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Biomedical subjects

R W Guenther

Publications and source records attributed to R W Guenther.

36 records · Page 2Linked to original sources
PubMed1990

Color-coded image-directed Doppler sonography compared with digital subtraction angiography in the follow-up of percutaneous vascular endoprostheses.

Color-coded image-directed Doppler sonography (CCIDS) was used in the follow-up of self-expandable vascular endoprostheses and was compared with the results of digital subtraction angiography and Doppler pressure indices. The stents were implanted in iliac and femoral arteries or hemodialysis fistulae of 26 patients. The aim of the study was to evaluate the potential of the new imaging method to identify local flow patterns inside of vascular endoprostheses. The stents were identified by sonography in all cases; laminar flow was represented in CCIDS by homogeneous Doppler signals. In case of a distinctly reduced lumen, intravenous digital subtraction angiography (DSA) and CCIDS were both able to identify the stenotic process; however, CCIDS was superior in the demonstration of minute flow irregularities. No different flow patterns were detected in comparing recent with older vascular implants.

Angiography, Digital Subtraction↗
PubMed1990

Fine caliber cholangioscopy.

The miniaturized diameters of endoscopes (miniendoscopes) allow percutaneous access for endoscopic visualization of the extrahepatic and intrahepatic biliary system. Practical aspects of different miniendoscopes in an experimental model are described. Clinically, fine caliber cholangioscopy is helpful in detection of retained biliary stones. Nevertheless, discrimination of benign and malignant stenosis remains difficult, and simultaneous intervention under endoscopic guidance is compromised by the low steerability of the instruments.

Animals↗
PubMed1989

Thermal laser-induced stenosis of the common bile duct. An alternative model for experimental research.

An experimental model of bile duct stenosis and occlusion in dogs is presented. After percutaneous cholecystostomy of the gallbladder, which had been affixed to the abdominal wall during laparotomy four weeks earlier, a standard 2 mm laser heat probe adapted to an Nd:YAG laser (1,064 nm) was advanced inside the proximal common bile duct in 12 animals, using 6 or 7 F sheaths. The proximal part of the common bile duct was exposed to laser pulses of 6 to 10 Watts for one second. Within 3 to 15 days, total occlusion or severe stenosis of the common bile duct consistently occurred and was verified by follow-up percutaneous cholecystocholangiography. No perforations occurred. Compared with other models, laser thermal damage is an easy and reliable method of producing bile duct stenoses for experimental purposes.

Alanine Transaminase↗
PubMed1989

Urinary bladder neoplasms: evaluation with contrast-enhanced MR imaging.

Forty-eight patients with urinary bladder neoplasms were examined with magnetic resonance imaging before and after intravenous administration of gadolinium diethylene-triaminepentaacetic acid (DTPA). Spin-echo sequences with short repetition and echo times were used in all patients; in 20 a gradient-echo technique was used to perform sequential imaging. In 31 patients ratios of tumor signal intensity to that of fat, muscle, and bone marrow were calculated before and after Gd-DTPA enhancement on T1-weighted spin-echo images. Increases in tumor signal intensity on T1-weighted spin-echo images were statistically significant after contrast enhancement (alpha = 1%, P less than .0001). The average rise in relative signal intensity after contrast enhancement was 120% for the tumor-fat ratio (tumor-marrow ratio, 105%; tumor-muscle ratio, 85%). Tumor signal intensity peaked within 120 seconds and remained on a plateau for up to 45 minutes. Necrotic tissue within the tumor, seen in three cases, was detectable only on contrast-enhanced images.

Adult↗
PubMedDate not supplied

MRI-guided biopsy of bone in a hybrid system.

