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Biomedical subjects

R W Guenther

Publications and source records attributed to R W Guenther.

At least 19 recordsLinked to original sources
PubMed2004

[Imaging of the abdominal wall: combination of tissue-harmonic-imaging and extended field-of-view sonography].

PURPOSE: To evaluate the combined use of extended field-of-view sonography and tissue harmonic imaging (THI) for assessment of the abdominal wall. MATERIALS AND METHODS: In 32 patients (25 patients without and 7 patients with abdominal wall pathologies) extended field-of-view sonography of the abdominal wall was performed with and without THI using a 7.5 MHz ultrasound transducer. Images with a scan length of 60 cm were acquired above and below the arcuate line. The images were independently assessed by two observers regarding visibility of the anatomic structures and delineation of pathological changes using a 4-point grading scale. Furthermore, the influence of the extent of the subcutaneous fat on the image quality was assessed. For statistical analysis, kappa coefficients, Fisher"s exact test and a repeated measurement analysis of variance (ANOVA) were applied. RESULTS: In all patients, delineation of the abdominal wall was possible with diagnostic image quality. Abdominal wall pathologies were concurrently diagnosed for extended field-of-view sonography with and without utilization of THI. Image quality was rated better with THI when compared to extended field-of-view B-Mode sonography. In comparison to extended field-of-view B-Mode sonography, the agreement between both readers regarding image quality was markedly improved using extended field-of-view sonography in combination with THI. With increasing thickness of the subcutaneous fat layer, image quality was rated significantly better using THI than B-Mode ultrasound. CONCLUSION: Combined use of extended field-of-view sonography and THI improves image quality and documentation of ultrasound examinations. Especially in obese patients, the use of THI is advantageous. Therefore, abdominal wall ultrasound gains additional value in the preoperative planning.

Abdominal Wall↗
PubMed2001

MR-guided percutaneous drainage of abdominal fluid collections in combination with X-ray fluoroscopy: initial clinical experience.

The aim of this study was to examine the feasibility of a hybrid interventional MR system, which combines a closed bore magnet with a C-arm fluoroscopy unit for percutaneous drainage of abdominal fluid collections. During the past 2 years, we have performed four drainage procedures in four patients (mean age 47 years). Three patients had abscesses (psoas muscle, kidney, subphrenic location) and the fourth patient had a recurrent splenic cyst. All procedures were performed on an interventional MR system consisting of a 1.5-T ACS-NT scanner combined with a specially shielded C-arm. The drainages were guided by T1-weighted fast gradient-echo images, T2-weighted single-shot turbo spin-echo images or both. A standard 18 G (1.2 mm) nonferromagnetic stainless steel needle with a Teflon sheath was used for the punctures following which a 0.89 mm nitinol guidewire was inserted into the fluid collection. Thereafter, the patient was positioned in the immediate adjacent fluoroscopy unit and a drainage catheter was placed under fluoroscopic control. All drainage catheters were successfully placed into the fluid collections, as proven by fluid aspiration and resolution of the collection. The mean time needed for the entire drainage procedure (MR and fluoroscopy) was 110 min. No procedure-related complications occurred. It is feasible to perform drainage procedures on a closed-bore MR scanner. The multiplanar imaging capabilities of MR are particularly helpful for fluid collections in the subphrenic location.

Abdominal Abscess↗
PubMed2001

Improved in-stent magnetic resonance angiography with high flip angle excitation.

RATIONALE AND OBJECTIVES: To optimize the intraluminal signal intensity of a nitinol stent by performing contrast-enhanced three-dimensional magnetic resonance angiography (CE-MRA) with varying flip angles (FAs). METHODS: Contrast-enhanced magnetic resonance angiography at 1.5 T and FAs of 30 degrees, 100 degrees, and 150 degrees was performed on five sheep with 10 iliac nitinol stents (Memotherm-FLEXX). Maximum-intensity projections (MIPs) and composite images of MIPs were performed and compared. RESULTS: Reconstructed MIPs at an FA of 150 degrees showed a slightly disturbed lumen visibility inside the stent accompanied by low-grade lumen visibility outside the stent and vice versa for an FA of 30 degrees. Composite images of a 30 degrees MIP added to a 150 degrees MIP resulted in improved image quality compared with the standard MIP of a single FA. CONCLUSIONS: Signal loss due to radiofrequency shielding inside nitinol stents imaged by CE-MRA can be reduced by applying high FAs. Composite MIP images allow simultaneous visualization of the lumen inside as well as outside the stent.

Alloys↗
PubMed2001

Diffusion-weighted MR imaging for differentiation of benign fracture edema and tumor infiltration of the vertebral body.

