Wolfhard Semmler

Publications of Wolfhard Semmler

• Two eyes see more than one: double echo stereoscopic MRA for rapid 3D visualization of vascular structures.

  Authors: Alexander Brunner, Florian Maier, Axel Joachim Krafft, Wolfhard Semmler, Michael Bock

  Magma (New York, N.Y.). 04/2012;

  OBJECT: A three-dimensional (3D) visualization of the target region during intravascular interventions in real-time is challenging since the acquisition of a time-consuming 3D dataset is required. InOBJECT: A three-dimensional (3D) visualization of the target region during intravascular interventions in real-time is challenging since the acquisition of a time-consuming 3D dataset is required. In this work, a novel stereoscopic double echo sequence for achieving 3D depth perception by sampling only two oblique projection images is presented. MATERIALS AND METHODS: A double echo (DE) FLASH pulse sequence was developed to acquire continuously stereoscopic image pairs of the vascular target anatomy. Stereo image data were displayed on a stereoscopic 3D LCD monitor in real time after image reconstruction. Phantom experiments followed by a depth perception test were performed to assess the usability of the stereo image pairs for 3D visualization. In an animal experiment the sequence was tested in vivo and was compared with a slower interleaved (IL) sequence variant. RESULTS: In the phantom experiments an SNR difference of 6 % between left and right image was found which did not influence the depth perception. The DE acquisition was superior to the IL sequence (SNR(DE) = 10.3, 2.3 images/s over SNR(IL) = 7.1, 1.7 images/s), and during contrast enhancement the abdominal arterial vasculature was clearly perceived as a 3D structure. CONCLUSION: A novel stereoscopic DE pulse sequence can be utilized for the fast 3D stereoscopic visualization of vascular structures in real-time.

• Coaxial waveguide MRI.

  Authors: Stefan Alt, Marco Müller, Reiner Umathum, Armin Bolz, Peter Bachert, Wolfhard Semmler, Michael Bock

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 04/2012; 67(4):spcone.

  Field distributions of the simulation with the virtual family phantom. The SAR distribution through the center of the body is shown in (a). Exposure is almost completely concentrated in the imagingField distributions of the simulation with the virtual family phantom. The SAR distribution through the center of the body is shown in (a). Exposure is almost completely concentrated in the imaging gap. The excitation field B +1 is shown within two coronal slices through the body (b,c). The central signal void is seen in (c), while the other slices show a more homogeneous field distribution. In (d) the region indicated in (c) is magnified and the energy flux depicted by the Poynting vectors is shown.While the energy flows in propagation direction near the edge of the conductor, it bends toward the body surfaces near the phantom from the article by Alt et al (pp 1173-1182).

• Lung ventilation- and perfusion-weighted Fourier decomposition magnetic resonance imaging: In vivo validation with hyperpolarized (3) He and dynamic contrast-enhanced MRI

  Authors: Grzegorz Bauman, Alexander Scholz, Julien Rivoire, Maxim Terekhov, Janet Friedrich, Andre de Oliveira, Wolfhard Semmler, Laura Maria Schreiber, Michael Puderbach

  Magnetic Resonance in Medicine. 03/2012;

  The purpose of this work was to validate ventilation-weighted (VW) and perfusion-weighted (QW) Fourier decomposition (FD) magnetic resonance imaging (MRI) with hyperpolarized (3) He MRI and dynamicThe purpose of this work was to validate ventilation-weighted (VW) and perfusion-weighted (QW) Fourier decomposition (FD) magnetic resonance imaging (MRI) with hyperpolarized (3) He MRI and dynamic contrast-enhanced perfusion (DCE) MRI in a controlled animal experiment. Three healthy pigs were studied on 1.5-T MR scanner. For FD MRI, the VW and QW images were obtained by postprocessing of time-resolved lung image sets. DCE acquisitions were performed immediately after contrast agent injection. (3) He MRI data were acquired following the administration of hyperpolarized helium and nitrogen mixture. After baseline MR scans, pulmonary embolism was artificially produced. FD MRI and DCE MRI perfusion measurements were repeated. Subsequently, atelectasis and air trapping were induced, which followed with FD MRI and (3) He MRI ventilation measurements. Distributions of signal intensities in healthy and pathologic lung tissue were compared by statistical analysis. Images acquired using FD, (3) He, and DCE MRI in all animals before the interventional procedure showed homogeneous ventilation and perfusion. Functional defects were detected by all MRI techniques at identical anatomical locations. Signal intensity in VW and QW images was significantly lower in pathological than in healthy lung parenchyma. The study has shown usefulness of FD MRI as an alternative, noninvasive, and easily implementable technique for the assessment of acute changes in lung function.

