T1 effects of a bolus-injectable superparamagnetic iron oxide, SH U 555 A: dependence on field strength and plasma concentration--preliminary clinical experience with dynamic T1-weighted MR imaging

Direct observation of NMR transverse relaxation in nanopatterned clusters of iron oxide particles

PURPOSE

We aim to verify predictions showing T2 relaxation rate of nanoparticle clusters and its dependence on spacing, size, geometry, and pulse sequence.

METHODS

We performed a laboratory validation study using nanopatterned arrays of iron oxide nanoparticles to precisely control cluster geometry and image diverse samples using a 4.7T MRI scanner with a T2 -weighted fast spin-echo multislice sequence. We applied denoising and normalization to regions of interest and estimated relative R2 for each relevant nanoparticle array or nanocluster array. We determined significance using an unpaired two-tailed t-test or one-way analysis of variance and performed curve fitting.

RESULTS

We measured a density-dependent T2 effect (p = 8.9976 × 10-20 , one-way analysis of variance) and insignificant effect of cluster anisotropy (p = 0.5924, unpaired t-test) on T2 relaxation. We found negative quadratic relationships (-0.0045[log τD ]2 -0.0655[log τD ]-2.7800) for single nanoparticles of varying sizes and for clusters (-0.0045[log τD ]2 -0.0827[log τD ]-2.3249) for diffusional correlation time τD  = rp 2 /D. Clusters show positive quadratic relationships for large (3.8615 × 10-6 [dpp /rp ]2 -9.3853 × 10-5 [dpp /rp ]-2.0393) and exponential relationships for small (-2.0050[dpp /rp ]0.0010 ) clusters. Calculated R2 peak values also align well with in silico predictions (7.85 × 10-4  ms compared with 1.47 × 10-4 , 4.23 × 10-4 , and 5.02 × 10-4  ms for single iron oxide nanoparticles, 7.88 × 10-4  ms compared with 5.24 × 10-4  ms for nanoparticle clusters).

CONCLUSION

Our verification affirms longstanding in silico predictions and demonstrates aggregation-dependent behavior in agreement with previous Monte Carlo simulation studies.

Designing Smart Iron Oxide Nanoparticles for MR Imaging of Tumors

Iron oxide nanoparticles (IONPs) possess unique magnetism and good biocompatibility, and they have been widely applied as contrast agents (CAs) for magnetic resonance imaging (MRI). Traditional CAs typically show a fixed enhanced signal, thus exhibiting the limitations of low sensitivity and a lack of specificity. Nowadays, the progress of stimulus-responsive IONPs allows alteration of the relaxation signal in response to internal stimuli of the tumor, or external stimuli, thus providing an opportunity to overcome those limitations. This review summarizes the current status of smart IONPs as tumor imaging MRI CAs that exhibit responsiveness to endogenous stimuli, such as pH, hypoxia, glutathione, and enzymes, or exogenous stimuli, such as magnets, light, and so on. We discuss the challenges and future opportunities for IONPs as MRI CAs and comprehensively illustrate the applications of these stimuli-responsive IONPs. This review will help provide guidance for designing IONPs as MRI CAs and further promote the reasonable design of magnetic nanoparticles and achieve early and accurate tumor detection.

Lysosomal nanotoxicity: Impact of nanomedicines on lysosomal function

Although several nanomedicines got clinical approval over the past two decades, the clinical translation rate is relatively small so far. There are many post-surveillance withdrawals of nanomedicines caused by various safety issues. For successful clinical advancement of nanotechnology, it is of unmet need to realize cellular and molecular foundation of nanotoxicity. Current data suggest that lysosomal dysfunction caused by nanoparticles is emerging as the most common intracellular trigger of nanotoxicity. This review analyzes prospect mechanisms of lysosomal dysfunction-mediated toxicity induced by nanoparticles. We summarized and critically assessed adverse drug reactions of current clinically approved nanomedicines. Importantly, we show that physicochemical properties have great impact on nanoparticles interaction with cells, excretion route and kinetics, and subsequently on toxicity. We analyzed literature on adverse reactions of current nanomedicines and hypothesized that adverse reactions might be linked with lysosomal dysfunction caused by nanomedicines. Finally, from our analysis it becomes clear that it is unjustifiable to generalize safety and toxicity of nanoparticles, since different particles possess distinct toxicological properties. We propose that the biological mechanism of the disease progression and treatment should be central in the optimization of nanoparticle design.

Chemistry of MRI Contrast Agents: Current Challenges and New Frontiers

Tens of millions of contrast-enhanced magnetic resonance imaging (MRI) exams are performed annually around the world. The contrast agents, which improve diagnostic accuracy, are almost exclusively small, hydrophilic gadolinium(III) based chelates. In recent years concerns have arisen surrounding the long-term safety of these compounds, and this has spurred research into alternatives. There has also been a push to develop new molecularly targeted contrast agents or agents that can sense pathological changes in the local environment. This comprehensive review describes the state of the art of clinically approved contrast agents, their mechanism of action, and factors influencing their safety. From there we describe different mechanisms of generating MR image contrast such as relaxation, chemical exchange saturation transfer, and direct detection and the types of molecules that are effective for these purposes. Next we describe efforts to make safer contrast agents either by increasing relaxivity, increasing resistance to metal ion release, or by moving to gadolinium(III)-free alternatives. Finally we survey approaches to make contrast agents more specific for pathology either by direct biochemical targeting or by the design of responsive or activatable contrast agents.

On the use of superparamagnetic hydroxyapatite nanoparticles as an agent for magnetic and nuclear in vivo imaging

The identification of alternative biocompatible magnetic NPs for advanced clinical application is becoming an important need due to raising concerns about iron accumulation in soft issues associated to the administration of superparamagnetic iron oxide nanoparticles (NPs). Here, we report on the performance of previously synthetized iron-doped hydroxyapatite (FeHA) NPs as contrast agent for magnetic resonance imaging (MRI). The MRI contrast abilities of FeHA and Endorem® (dextran coated iron oxide NPs) were assessed by ¹H nuclear magnetic resonance relaxometry and their performance in healthy mice was monitored by a 7 Tesla scanner. FeHA applied a higher contrast enhancement, and had a longer endurance in the liver with respect to Endorem® at iron equality. Additionally, a proof of concept of FeHA use as scintigraphy imaging agent for positron emission tomography (PET) and single photon emission computed tomography (SPECT) was given labeling FeHA with ^99mTc-MDP by a straightforward surface functionalization process. Scintigraphy/x-ray fused imaging and ex vivo studies confirmed its dominant accumulation in the liver, and secondarily in other organs of the mononuclear phagocyte system. FeHA efficiency as MRI-T₂ and PET-SPECT imaging agent combined to its already reported intrinsic biocompatibility qualifies it as a promising material for innovative nanomedical applications.

STATEMENT OF SIGNIFICANCE

The ability of iron-doped hydroxyapatite nanoaprticles (FeHA) to work in vivo as imaging agents for magnetic resonance (MR) and nuclear imaging is demonstrated. FeHA applied an higher MR contrast in the liver, spleen and kidneys of mice with respect to Endorem®. The successful radiolabeling of FeHA allowed for scintigraphy/X-ray and ex vivo biodistribution studies, confirming MR results and envisioning FeHA application for dual-imaging.

