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  • 1
    Keywords: Germany ; imaging ; TISSUE ; RESOLUTION ; radiation ; PATIENT ; CONTRAST ; MR ; MRI ; MAGNETIC-RESONANCE ; magnetic resonance imaging ; ACQUISITION ; HEALTH ; RATES ; ANGIOGRAPHY ; nuclear medicine ; RECONSTRUCTION ; 2D ; CATHETER TRACKING ; 3D ; TECHNOLOGY ; COILS ; occupational health ; PLACEMENT
    Abstract: At present, interventional procedures, such as stent placement, are performed under X-ray image guidance. Unfortunately with X-ray imaging, both patient and interventionalist are exposed to ionising radiation. Furthermore, X-ray imaging is lacking soft tissue contrast and is not capable of true 3-D displays of either interventional device or tissue morphology. Magnetic resonance imaging (MRI) offers excellent soft tissue contrast, 3-D acquisition techniques, as well as rapid image acquisition and reconstruction. Despite these advantages, MR-guided interventions are challenging owing to the limited access to the patient, strong magnetic and radio-frequency fields that require special interventional devices, inferior image frame rates and spatial resolution, and high MRI scanner noise. For MR-guided intravascular interventions, where access to the target organ is achieved through catheters, dedicated hardware and automated image slice positioning techniques have been developed. We illustrate that MR-guided renal embolisations can be performed in closed-bore high-field MR scanners
    Type of Publication: Journal article published
    PubMed ID: 16464829
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  • 2
    Keywords: Germany ; imaging ; SYSTEM ; SYSTEMS ; RESOLUTION ; TIME ; MARKER ; MR ; SEQUENCE ; SEQUENCES ; SIGNAL ; SUSCEPTIBILITY ; FIELD ; MAGNETIC-RESONANCE ; ACQUISITION ; RELAXATION ; TRACKING ; BIOPSY ; RE ; INTERVENTIONAL DEVICES ; INFUSION ; ENHANCEMENT ; SIZE ; COILS ; technique ; VIEW ; RARE ; CATHETERS ; DEFT ; device localization ; fast MRI ; INNER VOLUME ; inner volume imaging ; local look (LoLo) ; percutaneous intervention ; WIRES
    Abstract: Percutaneous MR-guided interventions with needles require fast pulse sequences to image the needle trajectory with minimal susceptibility artifacts. Spin-echo pulse sequences are well suited for reducing artifact size; however, even with single-shot turbo spin-echo techniques, such as rapid acquisition with relaxation enhancement (RARE) or half-Fourier acquisition single-shot turbo spin-echo (HASTE), fast imaging remains challenging. In this work we present a HASTE pulse sequence that is combined with inner-volume excitation to reduce the scan time and limit the imaging field of view (FOV) to a small strip close to the needle trajectory (targeted-HASTE). To compensate for signal saturation from fast repeated acquisitions, a magnetization restore pulse (driven equilibrium Fourier transform (DEFT)) is used. The sequence is combined with dedicated active marker coils to measure the position and orientation of the needle so that the targeted-HASTE image slice is automatically repositioned. In an animal experiment the coils were attached to an MR-compatible robotic assistance system for MR-guided interventions. Needle insertion and infusion via the needle could be visualized with a temporal resolution of 1 s, and the needle tip could be localized even in the presence of a stainless steel mandrel
    Type of Publication: Journal article published
    PubMed ID: 16795081
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  • 3
    ISSN: 1432-2102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2102
    Keywords: Schlüsselwörter MRT ; Funktionelle Bildgebung ; Schnelle Sequenzen ; Schnarchen ; OSA ; Key words MRI ; Functional imaging ; Ultrafast sequences ; Snoring ; Obstructive sleep apnea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Functional imaging of the pharynx used to be the domain of cineradiography, CT and ultrafast CT. The development of modern MRI techniques led to new access to functional disorders of the pharynx. The aim of this study was to implement a new MRI technique to examine oropharyngeal obstructive mechanisms in patients with obstructive sleep apnea (OSA). Sixteen patients suffering from OSA and 6 healthy volunteers were examined on a 1.5 T whole-body imager (“Vision”, Siemens, Erlangen Medical Engineering, Germany) using a circular polarized head coil. Imaging was performed with 2D flash sequences in midsagittal and axial planes. Patients and volunteers were asked to breathe normally through the nose and to simulate snoring and the Mueller maneuver during magnetic resonance imaging (MRI). Prior to MRI, all patients underwent an ear, nose and throat (ENT) examination, functional fiberoptic nasopharyngoscopy and polysomnography. A temporal resolution of 6 images/s and an in-plane resolution of 2.67 × 1.8 mm were achieved. The mobility of the tongue, soft palate and pharyngeal surface could be clearly delineated. The MRI findings correlated well with the clinical examinations. We propose ultrafast MRI as a reliable and non-invasive method of evaluating pharyngeal obstruction and their levels.
