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Biomedical subjects

R W Günther

Publications and source records attributed to R W Günther.

At least 19 recordsLinked to original sources
PubMed2006

New experimental model of sinus and cortical vein thrombosis in pigs for MR imaging studies.

INTRODUCTION: Diagnosis of cerebral sinus vein thrombosis is still a challenge for imaging. MRI and MRA play a major role in sinus imaging. For further development of MR techniques, MR-compatible animal models are required. The aim of this study was to develop an animal model for sinus thrombosis and additional cortical vein thrombosis with a clot of human blood for MR imaging studies. METHODS: A combined surgical and interventional approach was carried out in 13 pigs. After minimal invasive surgical access to the anterior superior sagittal sinus and cortical vein, thrombosis with human blood was induced using an interventional catheter approach. MR imaging was performed prior to and after thrombus induction. RESULTS: Sinus thrombosis was induced in 12 of 13 animals. Three animals suffered acute subdural haemorrhage; one of these animals died during the intervention, and one died after thrombus induction. MR imaging of the thrombosed sinus could easily be performed without significant artefacts in 11 of 13 animals. CONCLUSION: This new model of sinus and cortical vein thrombosis with a clot of human blood allows artefact-free imaging studies on MR.

Animals↗
PubMed2006

[First results with catheter and magnetically guided and detached polymerized ferromagnetic particle filaments and heat-induced particle release using the Stereotaxis Niobe system].

PURPOSE: To develop a new technique for intravascular guidance and the release of magnetized ferromagnetic nanoparticles using a polymerized filament by means of an external magnetic field. MATERIALS AND METHODS: Ferromagnetic nanoscaled beads were embedded in temperature-sensitive gels to form filaments after polymerization. Deflection of the filaments was assessed in a Stereotaxis Niobe magnetic navigation system (MNS) in comparison with dedicated guide wires. The curvature was measured as a surrogate parameter for deflection. In combination with commercially available catheters, the filaments were navigated in a perfused aneurysmatic vessel model and a perfused branched vessel model under the influence of two permanent magnets of the Niobe MNS. The magnetic field vector was varied in all three dimensions. After positioning, the magnetic colloid-containing filaments were exposed to an electromagnetic field of 45 kA/m, 200 kHz for a period of 5 minutes for non-invasive heating. RESULTS: The filaments showed superior deflectability compared to the dedicated guide wires (p = 0.0091). The curvature was 0.54 +/- 0.12 mm(-1) for the filaments and 0.33 +/- 0.21 mm(-1) for the guide wires. In combination with angiography catheters, magnetic guidance and accumulation of specially designed filaments were possible in the perfused vessel model. Inductive heating allowed non-invasive disintegration and releasing of the nanoparticles in all filaments. CONCLUSION: This feasibility study shows that magnetic guidance and targeting of a specially designed magnetic colloid-containing filament and subsequent disintegration are feasible. This technique offers the potential for controlled local drug release.

Aneurysm↗
PubMed2006

[Technical Note: Subclavian artery misplacement of a 12F Shaldon catheter: percutaneous repair with a local closure device under temporary balloon tamponade].

A case of subsequent percutaneous repair using a local closure device with a collagen block (VasoSeal(R)) and temporary balloon tamponade after inadvertent subclavian artery misplacement of a 12F Shaldon catheter is reported. Balloon occlusion safely prevented displacement of collagen into the vascular lumen by occluding the 12F entry site. Furthermore, collagen-induced coagulation was facilitated.

Aged↗
PubMed2006

Evaluation of femoral head vascularization in slipped capital femoral epiphysis before and after cannulated screw fixation with use of contrast-enhanced MRI: initial results.

In this study we used contrast-enhanced magnetic resonance imaging (MRI) to evaluate the vascularization of the femoral head in children with slipped capital femoral epiphysis (SCFE) before and after cannulated screw fixation. Eleven consecutive children with SCFE, seven boys and four girls, aged 10-15 years were included in the study. There were no preslips; four children had acute, three acute-on-chronic, and four chronic SCFE. The MRI examinations were performed in a 1.5 Tesla MR scanner with use of a coronal STIR sequence, a coronal contrast-enhanced T1-weighted spin-echo sequence, and a sagittal three-dimensional gradient-echo sequence. Morphology, signal intensities, and contrast-enhancement of the femoral head were assessed by two radiologists in consensus. Morphologic distortion of the physis, bone marrow edema within the metaphysis and epiphysis, and joint effusion were the preoperative MRI findings of SCFE in each child. In nine children, the vascularization of the femoral head before and after surgery was normal. In one child, a preoperative avascular zone in the superolateral aspect of the epiphysis revascularized completely after surgery. One child with severe SCFE developed avascular necrosis of the femoral head after open reduction of the slip. We conclude that MRI allows for accurate evaluation of the femoral head vascularization before and after surgery in children with SCFE.

