[A Method for Evaluating the T2∗-weighting Effect in MRI]

PURPOSE

To propose a method for evaluating the T₂*-weighting effect in MRI.

METHODS

Multiple solutions with different concentrations of a superparamagnetic iron oxide contrast agent were made and their signal intensities on T₂*-weighted images were measured. The relationship between iron concentration and signal intensity was determined, and we simulated an iron concentration map representing a simplified model of a brain microbleed and converted the pixel values in the map to signal intensity based on the determined relationship, generating a simulated T₂*-weighted image. An 'S-value' parameter was defined to evaluate the low-intensity regions in the simulated image. S-values were obtained using T₂*-weighted sequences acquired with different echo time (TE) values on three MRI scanners (Philips 1.5 T, GE 3.0 T, and Siemens 3.0 T). Another parameter (A-value) defined by the American Society for Testing and Materials (ASTM-F2119) for assessing artifacts was applied to evaluate the weighting effect in the T₂*-weighted image of a laboratory-made susceptibility-effect phantom.

RESULTS

With all three scanners, the S-values increased as the TE increased, indicating enhancement of the T₂*-weighting effect. For every TE, the S-values obtained for the Philips scanner were the largest, followed by those for the GE and Siemens scanners. The results of this comparative evaluation were similar to those obtained using A-values.

CONCLUSION

Comparisons with the established A-value parameter showed our proposed method for the quantitative evaluation of the T₂*-weighting effect using S-values to be valid. The proposed method has the advantage that the S-values do not depend on a specific susceptibility-effect phantom.

A Comprehensive Grading System for a Magnetic Sentinel Lymph Node Biopsy Procedure in Head and Neck Cancer Patients

Simple Summary

With 30% of clinically negative early-stage oral cancer patients harboring occult metastasis, an accurate staging of metastatic lymph nodes (LN) is of utmost importance for treatment planning. A magnetic sentinel lymph node biopsy (SLNB) procedure is offered as an alternative to conventional SLNB in oral oncology, however, a grading system is missing. A proper grading system is preferred to connect the different components of the magnetic SLNB: preoperative imaging, intraoperative detection, and histopathological examination of sentinel lymph nodes (SLNs). This study aims to provide a first grading system based on the distribution of a magnetic tracer, by means of preoperative magnetic resonance imaging (MRI), intraoperative estimation of iron content, and histopathological assessment of resected nodes. Pre- and post-operative MRI and harvested SLNs of eight tongue cancer patients with successful magnetic SLNB procedure were used for analyses.

Abstract

A magnetic sentinel lymph node biopsy ((SLN)B) procedure has recently been shown feasible in oral cancer patients. However, a grading system is absent for proper identification and classification, and thus for clinical reporting. Based on data from eight complete magnetic SLNB procedures, we propose a provisional grading system. This grading system includes: (1) a qualitative five-point grading scale for MRI evaluation to describe iron uptake by LNs; (2) an ex vivo count of resected SLN with a magnetic probe to quantify iron amount; and (3) a qualitative five-point grading scale for histopathologic examination of excised magnetic SLNs. Most SLNs with iron uptake were identified and detected in level II. In this level, most variance in grading was seen for MRI and histopathology; MRI and medullar sinus were especially highly graded, and cortical sinus was mainly low graded. On average 82 ± 58 µg iron accumulated in harvested SLNs, and there were no significant differences in injected tracer dose (22.4 mg or 11.2 mg iron). In conclusion, a first step was taken in defining a comprehensive grading system to gain more insight into the lymphatic draining system during a magnetic SLNB procedure.

