Quantification of renal blood flow with contrast-enhanced ultrasound

Diaphragm blood flow: new avenues for human translation

The rhythmic contraction of the diaphragm facilitates continuous pulmonary ventilation essential for life. Adequate blood flow to the diaphragm is critical to continuously support contractile function, as an imbalance in nutritive supply and demand can lead to diaphragm insufficiency, patient morbidity, and mortality. Given oxygen supply to the diaphragm is key to its function, it is no surprise that more than 200 animal studies have investigated diaphragm blood flow ([Formula: see text]) regulation over the past century. This work has advanced our understanding of the diaphragm's circulatory control (i.e., regional blood flow heterogeneity and mechanical impediment) and response to a variety of conditions, including eupnea, exercise, hypoxia, hypercapnia, hemorrhage, mechanical ventilation, and pharmacological interventions. However, due to the relative inaccessibility of the diaphragm, few studies have been conducted in humans since [Formula: see text] measurements have historically required highly invasive and technically challenging techniques that are not conducive to routine use. Thus, our current understanding of [Formula: see text] is informed almost exclusively by animal work with conflicting findings, and its translation to humans is hindered by species-dependent variability in diaphragmatic structure and function. Novel approaches have been developed to quantify respiratory muscle blood flow in humans using minimally invasive techniques. More recently, contrast-enhanced ultrasound (CEUS) is a promising approach for quantifying [Formula: see text] in humans, independent from other respiratory muscles. Using novel approaches to quantify [Formula: see text] in humans, future research can aim to advance our understanding of [Formula: see text] in humans in health and disease, including exercise, sex-based comparisons, and critical care.

Evaluation of melittin-induced acute kidney injury in different degrees in rats by contrast-enhanced ultrasound techniques

To evaluate the renal perfusion of acute kidney injury (AKI) induced by melittin in the rats using contrast-enhanced ultrasound (CEUS). Twenty-four healthy male SD rats were randomly divided into high concentration of melittin group, low concentration of melittin group and control group with 8 rats in each group. Melittin was injected through the rats' right femoral vein, to establish a rat model of AKI. Twelve hours later, CEUS and its Quantitative analysis of TIC parameters was performed. Blood samples from rats were taken to detect creatinine (Cr), right kidney was removed to perform HE staining and apoptosis markers (BAX,Bcl-2,Casepase3) assessment. The correlations among the quantitative parameters of CEUS TIC, Cr and apoptosis marker of PCR were analyzed.Results shows: 1.The quantitative parameters of CEUS TIC(Peak, TP, AUC, MTT) and apoptosis markers PCR parameters (BAX, Bcl-2, Casepase3) were significantly different among three groups (p < 0.01);2. Correlation analysis: Within the high concentration group: There was a correlation among the quantitative parameters of CEUS TIC, cr and apoptosis marker of PCR;In the low concentration group: There was a correlation between the quantitative parameters of CEUS TIC and the parameters of apoptosis marker of PCR, but There was no correlation between Cr and the former two. CEUS can provide a sensitive,real-time,non-invasive technique to detect and evaluate the degree of AKI earlier than Cr.

Effect of intrarenal pelvic pressure on pyelo-tubular backflow and renal cortical blood perfusion during mini-percutaneous nephrolithotomy

PURPOSE

To investigate the effects of intrarenal pelvic pressure (IPP) on pyelo-tubular backflow and renal cortical blood perfusion during mini-percutaneous nephrolithotomy (MPCNL).

METHODS

Dynamic changes in pyelo-tubular backflow and renal cortical blood perfusion were studied in six patients undergoing MPCNL using dynamic contrast-enhanced ultrasonography (CEUS) and IPP monitoring.

RESULTS

CEUS of intrarenal pelvic perfusion revealed that renal tubules began to exhibit contrast agent reflux when IPP exceeded 34 mmHg during the MPCNL procedure. There was a positive correlation between renal tubule contrast agent reflux and IPP (P < 0.05). Intravenous CEUS of renal cortical blood flow demonstrated that both intrarenal pelvic perfusion time and IPP during MPCNL significantly affected renal cortical blood perfusion. Intrarenal pelvic perfusion time and pressure were negatively correlated with contrast agent peak intensity (PI) and area under the curve (AUC) (P < 0.05). Longer intrarenal pelvic perfusion times and higher pressures resulted in decreased renal cortical blood perfusion.

CONCLUSION

This study directly confirmed through dynamic CEUS and real-time IPP monitoring that an increase in IPP above the threshold of approximately 34 mmHg during MPCNL in patients leads to reflux through the renal tubules and a significant decrease in renal cortical blood perfusion. The safe upper limit for intrarenal pelvic perfusion pressure during MPCNL is approximately 34 mmHg.

Quantifying Diaphragm Blood Flow With Contrast-Enhanced Ultrasound in Humans

BACKGROUND

Despite the known interplay between blood flow and function, to our knowledge, there is currently no minimally invasive method to monitor diaphragm hemodynamics. We used contrast-enhanced ultrasound to quantify relative diaphragm blood flow (Q˙DIA) in humans and assessed the technique's efficacy and reliability during graded inspiratory pressure threshold loading. We hypothesized that: (1) Q˙DIA would linearly increase with pressure generation, and (2) that there would be good test-retest reliability and interanalyzer reproducibility.

RESEARCH QUESTION

Can we validate what is, to our knowledge, the first minimally invasive method to measure relative diaphragm blood flow in humans?

STUDY DESIGN AND METHODS

Quantitative contrast-enhanced ultrasound of the costal diaphragm was performed in healthy participants (10 male participants, 6 female participants; mean age 28 ± 5 years; BMI 22.8 ± 2.0 kg/m) during unloaded breathing and three stages of loaded breathing on two separate days. Gastric and esophageal balloon catheters measured transdiaphragmatic pressure. Ultrasonography was performed during a constant-rate IV infusion of lipid-stabilized microbubbles following each stage. Ultrasound images were acquired after a destruction-replenishment sequence and diaphragm specific time-intensity data were used to determine Q˙DIA by two individuals.

RESULTS

Transdiaphragmatic pressure for unloaded and each loading stage were 15.2 ± 0.8, 26.1 ± 0.8, 34.6 ± 0.8, and 40.0 ± 0.8 percentage of the maximum, respectively. Q˙DIA increased with each stage of loading (3.1 ± 3.1, 6.9 ± 3.6, 11.0 ± 4.9, and 13.5 ± 5.4 acoustic units/s; P < .0001). The linear relationship between diaphragmatic flow and pressure was reproducible from day to day. Q˙DIA had good to excellent test-retest reliability (0.86 [0.77, 0.92]; P < .0001) and excellent interanalyzer reproducibility (0.93 [0.90, 0.95]; P < .0001) with minimal bias.

INTERPRETATION

Relative Q˙DIA measurements had valid physiological underpinnings, were reliable day-to-day, and were reproducible analyzer-to-analyzer. This study indicated that contrast-enhanced ultrasound is a viable, minimally invasive method for assessing costal Q˙DIA in humans and may provide a tool to monitor diaphragm hemodynamics in clinical settings.

Ultrasound-responsive microbubbles and nanodroplets: A pathway to targeted drug delivery

Ultrasound-responsive agents have shown great potential as targeted drug delivery agents, effectively augmenting cell permeability and facilitating drug absorption. This review focuses on two specific agents, microbubbles and nanodroplets, and provides a sequential overview of their drug delivery process. Particular emphasis is given to the mechanical response of the agents under ultrasound, and the subsequent physical and biological effects on the cells. Finally, the state-of-the-art in their pre-clinical and clinical implementation are discussed. Throughout the review, major challenges that need to be overcome in order to accelerate their clinical translation are highlighted.

Renal medullary perfusion differs from that in renal cortex in patients with sepsis associated acute kidney injury and correlates with renal function prognosis: A prospective cohort study

BACKGROUND

Renal perfusion status remains poorly studied at the bedside during sepsis associated acute kidney injury (AKI). The aim of the study is to examine renal cortical and medullary perfusion using renal contrast enhanced ultrasound (CEUS) in septic patients.

METHODS

In this single-center, prospective longitudinal study, septic patients were enrolled. Renal ultrasonography was performed within 24 hours of ICU admission (D1), then repeated at D3, D5 and D7. Each measurement consisted of three destruction replenishment sequences that were recorded for delayed analysis with dedicated software (Vuebox). Renal cortex and medulla perfusion were quantified by measuring time to peak (TTP). Receiver operating characteristic (ROC) analysis was used to evaluate 28-day renal prognosis.

