 cells and C. elegans (a small nematode). This study demonstrates the T1, T2 MRI-FI multi-functionality of lactobionic acid coated mixed gadolinium–europium oxide nanoparticles.

Prostate stem cell antigen-targeted nanoparticles with dual functional properties: in vivo imaging and cancer chemotherapy

Background:We designed dual-functional nanoparticles for in vivo application using a modified electrostatic and covalent layer-by-layer assembly strategy to address the challenge of assessment and treatment of hormone-refractory prostate cancer.Methods:Core-shell nanoparticles were formulated by integrating three distinct functional components, ie, a core constituted by poly(D,L-lactic-co-glycolic acid), docetaxel, and hydrophobic superparamagnetic iron oxide nanocrystals (SPIONs), a multilayer shell formed by poly(allylamine hydrochloride) and two different sized poly(ethylene glycol) molecules, and a single-chain prostate stem cell antigen antibody conjugated to the nanoparticle surface for targeted delivery.Results:Drug release profiles indicated that the dual-function nanoparticles had a sustained release pattern over 764 hours, and SPIONs could facilitate the controlled release of the drug in vitro. The nanoparticles showed increased antitumor efficiency and enhanced magnetic resonance imaging in vitro through targeted delivery of docetaxel and SPIONs to PC3M cells. Moreover, in nude mice bearing PC3M xenografts, the nanoparticles provided MRI negative contrast enhancement, as well as halting and even reversing tumor growth during the 76-day study duration, and without significant systemic toxicity. The lifespan of the mice treated with these targeted dual-function nanoparticles was significantly increased (Chi-square = 22.514, P < 0.0001).Conclusion:This dual-function nanomedical platform may be a promising candidate for tumor imaging and targeted delivery of chemotherapeutic agents in vivo.

Solvothermal synthesis of cobalt ferrite nanoparticles loaded on multiwalled carbon nanotubes for magnetic resonance imaging and drug delivery

Multiwalled carbon nanotube (MWCNT)/cobalt ferrite (CoFe 2O 4) magnetic hybrids were synthesized by a solvothermal method. The reaction temperature significantly affected the structure of the resultant MWCNT/CoFe 2O 4 hybrids, which varied from 6 nm CoFe 2O 4 nanoparticles uniformly coated on the nanotubes at 180 °C to agglomerated CoFe 2O 4 spherical particles threaded by MWCNTs and forming necklace-like nanostructures at 240 °C. Based on the superparamagnetic property at room temperature and high hydrophilicity, the MWCNT/CoFe 2O 4 hybrids prepared at 180 °C (MWCNT/CoFe 2O 4-180) were further investigated for biomedical applications, which showed a high T 2 relaxivity of 152.8 Fe mM −1 s −1 in aqueous solutions, a significant negative contrast enhancement effect on cancer cells and, more importantly, low cytotoxicity and negligible hemolytic activity. The anticancer drug doxorubicin (DOX) can be loaded onto the hybrids and subsequently released in a sustained and pH-responsive way. The DOX-loaded hybrids exhibited notable cytotoxicity to HeLa cancer cells due to the intracellular release of DOX. These results suggest that MWCNT/CoFe 2O 4-180 hybrids may be used as both effective magnetic resonance imaging contrast agents and anticancer drug delivery systems for simultaneous cancer diagnosis and chemotherapy.

Synthesis of amino-group functionalized superparamagnetic iron oxide nanoparticles and applications as biomedical labeling probes

Superparamagnetic iron oxide (SPIO) nanoparticles were synthesized by coprecipitation technique and further functionalized with amino-group to obtain amino-group functionalized (amino-SPIO) nanoparticles. The X-ray diffraction results reveal the structure of amino-SPIO nanoparticles, from which the average iron core diameter is approximately 10 nm by calculation; while Zetasizer reveals their hydrodynamic diameter are mainly distributed in the range of 40–60 nm. These nanoparticles can be taken up by liver tissue, resulting in dramatically darkening of liver tissue under T2-magnetic resonance imaging (MRI). The spin–spin relaxivity coefficient of these nanoparticles is 179.20 mM−1 s−1 in a 1.5 T magnetic resonance system. In addition, amino-SPIO nanoparticles were conjugated to Tat (FITC) peptide and incubated with neural stem cells in vitro, the authors can detect the positive-labeling (labeled) neural stem cells showing green fluorescence, which indicates Tat (FITC) peptide-derivated amino-SPIO nanoparticles are able to enter cells. Furthermore, it was also find significant negative T2 contrast enhancement when compared with the non-nanoparticles-labeled neural stem cells in T2-weighted MRI. The amino-SPIO nanoparticles show promising potential as a new type of labeling probes, which can be used in magnetic resonance-enhanced imaging and fluorescence diagnosis.