Stimulus-Responsive Nanoparticle Magnetic Resonance Imaging Contrast Agents: Design Considerations and Applications

Magnetic resonance imaging (MRI) has been widely used for disease diagnosis because it can noninvasively obtain anatomical details of various diseases through accurate contrast between soft tissues. Over one-third of MRI examinations are performed with the assistance of contrast agents. Traditional contrast agents typically display an unchanging signal, thus exhibiting relatively low sensitivity and poor specificity. Currently, advances in stimulus-responsive contrast agents which can alter the relaxation signal in response to a specific change in their surrounding environment provide new opportunities to overcome such limitation. The signal changes based on stimulus also reflects the physiological and pathological conditions of the site of interests. In this review, how to design stimulus-responsive nanoparticle MRI contrast agents from the perspective of theory and surface design is comprehensively discussed. Key structural features including size, clusters, shell features, and surface properties are used for tuning the T₁ and T₂ relaxation properties. The reversible or non-reversible signal changes highlight the contrast agents have undergone structural changes based on certain stimulus, as an indication for disease diagnosis or therapeutic efficacy.

Synthesis and characterization of magnetic nanoparticles coated with polystyrene sulfonic acid for biomedical applications

The development of novel magnetic nanoparticles (MNPs) with satisfactory biocompatibility for biomedical applications has been the subject of extensive exploration over the past two decades. In this work, we synthesized superparamagnetic iron oxide MNPs coated with polystyrene sulfonic acid (PSS-MNPs) and with a conventional co-precipitation method. The core size and hydrodynamic diameter of the PSS-MNPs were determined as 8-18 nm and 50-200 nm with a transmission electron microscopy and dynamic light scattering, respectively. The saturation magnetization of the particles was measured as 60 emu g-1 with a superconducting quantum-interference-device magnetometer. The PSS content in the PSS-MNPs was 17% of the entire PSS-MNPs according to thermogravimetric analysis. Fourier-transform infrared spectra were recorded to detect the presence of SO3 - groups, which confirmed a successful PSS coating. The structural properties of the PSS-MNPs, including the crystalline lattice, composition and phases, were characterized with an X-ray powder diffractometer and 3D nanometer-scale Raman microspectrometer. MTT assay and Prussian-blue staining showed that, although PSS-MNPs caused no cytotoxicity in both NIH-3T3 mouse fibroblasts and SK-HEP1 human liver-cancer cells up to 1000 μg mL-1, SK-HEP1 cells exhibited significantly greater uptake of PSS-MNPs than NIH-3T3 cells. The low cytotoxicity and high biocompatibility of PSS-MNPs in human cancer cells demonstrated in the present work might have prospective applications for drug delivery.

Study of biodistribution and systemic toxicity of glucose functionalized SPIO/DOX micelles

The present study examined the cytotoxicity and magnetic resonance imaging (MRI) distribution of cancer-targeted, MRI-visible polymeric micelles that encapsulate doxorubicin (DOX) and superparamagnetic iron oxide (SPIO) and are conjugated with glucose as a targeting ligand. In this study, the micelles were investigated the clinical potential of glucose-micelles, in vitro cytotoxicity assays of nonencapsulating or SPIO-and-DOX-coencapsulating micelles were performed on L929 mouse fibroblasts, and we found that glucose-micelles did not exert in vitro cytotoxic effects. Next, in vitro MRI detectability of glucose SPIO micelles was evaluated at the loaded SPIO content of 2.5% and 50%, and it was found that glucose-micelles can increase MRI relaxivity (r₂*) at high SPIO loading. Furthermore, 50% SPIO micelles persisted in the blood circulation for up to 5 days (slow liver clearance) as determined by in vivo MRI. For in vivo toxicity evaluation, 50% SPIO/DOX micelles at a dose up to 18 (mg DOX)/(kg body weight) showed no impact on animal health according to clinical chemistry and clinical hematology laboratory testing. Altogether, these results indicate that glucose-micelles can serve as an effective and safe drug delivery system.

