Differences in the erythrocyte aggregation level between veins and arteries of normolipidemic and hyperlipidemic individuals

Automated Spontaneous Echo Contrast Detection Using a Multisequence Attention Convolutional Neural Network

OBJECTIVE

Spontaneous echo contrast (SEC) is a vascular ultrasound finding associated with increased thromboembolism risk. However, identification requires expert determination and clinician time to report. We developed a deep learning model that can automatically identify SEC. Our model can be applied retrospectively without deviating from routine clinical practice. The retrospective nature of our model means future works could scan archival data to opportunistically correlate SEC findings with documented clinical outcomes.

METHODS

We curated a data set of 801 archival acquisitions along the femoral vein from 201 patients. We used a multisequence convolutional neural network (CNN) with ResNetv2 backbone and visualized keyframe importance using soft attention. We evaluated SEC prediction performance using an 80/20 train/test split. We report receiver operating characteristic area under the curve (ROC-AUC), along with the Youden threshold-associated sensitivity, specificity, F1 score, true negative, false negative, false positive and true positive.

RESULTS

Using soft attention, we can identify SEC with an AUC of 0.74, sensitivity of 0.73 and specificity of 0.68. Without soft attention, our model achieves an AUC of 0.69, sensitivity of 0.71 and specificity of 0.60. Additionally, we provide attention visualizations and note that our model assigns higher attention score to ultrasound frames containing more vessel lumen.

CONCLUSION

Our multisequence CNN model can identify the presence of SEC from ultrasound keyframes with an AUC of 0.74, which could enable screening applications and enable more SEC data discovery. The model does not require the expert intervention or additional clinician reporting time that are currently significant barriers to SEC adoption. Model and processed data sets are publicly available at https://github.com/Ouwen/automatic-spontaneous-echo-contrast.

Quantitative Measurement of Erythrocyte Aggregation as a Systemic Inflammatory Marker by Ultrasound Imaging: A Systematic Review

This systematic review is aimed at answering two questions: (i) Is erythrocyte aggregation a useful biomarker in assessing systemic inflammation? (ii) Does quantitative ultrasound imaging provide the non-invasive option to measure erythrocyte aggregation in real time? The search was executed through bibliographic electronic databases CINAHL, EMB Review, EMBASE, MEDLINE, PubMed and the grey literature. The majority of studies correlated elevated erythrocyte aggregation with inflammatory blood markers for several pathologic states. Some studies used "erythrocyte aggregation" as an established marker of systemic inflammation. There were limited but promising articles regarding the use of quantitative ultrasound spectroscopy to monitor erythrocyte aggregation. Similarly, there were limited studies that used other ultrasound techniques to measure systemic inflammation. The quantitative measurement of erythrocyte aggregation has the potential to be a routine clinical marker of inflammation as it can reflect the cumulative inflammatory dynamics in vivo, is relatively simple to measure, is cost-effective and has a rapid turnaround time. Technologies like quantitative ultrasound spectroscopy that can measure erythrocyte aggregation non-invasively and in real time may offer the advantage of continuous monitoring of the inflammation state and, thus, may help in rapid decision making in a critical care setup.

Microfluidic-based speckle analysis for sensitive measurement of erythrocyte aggregation: A comparison of four methods for detection of elevated erythrocyte aggregation in diabetic rat blood

