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

Use of Contrast-Enhanced Ultrasonography to Evaluate Chronic Allograft Nephropathy in Rats and Correlations between Time-Intensity Curve Parameters and Allograft Fibrosis

This study quantitatively analyzed changes in the hemodynamic characteristics of renal allografts at different stages in a rat chronic allograft nephropathy (CAN) model as well as the relationship between hemodynamic parameters and renal allograft fibrosis using contrast-enhanced ultrasonography (CEUS). The experimental group used a CAN rat model (n = 30), and the control group used an orthotopic syngeneic renal transplant model (n = 30). After surgery, creatinine clearance rates were regularly monitored every 2 wk. The checking times were set at 4, 12 and 24 wk after surgery, which represent early, middle and late stage of CAN, respectively. At different stages of CAN, eight rats from each group were randomly selected for CEUS examination. Time-intensity curve (TIC) parameters, including rise time, peak intensity, mean transit time, area under the curve, wash-in slope, time-to-peak and α-smooth muscle actin (α-SMA) expression; Vimentin expression; and chronic allograft damage index scores were evaluated by linear correlation analysis. Before the creatinine clearance rate showed significant abnormalities, the renal allografts in the experimental group had already presented pathologic changes associated with CAN. In the early stage after surgery, compared to the TIC curve of the control group, the experimental group showed increased rise time, mean transit time, area under the curve and time-to-peak, and decreased wash-in slope (p < 0.05). Chronic allograft damage index scores and the expression levels of α-SMA and Vimentin proteins in renal allografts were correlated with TIC parameters (p < 0.05). Compared to creatinine clearance rate, CEUS can detect CAN at earlier stages. The correlations between TIC-related parameters and the expression levels of α-SMA and Vimentin in renal allografts indicate that CEUS is a feasible way to assess the degree of renal allograft fibrosis quantitatively.

Use of Contrast-Enhanced Ultrasound to Study Relationship between Serum Uric Acid and Renal Microvascular Perfusion in Diabetic Kidney Disease

Purpose. To investigate the relationship between uric acid and renal microvascular perfusion in diabetic kidney disease (DKD) using contrast-enhanced ultrasound (CEUS) method. Materials and Methods. 79 DKD patients and 26 healthy volunteers were enrolled. Renal function and urine protein markers were tested. DKD patients were subdivided into two groups including a normal serum uric acid (SUA) group and a high SUA group. Contrast-enhanced ultrasound (CEUS) was performed, and low acoustic power contrast-specific imaging was used for quantitative analysis. Results. Normal controls (NCs) had the highest levels of AUC, AUC1, and AUC2. Compared to the normal SUA DKD group, high SUA DKD patients had significantly higher IMAX, AUC, and AUC1 (P < 0.05). DKD patients with low urinary uric acid (UUA) excretion had significantly higher AUC2 compared to DKD patients with normal UUA (P < 0.05). Conclusion. Hyperuricemia in DKD patients was associated with a renal ultrasound image suggestive of microvascular hyperperfusion. The CEUS parameter AUC1 holds promise as an indicator for renal microvascular hyperperfusion, while AUC2 might be a useful indicator of declining glomerular filtration rate in DKD patients with decreased excretion of uric acid.

Diagnostic value of quantitative contrast-enhanced ultrasound (CEUS) for early detection of renal hyperperfusion in diabetic kidney disease

PURPOSE

To investigate the diagnostic value of quantitative contrast-enhanced ultrasound (CEUS) for early detection of renal hyperperfusion in diabetic kidney disease (DKD).

MATERIALS AND METHODS

55 DKD patients with estimated glomerular filtration rate (eGFR) >30 ml/min/1.73 m(2) and 26 normal controls (NCs) were enrolled. Clinical data was well documented. Blood samples were drawn for evaluation of renal function including blood urea nitrogen (BUN), serum creatinine (SCr) and serum uric acid (SUA), and urine samples were assayed for total protein quantification, and various microprotein markers. According to eGFR level, DKD patients were divided into early-stage DKD (eGFR ≥90 ml/min/1.73 m(2), n = 18) and middle-stage DKD (eGFR 30-90 ml/min/1.73 m(2), n = 37). Based on urinary microalbumin/creatinine ratio (MALB/UCR), early-stage DKD patients were further classified into two groups: MALB/UCR <10 g/mol (n = 11) and MALB/UCR ≥10 g/mol (n = 7). Then, CEUS was performed to observe the real-time renal perfusion, and low acoustic power contrast-specific imaging was used for quantitative analysis.