HER2/neu Antibody Conjugated Poly(amino acid)-Coated Iron Oxide Nanoparticles for Breast Cancer MR Imaging

Superparamagnetic iron oxide nanoparticles are widely used as nanoprobes for magnetic resonance imaging (MRI). Water-soluble iron oxide nanoparticles were synthesized by coating iron oxide nanoparticles with a hydrophilic, biocompatible, biodegradable poly(amino acid) derivative, poly(2-hydroxyethyl aspartamide) graft copolymer for negative contrast enhancement on T2 weighted MRI. HER2/neu antibodies were conjugated on the surface of poly(amino acid) coated iron oxide nanoparticles for the detection of breast cancer. The antibody-grafted iron oxide nanoparticles (PAION-Ab) were about 31.1 nm in diameter. The T2 relaxivity of PAION-Ab was 246 L·mmol(-1)·sec(-1) greater than that of the commercial product such as Feridex. PAION-Ab showed low cytotoxicity even at relatively high concentrations. Furthermore, Prussian blue staining and in vitro MRI study with SKBR-3, breast cancer cells overexpressing HER2/neu receptors indicated that PAION-Ab exhibited excellent cancer cell detection ability and enhanced signal intensities in the T2-weighted image.

Synthesis of PVP-coated ultra-small Fe3O4 nanoparticles as a MRI contrast agent

Ultra-small Fe(3)O(4) nanoparticles were prepared by using the coprecipitation method, in which the polyvinylpyrrolidone (PVP) serves as a stabilizer. The nanoparticles were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), infra spectrum (IR), X-ray photoelectron spectroscopy (XPS) and in vivo magnetic resonance imaging (MRI) test. The results showed that the particles' size was determined by the dripping rate and that PVP molecules played the role of preventing the aggregation and restricting the size of Fe(3)O(4) nanoparticles. The Fe(3)O(4) nanoparticles with diameter from 6.5 to 1.9 nm obviously exhibited negative contrast enhancement and concentrated at the target area guided by a permanent magnet.

Reply to the letter by Y. Ni et al. regarding ‘‘Expression of OATP1B3’’

We thank Y. Ni and colleagues [1] for their interest and suggestions regarding our article [2]. In liver imaging, the contrast between tumorous lesions and liver parenchyma is one of the more important factors in the detection of tumorous lesions in the liver; it also plays an important role in evaluating the nature of these lesions. In clinical practice, the signal intensity (SI) of tumorous lesions is usually assessed relative the SI of the surrounding liver parenchyma, and based on this assessment, the lesion is rated as hyperintense, isointense, or hypointense. Contrast enhancement (CE) of tumorous lesions in the liver is also often assessed relative to the SI (enhancement effects) of the surrounding liver parenchyma. Our study was designed to elucidate the mechanism underlying the uptake of gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) by hepatocellular carcinomas (HCCs). Our hypothesis was that the enhancement ratio (ER), an indicator of Gd-EOB-DTPA uptake by HCC, would provide an optimum index for assessing CE in HCCs. We therefore adopted the ER in our study. It is well known that the extent to which Gd-EOB-DTPA is taken up by the liver parenchyma cells is closely determined by the underlying hepatic function of these cells. For this reason, the observed SI in the liver parenchyma during the hepatobiliary phase is determined by the function of the liver. The value of signals such as the contrast ratio (CR) that also reflect the SI of the liver parenchyma can vary greatly depending on the extent of Gd-EOB-DTPA uptake by both the HCC and the liver parenchyma. The CE pattern also varies according to the extent of Gd-EOB-DTPA uptake by the liver parenchyma. For example, in cases of HCCs where the tumor SI changes from 300 (before infusion of the contrast agent) to 650 (after infusion of the contrast agent) (Table 1, Panel C of Ni’s article), the ER remains at 1.2 irregardless of changes in the SI (CE) of the background liver parenchyma. In CR and CE patterns, if the liver SI is \650, the CR is \1 [negative tumor contrast enhancement (TCE], but if the liver SI is [650, the CR is [1 (positive TCE). Given this background, it is evident that neither the CR or the CE pattern reflects solely the extent of Gd-EOB-DTPA uptake by HCC alone. Therefore, we believe that the ER serves as an optimum indicator of the extent of Gd-EOB-DTPA uptake by HCC. We would like to ask Y. Ni and colleagues to explain why they believe that our finding of differences in Gd-EOB-DTPA uptake being dependent on OATP1B3 expression may be insignificant. Several earlier reports have shown that the CE varies in relation to the grade of cancer differentiation. However, drugs need to pass through the cell membrane pump before they enter cells, and it is evident that drug uptake by cells varies in relation to the nature and function of the pump. Consequently, it is not 100% clear whether the degree of cancer differentiation is truly associated with drug uptake by cells. We conducted our study because we believe that a close association between the degree of cancer differentiation and drug uptake by cells cannot be accepted so long as the possible This author’s reply refers to the letter to the editor at doi: 10.1007/s00535-009-0174-z.