RESULTS

The study included 149 septic patients, including 70 non-AKI patients and 79 AKI patients. Both renal cortical and medullary TTP was longer in the AKI group than in the non-AKI group. The difference of TTP between renal cortex and medulla in AKI group was higher than that in the non-AKI group (p = 0.000). Medullary TTP on day 3 had the best performance in predicting the prognosis of 28-day renal function (AUC 0.673, 95% confidence interval 0.528-0.818, p = 0.024), and its cut-off value was 45 s with a sensitivity 52.2% and a specificity of 82.1%. Cortical TTP on day 3 also had the performance in predicting the prognosis of 28-day renal function (AUC 0.657, 95% confidence interval 0.514-0.800, p = 0.039), and its cut-off value was 33 s with a sensitivity 78.3% and a specificity of 55.0%.

CONCLUSION

Renal medullary perfusion alterations differ from those in cortex, with the medulla is worse. Simultaneous and dynamic assessment of cortical and medullary microcirculatory flow alterations necessary. TTP on day 3, especially medullary TTP, seems to be a relatively stable and useful indicator, which correlates with 28-day renal function prognosis in septic patients. Early correction of renal cortical and medullary perfusion alterations reduces the incidence of adverse renal events.

Quantitative evaluation of colorectal tumour vasculature using contrast-enhanced ultrasound: Correlation with angiogenesis and prognostic significance

BACKGROUND

Ultrasound is a vital tool for the diagnosis and management of colorectal cancer (CRC). Contrast-enhanced ultrasound (CEUS) is a non-invasive, safe, and cost-effective method for evaluating tumour blood vessels, that play a crucial role in tumour growth and progression.

AIM

To explore CEUS's role in the quantitative evaluation of CRC blood vessels and their correlation with angiogenesis markers and prognosis.

METHODS

This study prospectively enrolled 100 patients with CRC confirmed by histopathology. All patients received preoperative CEUS examinations. Quantitative parameters, such as peak intensity (PI), time to peak (TTP), and area under the curve (AUC), were derived from time-intensity curve (TIC) analysis. Tumour tissue samples were obtained during surgery and examined immunohistochemically to assess the expression of angiogenesis markers, including vascular endothelial growth factor (VEGF) and microvessel density (MVD). The correlation between CEUS parameters, angiogenesis markers, and clinicopathological features was evaluated using appropriate statistical tests.

RESULTS

Quantitative CEUS parameters (PI, TTP, and AUC) showed significant correlations with VEGF expression (P < 0.001) and MVD (P < 0.001), indicating a strong link between tumour blood vessels and angiogenesis. Increased PI, reduced TTP, and expanded AUC values were significantly related to higher tumour stage (P < 0.001), lymph node metastasis (P < 0.001), and distant metastasis (P < 0.001). Furthermore, these parameters were recognized as independent predictors of overall survival and disease-free survival in multivariate analysis (P < 0.001).

CONCLUSION

CEUS has a high potential in guiding treatment planning and predicting patient outcomes. However, more comprehensive, multicentre studies are required to validate the clinical utility of CEUS in CRC management.

Shell viscosity estimation of lipid-coated microbubbles

Understanding the shell rheology of ultrasound contrast agent microbubbles is vital for anticipating their bioeffects in clinical practice. Past studies using sophisticated acoustic and optical techniques have made enormous progress in this direction, enabling the development of shell models that adequately reproduce the nonlinear behaviour of the coated microbubble under acoustic excitation. However, there have also been puzzling discrepancies and missing physical explanations for the dependency of shell viscosity on the equilibrium bubble radius, which demands further experimental investigations. In this study, we aim to unravel the cause of such behaviour by performing a refined characterisation of the shell viscosity. We use ultra-high-speed microscopy imaging, optical trapping and wide-field fluorescence to accurately record the individual microbubble response upon ultrasound driving across a range of bubble sizes. An advanced model of bubble dynamics is validated and employed to infer the shell viscosity of single bubbles from their radial time evolution. The resulting values reveal a prominent variability of the shell viscosity of about an order of magnitude and no dependency on the bubble size, which is contrary to previous studies. We find that the method called bubble spectroscopy, which has been used extensively in the past to determine the shell viscosity, is highly sensitive to methodology inaccuracies, and we demonstrate through analytical arguments that the previously reported unphysical trends are an artifact of these biases. We also show the importance of correct bubble sizing, as errors in this aspect can also lead to unphysical trends in shell viscosity, when estimated through a nonlinear fitting from the time response of the bubble.

High-fidelity deep functional photoacoustic tomography enhanced by virtual point sources

Photoacoustic tomography (PAT), a hybrid imaging modality that acoustically detects the optical absorption contrast, is a promising technology for imaging hemodynamic functions in deep tissues far beyond the traditional optical microscopy. However, the most clinically compatible PAT often suffers from the poor image fidelity, mostly due to the limited detection view of the linear ultrasound transducer array. PAT can be improved by employing highly-absorbing contrast agents such as droplets and nanoparticles, which, however, have low clinical translation potential due to safety concerns and regulatory hurdles imposed by these agents. In this work, we have developed a new methodology that can fundamentally improve PAT's image fidelity without hampering any of its functional capability or clinical translation potential. By using clinically-approved microbubbles as virtual point sources that strongly and isotropically scatter the local pressure waves generated by surrounding hemoglobin, we can overcome the limited-detection-view problem and achieve high-fidelity functional PAT in deep tissues, a technology referred to as virtual-point-source PAT (VPS-PAT). We have thoroughly investigated the working principle of VPS-PAT by numerical simulations and in vitro phantom experiments, clearly showing the signal origin of VPSs and the resultant superior image fidelity over traditional PAT. We have also demonstrated in vivo applications of VPT-PAT for functional small-animal studies with physiological challenges. We expect that VPS-PAT can find broad applications in biomedical research and accelerated translation to clinical impact.

Is it time to re-think FAST? A systematic review and meta-analysis of Contrast-Enhanced Ultrasound (CEUS) and conventional ultrasound for initial assessment of abdominal trauma

BACKGROUND

The Focused Assessment with Sonography for Trauma (FAST) examination using conventional ultrasound has limited utility for detecting solid organ injury. Therefore, this systematic review and meta-analysis compares the performance of contrast-enhanced ultrasound (CEUS) to conventional ultrasound when used as the initial assessment for abdominal trauma prior to computed tomography (CT) imaging.

METHODS

A systematic literature search of major databases was conducted of human studies investigating the diagnostic accuracy of conventional ultrasound and CEUS occurring prior to CT imaging for abdominal trauma. The study followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. The quality of studies was evaluated using the QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies 2) tool. Paired pooled sensitivity and specificity between conventional ultrasound and CEUS were compared using data extracted from the eligible studies. Diagnostic odds ratio, number needed to diagnose values, and likelihood ratios were also determined.

RESULTS

Ten studies were included. More than half of the included studies demonstrated low risk of bias. Using McNemar's test to assess for paired binary observations, we found that CEUS had statistically higher sensitivity (0.933 vs. 0.559; two-tailed, P < 0.001) and specificity (0.995 vs. 0.979; two-tailed, P < 0.001) than conventional ultrasound in the setting of abdominal trauma, respectively. When divided into particular findings of clinical interest, CEUS had statistically higher sensitivity than conventional ultrasound in screening for active bleeding and injuries to all abdominal solid organs. CEUS also had superior diagnostic odds ratios, number needed to diagnose values, and likelihood ratios than conventional ultrasound.

CONCLUSION

The diagnostic value of CEUS was higher than that of conventional ultrasound for differentiating traumatic abdominal injuries when used as the initial assessment in the emergency department.

Intra- and Inter-Observer Variability of Quantitative Parameters Used in Contrast-Enhanced Ultrasound of Kidneys of Healthy Cats

Contrast-enhanced ultrasound (CEUS) is a non-invasive imaging technique which allows qualitative and quantitative assessment of tissue perfusion. Although CEUS offers numerous advantages, a major challenge remains the variability in tissue perfusion quantification. This study aimed to assess intra- and inter-observer variability for quantification of renal perfusion. Two observers with different levels of expertise performed a quantitative analysis of 36 renal CEUS studies, twice. The CEUS data were collected from 12 healthy cats at 3 different time points with a 7-day interval. The inter- and intra-observer agreement was assessed by the intraclass correlation coefficient. Within and between observers, a good agreement was demonstrated for intensity-related parameters in the cortex, medulla, and interlobular artery. For some parameters, ICC_inter was considerably lower than ICC_intra, mostly when the ROI encompassed the entire kidney or medulla. With the exception of time to peak (TTP) and mean transit time (mTTI), time-related and slope-related parameters showed poor agreement among observers. In conclusion, it may be advised against having the quantitative assessment of renal perfusion performed by different observers, especially if their experience levels differ. The cortical mTTI seemed to be the most appropriate parameter as it showed a favorable inter-observer agreement and inter-period agreement.