Iron oxide nanoparticles attenuate T helper 17 cell responses in vitro and in vivo

Iron oxide nanoparticles (IONPs) have been shown to attenuate T helper (Th)1 and Th2 cell-mediated immunity in ovalbumin (OVA)-sensitized mice. The objective of this study is to investigate the effects of IONPs on the immune responses of Th17 cells, a subset of T cells involved in various inflammatory pathologies. For in vivo study, a murine model of delayed-type hypersensitivity (DTH) was employed. BALB/c mice received a single dose of IONPs (0.2-10 mg iron/kg) via the tail vein 1 h prior to ovalbumin (OVA) sensitization. Their footpads were subcutaneously challenged with OVA to induce DTH reactions. The expression of Th17 cell-related molecules in inflamed footpads were examined by immunohistochemistry. For in vitro study, OVA-primed splenocytes were directly exposed to IONPs (1-100 μg iron/mL), and then re-stimulated with OVA in culture. The expression of Th17 cell-related molecules were measured by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. IONP administration attenuated the number of interleukin (IL)-6, IL-17, the transcription factor ROR-γ, and chemokine receptor 6 positive cells in OVA-challenged footpads, whereas the number of transforming growth factor-β, IL-23 and chemokine (C-C motif) ligand 20 positive cells was not altered. Direct exposure of OVA-primed splenocytes to IONPs suppressed the production of IL-6 and IL-17, and the mRNA expression of IL-17 and ROR-γt. These data indicate that exposure to IONPs attenuates Th17 cell responses in vivo and in vitro.

Albumin-based nanoparticles loaded with hydrophobic gadolinium chelates as T1-T2 dual-mode contrast agents for accurate liver tumor imaging

Magnetic resonance contrast agents with T₁-T₂ dual mode contrast capability have attracted considerable interest because they offer complementary and synergistic diagnostic information, leading to high imaging sensitivity and accurate diagnosis. Here, we reported a facile strategy to construct albumin based nanoparticles loaded with hydrophobic gadolinium chelates by hydrophobic interaction for magnetic resonance imaging (MRI). We synthesized a glycyrrhetinic acid-containing Gd-DOTA derivative (GGD) and loaded GGD molecules into BSA nanoparticles to form GGD-BSA nanoparticles (GGD-BSA NPs). The large size and porous structure endow GGD-BSA NPs with geometrical confinement, which restricts the tumbling of GGD and the diffusion of surrounding water molecules. As a result, GGD-BSA NPs exhibit ultrahigh T₁ and T₂ relaxivities, which are approximately 8-fold higher than those of gadolinium-based clinical contrast agents at 0.5 T. Besides, due to the intrinsic properties of their components, GGD-BSA NPs show good biocompatibility in vitro and in vivo, which warrants their great potential in clinical translation. Furthermore, GGD-BSA NPs show remarkable sensitivity in noninvasive detection of liver tumors by self-confirmed T₁-T₂ dual-mode contrast-enhanced MRI. All of these merits make GGD-BSA NPs a potential candidate for fruitful biomedical and preclinical applications.

Iron Oxide as an MRI Contrast Agent for Cell Tracking

Iron oxide contrast agents have been combined with magnetic resonance imaging for cell tracking. In this review, we discuss coating properties and provide an overview of ex vivo and in vivo labeling of different cell types, including stem cells, red blood cells, and monocytes/macrophages. Furthermore, we provide examples of applications of cell tracking with iron contrast agents in stroke, multiple sclerosis, cancer, arteriovenous malformations, and aortic and cerebral aneurysms. Attempts at quantifying iron oxide concentrations and other vascular properties are examined. We advise on designing studies using iron contrast agents including methods for validation.

Superparamagnetic iron oxide based MRI contrast agents: Current status of clinical application

Superparamagnetic iron oxide (SPIO) MR contrast agents are composed of nano-sized iron oxide crystals coated with dextran or carboxydextran. Two SPIO agents are clinically approved, namely: ferumoxides (Feridex in the USA, Endorem in Europe) with a particle size of 120 to 180 nm, and ferucarbotran (Resovist) with a particle size of about 60 nm. The principal effect of the SPIO particles is on T2* relaxation and thus MR imaging is usually performed using T2/T2*-weighted sequences in which the tissue signal loss is due to the susceptibility effects of the iron oxide core. Enhancement on T1-weighted images can also be seen with the smaller Resovist. Both Feridex and Resovist are approved specifically for MRI of the liver. The difference being that Resovist can be administered as a rapid bolus (and thus can be used with both dynamic and delayed imaging), whereas Feridex needs to be administered as a slow infusion and is used solely in delayed phase imaging. In the liver, these particles are sequestered by phagocytic Kupffer cells in normal reticuloendothelial system (RES), but are not retained in lesions lacking Kupffer cells. Consequently, there are significant differences in T2/T2* relaxation between normal tissue and lesions, resulting in increased lesion conspicuity and detectability. SPIO substantially increase the detectability of hepatic metastases. For focal hepatocellular lesions, SPIO-enhanced MR imaging exhibits slightly better diagnostic performance than dynamic CT. A combination of dynamic and static MR imaging technique using T1- and T2 imaging criteria appears to provide clinically more useful patterns of enhancement. Feridex and Resovist are also used for evaluating macrophage activities in some inflammatory lesions, but their clinical values remain to be further confirmed. The clinical development of Ferumoxtran (Combidex in the USA, Sinerem in Europe), designed for lymph node metastasis evaluation, is currently stopped.

Iron oxide nanoparticles suppressed T helper 1 cell-mediated immunity in a murine model of delayed-type hypersensitivity

Background

It was recently reported that iron oxide nanoparticles attenuated antigen-specific humoral responses and T cell cytokine expression in ovalbumin-sensitized mice. It is presently unclear whether iron oxide nanoparticles influence T helper 1 cell-mediated immunity. The present study aimed to investigate the effect of iron oxide nanoparticles on delayed-type hypersensitivity (DTH), whose pathophysiology requires the participation of T helper 1 cells and macrophages.

Methods

DTH was elicited by a subcutaneous challenge with ovalbumin to the footpads of mice sensitized with ovalbumin. Iron oxide nanoparticles (0.2–10 mg iron/kg) were administered intravenously 1 hour prior to ovalbumin sensitization. Local inflammatory responses were examined by footpad swelling and histological analysis. The expression of cytokines by splenocytes was measured by enzyme-linked immunosorbent assay.

Results

Administration of iron oxide nanoparticles, in a dose-dependent fashion, significantly attenuated inflammatory reactions associated with DTH, including the footpad swelling, the infiltration of T cells and macrophages, and the expression of interferon-γ, interleukin-6, and tumor necrosis factor-α in the inflammatory site. Iron oxide nanoparticles also demonstrated a suppressive effect on ovalbumin-stimulated production of interferon-γ by splenocytes and the phagocytic activity of splenic CD11b⁺ cells.

Conclusion

These results demonstrated that a single dose of iron oxide nanoparticles attenuated DTH reactions by suppressing the infiltration and functional activity of T helper 1 cells and macrophages in response to antigen stimulation.

A role of cellular glutathione in the differential effects of iron oxide nanoparticles on antigen-specific T cell cytokine expression

BACKGROUND

Accumulating evidence indicates that iron oxide nanoparticles modulate immune responses, and induce oxidative stress in macrophages. It was recently reported that iron oxide nanoparticles attenuated antigen-specific immunity in vivo, though the underlying mechanism remains elusive. The present study investigates the direct effect of iron oxide nanoparticles on antigen-specific cytokine expression by T cells, and potential underlying mechanisms.

