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Biomedical subjects

K Tiemann

Publications and source records attributed to K Tiemann.

At least 19 recordsLinked to original sources
PubMed2006

Biliary metal stents and air embolism: a note of caution.

Metal stents are a valuable treatment modality for patients with biliary obstruction. However, we present here two patients whose cases may serve as a warning about an unusual complication associated with these stents. We encountered this complication after endoscopic retrograde cholangiography for obstructed metal biliary stents. The first patient, an 87-year-old man with a benign biliary stricture, failed to regain consciousness after clearing of his stent using a Dormia basket and balloon catheter. Cerebral air embolism was diagnosed on cerebral computed tomography, and transesophageal echocardiography revealed a patent foramen ovale as a precipitating factor for paradoxical air embolism. He survived and was discharged with a residual hemiparesis. In the second patient, a 54-year-old man who had a history of a Billroth II operation and chronic pancreatitis and who had a portal cavernoma with biliary obstruction due to collateral veins, electromechanical dissociation complicated the balloon-catheter stent revision. Echocardiography performed during cardiopulmonary resuscitation showed major air embolism to the right heart. The patient died. These cases demonstrate that air may gain access to the venous system during therapeutic endoscopic procedures of this type. It is likely that the large diameter of metal stents and the potential for these stents to lacerate venous structures facilitate the entry of air into the venous circulation, an event which may have life-threatening consequences.

Aged, 80 and over↗
PubMed2006

Ruptured sinus of Valsalva aneurysm in two patients with subarterial ventricular septal defect.

Rupture of a sinus of Valsalva aneurysm (SVA) is a rare, but life-threatening, event and requires immediate recognition and intervention. We present two previously healthy and physically active patients who were 12 and 33 years of age when rupture of a right coronary SVA into the right ventricle occurred. A subarterial ventricular septal defect (VSD) was detectable in both patients. Cardiac surgery involved VSD closure as well as reconstruction of the aortic valve. Considering complications of subarterial VSD, such as aortic cusp prolapse, aortic insufficiency or SVA, we suggest close follow-up and surgical closure of the VSD in case of any aortic valve deformity.

Adult↗
PubMed2005

3D motion adapted gating (3D MAG): a new navigator technique for accelerated acquisition of free breathing navigator gated 3D coronary MR-angiography.

This study aimed to evaluate the influence of a new navigator technique (3D MAG) on navigator efficiency, total acquisition time, image quality and diagnostic accuracy. Fifty-six patients with suspected coronary artery disease underwent free breathing navigator gated coronary MRA (Intera, Philips Medical Systems, 1.5 T, spatial resolution 0.9x0.9x3 mm3) with and without 3D MAG. Evaluation of both sequences included: 1) navigator scan efficiency, 2) total acquisition time, 3) assessment of image quality and 4) detection of stenoses >50%. Average navigator efficiencies of the LCA and RCA were 43+/-12% and 42+/-12% with and 36+/-16% and 35+/-16% without 3D MAG (P<0.01). Scan time was reduced from 12 min 7 s without to 8 min 55 s with 3D MAG for the LCA and from 12 min 19 s to 9 min 7 s with 3D MAG for the RCA (P<0.01). The average scores of image quality of the coronary MRAs with and without 3D MAG were 3.5+/-0.79 and 3.46+/-0.84 (P>0.05). There was no significant difference in the sensitivity and specificity in the detection of coronary artery stenoses between coronary MRAs with and without 3D MAG (P>0.05). 3D MAG provides accelerated acquisition of navigator gated coronary MRA by about 19% while maintaining image quality and diagnostic accuracy.

Aged↗
PubMed2005

[3D motion adapted gating: a new navigator technique to shorten the acquisition time for coronary MRA].