OBJECTIVE: The aim of this study was to investigate diffusion-weighted MR imaging for differentiation of benign fracture edema and tumor infiltration with and without accompanying fracture. SUBJECTS AND METHODS: In 10 volunteers, diffusion-weighted spin-echo, fat-suppressed spin-echo, and stimulated-echo sequences were optimized on a clinical 1.5-T scanner. In 34 patients, MR imaging with and without diffusion-sensitizing gradients (b = 598 sec/mm(2) in spin-echo and fat-suppressed spin-echo, b = 360 sec/mm(2) in stimulated-echo) was performed. Thirty-five lesions were analyzed, with 18 caused by acute (< or =10 days old) osteoporotic or traumatic fractures and 17 caused by untreated malignant vertebral infiltration including nine fractures. Signal attenuation in diffusion-weighted images and contrast-to-noise ratio were calculated. The diffusion-weighted images were analyzed by two radiologists. RESULTS: Images from three of 34 patients were excluded because of motion artifact. In osteoporotic and traumatic fractures, a strong signal attenuation of bone marrow edema was seen. In contrast to this, malignant-tumor infiltration caused only minor signal attenuation (p < 0.05), independent of accompanying pathologic fracture. All sequences showed identical changes of signal intensities. In four patients, initial diagnosis was changed by the findings in the diffusion-weighted images. CONCLUSION: Diffusion-weighted spin-echo, fat-suppressed spin-echo, and stimulated-echo sequences are equally suitable for imaging of the spine. Calculation of signal attenuation and observation of signal characteristics allowed differentiation of benign fracture edema and tumor infiltration and provided excellent distinction between benign and malignant vertebral fractures in our series.

Adult↗
PubMed2000

Real-time MR fluoroscopy for MR-guided iliac artery stent placement.

The purpose of this study was to test the feasibility of real-time magnetic resonance (MR) guidance of iliac artery stent placement. Radial scanning together with the sliding window reconstruction technique was implemented on a 1.5 T magnet, yielding a frame rate of 20 images per second. Seven prototype nitinol ZA stents were deployed in iliac arteries of living pigs under MR control. All stents were well visualized on the radial MR images, allowing depiction of the mounted stents as well as stent deployment without anatomy-obscuring artifacts. Stent placement was sucessful in all cases and took 6 minutes on average. The position of the stents was correctly visualized by real-time radial MR scanning, as proved by digital subtraction X-ray angiography. Combined radial scanning and the sliding window reconstruction technique allow real-time MR-guided stent placement in iliac arteries.

Alloys↗
PubMed2000

MR evaluation of stent patency: in vitro test of 22 metallic stents and the possibility of determining their patency by MR angiography.

RATIONALE AND OBJECTIVES: To determine the extent to which visualization of intrastent anatomy in stents of different composition and design is possible by using contrast-enhanced MR angiography. METHODS: Twenty-two MR-compatible stents, most of which had a diameter of 8 mm, were positioned in a phantom filled with aqueous gadolinium solution. Coronal and axial spoiled three-dimensional gradient-echo sequences were performed. Images were acquired with stents positioned at varying angulations to the main magnetic field B0. Profiles orthogonal to the stent axis allowed measurement of artifact sizes independent of window width and center. RESULTS: Oriented along B0, the Cragg, Corvita, Passager, Wallstent, Strecker, Impag, Perflex, and ZA stents allowed visualization of more than 48% of the lumen. The Memotherm, Smart, and Jostent SelfX stents showed a prominent reduction of the inner lumen to below 41%. The lumina of the covered Jostent, Palmaz, Sinus, and Symphony stents were completely obscured. The Impag, Perflex, and Strecker tantalum stents showed growing artifact sizes and a lumen reduction of at least 40% with increasing angulation to B0. CONCLUSIONS. Evaluation of the inner stent lumen by applying contrast-enhanced, three-dimensional gradient-echo sequences is not possible for the majority of stents because of their large artifacts. These depend on the stent type and orientation to B0. Even stents made of nitinol and cobalt alloys only allow qualitative patency assessment but no quantification of stenosis.

Artifacts↗
PubMed1999

Treatment of hemodialysis-related central venous stenosis or occlusion: results of primary Wallstent placement and follow-up in 50 patients.

PURPOSE: To analyze the effectiveness of stent placement as the primary treatment for central venous obstruction in patients undergoing hemodialysis. MATERIAL AND METHODS: Fifty-seven Wallstents were placed in 50 patients with symptomatic shunt dysfunction and arm swelling due to central venous obstruction. Technical success, complication, and patency rates were evaluated. RESULTS: Stent deployment was successful in all patients, and early rethrombosis (within 1 week) was noted in one patient (2%). Seventy-three episodes of reobstruction occurred and were treated percutaneously with angioplasty alone in 54 cases (74%). Nineteen cases (26%) necessitated additional stent placement. The 3-, 6-, 12-, and 24-month primary patency rates were 92%, 84%, 56%, and 28%, respectively. Cumulative overall stent patency was 97% after 6 and 12 months, 89% after 24 months, and 81% after 36 and 48 months. CONCLUSION: In the treatment of brachiocephalic and subclavian venous obstruction, stent placement shows excellent technical results and helps preserve vascular access for a substantial period. Multiple repeat interventions are, however, frequently required to maintain patency.

