Biomedical subjects

A Bücker

Publications and source records attributed to A Bücker.

At least 37 records · Page 2Linked to original sources

PubMed2001

Nephron-sparing percutaneous ablation of a 5 cm renal cell carcinoma by superselective embolization and percutaneous RF-ablation.

PURPOSE: To report on the nephron-sparing, percutaneous ablation of a large renal cell carcinoma by combined superselective embolization and percutaneous radiofrequency ablation. MATERIALS AND METHODS: A 5 cm renal cell carcinoma of a 43-year-old drug abusing male with serologically proven HIV, hepatitis B and C infection, who refused surgery, was superselectively embolized using microspheres (size: 500 - 700 microm) and a platinum coil under local anesthesia. Percutaneous radiofrequency ablation using a 7 F LeVeen probe (size of expanded probe tip: 40 mm) and a 200 Watt generator was performed one day after transcatheter embolization under general anesthesia. RESULTS: The combined treatment resulted in complete destruction of the tumor without relevant damage of the surrounding healthy renal tissue. The patient was discharged 24 hours after RF ablation. No complications like urinary leaks or fistulas were observed and follow up CT one day and 4 weeks after the radiofrequency intervention revealed no signs of residual tumor growth. CONCLUSION: The combined transcatheter embolization and percutaneous radiofrequency ablation of renal cell carcinoma has proved technically feasible, effective, and safe in this patient. It may be offered as an alternative treatment to partial or radical nephrectomy under certain circumstances.

Adult↗

PubMed2001

[Interstitial T1-weighted MR lymphography with use of the dendritic contrast agent Gadomer-17 in pigs].

PURPOSE: To investigate the enhancement of regional lymph nodes, lymph vessels and the thoracic duct after subcutaneous administration of the dendritic contrast agent Gadomer-17. MATERIALS AND METHODS: Interstitial T(1)-weighted MR lymphography was performed in 15 domestic pigs in a 1.5 T MR scanner using the body coil. The contrast agent was injected subcutaneously at a dose of 2.5, 10 and 20 micromol gadolinium/kg/bw (1.4 - 2.3 ml) in the hind legs of 5 pigs, respectively. T(1)-weighted coronal 3D-gradient-echo images were obtained 1 to 150 minutes and 24 hours after contrast material injection. RESULTS: Inguinal lymph nodes, iliac lymph nodes and lymph vessels showed peak enhancement within 10 minutes after subcutaneous administration of the contrast agent. The enhancement of the lymphatic system decreased slowly until 150 minutes post injection. The time-response study, which was performed for inguinal and iliac lymph nodes, revealed the best lymphographic effect for Gadomer-17 at a dose of 10 micromol gadolinium/kg/bw. At this dose the paraaortic lymph nodes and the thoracic duct were also best visualized. CONCLUSION: Interstitial administration of the evaluated dendritic contrast agent Gadomer-17 is highly efficient for the performance of T(1)-weighted MR lymphography in regional lymph nodes, lymph vessels and the thoracic duct.

Animals↗

PubMed2001

Interstitial T1-weighted MR lymphography: lipophilic perfluorinated gadolinium chelates in pigs.

PURPOSE: To investigate the enhancement of the regional lymph nodes, lymphatic vessels, and thoracic duct after interstitial administration of lymphotropic perfluorinated gadolinium chelates at magnetic resonance (MR) imaging. MATERIALS AND METHODS: Two perfluorinated gadolinium chelates, gadofluoramide and gadofluorine 8, were injected subcutaneously into the hind legs of 10 pigs, respectively. Both contrast media were studied at doses of 10 and 25 micromol per kilogram of body weight. T1-weighted three-dimensional gradient-echo and maximum intensity projection images were obtained at 1.5 T between 1 and 210 minutes and 24 hours after injection. The contrast agents were qualitatively compared regarding enhancement and depiction of the regional lymph nodes, lymphatic vessels, and thoracic duct. RESULTS: The inguinal and iliac lymph nodes and lymphatic vasculature enhanced substantially within 10 minutes after subcutaneous administration of both lymphotropic contrast agents. Gadofluorine 8 showed a lymphographic effect superior to that of gadofluoramide. The paraaortic lymph nodes and thoracic duct were best visualized 10--50 minutes after injection of 25 micromol/kg of gadofluorine 8. Lymphatic system enhancement diminished after 2 hours, and the liver and bowel tract enhanced within 24 hours. CONCLUSION: Interstitial administration of perfluorinated gadolinium chelates offers great potential for T1-weighted MR lymphography with positive enhancement of the lymph nodes and lymphatic vasculature.

