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    Keywords: measurement ; CANCER ; tumor ; carcinoma ; CELL ; Germany ; MODEL ; THERAPY ; DIAGNOSIS ; imaging ; VOLUME ; TISSUE ; TUMORS ; PATIENT ; IMPACT ; blood flow ; MR ; MRI ; SEQUENCE ; BREAST ; LESIONS ; EXPERIENCE ; PLASMA ; METASTASIS ; PARAMETERS ; BENIGN ; CARCINOMAS ; SERIES ; contrast media ; dynamic MRI ; MANAGEMENT ; VOLUMES ; MASSES ; breast tumors ; capillary permeability ; CAPILLARY-PERMEABILITY ; CONTRAST ENHANCEMENT ; GD-DTPA ENHANCEMENT ; MAMMARY-TUMORS ; MEAN RESIDENCE TIMES ; REGIONAL BLOOD-FLOW
    Abstract: The purpose of this study was to quantify microcirculation and microvasculature in breast lesions by pharmacokinetic analysis of Gd-DTPA-enhanced MRI series. Strongly T-1-weighted MR images were acquired in 18 patients with breast lesions using a saturation-recovery-TurboFLASH sequence. Concentration-time courses were determined for blood, pectoral muscle, and breast masses and subsequently analyzed by a two-compartment model to estimate plasma flow and the capillary transfer coefficient per unit of plasma volume (F/V-P, K-PS/V-P) as well as fractional volumes of the plasma and interstitial space (f(P), f(I)). Tissue parameters determined for pectoral muscle (f(P) = 0.04 +/- 0.01, f(I) = 0.09 +/- 0.01, F/V-P = 2.4 +/- 1.3 min(-1), and K-PS/V-P = 1.2 +/- 0.5 min(-1)) and 10 histologically proven carcinomas (f(P) = 0.20 +/- 0.07, f(I) = 0.34 +/- 0.16, F/V-P = 2.4 +/- 0.7 min(-1), and K-PS/V-P = 0.86 +/- 0.62 min(-1)) agreed reasonable well with literature data. Best separation between malignant and benign lesions was obtained by the ratio K-PS/F (0.35 +/- 0.17 vs. 1.23 +/- 0.65). The functional imaging technique presented appears promising to quantitatively characterize tumor pathophysiology. Its impact on diagnosis and therapy management of breast tumors, however, has to be evaluated in larger patient studies
    Type of Publication: Journal article published
    PubMed ID: 15282828
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  • 3
    Keywords: measurement ; BLOOD ; Germany ; VOLUME ; TIME ; BLOOD-FLOW ; SIMULATION ; blood flow ; MR ; SIGNAL ; MAGNETIC-RESONANCE ; magnetic resonance imaging ; NMR ; ARTERY ; radiology ; 2D ; interventional ; STENOSIS ; catheterization ; intra-arterial flow measurements ; MR-compatible devices ; PULSEWAVE VELOCITY ; STENT PLACEMENT ; TARDUS
    Abstract: Flow measurements can be used to quantify blood flow during MR-guided intravascular interventional procedures. In this study, a fast flow measurement technique is proposed that quantifies flow velocities in the vicinity of a small RF coil attached to an intravascular catheter. Since the small RF coil receives signal from only a limited volume around the catheter, a spatially nonselective signal reception is employed. To enhance signal from flowing blood, and suppress unwanted signal contributions from static material, a slice-selective RF excitation is used. At a velocity sensitivity of 150 cm/s, a temporal resolution of 2 x TR = 10.2 ms can be achieved. The flow measurement is combined with an automatic slice positioning to facilitate measurements during interventional procedures. The influence of the catheter position in the blood vessel on the velocity measurement was analyzed in simulations. For blood vessels with laminar flow, the simulation showed a systematic deviation between catheter measurement and true flow between -15% and 80%. In four animal experiments, the catheter velocity measurement was compared with results from a conventional ECG-triggered 2D phase-contrast (PC) technique. The shapes of the velocity time curves in the abdominal aorta were nearly identical to the conventional measurements. A relative scaling factor of 0.69-1.19 was found between the catheter velocity measurement and the reference measurement, which could be partly explained by the simulation results. (C) 2004 Wiley-Liss, Inc
    Type of Publication: Journal article published
    PubMed ID: 15334577
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  • 4
    Keywords: Germany ; IMAGES ; imaging ; HEART ; RESOLUTION ; TIME ; MR ; MRI ; sensitivity ; TRACKING ; MAGNETIC-RESONANCE ANGIOGRAPHY ; RECONSTRUCTION ; 2D ; MATRIX ; CATHETER TRACKING ; active device tracking ; interventional MRI ; intravascular catheters ; COILS ; SENSE ; CATHETER ; cardiac MRI ; GRAPPA ; interactive real-time parallel MRI ; TSENSE ; ACTIVE CATHETER TRACKING