METHODS

Ovalbumin-primed splenocytes were exposed to iron oxide nanoparticles, followed by restimulation with ovalbumin. Cell viability, cytokine production, and cellular levels of glutathione and reactive oxygen species were measured.

RESULTS

The splenocyte viability and the production of interleukin-2 and interleukin-4 were unaffected, whereas interferon-γ production was markedly attenuated by iron oxide nanoparticles (10-100 μg iron/mL) in a concentration-dependent manner. Iron oxide nanoparticles also transiently diminished the intracellular level of glutathione, with a peak response at 6 hours posttreatment. The effects of iron oxide nanoparticles on interferon-γ and glutathione were attenuated by the presence of N-acetyl-L-cysteine, a precursor of glutathione. However, iron oxide nanoparticles did not influence the generation of reactive oxygen species.

CONCLUSION

Iron oxide nanoparticles induced a differential effect on antigen-specific cytokine expression by T cells, in which the T helper 1 cytokine IFN-γ was sensitive, whereas the T helper 2 cytokine interleukin-4 was refractory. In addition, the suppressive effect of iron oxide nanoparticles on interferon-γ was closely associated with the diminishment of glutathione.

A single exposure to iron oxide nanoparticles attenuates antigen-specific antibody production and T-cell reactivity in ovalbumin-sensitized BALB/c mice

Background:

Superparamagnetic iron oxide nanoparticles have been used in clinical applications as a diagnostic contrasting agent. Previous studies showed that iron oxide nanoparticles deposited in the liver and spleen after systemic administration. The present study investigated the effect of iron oxide nanoparticles on antigen-specific immune responses in mice sensitized with the T cell-dependent antigen ovalbumin (OVA).

Methods:

BALB/c mice were intravenously administered with a single dose of iron oxide nanoparticles (10–60 mg Fe/kg) 1 hour prior to OVA sensitization, and the serum antibody production and splenocyte reactivity were examined 7 days later.

Results:

The serum levels of OVA-specific IgG₁ and IgG_2a were significantly attenuated by treatment with iron oxide nanoparticles. The production of interferon-γ and interleukin-4 by splenocytes re-stimulated with OVA in culture was robustly suppressed in mice administered with iron oxide nanoparticles. The viability of OVA-stimulated splenocytes was also attenuated. In contrast, treatment with iron oxide nanoparticles did not affect the viability of splenocytes stimulated with concanavalin A, a T-cell mitogen.

Conclusion:

Collectively, these data indicate that systemic exposure to a single dose of iron oxide nanoparticles compromises subsequent antigen-specific immune reactions, including the serum production of antigen-specific antibodies, and the functionality of T cells.

Characterization of liver metastases: the efficacy of biphasic magnetic resonance imaging with ferucarbotran-enhancement

AIM

To retrospectively evaluate the efficacy of biphasic magnetic resonance imaging (MRI) of the liver with ferucarbotran-enhancement for the characterization of hepatic metastases.

MATERIALS AND METHODS

Thirty-six patients underwent MRI of the liver with separate acquisition of double-contrast enhancement consisting of gadolinium and ferucarbotran. A total of 106 focal hepatic lesions (51 metastases, 31 cysts, 23 haemangiomas, and one eosinophilic abscess) were included. Two sets of MRI were analysed: (1) ferucarbotran set: ferucarbotran-enhanced T1-weighted (T1W) dynamic imaging combined with ferucarbotran-enhanced T2*-weighted (T2*W) delayed imaging and (2) double set: gadolinium-enhanced T1W dynamic imaging combined with ferucarbotran-enhanced T2*W delayed imaging. The diagnostic accuracy of the two sets was evaluated using alternative free-response receiver operating characteristic curve analysis. Sensitivity and specificity were compared using the McNemar test. The enhancement pattern of focal hepatic lesions was analysed on gadolinium and ferucarbotran-enhanced T1W dynamic imaging.

RESULTS

There was no significant difference in the accuracy of characterizing hepatic metastases between the two sets. Sensitivity and specificity were not significantly different between the sets (p>0.05). Peripheral rim enhancement was exhibited in 57% of metastatic lesions on ferucarbotran-enhanced T1W dynamic imaging. The majority (96%) of hepatic haemangiomas demonstrated typical peripheral nodular enhancement with progression on ferucarbotran-enhanced T1W dynamic imaging and were easily differentiated from metastases.

CONCLUSION

Biphasic MRI of the liver with ferucarbotran-enhancement alone provided comparable diagnostic efficacy to double-contrast MRI for the characterization of hepatic metastases.

Classification and basic properties of contrast agents for magnetic resonance imaging

A comprehensive classification of contrast agents currently used or under development for magnetic resonance imaging (MRI) is presented. Agents based on small chelates, macromolecular systems, iron oxides and other nanosystems, as well as responsive, chemical exchange saturation transfer (CEST) and hyperpolarization agents are covered in order to discuss the various possibilities of using MRI as a molecular imaging technique. The classification includes composition, magnetic properties, biodistribution and imaging applications. Chemical compositions of various classes of MRI contrast agents are tabulated, and their magnetic status including diamagnetic, paramagnetic and superparamagnetic are outlined. Classification according to biodistribution covers all types of MRI contrast agents including, among others, extracellular, blood pool, polymeric, particulate, responsive, oral, and organ specific (hepatobiliary, RES, lymph nodes, bone marrow and brain). Various targeting strategies of molecular, macromolecular and particulate carriers are also illustrated.

Synthesis and characterization of PVP-coated large core iron oxide nanoparticles as an MRI contrast agent

The purpose of this study was to synthesize biocompatible polyvinylpyrrolidone (PVP)-coated iron oxide (PVP-IO) nanoparticles and to evaluate their efficacy as a magnetic resonance imaging (MRI) contrast agent. The PVP-IO nanoparticles were synthesized by a thermal decomposition method and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), and a superconducting quantum interface device (SQUID). The core size of the particles is about 8-10 nm and the overall size is around 20-30 nm. The measured r(2) (reciprocal of T(2) relaxation time) and r2∗ (reciprocal of T2∗ relaxation time) are 141.2 and 338.1 (s mM)(-1), respectively. The particles are highly soluble and stable in various buffers and in serum. The macrophage uptake of PVP-IO is comparable to that of Feridex as measured by a Prussian blue iron stain and phantom study. The signal intensity of a rabbit liver was effectively reduced after intravenous administration of PVP-IO. Therefore PVP-IO nanoparticles are potentially useful for T(2)-weighted MR imaging.