Adolescent↗
PubMed2006

Estimation of radiation exposure in low-dose multislice computed tomography of the heart and comparison with a calculation program.

The purpose of this study was to evaluate the achievable organ dose savings in low-dose multislice computed tomography (MSCT) of the heart using different tube voltages (80 kVp, 100 kVp, 120 kVp) and compare it with calculated values. A female Alderson-Rando phantom was equipped with thermoluminescent dosimeters (TLDs) in five different positions to assess the mean doses within representative organs (thyroid gland, thymus, oesophagus, pancreas, liver). Radiation exposure was performed on a 16-row MSCT scanner with six different routine scan protocols: a 120-kV and a 100-kV CT angiography (CTA) protocol with the same collimation, two 120-kV Ca-scoring (CS) protocols with different collimations and two 80-kV CS protocols with the same collimation as the 120-kV CS protocols. Each scan protocol was repeated five times. The measured dose values for the organs were compared with the values calculated by a commercially available computer program. Directly irradiated organs, such as the esophagus, received doses of 34.7 mSv (CTA 16x0.75 120 kVp), 21.9 mSv (CTA 16x0.75 100 kVp) and 4.96 mSv (CS score 12x1.5 80 kVp), the thyroid as an organ receiving only scattered radiation collected organ doses of 2.98 mSv (CTA 16x0.75 120 kVp), 1.97 mSv (CTA 16x0.75 100 kVp) and 0.58 mSv (CS score 12x1.5 80 kVp). The measured relative organ dose reductions from standard to low-kV protocols ranged from 30.9% to 55.9% and were statistically significant (P<0.05). The comparison with the calculated organ doses showed that the calculation program can predict the relative dose reduction of cardiac low photon-energy protocols precisely.

Coronary Angiography↗
PubMed2006

[Gastrointestinal bleeding. Diagnostics and therapy by interventional radiology].

Modern imaging modalities such as (multislice) helical CT allow new diagnostic strategies for gastrointestinal hemorrhage. Today, interventional radiology with superselective transcatheter embolization or TIPS procedures allow minimally invasive therapeutic management which can support or replace surgery. This review is a synopsis of the possibilities and relative merits of diagnostic and therapeutic radiological procedures for gastrointestinal bleeding. Which of them to use should be decided collaboratively by gastroenterologist, surgeon, and radiologist depending on local availability, personal experience, and individual patient factors.

Adult↗
PubMed2006

Impact of ECG gating in contrast-enhanced MR angiography for the assessment of the pulmonary veins and the left atrium anatomy.

PURPOSE: Implementation of ECG gating in contrast-enhanced MR angiography (ceMRA) for improved visualization of the pulmonary veins, the left atrium, and the thoracic vessels. MATERIALS AND METHODS: CeMRA was performed on twelve patients with a history of recurrent atrial fibrillation for the purpose of an intra-individual comparison with and without ECG gating on a 1.5 Tesla MR system (Gyroscan Intera, Philips Medical Systems, Best, NL). Objective image quality parameters such as the signal-to-noise ratio (SNR) of the blood and the contrast-to-noise ratio (CNR) between the blood and myocardium or lung parenchyma were analyzed. The contour sharpness of the pulmonary veins, left atrium, ascending aorta, and pulmonary trunk was also measured. In addition, the artifact level was subjectively assessed by two observers blinded with respect to the sequence parameters. Statistically significant differences (p < 0.05) between the procedures were analyzed using the Wilcoxon test and Pearson Chi-square test. RESULTS: The use of ECG gating in ceMRA significantly reduced artifacts caused by cardiac motion and vessel pulsation. This in turn lead to a significant increase in the contour sharpness of the left atrium and the thoracic vessels. In addition, higher SNR and CNR were found using ECG-gated ceMRA compared to standard ceMRA. CONCLUSION: The use of ECG gating in ceMRA results in artifact-free and sharper delineation of the structures of the heart and thoracic vessels.

Artifacts↗
PubMed2006

[Dose-reduced 16-slice multidetector-row spiral computed tomography in children with bronchoscopically suspected vascular tracheal stenosis -- initial results].