Animals↗

PubMed2001

Diagnosis of pulmonary arterial hypertension and pulmonary embolism with magnetic resonance angiography.

BACKGROUND: Pulmonary magnetic resonance angiography (PMRA) has been proven to be accurate for the diagnosis of suspected acute or chronic pulmonary embolism (PE). Only limited data exist on the reliability of PMRA for the diagnosis of acute and chronic pulmonary artery hypertension (PAH). The aim of this study was to determine the accuracy of PMRA in the differentiation between patients suffering from PAH of varying etiologies. METHODS: Fifty patients (21 women; mean [+/- SD] age, 52 +/- 16 years) were examined with gadolinium-enhanced PMRA for the evaluation of pulmonary artery (PA) disease. The diagnosis of PAH (ie, systolic PA pressure of > 35 mm Hg) was determined by Doppler echocardiography. The criteria for the diagnosis of chronic PAH by PMRA were dilated central PAs (diameter > 28 mm) and abnormal proximal-to-distal tapering of the PAs. The diagnostic criterion for acute and chronic PE was the presence of an intravascular filling defect. RESULTS: Chronic PAH was present in 18 patients, which was correctly identified by PMRA in 16 patients (sensitivity, 89%). All patients without PAH had normal findings on PMRA (specificity, 100%). Only 1 of 18 patients with normal findings on PMRA showed moderate chronic PAH (negative predictive value, 94%). PAH due to acute/subacute pulmonary thromboembolism (15 patients) was identified in all patients (sensitivity, 100%). Acute PAH was differentiated from chronic PAH in all cases by the detection of intravascular filling defects and the lack of abnormal proximal-to-distal tapering of PAs. CONCLUSIONS: PMRA is a promising noninvasive imaging modality for the identification of patients with acute or chronic PAH. This technique should be considered a sensitive and highly specific screening tool for suspected chronic PAH.

Acute Disease↗

PubMed2000

[Radial k-scanning for real-time MR imaging of central and peripheral pulmonary vasculature].

PURPOSE: To depict the central and peripheral pulmonary vessel anatomy with real-time radial MR scanning without respiratory control. METHODS: Three healthy volunteers and one patient with pulmonary embolism proven by spiral CT angiography were studied with a 1.5 T MR imaging system. First, a breath-hold, contrast-enhanced MR angiography was performed for comparison of accuracy. Gradient echo images (TR 16 ms, TE 4 ms, flip angle 18 degrees) were obtained applying a combination of radial scanning and the sliding window reconstruction technique. A dedicated back-projector allowed data reconstruction in real-time with a frame rate of 20 images per second. Scanning was performed during free breathing. RESULTS: The described technique depicted the central and peripheral portions of the normal pulmonary anatomy with comparable image quality as the 3D contrast-enhanced angiography. Visualization of the pulmonary emboli as demonstrated by spiral CT was possible. CONCLUSION: Real-time radial scanning allows promising image acquisition of the pulmonary vasculature without respiratory control. Further technical improvements and clinical trials are required to evaluate its role in the diagnosis of vascular pathologies.

Adult↗

PubMed2000

[Interventional magnetic resonance imaging--non-invasive imaging for interventions].