• Synthesis and in vitro evaluation of (68)Ga-DOTA-4-FBn-TN14003, a novel tracer for the imaging of CXCR4 expression.

  Authors: Ute Hennrich, Lisa Seyler, Martin Schäfer, Ulrike Bauder-Wüst, Michael Eisenhut, Wolfhard Semmler, Tobias Bäuerle

  Bioorganic & medicinal chemistry. 02/2012; 20(4):1502-10.

  The expression of the chemokine receptor CXCR4 in tumors is associated with tumor aggressiveness and poor prognosis for the patient and contributes to metastatic seeding. Therefore it is of highThe expression of the chemokine receptor CXCR4 in tumors is associated with tumor aggressiveness and poor prognosis for the patient and contributes to metastatic seeding. Therefore it is of high interest to find a specific PET tracer for the imaging of CXCR4 expression in tumors. The aim of this study was the synthesis, (68)Ga labeling and first evaluation of DOTA-4-FBn-TN14003 as a potential PET tracer for this purpose. DOTA-4-FBn-TN14003 was synthesized using solid phase peptide synthesis and radiolabeling of this versatile precursor was performed with (68)Ga, which was obtained from a (68)Ge/(68)Ga generator. (68)Ga-DOTA-4-FBn-TN14003 was reproducibly obtained in isolated radiochemical yields of 72.5±4.9% with an excellent radiochemical purity of >99.5%. Specific activities of up to 29.8±3.1GBq/μmol were achieved. In competition binding assays with SDF-1α, human T cell lymphoma Jurkat cells expressed high levels of CXCR4 whereas human breast cancer MDA-MB-231 cells expressed significantly lower levels of this chemokine receptor. The inhibition constants (IC(50)) of Ga-DOTA-4-FBn-TN14003 and 4-FBn-TN14003 to CXCR4 were determined in a competition assay against (125)I-SDF-1α using Jurkat as well as MDA-MB-231 cells. The IC(50) values of Ga-DOTA-4-FBn-TN14003 (1.99±0.31nM) and 4-FBn-TN14003 (4.07±1.00nM) proved to be comparable, indicating negligible influence of the metal complex. These results suggest (68)Ga-DOTA-4-FBn-TN14003 as a promising agent for the imaging of CXCR4 expression in tumors and metastases.

• Monitoring Molecular, Functional and Morphologic Aspects of Bone Metastases Using Non-Invasive Imaging.

  Authors: Tobias Bäuerle, Dorde Komljenovic, Wolfhard Semmler

  Current pharmaceutical biotechnology. 01/2012;

  Bone is among the most common locations of metastasis and therefore represents an important clinical target for diagnostic follow-up in cancer patients. In the pathogenesis of bone metastases,Bone is among the most common locations of metastasis and therefore represents an important clinical target for diagnostic follow-up in cancer patients. In the pathogenesis of bone metastases, disseminated tumor cells proliferating in bone interact with the local microenvironment stimulating or inhibiting osteoclast and osteoblast activity. Non-invasive imaging methods monitor molecular, functional and morphologic changes in both compartments of these skeletal lesions - the bone and the soft tissue tumor compartment. In the bone compartment, morphologic information on skeletal destruction is assessed by computed tomography (CT) and radiography. Pathogenic processes of osteoclast and osteoblast activity, however, can be imaged using optical imaging, positron emission tomography (PET), single photon emission CT (SPECT) and skeletal scintigraphy. Accordingly, conventional magnetic resonance imaging (MRI) and CT as well as diffusion-weighted MRI and optical imaging are used to assess morphologic aspects on the macroscopic and cellular level of the soft tissue tumor compartment. Imaging methods such as PET, MR spectroscopy, dynamic contrast-enhanced techniques and vessel size imaging further elucidate on pathogenic processes in this compartment including information on metabolism and vascularization. By monitoring these aspects in bone lesions, new insights in the pathogenesis of skeletal metastases can be gained. In translation to the clinical situation, these novel methods for the monitoring of bone metastases might be applied in patients to improve follow-up of these lesions, in particular after therapeutic intervention. This review summarizes established and experimental imaging techniques for the monitoring of tumor and bone cell activity including molecular, functional and morphological aspects in bone metastases.