Biochemical alterations in the plasma and red blood cell (RBC) membrane of diabetic blood lead to excessive erythrocyte aggregation (EA). EA would significantly impede the blood flow and increase the vascular flow resistance contributing to peripheral vascular diseases. In this study, a simple microfluidic-based method is proposed to achieve sensitive detection of hyperaggregation. When a blood sample is delivered into the device, images of blood flows are obtained with a short exposure time for a relatively long measuring time. A micro-particle image velocimetry technique was employed to monitor variation of the flow rate of blood as a function of time. Given that EA formation in the channel creates clear speckle patterns, the EA extent can be estimated by calculating a speckle area (ASpeckle) through a normalized autocovariance function. The hematocrit effect is assessed by comparing optical images transmitted through blood samples. EA variations caused by dextran treatment are quantitatively evaluated using characteristic time (λSpeckle) obtained by fitting the variations of ASpeckle. Other indices including number of RBCs in an aggregate (NRBC), characteristic time of erythrocyte sedimentation rate (λESR), and aggregation index estimated from ultrasound signals (AIEcho) are determined under different EA conditions using conventional techniques. The four different methods are applied to diabetic blood samples to compare their indices under hyperaggregation conditions. It is found that the proposed method can detect variation of EA reasonably, compared with conventional measurement techniques. These experimental demonstrations support the notion that the proposed method is capable of effectively monitoring the biophysical properties of diabetic blood.

The effect of flow acceleration on the cyclic variation of blood echogenicity under pulsatile flow

It has been shown that the echogenicity of blood varies during a flow cycle under pulsatile flow both in vitro and in vivo. In general, the echogenicity of flowing whole blood increases during the early systole phase and then reduces to a minimum at late diastole. While it has been postulated that this cyclic variation is associated with the dynamics of erythrocyte aggregation, the mechanisms underlying this increasing echogenicity with flow velocity remain uncertain. The effect of flow acceleration has also been proposed as an explanation for this phenomenon, but no specific experiments have been conducted to test this hypothesis. In addition, the influence of ultrasonic attenuation on the cyclic variation of echogenicity requires clarification. In the present study, a Couette flow system was designed to simulate blood flowing with different acceleration patterns, and the flow velocity, attenuation, and backscattering coefficient were measured synchronously from 20%- and 40%-hematocrit porcine whole blood and erythrocyte suspensions using 35-MHz ultrasound transducers. The results showed ultrasonic attenuation exerted only minor effects on the echogenicity of blood under pulsatile flow conditions. Cyclic variations of echogenicity were clearly observed for whole blood with a hematocrit of 40%, but no variations were apparent for erythrocyte suspensions. The echogenicity did not appear to be enhanced when instantaneous acceleration was applied to flowing blood in any case. These findings show that flow acceleration does not promote erythrocyte aggregation, even when a higher peak velocity is applied to the blood. Comparison of the results obtained with different accelerations revealed that the cyclic variation in echogenicity observed during pulsatile blood flow may be jointly attributable to the effect of shear rate and the distribution of erythrocyte on aggregation.

The acute effects of smoking on the cyclic variations in blood echogenicity of carotid artery

The objective of this research is to study the cyclic variations in echogenicity (CVE) as an acute response to smoking. CVEs, caused by the aggregation of red blood cells (RBC) were measured from the cross-sectional images of the common carotid artery using coded harmonic imaging of a commercial ultrasound system. The amplitude of the CVE (A(cve)) was analyzed among 28 smokers before and after smoking. A(cve) was increased in 22 smokers and decreased in six smokers after 1-2 cigarettes were smoked. Heart rate (HR) was also estimated from the ultrasonic images before and after smoking. The smokers were optimally divided into two clusters with respect to the change in A(cve) and the intrinsic characteristics of smokers (i.e., daily consumed cigarettes and smoking years) through a two-step cluster analysis (TSCA). The increase in A(cve) after smoking was significantly higher in the heavy smoker cluster compared with the light smoker cluster. The results suggest that the acute changes in A(cve) in response to smoking are different between heavy smokers and light smokers. This preliminary study demonstrates the potential application of coded harmonic ultrasound imaging to detect or characterize RBC aggregation. In addition, the results may be useful for understanding the acute physiologic changes caused by smoking.