Designing multifunctional cancer-targeted nanosystem for magnetic resonance molecular imaging-guided theranostics of lung cancer

The integration of diagnosis and therapy is an effective way to improve therapeutic effects for cancer patients, which has acquired widely attentions from researchers. Herein, a multifunctional drug-loaded nanosystem (F/A-PLGA@DOX/SPIO) has been designed and synthesized to reduce the side effects of traditional chemotherapy drugs and realize simultaneous tumor diagnosis and treatment. The surface modification of folic acid (FA) and activatable cell-penetrating peptide (ACPP) endows the nanosystem with excellent cancer targeting capabilities, thus reducing toxicity to normal organs. Besides, the F/A-PLGA@DOX/SPIO nanosystem can serve as an excellent magnetic resonance imaging (MRI) T2-negative contrast agent. More importantly, according to in vitro experiments, the F/A-PLGA@DOX/SPIO nanosystem can promote the overproduction of reactive oxygen species (ROS) within A549 lung cancer cells, inducing cell apoptosis, greatly enhancing the antineoplastic effect. Furthermore, with the help of MRI technology, the targeting imaging of the F/A-PLGA@DOX/SPIO nanosystem within tumors and the dynamic monitoring of medicine efficacy can be realized. Therefore, this study provided a multifunctional drug-loaded F/A-PLGA@DOX/SPIO targeted nanosystem for magnetic resonance molecular imaging-guided theranostics, which has excellent potential for the application in tumor diagnosis and therapy.

Image-Based Analysis of Tumor Localization After Intra-Arterial Delivery of Technetium-99m-Labeled SPIO Using SPECT/CT and MRI

The aim of this study is to evaluate the localization of ^99mTc-labeled dextran-coated superparamagnetic iron oxide (SPIO) nanoparticles to the liver tumor using image-based analysis. We delivered ^99mTc-SPIO intravenously or intra-arterially (IA) with/without Lipiodol to compare the tumor localization by gamma scintigraphy, single-photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI) in a rabbit liver tumor. The gamma and SPECT image-based analysis shows that the uptake ratio of the tumor to the normal liver parenchyma is highest after delivery of ^99mTc-SPIO with Lipiodol IA and that well correlates with the trend of the signal decrease in the liver MRIs. Intra-arterial delivery of SPIO with Lipiodol might be a good drug delivery system targeting the hepatic tumors, as confirmed by image-based analysis.

A comprehensive literatures update of clinical researches of superparamagnetic resonance iron oxide nanoparticles for magnetic resonance imaging

This paper aims to update the clinical researches using superparamagnetic iron oxide (SPIO) nanoparticles as magnetic resonance imaging (MRI) contrast agent published during the past five years. PubMed database was used for literature search, and the search terms were (SPIO OR superparamagnetic iron oxide OR Resovist OR Ferumoxytol OR Ferumoxtran-10) AND (MRI OR magnetic resonance imaging). The literature search results show clinical research on SPIO remains robust, particularly fuelled by the approval of ferumoxytol for intravenously administration. SPIOs have been tested on MR angiography, sentinel lymph node detection, lymph node metastasis evaluation; inflammation evaluation; blood volume measurement; as well as liver imaging. Two experimental SPIOs with unique potentials are also discussed in this review. A curcumin-conjugated SPIO can penetrate brain blood barrier (BBB) and bind to amyloid plaques in Alzheime's disease transgenic mice brain, and thereafter detectable by MRI. Another SPIO was fabricated with a core of Fe3O4 nanoparticle and a shell coating of concentrated hydrophilic polymer brushes and are almost not taken by peripheral macrophages as well as by mononuclear phagocytes and reticuloendothelial system (RES) due to the suppression of non-specific protein binding caused by their stealthy ''brush-afforded'' structure. This SPIO may offer potentials for the applications such as drug targeting and tissue or organ imaging other than liver and lymph nodes.