Correlation between serum cystatin C level and renal microvascular perfusion assessed by contrast-enhanced ultrasound in patients with diabetic kidney disease

OBJECTIVES

To investigate the relationship between serum cystatin C (CysC) levels and renal microvascular perfusion in patients with diabetic kidney disease (DKD).

METHODS

A total of 57 patients with high CysC levels and 45 patients with normal CysC levels were enrolled. Data on clinical characteristics and laboratory examination results were also collected. Contrast-enhanced ultrasound (CEUS) of the kidneys was successively performed. The time-intensity curve (TIC) and related quantitative parameters of the kidneys were obtained by CEUS and the correlations between CysC and CEUS parameters were analyzed.

RESULTS

Compared to the normal CysC group, the high CysC group had significantly lower wash-in area under the curve (WiAUC), wash-out area under the curve (WoAUC), and wash-in and wash-out area under the curve (WiWoAUC). In the normal CysC group, patients with Stage III chronic kidney disease (CKD) had higher AUCs than those with Stage I-II CKD (p < 0.05). In the high CysC group, patients with Stage IV-V CKD had lower wash-in AUC compared to patients with Stage I-II CKD (p = 0.023). The renal cortex microvascular perfusion parameters AUCs were positively correlated with the estimated glomerular filtration rate (GFR) (r = 0.280, 0.222, and 0.243), and CysC was inversely correlated with AUCs (r= -0.299, -0.251, and -0.273).

CONCLUSIONS

CEUS parameters reflected changes in renal microvascular perfusion in patients with DKD, while AUCs might be useful indicators of declining GFR in DKD patients with increased CysC.

Factors influencing the time-intensity curve analysis of contrast-enhanced ultrasound in kidney transplanted patients: Toward a standardized contrast-enhanced ultrasound examination

Background

Time-intensity curve analysis (TIC analysis) based on contrast-enhanced ultrasound (CEUS) provides quantifiable information about the microcirculation of different tissues. TIC analysis of kidney transplantations is still a field of research, and standardized study protocols are missing though being mandatory for the interpretation of TIC parameters in the clinical context. The aim of this study was to evaluate the impact of different sizes and forms of regions of interest (ROIs) on the variance of different TIC parameters and the level of interoperator variance between the different ROI methods in kidney transplantations.

Methods

In 25 renal transplanted patients, 33 CEUS of the transplanted kidney were performed, and TIC analysis with ROIs sized 5 mm2 (ROI5), 10 mm2 (ROI10), and ROIs circumscribing the outlines of anatomical regions (ROI Anat ) were analyzed based on CEUS examination. The TIC analysis was repeated by a second independent operator for ROI5 and ROI Anat .

Results

Statistical analysis revealed significant differences between TIC parameters of different ROI methods, and overall, the interoperator variance was low. But a greater ROI surface (ROI10) led to higher values of the intensity parameters A and AUC compared with ROI5 (p < 0.05). The difference in the ROI form led to high variation of certain TIC parameters between ROI5 and ROI Anat in the myelon [intraclass correlation coefficient (A, ICC = 0.578 (0.139-0.793); TIC parameter (TTP); and ICC = 0.679 (0.344-0.842) (p < 0.05)]. A mean variation of 1 cm of the depth of ROI5 in the cortex did not show significant differences in the TIC parameters, though there was an impact of depth of ROI Anat on the values of TIC parameters. The interoperator variance in the cortex was low and equal for ROI5 and ROI Anat , but increased in the myelon, especially for ROI Anat . Furthermore, the analysis revealed a strong correlation between the parameter AUC and the time interval applied for the TIC analysis in the cortex and myelon (r = 0.710, 0.674, p < 0.000).

Conclusion

Our findings suggest the application of multiple ROIs of 5 mm2 in the cortex and medulla to perform TIC analysis of kidney transplants. For clinical interpretation of AUC, a standardized time interval for TIC analysis should be developed. After the standardization of the TIC analysis, the clinical predictive value could be investigated in further studies.

Persistent Coronary Vasomotor Tone During Myocardial Ischemia Occurs at the Capillary Level and May Involve Pericytes

Background

There is persistent coronary vasomotor tone during myocardial ischemia, despite ongoing coronary arteriolar dilatation. The mechanism underlying this vasodilatory tone, which can be unmasked by coronary vasodilators, is unclear. We hypothesized that persistent microvascular resistance during myocardial ischemia occurs at the level of capillaries and may be caused by pericytes.

Methods

We studied nine instrumented dogs where coronary blood flow and coronary driving pressure were reduced to half by placement of stenoses. Myocardial blood flow and myocardial blood volume were measured with myocardial contrast echocardiography before and during adenosine administration. In three animals, the heart was perfusion-fixed under these conditions for electron microscopic assessment of capillary and pericyte size.

Results

During ischemia, myocardial blood volume decreased and myocardial vascular resistance remained unchanged. Adenosine administration reversed the decline in myocardial blood volume and decreased myocardial vascular resistance. Electron microscopy showed larger capillaries in ischemic beds receiving adenosine than ischemic beds not receiving adenosine. Pericytes in beds receiving adenosine also tended to be larger.

Conclusion

Capillaries are the site of persistent vasomotor tone during myocardial ischemia; any other site of vascular regulation (arterioles or venules) cannot explain these myocardial contrast echocardiography findings, which are confirmed on post-mortem electron microscopic examination. The decrease in capillary size is likely caused by pericyte contraction in an attempt to maintain a constant capillary hydrostatic pressure. Adenosine relaxes pericytes, restores myocardial blood volume, reduces myocardial vascular resistance, and improves regional function during ischemia. These findings could have important therapeutic implications.

Association of Contrast-Enhanced Ultrasound-Derived Kidney Cortical Microvascular Perfusion with Kidney Function

BACKGROUND

Individuals with chronic kidney disease (CKD) have decreased kidney cortical microvascular perfusion, which may lead to worsening kidney function over time, but methods to quantify kidney cortical microvascular perfusion are not feasible to incorporate into clinical practice. Contrast-enhanced ultrasound (CEUS) may quantify kidney cortical microvascular perfusion, which requires further investigation in individuals across the spectrum of kidney function.

METHODS

We performed CEUS on a native kidney of 83 individuals across the spectrum of kidney function and calculated quantitative CEUS-derived kidney cortical microvascular perfusion biomarkers. Participants had a continuous infusion of the microbubble contrast agent (Definity) with a flash-replenishment sequence during their CEUS scan. Lower values of the microbubble velocity (β) and perfusion index (β×A) may represent lower kidney cortical microvascular perfusion. Multivariable linear regression models tested the associations of the microbubble velocity (β) and perfusion index (β×A) with estimated glomerular filtration rate (eGFR).

RESULTS

Thirty-eight individuals with CKD (mean age±SD 65.2±12.6 years, median [IQR] eGFR 31.5 [18.9-41.5] ml/min per 1.73 m²), 37 individuals with end stage kidney disease (ESKD; age 54.8±12.3 years), and eight healthy volunteers (age 44.1±15.0 years, eGFR 117 [106-120] ml/min per 1.73 m²) underwent CEUS without side effects. Individuals with ESKD had the lowest microbubble velocity (β) and perfusion index (β×A) compared with individuals with CKD and healthy volunteers. The microbubble velocity (β) and perfusion index (β×A) had moderate positive correlations with eGFR (β: r_s=0.44, P<0.001; β×A: r_s=0.50, P<0.001). After multivariable adjustment, microbubble velocity (β) and perfusion index (β×A) remained significantly associated with eGFR (change in natural log transformed eGFR per 1 unit increase in natural log transformed biomarker: β, 0.38 [95%, CI 0.17 to 0.59]; β×A, 0.79 [95% CI, 0.45 to 1.13]).

CONCLUSIONS

CEUS-derived kidney cortical microvascular perfusion biomarkers are associated with eGFR. Future studies are needed to determine if CEUS-derived kidney cortical microvascular perfusion biomarkers have prognostic value.

Quantitative assessment of renal perfusion in children with UPJO by contrast enhanced ultrasound: A pilot study

BACKGROUND

Contrast-enhanced ultrasound (CEUS) is a new potential modality for the quantitative evaluation of the microvascular perfusion of a parenchymal organ.