As a prerequisite for MR-guidance of interventional procedures, instruments have to be well depicted in the MR image without obscuring or distorting the underlying anatomy. For non-vascular interventions the imaging speed has to be in the range of seconds while control of vascular interventions requires real time imaging speed. The imaging contrast has to be maintained as well as a high spatial resolution. Furthermore, sufficient patient access has to be provided by the MR scanner. Neither an ideal magnet nor the optimal single sequence are available to fulfill the above-mentioned criteria. The type of sequence--gradient echo versus spin echo--together with changing of the echo time and phase encoding direction will ensure an appropriate size of the artifact and thereby of the appearance of the instrument in the MR image. The feasibility of non-vascular MR-guided interventions has been proved at field strengths ranging from 0.064 T to 1.5 T. Bone biopsies, soft tissue biopsies, drainages, and control of interstitial thermo- and cryotherapy have been reported. For vascular interventions, different real time MR strategies are currently under investigation. The development of dedicated catheters and guide wires has enabled MR-guided dilatations, stenting, placement of vena cava filters, and TIPS procedures. Considering the fast progress being made in this field, there can be no question that interventional MRI will become a well-accepted clinical tool offering potential advantages such as excellent soft tissue contrast, multiplanar imaging, flow measurements, high resolution imaging of vessel walls, and lack of ionizing radiation.

Artifacts↗

PubMed2000

[MRI of osteomyelitis: sensitivity and specificity of STIR sequences in comparison with contrast-enhaned T1 spin echo sequences].

PURPOSE: To evaluate the need for additional MR sequences including administration of Gd-DTPA after inconspicuous Short-Tau Inversion-Recovery (STIR) sequence to exclude the diagnosis of osteomyelitis. MATERIAL AND METHODS: 112 MR examinations of 79 patients acquired for the detection of possible osteomyelitis were analyzed retrospectively. All examinations were performed at 0.5 T including STIR, T1-weighted spin echo sequences (T1 SE) before and after application of Gd-DTPA. Additionally, 93 T2-weighted spin echo sequences were available. The examinations were analyzed by two experienced radiologists. First, the STIR sequences were studied, followed by the T1 SE images before and after administration of contrast material. Finally, the T2-weighted images were evaluated. Diagnoses were confirmed by operation (22), biopsy (10), and follow-up (80). RESULTS: In 53 cases osteomyelitis was diagnosed, while the remaining 59 cases suffered from another disease. The sensitivity of the STIR sequence was 100% while the specificity for osteomyelitis was 49.2%. The specificity increased to 79.7% by including T1 SE images into the analysis and reached 83.1% after considering the contrast enhanced images. T2-weighted images yielded no additional information. CONCLUSION: The combination of STIR and T1SE images shows a high sensitivity and specificity for osteomyelitis, thus obviating the need for any additional examinations.

Adolescent↗

PubMed2000

A perspective on needle artifacts in MRI: an electromagnetic model for experimentally separating susceptibility effects.

A thorough understanding of artifacts caused by metallic instruments is essential for the guidance of interventional procedures by magnetic resonance imaging (MRI), because the accurate localization of each instrument is mandatory for this. In the past, this problem has been addressed by several groups, using theoretical, as well as experimental approaches. The artifacts associated with MRI are caused by geometry distortion and intravoxel dephasing. Usually, both effects mingle in the image, and depending on the pulse sequences and its parameters used for data acquisition, these effects are reflected in the image with different magnitude. In this paper we shortly present the well-known mathematical background of the two underlying effects. Mathematically, both can be treated separately. Here, we propose a new electromagnetic model which also allows to experimentally separate the effects better than by comparing spin-echo and gradient-echo images of the same object. With this new model, both effects-geometry distortion and intravoxel dephasing-are demonstrated separately using the same gradient-echo pulse sequence for all scans and adjusting the fields of the model properly. Furthermore, as this model allows to adjust both effects independently, it is used to study different weightings of both effects when they appear simultaneously in the image.