• Response.

  Authors: Angela Heinrich, Anne Szostek, Frauke Nees, Patric Meyer, Herta Flor, Wolfhard Semmler

  Journal of magnetic resonance imaging : JMRI. 01/2012; 35(1):237.

• A novel PET tracer for the imaging of αvβ3 and αvβ5 integrins in experimental breast cancer bone metastases.

  Authors: Ute Mühlhausen, Dorde Komljenovic, Maren Bretschi, Karin Leotta, Michael Eisenhut, Wolfhard Semmler, Tobias Bäuerle

  Contrast media & molecular imaging. 11/2011; 6(6):413-20.

  The aim of this study was the evaluation of (68)Ga-DOTA-E-[c(RGDfK)](2) as a novel PET tracer to image αvβ3 and αvβ5 integrins. For this purpose, DOTA-E-[c(RGDfK)](2) was labeled with (68)Ga, whichThe aim of this study was the evaluation of (68)Ga-DOTA-E-[c(RGDfK)](2) as a novel PET tracer to image αvβ3 and αvβ5 integrins. For this purpose, DOTA-E-[c(RGDfK)](2) was labeled with (68)Ga, which was obtained from a (68)Ge/(68)Ga generator, purified by solid-phase extraction and the radiochemical purity analyzed by radio-RP-HPLC. (68) Ga-DOTA-E-[c(RGDfK)](2) was obtained reproducibly in radiochemical yields of 60 ± 6% and with an excellent radiochemical purity of >99%. In nude rats bearing bone metastases after injection of MDA-MB-231 human breast cancer cells, biodistribution studies were performed to evaluate the accumulation of the radiotracer in selected organs, blood and bone metastases 0.5, 1, 2 and 3 h post injection. A rapid uptake into the bone metastases and rapid blood clearance was observed, resulting in tumor-blood ratios of up to 26.6 (3 h post injection) and tumor-muscle ratios of up to 7.9 (3 h post injection). A blocking experiment with coinjected αvβ3/αvβ5 antagonist showed the tumor uptake to be receptor-specific. In an initial in vivo micro PET evaluation of the tracer using the same animal model, the bone metastasis was clearly visualized. These results suggest that (68)Ga-DOTA-E-[c(RGDfK)](2) is a promising PET tracer suitable for the imaging of αvβ3 and αvβ5 integrins in bone metastases. This novel PET tracer should be further evaluated concerning its usefulness for early detection of bone metastases and monitoring treatment response of these lesions.

• Coaxial waveguide MRI.

  Authors: Stefan Alt, Marco Müller, Reiner Umathum, Armin Bolz, Peter Bachert, Wolfhard Semmler, Michael Bock

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 10/2011;

  As ultrahigh-field MR imaging systems suffer from the standing wave problems of conventional coil designs, the use of antenna systems that generate travelling waves was suggested. As a modificationAs ultrahigh-field MR imaging systems suffer from the standing wave problems of conventional coil designs, the use of antenna systems that generate travelling waves was suggested. As a modification to the original approach, we propose the use of a coaxial waveguide configuration with interrupted inner conductor. This concept can focus the radiofrequency energy to the desired imaging region in the human body and can operate at different Larmor frequencies without hardware modifications, as it is not limited by a lower cut-off frequency. We assessed the potential of the method with a hardware prototype setup that was loaded with a tissue equivalent phantom and operated with imaging areas of different size. Signal and flip angle distributions within the phantom were analyzed, and imaging at different Larmor frequencies was performed. Results were compared to a finite difference time domain simulation of the setup that additionally provides information on the spatial distribution of the specific absorption rate load. Furthermore, simulation results with a human model (virtual family) are presented. It was found that the proposed method can be used for MRI at multiple frequencies, achieving transmission efficiencies similar to other travelling wave approaches but still suffers from several limitations due to the used mode of wave propagation. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.

• Advanced fit of the diffusion kurtosis tensor by directional weighting and regularization.