Cyclic and radial variation of the echogenicity of blood in human carotid arteries observed by harmonic imaging

To better understand the characteristics of erythrocyte aggregation in flowing blood, echogenicity variation in blood was observed both in vitro and in vivo. However, few noninvasive observations of blood echogenicity variation during the cardiac cycle in human arteries have been reported. In the present study, to reduce the dynamic range between the blood vessel lumen and the surrounding tissue, coded harmonic images were acquired from human carotid arteries using a GE LOGIQ 700 Expert system (GE, Milwaukee, WI, USA) with an M12L probe, which enabled the noninvasive detection of the cyclic and radial variation of echogenicity in arterial vessels. It was found that blood echogenicity increased during systole, reaching a maximum at peak systole and then decreased to a weak level during diastole. The echogenicity profiles of blood along the vessel diameter were found to be approximately parabolic in the cardiac cycle, except for the hypoechoic zone near the center of the vessel at peak systole. The present results for human carotid arteries corroborate previous in vitro observations that showed a cyclic and radial variation of blood echogenicity, which was thought to be caused by the enhancement of erythrocyte aggregation due to the combined effects of flow acceleration and shear rate during systole.

Physical properties of tissues relevant to arterial ultrasound imaging and blood velocity measurement

A review was undertaken of physical phenomena and the values of associated physical quantities relevant to arterial ultrasound imaging and measurement. Arteries are multilayered anisotropic structures. However, the requirement to obtain elasticity measurements from the data available using ultrasound imaging necessitates the use of highly simplified constitutive models involving Young's modulus, E. Values of E are reported for healthy arteries and for the constituents of diseased arteries. It is widely assumed that arterial blood flow is Newtonian. However, recent studies suggest that non-Newtonian behavior has a strong influence on arterial flow, and the balance of published evidence suggests that non-Newtonian behavior is associated primarily with red cell deformation rather than with aggregation. Hence, modeling studies should account for red cell deformation and the shear thinning effect that this produces. Published literature in healthy adults gives an average hematocrit and high-shear viscosity of 0.44 +/- 0.03 and 3.9 +/- 0.6 mPa.s, respectively. Published data on the acoustic properties of arteries and blood is sufficiently consistent between papers to allow compilation and derivation of best-fit equations summarizing the behavior across a wide frequency range, which then may be used in future modeling studies. Best-fit equations were derived for the attenuation coefficient vs. frequency in whole arteries (R(2) = 0.995), plasma (R(2) = 0.963) and blood with hematocrit near 45% (R(2) = 0.999), and for the backscatter coefficient vs. frequency from blood with hematocrit near 45% (R(2) = 0.958).

Non-Gaussian statistics and temporal variations of the ultrasound signal backscattered by blood at frequencies between 10 and 58 MHz

Very little is known about the blood backscattering behavior and signal statistics following flow stoppage at frequencies higher than 10 MHz. Measurements of the radio frequency (rf) signals backscattered by normal human blood (hematocrit = 40%, temperature = 37 degrees C) were performed in a tube flow model at mean frequencies varying between 10 and 58 MHz. The range of increase of the backscattered power during red blood cell (RBC) rouleau formation was close to 15 dB at 10 and 36 MHz, and dropped, for the same blood samples, below 8 dB at 58 MHz. Increasing the frequency from 10 to 58 MHz raised the slope of the power changes at the beginning of the kinetics of aggregation, and could emphasize the non-Gaussian behavior of the rf signals interpreted in terms of the K and Nakagami statistical models. At 36 and 58 MHz, significant increases of the kurtosis coefficient, and significant reductions of the Nakagami parameter were noted during the first 30 s of flow stoppage. In conclusion, increasing the transducer frequency reduced the magnitude of the backscattered power changes attributed to the phenomenon of RBC aggregation, but improved the detection of rapid growth in aggregate sizes and non-Gaussian statistical behavior.