Proper definitions of MRI contrast enhancement in liver tumors

Dear Editor, As researchers working in the field of contrast agents (CAs) for use in magnetic resonance imaging (MRI), we would like to congratulate Narita et al. on the results reported in their recently published article ‘‘Expression of OATP1B3 determines uptake of Gd-EOB-DTPA in hepatocellular carcinoma’’ [1] showing that overexpression of OATP1B3 is related to Gd-EOB-DTPA accumulation or positive contrast enhancement (CE) in certain hepatocellular carcinomas (HCCs). These results were obtained using biomics technologies on clinical patients. However, a number of apparent points in the article have drawn our attention and motivated us to initiate the discussion presented here. Originally, hepatobiliary MRI CAs, including gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA), were developed to improve lesion detectability by specifically enhancing liver signal intensity (SI) and leaving the hepatic tumor unenhanced, i.e., negative tumor contrast enhancement (TCE) on T1-weighted MRI [2]. However, 15 years ago Ni et al. [3] first reported the very rare but remarkable positive TCE, which was best distinguishable during the hepatobiliary phase around 30 min following the injection of Gd-EOB-DTPA in rats with chemically induced HCCs. This phenomenon was found to be associated with certain highly differentiated HCCs and with benign hepatocytic nodules, as evident by the histopathology [3, 4]. For many years, in the early clinical trials, this Gd-EOB-DTPA-induced positive TCE was either absent or ignored [5, 6], and it has only been recently reported after this agent has been widely applied in clinical patients [1, 7, 8]. The HCC lesion with positive TCE that is shown in Fig. 1D of the article by Narita et al. [1] is to date the closest clinical finding comparable to what has been reported in rats [3, 4, 9]. In contrast, other experimental studies have failed to convincingly demonstrate the true positive TCE in rodent hepatic tumor models [10, 11]. Hence, a proper definition of CE in liver tumors becomes crucial, particularly with regard to the use of liver-specific MRI CAs. Similar to the procedure adopted by Narita et al. in their study [1], a number of other researchers have used the enhancement ratio (ER), where ER = (SIpostcontrast SIprecontrast)/SIprecontrast, or the relative enhancement (RE), where RE(%) = (SIpost SIpre)/SIpre 9 100, in their experimental studies. This ratio only takes the tumor SI into account—irrespective of the changes in the SI of the surrounding liver, which is the main target of hepatobiliary CAs [11]. Other researchers have used criteria that do not reflect the real tumor-to-liver contrast on Gd-EOB-DTPAenhanced MR images, such as a tumor said to be positively enhanced did not really display a positive TCE pattern [10, 12]. Logically, a negative or positive TCE can only be defined when the SI of the tumor is measured as being either lower or higher than that of the liver, based on visualization on the postcontrast MRI scan, as shown in Fig. 1D of Narita et al. [1] and in animal results [3, 4, 9]. The most straightforward approach is to calculate the postcontrast tumor-to-liver contrast ratio (CR), i.e., CR = SItumor/SIliver. When CR [ 1 or CR \ 1, a positive An answer to this letter to the editor is available at doi: 10.1007/s00535-009-0176-x.