  Authors: Tristan A Kuder, Bram Stieltjes, Peter Bachert, Wolfhard Semmler, Frederik B Laun

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 08/2011;

  The diffusional kurtosis is an indicator for diffusion restrictions in biological tissue. It is observed experimentally that the kurtosis is largest for directions perpendicular to the fiberThe diffusional kurtosis is an indicator for diffusion restrictions in biological tissue. It is observed experimentally that the kurtosis is largest for directions perpendicular to the fiber direction in white matter. The directional dependence of the kurtosis can be described by the diffusion kurtosis tensor. Since the intention of diffusion kurtosis imaging is to detect diffusion restrictions, the fit of the kurtosis tensor should be dominated by directions perpendicular to the fibers. In this work, it is shown that the basic approach, which is solving the occurring linear system by a pseudoinverse matrix, may completely fail in this regard if the diffusion is highly anisotropic. This problem is solved by adapting the weights of the fit-and thus emphasizing directions of restricted water motion-using a direct fit of the kurtosis tensor to the measured kurtosis values. Moreover, due to its large number of degrees of freedom, the kurtosis tensor can assume complicated shapes resulting in a fit which is sensitive to noise. This article demonstrates that the quality of the kurtosis tensor calculation can be further improved if the fit is regularized by suppressing too large and too small kurtosis tensor values and thus restricting the possible tensor shapes. Magn Reson Med, 2011. © 2011 Wiley-Liss, Inc.

• Determination of the defining boundary in nuclear magnetic resonance diffusion experiments.

  Authors: Frederik Bernd Laun, Tristan Anselm Kuder, Wolfhard Semmler, Bram Stieltjes

  Physical review letters. 07/2011; 107(4):048102.

  While nuclear magnetic resonance diffusion experiments are widely used to resolve structures confining the diffusion process, it has been elusive whether they can exactly reveal these structures.While nuclear magnetic resonance diffusion experiments are widely used to resolve structures confining the diffusion process, it has been elusive whether they can exactly reveal these structures. This question is closely related to x-ray scattering and to Kac's "hear the drum" problem. Although the shape of the drum is not "hearable," we show that the confining boundary of closed pores can indeed be detected using modified Stejskal-Tanner magnetic field gradients that preserve the phase information and enable imaging of the average pore in a porous medium with a largely increased signal-to-noise ratio.

• MR safety: simultaneous B0, dΦ/dt, and dB/dt measurements on MR-workers up to 7 T.

  Authors: Jens Groebner, Reiner Umathum, Michael Bock, Axel J Krafft, Wolfhard Semmler, Jaane Rauschenberg

  Magma (New York, N.Y.). 07/2011; 24(6):315-22.

  The EU directive on safety requirements (2004/40/EC) limits the exposure to time varying magnetic fields to dB /dt=200 mT/s. This action value is not clearly defined as it considers only the temporalThe EU directive on safety requirements (2004/40/EC) limits the exposure to time varying magnetic fields to dB /dt=200 mT/s. This action value is not clearly defined as it considers only the temporal change of the magnitude of B. Thus, only the translational motion in the magnet's fringe field is considered and rotations are neglected. A magnetic field probe was constructed to simultaneously record the magnetic flux density B(x, y, z) with a 3-axis Hall sensor and the induced voltage due to movements with a set of three orthogonal coils. Voltages were converted into time-varying magnetic flux d Φ(x, y, z)/dt serving as an exposition parameter for both translations and rotations. To separate the two types of motion, d B/dt was additionally calculated on the basis of the Hall sensor's data. The calibrated probe was attached to the forehead of 8 healthcare workers and 17 MR physicists, and B and dΦ/dt were recorded during standard operating procedures at three different MR systems up to 7 T. The maximum percentage of the translational motion referring the data including both translations and rotations amounts to 32%. During volunteer measurements, maximum exposure values of dΦ/dt=21 mWb/s, dB/dt=1.40 T/s and |B|=2.75 T were found. The findings in this work indicate that both translations and rotations in the vicinity of an MR system should be taken into account, and that a single regulatory action level might not be sufficient.

• Effects of static magnetic fields on cognition, vital signs, and sensory perception: a meta-analysis.

  Authors: Angela Heinrich, Anne Szostek, Frauke Nees, Patric Meyer, Wolfhard Semmler, Herta Flor

  Journal of magnetic resonance imaging : JMRI. 07/2011; 34(4):758-63.