Echogenicity variations from porcine blood I: the "bright collapsing ring" under pulsatile flow

The temporal and radial variations of the echogenicity from porcine blood were investigated using a linear M12L transducer with a GE LOGIQ 700 Expert system. The "bright collapsing ring" (BRCR) phenomenon, a bright echogenic ring converging from the periphery to the center of the tube wall and eventually collapsing during a pulsatile cycle in cross-sectional B-mode images, was observed from porcine blood in a mock flow loop within a 0.95-cm diameter tube under certain flow conditions. The BRCR phenomenon from porcine blood was stronger as the peak speed was increased from 10 to 25 cm/s, and the mean echogenicity and the "black hole" (BLH) phenomenon, a central echo-poor zone surrounded by a bright hyperechoic zone, became weaker. As stroke rate was increased from 20 to 60 beats/min (bpm), both the BRCR and the BLH phenomena became weaker. These two phenomena were observed at three transmitting frequencies (9, 11 and 13 MHz). As hematocrit was increased from 12 to 45%, the BRCR phenomenon became more apparent. The nonlinear behavior of backscatter as a function of hematocrit reaching a maximum at hematocrit of 10 approximately 20% was observed near the tube wall, but it changed at the center of the tube, indicating the importance of hemodynamics on the ultrasonic backscatter from flowing blood. The combined effects of shear rate and acceleration on red blood cell aggregation are suggested as a possible mechanism for these phenomena.

Application of validated ultrasound indices to investigate erythrocyte aggregation in pigs. Preliminary in vivo results

Although some studies concerning the ultrasound (US) characterization of erythrocyte aggregation reported in the literature have been conducted in vivo, none of them has led to quantitative indices. To achieve this objective, we first finalized a method on a hydrodynamic bench. Particularly, we define a kinetic protocol consisting of applying a 200 s(-1) shear rate followed up by a rapid decrease to reach a residual shear rate between 0 to 32 s(-1). From the backscattered intensity curve recorded all along the kinetic procedure, US dynamic parameters were defined and validated by correlation with reference laser indices obtained with the same model suspensions of erythrocytes (different concentrations of dextran 70 kD). A particular interesting behavior has been demonstrated when studying aggregation vs. the residual shear rate applied. The aim of the present study was to test the applicability of this aggregation kinetics protocol during in vivo investigations in pigs and possibly to recover the same aggregating behavior. The backscattered intensity was recorded all along the kinetic procedure as defined in vitro. Taking the derivative of the velocity profile recorded on 56 electronic windows, the shear rate was finely computed in the same measurement window where the backscattered intensity was calculated. Each US parameter could, therefore, be correlated with the residual shear rate corresponding to the same depth of measurement. We found that the blood aggregation behavior was identical to that observed in vitro. Apparently, a specific range of residual shear rates accelerates the activation of the aggregation process and the final aggregation level attained.

Power Doppler ultrasound scan imaging of the level of red blood cell aggregation: an in vitro study

PURPOSE

The purpose of this study was to evaluate the effect of the shear rate on red blood cell (RBC) aggregation with power Doppler ultrasound scanning (PDU), pulsed-wave Doppler scanning, and color Doppler flow imaging.

METHODS

Equine and porcine blood were circulated with a steady flow in a phantom with a diameter of 9.52 mm. The color Doppler flow imaging mode was used to estimate the velocity profile and the shear rate across the tube. A transfer function that related the Doppler scan power, measured in gray level with the PDU method, to the power, measured in decibels with the pulsed-wave Doppler scan technique, was used to estimate the echogenicity of blood and the level of aggregation.

RESULTS

For the four experiments reported, the power peaked at low shear rates probably because of increased RBC collisions and aggregation and then decreased thereafter because of disaggregation. The largest power variations were measured at shear rates of less than 40 seconds -1. At flow rates that varied between 75 and 500 mL/min, the echogenicity was low near the wall of the tube, increased toward the middle, and decreased at the tube center. The Doppler scan power was uniform across the tube at flow rates of 750 and 1000 mL/min.

CONCLUSION

PDU is reliable to quantify the echogenicity of blood and the level of RBC aggregation. In comparison with other methods proposed to measure RBC aggregation, ultrasound scanning is applicable in vivo and may help to improve our basic understanding of the relationship between the hemodynamic of the circulation and RBC aggregation in human vessels.