    Notes: Zusammenfassung Die funktionelle Bildgebung des Pharynx war bisher eine Domäne der Hochfrequenzröntgenkinematographie, der Computertomographie (CT) und der ultraschnellen Computertomographie. Die Entwicklung moderner Techniken in der Magnetresonanztomographie (MRT) führte zu neuen Ansätzen in der Diagnostik pharyngealer Dysfunktionen. Ziel der vorliegenden Studie war die Implementierung neuer schneller MR-Sequenzen, um Verschlußmechanismen entlang des Pharnyxschlauches bei Patienten mit obstruktiver Schlafapnoe (OSA) zu untersuchen. 16 Patienten mit OSA und 6 gesunde Probanden wurden an einem 1,5-T-Ganzkörpermagnetresonanztomographen („Vision“, Siemens Medizintechnik, Erlangen) mit einer zirkularpolarisierten Kopfspule untersucht. Die Bildgebung erfolgte mit schnellen 2D-FLASH-(Fast-low-angle-shot-) Sequenzen in sagittaler und axialer Schichtführung. Patienten und Probanden führten folgende Atemmanöver während der MRT durch: ruhige Nasenatmung bei geschlossenem Mund, Schnarchsimulation und Müller-Manöver. Vor der MRT unterzogen sich die OSA-Patienten einer HNO-ärztlichen Untersuchung, einer funktionellen flexiblen Nasopharyngoskopie und einer Polysomnographie. Mit der 2D-FLASH-Sequenz wurde eine Bildfolge von 6 Bildern/s und eine Ortsauflösung von 2,67 × 1,8 mm erreicht. Die Bewegungen der Zunge, des weichen Gaumens, der Uvula und der Pharynxwände konnten mit Hilfe der MRT dynamisch wiedergegeben werden. Die Darstellung der erhöhten Kollapsneigung der pharyngealen Weichteile bei den OSA-Patienten gelang ebenfalls mit der MRT. Diese Ergebnisse korrelierten gut mit den Untersuchungen der funktionellen flexiblen Nasopharyngoskopie. Die ultraschnelle MRT scheint als zuverlässige, nichtinvasive Methode zur Diagnostik der OSA geeignet zu sein.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    European radiology 9 (1999), S. 979-997 
    ISSN: 1432-1084
    Keywords: Key words: MR imaging ; MR angiography ; Cine MR imaging ; Nuclear magnetic resonance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The intention of this article is to provide an overview of all MR imaging techniques that are accessible on most of commercially available scanners and have the potential to be used in routine clinical applications. The techniques implemented by the major vendors are briefly explained, including a comparison of the commonly used acronyms. A classification scheme is introduced which provides a reasonable illustration of similarities and differences between various techniques. The imaging techniques are divided into two main groups, the spin-echo and gradient-echo sequences. Within each group is the basic sequence, those which require a preparation of the magnetization, those which use multiple echoes to fill the k-space and those which are performed in a single shot. For each technique the typical clinical applications are listed or the potential applications which have been published.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    European radiology 9 (1999), S. 1032-1046 
    ISSN: 1432-1084
    Keywords: Key words: MR imaging ; Contrast mechanisms ; Proton density ; T1 ; T2 ; Spin echo ; Gradient echo ; Turbo spin echo ; Echo-planar imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. This paper is a brief introduction to tissue-specific parameters and the utilization of various MR imaging sequences to display these parameters in order to differentiate normal from pathologic tissue and function. The three dominant tissue-specific parameters discussed are proton density, longitudinal relaxation time T1, and transverse relaxation time T2. For the utilization of gradient-echo sequences, transverse relaxation time T2* is introduced, more dependent on the environment or tissue interfaces than on the tissue itself. Another tissue-specific parameter is the concentration of macromolecules and their hydration layers as targeted with magnetization transfer imaging. Still another tissue-specific parameter is the chemical environment. Functional parameters