Adult↗
PubMed1997

Esophageal perforation: comparison of use of aqueous and barium-containing contrast media.

PURPOSE: To assess the need for follow-up esophagography with barium-containing contrast medium after examination with a water-soluble contrast medium in the detection of esophageal perforation. MATERIALS AND METHODS: Sixty-seven patients suspected of having esophageal perforation were examined prospectively with use of an aqueous contrast medium during a 1-year period. The examinations were performed with a digital fluoroscopy unit. Eighteen patients without proved extravasation at esophagography performed with aqueous contrast medium and without other contraindications underwent esophagography with barium-containing contrast medium. RESULTS: In four of 18 patients (22%) with unremarkable findings at esophagography performed with a water-soluble contrast medium, a perforation was detected subsequently with use of a barium-containing contrast medium. No complications related to barium extravasation occurred. CONCLUSION: Patients suspected of having esophageal perforation and who have unremarkable findings at esophagography with water-soluble contrast media need to undergo follow-up esophagography with a barium-containing contrast medium. The use of a digital fluoroscopy unit does not obviate the follow-up examination.

Adult↗
PubMed1996

Hemodialysis fistulas and grafts: use of cutting balloons to dilate venous stenoses.

To evaluate percutaneous transluminal angioplasty (PTA) with a cutting balloon performed in stenosed hemodialysis fistulas and grafts, 19 venous lesions in 15 patients were treated with a cutting balloon with an inflated diameter of 3-6 mm. The grade of stenosis ranged from 40% to 90% (mean, 65% +/- 15 [standard deviation]). Cutting PTA was performed before conventional PTA in seven patients and was followed with conventional PTA with larger balloons in seven patients. The balloon expanded completely in all patients, and no balloon waist remained. The mean grade of stenosis decreased to 14% +/- 9. Cutting PTA increased the technical success of balloon dilation of hemodialysis fistulas and grafts.

Aged↗
PubMed1995

Primary stent placement for chronic iliac artery occlusions: follow-up results in 103 patients.

PURPOSE: To report results of primary stent placement for treatment of chronic iliac artery occlusions. MATERIALS AND METHODS: The authors placed 154 primary stents in 103 patients with iliac artery occlusions of at least 3 months duration. Mean length of the occluded segments was 5.1 cm. All patients had symptoms, with claudication or trophic changes. Mean ankle-arm index at rest was 0.48. Follow-up included angiography, Doppler ultrasound, and clinical examination. RESULTS: Ninety-nine patients demonstrated clinical improvement, with relief or improvement of claudication. Complications that required percutaneous or surgical intervention occurred in six patients; minor complications occurred in another six. Embolization occurred in five patients. Primary patency was 87% after 1 year, 83% after 2 years, and 78% after 4 years; secondary patency was 94%, 90%, and 88% at 1 year, 2 years, and 4 years, respectively. CONCLUSION: Primary stent placement should be the treatment of choice in unilateral chronic iliac artery occlusion.

Angiography, Digital Subtraction↗
PubMed1995

Venous stenosis and occlusion in hemodialysis shunts: follow-up results of stent placement in 65 patients.

PURPOSE: To provide follow-up data on the use of self-expanding stents in hemodialysis fistulas to improve the technical success of balloon angioplasty. MATERIALS AND METHODS: Ninety-two self-expanding vascular stents were placed in 65 patients (29 men and 36 women 25-79 years of age; mean, 57.6 years) with failing hemodialysis fistulas or shunts. RESULTS: Stent placement was successful in all patients, but rethrombosis of the shunt occurred in six patients (10%) within 1 week. There were 96 episodes of reobstruction. In 87 cases, percutaneous or combined surgical and percutaneous repeat intervention was performed. The cumulative shunt function rate was 88% after 6 months, 86% after 1 year, and 77% after 2 years. CONCLUSION: Stent placement in hemodialysis fistulas helps treat lesions that cannot be adequately treated with percutaneous transluminal angioplasty (PTA) alone but has a follow-up patency rate similar to that of PTA. Standard central venous stents have a better patency rate than after PTA.

Adult↗
PubMed1995

Late reobstruction in iliac arterial stents: percutaneous treatment.