Contrast agents: magnetic resonance

Even though the intrinsic magnetic resonance imaging (MRI) contrast is much more flexible than in other clinical imaging techniques, the diagnosis of several pathologies requires the involvement of contrast agents (CAs) that can enhance the difference between normal and diseased tissues by modifying their intrinsic parameters. MR CAs are indirect agents because they do not become visible by themselves as opposed to other imaging modalities. The signal enhancement produced by MRI CAs (i.e., the efficiency of the CAs) depends on their longitudinal (r1) and transverse (r2) relaxivity (expressed in s(-1) mmol(-1) 1), which is defined as the increase of the nuclear relaxation rate (the reciprocal of the relaxation time) of water protons produced by 1 mmol per liter of CA. Paramagnetic CAs (most of them complexes of gadolinium) are frequently used in clinics as extracellular, hepatobiliary or blood pool agents. Low molecular weight paramagnetic CAs have similar effects on R1 and R2, but the predominant effect at low doses is that of T1 shortening (and R1 enhancement). Thus, organs taking up such agents will become bright in a T1-weighted MRI sequence; these CAs are thus called positive contrast media. The CAs known as negative agents influence signal intensity mainly by shortening T2* and T2, which produces the darkening of the contrast-enhanced tissue. These CAs are generally composed of superparamagnetic nanoparticles, consisting of iron oxides (magnetite, Fe3O4, maghemite, gammaFe2O3, or other ferrites). Iron oxide nanoparticles are taken up by the monocyte-macrophage system, which explains their potential application as MRI markers of inflammatory and degenerative disorders. Most of the contemporary MRI CAs approved for clinical applications are non-specific for a particular pathology and report exclusively on the anatomy and the physiological status of various organs. A new generation of MRI CAs is progressively emerging in the current context of molecular imaging, agents that are designed to detect with a high specificity the cellular and molecular hallmarks of various pathologies.

Cardiac magnetic resonance imaging at 3.0 T

Cardiovascular magnetic resonance imaging (MRI) has gained widespread acceptance for the assessment of cardiovascular disease. Cardiac MRI requires fast data acquisition schemes because of constraints imposed by physiological motion of cardiac structures and blood flow, which dictate the suitable window of data acquisition. The ongoing improvement of MRI hardware and the development of tailored imaging techniques have been the cornerstones for rapid progress in cardiac MRI. Cardiac MRI at 3.0 T holds the promise to overcome some of the signal-to-noise (SNR) limitations, especially for techniques with borderline SNR at 1.5 T (eg, myocardial perfusion, assessment of viability, or imaging of coronary arteries). The improved SNR at 3.0 T can be used to increase the spatial resolution and/or reduce imaging time. It was shown that all applications of cardiac imaging at 1.5 T seem feasible also at 3.0 T and predominantly provide similar or improved image quality. Although specific absorption rate limitations and susceptibility effects remain a primary concern, the combination of high-field strength examinations with parallel imaging has increased the performance of techniques such as steady-state free-precession at 3.0 T. Therefore, the signal-to-noise and the contrast-to-noise ratios advantages at 3.0 T and the resulting potential benefit for an improved diagnostic value will constantly fuel further developments in this area and pave the way for novel, promising imaging techniques.

Focal nodular hyperplasia: Intraindividual comparison of dynamic gadobenate dimeglumine- and ferucarbotran-enhanced magnetic resonance imaging

PURPOSE

To intraindividually compare the enhancement pattern of focal nodular hyperplasia (FNH) after dynamic administration of two bolus-injectable liver-specific MR contrast agents, ferucarbotran and gadobenate dimeglumine.

MATERIALS AND METHODS

A total of 19 patients with 24 FNHs underwent gadobenate dimeglumine- and ferucarbotran-enhanced MRI during the hepatic arterial-dominant phase (HAP; 25 seconds), the portal-venous phase (PVP; 60 seconds), and the equilibrium phase (EP; 180 seconds). Hepatospecific phases were acquired on T1-weighted images 120 minutes after gadobenate dimeglumine administration, and on T2-weighted images 10 minutes after ferucarbotran administration. Lesion enhancement was independently analyzed by two observers. The kappa statistic was determined to evaluate the agreement between the enhancement patterns of the lesions.

RESULTS

On gadobenate dimeglumine-enhanced MR images during HAP, PVP, and EP, FNHs were: hyperintense (24/20/13); isointense (0/4/11); and hypointense (0/0/0). On ferucarbotran-enhanced MR images during HAP, PVP, and EP, FNHs were: hyperintense (2/0/0); isointense (16/9/14); and hypointense (6/15/10). Overall, poor agreement between both contrast agents was observed. During the hepatospecific phases, most (20/24; 83%) FNHs showed a typical enhancement pattern during the delayed hepatospecific phase.

CONCLUSION

The dynamic enhancement pattern of FNHs is significantly different between gadobenate dimeglumine- and ferucarbotran-enhanced MRI. With respect to hepatospecific phase, the majority of FNHs showed a typical behavior on both contrast agents.

MRI monitoring of neuroinflammation in mouse focal ischemia

BACKGROUND AND PURPOSE

A growing body of evidence suggests that inflammatory processes are involved in the pathophysiology of stroke. Phagocyte cells, involving resident microglia and infiltrating macrophages, secrete both protective and toxic molecules and thus represent a potential therapeutic target. The aim of the present study was to monitor phagocytic activity after focal cerebral ischemia in mice.

METHODS

Ultrasmall superparamagnetic particles of iron oxide (USPIO) were intravenously injected after permanent middle cerebral artery occlusion and monitored by high resolution MRI for 72 hours.

RESULTS

We here present the first MRI data showing in vivo phagocyte-labeling obtained in mice with focal cerebral ischemia. USPIO-enhanced MRI kinetic analysis disclosed an inflammatory response surrounding the ischemic lesion and in the contralateral hemisphere via the corpus callosum. The imaging data collected during the first 36 hours postinjury suggested a spread of USPIO-related signal from ipsi- to contralateral hemisphere. Imaging data correlated with histochemical analysis showing inflammation remote from the lesion and ingestion of nanoparticles by microglia/macrophages.

CONCLUSIONS

The present study shows that MR-tracking of phagocyte cells is feasible in mice, which may have critical therapeutic implications given the potential neurotoxicity of activated microglia/macrophages in central nervous system disorders.

Optimal TE for SPIO-enhanced gradient-recalled echo MRI for the detection of focal hepatic lesions

OBJECTIVE

The objective of our study was to determine the optimal TE for superparamagnetic iron oxide (SPIO)-enhanced gradient-recalled echo (GRE) MRI for the detection of focal hepatic lesions.

MATERIALS AND METHODS

Ferucarbotran-enhanced GRE sequences, performed on a 1.5-T MR system, were used to evaluate 131 lesions (38 hepatocellular carcinomas, 37 metastases, 21 hemangiomas, 7 cholangiocarcinomas, 15 cysts, and 13 miscellaneous lesions) at four different TEs: 9, 13.5, 18, and 22.5 milliseconds. The lesion-to-liver signal difference-to-noise ratio (SDNR) was compared among the four GRE sequences by paired Student's t tests and among lesion types by an independent samples Student's t test. The McNemar test was used to compare the sensitivity for the detection of focal hepatic lesions. Wilcoxon's signed rank test was used to compare the subjective lesion conspicuity.

RESULTS

The SDNRs of lesions on GRE images obtained at a TE of 13.5 milliseconds (mean +/- SD, 60 +/- 24) were significantly (p < 0.001) higher than those at TEs of 9 (55 +/- 23), 18 (55 +/- 22), and 22.5 milliseconds (47 +/- 19). The SDNR was highest at a TE of 13.5 milliseconds for SPIO-uptake lesions and was comparable on images obtained with TEs of 18 and 13.5 milliseconds for non-SPIO-uptake lesions. The non-SPIO-uptake lesions showed a significantly higher SDNR than the SPIO-uptake lesions at a TE of 22.5 milliseconds (p = 0.007). The overall sensitivity for lesion detection was not significantly different among the four GRE sequences, and the subjective ratings of lesion conspicuity were comparable for images obtained using TEs of 8, 13.5, and 18 milliseconds, but the ratings of lesion conspicuity were significantly lower for images obtained using a TE of 22.5 milliseconds (p < 0.001).

