[Molecular imaging of apoptosis in cardiovascular diseases]. / Molekulare Bildgebung der Apoptose bei kardiovaskulären Erkrankungen.

Molecular imaging of functional parameters such as apoptosis (programmed cell death) in vivo opens new possibilities in clinical diagnostic and scientific research. Especially in the case of cardiovascular diseases that are mainly responsible for both morbidity and mortality in Western industrial nations, innovative non-invasive examination strategies are necessary for early diagnosis of these diseases. Since apoptosis unlike necrosis is present even after minor alterations of the microenvironment of cells and has been shown to be involved in a large number of cardiovascular diseases, there are currently several experimental studies underway with the goal of imaging apoptosis in vivo. The review discusses the basics of apoptosis in myocardial infarction, myocarditis, atherosclerosis, restenosis after angioplasty and stent implantation, currently used imaging techniques, achieved results, and future possibilities for molecular imaging of apoptosis.

The coeliac aneurysm: a rare cause of abdominal pain.

Visceral artery aneurysms (VAA) represent 0.1-0.2% of all vascular aneurysms. For VAA's etiology, congenital or arteriosclerotic factors, media defects, infections, vasculitis and trauma are discussed. Ultrasound, CT scan and magnetic resonance imaging underline the diagnosis of VAA. The low perioperative morbidity and mortality and the excellent surgical longterm results justify the prophylactic therapy also from asymptomatic VAA because the mortality of ruptured VAA is close to 100%. The radiological interventional treatment is indicated for only selected patients whereas an advantage is not verified yet.

[Determination of the renal blood flow in macro- and microcirculation by means of pulse inversion imaging]. / Bestimmung des renalen Blutflusses in Makro- und Mikrozirkulation mittels 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.

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.

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.

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.

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.