You have accessJournal of UrologyImaging/Radiology: Uroradiology II1 Apr 2015MP11-19 MAGNETIC RESONANCE VISIBILITY OF IRON LABELED MESENCHYMAL STEM CELLS FOR ENDOSCOPIC INJECTION INTO THE PORCINE URETHRAL SPHINCTER Susanne Will, Karl-Dietrich Sievert, Martin Vaegler, Petros Martirosian, Frank Eibofner, Fritz Schick, Jörg Schmehl, Gerd Grözinger, Rüdiger Bantleon, Konstantin Nikolaou, and Ulrich Kramer Susanne WillSusanne Will More articles by this author , Karl-Dietrich SievertKarl-Dietrich Sievert More articles by this author , Martin VaeglerMartin Vaegler More articles by this author , Petros MartirosianPetros Martirosian More articles by this author , Frank EibofnerFrank Eibofner More articles by this author , Fritz SchickFritz Schick More articles by this author , Jörg SchmehlJörg Schmehl More articles by this author , Gerd GrözingerGerd Grözinger More articles by this author , Rüdiger BantleonRüdiger Bantleon More articles by this author , Konstantin NikolaouKonstantin Nikolaou More articles by this author , and Ulrich KramerUlrich Kramer More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2015.02.400AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES To improve the muscles of the urethral sphincter, different aspects of cell-based treatments should be investigated. Local injection of therapeutic mesenchymal stem cells (MSC) has been proved as a promising approach for tissue regeneration. The aim of this study was to evaluate the effects of superparamagnetic iron oxide (SPIO) cell labeling on the visualization of therapeutic MSC and validate in vitro and in vivo using mini-pig animal models. After injection into the porcine urethral sphincter, the labeled cells were monitored up to six months using MRI. METHODS MSC were labeled with SPIO particles for analysis of migration and viability. Phantom MR measurements were performed in order to evaluate labeling effects. For short and long term studies, iron labeled MSCs were endoscopically injected into the porcine urethral sphincter and monitored on a 3T MRI scanner. The animals were examined three weeks, three and six months after MSC injection. High resolution anatomical images of the urethral sphincter were measured to detect SPIO particles using a fast-spin-echo sequence. A gradient echo sequence with multiple echo times was utilized to visually identify and verify locations of iron particles. The distribution of injected cells was then correlated with histological findings (see Figure). RESULTS Functional analysis of cell parameters after iron labeling showed no effects on proliferation and differentiation of the cells. The adherence increased with a higher iron dose, and the ability to migrate decreased presumably the effect of iron labeling. Measurements of the sphincter muscle in the mini-pig clearly demonstrated visible iron deposits inside the sphincter muscle. Additionally, iron depositions could be verified in all time periods after stem cell injection. The comparison of MRI and tissue sections illustrated preeminent correlation of location and dilatation of iron depots. CONCLUSIONS SPIO-labeled MSC injection into the porcine urethral sphincter and subsequent evaluation with highly resolved MR data acquisition allows sensitive tracking of MSC for several months without any biological effects. Against common knowledge iron deposits within the cells were detectable and correlated histologically even six months after injection. © 2015 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 193Issue 4SApril 2015Page: e126-e127 Advertisement Copyright & Permissions© 2015 by American Urological Association Education and Research, Inc.Metrics Author Information Susanne Will More articles by this author Karl-Dietrich Sievert More articles by this author Martin Vaegler More articles by this author Petros Martirosian More articles by this author Frank Eibofner More articles by this author Fritz Schick More articles by this author Jörg Schmehl More articles by this author Gerd Grözinger More articles by this author Rüdiger Bantleon More articles by this author Konstantin Nikolaou More articles by this author Ulrich Kramer More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Purpose: To evaluate the distribution of superparamagnetic iron oxide (SPIO)-labeled cells in a perfused segment of a porcine artery and to estimate the number of adherent cells by means of magnetic resonance (MR) imaging.Materials and Methods: Six vessel specimens (diameters between 0.8 and 1.2 cm) were placed in a bioreactor system, and 2 x 10(4) to 1 x 10(6) SPIO-labeled endothelial colony-forming cells were injected into the artery within the perfused reactor. The area of resulting signal extinctions at the inner wall of the vessels was quantified on MR iniages by using a high-resolution T2*-weighted sequence with a slice-by-slice approach. After imaging, the labeled cells were quantified histologically.Results: The total iron load of each cell was 56.5 pg +/- 14.4. In the applied range of 2 x 10(4) to 1 x 10(6) cells per vessel, the area of iron-induced signal extinction at the vessel wall on T2*-weighted imaging corresponded to the histologically detected cell 1 number (r 0.98, P < .001).Conclusions: A correlation between the area of signal extinction and the number of labeled cells at-the vessel wall was found. This might help to evaluate dose rates in. further clinical applications of intravascalar cell-based therapies.