that influence the contrast are diffusion, perfusion, flow, or motion. The sequence-related utilization of these tissue-specific parameters start with magnetization preparation as in spectral suppression of fat signal, relaxation-dependent elimination of fat or cerebrospinal fluid (CSF) signal, simple inversion pulse, magnetization transfer saturation, or diffusion weighting. Possible contrast mechanisms for the tissue-specific parameters are discussed for each of the commonly used sequences, whether of spin-echo type or of gradient-echo type, with or without magnetization preparation, conventional single-echo acquisition, or contemporary multiecho acquisition.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1435-1285
    Keywords: Schlüsselwörter NMR-Angiographie – Atemgating – Koronarstenose ; Key words MR angiography – respiratory gating – coronary artery stenosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary Respiratory gated MR coronary angiography is a new MR imaging technique which permits reconstruction of the coronary arteries from a three-dimensional data set obtained from contiguous parallel sections. In this study, respiratory gated MR angiography was applied to assess significant coronary artery stenoses (≥ 50%). MR imaging was performed in 68 patients (50 men, 18 women) who had been referred to cardiac catheterization because of suspected or known coronary artery disease. The evaluation of coronary artery stenoses was performed in a blindes manner in the proximal, middle, and distal vessel segments after multiplanar coronary reconstruction of the MR images. Of the 680 coronary segments, 275 (40%) were located outside the imaging volume and were, therefore, excluded from further analysis. The highest sensitivity for stenosis detection was found in the proximal left anterior descending (LAD) and right coronary artery (RCA) with 75% and 71%, respectively. The overall sensitivity, however, was low with 48%. The overall specificity was 92%. The positive and negative predictive values were 67% and 85%, respectively. This study shows that significant coronary artery stenoses, especially in the proximal LAD and RCA, can be correctly identified using respiratory gated MR angiography. However, further technical improvements are necessary before this method may become a reliable diagnostic tool in clinical practice.
    Notes: Zusammenfassung Die atemkontrollierte NMR-Angiographie ist eine neue Abbildungstechnik in der Kernspintomographie, die es erlaubt, einen dreidimensionalen Bilddatensatz des Herzens zu akquirieren und hieraus einzelne Koronararterien zu rekonstruieren. In dieser Studie sollte die Beurteilbarkeit von signifikanten Koronararterienstenosen (≥ 50%) mittels atemkontrollierter NMR-Angiographie untersucht werden. Die NMR-Untersuchung erfolgte bei 68 Patienten (50 Männer, 18 Frauen), bei denen aufgrund einer vermuteten oder bekannten koronaren Herzerkrankung eine Herzkatheteruntersuchung durchgeführt wurde. Die Stenosebeurteilung erfolgte nach multiplanarer Gefäßrekonstruktion im proximalen, mittleren und distalen Koronarsegment ohne Kenntnis des tatsächlichen angiographischen Befundes. 275 von 680 Koronarsegmenten (40%) lagen außerhalb des Abbildungsvolumens und wurden von der Auswertung ausgeschlossen. Die Sensivität für die Erkennung signifikanter Stenosen lag im proximalen Verlauf des Ramus interventricularis anterior (RIVA) mit 75% und der rechten Koronararterie (RCA) mit 71% am höchsten. Die Gesamtsensitivität war allerdings mit 48% niedrig bei einer Spezifität von 92%. Der positive und negative Vorhersagewert lag bei 67% und 85%. Diese Studie zeigt, daß signifikante Koronararterienstenosen, insbesondere des proximalen RIVA und der RCA, mittels atemkontrollierter NMR-Angiographie erkannt werden können. Weitere technische Verbesserungen sind notwendig, um die Methode in der klinischen Routinediagnostik zuverlässig einsetzen zu können.
    Type of Medium: Electronic Resource
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