CONCLUSION

For ferucarbotran-enhanced MRI, lesion SDNR was highest on images obtained using a TE of 13.5 milliseconds, but the sensitivity and lesion conspicuity were comparable at TEs of 9 and 18 milliseconds. The SDNR of liver lesions varied according to the lesion's potential capability of taking up SPIO agents.

Changes in signal-to-noise ratios and contrast-to-noise ratios of hypervascular hepatocellular carcinomas on ferucarbotran-enhanced dynamic MR imaging

PURPOSE

To verify changes in the signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) of hypervascular hepatocellular carcinomas (HCCs) on ferucarbotran-enhanced dynamic T1-weighted MR imaging.

MATERIALS AND METHODS

Fifty-two patients with 61 hypervascular HCCs underwent ferucarbotran-enhanced dynamic MR imaging, and then hepatic resection. Hypervascular HCCs were identified when definite enhancement was noted during the arterial dominant phase of three-phase MDCT. Dynamic MR Images with T1-weighted fast multiplanar spoiled gradient-recalled echo sequence (TR200/TE4.2) were obtained before and 20 s, and 1, 3, 5, and 10 min, after bolus injection of ferucarbotran. We estimated the signal intensities of tumors and livers, and calculated the SNRs and CNRs of the tumors.

RESULTS

On ferucarbotran-enhanced dynamic MR imaging, SNR measurements showed a fluctuating pattern, namely, an increase in SNR followed by a decrease and a subsequent increase (or a decrease in SNR followed by a increase and a subsequent decrease) in 50 (82.0%) of 61 tumors, a single-peak SNR pattern (highest SNR on 20 s, 1, 3, or 5 min delayed images followed by a decrease) in seven (11.5%), and a decrease in SNR followed by an increase in four (6.6%). Maximum absolute CNRs with positive value were noted on 10 min delayed images in 41 (67.2%) tumors, and maximum absolute CNRs with negative value were observed on 20 s delayed images in 12 (19.7%) and on 1 min delayed images in eight (13.1%).

CONCLUSION

Despite showing various SNR and CNR changes, the majority of hypervascular HCCs demonstrated a fluctuating SNR pattern on ferucarbotran-enhanced dynamic MR imaging and a highest CNR on 10 min delayed image, which differed from the classic enhancement pattern on multiphasic CT.

Detection of hepatic metastasis: manganese- and ferucarbotran-enhanced MR imaging

PURPOSE

To compare the mangafodipir trisodium (MnDPDP)-enhanced and ferucarbotran-enhanced magnetic resonance imaging (MRI) for the detection of hepatic metastases.

MATERIAL AND METHODS

Twenty patients with known hepatic metastasis underwent MR imaging using mangafodipir trisodium and ferucarbotran in at least 1-day intervals. Thirty-eight metastases were confirmed either histologically or clinically. Two radiologists independently reviewed the MnDPDP-enhanced and ferucarbotran-enhanced sets in a random order. The sensitivity and accuracy of lesion detection and the ability to distinguish a benign lesion from a malignant lesion were compared by the areas (Az) under the receiver operating characteristic (ROC) curve. The lesion-liver contrast-to-noise ratios (CNR) were compared by paired t-test.

RESULTS

The overall accuracy for detecting metastases was not significantly different between the MnDPDP set (Az=0.912 and 0.913 for reader 1 and 2, respectively) and the SPIO set (Az=0.920 and 0.950). The CNR at the MnDPDP-enhanced images and the SPIO-enhanced images were not significantly different (P=0.146).

CONCLUSION

Both MnDPDP- and ferucarbotran-enhanced MRI have a comparable accuracy in detecting hepatic metastasis.

Focal liver lesions: SPIO-, gadolinium-, and ferucarbotran-enhanced dynamic T1-weighted and delayed T2-weighted MR imaging in rabbits

PURPOSE

To compare a superparamagnetic iron oxide (SPIO), VSOP-C184, with a gadopentetate dimeglumine with regard to signal-enhancing effects on T1-weighted dynamic magnetic resonance (MR) images and with another SPIO contrast medium with regard to signal-reducing effects on delayed T2-weighted MR images.

MATERIALS AND METHODS

All experiments were approved by the responsible Animal Care Committee. Twenty rabbits (five for each contrast agent and dose) implanted with VX-2 carcinoma were imaged at 1.5 T. VSOP-C184 at 0.015 and 0.025 mmol Fe/kg was compared with gadopentetate dimeglumine at 0.15 mmol Gd/kg and ferucarbotran at 0.015 mmol Fe/kg. The imaging protocol comprised a T1-weighted dynamic gradient-echo (GRE) MR before injection and at 6-second intervals for up to 42 seconds after injection and a T2-weighted turbo spin-echo MR before and 5 minutes after injection. Images were evaluated quantitatively, and contrast media were compared by using nonparametric analysis of variance.

RESULTS

At dynamic T1-weighted GRE MR imaging with 0.015-mmol Fe/kg VSOP-C184, 0.025-mmol Fe/kg VSOP-C184, gadopentetate dimeglumine, and ferucarbotran, the median peak contrast-to-noise ratio (CNR) was 20.7 (25th percentile, 16.3; 75th percentile, 22.6), 24.2 (25th percentile, 19.3; 75th percentile, 28.5), 16.4 (25th percentile, 13.7; 75th percentile, 20.3), and 14.0 (25th percentile, 11.4; 75th percentile, 16.8), respectively. Both doses of VSOP-C184 yielded significantly higher CNR (P < .05) than the other two agents. At T2-weighted turbo spin-echo imaging with 0.015-mmol Fe/kg VSOP-C184, 0.025-mmol Fe/kg VSOP-C184, gadopentetate dimeglumine, and ferucarbotran, the median CNR was 15.0 (25th percentile, 13.4; 75th percentile, 21.3), 15.7 (25th percentile, 14.5; 75th percentile, 19.8), 11.3 (25th percentile, 8.2; 75th percentile, 12.2), and 15.7 (25th percentile, 12.5; 75th percentile, 22.4), respectively. There was no significant difference between VSOP-C184 and ferucarbotran; both had a significantly higher CNR than did gadopentetate dimeglumine.

CONCLUSION

VSOP-C184 produces higher liver-to-tumor contrast at dynamic T1-weighted imaging than does gadopentetate dimeglumine; at delayed T2-weighted imaging, the contrast is comparable to that achieved with ferucarbotran.

Comparison of Gadolinium-BOPTA and Ferucarbotran-Enhanced Three-Dimensional T1-Weighted Dynamic Liver Magnetic Resonance Imaging in the Same Patient

OBJECTIVES

We sought to compare signal changes using Ferucarbotran and gadobenate dimeglumine (Gd-BOPTA) in dynamic 3D T1-weighted (T1w) GRE imaging of the liver.

MATERIAL AND METHODS

Thirty patients were prospectively included in the study. All patients underwent 2 high-field magnetic resonance (MR) examinations: first with Gd-BOPTA (Gd) and then after a mean interval of 4 days with ferucarbotran (Feru). Dynamic MRI was obtained with a 3D T1w GRE sequence (TR 6.33, TE 2.31, flip angle 20 degrees ). Contrast enhanced scans were assessed before intravenous injection of the contrast agent (precontrast), and postcontrast during the arterial phase (30 seconds), portal venous phase (60 seconds), and equilibrium phase (120 seconds). The signal intensities (SIs) of liver, spleen, aorta, and portal vein were defined by region of interest measurements. Signal intensity changes (SICs) and percentage signal intensity change (PSIC) were calculated using the formulas SIC=(SI pre - SI post)/SI pre and PSIC=SIC x 100%.

