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Biomedical subjects

M Lenhart

Publications and source records attributed to M Lenhart.

At least 55 records · Page 3Linked to original sources
PubMed2000

[Therapy of iliac artery lesions with a new premounted balloon-expandable stent ("Flexible Iliac Bridge Stent")].

PURPOSE: Evaluation of the handling, technical success rate and six month patency rate of a new, premounted balloon-expandable stent in iliac artery lesions. MATERIALS AND METHODS: In a prospective study 26 stenoses and 3 occlusions of the iliac arteries were primary treated in 24 patients (Fontaine IIa-III, mean age 60.4 year) with the "Flexible Iliac Bridge Stent" (Medtronic AVE, Düsseldorf). Five patients had bilateral stenoses. The ankle-brachial index (ABI) in rest and after exercise was determined before the intervention as well as 1-3 days, 1 and 6 months after the Intervention. The handling and visibility of the stent was scored on a three grade scale by the operators. Follow-up angiography including intraarterial pressure measurement was performed in 17 out of 24 patients (21 out of 29 lesions) after 6 months. RESULTS: All 29 lesions were treated with technical success by implantation of 36 stents. The mean degree of the stenoses before intervention was 72.7 +/- 13.8% (+/- 1 standard deviation) and less than 5% in all cases postinterventionally. The mean pressure gradient before and after stent placement was 21 +/- 13.1 mm Hg and 0.8 +/- 2.3 mm Hg, respectively. The Fontaine stage improved by at least one in all patients. The mean ABI at rest improved from 0.63 +/- 0.15 to 0.89 +/- 0.16, and after exercise from 0.46 +/- 0.17 to 0.8 +/- 0.2, respectively. At 6 months 2 lesions out of 21 (9.5%) showed a restenosis of 55% and 70% with an intraarterial pressure gradient of 16 mm Hg and 27 mm Hg, respectively. After 6 months the mean ABI at rest decreased to 0.83 +/- 0.13, and to 0.72 +/- 0.14 after exercise. Handling and visibility was scored as good by all operators. CONCLUSION: Endoluminal therapy of iliac artery lesions with the used stent is safe and effective. The six month patency rate is comparable to the published data of other stents.

Adult↗
PubMed2000

[Contrast media-enhanced MR angiography of the lower extremity arteries using a dedicated peripheral vascular coil system. First clinical results].

PURPOSE: To evaluate contrast enhanced magnetic resonance angiography (ceMRA) of the pelvic and peripheral arteries with a dedicated peripheral vascular coil system and automated table-feed technique in patients with arterial occlusive disease. METHODS: Three-dimensional gadolinium-enhanced MR angiography in a two-step automatic table feed technique was performed in 45 patients using a 1.5 Tesla imager (Magnetom Symphony, Siemens). The pelvic arteries were imaged with a single injection of contrast material. The upper and the lower leg were imaged with a second injection of contrast material in an automated table feed technique using a dedicated vascular coil system. In 20 patients ceMRA was compared with digital subtraction angiography (DSA) as the standard of reference and in 25 patients ceMRA was performed solely. RESULTS: Sensitivity and specificity for grading significant stenoses > or = 50% and occlusions (in parenthesis) were in the pelvic arteries 94.7%, 96.8%, (100%, 100%), in the arteries of the upper leg 92.3%, 93.3% (87.5%, 100%) and in the arteries of the lower leg 96.5%, 95.8%, (95.2%, 96.8%), respectively. Depiction of the runoff vessels of the lower leg was excellent in ceMRA. CeMRA was of diagnostic quality in all the patients. CONCLUSION: Contrast-enhanced MRA using a dedicated peripheral vascular coil system increases the diagnostic quality of the lower leg. The runoff vessels can be evaluated. Thus, ceMRA in the presented technique is a diagnostic alternative to arterial angiography.

Adult↗
PubMed2000

Morphology and hemodynamics in dissection of the descending aorta. Assessment with MR imaging.

PURPOSE: To obtain morphologic and functional information in patients with dissection of the descending aorta using contrast-enhanced MR angiography (MRA) and MR blood flow quantification of the true and false lumina. MATERIAL AND METHODS: Fourteen patients were studied prospectively using a 1.5 T unit. MRA was performed with a 3D FISP sequence (TR/TE/flip angle 4.7/1.9 ms/30 degrees) after injection of 0.2 mmol Gd-DTPA per kg b.w. Flow quantification with phase velocity mapping was done at the level of the diaphragm using a 2D FLASH technique (TR/TE/flip angle 28/6.5 ms/30 degrees) with an average temporal resolution of 23 frames per cardiac cycle (34 ms). A spectral broadening index was applied to quantify the amount of flow irregularity within both channels of the aorta. Extension of the dissection and involvement of the major branch vessels were analyzed. RESULTS: The mean flow volume per minute was 1,982 ml (SD 1,083 ml) in the true and 1,052 ml (SD 763 ml) in the false lumen. Average peak-velocities were 98 cm/s (SD 33 cm/s) in the true channel and 47 cm/s (SD 26 cm/s) in the false channel. Ten patients had bidirectional flow in the false lumen with a reflux volume ranging between 6.8% and 98%. Only 1 patient presented with bidirectional flow in the true lumen (reflux volume 15%). A significantly higher degree of flow irregularity was found in the false lumen compared with the true channel. CONCLUSION: Different hemodynamic patterns were found in aortic dissection. Their prognostic value and the impact on therapy, specifically percutaneous interventional procedures, have to be further studied.

