Contrast-enhanced ultrasound analysis of renal perfusion in normal micropigs

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.

Technological Advances in Diagnostic Imaging in Exotic Pet Medicine

Diagnostic imaging relies on interpretation of interactions between the body tissue and various energies, such as x-rays, ultrasound, and magnetic or nuclear energies, to differentiate normal from abnormal tissues. Major technological improvements regarding emission and detection of the energetic waves, as well as reconstruction and interpretation of the images, have occurred. These advances made possible visualization of smaller structures, quantitative evaluation of functional processes, and development of unique imaging-guided procedures. This article reviews the technological advances that allowed development of cone beam computed tomography, dual-energy x-ray absorptiometry, and contrast-enhanced ultrasonography, which all could have applications in exotic pet medicine.

Contrast-enhanced ultrasound: A promising method for renal microvascular perfusion evaluation

This article reviews the application of contrast-enhanced ultrasound (CEUS) in gauging renal microvascular perfusion in diverse renal diseases. The unique nature of the contrast agents used in CEUS provides real-time and quantitative imaging of the vasculature. In addition to the traditional use of CEUS for evaluation of kidney masses, it also emerges as a safe and effective imaging approach to assess microvascular perfusion in diffuse renal lesions, non-invasively. Although the precise CEUS parameters that may best predict disease still warrant systematic evaluation, animal models and limited clinical trials in humans raise hopes that CEUS could outcompete competing modalities as a first-line tool for assessing renal perfusion non-invasively, even in ailments such as acute kidney injury and chronic kidney disease.

Contrast-enhanced ultrasound of both kidneys in healthy, non-anaesthetized cats

Background

Changes in perfusion are considered to play a key role in the pathophysiology of renal disease. Contrast-enhanced ultrasound (CEUS) has shown a promising diagnostic imaging technique to non-invasively and repetitively quantify tissue perfusion. Examination protocols have varied between studies regarding US equipment, quantification software, the use of sedation or anaesthesia, and animals. The purpose of the present study was, to assess the feasibility of a standardized CEUS protocol for perfusion analysis of both kidneys in nine healthy, non-anaesthetized cats.

Results

CEUS was fairly tolerable for all but one cat. In 6/18 kidneys (2 left, 4 right), a second contrast medium injection was needed due to motion artifacts. Perfusion variables such as peak intensity (PI), wash-in slope (WI_S), wash-out slope (WO_S) and mean transit time (MTT) did not significantly differ between left and right renal cortex and medulla nor between the cranial and caudal renal cortex within each kidney. In contrast, for all kidneys, mean PI, WI_S, and MTT were significantly higher in the cortex than in the medulla (P = 0.001, 0.012 and <0.001, respectively).

Conclusions

The herein reported CEUS protocol and the perfusion measurements may serve as a baseline protocol and normal reference values for the evaluation of feline patients. However, the protocol and results may be of limited value in uncooperative animals.

Effects of high-fat diet and losartan on renal cortical blood flow using contrast ultrasound imaging

Obesity-related kidney disease occurs as a result of complex interactions between metabolic and hemodynamic effects. Changes in microvascular perfusion may play a major role in kidney disease; however, these changes are difficult to assess in vivo. Here, we used perfusion ultrasound imaging to evaluate cortical blood flow in a mouse model of high-fat diet-induced kidney disease. C57BL/6J mice were randomized to a standard diet (STD) or a high-fat diet (HFD) for 30 wk and then treated either with losartan or a placebo for an additional 6 wk. Noninvasive ultrasound perfusion imaging of the kidney was performed during infusion of a microbubble contrast agent. Blood flow within the microvasculature of the renal cortex and medulla was derived from imaging data. An increase in the time required to achieve full cortical perfusion was observed for HFD mice relative to STD. This was reversed following treatment with losartan. These data were concurrent with an increased glomerular filtration rate in HFD mice compared with STD- or HFD-losartan-treated mice. Losartan treatment also abrogated fibro-inflammatory disease, assessed by markers at the protein and messenger level. Finally, a reduction in capillary density was found in HFD mice, and this was reversed upon losartan treatment. This suggests that alterations in vascular density may be responsible for the elevated perfusion time observed by imaging. These data demonstrate that ultrasound contrast imaging is a robust and sensitive method for evaluating changes in renal microvascular perfusion and that cortical perfusion time may be a useful parameter for evaluating obesity-related renal disease.