To evaluate and compare artefact configuration and diameters in a magnetic resonance (MR)-compatible prototype microwave (MW) applicator and a standard MR-compatible radiofrequency (RF) applicator for MR-guided tumour ablation.

Direct stem cell therapies for functionally impaired tissue require a sufficient number of cells in the target region and a method for verifying the fate of the cells in the subsequent time course. In vivo MRI of iron labeled mesenchymal stem cells has been suggested to comply with these requirements. The study was conducted to evaluate proliferation, migration, differentiation and adhesion effects as well as the obtained iron load of an iron labeling strategy for mesenchymal stem cells. After injection into the porcine urethral sphincter, the labeled cells were monitored for up to six months using MRI.Mesenchymal stem cells were labeled with ferucarbotran (60/100/200 µg/mL) and ferumoxide (200 µg/mL) for the analysis of migration and viability. Phantom MR measurements were made to evaluate effects of iron labeling. For short and long term studies, the iron labeled cells were injected into the porcine urethral sphincter and monitored by MRI. High resolution anatomical images of the porcine urethral sphincter were applied for detection of the iron particles with a turbo‐spin‐echo sequence and a gradient‐echo sequence with multiple TE values. The MR images were then compared with histological staining.The analysis of cell function after iron labeling showed no effects on proliferation or differentiation of the cells. Although the adherence increases with higher iron dose, the ability to migrate decreases as a presumed effect of iron labeling.The iron labeled mesenchymal stem cells were detectable in vivo in MRI and histological staining even six months after injection.Labeling with iron particles and subsequent evaluation with highly resolved three dimensional data acquisition allows sensitive tracking of cells injected into the porcine urethral sphincter for several months without substantial biological effects on mesenchymal stem cells. Copyright © 2015 John Wiley & Sons, Ltd.

Objective: On a 3-T magnetic resonance scanner, morphologic and perfusion changes of 9 patients with rheumatoid arthritis were evaluated after start of anti-interleukin 6 receptor antibody Tocilizumab (TCZ) treatment.Methods: Morphologic and perfusion-based magnetic resonance imaging (MRI) parameters were assessed before and 4, 12, and 24 after the start of TCZ treatment. Furthermore, serologic biomarkers and clinical assessment scores were evaluated 4, 12, 24, and 52 weeks after treatment initiation.Results: Results of MRI parameters showed significant group differences between responders and nonresponders for synovial volume, transfer constant, and blood plasma volume fraction already at week 12 as well as relative enhancement and rate of early enhancement at week 24.Conclusions: Considering the temporal change of perfusion-derived MRI parameters (transfer constant, blood plasma volume fraction, relative enhancement, and rate of early enhancement) as well as morphologic MRI parameters (synovial volume measurements), a quantifiable assessment of response to TCZ therapy in rheumatoid arthritis seems possible at an even earlier time point compared with clinical assessment scores, whereas serologic biomarkers proved nonspecific in this respect.

PURPOSE:In interventional magnetic resonance imaging, instruments can be equipped with conducting wires for visualization by current application. The potential of sequence triggered application of transient direct currents in balanced steady-state free precession (bSSFP) imaging is demonstrated.METHODS:A conductor and a modified catheter were examined in water phantoms and in an ex vivo porcine liver. The current was switched by a trigger pulse in the bSSFP sequence in an interval between radiofrequency pulse and signal acquisition. Magnitude and phase images were recorded. Regions with transient field alterations were evaluated by a postprocessing algorithm. A phase mask was computed and overlaid with the magnitude image.RESULTS:Transient field alterations caused continuous phase shifts, which were separated by the postprocessing algorithm from phase jumps due to persistent field alterations. The overlaid images revealed the position of the conductor. The modified catheter generated visible phase offset in all orientations toward the static magnetic field and could be unambiguously localized in the ex vivo porcine liver.CONCLUSIONS:The application of a sequence triggered, direct current in combination with phase imaging allows conspicuous localization of interventional devices with a bSSFP sequence.

