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  • 1
    Keywords: Germany ; PERFUSION ; imaging ; VISUALIZATION ; TISSUE ; radiation ; kidney ; QUALITY ; renal ; animals ; CONTRAST ; INTERVENTION ; CONTRAST AGENT ; MR ; MAGNETIC-RESONANCE ; arteries ; TRACKING ; CELL CARCINOMA ; INTERVENTIONAL DEVICES ; ANGIOPLASTY ; ARTERY STENT PLACEMENT ; ENDOVASCULAR PROCEDURES ; ENHANCED MR-ANGIOGRAPHY ; FLUOROSCOPY ; magnetic resonance imaging,renal cancer,embolization,interventional radiology ; PIG MODEL
    Abstract: Rationale and Objectives: Magnetic resonance (MR)-guidance of endovascular interventions offers various advantages, including the absence of ionizing radiation, excellent soft tissue contrast, and multiplanar and functional imaging capabilities. The objective of this study was to assess the feasibility of MR-guided renal embolization using active catheter tracking with automatic slice positioning and intraarterial contrast-enhanced MR angiography (MRA).Materials and Methods: MR-guided embolization of 16 kidneys was attempted in 15 pigs using real-time tracking of active 5-Fr. catheters, Embolization was monitored by selective intraarterial projection MRA. Intraarterial three-dimensional (3D) MRA was used for the assessment of embolization results. Additional pathologic correlation was available in 2 animals. The image quality of intraarterial 3D contrast-enhanced-MRA was rated by an independent radiologist who was not involved in the animal experiments.Results: Active catheter tracking with automatic slice positioning allowed reliable catheter guidance and catheterization of the renal artery in all animals. Embolization was successful in all kidneys (11 left, 5 right), as verified by intraarterial 3D contrast-enhanced MRA (ce-MRA) and/or pathology. The image quality of intraarterial 3D ce-MRA was rated excellent in 10 animals, moderate in 4 animals, and poor in 1 animal.Conclusion: Renal embolization using active catheter tracking and intraarterial ce-MRA is feasible. Selective intraarterial ce-MRA allows the assessment of blood supply and organ perfusion before, during, and after therapeutic interventions, thereby complementing MR-guided endovascular interventions
    Type of Publication: Journal article published
    PubMed ID: 14734926
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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
  • 6
    Keywords: Germany ; imaging ; VISUALIZATION ; TIME ; renal ; CONTRAST ; INTERVENTION ; MR ; SEQUENCE ; MAGNETIC-RESONANCE ; ACQUISITION ; arteries ; VASCULATURE ; INTERFACE ; TRACKING ; ANGIOGRAPHY ; 2D ; MOVEMENT ; CATHETER TRACKING ; GUIDANCE ; GUIDEWIRES ; INTERVENTIONAL DEVICES ; magnetic resonance imaging,radiology,interventional,catheterization,interactive contrast change,real ; TRUEFISP
    Abstract: Purpose: To implement and optimize a real-time pulse sequence and user interface to perform intravascular interventions using active catheter tracking.Materials and Methods: In magnetic resonance (MR)-guided interventions, small radio-frequency coils can be used to rapidly determine the device position (active tracking). In this work, active catheter tracking was combined with a dedicated real-time pulse sequence and user interface. The pulse sequence offered the imaging contrasts fast low angle shot (FLASH), true Fast imaging with steady state precession (TrueFISP), and projection MR digital subtraction angiography (MR-DSA), which could be selected by the radiologist from within the scanner room at any time during the intervention. Automatic slice positioning was added to the real-time pulse sequence so that the location of the tracking coils defined the image slice position and orientation. The technique was assessed in phantoms and animal experiments.Results: At a reaction time of 24 msec and a frame rate of three images per second, the movement of an active intravascular catheter could be monitored in the aorta and the renal arteries of a pig. With interactive contrast and orientation changes, the renal vasculature could be assessed by a fully MR-guided catheterization in less than 10 minutes.Conclusion: With carefully designed active catheters, a dedicated user interface, and an optimized pulse sequence intravascular interventions can successfully be performed by a single operator from within the MR scanner room
    Type of Publication: Journal article published
    PubMed ID: 15112307
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  • 7
    Keywords: Germany ; ALGORITHM ; IMAGES ; imaging ; HEART ; TIME ; INTERVENTION ; MRI ; SIGNAL ; MAGNETIC-RESONANCE ; RATES ; SELECTION ; TRACKING ; RECONSTRUCTION ; SUBSET ; CATHETER TRACKING ; INCREASE ; active device tracking ; interactive real-time MRI ; interventional MRI ; intravascular catheters ; COILS ; CATHETER ; ACTIVE CATHETER TRACKING ; image reconstruction optimization ; PHASED-ARRAY
    Abstract: MR-guided intravascular interventions require image update rates of up to 10 images per second, which can be achieved using parallel imaging. However, parallel imaging requires many coil elements, which increases reconstruction times and thus compromises real-time image reconstruction. In this study a dynamic coil selection (DCS) algorithm is presented that selects a subset of receive coils to reduce image reconstruction times. The center-of-sensitivity coordinates and the relative signal intensities are determined for each coil in a prescan. During the intervention m coils are selected for reconstruction using a coil ranking based on the distance to the current slice or catheter position. In a phantom experiment for m = 6, an optimal signal-to-background ratio (SBR) was achieved and foldover artifacts were avoided. In three animal experiments involving catheter manipulation in the aorta and the right heart chamber, the anatomy was successfully visualized at frame rates of about 5 Hz using active catheter tracking
    Type of Publication: Journal article published
    PubMed ID: 17029224
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  • 8
    Keywords: COMBINATION ; Germany ; imaging ; VISUALIZATION ; COMPONENTS ; MR ; MRI ; SEQUENCE ; SIGNAL ; MAGNETIC-RESONANCE ; DESIGN ; COMPONENT ; LOCALIZATION ; TRACKING ; ANGIOGRAPHY ; ORIENTATION ; FEASIBILITY ; DEVICES ; CATHETER TRACKING ; TRUEFISP ; ASSEMBLIES ; assembly ; DELINEATION ; MR pulse sequence ; STENT PLACEMENT ; active device tracking ; CURVATURE ; interactive real-time MRI ; interventional MRI ; intravascular catheters ; radio-frequency coil design
    Abstract: In active catheter tracking, small RF coils are attached to the catheter for localization. For interactive catheter steering at vessel branchings, it is necessary to visualize not only a single point near the catheter tip but also the entire shape and orientation of the catheter's distal end. Therefore, a 35-mm-long twisted-pair RF coil was added to a 5 French intravascular catheter with a single tip-tracking coil. With the use of small nonmagnetic electronic components at the catheter tip, and a special switching circuitry outside the catheter, the coil assembly could be operated in two different modes. During MRI, the tip-tracking coil was detuned so that the MR signal was received by the visualization coil only. During tracking, detuning was switched off and the MR signal was predominantly received by the more sensitive tracking coil. The catheter was used in combination with a MR pulse sequence with automatic slice positioning so that the current imaging slice was always placed at the position of the catheter tip. Phantom and animal experiments showed that the catheter tip is better visualized with the combined approach than with a tracking coil alone
    Type of Publication: Journal article published
    PubMed ID: 15236390
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