  To evaluate whether cognitive processes, sensory perception, and vital signs might be influenced by static magnetic fields in magnetic resonance imaging (MRI), which could pose a risk for healthTo evaluate whether cognitive processes, sensory perception, and vital signs might be influenced by static magnetic fields in magnetic resonance imaging (MRI), which could pose a risk for health personnel and patients, we conducted a meta-analysis of studies that examined effects of static magnetic fields. Studies covering the time from 1992 to 2007 were selected. Cohen's d effects sizes were used and combined in different categories of neuropsychology (reaction time, visual processing, eye-hand coordination, and working memory). Additionally, effects of static magnetic fields on sensory perception and vital signs were analyzed. In the category "neuropsychology," only effects on the visual system were homogeneous, showing a statistically significant impairment as a result of exposure to static magnetic fields (d = -0.415). Vital signs were not affected and effects on sensory perceptions included an increase of dizziness and vertigo, primarily caused by movement during static magnetic field gradient exposures. The number of studies dealing with this topic is very small and the experimental set-up of some of the analyzed studies makes it difficult to accurately determine the effects of static magnetic fields by themselves, excluding nonspecific factors. The implications of these results for MRI lead to suggestions for improvement in research designs.

• 3 Tesla sodium inversion recovery magnetic resonance imaging allows for improved visualization of intracellular sodium content changes in muscular channelopathies.

  Authors: Armin Michael Nagel, Erick Amarteifio, Frank Lehmann-Horn, Karin Jurkat-Rott, Wolfhard Semmler, Lothar R Schad, Marc-André Weber

  Investigative radiology. 07/2011; 46(12):759-66.

  To implement different sodium (²³Na)-magnetic resonance imaging (MRI) contrasts at 3 Tesla and to evaluate if a weighting toward intracellular sodium can be achieved, using 2 rare muscularTo implement different sodium (²³Na)-magnetic resonance imaging (MRI) contrasts at 3 Tesla and to evaluate if a weighting toward intracellular sodium can be achieved, using 2 rare muscular channelopathies as model diseases. Both lower legs of 6 patients with hypokalemic periodic paralysis (HypoPP), 5 patients with paramyotonia congenita (PC), and 5 healthy volunteers were examined on a 3 Tesla system with 3 different ²³Na-MRI pulse sequences. HypoPP and PC are rare muscle diseases, which are well characterized by elevated myoplasmic sodium at rest and after cooling, respectively. Intra- and interindividual comparisons were performed before and after provocation of one lower leg muscle. Three different ²³Na-MRI sequences were applied: (i) The total tissue sodium concentration was measured using a spin-density sequence (²³Na-TSC). (ii) A T1-contrast was applied to assess whether the known changes of the intracellular sodium concentration can be visualized by T1-weighting (²³Na-T1). (iii) An inversion recovery (²³Na-IR) sequence was used to utmost suppress the sodium signal from extracellular or vasogenic edema. Furthermore, a potential influence of the temperature dependency of the sodium relaxation times was considered. Additionally, H-MRI was performed to examine potential lipomatous or edematous changes. In HypoPP, all Na sequences showed significantly (P<0.05) higher signal intensities compared with PC patients and healthy subjects. In muscles of PC patients, provocation induced a significant (P=0.0007) increase (>20%) in the muscular ²³Na-IR signal and a corresponding decrease of muscle strength. Additionally, a tendency to higher ²³Na-T1 (P=0.07) and ²³Na-TSC (P=0.07) signal intensities was observed. Provocation revealed no significant changes in ¹H-MRI. In volunteers and in the contralateral, not cooled lower leg, there were no significant signal intensity changes after provocation. Furthermore, the ²³Na-IR sequence allows for a suppression of signal emanating from intravascular sodium and vasogenic edema. Our results indicate that the ²³Na-IR sequence allows for a weighting toward intracellular sodium. The combined application of the ²³Na-TSC and the ²³Na-IR sequence enables an improved analysis of pathophysiological changes that occur in muscles of patients with muscular channelopathies.

• Cilengitide inhibits metastatic bone colonization in a nude rat model.

  Authors: Maren Bretschi, Maximilian Merz, Dorde Komljenovic, Martin R Berger, Wolfhard Semmler, Tobias Bäuerle

  Oncology reports. 07/2011; 26(4):843-51.