Adult↗
PubMed2000

Magnetic resonance monitoring of stent deployment: in vitro evaluation of different stent designs and stent delivery systems.

RATIONALE AND OBJECTIVES: To evaluate MR imaging features of commercially available stents before, during, and after in vitro deployment as a step toward MR-guided stent deployment. METHODS: Fourteen stents were deployed in a phantom under MR monitoring at 1.5 T by using a gradient-echo sequence. Device visibility was rated on a four-point scale (excellent, fair, poor, not visible). RESULTS: The Memotherm stent and the rolling membrane (RM) Wallstent showed excellent stent visibility and at least fair scores for artifact-induced narrowing of the stent lumen. Three stents (Palmaz, AVE, Easy Wallstent) showed excellent visibility of the stent but no visible lumen. Five stents (Strecker, Accuflex, Hemobahn, Passager, Sinus) displayed fair visibility. The delivery catheters of four stent systems (Smart, Vascucoil, Symphony, ZA) displayed severe black hole artifacts. CONCLUSIONS: The imaging features of several stent systems might be suitable for MR-guided intervention. The Memotherm and the Wallstent RM combine good visibility of the stent and the lumen.

Blood Vessel Prosthesis↗
PubMed2000

Chest radiography with a large-area detector based on cesium-iodide/amorphous-silicon technology: image quality and dose requirement in comparison with an asymmetric screen-film system.

The purpose of this study was to evaluate a large-area, flat-panel X-ray detector, which uses cesium-iodide (CsI) and amorphous silicon (a-Si). Conventional images were compared with digital images acquired with equal dose (2.5 microGy) and with 50% dose reduction. Fifteen consecutive patients were studied prospectively using an asymmetric screen-film system (detector dose, 2.5 microGy). Digital images were taken from the same patients in a posteroanterior view with detector doses of 2.5 and 1.25 microGy, respectively. The CsI/a-Si active-matrix imager had a panel-size of 43 x 43 cm, a matrix of 3 x 3k, and a pixel-pitch of 143 microm. Hard copies were presented in a random order to eight independent observers, who rated image quality according to six subjective quality criteria. Statistical significance of differences was evaluated with Student's t test for paired samples (confidence level, 95%). Digital radiographs with 2.5 and 1.25 microGy were superior to conventional images regarding all quality criteria. Statistically significant differences were observed for five of six criteria at a detector dose of 2.5 microGy and for only one quality feature at 1.25 microGy. Flat-panel digital imagers based on CsI/a-Si technique have the potential to replace conventional systems and might allow a reduction of radiation dose by 50% without loss of image quality.

Adult↗
PubMed2000

Stent appearance at contrast-enhanced MR angiography: in vitro examination with 14 stents.

PURPOSE: To evaluate signal intensity changes influencing assessment of stent patency at contrast material-enhanced magnetic resonance (MR) angiography. MATERIALS AND METHODS: By using an in vitro model, 14 stents-nine nitinol, one tantalum, two stainless steel, and two cobalt alloy-were investigated regarding their appearance at MR imaging. A vascular phantom consisting of tubes filled with 2.00 mmol/L gadopentetate dimeglumine in saline solution was studied in different orientations within the magnetic field. Imaging was performed with a fast three-dimensional gradient-echo sequence (4. 70/1.89 [repetition time msec/echo time msec]). Relative signal intensity reduction within the stents and the degree of artificial narrowing of the stent lumen were calculated. RESULTS: The stent lumen was visible within 13 stents. A total signal void inside the stent lumen appeared in only one cobalt alloy stent. Artificial narrowing of the diameter was less than 33% in 10 of 14 stents. The tantalum stent and four nitinol stents seemed best suited for contrast-enhanced MR angiography. A bandlike artifact occurred at the ends of the stents when positioned along the readout direction. CONCLUSION: To differentiate between artifacts and stenoses, knowledge of the degree of signal intensity reduction and artificial lumen narrowing within vascular stents is essential. Stent geometry, relative orientation to the magnetic field, and alloy composition influence signal intensity alteration within the stent lumen.