Artifacts↗

PubMed2000

Transesophageal 3-dimensional echocardiography: in vivo determination of left ventricular mass in comparison with magnetic resonance imaging.

The objective of this study was to assess the accuracy and reproducibility of transesophageal 3-dimensional echocardiography (3DE) in comparison with magnetic resonance imaging (MRI) for the in vivo calculation of left ventricular mass (LVM). In addition, mass values obtained by M-mode echocardiography were compared with those calculated by MRI. Three-dimensional reconstruction of the left ventricle was performed from a transesophageal and transgastric transducer position with a multiplane transducer in 20 patients. Left ventricular mass was calculated from both transducer positions by using slices of various thicknesses, ranging from 5 to 20 mm. Reproducibility was determined by 5 repeated measurements of mass in each of 5 randomly selected left ventricles. M-mode echocardiography was performed according to the method described by Devereux. For MRI, multiple short-axis views with 10-mm slice thickness were acquired in inspiration hold. Correlation was high for mass determined by 3DE and MRI (for 10-mm slice thickness: r = 0.99; y = 0.99 x - 0.7 g; standard error of estimate = 8.5 g; P <.001). There was no statistical bias, and the limits of agreement ranged from +/-16.4 g to +/-27.2 g, depending on the slice thickness. Variability was lowest for a slice thickness of 10 mm (SD +/- 8.2 g). The reproducibility of mass determination was excellent (mean width of the 95% CI 12.8 g). Left ventricular mass values calculated from the transgastric and transesophageal transducer position were not different from each other (mean bias 0.6 +/- 9.1 g; P = ns). M-mode-based LVM calculations showed systematic overestimation and large measurement variability (bias 23.7 g; 95% CI +/- 92.8 g). Compared with MRI, transesophageal 3DE is an accurate and reproducible method for the determination of LVM and clearly superior to M-mode echocardiography.

Adult↗

PubMed1999

Interventional MR imaging: percutaneous abdominal and skeletal biopsies and drainages of the abdomen.

Since the introduction of open magnets and short-bore closed magnets, and the availability of fast imaging sequences, MR imaging has become a tool for guidance and control of percutaneous nonvascular and vascular procedures. In general, percutaneous biopsies or drainages require no specific hardware or software modifications. For lesion localization and control of the needle track, simple fast imaging sequences such as fast T1-weighted gradient-echo techniques or fast single-shot T2-weighted spin-echo sequences are sufficient and can be applied depending on the best tissue-to-lesion contrast. Typical scan times range from 1 to 3 s. Different types of biopsy needles are commercially available, allowing sampling of sufficient amounts of tissue. For drainage procedures non-ferromagnetic materials, such as nitinol wires, should be preferred to minimize image distortion by metallic artifacts. Indications for percutaneous biopsies include subdiaphragmatic liver lesions, lesions poorly visible on ultrasound or contrast-enhanced computed tomography, and lesions of the bone marrow characterized by an unspecific bone marrow edema. For percutaneous drainages, subdiaphragmatic lesions appear to be a good indication. With some experience the procedure time is not longer than that under CT or US guidance.

Abdomen↗

PubMed1999

Experimental treatment of early chronic iliac vein thrombosis with a modified hydrodynamic thrombectomy catheter: preliminary animal experience.

PURPOSE: To evaluate the efficacy and safety of a new hydrodynamic catheter for removal of chronic iliac vein thrombus. METHODS: Unilateral iliac vein thrombosis was induced in seven pigs by combining permanent coil and temporary balloon occlusion. Thrombectomy was performed with a new hydrodynamic catheter (10 F S.E.T.) 3 days after thrombus induction. After thrombectomy, the animals were killed and the iliac veins were examined histologically. RESULTS: Complete thrombectomy (100% thrombus removal) was achieved in three of seven animals, 75% removal in three of seven animals, and only 30% removal in one animal. The average thrombus removal was 75%. Successful re-establishment of flow was achieved in five of seven cases. Histologically, the thrombi were partially organized, meeting the histologic criteria for early chronic venous thrombosis. Minor venous wall damage caused by the thrombectomy procedure without acute hemodynamic consequences was observed in four of seven cases. CONCLUSION: The 10-F S.E.T. catheter was reasonably effective in removing chronic iliac vein thrombus with no hemodynamically significant complications.