    Abstract: In this work active MR catheter tracking with automatic slice alignment was combined with an autocalibrated parallel imaging technique. Using an optimized generalized autocalibrating partially parallel acquisitions (GRAPPA) algorithm with an acceleration factor of 2, we were able to reduce the acquisition time per image by 34%. To accelerate real-time GRAPPA image reconstruction, the coil sensitivities were updated only after slice reorientation. For a 2D trueFISP acquisition (160 x 256 matrix, 80% phase matrix, half Fourier acquisition, TR = 3.7 ms, GRAPPA factor = 2) real-time image reconstruction was achieved with up to six imaging coils. In a single animal experiment the method was used to steer a catheter from the vena cava through the beating heart into the pulmonary vasculature at an image update rate of about five images per second. Under all slice orientations, parallel image reconstruction was accomplished with only minor image artifacts, and the increased temporal resolution provided a sharp delineation of intracardial structures, such as the papillary muscle
    Type of Publication: Journal article published
    PubMed ID: 16683261
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  • 5
    Keywords: Germany ; IN-VIVO ; THERAPY ; VIVO ; imaging ; QUANTIFICATION ; SYSTEM ; TOOL ; MICE ; ACTIVATION ; INJURIES ; MRI ; MAGNETIC-RESONANCE ; magnetic resonance imaging ; MOUSE-BRAIN ; DAMAGE ; magnetic resonance imaging (MRI) ; RAT-BRAIN ; CD95 ; RE ; INCREASE ; RECOVERY ; manganese ; in vivo ; EXTENT ; CORD ; therapy monitoring ; CONNECTIONS ; MEMRI ; MNCL2 ; spinal cord injury (SCI)
    Abstract: In past decades, much effort has been invested in developing therapies for spinal injuries. Lack of standardization of clinical read-out measures, however, makes direct comparison of experimental therapies difficult. Damage and therapeutic effects in vivo are routinely evaluated using rather subjective behavioral tests. Here we show that manganese-enhanced magnetic resonance imaging (MEMRI) can be used to examine the extent of damage following spinal cord injury (SCI) in mice in vivo. Injection of MnCl2 solution into the cerebrospinal fluid leads to manganese uptake into the spinal cord. Furthermore, after injury MEMRI-derived quantitative measures correlate closely with clinical locomotor scores. Improved locomotion due to treating the detrimental effects of SCI with an established therapy (neutralization of CD95Ligand) is reflected in an increase of manganese uptake into the injured spinal cord. Therefore, we demonstrate that MEMRI is a sensitive and objective tool for in vivo visualization and quantification of damage and functional improvement after SCI. Thus, MEMRI can serve as a reproducible surrogate measure of the clinical status of the spinal cord in mice, potentially becoming a standard approach for evaluating experimental therapies
    Type of Publication: Journal article published
    PubMed ID: 16602070
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  • 6
    Keywords: brain ; SPECTRA ; Germany ; human ; IN-VIVO ; MODEL ; VIVO ; imaging ; RESOLUTION ; NUCLEAR-MEDICINE ; MR ; SEQUENCE ; SIGNAL ; MR spectroscopy ; spectroscopic imaging ; SPECTROSCOPY ; NMR-SPECTROSCOPY ; NUCLEUS ; PREDICTION ; sensitivity ; nuclear medicine ; radiology ; HEALTHY-VOLUNTEERS ; ENHANCEMENT ; human brain ; methods ; NUCLEAR ; technique ; FMRI ; USA ; in vivo ; SPECTRUM ; AGREEMENT ; MEDICINE ; HUMAN-CALF-MUSCLE ; medical imaging ; RESONANCE ; PHOSPHOCREATINE ; CHEMICAL-SHIFT ; echo-planar spectroscopic imaging human brain ; fast spectroscopic imaging ; nuclear Overhauser effect (NOE) ; P-31 ; phosphorus magnetic resonance spectroscopy
    Abstract: Echo-planar spectroscopic imaging (EPSI) is one of the fastest spectroscopic imaging (SI) methods. It has been applied to H-1 MR spectroscopy (MRS) studies of the human brain in vivo. However, to our knowledge, EPSI with detection of the P-31 nucleus to monitor phosphorus-containing neurometabolites has not yet been considered. In this work, eight different P-31-{H-1} EPSI sequence versions with spectral widths ranging from P-31 Hz to 2.27 kHz were implemented on a clinical 1.5T whole-body MR tomograph. The sequence versions utilized the heteronuclear nuclear Overhauser effect (NOE) for P-31 signal enhancement. The sensitivity observed in experiments with model solutions was in good agreement with theoretical predictions. In vivo measurements performed on healthy volunteers (N=16) demonstrated the feasibility of performing two-dimensional (2D) P-31-{H-1} EPSI in the human brain, and the technique enabled fast acquisition of well-resolved localized spectra
    Type of Publication: Journal article published
    PubMed ID: 17390361
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  • 7
    Keywords: MODELS ; SYSTEM ; TISSUE ; MRI ; MAGNETIC-RESONANCE ; PROTON ; high-field MRI ; BIOLOGICAL TISSUES ; DIELECTRIC-PROPERTIES ; radiofrequency electronics ; travelling wave MRI ; waveguides
    Abstract: 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 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. (c) 2011 Wiley Periodicals, Inc.