PURPOSE: A major problem of free breathing coronary MR angiography (MRA) with respiratory navigator gating is low navigator efficiency and prolonged scan time due to irregular breathing patterns. 3D motion adapted gating (MAG) is a new adaptive navigator technique, which adapts in real time to changes of the end-expiratory position of diaphragm. This study evaluates the influence of 3D MAG on coronary MRA. METHODS AND MATERIALS: In 3D MAG, two additional gating windows are grouped around the conventional window. Additionally, each gating window is divided into three bands assigned to different portions of the k-space. The scan is terminated when three consecutive bands are filled and one complete image data set is collected. Free breathing navigator-gated coronary MRA was performed on 48 patients with suspected coronary artery disease. In random order, each patient underwent an ECG-gated, a 3D segmented k-space gradient echo sequence using 3D MAG and a conventional navigator technique. The coronary MRA was evaluated and compared using the following parameters: 1. navigator efficiency and scan time; 2. visualized coronary artery length; 3. qualitative assessment of image quality; and 4. detection of stenoses > 50 % in comparison with catheter angiography. RESULTS: Coronary MRA with 3D MAG had a significant increase in the average navigator efficiency (46 % +/- 12 % vs. 38 % +/- 12 %, p < 0.05), resulting in a significantly shorter scan time (mean: 18 % +/- 4 %, p < 0.05) for coronary MRA with 3D MAG compared to conventional navigator technique. Scans with and without 3D MAG had no significant differences in the continuously visualized vessel lengths, in the assessed image quality and in the sensitivity and specificity (83 % and 89 % vs. 83 % and 88 %, p > 0.05) of detecting coronary artery stenoses > 50 %. CONCLUSION: The 3D MAG technique improves the navigator efficiency and significantly (p < 0.05) shortens the scan time of navigator gated coronary MRA while maintaining image quality and diagnostic accuracy in the detection of coronary artery stenoses.

Adult↗
PubMed2005

[Long-term fate of left atrial thrombi and incidence of cerebral embolism under continuous anticoagulation therapy].

PURPOSE: Patients (pts.) with atrial fibrillation (AF) and atrial thrombi are known to have an increased risk for cerebral embolism. However, little is known about the clinical course of atrial thrombi and the incidence of cerebral embolism in those patients during anticoagulation therapy. The high sensitivity of MR imaging (MRI) including diffusion-weighted imaging (DWI) suggests that this technique could provide an improved estimate of cerebral embolism associated with the presence of left atrial thrombi. The aims of this prospective study were to evaluate 1) the prevalence of clinically silent and apparent cerebral embolism in pts. with newly diagnosed AF and atrial thrombi using MRI/DWI, 2) the long-term fate of atrial thrombi under continues anticoagulation therapy and 3) the incidence of cerebral embolism during a follow-up period of 12 months with continuous anticoagulation therapy. MATERIALS AND METHODS: The study group consisted of 32 pts. with 1) newly diagnosed AF and evidence of left atrial (LA) thrombi detected by TEE and 2) a new start of anticoagulation therapy [International Normalized Ratio (INR) 2.0 - 3.0]. 19 pts. with 1) newly diagnosed AF and no evidence of atrial thrombi and 2) an equivalent anticoagulation regimen served as the control group. In both groups a) MRI/DWI studies of the brain (weeks 0, 4, 8, 12, 20, 28, 36, 44, and 52), b) transesophageal echocardiographic studies (TEE) for assessment of LA-Thrombi (weeks 0 and 52) and c) clinical neurological assessments (weeks 0, 20 and 52) were performed. RESULTS: In the study group (AF and LA-Thrombi) 11 out of 32 pts. (34 %) displayed signs of acute (n = 8) or chronic (n = 3) cerebral embolism in the initial MRI studies. In 4 out of 32 pts. (13 %), MRI/DWI depicted new or additional cerebral emboli (n = 12) during the follow-up period despite continuous anticoagulation therapy. 2 (n = 2/4; 50 %) of these patients had clinically apparent neurological deficits. In the control group 1 out of 19 pts. (5 %) showed evidence of chronic cerebral embolism as assessed by MRI/DWI at the beginning of the study (week 0). No embolic cerebral lesions were detected during the 12-month follow-up. Within 12 months only 63 % (n = 20/32) of LA thrombi in the study group resolved completely under anticoagulation. CONCLUSION: 1. The incidence of clinically inapparent cerebral emboli in pts. with newly diagnosed AF and atrial thrombi is much higher than the incidence of clinically apparent emboli and has been underestimated in the past. 2. New cerebral embolism may occur even with continued effective anticoagulation therapy in 13 % of pts. 3. Only 63 % of atrial thrombi resolve completely within 12 months under anticoagulation therapy.

Aged↗
PubMed2004

Transcatheter PFO closure with a prominent Eustachian valve.