Animals↗

PubMed1998

MR-guided interstitial cryotherapy of the liver with a novel, nitrogen-cooled cryoprobe.

The purpose of the study was to test a newly developed, MR-compatible, liquid nitrogen-cooled cryoprobe. The probe has an outer diameter of 3.5 mm and was specifically developed for percutaneous, MR-guided, interstitial cryotherapy. The probe was inserted percutaneously into the livers of 10 rabbits. The cryotherapy procedure was monitored with a surface coil in a 1.5 Tesla magnet using a gradient echo sequence. Follow-up examinations were performed 3 and 7 days after the freezing procedure using T1- and T2-weighted spin echo sequences. At 7 days the animals were sacrificed and the cryolesions were examined histologically. The cryoprobe enabled artifact-free MR imaging of the "iceball" formation during freezing of the rabbit liver. After 1 min of freezing, the iceball at the tip of the probe showed an average maximum diameter of 10.8 mm. No bleeding complications were observed during or after the freezing procedure. Histologic examination 7 days after cryotherapy confirmed that the liver lesions were the same size as had been predicted by the images of the acute iceball. This new, percutaneously inserted, MR-compatible, liquid-nitrogen cooled cryoprobe allows accurate, artifact-free MR imaging of interstitial cryotherapy.

Animals↗

PubMed1998

[Interventional MR tomography: equipment concepts].

Interventional MRI is one of the most recent developments of clinical MR imaging. Because of the development of open MR systems and very compact high-field systems, a number of interventional procedures are already possible today under MR control and will be tested in experimental and clinical investigations. The currently commercially available systems differ with respect to their static magnetic field strength, their gradient systems and patient access. In addition, there are differences concerning their space requirements and costs. All systems have components facilitating interventional procedures. In this article we discuss the advantages and shortcomings of these commercially available systems and look at future developments in interventional MR equipment.

Equipment Design↗

PubMed1998

Plasma protein binding of gyrase inhibitors.

Plasma protein binding of a wide range of gyrase inhibitors in clinical practice or trials has been determined by ultrafiltration to determine structure-protein binding relationships. The protein binding was independent of overall lipophilicity. In particular, the "western" part of the "quinolone" skeleton, consisting of a heterocyclus at position 7 and varying substituents at position 8, strongly influences the extent of protein binding, indicating that this part interacts with the plasma protein. In contrast, substituents in position N1 do not show an effect on the protein binding in this series of compounds.

Adsorption↗

PubMed1998

[Experimental evaluation of superparamagnetic iron oxide particles in pulmonary MR angiography].

PURPOSE: Initial experimental results of contrast-enhanced pulmonary MR angiography using the new superparamagnetic iron oxide blood pool agent FeO-BPA. METHOD: Pulmonary MRA was performed in 7 domestic pigs using a cardiac-triggered coronal T1-weighted FFE-Sequence before and up to 90 minutes after contrast injection obtained on a 1.5 T magnet with a standard gradient equipment. A dose of 4 mg Fe/kg bodyweight was used for MRA. The images were qualitatively assessed and compared with X-ray i.v.-DSA. RESULTS: The injection of FeO-BPA allows the acquisition of unsaturated in-plane images of the pulmonary vascular tree down to the first order subsegmental branches including vessel diameters of approximately 1.5 mm. In the normal non-occluded vasculature, no signal void is seen in the TE range of 2.8-5.5 ms secondary to exceeding susceptibility effects which are caused by the iron oxide accumulation. Even 90 minutes after injection of FeO-BPA, assessment of the pulmonary vasculature is still satisfactory. CONCLUSIONS: In the animal experiment, the use of the blood pool agent FeO-BPA provides detailed pulmonary angiograms even on a magnet with a conventional gradient system. The major advantage is the comfortable diagnostic window of > 1.5 hours which also portends its utility for future MR-guided pulmonary interventions.

