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A Bücker

Publications and source records attributed to A Bücker.

At least 55 records · Page 3Linked to original sources
PubMed1998

[Stent placement with real time MRI guidance: initial animal experiment experiences].

PURPOSE: The aim of this study was to test the feasibility of iliac artery stent placement under MR guidance with real-time MR radial scanning in an animal model. MATERIALS AND METHODS: The experiments were performed on three pigs in a 1.5 T scanner. Radial scanning with a gradient echo technique (TR 8.4 ms, TE 3.6 ms, flip angle 10 degrees) was used. A dedicated backprojector performed the reconstruction of the raw data in real-time. The resulting MR-images were displayed on LCD screens beside the magnet. The sliding window reconstruction technique allowed image acquisition at a frame rate of 16 images per second. MR-compatible self-expanding stents with a diameter of 8 mm and a length of 3 cm were placed into the left iliac artery. Their positions were verified by digital subtraction angiography (DSA) and compared to MRI. RESULTS: All stents were successfully placed. Stent positions as monitored by real-time MR were identical to those seen on DSA images. The time needed for exact positioning of the scan plane ranged from 15 to 30 minutes. Stent placement itself took 8 minutes on average. CONCLUSION: Radial scanning applied together with the sliding window reconstruction technique allows placement of stents in iliac arteries under real-time MR control.

Angioplasty, Balloon↗
PubMed1998

Device visualization for interventional MRI using local magnetic fields: basic theory and its application to catheter visualization.

This paper addresses one of the major problems in Interventional magnetic resonance imaging (MRI): the visualization of interventional devices. For visualization locally induced magnetic fields are used, which disturb the homogeneity of the main magnetic field of the MR scanner. This results in signal loss in the vicinity of the device due to intravoxel dephasing, and leads to a disturbance of the phase image. The local fields are established by a low current in a closed copper loop along the device. This method will be introduced as a means for catheter visualization. The basic theory behind this method is presented. Simulations are performed to determine the effect of intravoxel dephasing, without interfering effects like susceptibility or radio-frequency artifacts. Scanned and simulated data is used to verify the theoretical consideration. Different configurations of wire loops are discussed and two types of catheter visualization scans are proposed. Results from a pig study show that this methods holds promise for intravascular interventions under MRI guidance.

Animals↗
PubMed1998

Gadolinium-enhanced excretory MR urography after low-dose diuretic injection: comparison with conventional excretory urography.

PURPOSE: To evaluate the clinical utility and morphologic accuracy of gadolinium-enhanced excretory magnetic resonance (MR) urography after low-dose diuretic injection and to correlate the results with those of conventional urography. MATERIALS AND METHODS: In 71 patients with urologic symptoms, excretory MR urography was performed after intravenous injection of 5-10 mg furosemide and, 30-60 seconds later, 0.1 mmol of gadopentetate dimeglumine per kilogram of body weight. The MR urograms were interpreted by three radiologists, who were blinded to the clinical outcome, and subsequently compared with conventional urograms. RESULTS: Injection of furosemide before contrast material led to rapid, uniform gadolinium distribution inside a sufficiently distended collecting system such that there was no excessive concentration of gadolinium in the urine. In patients with normal or moderately reduced excretory function, this effect allowed complete visualization of the urinary tract within 5-20 minutes of contrast material injection while minimizing gadolinium-related endoluminal T2* effects. The clinical course helped verify almost all MR urographic results. The MR urographic technique was significantly superior to conventional urography in the assessment of the ureters and bladder (P < .0001). Delineation of small caliceal abnormalities is still problematic. The best depiction of the pelvicaliceal system was obtained with fat-suppressed MR imaging, although it was still slightly inferior to conventional urography (P < .05). CONCLUSION: Gadolinium-enhanced excretory MR urography performed after low-dose diuretic injection is a promising and accurate alternative to conventional excretory urography for imaging the morphology of the urinary tract.

Adult↗
PubMed1998

Abdominal MR angiography performed using blood pool contrast agents: comparison of a new superparamagnetic iron oxide nanoparticle and a linear gadolinium polymer.