We report the successful PFO closure in a 57-year old woman with complex atrial anatomy. To avoid the risk of interfering with the occluder device due to a prominent Eustachian valve, a Helex Septal Occluder was implanted. Differential therapeutic considerations and specific device characteristics are outlined.

Cardiac Catheterization↗
PubMed2004

[Determination of the renal blood flow in macro- and microcirculation by means of pulse inversion imaging].

PURPOSE: To evaluate whether real-time and intermittent pulse inversion technology (PI) allows the analysis of blood flow in renal macro- and microcirculation. MATERIALS AND METHODS: The experiments were performed in a kidney perfusion phantom as an experimental model for the assessment of contrast replenishment in vascular regions of high flow velocity (medulla) and low flow velocity (cortex). During continuous infusion (0.03 ml/min) of Optison, contrast replenishment kinetics were assessed with intermittent PI at high emission power (MI: 1.3, with increasing trigger intervals) and with real-time PI at low emission power (MI: 0.09) at variable renal arterial blood flow (15 - 65 ml/min), using an HDI-5000 ultrasound unit (Philips Medical Systems). Regions of interest were placed in the major arteries of the medulla and the renal cortex to obtain replenishment curves of the macro- and microcirculation. Non-linear curve fitting was performed using the mathematical model y = A (1-e (-beta t)) with A as the parameter describing blood volume and beta as the parameter describing the speed of contrast replenishment. RESULTS: Replenishment curves could be obtained in all analyzed renal segments. For intermittent and real-time PI a strong linear correlation was found between renal arterial blood flow and A*beta (intermittent PI: cortex: R = 0.97; medulla: R = 0.98; real-time PI: cortex: R = 0.99; medulla: R = 0.96). The differences between the slopes of the regression lines (cortex: high power vs. low power, p = 0.844; medulla: high power vs. low power, p = 0.444) were not significant. CONCLUSION: Intermittent and real-time PI allows the assessment of renal blood flow in different vessel compartments.

Albumins↗
PubMed2004

[The value of applying nitroglycerin in 3D coronary MR angiographie with real-time navigation technique].

PURPOSE: Nitroglycerin administration results in dilation of epicardial coronary vessels and in an increase in coronary blood flow, and has been suggested to improve MR coronary angiography. This study evaluates systematically whether administration of nitroglycerin improves the visualization of coronary arteries and, as a result, the detection of coronary artery stenosis during free breathing 3D coronary MR angiography. MATERIALS AND METHODS: Coronary MR angiography was performed in 44 patients with suspected coronary artery disease at a 1.5 Tesla System (Intera, Philips Medical Systems) (a) with and (b) without continuous administration of intravenous nitroglycerin at a dose rate of 2.5 mg/h, using an ECG gated gradient echo sequence with real-time navigator correction (turbo field echo, in-plane resolution 0.70 x 0.79 mm(2), acquisition window 80 ms). Equivalent segments of the coronary arteries in the sequences with and without nitroglycerin were evaluated for visualized vessel length and diameter, qualitative assessment of visualization using a four point grading scale and detection of stenoses > 50 %. Catheter coronary angiography was used as a gold-standard. RESULTS: No significant differences were found between scans with and without nitroglycerin as to average length of the contiguously visualized vessel length (p > 0.05) and diameter (p > 0.05). There was also no significant difference in the coronary MR angiography with and without nitroglycerin in the average qualitative assessment score of the visualization of LM, proximal LAD, proximal CX, and proximal and distal RCA (2.1 +/- 0.8 and 2.2 +/- 0.7; p > 0.05). Sensitivity (77 % [17/22] vs. 82 % [18/22] p > 0.05) and specificity (72 % [13/18] vs. 72 % [13/18] p > 0.05) for the detection of coronary artery stenosis also did not differ significantly between scans with and without intravenous administration of nitroglycerin. CONCLUSION: Administration of nitroglycerin does not improve visualization of the coronary arteries and detection of coronary artery stenosis in free breathing 3D coronary MR angiography.

Coronary Angiography↗
PubMed2004

Tumour suppression induced by the macrophage activating lipopeptide MALP-2 in an ultrasound guided pancreatic carcinoma mouse model.