Purpose: Instrument visualization in interventional magnetic resonance imaging (MRI) is commonly performed via susceptibility artifacts. Unfortunately, this approach suffers from limited conspicuity in inhomogeneous tissue and disturbed spatial encoding. Also, susceptibility artifacts are controllable only by sequence parameters. This work presents the basics of a new visualization method overcoming such problems by applying sequence-triggered direct current (DC) pulses in spin-echo (SE) imaging. SE phase images allow for background free current path localization.Methods: Application of a sequence-triggered DC pulse in SE imaging, e. g., during a time period between radiofrequency excitation and refocusing, results in transient field inhomogeneities. Dependent on the additional z-magnetic field from the DC, a phase offset results despite the refocusing pulse. False spatial encoding is avoided by DC application during periods when read-out or slice-encoding gradients are inactive. A water phantom containing a brass conductor (water equivalent susceptibility) and a titanium needle (serving as susceptibility source) was used to demonstrate the feasibility. Artifact dependence on current strength and orientation was examined.Results: Without DC, the brass conductor was only visible due to its water displacement. The titanium needle showed typical susceptibility artifacts. Applying triggered DC pulses, the phase offset of spins near the conductor appeared. Because SE phase images are homogenous also in regions of persistent field inhomogeneities, the position of the conductor could be determined with high reliability. Artifact characteristic could be easily controlled by amperage leaving sequence parameters unchanged. For an angle of 30. between current and static field visualization was still possible.Conclusions: SE phase images display the position of a conductor carrying pulsed DC free from artifacts caused by persistent field inhomogeneities. Magnitude and phase images are acquired simultaneously under the same conditions without the use of extra measurement time. The presented technique offers many advantages for precise instrument localization in interventional MRI. (C) 2014 American Association of Physicists in Medicine.

One major source affecting the precision of bone structure analysis in quantitative magnetic resonance imaging (qMRI) is inter- and intraoperator variability, inherent in delineating and tracing regions of interest along longitudinal studies. In this paper an automated analysis tool, featuring bone marrow segmentation, region of interest generation, and characterization of cancellous bone of articular joints is presented. In evaluation studies conducted at the knee joint the novel analysis tool significantly decreased the standard error of measurement and improved the sensitivity in detecting minor structural changes. It further eliminated the need of time-consuming user interaction, and thereby increasing reproducibility.

A technique for generation of positive contrast near susceptibility alterations utilizing echo‐shifts in k‐space is introduced, based on altered Larmor‐frequencies and resulting phase‐shifts accumulating during the echo‐time at the site of local magnetic field gradients. 3D gradient‐echo raw‐data is acquired and weighted with an inverse Hanning filter. The filter partly suppresses central raw‐data points, while maintaining outer areas. Reconstruction of the filtered raw‐data results in images where pixels with apparent magnetic field gradients are highlighted against homogeneous pixels. Further processing steps are introduced to remove remaining intensities in the homogeneous parts of the filtered image. Feasibility is shown by an agar phantom containing magnetically labeled cells, with concentrations of 25, 50, 100, and 250 cells/μL, and by images of the human head. The technique allows detection of echo‐shifted pixels with automatic suppression of magnetically homogeneous parts while keeping post‐processing time short. Fewer than four labeled cells per pixel were clearly displayed with positive contrast. Application to the human head shows bright veins and complete suppression of homogeneous regions. The presented technique has high potential for specific detection of low concentrations of labeled cells or susceptibility altered regions in vivo with positive contrast, whereas areas with low spin density are not highlighted. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.

PURPOSE:State of the art to access radiofrequency (RF) heating near implants is computer modeling of the devices and solving Maxwell's equations for the specific setup. For a set of input parameters, a fixed result is obtained. This work presents a theoretical approach in the alternating current (ac) limit, which can potentially render closed formulas for the basic behavior of tissue heating near metallic structures. Dedicated experiments were performed to support the theory.METHODS:For the ac calculations, the implant was modeled as an RLC parallel circuit, with L being the secondary of a transformer and the RF transmission coil being its primary. Parameters influencing coupling, power matching, and specific absorption rate (SAR) were determined and formula relations were established. Experiments on a copper ring with a radial gap as capacitor for inductive coupling (at 1.5 T) and on needles for capacitive coupling (at 3 T) were carried out. The temperature rise in the embedding dielectric was observed as a function of its specific resistance using an infrared (IR) camera.RESULTS:Closed formulas containing the parameters of the setup were obtained for the frequency dependence of the transmitted power at fixed load resistance, for the calculation of the resistance for optimum power transfer, and for the calculation of the transmitted power in dependence of the load resistance. Good qualitative agreement was found between the course of the experimentally obtained heating curves and the theoretically determined power curves. Power matching revealed as critical parameter especially if the sample was resonant close to the Larmor frequency.CONCLUSIONS:The presented ac approach to RF heating near an implant, which mimics specific values for R, L, and C, allows for closed formulas to estimate the potential of RF energy transfer. A first reference point for worst-case determination in MR testing procedures can be obtained. Numerical approaches, necessary to determine spatially resolved heating maps, can be supported.

