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Biomedical subjects

T Schlosser

Publications and source records attributed to T Schlosser.

15 recordsLinked to original sources
PubMed2006

[MR coronary angiography with MS-325, a blood pool contrast agent: comparison of an inversion recovery steady-state free precession with an inversion recovery fast low angle shot sequence in volunteers].

PURPOSE: To compare the signal-to-noise and contrast-to-noise ratio as well as the image quality of 3D inversion recovery steady-state free precession (IR-SSFP) and 3D inversion recovery fast low angle shot (IR-FLASH) sequences for contrast-enhanced breath-hold MRCA. MATERIALS AND METHODS: 24 healthy volunteers (10 female, 14 male, mean age 29.8 +/- 6.1 years) were involved in this study. All examinations were performed on a 1.5 T MR scanner (Magnetom Sonata, Siemens, Germany) after injection of 0.05 mmol/kg body weight MS-325 (EPIX Pharmaceuticals, Cambridge, MA and Schering AG, Berlin, Germany). MRCA was performed using IR-SSFP (TR 3.8 ms, TE 1.6 ms, FA 65 degrees , 35 phase encoded steps, bandwidth 540 Hz/pixel, slice thickness 1.5 mm, in-plane resolution 1.2 x 0.9 - 1.4 x 1.0 mm) and IR-FLASH (TR 3.8 ms, TE 1.6 ms, FA 25 degrees , bandwidth 490 Hz/pixel, slice thickness 1.5 mm, in-plane resolution 1.2 x 0.9 - 1.4 x 1.0 mm) sequences. For all scans the inversion time was set to null the signal intensity of the myocardium. Signal-to-noise ratio (SNR) as well as contrast-to-noise ratio (CNR) measurements (blood versus myocardium) were performed. The image quality was assessed based on a 5-point scale ranging from 1 (excellent) to 5 (non-diagnostic) by two radiologists in consensus. RESULTS: The mean signal-to-noise ratio of blood (27.7 +/- 4.7 vs. 22.6 +/- 4.9, P < 0.0001) and the contrast-to-noise ratio (21.0 +/- 4.3 vs. 15.8 +/- 4.3, P < 0.0001) showed significantly higher values for IR-SSFP sequences. The mean image quality scores were significantly higher for SSFP (3.6 +/- 0.7) than FLASH (2.8 +/- 0.9) sequences (P < 0.05). CONCLUSION: IR-SSFP sequences show a considerable overall improvement in image quality compared to IR-FLASH sequences for MRCA after injection of a gadolinium-based blood pool contrast agent.

Adult↗
PubMed2005

Comparative study of the degradation of polylactide and polytartrate implants in vitro.

Poly(D/L-lactide (PLA) and 2',3'-(1',4'-diethyl-L-tartryl)-poly-(2,3-O-isopropylidene)L-tartrate (PTA) were investigated with respect to their hydrolytic degradation. Implants were made of compressed polymer and melted polymer. They were immersed in a buffer solution (pH 7.4) and stored in a water bath at 30 degrees C. Change of surface morphology, content of water, glass transition temperature, existence of crystalline degradation products and decrease of average molecular weight were used to assess the extent of hydrolytic degradation. Glass transition temperature of PTA devices, which is influenced by content of absorbed water, decreased more rapidly in comparison to the implants made of PLA. The importance of non-freezing water accumulated at the ester linkages for the hydrolytic degradation could be shown. Decrease in average molecular weight was determined by measuring intrinsic viscosities and using the Staudinger equation. The average molecular weight of PLA implants decreased for compressed and melted devices from 17400 to 5000 and 8500, respectively, during 7 weeks of immersing. Implants made of PTA (average molecular weight of about 23000) provided an average molecular weight of approximately 1 000 after 3 weeks storage in the buffer solution.

Buffers↗
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↗
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↗
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

Stimulated acoustic emission: pseudo-Doppler shifts seen during the destruction of nonmoving microbubbles.

The purpose of this study was to evaluate the appearance and the characteristics of stimulated acoustic emission (SAE) as an echo contrast-specific color Doppler phenomenon with impact on myocardial contrast echocardiography (MCE). Stationary microbubbles of the new contrast agent SH-U 563A (Schering AG) were embedded within a tissue-mimicking gel material. Harmonic power Doppler imaging (H-PDI), color Doppler and pulse-wave Doppler data were acquired using an HDI-5000 equipped with a phased-array transducer (1.67/3.3 MHz). In color Doppler mode, bubble destruction resulted in random noise like Doppler signals. PW-Doppler revealed short "pseudo-Doppler" shifts with a broadband frequency spectrum. Quantification of SAE events by H-PDI demonstrated an exponential decay of signal intensities over successive frames. A strong linear relationship was found between bubble concentration and the square root of the linearized H-PDI signal for a range of concentrations of more than two orders of magnitude (R = 0.993, p < 0.0001). Intensity of the H-PDI signals correlated well with emission power (R = 0.96, p = 0.0014). SAE results from disintegration of microbubbles and can be demonstrated by all Doppler imaging modalities, including H-PDI. Intensity of SAE signals is influenced by the applied acoustic power and correlates highly with the concentration of microbubbles. Because intensity of SAE signals correlates highly with echo contrast concentrations, analysis of SAE signals might be used for quantitative MCE.

Acoustics↗
PubMed2000

Are microbubbles free flowing tracers through the Myocardium? Comparison of indicator-dilution curves obtained from dye dilution and echo contrast using harmonic power Doppler imaging.