BACKGROUND AND AIM: Carcinoma of the exocrine pancreas has a particularly poor prognosis. Therefore, novel therapeutic strategies such as immunotherapy are required. Here we investigated the immunomodulatory capacity of macrophage activating lipopeptide 2 (MALP-2), which binds to toll-like receptors 2 and 6 and induces activation of nuclear factor kappaB in monocytes. This causes the release of early stage leucocyte attracting chemokines and proinflammatory cytokines. METHODS: MALP-2 was tested in a new orthotopic ultrasound guided pancreatic cancer mouse model. This model is close to the biological situation and avoids the stress and immunostimulation caused by laparotomy. Cells from the syngeneic, highly aggressive, and metastatic cell line Panc 02 were administered orthotopically, by ultrasound guidance, to C57bl/6 mice. MALP-2 was administered intratumorally or intraperitoneally and tumour growth, immune status, and leucocyte infiltration at the tumour site were determined. RESULTS: We showed a tumour suppressive effect induced by a single injection of MALP-2. Median survival increased from 21 to 30 days (p<0.002). Combining chemotherapy (gemcitabine) with MALP-2 treatment caused further prolonged survival (median survival 27 days with chemotherapy alone v 37 days for combined treatment; p<0.0002). The life prolonging effect was paralleled by a significant increase in cytotoxic T cells, restoration of beta2 integrin expression on lymphocytes, and high expression of CD45RB on T helper cells. Immunohistochemical stains showed strong cytotoxic T lymphocyte and natural killer cell infiltration. CONCLUSIONS: In conclusion, in a model of orthotopic pancreatic cancer in mice, we induced a tumour suppressive effect by treatment with a synthetic lipopeptide. Treatment with MALP-2 could be an option for immunotherapy in pancreatic cancer.

Adenocarcinoma↗
PubMed2003

Do we still need CK-MB in coronary artery bypass grafting surgery?

AIM: The aim of this study was to evaluate the role of cardiac Troponin I (cTnI) and CK-MB for early prediction of outcome of patients undergoing coronary artery bypass grafting (CABG) surgery. METHODS: In 134 consecutive patients undergoing CABG-surgery blood samples were analyzed for cTnI concentration and CK-MB activity. ECG, hemodynamic parameters and the need for inotropic support, were continuously registered. Patients were divided into group A (uneventful course), group B (ischemia by ECG, hemodynamic stability) and group C (ischemia by ECG and IABP). RESULTS: After removal of X-clamp an increase cTnI and CK-MB was observed in all patients. Five hrs after stop of CPB group A (8.3+/-4.2 microg/L) had lower cTnI values compared to group B (14.8+/-5.3 microg/L) (p=0.035) and C (54+/-22.8 microg/L) (p=0.023). The cut off value was 14.8 microg/L. Sensitivity and specificity (99%/97%) was higher for cTnI than for CK-MB (90%/30%). The positive predictive value of outcome was better for cTnI (86%) than for CK-MB (33%). CONCLUSION: CTnI is a specific and sensitive marker for evaluation of perioperative myocardial ischemia (PMI). Additional determination of CK-MB activity does not provide further clinical information. CTnI should be the marker of first choice in CABG surgery.

Aged↗
PubMed2002

Use of hop (Humulus lupulus) agricultural by-products for the reduction of aqueous lead(II) environmental health hazards.

The agricultural by-products of the hop plant (Humulus lupulus L.) were investigated to determine their potential for use in the removal of heavy lead(II) ions from contaminated aqueous solutions. Separate batch laboratory experiments were performed to establish the optimal binding pH, time exposures, and capacity of the metal adsorption for lead(II) ions by dried and ground hop leaves and stems biomass. Results from these studies have shown a pH dependent binding trend from pH 2-6, with optimum binding occurring around pH 5.0. Time dependency experiments showed a rapid adsorption of lead(II) ions within the first 5 min of contact. Binding capacity experiments demonstrated that 74.2mg of lead(II) were bound per gram of leaf biomass. Similarly overall capacity was seen for the leaves and stems. Desorption of 99% of the bound lead(II) ions was achieved by exposing the metal laden biomass to 0.5M sodium citrate. Further experiments were performed with silica-immobilized hop tissues to determine the lead(II) binding ability under flow conditions. Comparison studies were performed with ion-exchange resins to evaluate the binding ability and to gain further insight into the metal binding mechanism. X-ray absorption spectroscopy experiments were also utilized to gain further insight into the possible lead(II) binding mechanism by the hop plant tissue. Results from these studies indicate that carboxyl ligands are involved in the binding of lead(II) from aqueous solution. These findings show that the use of hop agricultural waste products may be a viable alternative, for the removal and recovery of aqueous lead(II) ions from contaminated waters.