OBJECTIVE: We evaluated and compared two different experimental blood pool contrast agents for abdominal MR angiography in an animal model. MATERIALS AND METHODS: In seven pigs, coronal T1-weighted three-dimensional fast field-echo images were obtained on a conventional 1.5-T MR imaging system before and after i.v. injection of the ultrasmall superparamagnetic iron oxide agent FeO-BPA. In another seven pigs, MR angiograms were acquired using the gadolinium polymer WIN 22181. Enhanced images were obtained 5-210 min after injection of FeO-BPA and 1-120 min after injection of WIN 22181. RESULTS: Both blood pool agents yielded detailed angiograms of the abdominal vascular tree when imaging lasted 2 min. In-plane running vessels were imaged without saturation effects and with equivalent maximum signal-to-noise ratios. Half the maximum signal-to-noise ratio was reached 150 min after injection of FeO-BPA, whereas this interval was approximately 70 min for the gadolinium polymer. Because of these different imaging half-life periods, the effective diagnostic window provided by FeO-BPA was six to eight times longer than that of WIN 22181. In the liver, the vascular T1 shortening and the parenchymal T2* effect of FeO-BPA complemented each other, resulting in an optimal contrast-to-noise ratio significantly higher than that achieved with WIN 22181. This "double-contrast effect" in the liver was especially helpful when obtaining detailed MR portograms. CONCLUSION: The blood pool agents FeO-BPA and WIN 22181 can be used to produce high-quality abdominal MR angiograms on standard MR imaging equipment. The contrast-to-noise ratio of hepatic vessels is best on iron oxide-enhanced images because of a T1-T2* synergistic effect in the liver. The longer diagnostic window provided by FeO-BPA coupled with the option of in-plane imaging suggests the usefulness of FeO-BPA in future MR imaging-guided vascular interventions.

Abdomen↗
PubMed1997

Catheter visualization using locally induced, actively controlled field inhomogeneities.

A new technique for visualization of interventional devices using MR is presented. A prototype catheter was equipped with a thin copper wire loop, leading from the proximal end to the tip and back. A small current (10-150 mA) through these two parts of a wire induces a local magnetic field along the catheter. Introduction of this catheter into the main magnetic field of the MR imager locally disturbs the homogeneity of the magnetic field. Image locations within the locally induced fields appear dark due to signal loss, and the extent of this effect can be varied during the procedure by simply adjusting the current. Different dedicated wire configurations allow visualization of the catheter in its whole length or in parts, i.e., with markers for balloons. Fast gradient echo sequences that provide a bright signal from inflowing blood are used for rapid imaging.

Animals↗
PubMed1997

Radiological assessment of artificial bone defects in the floor of the maxillary sinus.

OBJECTIVE: To compare dental radiographs and axial high resolution (HR) CT scans for the identification of artificial bone defects between the maxillary sinus and the roots of the adjacent teeth and to evaluate the accuracy of HR-CT. METHODS: Artificial bone defects of different dimensions were produced in the antral floor adjacent to 40 roots of 23 premolars and molars in 21 human autopsy specimens of the posterior maxilla. Periapical radiographs were obtained together with 1 mm axial HR-CT scans. The macroscopic and radiological findings of both sets of images were compared. Histological sections were prepared corresponding to the CT scans and the accuracy of the scans evaluated by measurement of five parameters. RESULTS: None of the artificial bone defects could be identified on the dental radiographs. In contrast 62.5% of the antral bone defects could be identified in the axial HR-CT scans. Identification of their margins depended on the location on the tooth root, adjacent bone morphology and visualization of the periodontal ligament space. When the periodontal ligament space was visualised identification of an antral floor between 0.2 and 0.5 mm thick was feasible. CONCLUSION: In certain clinical situations HR-CT is appropriate for identifying antral bone detects between the maxillary sinus and the roots of the adjacent teeth.

Alveolar Process↗
PubMed1997

[Preoperative spiral CT cholangiography with 3-dimensional surface reconstruction: the anatomical imaging potentials, limits and application strategies].

PURPOSE: Evaluation of CT cholangiography compared to i.v. cholangiography concerning its diagnostic value before laparoscopic cholecystectomy and optimisation of CT cholangiography. METHOD: I.v. and CT cholangiographies of 54 patients were retrospectively evaluated by two radiologists. The time interval between contrast infusion and CT was correlated with the assessment of CT cholangiographies to detect the optimal timing for CT scanning. RESULTS: CT cholangiography was judged to be generally better than i.v. cholangiography. The optimal time interval for CT scanning is between 30 min and 60 min post contrast infusion. CONCLUSION: CT cholangiography should replace the conventional tomograms if i.v. cholangiography does not yield sufficient depiction of the biliary tree. It should be performed within 60 min post contrast infusion. Complete abolishment of i.v. cholangiography is not warranted. This is due to the fact that conventional cholangiography can sufficiently delineate the biliary tree and thereby reduce x-ray exposure and cost compared to initial performance of CT cholangiography.