OBJECTIVE

To prospectively and quantitatively analyse the role of CEUS in evaluating renal perfusion for assessing renal function in children with ureteropelvic junction obstruction (UPJO).

METHODS

The study protocol was approved by the local ethics committee, and written informed consent was obtained from the patients' parents or guardians. Ultrasonography, CEUS, and radioisotope renography were performed for 51 children (42 boys, 9 girls; mean age, 6.75 ± 4.14 years) with unilateral UPJO. The slope of the ascending curve (A), time to peak (TTP), peak intensity (PI), and area under the curve (AUC) were recorded during CEUS; quantitative data were calculated by QLab system (semiautomated border tracking, Philips Healthcare) software. Sensitivity and specificity values were determined for CEUS with respect to radioisotope renography.

RESULTS

CEUS was used to evaluate 102 kidneys in 51 patients, for which the perfusion time-intensity curve (TIC) was determined. The TIC of renal cortical perfusion in all groups showed an asymmetrical single-peak curve, which could be clearly distinguished between the experimental group and the control group. Compared with the control group, the experimental group showed a markedly prolonged TTP but a significantly decreased A (P < 0.05). There was no significant correlation between the AUC, PI and differential renal function (DRF), but the correlation coefficient between TTP, A and DRF remained significant (p < 0.001).The receiver operating characteristic (ROC) curves drawn to differentiate DRF using the TTP value yielded an area under the ROC curve (AUROC) of 0.86. For a quantitative assessment of DRF less than 40% by CEUS, the sensitivity and specificity values were 92.86% and 76.14%, respectively.

DISCUSSION

Unlike in previous studies, no significant difference in the AUC or PI was found between the control group and the experimental group in this study (P > 0.05). Renal blood perfusion could not be evaluated overall by CEUS. Parenchymal thinning may be considered a limitation to CEUS.

CONCLUSIONS

This preliminary experience represents the first report of evaluating the diagnostic value of CEUS in assessing renal function in children with UPJO. CEUS is a highly sensitive, rapid, and cost-effective diagnostic imaging modality for detecting and monitoring renal function noninvasively.

Ultrasonographic assessment of renal perfusion in bitches with mammary carcinoma treated with long-term carprofen

The aim of this study was to evaluate renal hemodynamics, routine clinical and laboratory parameters used to estimate renal function, and clinical evolution during six months in bitches with mammary carcinomas that underwent mastectomy and were treated (TG) or not (CG) with carprofen for three months after surgery. Twenty-six bitches with mammary carcinoma were equally distributed into TG that received carprofen 4.4 mg/kg/day for 90 days and CG that did not receive anti-inflammatory medication. Renal artery Doppler flowmetry, contrast-enhanced ultrasound (CEUS) of renal parenchyma, haematological, biochemical and clinical analyses were obtained once a month. These data were compared between groups and time via analysis of variance (ANOVA) in a completely randomized design with repeated measures (P < 0.05). On B-mode ultrasound, the area of the renal artery was greater (P = 0.0003) in the TG. Regarding laboratory findings, haematocrit and haemoglobin were similar in both groups, showing a significant and gradual increase after three months of treatment; MCV, MHC, and MCHC were increased (P < 0.05) and lymphocyte and band counts decreased (P < 0.05) in the TG. Regarding biochemical tests, ALT was the only parameter with a significant difference, being higher (P = 0.0272) in the treated group. It can be concluded that the use of carprofen for 90 days causes minimal changes in renal perfusion, erythrocyte parameters and ALT activity, and reduces the proportion of blood inflammatory cells. Therefore, use of this medication can be carried out safely in patients who require auxiliary cancer treatment.

Quantitative Evaluation of Renal Cortex Perfusion Using Contrast-Enhanced Ultrasound Imaging Parameters in Ischemia-Reperfusion Injury in Rabbits

The aim of this study was to evaluate blood perfusion of the renal cortex during ischemia-reperfusion (I/R) injury using quantitative contrast-enhanced ultrasound (CEUS) parameters. In this experiment, 24 rabbits were randomly divided into four groups (N = 6): sham-operated group, 24-h post-operation for I/R injury group (24-h I/R), 3-d post-operation for I/R injury group (3-d I/R) and 5 d post-operation for I/R injury group (5 d I/R). All quantitative CEUS parameters were monitored and included the gradient from the start frame to the peak frame (Grad), area under the curve (Area), time-to-peak (TTP), difference between B(intercept intensity at t=0) and A(the intensity attenuation t= 0) and arrival time (AT). Subsequently, we analyzed the changes in these parameters, as well as the correlation between changes in CEUS parameters and pathological parameters. AT and TTP values peaked 3 d after I/R surgery, which correlated with the most significant pathological changes at the same time point. These parameters (such as AT, TTP and Grad) may be useful in dynamically monitoring the severity of tissue damage at the early stage of I/R injury.

Effects of ulinastatin on renal perfusion evaluated by Doppler ultrasonography in a porcine model of septic shock

The present study aimed to evaluate the effect of ulinastatin (UTI) on renal perfusion using Doppler ultrasonography in a porcine model of septic shock induced by smoking inhalation and live methicillin-resistant Staphylococcus aureus instillation. A total of 32 healthy Landrace pigs were randomly assigned into the following four groups: Sham group (SH; n=5), septic shock group (SS; n=9), septic shock treated with vancomycin (15 mg/kg) group (VAN; n=9) and septic shock treated with UTI (50,000 U/kg) + vancomycin (UTI; n=9) group. Renal perfusion was evaluated by contrast-enhanced ultrasound (CEUS) at baseline and at the end of the protocol (24 h). The spectrum of interlobar or arcuate artery was selected to calculate the corrected resistive index (cRI). Sulphur hexafluoride microbubbles were bolus injected via a venous catheter. The peak intensity (Pi) and area under curve (AUC) were calculated using a time-intensity curve. Compared with the baseline group, cRI was increased significantly at the end of the protocol, except for that in the SH group, whereas Pi decreased significantly after injury in all experimental groups but was higher in the UTI group compared with that in the SS and VAN groups (both P<0.001). Linear correlation was found between the cardiac output (CO) and Pi (R²=0.752; P<0.001). The AUC was significantly decreased after injury in the SS and VAN groups compared with the baseline group. All parameters detected by CEUS were improved in the UTI group, and significant differences were found between the UTI and SS or VAN group (all P<0.05). In conclusion, acute renal injury, which occasionally occurs during septic shock, is accompanied with a significantly lower perfusion rate in the renal microcirculation. By contrast, UTI can significantly improve renal perfusion, which can be reliably evaluated using CEUS.

Impact of region-of-interest size and location on quantitative contrast-enhanced ultrasound of canine splenic perfusion

Background

During contrast enhanced ultrasound (CEUS), the features of the regions of interest (ROI) can affect the value of the perfusion-related parameters obtained from a time intensity curve (TIC). In veterinary medicine, conflicting have been reported on the influence of ROI size and location on renal CEUS. There are some disagreeing evidences regarding the optimal method for selecting ROI in quantitative analysis of renal perfusion using CEUS.

The aim of this study was to evaluate the effect of the size and location of ROIs in the spleen of conscious dogs on perfusion variables determined using sulphur hexafluoride contrast-enhanced ultrasounds.

Results

A prospective observational study on 15 client-owned mixed-breed adult dogs was performed using a system equipped with contrast-tuned imaging technology. Qualitative and quantitative assessments of the spleen enhancement pattern were carried out. Three square ROIs (0.05 cm²) were manually drawn in a row and spaced 1 mm apart, placing adjacent ROIs at three different depths. Three medium rectangular ROIs (0.3 cm²) include the 3 smallest ROIs in each row, indicated by the letters A, B and C, and a single large square ROI (1 cm²) was drawn containing all previous ROIs. Software analysis of time-intensity curves generated within each ROI allowed us to calculate the perfusion-related parameters: peak enhancement, time to peak, regional blood flow, mean transit time and regional blood volume.

The coefficient of variation for all blood-related parameters was always lower in the larger ROI than in the other smaller ROIs. ROI A and B, positioned proximally and medially, levels respectively, showed similar coefficients of variation to the largest ROI. The analysis of variance model exhibited a significant effect of location and size of the ROIs in the quantitative analysis of canine spleen perfusion, with a reduction of perfusion-related parameters in the distal ROI.

Conclusions

The recommendation for a quantitative CEUS examination of a dog’s spleen is to analyze splenic perfusion by drawing a sufficiently large ROI proximal to the ultrasound beam on the splenic parenchyma. This may be of clinical relevance in the diagnosis of splenic diseases.