Angiography, Digital Subtraction↗

PubMed1998

[MRI-guided percutaneous nephrostomy of the contrast-enhanced, nondilated upper urinary tract: initial experimental results].

PURPOSE: To evaluate technique and practicability of MR-guided percutaneous nephrostomy (MRPCN) in an animal model. METHODS: In three domestic pigs, a unilateral percutaneous nephrostomy tube was placed into the nondilated collecting system using exclusively MR-guidance with a standard 1.5 T scanner. The urinary tract was visualized by intravenous injection of Gd-DTPA and low-dose furosemide. The entire interventional procedure was controlled using a T1-weighted "dual stack" 2 D TFE sequence in two orthogonal planes. RESULTS: In all three animals, the puncture needle was safely directed into the nondilated target calyx. Even slight deviations of the needle from the optimal path were readily detected on both MR image planes which enabled immediate correction. This technique successfully achieved a "first attempt" puncture of the targeted calyx in each animal. Over a nitinol guidewire a 5 F catheter was placed into the renal pelvis. Its dysprosium labelled tip was accurately delineated on contrast-enhanced MR images. CONCLUSIONS: Percutaneous nephrostomy under MR guidance is a very feasible technique for puncturing the nondilated pelvicalyceal system. This procedure offers some advantages over the current standard modalities.

Animals↗

PubMed1998

[A new MR-(and CT-) compatible bone biopsy system: first clinical results].

PURPOSE: To describe the development and clinical evaluation of a new, hand-powered or alternatively motor-driven, MRI and CT compatible percutaneous bone biopsy system. MATERIALS AND METHODS: A new coaxial drill system (Cook Europe A/S) was designed for percutaneous, MR-guided bone biopsies and powered either by hand or an optional motor (10-250 rotations/minute using 6 bar [88.2 PSI] compressed air). The system has been used in 23 patients. Fourteen procedures were performed in a 1.5 T MR scanner (Philips-Gyroscan ACS-NT) which has an attached C-arm (Philips-BV 212-Angio) in case fluoroscopy is required, and 9 procedures in a CT scanner (Siemens-Somatom Plus). RESULTS: Driven by hand or by the pneumatic motor unit, the system achieved safe and accurate MR-guided access to all of the lesions and was even able to penetrate osteosclerotic lesions. MR- or CT-guided percutaneous biopsy yielded a correct diagnosis in all but 5 cases. No procedural complications occurred. CONCLUSION: MR-guided percutaneous bone biopsy performed with the new coaxial drill system was found to be safe and reliable, and suitable for obtaining histological specimens from skeletal lesions even when covered with thick cortical or sclerotic bone.

Biopsy↗

PubMed1998

[Real-time MRI with radial k-radial scanning technique for control of angiographic interventions].

PURPOSE: To test the feasibility of real-time MR controlled guidance of field-inhomogeneity catheters in vitro and in vivo as a first step to MR-guided angiographic interventions. METHODS: Applying a combination of radial scanning with the sliding window reconstruction technique, a frame rate of 23 low resolution images per second was achieved. Field inhomogeneity catheters were steered through a flow phantom and into the renal arteries of a pig. RESULTS: It was possible to visualize flow or, respectively, vessels and to depict catheter movements. This enabled real-time MR-guidance of the catheter into the renal arteries of the flow phantom and into those of the pig. CONCLUSIONS: The new technique yields a sufficiently high temporal resolution for MR-guidance of catheters through vessels.

Angiography↗