PURPOSE: To retrospectively analyze in a nonrandomized fashion the efficacy of percutaneous reintervention in obstructed iliac stents. MATERIALS AND METHODS: In 21 symptomatic patients with iliac lesions, 26 reinterventions (16 for stent occlusion and 10 for stent stenosis) were performed. Restenoses were treated with balloon dilation and either atherectomy or stent placement. Reocclusions were treated with atherectomy or aspiration thrombectomy and then recanalization with balloon dilation and selective stent placement. RESULTS: Balloon angioplasty for stent stenosis was effective in all but one patient. Recanalization was successful in 14 of 16 patients with stent occlusion. The mean period of patency after reintervention was 18 months +/- 15. Cumulative stent stenosis patency after reintervention was 87% after 1 year. Stent occlusion patency was 57%. Recurrent stent obstruction occurred in eight of 24 (33%) patients with successful primary interventions. CONCLUSION: Percutaneous reintervention for both stent stenosis and occlusion is feasible with a moderate complication rate and may be attempted before surgery.

Angioplasty, Balloon↗
PubMed1992

Percutaneous embolectomy: in vitro investigations of the self-expanding tulip sheath.

A self-expanding sheath with a tulip-shaped distal end was designed for performance of percutaneous embolectomy. Its ability to retrieve clots was tested in an in vitro flow model; results were compared with those obtained with a conventional 10-F sheath. Simulated embolectomy of clots weighing 0.1-1.5 g was performed with a 0.75-mL Fogarty balloon on a 4-F catheter. The clot material that embolized distally during the procedure was sampled and quantified. No effective embolectomy was performed via a conventional sheath. With the tulip sheath, however, complete clot removal was achieved unless the clot size exceeded the tulip volume. On the basis of results of in vitro testing, the tulip design is promising for use in several applications during percutaneous interventions.

Catheterization↗
PubMed1990

Tissue response of the biliary and digestive system of rabbits after MTBE infusion into the gallbladder.

We evaluated the tissue response of the biliary and digestive system after Methyl-tert-Butyl-Ether (MTBE) gallbladder infusion in 32 rabbits. After laparotomy, MTBE (5-11 ml) was infused into the gallbladder for eight hours. Animals were sacrificed after eight hours or after two months. Control animals received saline solution infusion into the gallbladder. Afterwards the gallbladder, the common bile duct, the liver, the pancreas and the duodenum were examined histologically. All animals receiving MTBE had different degrees of gallbladder necrosis, common bile duct necrosis and necrosis of intrahepatic bile ducts. After two months, scar formation and a hyperplastic cholecystitis were observed. Control animals did not have comparable tissue reactions; only small areas of necrosis in the gallbladder and the common bile duct occurred after eight hours. The gallbladder, common bile duct and liver remained unchanged in those animals which survived two months. Although the results of this animal study cannot be directly transferred to humans, the data suggest that MTBE should be used in gallstone therapy with caution, and that if it is used, a well-controlled follow-up of these patients is necessary.

Animals↗
PubMed1990

Vascular tissue ablation by an erbium-YAG laser: a fiber-transmittable pulsed laser in the infrared range.

Vascular tissue ablation by an erbium:YAG laser of 2,940 nm was tested in-vitro with the application of increasing energies from 20 to 80 mJ per pulse. Effective ablation of normal vascular tissue, lipomatous atheromas and calcified plaques was achieved. Penetration depth was considerably diminished in the presence of calcifications. The lasered craters showed smooth surfaces and were regularly shaped. The solid state erbium:YAG, which is transmittable by fluoride fibers, offers theoretical advantages for laser angioplasty.

Aortic Diseases↗
PubMed1990

Aspiration catheter for percutaneous thrombectomy: clinical results.

The clinical application of an aspiration thrombectomy system is presented. The system consists of a 7-F Teflon catheter with a rotating coaxial propeller-tipped wire. Thrombectomy was successful in treating occlusion of two femoropopliteal arteries and one hemodialysis implant but was not completely successful in a draining shunt vein. Preliminary results are encouraging; mechanical thrombectomy may offer an alternative to local lysis therapy.

Aged↗
PubMed1990

Mechanical revascularization of occluded iliac arteries with use of self-expandable endoprostheses.

Self-expandable endoprostheses were used to restore the vascular lumen following mechanical recanalization of iliac occlusions without preceding thrombolytic therapy. During a 24-month period 48 of 68 occlusions were successfully recanalized. The vessel lumen was restored with the combined use of dilation with an "undersized" balloon and subsequent stent insertion. Early reocclusion occurred in two patients; the patency rate at 6 months was 93.3% (28 of 30 patients). Restenosis prompted repeat intervention in two patients. Percutaneous transluminal angioplasty combined with the use of self-expandable stents is a promising alternative to vascular surgery, although techniques for safely crossing the occluded segment require further improvement.

Adult↗