PURPOSE: To evaluate the diagnostic accuracy of contrast-enhanced dose-reduced 16-slice multidetector-row CT (MDCT) in newborns and infants with fiberoptic bronchoscopically suspected vascular-induced tracheal stenosis. MATERIALS AND METHODS: 12 children (4 days to 3 years, 1.2 - 13.5 kg body weight) were examined using i. v. contrast-enhanced 16-slice MDCT (SOMATOM Sensation 16, Forchheim, Germany) without breath-hold and under sedation (11/12). All MDCTs were performed with a dose reduction. The beam collimation was 16 x 0.75 mm, except in the case of one child. MPRs along the tracheal axis in the x-, y- and z-directions and volume-rendering-reconstructions (VRTs) were calculated based on a secondary raw data set in addition to conventional axial slices. 2 radiologists used a three-point grade scale to evaluate the image quality, motion, and contrast media artifacts as well as the usefulness of the 2D- and 3D-reconstructions for determining the diagnosis. Statistical analysis was performed on the basis of a Kappa test. RESULTS: In all cases the cause of the fiberoptic bronchoscopically suspected tracheal stenosis was revealed: compression due to the brachiocephalic trunk (n = 7), double aortic arch (n = 2), lusorian artery (n = 1), vascular compression of the left main bronchus (n = 2). In 3 patients further thoracic anomalies, such as tracheobronchial (n = 2), and vascular (n = 2) and vertebral (n = 1) anomalies were found. The attenuation in the anomalous vessels was 307 +/- 140 HU. The image noise was 9.8 +/- 1.9 HU. The mean dose reduction was 82.7 +/- 3.2 % compared to a standard adult thoracic CT. All examinations were rated as diagnostically good (median 1, range 1, k = 1). 3D images did not show any stair artifacts (median 2, range 1 - 2, k = 1). The image noise was minor to moderate and hardly any motion artifacts were seen (median 1, range 1 - 2, k = 0.8). Contrast media artifacts were rated zero to minor (median 1.5, range 1 - 2, k = 0.676). MPRs (median 1, range 1, k = 1) and VRTs (median 1, range 1, k = 1) were found to be useful for diagnosis. Subsequent vascular surgery was performed on 8 patients. CONCLUSION: Contrast-enhanced dose-reduced 16-slice MDCT is effective for demonstrating the cause of fiberoptic bronchoscopically suspected vascular-induced tracheal stenosis even in very small and severely ill children despite the small contrast media amount and free breathing.

Airway Obstruction↗
PubMed2006

[Contrast-enhanced MR and MSCT for the assessment of myocardial viability].

Over the last decade magnetic resonance (MR) imaging has become a well-established method for visualizing myocardial viability. Multislice spiral computed tomography (MSCT) has also recently proven to be a reliable method for assessing the myocardium for this indication. This review extensively describes the changes in acute and chronic myocardial infarction including the differentiation of stunned or hibernating myocardium. This review focuses on delayed myocardial contrast enhancement as a key concept of viability imaging. Myocardial perfusion imaging as well as the use of alternative contrast agents are introduced. Pathophysiology is correlated to the changes observed in MR imaging and MSCT. The clinical impact of the imaging findings is described.

Contrast Media↗
PubMed2006

64-slice computed tomography assessment of coronary artery stents: a phantom study.

PURPOSE: To compare the use of a new 64-slice computed tomography (CT) scanner with 16-slice CT in the visualization of coronary artery stent lumen. MATERIAL AND METHODS: Eight different coronary artery stents, each with a diameter of 3 mm, were placed in a static chest phantom. The phantom was positioned in the CT gantry at an angle of 0 degrees and 45 degrees towards the z-axis and examined with both a 64-slice and a 16-slice CT scanner. Effective slice thickness was 0.6 mm with 64-slice CT and 1 mm with 16-slice CT. A reconstruction increment of 0.3 mm was applied in both scanners. Image quality was assessed visually using a 5-point grading scale. Stent diameters were measured and compared using paired Wilcoxon tests. RESULTS: Artificial lumen reduction was significantly less with 64-slice than with 16-slice CT. Average visible stent lumen was 53.4% using 64-slice CT and 47.5% with 16-slice MSCT. Most severe artifacts were seen in stents with radiopaque markers. Using 64-slice CT, image noise increased by approximately 30% due to thinner slice thickness. CONCLUSION: Improved spatial resolution of 64-slice CT resulted in superior assessment of coronary artery stent lumen compared to 16-slice CT. However, a relevant part of the stent lumen is still not assessable with multi-slice CT.