    Type of Publication: Journal article published
    PubMed ID: 22021117
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  • 8
    Keywords: brain ; SIMULATION ; WATER DIFFUSION ; Tensor ; FIELD-GRADIENT ; RESTRICTED DIFFUSION ; SPIN-ECHO ; EDGE ENHANCEMENT
    Abstract: One main interest of nuclear magnetic resonance (NMR) diffusion experiments is the investigation of boundaries such as cell membranes hindering the diffusion process. NMR diffusion measurements allow collecting the signal from the whole sample. This mainly eliminates the problem of vanishing signal at increasing resolution. It has been a longstanding question if, in principle, the exact shape of closed pores can be determined by NMR diffusion measurements. In this work, we present a method using short diffusion gradient pulses only, which is able to reveal the shape of arbitrary closed pores without relying on a priori knowledge. In comparison to former approaches, the method has reduced demands on relaxation times due to faster convergence to the diffusion long-time limit and allows for a more flexible NMR sequence design, because, e.g., stimulated echoes can be used.
    Type of Publication: Journal article published
    PubMed ID: 23065736
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  • 9
    Keywords: FLOW ; SUSCEPTIBILITY ; HYPOXIA ; DIFFUSION ; WHOLE-BLOOD ; LEVEL-DEPENDENT BOLD ; RELAXATION-TIME ; CLASSICAL PERFUSION ; QUANTITATIVE T-2 ; F-19 MRI
    Abstract: PurposeTo present a novel imaging strategy for noninvasive measurement of tumor oxygenation using MR imaging of endogenous blood and tissue water. Theory and MethodsThe proposed approach for oxygen partial pressure (pO(2)) estimation is based on intravoxel incoherent motion diffusion MRI and the dependence of the blood R-2 relaxation rate on the inter-echo spacing measured using a multiple spin-echo Carr-Purcell-Meiboom-Gill sequence and weak-field diffusion model. The accuracy of the approach was validated by comparison with F-19 MRI oximetry. ResultsThe results in eight rats at 4.7 T showed that tumors have longer T-1 (1980186 ms) and T-2 (59 +/- 9 ms) relaxation times, heterogeneous blood volume fraction (0.23 +/- 0.1), oxygen saturation level (Y) (0.53 +/- 0.12), and pO(2) (36 +/- 15 mmHg) distributions compared with normal muscle (T-1 1480 +/- 86 ms, T-2 29 +/- 2 ms, blood volume fraction 0.22 +/- 0.03, Y 0.49 +/- 0.06, and pO(2) 39 +/- 5 mmHg). pO(2) estimates based on the novel H-1 approach were essentially identical with F-19 observations. ConclusionThe study indicates that noninvasive measurement of tumor pO(2) using H-1 MRI derived multiparametric maps is feasible and could become a valuable tool to evaluate tumor hypoxia.
    Type of Publication: Journal article published
    PubMed ID: 23447121
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  • 10
    Keywords: SIMULATIONS ; validation ; DESIGN ; TRACKING ; FEATURES ; FRAMEWORK ; human brain ; TRACTOGRAPHY ; IN-DIFFUSION MRI ; SPHERICAL DECONVOLUTION
    Abstract: PurposePhantom-based validation of diffusion-weighted image processing techniques is an important key to innovation in the field and is widely used. Openly available and user friendly tools for the flexible generation of tailor-made datasets for the specific tasks at hand can greatly facilitate the work of researchers around the world. MethodsWe present an open-source framework, Fiberfox, that enables (1) the intuitive definition of arbitrary artificial white matter fiber tracts, (2) signal generation from those fibers by means of the most recent multi-compartment modeling techniques, and (3) simulation of the actual MR acquisition that allows for the introduction of realistic MRI-related effects into the final image. ResultsWe show that real acquisitions can be closely approximated by simulating the acquisition of the well-known FiberCup phantom. We further demonstrate the advantages of our framework by evaluating the effects of imaging artifacts and acquisition settings on the outcome of 12 tractography algorithms. ConclusionOur findings suggest that experiments on a realistic software phantom might change the conclusions drawn from earlier hardware phantom experiments. Fiberfox may find application in validating and further developing methods such as tractography, super-resolution, diffusion modeling or artifact correction.
    Type of Publication: Journal article published
    PubMed ID: 24323973
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