RESULTS

Positive signal enhancement was observed after intravenous injection of Feru during all dynamic measurements, whereas the mean SI values were lower compared with Gd. During the portal venous phase the mean SI of Gd was up to a factor of 2.1 higher (portal vein). The widest difference of SIC was observed during the equilibrium phase for liver parenchyma (Gd, 1.03; Feru, 0.24). The dynamic signal courses were similar for liver, portal vein and aorta. Different signal courses were obtained for the spleen.

CONCLUSIONS

Feru-enhanced T1w dynamic images demonstrated significant signal increases for liver, vessels, and spleen but overall lower signal intensities than Gd-BOPTA. The dynamic signal courses of ferucarbotran were similar to that of Gd-BOPTA during ll perfusion phases except in the spleen. Thus, it may be possible to detect typical enhancement pattern of focal liver lesions with Feru-enhanced dynamic T1w MRI.

Detection of Portal Perfusion Abnormalities

OBJECTIVE

To estimate the accuracy, sensitivity, and specificity of 3 ferucarbotran-enhanced magnetic resonance (MR) imaging sequences prospectively for the detection of nontumoral portal perfusion abnormalities.

METHODS

Thirty-nine noncirrhotic patients with liver metastases underwent computed tomography during arterial portography (CTAP) and MR imaging comprising T1-weighted gradient recalled echo (GRE), T2-weighted fast spin echo (FSE), and T2*-weighted GRE sequences with and without ferucarbotran. Magnetic resonance images were reviewed by 4 blinded observers for rating based on the confidence scale. The accuracy, sensitivity, and specificity for each sequence were measured by receiver operating characteristic analysis. Contrast-to-noise ratio (CNR) and relative signal-to-noise ratio changes were statistically compared.

RESULTS

Thirty-nine nontumoral perfusion defects were observed in 22 patients by CTAP. Receiver operating characteristic analysis showed the accuracy was higher for T2*-weighted GRE (0.884) than for T1-weighted GRE (0.572) and T2-weighted FSE (0.597). T2*-weighted imaging achieved the highest sensitivity (81.4%) and the lowest specificity (86.6%). Postenhanced T2*-weighted imaging achieved the highest CNR (19.3 +/- 9.2).

CONCLUSIONS

T2*-weighted imaging was the most accurate and sensitive method for detecting portal perfusion abnormalities compared with T1- or T2-weighted imaging, whereas T1- or T2-weighted imaging is superior in specificity to T2*-weighted imaging during ferucarbotran-enhanced MR imaging.

Application of superparamagnetic iron oxide to imaging of hepatocellular carcinoma

Superparamagnetic iron oxide (SPIO) particles are as MR contrast media composed of iron oxide crystals coated with dextran or carboxydextran. These particles are sequestered by phagocytic Kupffer cells in normal reticuloendothelial system (RES), but are not retained in tumor tissue. Consequently, there are significant differences in T2/T2* relaxation between normal RES tissue and tumors, which result in increased lesion conspicuity and detectability. The introduction of SPIO has been expected to substantially increase the detectability of hepatic metastases. For focal hepatocellular lesions, it has been documented that SPIO-enhanced MR imaging exhibits slightly better diagnostic performance than dynamic helical CT in the detection of hypervascular hepatocellular carcinoma (HCC). A combination of dynamic and static MR imaging technique using T1- and T2 imaging criteria appears to provide clinically more useful patterns of enhancement. SPIO-enhanced MR imaging also provides information useful for differential diagnosis, via enhancement of RES-containing tumors. With the exploitation of rapid T2*-sensitive sequences, SPIO-enhanced dynamic MR imaging may become comparable to gadolinium-enhanced dynamic MR imaging and dynamic studies with multidetector-row CT. SPIO-enhanced MR imaging plays an important role in therapeutic decision-making for patients with HCC.

Comparison of magnetic properties of MRI contrast media solutions at different magnetic field strengths

RATIONALE AND OBJECTIVES

To characterize and compare commercially available contrast media (CM) for magnetic resonance imaging (MRI) in terms of their relaxivity at magnetic field strengths ranging from 0.47 T to 4.7 T at physiological temperatures in water and in plasma. Relaxivities also were quantified in whole blood at 1.5 T.

METHODS

Relaxivities of MRI-CM were determined by nuclear magnetic resonance (NMR) spectroscopy at 0.47 T and MRI phantom measurements at 1.5 T, 3 T, and 4.7 T, respectively. Both longitudinal (T1) and transverse relaxation times (T2) were measured by appropriate spin-echo sequences. Nuclear magnetic resonance dispersion (NMRD) profiles were also determined for all agents in water and in plasma.

RESULTS

Significant dependencies of relaxivities on the field strength and solvents were quantified. Protein binding leads to both increased field strength and solvent dependencies and hence to significantly altered T1 relaxivity values at higher magnetic field strengths.

CONCLUSIONS

Awareness of the field strength and solvent associated with relaxivity data is crucial for the comparison and evaluation of relaxivity values. Data observed at 0.47 T can thus be misleading and should be replaced by relaxivities measured at 1.5 T and at 3 T in plasma at physiological temperature.

Hepatocellular carcinoma in cirrhosis: enhancement patterns at dynamic gadolinium- and superparamagnetic iron oxide-enhanced T1-weighted MR imaging

PURPOSE

To prospectively compare intraindividual differences in enhancement patterns between gadolinium- and superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance (MR) imaging in patients with histologically proved hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Twenty-two patients (18 men, four women; mean age, 58.9 years) with 36 pathologically proved HCC lesions underwent contrast material-enhanced dynamic T1-weighted gradient-echo MR imaging twice. Gadopentetate dimeglumine was used at the first session. After a mean interval of 5 days, a second session was performed with a bolus-injectable SPIO agent, ferucarbotran. Qualitative analysis of contrast enhancement patterns with each agent during hepatic arterial, portal venous, and equilibrium phases was performed by two readers who classified lesions as isointense, hypointense, or hyperintense compared with surrounding liver parenchyma and searched for presence of hyperintense peritumoral ring enhancement. Results of signal intensity analysis during different vascular phases at both sessions were compared by using the McNemar test, and kappa statistic was used to evaluate agreement between signal intensity and enhancement pattern of lesions during different vascular phases.

RESULTS

On gadolinium-enhanced hepatic arterial phase images, HCC lesions (n = 36) were hyperintense in 21 (58%) cases, hypointense in 10 (28%), and isointense in five (14%). On ferucarbotran-enhanced hepatic arterial phase images, HCC lesions were isointense in 18 (50%) cases, hypointense in 11 (31%), and hyperintense in seven (19%). On gadolinium-enhanced portal venous and equilibrium phase images, respectively, HCC lesions were hypointense in 17 (47%) and 21 (58%) cases, hyperintense in 10 (28%) cases and one (3%) case, and isointense in nine (25%) and 14 (39%) cases. On ferucarbotran-enhanced portal venous and equilibrium phase images, respectively, HCC lesions were hypointense in 15 (42%) and 11 (31%) cases, hyperintense in three (8%) and three (8%) cases, and isointense in 18 (50%) and 22 (61%) cases.

CONCLUSION

For HCC, contrast enhancement pattern on T1-weighted gradient-echo MR images shows marked variability with gadolinium or SPIO contrast agents.

