Biomedical subjects

Andreas Mahnken

Publications and source records attributed to Andreas Mahnken.

7 recordsLinked to original sources

PubMed2006

Renal tumors.

The treatment of RCC is rapidly changing. The introduction of minimally invasive thermal ablation techniques offers a safe and accurate alternative to open surgery in the treatment of renal tumors. Because of its technical benefits, percutaneous radiofrequency ablation took the lead among these minimally invasive techniques. Supported by convincing results from experimental studies, patient data prove this procedure to be safe and efficient. As a minimally invasive and nephron-sparing technique, it is well suited for patients with a single kidney, multiple tumors, or contraindications for open surgery.

Aged↗

PubMed2005

Peripheral artery stent visualization and in-stent stenosis analysis in 16-row computed tomography: an in-vitro evaluation.

The accuracy of 16-row multidetector CT in the visualization of different peripheral artery stents and in the appraisal of in-stent stenosis was assessed. Nine different stent types (nitinol and stainless steel) with three diameters (6, 8 and 10 mm) were used; altogether 27 stents were analyzed in a barrel-shaped vascular model. Low-grade (<40%) and high-grade (>60%) in-stent stenoses were simulated by polyurethane sticks (70 HU) of differing diameters (2-6 mm). Imaging was performed with 16x0.75-mm detector collimation, 130 mAs, 120 kV, 12-mm table feed/rotation, 1.0-mm slice thickness and 0.5-mm increment. The stent diameter, strut thickness, in-stent attenuation values, degree and degree of in-stent stenosis were evaluated. Nitinol stents showed significantly (P<10-6) less stent lumen narrowing, artificial strut thickening and overestimation of the degree of in-stent stenoses than stainless steel stents. In-stent attenuation values and artificial strut thickening were significantly (P<10-6) lower in 10- and 8-mm stents than in 6-mm stents. Stent lumen narrowing was significantly less in 10-mm stents than in 8-mm (P<10-4) or 6-mm (P<10-6) stents. In-stent stenoses were significantly overestimated, irrespective of the stent diameter. In 6-mm stents overestimation was significantly higher than in 8-mm (P<0.01) or 10-mm stents (P<10-6). Under in-vitro conditions 16-row MDCT allowed an accurate identification of in-stent stenosis, but significantly overestimated the effective degree of the stenosis.

Constriction, Pathologic↗

PubMed2005

Artifact-free coronary magnetic resonance angiography and coronary vessel wall imaging in the presence of a new, metallic, coronary magnetic resonance imaging stent.

BACKGROUND: Coronary in-stent restenosis cannot be directly assessed by magnetic resonance angiography (MRA) because of the local signal void of currently used stainless steel stents. The aim of this study was to investigate the potential of a new, dedicated, coronary MR imaging (MRI) stent for artifact-free, coronary MRA and in-stent lumen and vessel wall visualization. METHODS AND RESULTS: Fifteen prototype stents were deployed in coronary arteries of 15 healthy swine and investigated with a double-oblique, navigator-gated, free-breathing, T2-prepared, 3D cartesian gradient-echo sequence; a T2-prepared, 3D spiral gradient-echo sequence; and a T2-prepared, 3D steady-state, free-precession coronary MRA sequence. Furthermore, black-blood vessel wall imaging by a dual-inversion-recovery, turbo spin-echo sequence was performed. Artifacts of the stented vessel segment and signal intensities of the coronary vessel lumen inside and outside the stent were assessed. With all investigated sequences, the vessel lumen and wall could be visualized without artifacts, including the stented vessel segment. No signal intensity alterations inside the stent when compared with the vessel lumen outside the stent were found. CONCLUSIONS: The new, coronary MRI stent allows for completely artifact-free coronary MRA and vessel wall imaging.

Animals↗

PubMed2004

Repeated generation of the pulmonary pressure-volume curve may lead to derecruitment in experimental lung injury.

OBJECTIVE: Measurements from the pulmonary pressure-volume (PV) curve have been proposed to adjust ventilator settings. We investigated the effects of repeated construction of an inflation PV curve implemented in a standard ventilator on recruitment or derecruitment in acutely injured lungs. DESIGN AND SETTING: Prospective experimental animal study in eight anesthetized and mechanically ventilated pigs. INTERVENTIONS: Acute lung injury was induced by lung lavage and animals were ventilated in volume controlled mode with PEEP 10 cmH(2)O. The PV curve was constructed five times repeatedly by constant pressure rise, after which ventilation with the preset PEEP was resumed immediately. Studies of hemodynamics, lung mechanics, blood gases and computed tomography were carried out before and after maneuvers. MEASUREMENTS AND RESULTS: Derecruitment was assessed as an increase in nonaerated lung volume (V(NON)), and V(PEEP) was the end-expiratory volume difference between PEEP and ZEEP. There was a significant decrease in PaO(2) from 90.4+/-33.3 to 70.9+/-36.3 mmHg and a rise in venous admixture from 47.8+/-12.7 to 59.1+/-16.6%. V(PEEP) was reduced from 244 to 202 ml. A corresponding decrease in normally aerated lung volume was observed, while regression analysis revealed increase in V(NON) depending on the amount of preexisting atelectasis. CONCLUSIONS: Repeated generation of the PV curve with a readily available tool resulted in worsened oxygenation. Derecruitment of the lungs occurred with loss of PEEP at the start of the maneuver, which could not be recovered by a maximum inflation pressure of 40 cmH(2)O. Repeated use of the investigated tool should be cautioned, and users should consider measures to preserve aerated lung volumes.