Magnetic resonance imaging studies on gadonanotube‐reinforced biodegradable polymer nanocomposites

We report about the in vitro cytotoxicity and MRI studies of Gd(3+)ions-doped ultra-short single-walled carbon nanotube (gadonanotubes), gadonanotubes- reinforced poly(lactic-co-glycolic acid) (PLGA) polymer nanocomposites and in vivo small animal MRI studies using the gadonanotubes. These studies were performed to explore the suitability of gadonanotubes-reinforced PLGA polymer nanocomposite as a model scaffold for noninvasive magnetic resonance imaging (MRI) to evaluate nanotube release during the degradation process of the scaffold and their biodistribution upon release from the polymer matrix in vivo. The gadonanotubes at 1-100 ppm and the gadonanotubes/PLGA nanocomposites (2 wt % gadonanotubes) did not show any cytotoxicity in vitro as demonstrated using the LIVE/DEAD viability assay. For the first time, r(2) relaxivity measurements were obtained for the superparamagnetic gadonanotubes. In vitro 7T MRI of the superparamagnetic gadonanotubes ([Gd] = 0.15 mM) suspended in a biocompatible 1% Pluronic F127 solution, gave a r(2) value of 578 mM(-1) s(-1). Upon subcutaneous injection of the gadonanotubes suspension into the dorsal region of rats, the high r(2) value translated into excellent and prolonged negative contrast enhancement of in vivo T(2)weighted proton MRI images. The in vitro characterization of the nanocomposite discs and their degradation process by MRI, showed strong influence of the gadonanotube on water proton relaxations. These results indicate that the gadonanotubes/PLGA nanocomposites are suitable for further in vivo studies to track by MRI the biodegradation release and biodistribution of gadonanotubes.

Magnetic Nanoparticles for Early Detection of Cancer by Magnetic Resonance Imaging.

This article provides a brief overview of recent progress in the synthesis and functionalization of magnetic nanoparticles and their applications in the early detection of malignant tumors by magnetic resonance imaging (MRI). The intrinsic low sensitivity of MRI necessitates the use of large quantities of exogenous contrast agents in many imaging studies. Magnetic nanoparticles have recently emerged as highly efficient MRI contrast agents because these nanometer-scale materials can carry high payloads while maintaining the ability to move through physiological systems. Superparamagnetic ferrite nanoparticles (such as iron oxide) provide excellent negative contrast enhancement. Recent refinement of synthetic methodologies has led to ferrite nanoparticles with narrow size distributions and high crystallinity. Target-specific tumor imaging becomes possible through functionalization of ferrite nanoparticles with targeting agents to allow for site-specific accumulation. Nanoparticulate contrast agents capable of positive contrast enhancement have recently been developed in order to overcome the drawbacks of negative contrast enhancement afforded by ferrite nanoparticles. These newly developed magnetic nanoparticles have the potential to enable physicians to diagnose cancer at the earliest stage possible and thus can have an enormous impact on more effective cancer treatment.

Visualization and Quantification of Intraperitoneal Tumors by In Vivo Computed Tomography Using Negative Contrast Enhancement Strategy in a Mouse Model of Ovarian Cancer

Small animal computed tomography (CT) has poor intrinsic soft tissue contrast, limiting evaluation of intra-abdominal structures. Using standard intravascular-extracellular intravenous contrast (IE-IV) alone is theoretically limited by long acquisition times of traditional small animal scanners that may result in equilibration. We assessed whether a negative contrast strategy of enhancing normal tissue surrounding tumor, instead of the tumor itself, can visualize and quantify intraperitoneal (IP) cancer in a mouse model. Two and a half weeks after IP injection of Hey A8 cells, four groups of three animals each were administered serial dilutions of IV Fenestra LC (RES-IV), oral Gastroview, and IP Optiray 320. Another group of three animals was administered IV Optiray 320 (IE-IV), oral Gastroview, and IP Optiray 320 in successive combinations. Both groups were imaged by CT. Tumor and organ Hounsfield units were measured, and visualization was assessed. With increasing contrast amount, the Hounsfield unit of organs generally increased, whereas that of tumor remained essentially stable. The visualization of abdominal organs and tumor also generally increased with increasing contrast amount. Visualization of tumor and its margins adjacent to liver, spleen, and stomach was significantly better on administering RES-IV. However, for tumor adjacent to bladder, both IE-IV and RES-IV were equivalent. In vivo CT-derived tumor weights correlated highly with ex vivo tumor weights (r = 0.96, P < .0001, n = 15). Thus, CT using negative contrast enhancement strategy allows visualization and quantification of IP tumors. Such a strategy will also enable anatomic localization of functional signal for combination/molecular imaging.