Superparamagnetic iron oxide particles can be utilized to label cells for immune cell and stem cell therapy. The labeled cells cause significant field distortions induced in their vicinity, which can be detected with magnetic resonance imaging (MRI). In conventional imaging, the signal voids arising from the field distortions lead to negative contrast, which is not desirable, as detection of the cells can be masked by native low signal tissue. In this work, a new method for visualizing magnetically labeled cells with positive contrast is proposed and described. The technique presented is based on the susceptibility-weighted imaging (SWI) post-processing algorithm. Phase images from gradient-echo sequences are evaluated pixel by pixel, and a mask is created with values ranging from 0 to 1, depending on the phase value of the pixel. The magnitude image is then multiplied by the mask. With an appropriate mask function, positive contrast in the vicinity of the labeled cells is created. The feasibility of this technique is proved using an agar phantom containing superparamagnetic iron oxide particles-labeled cells and an ex vivo bovine liver. The results show high potential for detecting even small labeled cell concentrations in structurally inhomogeneous tissue types.

BACKGROUND:For clinical applications of mesenchymal stem cells (MSCs), labeling and tracking is crucial to evaluate cell distribution and homing. Magnetic resonance imaging (MRI) has been successfully established detecting MSCs labeled with superparamagnetic particles of iron oxide (SPIO). Despite initial reports that labeling of MSCs with SPIO is safe without affecting the MSC's biology, recent studies report on influences of SPIO-labeling on metabolism and function of MSCs. Exposition of cells and tissues to high magnetic fields is the functional principle of MRI. In this study we established innovative labeling protocols for human MSCs using clinically established SPIO in combination with magnetic fields and investigated on functional effects (migration assays, quantification of colony forming units, analyses of gene and protein expression and analyses on the proliferation capacity, the viability and the differentiation potential) of magnetic fields on unlabeled and labeled human MSCs. To evaluate the imaging properties, quantification of the total iron load per cell (TIL), electron microscopy, and MRI at 3.0 T were performed.RESULTS:Human MSCs labeled with SPIO permanently exposed to magnetic fields arranged and grew according to the magnetic flux lines. Exposure of MSCs to magnetic fields after labeling with SPIO significantly enhanced the TIL compared to SPIO labeled MSCs without exposure to magnetic fields resulting in optimized imaging properties (detection limit: 1,000 MSCs). Concerning the TIL and the imaging properties, immediate exposition to magnetic fields after labeling was superior to exposition after 24 h. On functional level, exposition to magnetic fields inhibited the ability of colony formation of labeled MSCs and led to an enhanced expression of lipoprotein lipase and peroxisome proliferator-activated receptor-gamma in labeled MSCs under adipogenic differentiation, and to a reduced expression of alkaline phosphatase in unlabeled MSCs under osteogenic differentiation as detected by qRT-PCR. Moreover, microarray analyses revealed that exposition of labeled MSCs to magnetic fields led to an up regulation of CD93 mRNA and cadherin 7 mRNA and to a down regulation of Zinc finger FYVE domain mRNA. Exposition of unlabeled MSCs to magnetic fields led to an up regulation of CD93 mRNA, lipocalin 6 mRNA, sialic acid acetylesterase mRNA, and olfactory receptor mRNA and to a down regulation of ubiquilin 1 mRNA. No influence of the exposition to magnetic fields could be observed on the migration capacity, the viability, the proliferation rate and the chondrogenic differentiation capacity of labeled or unlabeled MSCs.CONCLUSIONS:In our study an innovative labeling protocol for tracking MSCs by MRI using SPIO in combination with magnetic fields was established. Both, SPIO and the static magnetic field were identified as independent factors which affect the functional biology of human MSCs. Further in vivo investigations are needed to elucidate the molecular mechanisms of the interaction of magnetic fields with stem cell biology.