Dual-Targeting Lactoferrin-Conjugated Polymerized Magnetic Polydiacetylene-Assembled Nanocarriers with Self-Responsive Fluorescence/Magnetic Resonance Imaging for In Vivo Brain Tumor Therapy

Maintaining a high concentration of therapeutic agents in the brain is difficult due to the restrictions of the blood-brain barrier (BBB) and rapid removal from blood circulation. To enable controlled drug release and enhance the blood-brain barrier (BBB)-crossing efficiency for brain tumor therapy, a new dual-targeting magnetic polydiacetylene nanocarriers (PDNCs) delivery system modified with lactoferrin (Lf) is developed. The PDNCs are synthesized using the ultraviolet (UV) cross-linkable 10,12-pentacosadiynoic acid (PCDA) monomers through spontaneous assembling onto the surface of superparamagnetic iron oxide (SPIO) nanoparticles to form micelles-polymerized structures. The results demonstrate that PDNCs will reduce the drug leakage and further control the drug release, and display self-responsive fluorescence upon intracellular uptake for cell trafficking and imaging-guided tumor treatment. The magnetic Lf-modified PDNCs with magnetic resonance imaging (MRI) and dual-targeting ability can enhance the transportation of the PDNCs across the BBB for tracking and targeting gliomas. An enhanced therapeutic efficiency can be obtained using Lf-Cur (Curcumin)-PDNCs by improving the retention time of the encapsulated Cur and producing fourfold higher Cur amounts in the brain compared to free Cur. Animal studies also confirm that Lf targeting and controlled release act synergistically to significantly suppress tumors in orthotopic brain-bearing rats.

Sentinel lymph node identification using superparamagnetic iron oxide particles versus radioisotope: The French Sentimag feasibility trial

BACKGROUND AND OBJECTIVES

The French Sentimag feasibility trial evaluated a new method for the localization of breast cancer sentinel lymph node (SLN) using Sienna+®, superparamagnetic iron oxide particles, and Sentimag® detection in comparison to the standard technique (isotopes ± blue dye).

METHODS

We conducted a prospective multicentric paired comparison trial on 115 patients. SLN localization was performed using both the magnetic technique and the standard method. Detection rate and concordance between magnetic and standard tracers were calculated. Post-operative complications were assessed after 30 days.

RESULTS

Results are based on 108 patients. SLN identification rate was 98.1% [93.5-99.8] for both methods, 97.2% [92.1-99.4] for Sienna+® and 95.4% [89.5-98.5] for standard technique. A mean of 2.1 SLNs per patient was removed. The concordance rate was 99.0% [94.7-100.0%] per patient and 97.4% [94.1-99.2] per node. Forty-six patients (43.4%) had nodal involvement. Among involved SLNs, concordance rate was 97.7% [88.0-99.9] per patient and 98.1% [90.1-100.0] per node.

CONCLUSIONS

This new magnetic tracer is a feasible method and a promising alternative to the isotope. It could offer benefits for ambulatory surgery or sites without nuclear medicine departments. J. Surg. Oncol. 2016;113:501-507. © 2016 Wiley Periodicals, Inc.

Quantitative "Hot Spot" Imaging of Transplanted Stem Cells using Superparamagnetic Tracers and Magnetic Particle Imaging (MPI)