Whole-body MRI at high field: technical limits and clinical potential

This review seeks to clarify the most important implications of higher magnetic field strength for clinical examinations of the whole body. An overview is provided on the resulting advantages and disadvantages for anatomical, functional and biochemical magnetic resonance examinations in different regions of the body. It is demonstrated that susceptibility-dependent imaging, chemical shift selective (e.g., fat-suppressed) imaging, and spectroscopic techniques clearly gain from higher field strength. Problems due to shorter wavelength and higher radio frequency energy deposition at higher field strength are reported, especially in examinations of the body trunk. Thorax examinations provided sufficient homogeneity of the radio frequency field for common examination techniques in most cases, whereas abdominal and pelvic imaging was often hampered by undesired dielectric effects. Currently available and potential future strategies to overcome related limitations are discussed. Whole-body MRI at higher field strength currently leads to clearly improved image quality using a variety of established sequence types and for examination of many body regions. But some major problems at higher field strength have to be solved before high-field magnetic resonance systems can really replace the well-established and technically developed magnetic resonance systems operating at 1.5 T for each clinical application.

MRT der Leber

The liver is a common site for various benign and malignant focal lesions. The initial modality for assessing liver lesions is ultrasound or CT. MRI with its superior soft tissue contrast offers multiple advantages over other imaging modalities. Contrast agents have been developed that increase the detection rate and provide more specific information in comparison to unenhanced techniques. In the mean time three classes are available for MR imaging of the liver: extracellular gadolinium chelates, hepatobiliary and reticulo-endothelia, superparamagnetic agents. We describe in this review the most common focal lesions, their diagnostic possibilities, and the imaging protocols. Clinical use of these contrast agents facilitates detection and differential diagnosis of focal liver lesions that may help to avoid invasive procedures such as biopsy for lesion characterization.

Detection of malignant hepatic tumors with ferumoxide-enhanced MR imaging: usefulness of multishot and single-shot fast spin echo sequences

The purpose of our study was to assess whether respiratory-triggered multishot fast spin echo (MS-FSE) and breath-hold half-Fourier single-shot fast spin echo (SS-FSE) images, in addition to breath-hold T(2)*-weighted gradient recalled echo (GRE) images, increase observer performance in the detection of malignant hepatic tumors with ferumoxide-enhanced magnetic resonance (MR) imaging. Ferumoxide-enhanced MR images obtained from 48 patients with 83 malignant hepatic tumors were retrospectively reviewed by three independent off-site readers. In the first image review, GRE images alone were reviewed. Then, MS-FSE images were added for the first combination review. Finally, SS-FSE images were added for the second combination review. Observer performances were tested by McNemar's test and receiver-operating-characteristic analysis for the clustered data. Sensitivity for hepatocellular carcinomas, metastases, and malignant hepatic tumors overall was significantly (p < 0.05) higher with GRE and MS-FSE combined and GRE, MS-FSE and SS-FSE combined than with GRE alone. For metastases, the Az value was significantly (p < 0.05) higher with GRE and MS-FSE combined, and GRE, MS-FSE and SS-FSE combined than with GRE alone. We confirmed the incremental value of ferumoxide-enhanced MR imaging by obtaining MS-FSE and SS-FSE images in addition to GRE images in the detection of malignant hepatic tumors.

Detection of malignant hepatic tumors with ferumoxides-enhanced MRI: comparison of five gradient-recalled echo sequences with different TEs

OBJECTIVE

The purpose of our study was to compare the detectability of malignant hepatic tumors on ferumoxides-enhanced MRI using five gradient-recalled echo sequences at different TEs.

MATERIALS AND METHODS

Ferumoxides-enhanced MRIs obtained in 31 patients with 50 malignant hepatic tumors (33 hepatocellular carcinomas, 17 metastases) were reviewed retrospectively by three independent offsite radiologists. T1-weighted gradient-recalled echo images with TEs of 1.4 and 4.2 msec; T2*-weighted gradient-recalled echo images with TEs of 6, 8, and 10 msec; and T2-weighted fast spin-echo images of livers were randomly reviewed on a segment-by-segment basis. Observer performance was tested using the McNemar test and receiver operating characteristic analysis for the clustered data. Lesion-to-liver contrast-to-noise ratio was also assessed.

RESULTS

Mean lesion-to-liver contrast-to-noise ratios were negative and lower with gradient-recalled echo at 1.4 msec than with the other sequences. Sensitivity was higher (p < 0.05) with gradient-recalled echo at 6, 8, and 10 msec and fast spin-echo sequences (75-83%) than with gradient-recalled echo sequences at 1.4 and 4.2 msec (46-48%), and was higher (p < 0.05) with gradient-recalled echo sequence at 8 msec (83%) than with gradient-recalled echo at 6 msec and fast spin-echo sequences (75-78%). Specificity was comparably high with all sequences (95-98%). The area under the receiver operating characteristic curve (A(z)) was greater (p < 0.05) with gradient-recalled echo at 6, 8, and 10 msec and fast spin-echo sequences (A(z) = 0.91-0.93) than with gradient-recalled echo sequences at 1.4 and 4.2 msec (A(z) = 0.82-0.85).

CONCLUSION

In the detection of malignant hepatic tumors, gradient-recalled echo sequences at 8 msec showed the highest sensitivity and had an A(z) value and lesion-to-liver contrast-to-noise ratio comparable with values from gradient-recalled echo sequences at 6 and 10 msec and fast spin-echo sequences.

Perilesional hyperintense rim of malignant hepatic tumors on ferumoxide-enhanced T1-weighted gradient-echo MR images: correlation between MR imaging and histopathologic findings

PURPOSE

To correlate the perilesional hyperintense rim of malignant hepatic tumors seen on ferumoxide-enhanced T1-weighted gradient-echo (GE) MR images with histopathologic findings.

MATERIALS AND METHODS

In 13 tumors in 12 patients, T1-weighted GE images (TE of 1.4 msec, flip angle of 90 degrees) obtained after IV administration of ferumoxide were evaluated. MR imaging was initiated within one hour of the completion of ferumoxide administration. Surgical resection for tumors was performed within an interval of two weeks of the MR imaging. Resected specimens were histopathologically examined for peritumoral sinusoidal congestion, desmoplastic reaction, compressed hepatic parenchyma, lymphocytic infiltration, and vascular proliferation.

RESULTS

In twelve tumors (92%), prominently (N = 2), moderately (N = 5), and mildly to minimally (N = 5), a perilesional hyperintense rim was observed. Among histopathologic findings, the degree of peritumoral sinusoidal congestion correlated (R =.75, P <.04) with the degree of perilesional hyperintense rim. The thickness of the perilesional hyperintense rim showed a moderate positive correlation (R =.65, P <.02) with the thickness of peritumoral area with sinusoidal congestion.

CONCLUSION

Perilesional hyperintense rim of malignant hepatic tumors on ferumoxide-enhanced T1-weighted GE images may correlate with sinusoidal congestion surrounding malignant hepatic tumors.

MR image-guided endovascular procedures with the ultrasmall superparamagnetic iron oxide SH U 555 C as an intravascular contrast agent: study in pigs

PURPOSE

To evaluate the feasibility of using the ultrasmall superparamagnetic iron oxide (USPIO) SH U 555 C as an intravascular contrast agent for magnetic resonance (MR) image-guided vascular procedures with an open MR imaging system.