RESULTS

The renal perfusion images of CEUS were well developed successively. The corresponding perfusion curves based on echo-power signals in time series were constructed. Quantitative analysis showed that area under the descending curve (AUC2) was significantly increased in early-stage DKD compared to middle-stage DKD (p < 0.05), but AUC showed no significant difference. Further comparison between different MALB/UCR levels of early-stage DKD showed that patients with MALB/UCR ≥10 g/mol had significantly increased levels of AUC, AUC2 and proteinuria than patients with low MALB/UCR (p < 0.05). Also, high MALB/UCR DKD patients had increased proteinuria but similar eGFR compared to low MALB/UCR patients.

CONCLUSION

Renal microvascular hyperperfusion may be responsible for overt proteinuria until decline of renal filtration in DKD. AUC2 could be an early and sensitive marker for early renal injury and renal microvascular hyperperfusion in DKD.

Mesenchymal stem cell transplantation enhancement in myocardial infarction rat model under ultrasound combined with nitric oxide microbubbles

OBJECTIVE

This study evaluated the effects of ultrasound combined with the homemade nitric oxide (NO) micro-bubble destruction on the in vitro proliferation, apoptosis, and migration of mesenchymal stem cells (MSCs). Furthermore, we studied whether or not irradiation of the NO micro-bubble combined with bone-marrow derived MSC infusion had a better effect on treating myocardial infarction. The possible mechanism of MSC delivery into the infarcted myocardium was also investigated.

METHODS

The murine bone marrow-derived MSCs were isolated, cultured, irradiated, and combined with different concentrations of NO microbubbles. MTT proliferation assay, annexin V-FITC apoptosis detection, migration assay, and RT-PCR were performed 24 h after the irradiation. The NO micro-bubbles was a intravenously injected, followed by the infusion of MSCs, which were labeled by CM-Dil. Myocardium was harvested 48 h later and the distribution of MSCs was observed by laser scanning confocal microscope after frozen sectioning. Echocardiography, histological examination, RT-PCR, and western blotting were performed four weeks after the cell transplantation.

RESULTS

Ultrasound combined with 1:70 NO micro-bubbles had no significant impact on the proliferation or apoptosis of MSCs. Transwell chamber findings demonstrated that MSCs migrated more efficiently in group that underwent ultrasound combined with 1:70 NO micro-bubbles. The Real-time PCR results indicated that the expression of CXCR4 was much higher in the group undergoing ultrasound combined with 1:70 NO micro-bubbles. The normalized fluorescence intensity greatly increased in the group of US+NO micro-bubbles and the cardiac function was also markedly improved. Immunohistochemical staining showed that the capillary density was much greater in the group of US+NO micro-bubbles as compared to that of the other groups. RT-PCR and western blotting also revealed a higher SDF-1 and VEGF expression in the group of US+NO micro-bubbles.

CONCLUSIONS

NO micro-bubbles could be used in the cell transplantation, which efficiently promoted the MSC homing into the infarcted myocardium.

Visualization of multimodal polymer-shelled contrast agents using ultrasound contrast sequences: an experimental study in a tissue mimicking flow phantom

Background

A multimodal polymer-shelled contrast agent (CA) with target specific potential was recently developed and tested for its acoustic properties in a single element transducer setup. Since the developed polymeric CA has different chemical composition than the commercially available CAs, there is an interest to study its acoustic response when using clinical ultrasound systems. The aim of this study was therefore to investigate the acoustic response by studying the visualization capability and shadowing effect of three polymer-shelled CAs when using optimized sequences for contrast imaging.

Methods

The acoustic response of three types of the multimodal CA was evaluated in a tissue mimicking flow phantom setup by measuring contrast to tissue ratio (CTR) and acoustic shadowing using five image sequences optimized for contrast imaging. The measurements were performed over a mechanical index (MI) range of 0.2-1.2 at three CA concentrations (10⁶, 10⁵, 10⁴ microbubbles/ml).