Adult↗
PubMed1997

[Catheter visualization in MR-tomography: initial experimental results with field-inhomogeneity catheters].

PURPOSE: To assess the feasibility of a new developed field inhomogeneity catheter for interventional MR imaging in vivo. MATERIALS AND METHODS: Three different prototypes of a field inhomogeneity catheter were investigated in 6 pigs. The catheters were introduced in Seldinger technique via the femoral vessels over a guide wire on an interventional MR system (Philips Gyroscan NT combined with a C-arm fluoroscopy unit [Philips BV 212]). Catheters were placed in veins and arteries. The catheter position was controlled by a fast gradient echo sequence (Turbo Field Echo [TEE]). RESULTS: Catheters were introduced over a guide wire without complications in all cases. Using the field inhomogeneity concept, catheters were easily visualised in the inferior vena cava and the aorta by the fast gradient echo technique on MR in all cases. Although aortic branches were successfully cannulated, the catheters were not displayed by the TFE technique due to the complex and tortuous anatomy. All animals survived the experiments without complications. CONCLUSION: MR guided visualization of a field inhomogeneity catheter is a simple concept which can be realised on each MR scanner and may allow intravascular MR guided interventions in future.

Animals↗
PubMed1997

[Flow direction-sensitive spin-echo MR angiography].

New blood pool contrast agents yield a significant shortening of T1 of blood. Consequently, the usual techniques of time-of-flight and phase-contrast angiographies cannot produce angiograms sensitive to one flow direction, even if saturation slabs are applied. It was our aim to test the hypothesis of displaying arterial and venous flow selectively with a specially designed spin echo sequence even after administration of contrast agents. Parallel slice selective 90-degree and 180-degree pulses were applied. The distance between slices could be varied. It was attempted to obtain MR angiographies that were flow sensitive for one direction only. We performed flow phantom studies without the use of contrast media and first in vivo experiments in pigs after administration of iron oxide particles. With our modified spin echo sequence unidirectional flow can be displayed, whereas stationary tissue is totally suppressed. There are no special demands for the hardware and no additional postprocessing needs to be performed. The locally off-centred 90-degree and 180-degree pulses are responsible for this. Exclusively, protons excited by the 90-degree pulse and flowing into the slice of the 180-degree pulse will be refocused and only such protons will give rise to signal in the images.

Animals↗
PubMed1997

[T1-weighted excretory MR urography using GD-DTPA after low-dose diuretic administration].

PURPOSE: Assessment of the morphology of the urinary tract by gadolinium (Gd)-enhanced T1-weighted MR-urography (MRU) and precontrast diuretic injection. METHODS: MRU was performed in 5 patients using Gd-DTPA-enhanced coronal T1-weighted 3D-gradient-echo sequences with different spatial resolution. Prior to contrast injection, 10 mg of furosemide were administered intravenously. RESULTS: Secondary to the precontrast furosemide injection, the increase of the renal excretion rate allows complete visualisation of the entire collecting system within 10 minutes following Gd injection. Maximum intensity projections provide a three-dimensional overview of the ureters separate from the bladder. To achieve detailed anatomic imaging of the calices, both optimal distension and high resolution sequences are prerequisites which cannot be realized by means of survey urograms only. CONCLUSIONS: Contrast-enhanced excretory MRU performed after injection of a diuretic offers a rapid approach to visualising the morphology of the nondilated urinary tract. Imaging of caliceal details must be done with high-resolution 3D-gradient-echo sequences.

Adult↗
PubMed1997

[Cava filter placement under MRI control. Experimental in vitro and in vivo studies].

PURPOSE: An instrument has been developed for the introduction of caval filters which can be used with MRI; it has been investigated in in vitro and in in vivo experiments. MATERIAL AND METHOD: The ferromagnetic components of a commercially available instrument for the femoral introduction of the MR-eye Tulip IVC filter were changed for similar, non-ferromagnetic parts and the lock and dilator marked with dysprosium oxide rings. The instrument was used in a flow phantom and in animal experiments (two domestic pigs) in order to insert filters under MRI control on a 1.5 T Philips Gyroscan with integrated mobile digital subtraction angiography. RESULTS: Both in vitro and in vivo, the introducer, catheter and caval filter could be identified by MRI and positioned under MRI control. The position of the filter as indicated by MRI corresponded with radiological and macroscopic findings in all cases (5 phantoms, 2 pigs). CONCLUSION: The early experimental results indicate that percutaneous introduction of caval filters with placement under MRI control is possible.