The Diagnostic Value of Contrast-Enhanced Ultrasound for Monitoring Complications After Kidney Transplantation-A Systematic Review and Meta-Analysis

RATIONALE AND OBJECTIVES

Contrast-enhanced ultrasound (CEUS) has increasingly gained acceptance in the postoperative evaluation of kidney-transplantation recipients. Our meta-analysis aims to evaluate the diagnostic accuracy of CEUS in identifying post-transplantation complications.

MATERIALS AND METHODS

PubMed, Scopus, Ovid Medline, and Cochrane databases were searched from their inception until February 28, 2020, for diagnostic test accuracy studies comparing CEUS to a reference standard for monitoring complications after kidney transplantation. A meta-analysis was conducted to calculate the pooled sensitivity, specificity, accuracy, and diagnostic odds ratio using a bivariate random effects model. Sensitivity analysis was performed using R software by stratifying the studies based on study design, sample size, age, and origin of the study to evaluate the influence of these factors on the overall effect.

RESULTS

Two independent reviewers analyzed 285 publications, out of which 29 were determined directly relevant and 12 (with a total of 542 cases) contained all required data for the meta-analysis. The overall sensitivity of included studies was estimated to be 0.86 (95% confidential interval (CI); 0.78--0.92). Similarly, the overall specificity was estimated to be 0.90 (95% CI; 0.82-0.94). Log diagnostic odds ratio was 4.25 (95% CI; 3.43-5.07), and the area under the curve of the pooled receiver operating characteristic was 0.94. Stratified sensitivity analyses showed study design, sample size, age group, and origin of the study had no significant impact on the overall diagnostic value of CEUS.

CONCLUSION

Evidence suggests that CEUS is a potentially effective and accurate method to evaluate a variety of complications such as rejection, vascular complications, and malignancies after kidney transplantation.

Contrast-enhanced ultrasound assessed renal microvascular perfusion may predict postoperative renal complications following colorectal surgery

Colorectal surgery is associated with an above-average mortality rate of approximately 15%. During surgery, maintenance of vital organ perfusion is essential in order to reduce postoperative mortality and morbidity, with renal perfusion of particular importance. Oesophageal Doppler monitors (ODM) are commonly used to try and provide accurate measures of fluid depletion during surgery; however, it is unclear to what extent they reflect organ perfusion. In addition, it is not known whether macro- and/ or microvascular perfusion indices are associated with renal complications following colorectal surgery. Thirty-two participants scheduled for colorectal surgery had three measures of macro- and microvascular renal blood flow via contrast enhanced ultrasound (CEUS), and simultaneous measures of cardiac output indices via ODM: (i) pre-operatively; (ii) intra-operatively at the mid-point of operation, and (iii) after the conclusion of surgery. The Postoperative Morbidity Survey (POMS) was used to assess postoperative complications. Intra-operatively, there was a significant correlation between renal microvascular flow (RT) and renal macrovascular flow (TTI) (ρ = 0.52; p = 0.003). Intra-operative TTI, but not RT, was associated with cardiac index (ρ = -0.50; p=0.0003). Intra-operative RT predicted increases in renal complications (OR 1.46; 95% CI 1.03-2.09) with good discrimination (C-statistic, 0.85). Complications were not predicted by TTI or ODM-derived indices. There was no relationship between RT and TTI before or after surgery. ODM measures of haemodynamic status do not correlate with renal microvascular blood flow, and as such are likely not suitable to determine vital organ perfusion. Only CEUS-derived measures of microvascular perfusion were predictive of postoperative renal complications.

Hierarchical Temporal Attention Network for Thyroid Nodule Recognition Using Dynamic CEUS Imaging

Contrast-enhanced ultrasound (CEUS) has emerged as a popular imaging modality in thyroid nodule diagnosis due to its ability to visualize vascular distribution in real time. Recently, a number of learning-based methods are dedicated to mine pathological-related enhancement dynamics and make prediction at one step, ignoring a native diagnostic dependency. In clinics, the differentiation of benign or malignant nodules always precedes the recognition of pathological types. In this paper, we propose a novel hierarchical temporal attention network (HiTAN) for thyroid nodule diagnosis using dynamic CEUS imaging, which unifies dynamic enhancement feature learning and hierarchical nodules classification into a deep framework. Specifically, this method decomposes the diagnosis of nodules into an ordered two-stage classification task, where diagnostic dependency is modeled by Gated Recurrent Units (GRUs). Besides, we design a local-to-global temporal aggregation (LGTA) operator to perform a comprehensive temporal fusion along the hierarchical prediction path. Particularly, local temporal information is defined as typical enhancement patterns identified with the guidance of perfusion representation learned from the differentiation level. Then, we leverage an attention mechanism to embed global enhancement dynamics into each identified salient pattern. In this study, we evaluate the proposed HiTAN method on the collected CEUS dataset of thyroid nodules. Extensive experimental results validate the efficacy of dynamic patterns learning, fusion and hierarchical diagnosis mechanism.

Comparison of Renal Blood Flow Using Maximum Slope-Based Computed Tomography Perfusion and Ultrasound Flow Probe in Healthy Dogs

Computed tomography (CT) perfusion can analyze tissue perfusion and quantitative parameters, including blood flow, blood volume, and transit time. CT perfusion has been used for evaluating split renal function. However, its applicability in veterinary medicine was not validated. This study aimed to evaluate the correlation of renal blood flow (RBF) derived by maximum slope-based CT perfusion and an ultrasonic flow probe and assess the effect of the presence of a pre-existing contrast medium on CT perfusion in the kidneys. In five healthy purpose-bred beagles, CT perfusion was performed at the level of the left renal hila after injection of 1 mg/kg iohexol, during measuring RBF with an ultrasonic flow probe placed on the left renal artery. After post-contrast CT scan with injection of 2 mg/kg iohexol, CT perfusion scan was repeated with the same protocol used in the first perfusion study. The CT perfusion derived RBF was analyzed based on the maximum slope and was compared with the true RBF obtained using an ultrasonic flow probe. Results indicated that CT perfusion derived RBF was significantly correlated with true RBF, although CT perfusion derived RBF did not match the absolute value of the true RBF. It was correlated with the true RBF, even in the presence of a pre-existing contrast medium in the kidney. CT perfusion can estimate the change in individual renal perfusion non-invasively, and this method can be used supplementary to the conventional CT protocol in clinic.

Clinical and ultrasound variables for early diagnosis of septic acute kidney injury in bitches with pyometra

The aetiology of septic acute kidney injury (AKI) is not completely elucidated. Early identification of AKI in septic patients is considered to improve survival rate since it allows rapid treatment onset. We evaluated clinical, haematological, urinary, B-mode, spectral Doppler, and contrast-enhanced ultrasound variables in 20 bitches with pyometra as sepsis models and 12 healthy controls. All animals with pyometra presented some degree of renal damage on histological examination; however, sequential organ failure assessment (SOFA) classified only 40% cases with sepsis. AKI derived from systemic infection was identified in 57% of cases with hypoperfusion and in 22% with inflammation, being an affection of multifactorial origin. Among the evaluated parameters, urinary protein/creatinine ratio >0.15, serum albumin <2.94 mg/dL, time-averaged minimum velocity <21.5 cm/s, renal length/aorta diameter ratio >5.93, pulsatility index >1.53, haematocrit <45%, time-averaged maximum velocity <45.7 cm/s, haemoglobin <16 g/dL, leukocytes >12.53 × 103/uL, and cortical contrast peak intensity <69%, in the order of accuracy, are significant indicators of septic AKI with an accuracy >80%. Thus, AKI is a very prevalent condition in septic patients, derived mainly from changes in renal perfusion and inflammation. Additionally, reviewing the SOFA score parameters is suggested to identify renal failure.