BACKGROUND: Harmonic power Doppler imaging (H-PDI) has been introduced into the field of contrast echocardiography as a contrast-specific imaging modality. However, there has been considerable skepticism as to whether H-PDI would be quantifiable, because it depends on the destruction of microbubbles and has more complex signal processing than gray scale imaging. The aim of the present study was to evaluate the relationship between the concentration of microbubbles and the resulting H-PDI signals even under conditions where bubble destruction is most likely. Furthermore, we evaluated whether microbubbles of Levovist freely pass the microcirculation, which is a prerequisite for the assessment of myocardial blood flow. METHODS AND RESULTS: A strong positive correlation was found between the H-PDI signals and the amount of microbubbles up to the onset of acoustic shadowing (r = 0. 968, P<0.001). Time-intensity curves for H-PDI of air-filled microbubbles were compared with time-concentration curves of indocyanine green (ICG) in both a flow phantom and a working heart setup. The mean transit times (MTTs) through the myocardium of both agents were compared after a bolus injection into the left coronary artery. A close correlation was observed between 1/MTT and flow in both setups (r>0.98, P<0.0001). However, at high flow rates, the MTTs of the microbubbles were slightly, albeit not significantly, faster than those of indocyanine green. CONCLUSIONS: We conclude that microbubbles fulfill the prerequisites of free flowing tracers through the myocardium. Furthermore, H-PDI technology allows a reliable assessment of time-concentration curves of air-filled microbubbles up to the onset of acoustic shadowing.

Animals↗
PubMed2000

Stimulated acoustic emission detected by transcranial color doppler ultrasound : a contrast-specific phenomenon useful for the detection of cerebral tissue perfusion.

BACKGROUND AND PURPOSE: Experimental and clinical data suggest that insonation of echo-contrast agents with high acoustical power produces disintegration of microbubbles, resulting in a pseudo-Doppler phenomenon called stimulated acoustic emission (SAE). The purpose of this study was to investigate whether SAE might be detected by transcranial color Doppler imaging and whether these signals might be used for cerebral tissue perfusion measurements. METHODS: Nonmoving microbubbles (SHU 563 A) were insonated in vitro through the temporal parts of a human cadaver skull, and contrast signals were detected by velocity-coded color Doppler and power Doppler recordings. Transcranial color as well as power Doppler investigations were performed in 10 healthy volunteers with the echo-contrast agent Levovist (SHU 508 A). RESULTS: Color Doppler signals indicating SAE were observed in vitro and in transcranial human investigations. These signals were characterized by a mosaic of color Doppler pixels ranging over the full color scale. Apparent velocity information and spatial distribution of SAE signals changed from image frame to image frame. In the experimental model, the intensity of SAE signals decreased exponentially over time. With an increase of acoustic power, there was a significant increase of the maximum signal intensity (P<0.01) and a significantly shortened signal duration (P<0.01), consistent with stronger and more rapid disintegration. In humans, SAE signals were clearly detected in cerebral tissue regions. The intensity of SAE signals in those regions (eg, temporal cortex, 3.7+/-1.2 dB) was approximately 8 times lower than the signal enhancement in the major cerebral arteries (eg, in the MCA, 29.5+/-5.6). CONCLUSIONS: Echo-contrast specific color Doppler signals known as SAE are detectable by transcranial color and power Doppler sonography. Signals due to SAE might represent tissue perfusion, thereby providing a method for imaging flow with transcranial ultrasound.

Adult↗
PubMed1986

Li+ as substrate of the synaptosomal Na+/H+ antiporter.

The influence of replacing external Na+ by choline+ on Li+ uptake into rat cortical synaptosomes was studied. Tetraphenylphosphonium+ and methylamine distribution techniques were used to estimate the plasma membrane potential and the transmembrane H+ gradients, respectively. H+ efflux was monitored by automatic titration in the pH-stat mode. In the Na+- and K+-free medium, synaptosomes concentrated Li+ about 10-fold at 1 mM Li+o in the presence of ouabain. Varying external free Ca2+ between 13 and 300 microM, or addition of MgCl2 had no effect on Li+ uptake. Ouabain-insensitive Li+ transport was separated into two components: 1) non-saturable Li+ influx with a rate constant of 0.6/min; 2) saturable uptake, which obeyed Michaelis-Menten kinetics (Km, 2.0 mM Li+; Vmax, 7.3 mmol of Li+/liter and min). Li+ uptake was competitively inhibited by amiloride (Ki, 3.2 microM; Hill coefficient, 1.0) and external Na+ (Ki, 5.8 mM). External Li+ scarcely accelerated Na+ efflux and phloretin failed to inhibit Li+ uptake, indicating that Li+ uptake was not directly coupled to Na+ gradient. Because of a reversal of the H+ transport by the pHi-regulating system, synaptosomes accumulated acid in the Na+-free medium. Li+ influx was electroneutral, but impaired H+ gradients and was coupled to the simultaneous release of stoichiometric amounts of H+ at less than 3 mM Li+o. Uptake of Li+ was linearly related to H+ gradients imposed onto the plasma membrane by varying external pH. In the steady state, internal Li+ was close to the value predicted for passive distribution. It is concluded that in Na+-free media Li+ uptake at low external Li+ is predominantly driven by transmembrane H+ gradients. The stoichiometric exchange of Li+ for H+ is mediated by the Na+/H+ antiporter. The Li+ distribution ratio is close to the electrochemical activity coefficient since protons are passively distributed across the synaptosomal plasma membrane in the absence of external Na+.

Animals↗