Animals↗
PubMed1997

[MR-guided biopsies with high-resolution ultrafast T2-weighted turbo spin-echo sequence LoLo: initial clinical experience].

PURPOSE: The feasibility of the "LoLo"-technique for MR guidance of biopsy procedures was tested. MATERIAL AND METHODS: MR-guided biopsies were performed on 10 patients employing a 1.5 T system. The "LoLo"-technique used is a single shot turbo spin echo technique. Only a small field of view is covered in order to yield images with a resolution of 1 mm2 in 600 ms. The orthogonal orientation of the slice selective radio frequency pulses to each other prevents foldover artifacts. RESULTS: No complications occurred. All biopsy procedures yielded sufficient material to diagnose the underlying disease. The "LoLo"-technique enabled good depiction of the needle tip in all cases. T2-weighted contrast typical for turbo spin echo images was observed. No foldover artifacts were detectable. CONCLUSION: MR-guided biopsies are possible with the "LoLo"technique. Compared to gradient echo sequences T2-weighting and smaller susceptibility artifacts proved to be advantageous.

Adult↗
PubMed1997

Interventional magnetic resonance. Initial clinical experience with a 1.5-tesla magnetic resonance system combined with c-arm fluoroscopy.

RATIONALE AND OBJECTIVES: The authors evaluate the feasibility of performing magnetic resonance (MR) procedures on a 1.5-tesla (T) system combined with conventional c-arm fluoroscopy. METHODS: A 1.5-T MR imaging system was combined with a conventional c-arm fluoroscopy unit in one room. The two systems were connected via a floating table top. Twenty-six interventional procedures (biopsies, MR-portography, percutaneous alcohol injection, laser ablation, fluid aspiration, and breast marking) were performed in 22 patients under MR, fluoroscopic control, or both. For MR guidance, fast gradient echo sequences were used, initiated from a panel at the front of the magnet. Images were displayed on an liquid crystal display screen positioned on the magnet. RESULTS: All MR-guided procedures were performed successfully without complications. The addition of c-arm fluoroscopy was useful for bone interventions and MR-portography. All diagnostic biopsies yielded sufficient amounts of tissue for histologic diagnosis. In breast lesions, the target identified on dynamic MR imaging was marked correctly in each case. In interstitial laser thermotherapy the laser effect could be visualized, and in percutaneous ethanol injection the distribution of the alcohol could be seen. Both imaging systems worked without image distortions and high-quality MR images were obtained. CONCLUSIONS: The combination of a 1.5-T MR imager with a c-arm fluoroscopy system seems to be a promising technical solution for performing interventional MR procedures.

Adult↗
PubMed1997

Contrast-enhanced magnetic resonance urography. First experimental results with a polymeric gadolinium bloodpool agent.

RATIONALE AND OBJECTIVES: The authors investigated the feasibility of contrast-enhanced excretory magnetic resonance urography to visualize the nonobstructed urinary tract with a macromolecular gadolinium-based bloodpool agent. METHODS: Excretory magnetic resonance imaging was performed in seven pigs using a T1-weighted three dimensional fast-field-echo sequence before and up to 120 minutes after administration of a gadolinium bloodpool prototype agent. RESULTS: During the first 15 minutes after injection, the urographic effect was predominantly poor. Visualization of the entire urinary tract was excellent in four pigs and incomplete but satisfactory in three 105 minutes after injection. Furosemide application was tested in one case, which improved image quality effectively. Corresponding to the physiological excretion rate, signal measurements in the renal parenchyma revealed a gradual decrease of the initially distinct contrast enhancement. CONCLUSIONS: T1-weighted contrast-enhanced magnetic resonance urography using a polymeric gadolinium bloodpool allows detailed visualization of the normal urinary tract, while information about the excretory function is obtained simultaneously. However, application of a diuretic seems to be essential to prevent lengthy examination duration.

Animals↗
PubMed1997

Furcation involvement: comparison of dental radiographs and HR-CT-slices in human specimens.