  Integrins αvβ3 and αvβ5 are considered to play an important role in the pathogenesis of breast cancer bone metastases. This study investigates the effects of the αvβ3/αvβ5 integrin-specific inhibitorIntegrins αvβ3 and αvβ5 are considered to play an important role in the pathogenesis of breast cancer bone metastases. This study investigates the effects of the αvβ3/αvβ5 integrin-specific inhibitor cilengitide during early metastatic bone colonization. The impact of cilengitide on the migration, invasion and proliferation of MDA-MB-231 human breast carcinoma cells as well as on bone resorption by osteoclasts was investigated in vitro. For in vivo experiments, nude rats were treated with cilengitide for 30 days starting one day after site-specific tumor cell inoculation in the hind leg, and the course of metastatic changes in bone was followed using flat-panel volumetric computed tomography (VCT) and magnetic resonance imaging (MRI). Vascular changes in bone metastases were investigated using dynamic contrast-enhanced (DCE-) MRI-derived parameters amplitude A and exchange rate coefficient kep. In vitro, cilengitide treatment resulted in a decrease in proliferation, migration and invasion of MDA-MB-231 cells, as well as of osteoclast activity. In vivo, the development of bone metastasis in the hind leg of rats was not prevented by adjuvant cilengitide treatment, but cilengitide reduced the volumes of osteolytic lesions and respective soft tissue tumors of developing bone metastases as assessed with VCT and MRI, respectively. DCE-MRI revealed significant changes in the A and kep parameters including decreased relative blood volume and increased vessel permeability after cilengitide treatment indicating vessel remodeling. In conclusion, during early pathogenic processes of bone colonization, cilengitide treatment exerted effects on tumor cells, osteoclasts and vasculature reducing the skeletal lesion size of experimental skeletal metastases.

• Cilengitide inhibits progression of experimental breast cancer bone metastases as imaged noninvasively using VCT, MRI and DCE-MRI in a longitudinal in vivo study.

  Authors: Tobias Bäuerle, Dorde Komljenovic, Maximilian Merz, Martin R Berger, Simon L Goodman, Wolfhard Semmler

  International journal of cancer. Journal international du cancer. 05/2011; 128(10):2453-62.

  The aim of this study was to investigate the effect of inhibiting αvβ(3)/α(v) β(5) integrins by cilengitide in experimentally induced breast cancer bone metastases using noninvasive imagingThe aim of this study was to investigate the effect of inhibiting αvβ(3)/α(v) β(5) integrins by cilengitide in experimentally induced breast cancer bone metastases using noninvasive imaging techniques. For this purpose, nude rats bearing established breast cancer bone metastases were treated with cilengitide, a small molecule inhibitor of αvβ(3) and αvβ(5) integrins (75 mg/kg, five days per week; n = 12 rats) and compared to vehicle-treated control rats (n = 12). In a longitudinal study, conventional magnetic resonance imaging (MRI) and flat panel volumetric computed tomography were used to assess the volume of the soft tissue tumor and osteolysis, respectively, and dynamic contrast-enhanced (DCE-) MRI was performed to determine functional parameters of the tumor vasculature reflecting blood volume and blood vessel permeability. In rats treated with cilengitide, VCT and MRI showed that osteolytic lesions and the respective bone metastatic soft tissue tumors progressed more slowly than in vehicle-treated controls. DCE-MRI indicated a decrease in blood volume and an increase in vessel permeability and immunohistology revealed increased numbers of immature vessels in cilengitide-treated rats compared to vehicle controls. In conclusion, treatment of experimental breast cancer bone metastases with cilengitide resulted in pronounced antiresorptive and antitumor effects, suggesting that αvβ(3)/αvβ(5) inhibition may be a promising therapeutic approach for bone metastases.

• The potential of relaxation-weighted sodium magnetic resonance imaging as demonstrated on brain tumors.

  Authors: Armin Michael Nagel, Michael Bock, Christian Hartmann, Lars Gerigk, Jan-Oliver Neumann, Marc-André Weber, Martin Bendszus, Alexander Radbruch, Wolfgang Wick, Heinz-Peter Schlemmer, Wolfhard Semmler, Armin Biller

  Investigative radiology. 05/2011; 46(9):539-47.