Contrast Media↗
PubMed2000

Time-resolved contrast-enhanced MR angiography of renal artery stenosis: diagnostic accuracy and interobserver variability.

OBJECTIVE: The purpose of this study was to evaluate diagnostic accuracy and interobserver variability of time-resolved three-dimensional gadolinium-enhanced MR angiography in the detection of renal artery stenosis in comparison with intraarterial digital subtraction angiography as the standard of reference. SUBJECTS AND METHODS: Forty consecutive patients (age range, 25-81 years; mean, 62.9 +/- 11.9 years) with suspected renal artery stenosis underwent intraarterial digital subtraction angiography and gadolinium-enhanced MR angiography, performed on a 1.5-T system with fast low-angle shot three-dimensional imaging (3.8/1.49 [TR/TE], 25 degrees flip angle, 10-sec acquisition time, and 1.5-mm partition thickness). Three time-resolved phases were obtained in a single breath-hold. Digital subtraction angiography and gadolinium-enhanced MR angiography were evaluated by four observers who studied 80 main renal arteries and 19 accessory vessels to evaluate the degree of stenosis. A stenosis reducing the intraarterial diameter by more than 50% was regarded as hemodynamically significant. Interobserver variability was calculated. RESULTS: Only one gadolinium-enhanced MR angiography study was not of diagnostic quality, as a result of failure of the power injector. All main branches were of diagnostic quality in 38 (97.4%) of the remaining 39 gadolinium-enhanced MR angiography studies. Seventeen (89.5%) of 19 accessory renal arteries were depicted with gadolinium-enhanced MR angiography. The overall sensitivity for significant stenoses was 92.9%. The overall specificity was 83.4%, and the overall accuracy was 85.9%. Interobserver variability of gadolinium-enhanced MR angiography exceeded that of digital subtraction angiography. CONCLUSION: Time-resolved three-dimensional gadolinium-enhanced MR angiography is a useful noninvasive method of screening suspected renal artery stenosis because of its easy application, short examination time, and high sensitivity despite of its higher interobserver variability.

Adult↗
PubMed2000

Analysis of the availability and completeness of previous radiological examinations related to plain films.

PURPOSE: To evaluate the availability and completeness of previous radiological examinations. MATERIAL AND METHODS: Seven different types of examinations were analysed separately: 1) chest examinations, 2) bedside chest examinations, 3) skeletal examinations, 4) angiographic examinations, 5) mammographic examinations, 6) CT examinations, and 7) MR examinations. A retrospective part of the study covered the calendar year 1997, while a prospective part referred to 1998. The sample size in each modality and each part of the study was 100 observations, resulting in a total number of 1,400 examinations. RESULTS: The average availability and completeness of radiographs in the retrospective analysis was 96.9% in 1997. The average availability and completeness of radiographs in the prospective analysis was 85.5% for the year 1998. This applied to necessary previous examinations of the same or different modality irrespective whether the examination was conducted internally or externally. CONCLUSION: The real loss rate of radiographs derived from the retrospective investigation was 3.1%. The prospective part of the study showed that 14.5% of the required previous internal and external examinations of the same or different modality were not available completely and in time to the examining radiologist.

Humans↗
PubMed1999

[Contrast medium-enhanced MR angiography of the pelvic and leg vessels with an automated table-feed technique].

PURPOSE: To evaluate contrast enhanced magnetic resonance angiography (ceMRA) with an automated table-feed technique in patients with arterio-occlusive disease for imaging of the pelvic and peripheral arteries. METHODS: Twenty-two patients underwent three-dimensional gadolinium-enhanced MR angiography in a three-step automatic table-feed technique on a Magnetom Symphony operating at 1.5 Tesla. Maximum intensity projection images (MIP) were generated from the subtracted and original studies. Image quality and venous contrast were evaluated by two groups of observers. 304 vessels (17 patients) were compared with DSA as the standard of reference. RESULTS: All examinations were performed without any technical problems. Diagnostic quality of the MIP of subtracted data sets was superior to that of the unsubtracted images. Venous overlay was 61% in the lower leg. In a total of 599 observations, a sensitivity of 96% (95%, 82%) and a specificity of 87% (88%, 99%) were high compared to DSA in the detection of significant stenoses > or = 50% (> or = 75%, occlusions). Interobserver correlation was good (linear correlation 0.9). CONCLUSION: Stepping-table digital subtraction contrast enhanced MRA is a promising technique in the diagnosis of peripheral arterio-occlusive disease.

Aged↗
PubMed1999

[Ischemic complications in aortic dissection--percutaneous treatment with balloon fenestration and stent implantation].