Magnetic labeling of stem cells enables their noninvasive detection by magnetic resonance imaging (MRI). In practical terms, most MRI studies have been limited to the visualization of local engraftment because other sources of endogenous hypointense contrast complicate the interpretation of systemic (whole-body) cell distribution. In addition, MRI cell tracking is inherently nonquantitative in nature. We report herein on the potential of magnetic particle imaging (MPI) as a novel tomographic technique for noninvasive “hot-spot” imaging and quantification of stem cells using superparamagnetic iron oxide (SPIO) tracers. Neural and mesenchymal stem cells, representing small and larger cell bodies, were labeled with 3 different SPIO tracer formulations, including 2 preparations (Feridex and Resovist) that have previously been used in clinical MRI cell-tracking studies. Magnetic particle spectroscopy measurements demonstrated a linear correlation between MPI signal and iron content for both free particles in homogeneous solution and for internalized and aggregated particles in labeled cells over a wide range of concentrations. The overall MPI signal ranged from 1 × 10⁻³ to 3 × 10⁻⁴ Am²/g Fe, which was equivalent to 2 × 10⁻¹⁴ to 1 × 10⁻¹⁵ Am² per cell, indicating that cell numbers can be quantified with MPI analogous to the use of radiotracers in nuclear medicine or fluorine tracers in ¹⁹F MRI. When SPIO-labeled cells were transplanted in the mouse brain, they could be readily detected by MPI at a detection threshold of about 5 × 10⁴ cells, with MPI/MRI overlays showing an excellent agreement between the hypointense MRI areas and MPI hot spots. The calculated tissue MPI signal ratio for 100 000 vs 50 000 implanted cells was 2.08. Hence, MPI can potentially be further developed for quantitative and easy-to-interpret, tracer-based noninvasive cell imaging, preferably with MRI as an adjunct anatomical imaging modality.

Susceptibility-weighted imaging for stem cell visualization in a rat photothrombotic cerebral infarction model

BACKGROUND

In cell therapy, magnetic resonance imaging (MRI) has been used to visualize superparamagnetic iron oxide (SPIO)-labeled stem cells homing to a lesion. Improving traceability is to utilize the sequence that maximizes sensitivity to the susceptibility effect of SPIO.

PURPOSE

To explore the best method by comparing the MRI sequences to visualize mesenchymal stem cells (MSCs) labeled with SPIO.

MATERIAL AND METHODS

Human bone marrow (hBM)-derived MSCs were labeled by internalization of SPIO nanoparticles. In vitro MRI was performed for the SPIO-labeled hBM-MSCs in tubes with T2-weighted (T2W), T2*-weighted (T2*W), and susceptibility-weighted images (SWI). Contrast-to-noise ratio (CNR) and volumes of dark signal of SPIO-labeled hBM-MSCs were obtained on images of each sequence. Photothrombotic cerebral infarction (PTCI) was induced in eight rats, and 2.5 × 10(5) SPIO-labeled hBM-MSCs were infused through the tail vein on the third day. In vivo MRI of the rat brain was performed using a 3.0 T MRI on the first, third, seventh, and 14th days. CNRspio was obtained on T2W imaging, T2*W imaging, and SWI. The dark signals were compared with the SPIO-positive cells of Prussian blue staining.

RESULTS

In vitro MRI of 5 × 10(5) SPIO-labeled hBM-MSCs showed the CNR and volume of dark signal to be 63, 517 mm(3) in SWI, 41, 228 mm(3) in T2*W imaging, and 56, 41 mm(3) in T2W imaging, respectively. In vivo MRI showed a dark signal surrounding the high signal intensity of PTCI. Pathologically, the dark signals were matched with SPIO-labeled hBM-MSC in the corresponding rat. The dark signal was most prominent in SWI, then T2*W imaging, and finally in T2W imaging (P <0.05). In SWI, other causes of dark signals were matched with the veins and the choroid plexuses on histopathology.

CONCLUSION

SWI can visualize SPIO-labeled hBM-MSCs more sensitively, earlier, and with larger size and greater contrast than T2W imaging and T2*W imaging.