Artifacts↗
PubMed2006

Radiation dose reduction to breast and thyroid during MDCT: effectiveness of an in-plane bismuth shield.

PURPOSE: To evaluate dose reduction and image deterioration using in-plane bismuth breast-shielding and thyroid-shielding for MDCT. MATERIAL AND METHODS: Skin and organ doses of thyroid and breast were measured with thermoluminescent dosimeters in a female Alderson-Rando Phantom with and without a 4-ply in-plane bismuth shield. Routine neck (120 kVp, 150 mAs(eff); 16 x 1.5 mm) and chest (120 kVp, 100 mAs(eff); 16 x 1.5 mm) scan protocols were simulated on a 16-row MDCT scanner in three different settings: without shielding, with the shield directly on the surface, and with a 1-cm-thick cotton spacer between surface and shield. Image noise was quantified and compared using the t test. RESULTS: On average, shielding resulted in a 47% organ-dose reduction for the thyroid and 32% for the breast. Placement of the spacer between shield and surface had no significant impact on the measured doses, but significantly decreased the image noise (P < 0.05). CONCLUSION: In-plane bismuth breast and thyroid shielding significantly decreases radiation dose in MDCT without deteriorating image quality.

Artifacts↗
PubMed2005

Radiological intervention to maintain vascular access.

Stenoses and thromboses of dialysis grafts and fistulae are common problems in patients with end stage renal disease (ESRD). Timely recognition and treatment of access-related complications are essential to achieve long-term access function. Minimally invasive percutaneous interventions are techniques of growing importance for the interventional community. While stenoses can typically be treated by balloon angioplasty (PTA), thrombotic lesions may necessitate the combination of mechanical devices and/or thrombolytic agents with ancillary PTA. In this article, interventional treatments for the failing arteriovenous (AV) access are presented and reviewed.

Angioplasty, Balloon↗
PubMed2005

Phase-inversion tissue harmonic imaging compared to fundamental B-mode ultrasound in the evaluation of the pathology of large and small bowel.

Our purpose was to compare phase-inversion harmonic imaging (PIHI) with conventional B-mode ultrasound (US) regarding image quality in the evaluation of bowel pathology. Forty-one patients prospectively underwent intestinal ultrasound scans with US and PIHI in randomly chosen order. Crucial technical parameters were standardized. Bowel morphology as well as perienteric pathology and complications were documented. In 24 cases, the ultrasound results were compared to those of other imaging modalities. Three radiologists evaluated (1) overall image quality, (2) lesion conspicuity and diagnostic confidence, and (3) detection of free fluid on hardcopy films. The ratings for image quality were compared using the two-sample paired t test for means and Bowker's test for symmetry (p=0.05). Compared to US, PIHI provided significantly better overall image quality, lesion conspicuity and diagnostic confidence, as well as better detection of free fluid (p< 0.05). Bowel wall pathology, detected by both modalities, showed good correlation to additional imaging modalities. In 12 patients (29.3%), a gain of crucial diagnostic information was observed with PIHI when compared to US. PIHI significantly enhances sonography of the intestine by offering better overall image quality, better visualization of bowel pathology and associated changes. Additionally, PIHI adds crucial diagnostic information in several patients.

Adolescent↗
PubMed2005

[Renovascular hypertension--diagnosis and therapy].

Atherosclerotic renal artery stenosis accounts for most cases of renovascular hypertension (RVH). Hypertensive patients with clinical features suggesting RVH should be submitted to further noninvasive evaluation including duplex Doppler ultrasonography, CT- or MR angiography. Invasive evaluation by contrast-enhanced angiography confirms the diagnosis of renal artery stenosis. However, neither diagnostic test reliably predicts the course of hypertension after revascularisation. The therapeutic approach in hypertensive patients with hemodynamically important renal artery stenosis includes medical or invasive therapy (renal percutaneous transluminal angioplasty, PTRA; renal arterial stent placement, PTRAS; surgical revascularisation). Randomized trials comparing invasive and conservative approaches demonstrated no differences in blood pressure control or renal function. Only patients with clear clinical indications should be submitted to interventional procedures as PTRA, PTRAS and surgical vascular intervention.

Angioplasty, Balloon↗
PubMed2005

Multi-slice CT for visualization of acute pulmonary embolism: single breath-hold subtraction technique.