In this in vitro study we compared dental radiographs and high resolution computed tomography (HR-CT) regarding identification and classification of the degree of horizontal and vertical furcation involvement. After removal of the soft tissue and metallic restorations of 18 dentate upper and lower jaws in the interradicular furcation region of 28 molars, bony defects of different dimensions were experimentally produced. The specimens were examined radiographically with standardized dental radiographs and 1.0 mm thick contiguous axial CT-scans. After identification of molars with artificial furcation involvement in the dental radiographs and axial CT-scans, the horizontal and vertical grades of furcation involvement were classified. Radiological identification and classification were compared with the macroscopic findings in the specimens. For quantitative histological-radiological comparison, corresponding microsections were prepared in the same plane as the axial CT-scans. In the dental radiographs the artificial furcation involvement in 6 of 28 (21%) molars was identified. In contrast, all 28 molars with involved furcations (100%) were identified in the axial CT-scans. The horizontal and vertical grades of furcation involvement were classified in the same way as the macroscopic findings, permitting comparison of histological sections and axial CT-scans. The HR-CT technique offers 3-dimensional assessment of the interradicular bone morphology in furcation involvement without overlying structures. The periradicular alveolar bone can be assessed on all sides of the roots. HR-CT scanning thus permits a high identification rate and classification of molars with involved furcations.

Alveolar Process↗
PubMed1997

Iliac arteries: plain and heparin-coated Dacron-covered stent-grafts compared with noncovered metal stents--an experimental study.

PURPOSE: To compare lumen patency, neointimal thickening, and local inflammatory reaction with noncovered metal stents and plain and heparin-coated Dacron-covered stent-grafts. MATERIALS AND METHODS: In each of 16 sheep, four prostheses were placed in the iliac arteries: a plain and a heparin-coated Dacron-covered Cragg stent-graft, a noncovered Cragg stent, and a noncovered Memotherm nitinol stent. Two prostheses were inserted in the iliac artery on each side. Patency was monitored with angiography and intravascular ultrasound (US). Eight animals were killed at 1-month follow-up, and the other eight at 6 month follow-up. Neointimal thickening and inflammatory foreign-body reaction to the prostheses were determined macroscopically and with light microscopy. RESULTS: More than 50% stenosis developed in 10 heparin-coated and three plain Dacron-covered stent-grafts but not in the noncovered stents. Two heparin-coated and one plain Dacron-covered stent-graft occluded completely. Neointimal thickening and inflammatory reaction were severe with the heparin-coated Dacron-covered stent-grafts, were less with the plain Dacron-covered stent-grafts, and were least with the noncovered stents. CONCLUSION: Neointimal thickening and inflammatory reaction significantly increased with covered compared with noncovered prostheses in the iliac arteries in sheep and were worst with heparin-coated Dacron-covered stent-grafts. If possible, use of noncovered stents should thus be preferred to use of Dacron-covered stent-grafts.

Alloys↗
PubMed1997

Perigraft inflammation due to Dacron-covered stent-grafts in sheep iliac arteries: correlation of MR imaging and histopathologic findings.

PURPOSE: To evaluate with magnetic resonance (MR) imaging the inflammatory perigraft response after implantation of Dacron-covered and noncovered arterial endovascular prostheses in sheep. MATERIALS AND METHODS: Four prosthesis types--two Dacron-covered nitinol stent-grafts (plain and heparin-coated) and two noncovered nitinol stents (Memotherm and Cragg)--were each inserted into the external iliac arteries of eight sheep. MR imaging before and after gadolinium enhancement was performed 5-8 days and 1 month after implantation (before the animals were killed). Macroscopic and microscopic examinations of the vessels were performed, and findings were correlated with those on MR images. RESULTS: Severe inflammatory perigraft responses to the heparin-coated Dacron-covered stent-grafts were found; MR images demonstrated contrast enhancement and edema. Macroscopic examination showed marked vascular wall thickening and adhesions around the Dacron fabric; microscopic examination showed a pronounced inflammatory foreign-body response. There was a moderate inflammatory response to the plain Dacron-covered stent-grafts and almost no response to noncovered stents. CONCLUSION: In sheep, MR imaging findings of perigraft soft-tissue edema and contrast enhancement correlated well with histopathologic findings of severe perigraft inflammation due to heparin-coated Dacron-covered stent-grafts.

Alloys↗