Demonstration of Improved Renal Congestion After Heart Failure Treatment on Renal Perfusion Imaging With Contrast-Enhanced Ultrasonography

Background: Renal congestion is a critical pathophysiological component of congestive heart failure (CHF). Methods and Results: To quantify renal congestion, contrast-enhanced ultrasonography (CEUS) was performed at baseline and after treatment in 11 CHF patients and 9 normal subjects. Based on the time-contrast intensity curve, time to peak intensity (TTP), which reflects the perfusion rate of renal parenchyma, and relative contrast intensity (RCI), an index reflecting renal blood volume, were measured. In CHF patients, TTP at baseline was significantly prolonged compared with that in controls (cortex, 10.8±3.5 vs. 4.6±1.2 s, P<0.0001; medulla, 10.6±3.0 vs. 5.1±1.6 s, P<0.0001), and RCI was lower than that in controls (cortex, -16.5±5.2 vs. -8.8±1.5 dB, P<0.0001; medulla, -22.8±5.2 vs. -14.8±2.4 dB, P<0.0001). After CHF treatment, RCI was significantly increased (cortex, -16.5±5.2 to -11.8±4.5 dB, P=0.035; medulla, -22.8±5.2 to -18.7±3.7 dB, P=0.045). TTP in the cortex decreased after treatment (10.8±3.5 to 7.6±3.1 s, P=0.032), but it was unchanged in the medulla (10.6±3.0 to 8.3±3.2 s, P=0.098). Conclusions: Renal congestion can be observed using CEUS in CHF patients.

Histological and blood chemistry examination of the rodent kidney after exposure to flash-replenishment ultrasound contrast imaging

The purpose of this work is to investigate whether imaging sequences of flash-replenishment contrast enhanced ultrasound (CEUS) of the kidney result in chronic or acute bioeffects. Kidneys of female Fischer 344 rats were imaged using the flash-replenishment technique. Animals were separated into four groups (N = 31). Imaging was conducted with a 4C1 probe, driven by an Acuson Sequoia system with Definity microbubbles as the ultrasound contrast agent. During the flash phase of the imaging sequence, one kidney in each animal was exposed to either a mechanical index (MI) of 1.0 or 1.9. For each MI, half of the animals were sacrificed shortly after imaging (4 h) or after 2 weeks. A blinded veterinary nephropathologist reviewed the histopathology of both the imaged and control (non-imaged) kidney. Blood urea nitrogen (BUN) was measured for each animal prior to imaging and at the time of necropsy. Histopathology assessments in both the 1.0 and 1.9 MI groups revealed no signs of hemorrhage at either the 4-h or 2-week time point. BUN showed minor but statistically significant elevations in both the 1.0 and 1.9 MI groups, but no significant difference was present at the 2-week time point in the 1.0 MI group. All BUN levels (at both time points) remained in the normal range. In conclusion, CEUS with flash-replenishment imaging sequences did not result in kidney bioeffects observable with histology at early or late time points. Increases in BUN levels were observed after imaging, but were minimized when using a moderate MI (1.0).

Contrast-enhanced ultrasound detects changes in microvascular blood flow in adults with sickle cell disease

In patients with sickle cell disease (SCD), poor outcome measures compromise the potential success of clinical trials. Contrast-enhanced ultrasound (CEUS) is a technique that can non-invasively quantify deep tissue microvascular blood flow. We tested the hypothesis that CEUS of forearm skeletal muscle could be used to: 1) assess microvascular abnormalities that occur during vaso-occlusive crisis; and 2) test new therapies for SCD that are targeted to improving the status of the microcirculation. We performed a prospective study, CEUS perfusion imaging of resting forearm muscle was performed in adults with SCD: 1) during and after a pain episode, and 2) before, during, and after a 24-hour infusion of the investigative agent, regadenoson, an adenosine A_2A agonist. CEUS destruction-replenishment time-intensity data were analyzed to measure microvascular blood flow, as well as its components, microvascular blood volume and flux rate. Serial CEUS measurements were obtained in 32 adults with SCD. For the studies during crisis, there was a 30% reduction in microvascular blood flow compared to steady-state (p = 0.031), a reduction that was largely due to microvascular flux rate. For the regadenoson group, a non-significant 25% increase in flux rate and 9% increase in microvascular blood flow compared to baseline were detected during infusion. In a study of adults with SCD, CEUS detected changes in microvascular blood flow associated with vaso-occlusive crises. No changes were found during an infusion of the adenosine A_2A agonist, regadenoson. This study provides preliminary evidence that CEUS could detect blood flow changes consistent with SCD physiology.

Prediction of renal allograft chronic rejection using a model based on contrast-enhanced ultrasonography

Objective

To evaluate the application of contrast‐enhanced ultrasonography (CEUS) for the diagnosis of renal allograft chronic rejection (CR).

Methods

A total of 104 patients who were suspected to have AR or CR were enrolled in this study (derivation group, n = 66; validation group, n = 38). Before biopsy, all patients received an ultrasound examination.

Results

In the CR group, rising time (RT) and time to peak (TTP) of medulla (RTm and TTPm, respectively) were significantly longer compared to those in the AR group. The kidney volume was significantly decreased in the CR group but was increased in the AR group. In the derivation group, age, change in kidney volume, and TTPm were identified as independent predictors by multivariate analysis. Based on the multivariate analysis results and area under receiver operating characteristic (ROC) curves (AUROCs) of individual markers, we constructed a new index as follows: P = −5.424 + 0.074 × age −9.818 × kidney volume change + 0.115 × TTPm; New Index = e^P/(1 + e^P). The new index discriminates CR from AR and had better AUROCs than any other parameters.

Conclusion

In conclusion, the new index provides a new diagnosis model for CR.

Time-intensity curve analysis of contrast-enhanced ultrasound is unable to differentiate renal dysfunction in the early post-transplant period - a prospective study

Background

Contrast enhanced ultrasonography (CEUS) assessment of kidney allografts mainly focuses on graft rejection. However, studies on delayed graft function (DGF) without acute rejection are still lacking. The aim of this study was to build a time-intensity curve (TIC) using CEUS in non-immunological DGF to understand the utility of CEUS in early transplantation.

Methods

Twenty-eight patients in the short-term postoperative period (<14 days) were divided according to the need for dialysis (early graft function [EGF] and [DGF]) and 37 subjects with longer than 90 days follow-up were divided into creatinine tertiles. Time to peak [TTP] and rising time [RT were compared between groups.

Results

EGF and DGF were similar, except for creatinine. In comparison to the late group, medullary TTP and RT were shorter in the early group as well as the delay regarding contrast arrival in the medulla (in relation to cortex) and reaching the medullary peak (in relation to artery and cortex). In the late group, patients with renal dysfunction showed shorter temporal difference to reach medullary peak in relation to artery and cortex.

Conclusions

Although it was not possible to differentiate EGF and DGF using TIC, differences between early and late groups point to blood shunting in renal dysfunction.

Renal perfusion parameters measured by contrast-enhanced ultrasound in healthy dogs demonstrate a wide range of variability in the long-term

Contrast-enhanced ultrasound may be helpful for detecting early renal microvascular damage and dysfunction in dogs. However, before this noninvasive imaging method can be tested as an early-stage screening tool in clinical patients, an improved understanding of long-term variation in healthy animals is needed. In this prospective, secondary, longitudinal, serial measurements study, variability of contrast-enhanced ultrasound renal perfusion parameters was described for eight healthy dogs, using seven time points and a period of 83 weeks. Dogs were sedated with butorphanol (0.4 mg/kg), and contrast-enhanced ultrasound of each kidney was performed after an intravenous bolus injection of a microbubble contrast agent (0.04 mL/kg). Time-intensity curves were created from regions-of-interest drawn in the renal cortex and medulla. Intensity-related parameters representing blood volume and time-related parameters representing blood velocity were determined. A random-effects model using restricted maximum likelihood was used to estimate variance components. Within-dog coefficient of variation was defined as the ratio of the standard deviation over the mean. Time-related parameters such as time-to-peak, rise and fall time had lowest within-dog variability. Intensity-related parameters such as peak enhancement, wash-in and wash-out area under the curve, total area under the curve, and wash-in and washout rates had high within-dog variability (coefficient of variation > 45%). Authors therefore recommend the use of time-related parameters for future studies of renal perfusion. Within-dog variability for bilateral kidney measurements was extremely low, therefore contrast-enhanced ultrasound may be particularly useful for detecting unilateral changes in renal perfusion. Future studies are needed to compare contrast-enhanced ultrasound findings in healthy dogs versus dogs with renal disease.

Vascular rejection in renal transplant: Diagnostic value of contrast-enhanced ultrasound (CEUS) compared to biopsy

BACKGROUND

Despite of the more potent immunosuppressive medication, vascular rejection is still a major issue after renal transplantation. Renal biopsy is the gold standard diagnostic to evaluate acute and chronic allograft rejection. As it is an invasive diagnostic there is the risk of complications like haematoma, arteriovenous fistulas, active bleeding or infection. Contrast-enhanced ultrasound is a non-invasive imaging modality that allows visualising renal transplant perfusion.

OBJECTIVE

To analyse the sensitivity and specificity of contrast-enhanced ultrasound (CEUS) compared to biopsy as gold standard in diagnosing vascular rejection in renal transplant patients.