PURPOSE: The purpose of our preliminary animal study was to evaluate the feasibility of a new subtraction technique for visualization of perfusion defects within the lung parenchyma in segmental and subsegmental pulmonary embolism (PE). MATERIALS AND METHODS: In three healthy pigs, PE were artificially induced by fresh human clot material. Within a single breath-hold, CT angiography (CTA) was performed on a 16-slice multi-slice CT scanner (SOMATOM Sensation 16; Siemens, Forchheim, Germany) before and after intravenous application of 80 mL of contrast-medium, followed by a saline chaser. Scan parameters were 120 kV and 100 mAs (eff.), using a collimation of 16 x 1.5 mm and a table speed/rot. of 36 mm (pitch: 1.5; rotation time: 0.5 s). A new 3D subtraction technique was developed, which is based on automated segmentation, non-linear spatial filtering and non-rigid registration. Data were analysed using a color-encoded "compound view" of parenchymal enhancement and CTA information displayed in axial, coronal and sagittal orientation. RESULTS: Subtraction was technically feasible in all three data sets. The mean scan time for each series was 4.7 s, interscan delay was 14.7 s, respectively. Therefore, an average breath-hold of approximately 24 s was required for the overall scanning procedure. Downstream of occluded segmental and subsegmental arteries, perfusion defects were clearly assessable, showing lower or missing enhancement compared to normally perfused lung parenchyma. In all pigs, additional peripheral areas with triangular shaped perfusion defects were delineated, considered typical for PE. CONCLUSIONS: Our initial results from the animal model studied show that perfusion imaging of PE is feasible within a single breath-hold. It allows a comprehensive assessment of perfusion deficits as the direct proof of a pulmonary embolus, can be combined with an indirect visual quantification of the density changes in the adjacent lung tissue.

Acute Disease↗
PubMed2005

Inversion prepared coronary MR angiography: direct visualization of coronary blood flow.

PURPOSE: Visualization of coronary blood flow by means of a slice-selective inversion pre-pulse in concert with bright-blood coronary MRA. MATERIALS AND METHODS: Coronary magnetic resonance angiography (MRA) of the right coronary artery (RCA) was performed in eight healthy adult subjects on a 1.5 Tesla MR system (Gyroscan ACS-NT, Philips Medical Systems, Best, NL) using a free-breathing navigator-gated and cardiac-triggered 3D steady-state free-precession (SSFP) sequence with radial k-space sampling. Imaging was performed with and without a slice-selective inversion pre-pulse, which was positioned along the main axis of the coronary artery but perpendicular to the imaging volume. Objective image quality parameters such as SNR, CNR, maximal visible vessel length, and vessel border definition were analyzed. RESULTS: In contrast to conventional bright-blood 3D coronary MRA, the selective inversion pre-pulse provided a direct measure of coronary blood flow. In addition, CNR between the RCA and right ventricular blood pool was increased and the vessels had a tendency towards better delineation. Blood SNR and CNR between right coronary blood and epicardial fat were comparable in both sequences. CONCLUSION: The combination of a free-breathing navigator-gated and cardiac-triggered 3D SSFP sequence with a slice-selective inversion pre-pulse allows for direct and directional visualization of coronary blood flow with the additional benefit of improved contrast between coronary and right ventricular blood pool.

Adult↗
PubMed2005

[Iliofemoral and iliocaval interventions in deep venous thrombosis].

Significant spontaneous thrombus disintegration in deep venous thrombosis (DVT) occurs very infrequently. On the contrary, these thrombi are prone to appositional growth and migration into the pulmonary arteries. The development of chronic venous insufficiency due to postthrombotic syndrome is a frequent consequence of DVT. Therapeutic options in DVT include anticoagulation and recanalising procedures such as thrombolysis and thrombectomy. After appropriate indication assessment, the interventional radiologist can offer an efficacy-proven minimally-invasive vessel restitution approach by performing locoregional thrombolysis, pharmacomechanical therapy or, particularly in iliocaval thrombosis, mechanical thrombectomy. These methods not only serve to restitute of vessel patency, but also allow preserving venous valve function. In DVT with recurrent pulmonary embolism, retrievable filters with extended implantation duration can be deployed. In chronic proximal venous flow obstruction or in case of significant residual stenosis after thrombolysis, balloon angioplasty with stent implantation is the treatment modality of choice. Consequently, the radiologist can adopt an important role in the treatment of extensive venous disease. In this article, the treatment modalities concerning iliofemoral and iliocaval thrombosis are demonstrated and illustrated.

Blood Vessel Prosthesis↗