Results

The CTR-values were found to vary with the applied contrast sequence, MI and CA. The highest CTR-values were obtained when a contrast sequence optimized for higher MI imaging was used. At a CA concentration of 10⁶ microbubbles/ml, acoustic shadowing was observed for all contrast sequences and CAs.

Conclusions

The CAs showed the potential to enhance ultrasound images generated by available contrast sequences. A CA concentration of 10⁶ MBs/ml implies a non-linear relation between MB concentration and image intensity.

In vitro evaluation of the impact of ultrasound scanner settings and contrast bolus volume on time-intensity curves

The objective of this study was to assess in vitro the impact of ultrasound scanner settings and contrast bolus volume on time-intensity curves formed from dynamic contrast-enhanced ultrasound image loops. An indicator-dilution experiment was developed with an in vitro flow phantom setup used with SonoVue contrast agent (Bracco SpA, Milan, Italy). Imaging was performed with a Philips iU22 scanner and two transducers (L9-3 linear and C5-1 curvilinear). The following ultrasound scanner settings were investigated, along with contrast bolus volume: contrast-specific nonlinear pulse sequence, gain, mechanical index, focal zone depth, acoustic pulse center frequency and bandwidth. Four parameters (rise time, mean transit time, peak intensity, and area under the curve) were derived from time-intensity curves which were obtained after pixel by pixel linearization of log-compressed data (also referred to as video data) included in a region of interest. Rise time was found to be the parameter least impacted by changes to ultrasound scanner settings and contrast bolus volume; the associated coefficient of variation varied between 0.7% and 6.9% while it varied between 0.8% and 19%, 12% and 71%, and 9.2% and 66%, for mean transit time, peak intensity, and area under the curve, respectively. The present study assessed the impact of ultrasound scanner settings and contrast bolus volume on time-intensity curve analysis. One should be aware of these issues to standardize their technique in each specific organ of interest and to achieve accurate, sensitive, and reproducible data using dynamic contrast-enhanced ultrasound. One way to mitigate the impact of ultrasound scanner settings in longitudinal, multi-center quantitative dynamic contrast-enhanced ultrasound studies may be to prohibit any adjustments to those settings throughout a given study. Further clinical studies are warranted to confirm the reproducibility and diagnostic or prognostic value of time-intensity curve parameters measurements in a particular clinical scenario of interest, for example that of cancer patients undergoing vascular targeting therapies.

Assessment of global liver blood flow with quantitative dynamic contrast-enhanced ultrasound

OBJECTIVES

This study assessed the potential of quantitative analysis of contrast bolus kinetics to reflect global liver blood flow.

METHODS

A dynamic contrast-enhanced ultrasound flow phantom was developed. A peristaltic pump established constant volume flow ranging between 16.5 and 49.5 mL/min (2-mm tube) and 85.5 and 256.5 mL/min (5-mm tube). After bolus injection of 2 doses of a contrast agent, a region of interest was drawn over the cross section of the tube used for a particular acquisition; the rise time, peak intensity, and wash-in slope were derived from time-intensity curves. Twenty healthy volunteers and 25 patients with biopsy-proven colorectal liver metastases were scanned with dynamic contrast-enhanced ultrasound. The rise time, peak intensity, and wash-in slope were derived from hepatic artery and portal vein time-intensity curves. Hepatic artery/portal vein ratios of the parameters were also calculated.

RESULTS

In the in vitro experiment, the rise time decreased while the peak intensity and wash-in slope increased with increasing volume flow for both tube diameters and contrast bolus volumes. In the clinical study, the rise time was lowered in the hepatic artery but elevated in the portal vein, and the peak intensity and wash-in slope were elevated in the hepatic artery but lowered in the portal vein in patients with colorectal liver metastases compared with healthy volunteers, although not in a statistically significant manner. This finding was consistent with an increase in hepatic artery blood flow, a decrease in portal vein blood flow, or both in patients with colorectal liver metastases compared with healthy volunteers. Only the 3 hepatic artery/portal vein ratios of the parameters achieved statistical significance in differentiating healthy volunteers from patients with colorectal liver metastases (P < .05).