  : Total tissue sodium (Na) content is associated with the viability of cells and can be assessed by Na magnetic resonance imaging. However, the resulting total sodium signal (NaT) represents a: Total tissue sodium (Na) content is associated with the viability of cells and can be assessed by Na magnetic resonance imaging. However, the resulting total sodium signal (NaT) represents a volume-weighted average of different sodium compartments assigned to the intra- and extracellular space. In addition to the spin-density weighted contrast of NaT imaging, relaxation-weighted (NaR) sequences were applied. The aim of this study was to evaluate the potential of NaR imaging for tissue characterization and putative additional benefits to NaT imaging. : For NaT and NaR imaging, novel magnetic resonance imaging sequences were established and applied in 16 patients suffering from brain tumors (14 WHO grade I-IV and 2 metastases). All Na sequences were based on density-adapted three-dimensional radial projection reconstruction to obtain short echo times and high signal-to-noise ratio efficiency. : NaT imaging revealed increased signal intensities in 15 of 16 brain tumors before therapy. In addition, NaR imaging enabled further differentiation of these lesions; all glioblastomas demonstrated higher NaR signal intensities as compared with WHO grade I-III tumors. Thus, NaR imaging allowed for correct separation between WHO grade I-III and WHO grade IV gliomas. In contrast to the NaT signal, the NaR signal correlated with the MIB-1 proliferation rate of tumor cells. : These results serve as a proof of concept that NaR imaging reveals important physiological tissue characteristics different from NaT imaging. Furthermore, they indicate that the combined use of NaT and NaR imaging might add valuable information for the functional in vivo characterization of brain tissue.

• First multimodal embolization particles visible on x-ray/computed tomography and magnetic resonance imaging.

  Authors: Soenke H Bartling, Johannes Budjan, Hagit Aviv, Stefan Haneder, Bettina Kraenzlin, Henrik Michaely, Shlomo Margel, Steffen Diehl, Wolfhard Semmler, Norbert Gretz, Stefan O Schönberg, Maliha Sadick

  Investigative radiology. 03/2011; 46(3):178-86.

  Embolization therapy is gaining importance in the treatment of malignant lesions, and even more in benign lesions. Current embolization materials are not visible in imaging modalities. However, it isEmbolization therapy is gaining importance in the treatment of malignant lesions, and even more in benign lesions. Current embolization materials are not visible in imaging modalities. However, it is assumed that directly visible embolization material may provide several advantages over current embolization agents, ranging from particle shunt and reflux prevention to improved therapy control and follow-up assessment. X-ray- as well as magnetic resonance imaging (MRI)-visible embolization materials have been demonstrated in experiments. In this study, we present an embolization material with the property of being visible in more than one imaging modality, namely MRI and x-ray/computed tomography (CT). Characterization and testing of the substance in animal models was performed. To reduce the chance of adverse reactions and to facilitate clinical approval, materials have been applied that are similar to those that are approved and being used on a routine basis in diagnostic imaging. Therefore, x-ray-visible Iodine was combined with MRI-visible Iron (Fe3O4) in a macroparticle (diameter, 40-200 μm). Its core, consisting of a copolymerized monomer MAOETIB (2-methacryloyloxyethyl [2,3,5-triiodobenzoate]), was coated with ultra-small paramagnetic iron oxide nanoparticles (150 nm). After in vitro testing, including signal to noise measurements in CT and MRI (n = 5), its ability to embolize tissue was tested in an established tumor embolization model in rabbits (n = 6). Digital subtraction angiography (DSA) (Integris, Philips), CT (Definition, Siemens Healthcare Section, Forchheim, Germany), and MRI (3 Tesla Magnetom Tim Trio MRI, Siemens Healthcare Section, Forchheim, Germany) were performed before, during, and after embolization. Imaging signal changes that could be attributed to embolization particles were assessed by visual inspection and rated on an ordinal scale by 3 radiologists, from 1 to 3. Histologic analysis of organs was performed. Particles provided a sufficient image contrast on DSA, CT (signal to noise [SNR], 13 ± 2.5), and MRI (SNR, 35 ± 1) in in vitro scans. Successful embolization of renal tissue was confirmed by catheter angiography, revealing at least partial perfusion stop in all kidneys. Signal changes that were attributed to particles residing within the kidney were found in all cases in all the 3 imaging modalities. Localization distribution of particles corresponded well in all imaging modalities. Dynamic imaging during embolization provided real-time monitoring of the inflow of embolization particles within DSA, CT, and MRI. Histologic visualization of the residing particles as well as associated thrombosis in renal arteries could be performed. Visual assessment of the likelihood of embolization particle presence received full rating scores (153/153) after embolization. Multimodal-visible embolization particles have been developed, characterized, and tested in vivo in an animal model. Their implementation in clinical radiology may provide optimization of embolization procedures with regard to prevention of particle misplacement and direct intraprocedural visualization, at the same time improving follow-up examinations by utilizing the complementary characteristics of CT and MRI. Radiation dose savings can also be considered. All these advantages could contribute to future refinements and improvements in embolization therapy. Additionally, new approaches in embolization research may open up.