Animals↗

PubMed2004

New metallic MR stents for artifact-free coronary MR angiography: feasibility study in a swine model.

RATIONALE AND OBJECTIVES: The objective of this study was to investigate the potential for artifact-free coronary magnetic resonance angiography (cMRA) in the presence of dedicated metallic MR stents in vitro and in a swine model. METHODS: All investigations were performed at 1.5 T, applying a standard cMRA gradient echo sequence with a T2 preparation pulse. Two prototypes of each hand-woven, mechanically woven, and lasered Aachen Resonance Coronary MR Stents made out of an MR-compatible metallic alloy and dilated to 2.5 mm and 4 mm were examined in a water bath. RESULTS: Artifact behavior was judged independently by 2 radiologists as showing "no artifacts" for all tested stent types. Signal-to-noise ratios inside and outside of the stents were measured yielding a Pearson correlation coefficient of 0.98 (y = 1.22 + 0.92x). Nineteen stents (8 hand woven, 3 mechanically woven, 8 lasered) were deployed in coronary arteries of 19 domestic pigs and were examined by cMRA. Artifact behavior of the stents was analyzed by measuring the signal-to-noise ratio at the stent positions and compared with signal-to-noise ratio measurements outside of the stents, yielding a Pearson correlation coefficient of 0.90 (y = -0.75 + 1.06x). CONCLUSIONS: All 3 prototypes of coronary MR stents allowed complete visualization of the stent lumen and consequently determination of stent patency by cMRA.

Animals↗

PubMed2002

Long-term results 10 years after iliac arterial stent placement.

PURPOSE: To retrospectively evaluate results in 110 patients who had iliac arterial occlusive disease and were treated with stents before 1991. MATERIALS AND METHODS: From 1987 to 1990, 110 patients (mean age, 57 years) with iliac arterial occlusive disease (Fontaine stage IIa, seven patients; IIb, 95 patients; III, four patients; IV, four patients) underwent implantation of a self-expanding metal stent. Stenoses (n = 66) were treated after failed angioplasty, and occlusions (n = 60) were treated with primary stent placement. Follow-up included angiography and/or color duplex ultrasonography and clinical examination with ankle-brachial index measurement. Patients lost to follow-up were interviewed by using dedicated questionnaires administered by telephone and/or mail. If a patient was deceased, relatives and attending doctors were interviewed. RESULTS: The fate of 109 of the 110 patients was determined. Overall, 46 patients died: 18 within 5 years, 39 within 10 years, and seven after more than 10 years. The 5- and 10-year survival rates were 83% and 64%, respectively. Cardiovascular disease caused 23 deaths; malignant tumor caused 15. The cause of death remained unknown in five patients. Primary stent patency rates were 66% +/- 4.8 (standard error) after 5 years and 46% +/- 5.9 after 10 years; secondary patency rates were 79% +/- 4.2 after 5 years and 55% +/- 6.3 after 10 years (Kaplan-Meier test). Seventeen (16%) patients underwent surgical bypass of the aortoiliac arteries that involved the segment with the stent, 14 because of stent restenosis and three because of stenosis in other iliac arterial segments. CONCLUSION: The main cause of death in patients with intermittent claudication was cardiac disease. Long-term patency of iliac arterial stents was moderate.

Aged↗

PubMedDate not supplied

Regional thermoablation of local or metastatic renal cell carcinoma.

The objective of the study was to elucidate thermal based ablation techniques for local tumor control. Seven lesions of renal cell carcinoma (2 renal, 1 adrenal, 2 muscle, 1 hepatic, 1 bone) were treated under local (n=2) or general (n=6) anaesthesia with percutaneous cryoablation (CRA): CryoHit device or radiofrequency (RF) ablation (RFA): RF 3000). Treatment was palliative in 4 patients with progression after systemic therapies, and with curative intention in one organ confined tumor (patient with active HCV and HIV infection). Mean power for RFA was 165 watts. Duration of treatments was 10-91 min. No bleeding or urinary leakage was observed; no drainage or indwelling catheters necessary. Pain relief was sufficiently achieved by tramadol and novaminesulfon. Inpatient period on average was 4.25 days. CRA led to complete tumor destruction (CTD) of an adrenal mass (time to progression, 15+ months) and partial tumor destruction (PTD) of a lumbar lesion (19 months); RFA resulted in CTD of 3 lesions (liver, 9+ months; kidney, 1+, 13+ months) and PTD in 2 lesions (muscle and bone, 3 months). In conclusion, it was found that CRA and RFA are safe and effective methods to destroy metastatic RCC. Such minimal invasive techniques are favorable for palliative treatment (low performance status, surgical preconditions) and in conjunction with immunochemotherapy; A decreased risk of bleeding, the shorter duration of hospitalization and a faster recovery of the patient encourage minimal invasive percutaneous thermal based therapies due to life-quality and economic aspects. Treatment of primary renal cell carcinoma is currently under investigation.

Adult↗