Size and Surface Effects on the MRI Relaxivity of Manganese Ferrite Nanoparticle Contrast Agents

Superparamagnetic MnFe2O4 nanocrystals of different sizes were synthesized in high-boiling ether solvent and transferred into water using three different approaches. First, we applied a ligand exchange in order to form a water soluble polymer shell. Second, the particles were embedded into an amphiphilic polymer shell. Third, the nanoparticles were embedded into large micelles formed by lipids. Although all approaches lead to effective negative contrast enhancement, we observed significant differences concerning the magnitude of this effect. The transverse relaxivity, in particular r2*, is greatly higher for the micellar system compared to the polymer-coated particles using same-sized nanoparticles. We also observed an increase in transverse relaxivities with increasing particle size for the polymer-coated nanocrystals. The results are qualitatively compared with theoretical models describing the dependence of relaxivity on the size of magnetic spheres.

Folic acid‐PEG conjugated superparamagnetic nanoparticles for targeted cellular uptake and detection by MRI

We report the development and in vitro study of a nanoconjugate serving as a targeted magnetic resonance imaging (MRI) contrast enhancement agent for detection of cancer cells overexpressing the folate receptor. The nanoconjugate was synthesized by coating superparamagnetic iron oxide nanoparticles with covalently bound bifunctional poly(ethylene glycol) (PEG), followed by conjugation with folic acid (FA). The specificity of the nanoconjugate targeting cancerous cells was demonstrated by comparative intracellular uptake of the nanoconjugate and PEG-/dextran-coated nanoparticles by human adenocarcinoma HeLa cells. Preferential targeting to cancerous cells was studied by comparing the uptake of the nanoconjugate by HeLa cells and by non-FR expressing osteosarcoma MG-63 cells. Uptake of the nanoconjugate by HeLa cells after 4 h incubation was found to be a 12-fold higher than that of PEG- or dextran-coated nanoparticles as quantified by inductively coupled plasma spectroscopy. A significant negative contrast enhancement was observed with magnetic resonance (MR) phantom imaging for HeLa cells over MG-63 cells, when both were cultured with the nanoconjugate. Specificity of the nanoconjugate for folate receptors was also verified with a competitive inhibition assay, in which HeLa cells were incubated with both NP-PEG-FA and free FA. The bifunctional PEG used has amide linkages within the PEG chains that can form interchain hydrogen bonding, leading to improved stability of the PEG coating. Self-assembled PEG can be controlled at the molecular level and are suitable for nanoscale coatings.

Noninvasive detection of radiation-induced optic neuropathy by manganese-enhanced MRI.

Available imaging techniques have a limited ability to detect radiation-induced injury of the normal brain. In particular, there is no noninvasive method available for detection of structural or functional neuronal damage induced by radiation. This study was designed to determine whether MRI enhanced using the neuronal track tracer MnCl(2) can detect radiation-induced optic neuropathy. A single dose of radiation (35 Gy) was delivered to produce optic neuropathy in Fischer 344 rats by using a stereotactic method with a 6-mm dorsoventral secondary collimator. At 6 months after irradiation, MRI was performed in 1-mm sections using a 7-T magnetic field with the neuronal tracer MnCl(2) injected into the vitreous of the eye 24 h prior to imaging. The rats were then killed humanely for a histological study with hematoxylin and eosin, glial fibrillary acidic protein (Gfap) for the detection of astrocytic activity, Luxol Fast Blue/Periodic Acid Schiff (LFB/PAS) for the detection of myelinization status, and Bielschowski silver stain for axon status. In nonirradiated control animals, T1-weighted MRI with manganese vitreous injection revealed an optic nerve track that was brightly enhanced from the orbit to the optic chiasm. In the irradiated animals, there was clear evidence of the damage at the optic chiasm and optic nerves, with loss of axon and demyelinization within the site of irradiation upon histological examination. T1-weighted MRI with manganese vitreous injection showed an enhancing optic nerve posterior to the orbit. However, this enhancement disappeared at the site of irradiation. The area of loss of manganese contrast on the MRI scan correlated well with the area of histological abnormality showing axonal degeneration and demyelinization. Radiation-induced optic neuropathy was thus detected noninvasively by MRI with the antegrade neuronal tracer manganese, which exhibited negative contrast enhancement by causing loss of signal. This study represents the first demonstration of MR imaging of radiation-induced neuronal damage and could provide a means to explore the biological and functional integrity of neuronal pathways.