CONCLUSIONS

Surrogate measurements of liver blood flow may be derived from quantitative analysis of dynamic contrast-enhanced ultrasound studies. They may have potential for quick and easy assessment of altered hepatic hemodynamics.

Indicator dilution models for the quantification of microvascular blood flow with bolus administration of ultrasound contrast agents

Indicator dilution methods have a long history in the quantification of both macro- and microvascular blood flow in many clinical applications. Various models have been employed in the past to isolate the primary pass of an indicator after an intravenous bolus injection. The use of indicator dilution techniques allows for the estimation of hemodynamic parameters of a tumor or organ and thus may lead to useful diagnostic and therapy monitoring information. In this paper, we review and discuss the properties of the lognormal function, the gamma variate function, the diffusion with drift models, and the lagged normal function, which have been used to model indicator dilution curves in different fields of medicine. We fit these models to contrast-enhanced ultrasound time-intensity curves from liver metastases and the ovine corpora lutea. We evaluate the models' performance on the image data and compare their predictions for hemodynamic-related parameters such as the area under the curve, the mean transit time, the full-width at half-maximum, the time to the peak intensity, and wash-in time. The models that best fit the experimental data are the lognormal function and the diffusion with drift.

Investigation of the relationship of nonlinear backscattered ultrasound intensity with microbubble concentration at low MI

The aim of this study was to measure the relationship of image intensity with contrast agent concentration. In vitro experiments were performed with a flow phantom and a sulphur hexafluoride filled microbubble contrast agent (SonoVue) at different concentrations (0.004 per thousand to 4 per thousand) covering the range commonly encountered in clinical practice. The concentration of microbubbles in the contrast agent solutions was confirmed optically. Images were collected with a diagnostic ultrasound system (iU22, Phillips Medical Systems, Bothell, WA, USA) and with a nonlinear imaging technique (power modulation) at low mechanical index (MI=0.05) to avoid bubble destruction. The mean intensity within a region of interest was measured to produce time-intensity curves from linearized (absolute scale) data. The relationship of linearized image intensity to contrast agent concentration was found to be linear up to 1 per thousand and reached a plateau at approximately 2 per thousand. To operate in the linear range of the intensity-concentration relationship the contrast agent dose should be adjusted to avoid those high values in vivo and the highest dynamic range of the ultrasound system should be used to avoid unnecessary signal saturation.

Clinical Application of Harmonic Power Doppler Imaging in the Assessment of Myocardial Perfusion by Contrast Echocardiography

Myocardial contrast echocardiography has moved from the research laboratory to clinical echocardiography. As with any emerging technology, background information and understanding the process of image acquisition will help to integrate the technology into everyday practice. Harmonic power Doppler imaging (HPDI) is a high-power, triggered imaging modality used to assess myocardial perfusion. Contrast agents used in echocardiography provide microvascular tracers that enable HPDI to accurately visualize myocardial blood flow. This article aims to provide direction in the clinical performance of myocardial contrast echocardiography by providing background in the theory and physics of HPDI and a guide to the technical acquisition of images and recognition of artifacts that arise during HPDI.

In vitro and in vivo studies on continuous echo-contrast application strategies using SonoVue in a newly developed rotating pump setup

With emerging imaging strategies for contrast sonography (CS), there is a rising demand for the precise control of ultrasound (US) contrast agent delivery. Constant delivery minimizes artefacts and improves efficacy. The aim of this study was to evaluate the physical properties of the new contrast agent SonoVue and to evaluate the feasibility and accuracy of a new infusion approach using an automated infusion system for contrast agitation and delivery of echo-contrast agents. In vitro testing of infusion properties of SonoVue were performed in a capillary phantom mimicking tissue perfusion. Nonagitated standard infusion setups were compared with hand agitation and the new pump system with respect to possible artefacts, constancy of contrast effect and efficacy. In three volunteers, the new pump system was tested for constancy of contrast in large vessels. Without continuous agitation, continuous infusion of SonoVue resulted in bolus-like signal-intensity curves, along with substantial imaging artefacts. Additionally, homogenization of SonoVue significantly improved efficacy (p < 0.0001). No significant differences were found between hand agitation and homogenization by the new pump. In clinical settings, constant agitation using the new pump resulted in constant signal conditions in the carotid artery 3.72 +/- 0.46 units (U) after 5 min. Continuous agitation of SonoVue is mandatory for quantitative approaches. By the new infusion technique, CS could be performed for a reasonably long time period and efficacy is significantly improved (p < 0.0001). The new infusion technique might thereby allow routine application of constant infusion scenarios in clinical CS.