METHODS

A total of 57 renal transplant recipients with poor renal allograft function with initial diagnostic imaging between 2006 and 2017 were included in the study. Clinical data and imaging studies were analysed retrospectively. The diagnostic accuracy of CEUS in diagnosing vascular rejection of the renal transplant was compared to renal biopsy as gold standard. Out of 57 patients 7 patients showed signs of vascular rejection in biopsy. In 6 out of these 7 patients CEUS described irregularities in renal perfusion suspicious of vascular rejection.

RESULTS

CEUS showed a sensitivity of 85.7%, a specificity of 100%, a positive predictive value (PPV) of 100%, and a negative predictive value (NPV) of 98.0%.

CONCLUSIONS

CEUS is a safe, non-nephrotoxic imaging modality for the initial imaging of renal transplant recipients with elevated kidney function parameters suspicious of vascular rejection. Compared to renal biopsy as gold standard CEUS shows a high specificity and PPV in detecting signs of vascular rejection. Since sub-types of vascular rejection with cellular and humoral components with greater risk for allograft loss have been described renal biopsy is inevitable in these cases.

Acute kidney injury is associated with a decrease in cortical renal perfusion during septic shock

Background

Renal perfusion status remains poorly studied at the bedside during septic shock. We sought to measure cortical renal perfusion in patients with septic shock during their first 3 days of care using renal contrast enhanced ultrasound (CEUS).

Methods

We prospectively included 20 ICU patients with septic shock and 10 control patients (CL) without septic shock admitted to a surgical ICU. Cortical renal perfusion was evaluated with CEUS during continuous infusion of Sonovue (Milan, Italy) within the first 24 h (day 0), between 24 and 48 h (day 1) and after 72 h (day 3) of care. Each measurement consisted of three destruction replenishment sequences that were recorded for delayed analysis with dedicated software (Vuebox). Renal perfusion was quantified by measuring the mean transit time (mTT) and the perfusion index (PI), which is the ratio of renal blood volume (rBV) to mTT.

Results

Cortical renal perfusion was decreased in septic shock as attested by a lower PI and a higher mTT in patients with septic shock than in patients of the CL group (p = 0.005 and p = 0.03). PI values had wider range in patients with septic shock (median (min-max) of 74 arbitrary units (a.u.) (3–736)) than in patients of the CL group 228 a.u. (67–440)). Renal perfusion improved over the first 3 days with a PI at day 3 higher than the PI at day 0 (74 (22–120) versus 160 (88–245) p = 0.02). mTT was significantly higher in patients with severe acute kidney injury (AKI) (n = 13) compared with patients with no AKI (n = 7) over time (p = 0.005). The PI was not different between patients with septic shock with severe AKI and those with no AKI (p = 0.29).

Conclusions

Although hemodynamic macrovascular parameters were restored, the cortical renal perfusion can be decreased, normal or even increased during septic shock. We observed an average decrease in cortical renal perfusion during septic shock compared to patients without septic shock. The decrease in cortical renal perfusion was associated with severe AKI occurrence. The use of renal CEUS to guide renal perfusion resuscitation needs further investigation.

Contrast-enhanced ultrasound measurement of pancreatic blood flow dynamics predicts type 1 diabetes progression in preclinical models

In type 1 diabetes (T1D), immune-cell infiltration into the islets of Langerhans (insulitis) and β-cell decline occurs many years before diabetes clinically presents. Non-invasively detecting insulitis and β-cell decline would allow the diagnosis of eventual diabetes, and provide a means to monitor therapeutic intervention. However, there is a lack of validated clinical approaches for specifically and non-invasively imaging disease progression leading to T1D. Islets have a denser microvasculature that reorganizes during diabetes. Here we apply contrast-enhanced ultrasound measurements of pancreatic blood-flow dynamics to non-invasively and predictively assess disease progression in T1D pre-clinical models. STZ-treated mice, NOD mice, and adoptive-transfer mice demonstrate altered islet blood-flow dynamics prior to diabetes onset, consistent with islet microvasculature reorganization. These assessments predict both time to diabetes onset and future responders to antiCD4-mediated disease prevention. Thus contrast-enhanced ultrasound measurements of pancreas blood-flow dynamics may provide a clinically deployable predictive marker for disease progression in pre-symptomatic T1D and therapeutic reversal.

Contrast-enhanced ultrasonography in chronic glomerulonephritides: correlation with histological parameters of disease activity

PURPOSE

To compare contrast-enhanced ultrasonography (CEUS)-derived time-intensity (TI) curves with histological findings in kidneys of patients affected by chronic glomerulonephritides (GN) in the early stage of disease.

METHODS

Research ethics committee approval and patient written informed consent were obtained. Thirty-one patients who showed clinical and laboratory signs of GN, with preserved renal function, were consecutively enrolled. They underwent kidney CEUS, from which TI curves were obtained, and kidney biopsy. TI curves were compared with clinical data, ultrasound (US) Doppler, and histological parameters.

RESULTS

The persistence of contrast agent signal during the wash-out phase was found to be correlated with the degree of disease activity (p = 0.016) and in particular with the presence of mesangial hyperplasia (p = 0.008). No correlation was observed between TI curves and clinical or Doppler US-derived parameters.

CONCLUSIONS

The persistence of contrast agent signal in the wash-out phase of CEUS appears to reflect a disturbance of perfusion in glomerular capillaries in the early stages of GN. We found that the histological element directly correlated with the prolonged wash-out was mesangial hyperplasia.

Renal autoregulation and blood pressure management in circulatory shock

The importance of personalized blood pressure management is well recognized. Because renal pressure–flow relationships may vary among patients, understanding how renal autoregulation may influence blood pressure control is essential. However, much remains uncertain regarding the determinants of renal autoregulation in circulatory shock, including the influence of comorbidities and the effects of vasopressor treatment. We review published studies on renal autoregulation relevant to the management of acutely ill patients with shock. We delineate the main signaling pathways of renal autoregulation, discuss how it can be assessed, and describe the renal autoregulatory alterations associated with chronic disease and with shock.

Contrast-Enhanced Ultrasound for Assessing Renal Perfusion Impairment and Predicting Acute Kidney Injury to Chronic Kidney Disease Progression

AIMS

Acute kidney injury (AKI) is increasingly recognized as a major risk factor leading to progression to chronic kidney disease (CKD). However, the diagnostic tools for predicting AKI to CKD progression are particularly lacking. Here, we tested the utility of contrast-enhanced ultrasound (CEUS) for predicting progression to CKD after AKI by using both mild (20-min) and severe (45-min) bilateral renal ischemia-reperfusion injury mice.

RESULTS

Renal perfusion measured by CEUS reduced to 25% ± 7% and 14% ± 6% of the pre-ischemic levels in mild and severe AKI 1 h after ischemia (p < 0.05). Renal perfusion returned to pre-ischemic levels 1 day after mild AKI followed by restoration of kidney function. However, severe AKI caused persistent renal perfusion impairment (60% ± 9% of baseline levels) accompanied by progressive renal fibrosis and sustained decrease in renal function. Renal perfusion at days 1-21 significantly correlated with tubulointerstitial fibrosis 42 days after AKI. For predicting renal fibrosis at day 42, the area under the receiver operating characteristics curve of renal perfusion impairment at day 1 was 0.84. Similar changes in the renal image of CEUS were observed in patients with AKI-CKD progression.

INNOVATION

This study demonstrates that CEUS enables dynamic and noninvasive detection of renal perfusion impairment after ischemic AKI and the perfusion abnormalities shown by CEUS can early predict the progression to CKD after AKI.

CONCLUSIONS

These results indicate that CEUS enables the evaluation of renal perfusion impairment associated with CKD after ischemic AKI and may serve as a noninvasive technique for assessing AKI-CKD progression. Antioxid. Redox Signal. 27, 1397-1411.