MATERIALS AND METHODS

All experiments were performed with MR imaging at 0.2 T. MR image-guided interventions were performed in USPIO-enhanced vessels in four pigs. With near real-time MR image guidance (acquisition time, 0.64 second per section), the splenic and renal arteries were consecutively catheterized by using a susceptibility artifact-based catheter-guide wire combination. Angioplasty and stent implantation were performed four times in the renal artery and twice in the iliac artery. Intraaortal signal intensity (SI) was measured during the interventions.

RESULTS

After administration of SH U 555 C (40 micromol of iron per kilogram of body weight), a three-dimensional MR angiographic sequence was performed that allowed visualization of the abdominal and pelvic vessels that were as small as 2 mm in diameter. Catheterization, angioplasty, and stent implantation were successfully guided in the USPIO-enhanced vasculature. Sixty minutes after contrast agent injection, the mean aortic SI was 70% of the maximum measured enhancement levels.

CONCLUSION

One intravenous injection of SH U 555 C enabled long, continuous intravascular SI enhancement at MR angiography, and, in combination with susceptibility artifact-based device tracking, the injection allowed the performance of MR imaging-guided intravascular interventions in an open MR imaging system.

Characterization of focal liver lesions with superparamagnetic iron oxide-enhanced MR imaging: value of distributional phase T1-weighted imaging

OBJECTIVE

To determine the potential value of distributional-phase T1-weighted ferumoxides-enhanced magnetic resonance (MR) imaging for tissue characterization of focal liver lesions.

MATERIALS AND METHODS

Ferumoxides-enhanced MR imaging was performed using a 1.5-T system in 46 patients referred for evaluation of known or suspected hepatic malignancies. Seventy-three focal liver lesions (30 hepatocellular carcinomas (HCC), 12 metastases, 15 cysts, 13 hemangiomas, and three cholangiocarcinomas) were evaluated. MR imaging included T1-weighted double-echo gradient-echo (TR/TE: 150/4.2 and 2.1 msec), T2*-weighted gradient-echo (TR/TE: 180/12 msec), and T2-weighted turbo spin-echo MR imaging at 1.5 T before and after intravenous administration of ferumoxides (15 mmol/kg body weight). Postcontrast T1-weighted imaging was performed within eight minutes of infusion of the contrast medium (distributional phase). Both qualitative and quantitative analysis was performed.

RESULTS

During the distributional phase after infusion of ferumoxides, unique enhancement patterns of focal liver lesions were observed for hemangiomas, metastases, and hepatocellular carcinomas. On T1-weighted GRE images obtained during the distributional phase, hemangiomas showed a typical positive enhancement pattern of increased signal; metastases showed ring enhancement; and hepatocellar carcinomas showed slight enhancement. Quantitatively, the signal-to-noise ratio of hemangiomas was much higher than that of other tumors (p <.05) and was similar to that of intrahepatic vessels. This finding permitted more effective differentiation between hemangiomas and other malignant tumors.

CONCLUSION

T1-weighted double-echo FLASH images obtained soon after the infusion of ferumoxides, show characteristic enhancement patterns and improved the differentiation of focal liver lesions.

Efficacy of dynamic MRI with superparamagnetic iron oxide (SH U 555 A): vascularity evaluation in hepatocellular carcinoma

PURPOSE

A study was conducted to determine the possibility of evaluating the blood flow in cases of hypervascular hepatocellular carcinoma (HCC) by employing dynamic MRI with superparamagnetic iron oxide (SH U 555 A), which can be rapidly injected via an intravenous route.

METHODS

Six patients with hypervascular HCC (23 nodules) served as the subjects. Dynamic MRI includes images obtained at precontrast and at 10 (perfusion phase), 60, 120, 180, 240, 300 and 600 s after the start of injection of SH U 555 A. CT hepatic arteriography (CTHA) and CT during arterial portography (CTAP) were used as the standards of reference, and these were performed in all patients three days after dynamic MRI. The signal changes were evaluated at each phase, especially at the perfusion phase from the viewpoints of a lesion-to-liver contrast-to-noise ratio (CNR) and visual examination.

RESULTS

A total of 23 hypervascular HCC were detected on CTHA and CTAP. Of the 23 lesions, 17 were detected on SH U 555 A enhanced MRI. Incorrect timing during acquisition of the perfusion phase was considered in two cases with three lesions. Of 14 lesions, excluding two cases with incorrect timing, a reduction in the transient signal in the lesions at the perfusion phase was visually recognized in 10 lesions (71%). Significant differences were seen in tumor size between visible and non-visible tumors involving transient signal reduction (p< 0.05). CNR gradually increased after rapidly decreasing in the perfusion phase.

CONCLUSION

SH U 555 A enhanced MRI is valuable in limited cases. Evaluation of tumor blood flow employing dynamic MRI with SH U 555 A is affected by tumor size and requires optimal timing of the perfusion phase.

T1-weighted magnetic resonance imaging sequence appropriate for the evaluation of the longitudinal relaxation effect of superparamagnetic iron oxide: a phantom study

The goal of this study was to determine a T1-weighted magnetic resonance (MR) imaging sequence appropriate for evaluating the longitudinal relaxation effect of superparamagnetic iron oxide (ferumoxides) in a phantom study. An agarose phantom that included various concentrations of ferumoxides (0 - 0.5 mmol/l in 0.05 mmol/l increments) was examined for six types of T1-weighted imaging sequences using a 1.5-T MR unit. Three-dimensional (3D) fast spoiled gradient-echo (SPGR) imaging with a short echo time showed a strong linear correlation between the concentration of ferumoxides and the enhancement ratio. Two-dimensional (2D) fast SPGR imaging showed a high signal-to-noise ratio of the phantom even at low ferumoxides concentrations. These results suggest that 3D fast SPGR imaging is an appropriate technique for the evaluation of the longitudinal relaxation effect of ferumoxides, and that 2D fast SPGR imaging can be useful for evaluating the longitudinal relaxation effect at lower ferumoxides concentrations.

Use of a blood-pool contrast agent for MR-guided vascular procedures: feasibility of ultrasmall superparamagnetic iron oxide particles

RATIONALE AND OBJECTIVES

The purpose of this study was to examine the dose dependency of the intravascular signal intensity after injection of ultrasmall superparamagnetic iron oxide (USPIO) particles (SH U 555 C) in a rabbit model studied with a low-field-strength magnetic resonance (MR) imaging system. The results were used to facilitate MR-guided vascular procedures in a pig.

MATERIALS AND METHODS

All experiments were performed at 0.2 T. To determine the optimum USPIO (or SH U 555 C) dose for intravascular interventions, the authors acquired coronal three-dimensional MR angiographic images in 12 rabbits after injection of four dose levels (10, 20, 30, and 40 micromol of iron per kilogram body weight). The intraaortic signal intensities were measured in user-defined regions of interest. For numerical analysis, signal intensity enhancement was computed. Subsequently MR image-guided procedures were performed in USPIO-enhanced vessels in one pig.

RESULTS

The signal intensity evaluation shows a clear-cut dose dependence in both early and late phases after administration of SH U 555 C. A high-spatial-resolution MR angiogram acquired 20 minutes after injection yielded the best results with the highest dose (40 micromol of iron per kilogram); at that dose, intravascular enhancement was sufficient for vascular procedures for 60 minutes after injection.

CONCLUSION

SH U 555 C is a promising contrast agent for MR angiography and MR-guided vascular procedures in an open low-field-strength MR imager.