This is a report of our experience with percutaneous, MRI-guided biopsies in 25 patients with skeletal lesions using a 1.5-T MR hybrid system. Twenty-five consecutive patients with skeletal lesions were referred for MRI-guided biopsy. Biopsies were performed with a 1.5-T Philips Gyroscan (Philips Medical Systems, Best, The Netherlands) combined with a c-arm fluoroscopy. Specimens were obtained percutaneously either with a 14- or 18-gauge "side-slit" type of biopsy needle (n = 10 skeletal lesions that had penetrated through the cortex), or using a prototype coaxial drill system powered either by hand or an optional motor (n = 15 skeletal lesions still covered with cortical bone). All but two biopsies could be completed within the MR unit. For one patient, who required a transpedicular approach to a lumbar vertebra, and for one child, who required general anesthesia, we decided to switch to CT guidance. In 19 of the 25 cases (17 of the 23 cases performed in MR), the sample was sufficient and the histopathologic diagnosis was confirmed. Three patients had an inadequate sample, and three others had adequate samples but inaccurate results. No procedural complications occurred. Percutaneous biopsy of skeletal lesions performed under MRI-guidance was found to be safe and reasonably accurate. There were no procedural complications in our small series. MRI may be used as an alternative to CT, but its role vis-à-vis CT has yet to be ascertained.

Biopsy, Needle↗
PubMedDate not supplied

MR-guided biopsy using a T2-weighted single-shot zoom imaging sequence (Local Look technique).

The purpose of this study was to demonstrate the utility of a T2-weighted single shot turbo spin-echo technique--the so-called "Local Look" (LoLo) and more recently renamed "Zoom Imaging" technique--for MR-guided percutaneous interventions. We performed 28 procedures on 22 patients using a 1.5-T system for MR guidance. All procedures were controlled with the LoLo technique, which acquires T2-weighted images in 600 msec. This is achieved by using a small field of view (250 x 125 mm) along with a maximum echo train length, the so-called "single shot method." To prevent backfolding artifacts, the 90 degrees and 180 degrees pulses were oriented orthogonally to each other. Because signal is created only in the region in which the pulses overlap, no backfolding can occur from outside this area. Half of the biopsies were additionally monitored using a fast gradient-echo sequence, which was compared with the LoLo technique. All of the procedures were technically successful, and there were no procedural complications. The LoLo technique produced images that had good contrast between the lesion and the needle artifact, and the artifact size was smaller than that produced by the gradient-echo technique. Subjective judgment of the ability to accurately delineate the needle tip indicated that the LoLo technique was either superior to (73%) or equal to (27%) the gradient-echo sequence in all cases. The LoLo technique is an accurate and effective method for MR guidance of percutaneous procedures, because it shows good lesion contrast and small needle artifacts. The additional use of a gradient-echo sequence during the procedure planning stage is advisable in more difficult cases, particularly when adjacent blood vessels are a concern. Monitoring of the needle tip is best performed with the LoLo technique.

Artifacts↗
PubMedDate not supplied

Iliocaval stenosis and iliac venous thrombosis in retroperitoneal fibrosis: percutaneous treatment by use of hydrodynamic thrombectomy and stenting.

A case of bilateral iliac stenosis and caval stenosis due to retroperitoneal fibrosis was treated by caval stenting and iliac balloon angioplasty, but was complicated by subsequent iliac thrombosis. Venous thrombectomy was successfully achieved by hydrodynamic thrombectomy, and iliac patency was stabilized by bilateral stent insertion.

Angioplasty, Balloon↗
PubMedDate not supplied

A new motor-driven percutaneous bone biopsy system: technical note.

A new coaxial needle system was designed for percutaneous puncture of osteoclerotic lesions. Driven by a conventional motor unit, the instrument allows safe guidance even where difficult biopsy routes are used, and has been shown to penetrate radiopaque lesions. Preliminary clinical results from 29 patients are presented. The specimens obtained yielded a correct diagnosis in 28 cases. No major complications were observed.

Biopsy, Needle↗
PubMedDate not supplied

Stent placement on fresh venous thrombosis.