Adsorption↗
PubMed2001

Feasibility of the flash-replenishment concept in renal tissue: which parameters affect the assessment of the contrast replenishment?

The purpose of the study was to evaluate whether power pulse inversion (PPI) and pulse inversion (PI) techniques allow the measurement of indices of microcirculatory flow in real-time at low emission power using contrast microbubbles. PPI and PI imaging were performed in a kidney perfusion model during continuous infusion of Definity (0.12 mL/min). At steady state of tissue enhancement, contrast was destroyed by emission of echo bursts at high emission power (MI = 1.3). Consecutively, contrast replenishment was assessed at low emission power (MI = 0.09) in real-time imaging modes (PPI: 12 Hz; PI: 25 Hz). Regions-of-interest (ROI) of variable sizes were placed in the renal cortex and bigger arteries to compare replenishment of macro- and microcirculation. Nonlinear curve fitting was performed using the mathematical model y=s+A(1-e(-betat)), with A as the parameter describing blood volume and beta as a parameter describing the speed of microbubble contrast replenishment. Replenishment curves could be visually appreciated and quantitatively analyzed in all renal segments. A was significantly higher in bigger arteries compared to renal cortex (p < 0.001). beta was found to be significantly higher in the arteries as compared to the cortex (p < 0.001). The SD of beta diminishes with increasing size of the ROI. The acquisition of replenishment curves following ultrasound (US)-induced destruction of contrast microbubbles is feasible at low power using PPI and PI. Assessment of replenishment kinetics allows the differentiation between macro- and microcirculation. Size and position of the ROI have an important impact on the generation of replenishment curves in both imaging modalities, which has to be taken into account.

Animals↗
PubMed2001

The impact of emission power on the destruction of echo contrast agents and on the origin of tissue harmonic signals using power pulse-inversion imaging.

The purpose of this study was to determine the impact of emission power on ultrasound (US)-induced destruction of echocontrast microbubbles during real-time power pulse inversion imaging (PPI) in myocardial contrast echocardiography (MCE) and to evaluate the magnitude of noncontrast PPI signals arising from myocardial tissue at variable emission power to define the cut-off emission power for optimal MCE using low power technologies. In vitro studies were performed in a flow phantom using Optison, Definity and AFO 150. PPI signal intensity during real-time imaging at 27 Hz was compared with intermittent imaging at 0.1 Hz to evaluate bubble destruction at variable emission power (MI: 0.09 to 1.3). In healthy volunteers, PPI signal intensities during constant infusion of Optison(R) was studied in real-time PPI 22 HZ and during intermittent imaging triggered end-systolic frames every, every 3rd and every 5th cardiac cycle. In addition, the impact of emission power on nonlinear PPI signals from myocardial structures was studied. In vitro, there was a 40% decrease of real-time PPI signal intensity for Optison and AFO 150 at lowest emission power (0.09), whereas no signal loss was observed for Definity. Increase of emission power resulted in a faster decay for Optison(R) and AFO 150 as compared to Definity. In vivo, real-time PPI during continuous infusion of Optison(R) resulted in a 40% decrease of myocardial signal intensity as compared to intermittent imaging every 5th cardiac cycle, even at lowest possible emission power (mechanical index = 0.09). There was a strong positive relationship between MI and noncontrast myocardial PPI signals in all myocardial segments. PPI signal intensity was found to be lower than 1 dB only for extremely low emission power (MI < 0.2). Destruction of microbubbles during real-time imaging by use of PPI at low emission power varies considerably for different echo contrast agents. However, bubble destruction and the onset of tissue harmonic signals focus the use of real-time perfusion imaging to very low emission power.

Adult↗
PubMed2001

Blood flow assessment by ultrasound-induced destruction of echocontrast agents using harmonic power Doppler imaging: which parameters determine contrast replenishment curves?