• Optically detunable, inductively coupled coil for self-gating in small animal magnetic resonance imaging.

  Authors: Matthias Korn, Reiner Umathum, Jessica Schulz, Wolfhard Semmler, Michael Bock

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 03/2011; 65(3):882-8.

  An inductively coupled coil concept is presented, which improves the compensation of physiological motion by the self-gating (SG) technique. The animal is positioned in a conventional volume coilAn inductively coupled coil concept is presented, which improves the compensation of physiological motion by the self-gating (SG) technique. The animal is positioned in a conventional volume coil encompassing the whole animal. A small, resonant surface coil (SG-coil) is placed on the thorax so that its sensitive region includes the heart. Via inductive coupling the SG-coil amplifies selectively the MR signal of the beating heart. With an optical detuning mechanism, this coupling can be switched off during acquisition of the MR image information, whereas it is active during SG data sampling to provide the physiological information. In vivo experiments on a mouse show an amplification of the SG signal by at least 40%.

• Velocity navigator for motion compensated thermometry.

  Authors: Florian Maier, Axel J Krafft, Joshua P Yung, R Jason Stafford, Andrew Elliott, Rüdiger Dillmann, Wolfhard Semmler, Michael Bock

  Magma (New York, N.Y.). 03/2011; 25(1):15-22.

  Proton resonance frequency shift thermometry is sensitive to breathing motion that leads to incorrect phase differences. In this work, a novel velocity-sensitive navigator technique for triggering MRProton resonance frequency shift thermometry is sensitive to breathing motion that leads to incorrect phase differences. In this work, a novel velocity-sensitive navigator technique for triggering MR thermometry image acquisition is presented. A segmented echo planar imaging pulse sequence was modified for velocity-triggered temperature mapping. Trigger events were generated when the estimated velocity value was less than 0.2 cm/s during the slowdown phase in parallel to the velocity-encoding direction. To remove remaining high-frequency spikes from pulsation in real time, a Kalman filter was applied to the velocity navigator data. A phantom experiment with heating and an initial volunteer experiment without heating were performed to show the applicability of this technique. Additionally, a breath-hold experiment was conducted for comparison. A temperature rise of ΔT = +37.3°C was seen in the phantom experiment, and a root mean square error (RMSE) outside the heated region of 2.3°C could be obtained for periodic motion. In the volunteer experiment, a RMSE of 2.7°C/2.9°C (triggered vs. breath hold) was measured. A novel velocity navigator with Kalman filter postprocessing in real time significantly improves the temperature accuracy over non-triggered acquisitions and suggests being comparable to a breath-held acquisition. The proposed technique might be clinically applied for monitoring of thermal ablations in abdominal organs.

• Outer volume suppression in steady state sequences (OVSuSS) for percutaneous interventions.

  Authors: Jaane Rauschenberg, Axel J Krafft, Florian Maier, Patrik Zamecnik, Wolfhard Semmler, Michael Bock

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 02/2011; 66(1):123-34.

  Magnetic resonance-guided percutaneous interventions with needles require fast pulse sequences with acquisition times less than 1 s to image the needle trajectory within moving organs. To guide theMagnetic resonance-guided percutaneous interventions with needles require fast pulse sequences with acquisition times less than 1 s to image the needle trajectory within moving organs. To guide the movement of a rigid instrument with high sampling rate, an magnetic resonance imaging method was developed that reduces the acquisition time down to a few hundred milliseconds by restricting the field of view to a small stripe around the instrument trajectory. To maintain the dynamic steady state, saturation pulses for outer volume suppression were inserted into additional repetition time-intervals. These saturation intervals were combined with three sequence variants: a spoiled gradient echo sequence, an echo-shifted steady state free precession and a balanced steady state free precession sequence. The magnetization dynamics were analyzed by means of numerical optimized simulations. Results were compared with phantom experiments and an average signal-to-suppression-ratio of 15.5 could be achieved. With a field of view reduction of up to 12.5% an update rate of six images per second could be achieved. Finally, animal experiments demonstrated the fast and reliable needle tip visualization during percutaneous magnetic resonance-guided interventions with the help of a robotic assistance system.