PURPOSE: To report on the efficacy of fixing fresh venous thrombus to the venous wall by stent placement. METHODS: Seven patients underwent stenting to treat acute venous thrombosis. In two patients, the hemodialysis fistula was thrombosed with the thrombus extending into the brachial veins. In three patients, the hemodialysis fistula was patent but massive swelling of the ipsilateral arm was caused by proximal venous thrombosis. Two patients presented with iliac venous thrombosis within stented pelvic veins. Stent placement was preceded by other mechanical thrombectomy methods in all cases. RESULTS: Attachment of thrombus to the venous wall was successful in all cases treated. Acute rethrombosis did not occur. Follow-up patency in dialysis patients was 7.2 +/- 2.1 months. One patient had rethrombosis of the dialysis graft 3 months after primary treatment. Three patients developed restenosis within a mean period of 7.7 months. One shunt remained patent for 10 months with no event of reobstruction during follow-up. In both patients with iliac stent placement, the vein remained patent over a follow-up period of 8 and 12 months respectively. CONCLUSION: Stenting fresh venous thrombus can achieve immediate venous patency. It may be used as an alternative approach when all other percutaneous methods fail. Frequent restenosis within stented veins limits its use to very selected cases.

Aged↗
PubMedDate not supplied

In vitro evaluation of a rheolytic thrombectomy system for clot removal from five different temporary vena cava filters.

PURPOSE: To evaluate the feasibility of thrombus removal from temporary vena cava filters using a rheolytic thrombectomy device and to assess the embolization rate of this procedure. METHODS: Five temporary vena cava filters together with porcine thrombi were placed in a vena cava flow model (semitranslucent silicone tube of 23 mm diameter, pulsatile flow at a mean flow rate of 4 L/min). A rheolytic thrombectomy system (Hydrolyser) was used with a 9 Fr guiding catheter to remove the clots. The effluent was passed through filters of different size and the amount of embolized particles as well as the remaining thrombus were measured. RESULTS: Thrombus removal rates ranged from 85% to 100%. Embolization rates between 47% and 60% were calculated for the different filters. CONCLUSION: The Hydrolyser is able to remove sufficiently high amounts of thrombus from temporary vena cava filters. However, the amount of embolized particles makes it impossible to utilize this method without special precautions against embolization.

Animals↗
PubMedDate not supplied

Hydrodynamic thrombectomy of hemodialysis fistulas: first clinical results.

PURPOSE: A hydrodynamic thrombectomy system was used for the treatment of recent dialysis shunt thrombosis. PATIENTS AND METHODS: Sixteen shunt thromboses in 14 patients were included in the study. There were seven polytetrafluoroethylene grafts and nine native arteriovenous fistulas. Occlusion time ranged from 6 to 48 hours, and thrombus length ranged from 4 to 40 cm. RESULTS: Thrombectomy was technically successful in 15 of 16 instances. No significant residual thrombus was found in 15 cases. In one case, half of the thrombus remained in the vessel and the procedure failed technically. One embolus to the radial artery occurred after balloon dilation following hydrodynamic thrombectomy and was removed percutaneously. Early rethrombosis within 24 hours occurred in five shunts; four more rethrombosed within 2 weeks to 3 months. Eleven shunts were available for follow-up. Cumulative patency was 41% after 6 months. CONCLUSION: Hydrodynamic thrombectomy is a promising concept for declotting of both hemodialysis grafts and native shunts and may offer an alternative to thrombolysis and surgical thrombectomy.

Adult↗
PubMedDate not supplied

Use of a temporary caval filter to assist percutaneous iliocaval thrombectomy: experimental results.

PURPOSE: To test a new filter design that allows coaxial insertion of thrombectomy devices and active clot removal. MATERIALS AND METHODS: A prototype filter system was used in animal experiments. It is a transjugularly inserted coaxial system with a 16-F outer sheath and an inner tube that is covered by a tulip-shaped meshwork with a 22-mm diameter at its inserted end. The inner tube allows insertion of instruments up to 8 F. The filter was developed to assist with percutaneous mechanical thrombectomy in the iliofemoral and caval veins. The filter has been used as an assisting tool in nine sheep and eight pigs. It was combined with an impeller system in nine sheep for caval thrombectomy and with a hydrodynamic catheter for iliac thrombectomy in eight pigs after artificial induction of iliac or caval thrombosis. RESULTS: The filters captured emboli from the intervention in six of nine sheep. The amount of captured emboli was reduced within the filter cone by the impeller instrument in five of six instances. Residual thrombus was removed by closing the filter in five of six sheep. In pigs, the filter captured emboli in three cases during hydrodynamic embolectomy. Pulmonary embolization did not occur with the filter in place. After filter removal, minor pulmonary clot embolization occurred in one case. CONCLUSION: The temporary tulip filter was effective in these animal models in capturing and removing thrombus material that may dislodge from iliocaval veins during mechanical thrombectomy.