Quantitative Analysis of Hepatic Microcirculation in Rabbits After Liver Ischemia-Reperfusion Injury Using Contrast-Enhanced Ultrasound

Previous studies have shown that contrast-enhanced ultrasound (CEUS) can be used quantitatively to analyze microcirculation blood perfusion in hepatocellular carcinoma patients. However, limited data have described the application of CEUS in hepatic microcirculation after liver ischemic-reperfusion injury (IRI). The purpose of this study was to explore the use of CEUS quantitatively to assess liver microcirculation after liver IRI. We randomly sorted 45 New Zealand rabbits into 3 groups (15 in each). Group A was a control group in which the rabbits underwent laparotomy alone. In groups B and C, hepatic blood was blocked for 30 min. Simultaneously, rabbits in group C underwent left lateral lobe resection. After 30 min of ischemia, CEUS was conducted after 0 h, 1 h, 6 h and 24 h of reperfusion in the 3 groups. Time-intensity curves (TICs) for CEUS were constructed and quantitative parameters (maximum intensity [IMAX], rise time [RT], time to peak [TTP] and mean transit time [mTT]) were obtained. In addition, serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were computed to estimate liver function before the operation and at 0 h, 1 h, 6 h and 24 h after reperfusion, respectively. Pathologic changes in the liver after reperfusion were also observed. Simultaneously, the correlations between serum transaminase and a variety of quantitative analysis parameters were analyzed. In groups B and C, the IMAX value decreased; whereas RT, TTP, mTT and serum ALT and AST levels increased significantly in comparison with those in group A after 0 h and 1 h of reperfusion. The pathology revealed that erythrocytes were destroyed and microcirculation was disturbed. Then, at 6 h of reperfusion, the IMAX continued to decrease. Additionally, the levels of RT, TTP, mTT and serum ALT and AST increased in comparison with those at 1 h of reperfusion. The pathologic analysis revealed inflammatory cell aggregation and leukocyte infiltration. After 24 h of reperfusion, the IMAX was reduced in comparison with that of the 6-h group. The levels of RT, TTP, mTT and serum ALT and serum AST were increased in comparison with that of the 6-h group. These findings were in accordance with the pathologic analysis. In addition, serum transaminase had a negative correlation with IMAX (p < 0.001) and a positive correlation with RT, TTP and mTT (all p < 0.001). So, in conclusion, the quantitative analysis of CEUS can be used to assess hepatic microcirculation after liver IRI.

Entropy of Ultrasound-Contrast-Agent Velocity Fields for Angiogenesis Imaging in Prostate Cancer

Prostate cancer care can benefit from accurate and cost-efficient imaging modalities that are able to reveal prognostic indicators for cancer. Angiogenesis is known to play a central role in the growth of tumors towards a metastatic or a lethal phenotype. With the aim of localizing angiogenic activity in a non-invasive manner, Dynamic Contrast Enhanced Ultrasound (DCE-US) has been widely used. Usually, the passage of ultrasound contrast agents thought the organ of interest is analyzed for the assessment of tissue perfusion. However, the heterogeneous nature of blood flow in angiogenic vasculature hampers the diagnostic effectiveness of perfusion parameters. In this regard, quantification of the heterogeneity of flow may provide a relevant additional feature for localizing angiogenesis. Statistics based on flow magnitude as well as its orientation can be exploited for this purpose. In this paper, we estimate the microbubble velocity fields from a standard bolus injection and provide a first statistical characterization by performing a spatial entropy analysis. By testing the method on 24 patients with biopsy-proven prostate cancer, we show that the proposed method can be applied effectively to clinically acquired DCE-US data. The method permits estimation of the in-plane flow vector fields and their local intricacy, and yields promising results (receiver-operating-characteristic curve area of 0.85) for the detection of prostate cancer.

Oesophageal Doppler guided optimization of cardiac output does not increase visceral microvascular blood flow in healthy volunteers

BACKGROUND

Oesophageal Doppler monitoring (ODM) is used clinically to optimize cardiac output (CO) and guide fluid therapy. Despite limited experimental evidence, it is assumed that increasing CO increases visceral microvascular blood flow (MBF). We used contrast-enhanced ultrasound (CEUS) to assess whether ODM-guided optimization of CO altered MBF.

METHODS

Sixteen healthy male volunteers (62 ± 3·4 years) were studied. Baseline measurements of CO were recorded via ODM. Hepatic and renal MBF was assessed via CEUS. Saline 0·9% was administered to optimize CO according to a standard protocol and repeat CEUS performed. Time-intensity curves were constructed, allowing organ perfusion calculation via time to 5% perfusion (TT5). MBF was assessed via organ perfusion rise time (RT) (5-95%).

RESULTS

CO increased (4535 ± 241 ml/min versus 5442 ± 329 ml/min, P<0·0001) following fluid administration, whilst time to renal (22·48 ± 1·19 s versus 20·79 ± 1·31 s; P = 0·03), but not hepatic (28·13 ± 4·48 s versus 26·83 ± 1·53 s; P = 0·15) perfusion decreased. Time to renal perfusion was related to CO (renal: r = -0·43, P = 0·01). Hepatic nor renal RT altered following fluid administration (renal: 9·03 ± 0·86 versus 8·93 ± 0·85 s P = 0·86; hepatic: 27·86 ± 1·60 s versus 30·71 ± 2·19 s, P = 0·13). No relationship was observed between changes in CO and MBF in either organ (renal: r = -0·17, P = 0·54; hepatic: r = -0·07, P = 0·80).

CONCLUSIONS

ODM-optimized CO reduces time to renal perfusion but does not alter renal or hepatic MBF. A lack of relationship between microvascular visceral perfusion and CO following ODM-guided optimization may explain the absence of improved clinical outcome with ODM monitoring.

Effects of size and location of regions of interest examined by use of contrast-enhanced ultrasonography on renal perfusion variables of dogs

OBJECTIVE To determine effects of the size and location of regions of interest (ROIs) in the renal cortex of unsedated dogs on renal perfusion variables determined by use of contrast-enhanced ultrasonography (CEUS). ANIMALS 12 client-owned adult (1.5 to 2 years old) Labrador Retrievers (8 males and 4 females; mean ± SD body weight, 27 ± 1.6 kg). PROCEDURES Each dog received 2 bolus injections of sulfur hexafluoride during CEUS. Three small oval ROIs (area of each ROI, 0.11 cm(2)) located in a row with a distance of 1 mm between adjacent ROIs and 1 large oval ROI (area, 1 cm(2)) that encompassed the 3 smaller ROIs were manually drawn in the renal cortex. The ROIs were located at a depth of 1.5 to 2.0 cm in the near field of the renal cortex. Software analysis of time-intensity curves within each ROI was used to identify peak enhancement, time to peak enhancement, regional blood flow, and mean transit time. RESULTS The location and size of the ROIs of unsedated dogs did not cause significant differences in the mean values of the renal perfusion variables. CONCLUSIONS AND CLINICAL RELEVANCE The development of CEUS has provided a unique means for visually examining and quantifying tissue perfusion. Results of this study indicated that it was possible to use small or large ROIs during renal CEUS to evaluate renal perfusion in dogs.

The Natural History of Kidney Graft Cortical Microcirculation Determined by Real-Time Contrast-Enhanced Sonography (RT-CES)

Background

Kidney transplantation is the therapy of choice for end-stage kidney disease. Graft’s life span is shorter than expected due in part to the delayed diagnosis of various complications, specifically those related to silent progression. It is recognized that serum creatinine levels and proteinuria are poor markers of mild kidney lesions, which results in delayed clinical information. There are many investigation looking for early markers of graft damage. Decreasing kidney graft cortical microcirculation has been related to poor prognosis in kidney transplantation. Cortical capillary blood flow (CCBF) can be measured by real-time contrast-enhanced sonography (RT-CES). Our aim was to describe the natural history of CCBF over time under diverse conditions of kidney transplantation, to explore the influence of donor conditions and recipient events, and to determine the capacity of CCBF for predicting renal function in medium term.

Patients and Methods

RT-CES was performed in 79 consecutive kidney transplant recipients during the first year under regular clinical practice. Cortical capillary blood flow was measured. Clinical variables were analyzed. The influence of CCBF has been determined by univariate and multivariate analysis using mixed regression models based on sequential measurements for each patient over time. We used a first-order autoregression model as the structure of the covariation between measures. The post-hoc comparisons were considered using the Bonferroni correction.

Results

The CCBF values varied significantly over the study periods and were significantly lower at 48 h and day 7. Brain-death donor age and CCBF levels showed an inverse relationship (r: -0.62, p<0.001). Living donors showed higher mean CCBF levels than brain-death donors at each point in the study. These significant differences persisted at month 12 (54.5 ± 28.2 vs 33.7 ± 30 dB/sec, living vs brain-death donor, respectively, p = 0.004) despite similar serum creatinine levels (1.5 ± 0.3 and 1.5 ± 0.5 mg/dL). A sole rejection episode was associated with lower overall CCBF values over the first year. CCBF defined better than level of serum creatinine the graft function status at medium-term.

Conclusion

RT-CES is a non-invasive tool that can quantify and iteratively estimate cortical microcirculation. We have described the natural history of cortical capillary blood flow under regular clinical conditions.