Optimizing an ultrasound contrast agent's stability using in vitro attenuation measurements

RATIONALE AND OBJECTIVES

To evaluate the changes in the microbubble population of a currently available ultrasound contrast agent (USCA) through attenuation measurements to optimize its clinical use.

MATERIALS AND METHODS

The microbubble population from a galactose-based USCA (Levovist, Schering AG, Germany) was characterized in vitro using attenuation measurements. The effect of dose (0.1, 0.5, and 1 mL), concentrations (200, 300, and 400 mg mL(-1)) and time since reconstitution (2, 12, 22, and 32 minutes) was evaluated using two broadband pulses at different peak negative pressures (0.39 and 0.49 MPa) for a total of 72 injections.

RESULTS

Two minutes after reconstitution, a linear relationship was found between attenuation measurements and the amount of USCA (slope 0.92 dB x mg x cm(-1) ml(-1), R = 0.86). For a given dose and concentration, the microbubble stability was significantly reduced with the increase of the time since reconstitution, particularly for the lower concentrations.

CONCLUSIONS

The persistence and contrast effect of Levovist can be improved by using recommended minimum time since reconstitution and maximum concentration.

On the design of a capillary flow phantom for the evaluation of ultrasound contrast agents at very low flow velocities

Recently, a new imaging technology has become available that allows the evaluation of tissue perfusion using echo-contrast agents in real-time imaging: power pulse inversion imaging (PPI). Although numerous in vitro phantoms have been designed for different imaging modalities in ultrasound (US), there is a need for a phantom that mimics microcirculation and allows, in particular, the assessment of contrast replenishment kinetics following US-induced destruction of microbubbles using the new method. We, therefore, designed a new capillary flow phantom that takes the requirements of the new US imaging techniques and the physical properties of microbubbles into account and serves flow velocities in the range of microcirculation (1 to 10 mm/s). PPI studies were performed in the newly designed phantom. The contrast agent used was AF0150. We studied homogeneity of contrast distribution within the capillary phantom, constancy of contrast infusion, the dose-effect relationship and, finally, the feasibility of flow assessment using the method of contrast replenishment following US-induced microbubble destruction in a flow velocity range of 2.1 to 9.45 mm/s. Analysis of the replenishment kinetics was performed using the mathematical model f(t) = A(1 - e(-beta t)), with A representing the blood volume and beta the microbubble velocity. The new capillary phantom allowed homogeneous contrast opacification within the perfused capillaries independently of the flow. Constancy of signal intensity was achieved over a time period of almost 2 h, indicating constant contrast delivery. A strong linear correlation between the PPI signal and the contrast dose was found (r = 0.998). Analysis of the replenishment parameters revealed a strong linear relationship between parameter beta and flow (r = 0.994) as well as A * beta and flow (r = 0.984) in the observed flow range. The newly designed perfusion phantom for the evaluation of echo-contrast replenishment kinetics fulfills, at very low flow velocities, important prerequisites such as constancy of contrast delivery, homogeneity of contrast signals, linear dose-effect relation and minimal attenuation. Thus, the new phantom allows standardized analysis of contrast replenishment kinetics using real-time perfusion imaging techniques at flow velocities comparable to those of the microcirculation.

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.

Assessment of myocardial perfusion by power contrast imaging using a new echo contrast agent

In a patient with previously documented myocardial infarction, we assessed myocardial perfusion by using power contrast imaging and a newer intravenous echo contrast agent. The images were captured and stored digitally, and various image processing algorithms were used to assess myocardial perfusion. An apical perfusion defect was clearly visualized, and it correlated with radionuclide findings.