PURPOSE: To describe principles and results of percutaneous treatment of ischemic complications of aortic dissection. MATERIALS AND METHODS: In five cases (four patients) aortic dissection was clinically complicated by renal (n = 4), iliofemoral (n = 2) or mesenterial ischemia (n = 1). After evaluation by means of computed tomography, angiography, and manometry, treatment consisted of balloon fenestration of the intimal flap, stent placement or both. RESULTS: Eleven of 25 vascular beds were classified as ischemic. Treatment consisted of 11 balloon fenestration procedures in 3 patients, in one case supported by stent placement across the dissection membrane. Stents were placed in five renal arteries, one stent was placed in the true lumen of the aorta. One iliac artery was treated with balloon dilatation. One renal artery dissection became symptomatic after balloon fenestration and was treated successfully by stent placement. In all cases ischemia was resolved by endovascular treatment. All patients had persistent relief of symptoms. Mean follow-up time is 5.8 months. CONCLUSION: Ischemic complications of aortic dissection can be effectively and safely treated with stent placement and balloon fenestration.

Adult↗
PubMed1998

[Radiologic implantation of central venous portal systems in the forearm].

PURPOSE: To assess the safety and effectiveness of fluoroscopic guided brachial implanted central-venous miniport systems. PATIENTS AND METHODS: In 32 oncological patients a central-venous miniport system (Vital-Port, CPC-Cook) was implanted in the forearm. The group included 15 women and 17 men (range 33-78, mean 56 years). RESULTS: Technical success was 100%, in 6 patients vasospasm produced difficulties in catheter placement. In a total of 2878 patients days (range 3-445, mean 90 days) 5 complications occurred (15.6%, 1.7 on 1,000 catheterdays): In one patient (3.13%, 0.35/ 1000 d) the system was changed due to leakage of the catheter near the chamber. Four patients had minor complications: in one case excision of a suture line granuloma was necessary, one haematoma at the site of the chamber was treated with dressing, one patient had a wound dehiscence and one occluded catheter returned to patency by flushing the system with contrast material. Venous thrombosis, phlebitis, catheter dislocation, paravasation or system-related infection did not occur. CONCLUSION: Fluoroscopic guided peripheral central-venous port implantation is a safe and easy procedure with a high success rate and a low complication rate which can be performed in an outpatient setting.

Adult↗
PubMed1997

Cerebral CT angiography in the diagnosis of acute subarachnoid hemorrhage.

PURPOSE: To evaluate the usefulness of CT angiography (CTA) in the detection of intracranial aneurysms in patients with acute subarachnoid hemorrhage (SAH). MATERIAL AND METHODS: In 53 patients with nontraumatic SAH a helical contrast-enhanced CTA was performed. CTA data were reconstructed with maximum intensity projection (MIP). Each patient underwent selective arteriography of the cerebral vessels (as the gold standard). CTA (axial images and MIP reconstructions) and arteriography were evaluated separately and their diagnostic information was compared. RESULTS: In 14 of the 53 patients neither CTA nor angiography showed a vascular malformation. In the remaining 39 patients, angiography demonstrated a total of 51 aneurysms ranging in size from 3 mm to 16 mm. CTA missed one of these aneurysms, which was located at the internal carotid artery. 3-D CT reconstruction was slightly superior to arteriography in the demonstration of the neck, shape and direction of the aneurysms. Partial thrombosis of 3 aneurysms was demonstrated only by CTA. CONCLUSION: Although CTA cannot replace cerebral arteriography in the diagnostic work-up of acute SAH, it proved to be helpful in demonstrating the topographic anatomy of cerebral aneurysms and surrounding structures.

Acute Disease↗
PubMed1987

Substrate oxidation in kidney slices from acidotic and alkalotic rats: role in ammoniagenic adaptation.

The enhanced renal ammoniagenesis that occurs during acidosis may depend on oxidative processes. To determine this, oxygen consumption (Qo2) of renal slices from acidotic rats (medium pH 7.0) and alkalotic rats (medium pH 7.8) in the presence of 4 different substrates (glutamine, lactate, acetate and 2-oxoglutarate) was investigated. Incremental addition of any oxidizable substrate tested to the incubation medium increased Qo2 until a maximal rate was approached (approximately 17-58% above baseline). Comparing acidotic to alkalotic slices, Qo2 was significantly less at low concentrations of lactate and acetate before maximal Qo2 occurred. In contrast, Qo2 was relatively higher at low concentrations of 2-oxoglutarate and glutamine with acidotic compared to alkalotic slices. Accordingly, acid-base perturbations produce different patterns of Qo2 depending on the substrate and its concentration. These observations coupled with others are consistent with the hypothesis that a relative block in the oxidation of lactate and acetate during acidosis provides more NAD+ for glutamine oxidation and participates in acidotic regulation of renal glutamine metabolism.

Acetates↗