Animals↗
PubMedDate not supplied

Dosimetry of a 188rhenium-labeled self-expanding stent for endovascular brachytherapy in peripheral arteries.

PURPOSE: Radioactive stents have been proposed as endovascular irradiation device to prevent in-stent restenosis by inhibiting neointimal proliferation. 32P-stents have been used in several studies so far, but require large-scale labeling procedures and endovascular barotrauma for stent expansion supporting the development of edge restenosis. Purpose of this study was to establish dosimetry of a self-expanding nitinol stent for peripheral vascular disease, which was radiolabeled with 188rhenium (188Re) by a dip coating technique. METHODS AND MATERIALS: The surface of nitinol Memotherm FLEXX stents was polymer-coated providing functional NH(2) groups for diethylenetriaminepentaacetic acid (DTPA) binding, providing the ligand for the complexation of 188Re onto the stent surface. Stability of radiolabeling was tested over 48 h using an in vitro blood circulation (Chandler Loop). Radial and longitudinal dose distributions of a radiolabeled stent were obtained with a plastic scintillator dosimetry system. RESULTS: Stents with a length of 30 mm and a diameter of 8 mm were labeled with up to 33 MBq 188Re. A total of 69+/-4% of the labeled 188Re remained stable on the stent surface after 48 h. Ninety-five percent of the infinitely accumulated dose was supplied to the target tissue within 72 h. Including correction for radioactivity washout from the stent, the infinitely accumulated dose at 1 mm radial distance from the stent surface was 1.85+/-0.19 Gy/MBq 188Re/cm stent length. CONCLUSIONS: We developed a technique for radiolabeling of self-expanding nitinol stents with 188Re by dip coating and formation of 188Re chelate complexes. We provide dosimetry data useful for application of this beta-emitting stent for endovascular brachytherapy in peripheral vascular occlusive disease.

Brachytherapy↗
PubMedDate not supplied

MR imaging of the knee: three-dimensional volume imaging combined with fast processing.

A new examination protocol for patients with suspected meniscal or hyaline cartilage disorders is presented. Knees were imaged with a fast gradient echo imaging sequence with subsequent three-dimensional transformation. Data were transferred to an image processing system that allows reconstruction in any plane desired. Approximately 200 interactively positioned reconstructions are displayed and reviewed in approximately 10 min. Thirty-five patients with suspected meniscal or hyaline cartilage disorders were examined prospectively. All underwent subsequent arthroscopy. The magnetic resonance (MR) diagnosis showed an accuracy of 91.4% compared with arthroscopic findings. Owing to the short imaging time, the proposed procedure permits screening of knee joint disorders with MR.

Arthroscopy↗
PubMedDate not supplied

Circular spirit level guidance system for CT- and MR-guided punctures.

A circular spirit level guidance system was tested for control of CT- and MR-guided punctures. The device consists of a needle holder fixed to a ground plate and two protractors. This allows adjustment of the fixed needle according to the angulation of the supposed puncture path as measured on tomographic images. A circular spirit level is fixed to the needle and leveled. Now the needle can be removed from the needle holder; by leveling the circular spirit level during the puncture, the formerly adjusted angulation is achieved. The system was tested in vitro and in vivo (22 patients) under CT and MR guidance. The average needle deviation was measured to be 1.96 degrees in vitro and 2.51 degrees in vivo. This simple device allows accurate puncture under CT and MR guidance.

Humans↗