Efficient In vitro labeling rabbit bone marrow-derived mesenchymal stem cells with SPIO and differentiating into neural-like cells

Mesenchymal stem cells (MSCs) can differentiate into neural cells to treat nervous system diseases. Magnetic resonance is an ideal means for cell tracking through labeling cells with superparamagnetic iron oxide (SPIO). However, no studies have described the neural differentiation ability of SPIO-labeled MSCs, which is the foundation for cell therapy and cell tracking in vivo. Our results showed that bone marrow-derived mesenchymal stem cells (BM-MSCs) labeled in vitro with SPIO can be induced into neural-like cells without affecting the viability and labeling efficiency. The cellular uptake of SPIO was maintained after labeled BM-MSCs differentiated into neural-like cells, which were the basis for transplanted cells that can be dynamically and non-invasively tracked in vivo by MRI. Moreover, the SPIO-labeled induced neural-like cells showed neural cell morphology and expressed related markers such as NSE, MAP-2. Furthermore, whole-cell patch clamp recording demonstrated that these neural-like cells exhibited electrophysiological properties of neurons. More importantly, there was no significant difference in the cellular viability and [Ca(2+)]i between the induced labeled and unlabeled neural-like cells. In this study, we show for the first time that SPIO-labeled MSCs retained their differentiation capacity and could differentiate into neural-like cells with high cell viability and a good cellular state in vitro.

Diagnostic accuracy of MR imaging to identify and characterize focal liver lesions: comparison between gadolinium and superparamagnetic iron oxide contrast media

To compare the diagnostic value of gadolinium (Gd) and ultrasmall superparamagnetic iron oxide (SPIO) contrast media for characterization of focal liver lesions (FLL), we retrospectively evaluated the results of magnetic resonance (MR) imaging in 68 patients (40 M, 28 F, age from 22 to 81 yrs) of which 36 with diagnosis of colo-rectal cancer, 26 with hepatic cirrhosis and 6 with incidental imaging detection of FLL. MR (Gyroscan Intera 1.5 T, Philips Medical Systems) study was performed using T1 and T2 fast-field-echo (FFE) and T2 turbo-spin-echo (TSE) sequences in axial and coronal views. Dynamic multi-phases gadolinium Gd-enhanced T1-FFE-Bh images were obtained in arterial, portal and equilibrium phases, followed by SPIO-enhanced T2-FFE scans. A qualitative analysis of pre- and post-contrast MR images to classify FLL as benign or malignant was performed using a 3-point scoring system: 0= benign; 1= suspicious for malignancy; 2= malignant. A total of 118 lesions were evaluated. In particular, histology (n=18), cytology (n=14) or clinical-imaging follow-up data (n=86) demonstrated 4 adenomas, 29 cysts, 3 focal steatosis, 25 hemangiomas, 1 focal vascular abnormality, 5 fibrotic lesions as well as 13 regenerative nodules, 6 dysplastic, 14 hepatocellular carcinomas (HCC), 17 metastasis and 1 cholangiocarcinoma. For MR imaging, diagnostic accuracy, sensitivity, specificity, positive (PPV) and negative (NPV) predictive values of Gd vs. SPIO images were respectively 83% vs. 92%, 79% vs. 74%, 85% vs. 99% (P=0.002), 68% vs. 96% (P=0.005) and 91% vs. 90%, respectively. The results suggest that SPIO-MR provides a diagnostic incremental value, as specificity and PPV, particularly to characterize FLL compared to Gd-MR; thus, we strongly recommend the use of SPIO when liver lesion characterization is requested and Gd images are uncertain.

Ternary hybrid nanocomposites for gene delivery and magnetic resonance imaging of hepatocellular carcinoma cells

This paper describes comparative studies in magnetic resonance imaging (MRI) and gene deliveries toward hepatocellular carcinoma (HCC) HepG2 cells with ternary composites that consist of superparamagnetic iron oxide (SPIO) nanoparticles (NPs) (8-10 nm) with deferoxamine coating, circular plasmid DNA (~4 kb) equipped with green fluorescent probe, and branched polyethylenimine (PEI) (25 kDa, PDI 2.5). The packaging of the ternary complexes has been characterized by agarose gel retardation assay. By tuning the PEI/NP ratios and with a fixed DNA amount, different ternary composites have been employed for NP/gene transfection towards HepG2 cells, which have been characterized by in vitro MRI and green fluorescence protein (GFP) fluorescence.