OBJECTIVE: To evaluate the feasibility of flow determinations by contrast replenishment using harmonic power Doppler imaging (H-PDI). BACKGROUND: The application of indicator dilution principles on contrast echocardiography is limited by numerous methodical problems. Recently, a new method was introduced that relies on ultrasound-mediated microbubble destruction and evaluation of the contrast replenishment. METHODS: Definity, a perfluorocarbon-derived contrast agent under development, was continuously infused into a steady flow phantom and H-PDI registrations were performed within a silicone tube (d = 8 mm). Replenishment interval between destruction and imaging frame was varied from 0.04-2 seconds. Nonlinear curve fitting was performed using an exponential mathematical model. RESULTS: Strong linear correlation between contrast dose and maximum signal intensity as well as between flow and the slope variable beta of the replenishment curve was found for all settings (r > 0.96). Maximum signal intensity and contrast replenishment rate were found to be a function of emission power and were significantly influenced by depth and focus position. CONCLUSION: The feasibility of flow assessment using replenishment curves obtained by H-PDI was demonstrated. However, in experimental conditions, flow analysis was severely influenced by ultrasound system settings and imaging conditions such as emission power, sound field geometry, and investigation depth. For a clinical use of this promising approach, algorithms that take specific system settings and imaging conditions into account have to be found. Imaging modalities that enable a most homogeneous scan field are best suited for the assessment of contrast replenishment.

Contrast Media↗
PubMed2001

Continuous-infusion contrast-enhanced US: in vitro studies of infusion techniques with different contrast agents.

PURPOSE: To evaluate the infusion properties of three ultrasonographic (US) contrast agents and to compare different infusion techniques for achieving constant signals during harmonic power Doppler US. MATERIALS AND METHODS: In vitro studies were performed in a flow phantom. SH U 508A, NC100100, or FS069 was continuously infused at clinically usable doses and infusion rates. To assess agent-specific physical properties, these agents were administered by using a vertically fixed infusion pump and varying infusion start times. The contrast agents were administered by also using a horizontally oriented infusion pump that was either fixed or continuously rotated to homogenize the agent in the syringe. RESULTS: With SH U 508A and NC100100, constant signals were achieved, regardless of the infusion modality used. Compared with conventional infusion, the continuous homogenization of SH U 508A, although not necessary for signal constancy, increased the agent's usefulness (P <.05). With FS069, only continuous homogenization yielded constant signals (P <.001). CONCLUSION: Continuous infusion of SH U 508A or NC100100 provided constant harmonic power Doppler US signals, regardless of the infusion modality used. Because of the special physical properties of FS069, only homogenization produced constant harmonic power Doppler US signals during continuous infusion of this agent.

Contrast Media↗
PubMed2000

[Transthoracic echocardiography in endocarditis: a comparison of conventional and harmonic echocardiography].

BACKGROUND AND OBJECTIVE: Compared with conventional echocardiography (CEC) harmonic imaging (HEC) provides better resolution of the endocardial line and valvular apparatus. This prospective study was undertaken to compare the value of harmonic and conventional transthoracic echocardiography in endocarditis and compare them with standard transoesophageal echocardiography (TOE) and operative findings. PATIENTS AND METHOD: Conventional and harmonic echocardiographic imaging was compared in 30 patients (aged 58 +/- 17 years; 19 males and 11 females) with endocarditis clinically judged to require surgical intervention. The results of both methods were then compared with those of standard TOE and the intraoperative findings. RESULTS: Intraoperatively 15 floating structures, 9 abscesses and 5 perforations were demonstrated. Transoesophageal echocardiography was better than the standard method in diagnosing floating structures and detecting abscesses (15 vs. 10 vegetations, p < 0.05; 7 vs. 5 abscesses, p = 0.05). TOE was better than either method in the diagnosis of abscess. CONCLUSION: Harmonic transthoracic echocardiography is better than the conventional mode in diagnosing complications of endocarditis.

Abscess↗
PubMed2000

[Myocardial contrast echocardiography. Research instrument or already clinical application?].

Increasing interest has been focused on myocardial contrast echocardiography (MCE) since latest imaging technologies allow the detection of echocontrast agents within myocardial structures following intravenous injections. Although numerous studies on different aspects of pre-clinical and clinical applications have been published, MCE has not yet become a standard clinical application. This paper summarises and estimates the clinical value of the recent developments in this evolving field of research, particularly with regard to the new real-time perfusion imaging technologies.

Animals↗