The diagnostic value of contrast-enhanced ultrasound (CEUS) as a new technique for imaging of vascular complications in renal transplants compared to standard imaging modalities

Functional MRI to quantify perfusion changes of a renal allograft after embolization of an arteriovenous fistula

Acute allograft injury was observed in a 37-year-old woman within a few weeks after kidney transplantation. Neither renal ultrasound nor computerized tomography (CT) and magnetic resonance (MR) angiography revealed any anomaly. An MR protocol was then performed including arterial spin labeling and intravoxel incoherent motion diffusion weighted imaging. Both arterial spin labeling and the perfusion fraction in the diffusion weighted imaging showed decreased perfusion compared to reference values. The patient subsequently underwent angiography, where an arteriovenous fistula in the upper calix of the transplant kidney was detected and immediate embolization was performed. A second functional MR, performed one week later, demonstrated a 40% increase in organ perfusion. We conclude that functional MR with arterial spin labeling and intravoxel incoherent motion have the potential to provide complementary information of clinical value to conventional imaging for monitoring renal allografts.

Application value of shear-wave elastography combined with monochrome superb microvascular imaging in renal allograft chronic rejection

BACKGROUND

Conventional ultrasound (US), which include gray scale US and Doppler US, is the first-line imaging modality for the evaluation of renal allograft; however, conventional US indicators have limitations.

OBJECTIVE

To explore the application value of shear-wave elastography (SWE) combined with monochrome superb microvascular imaging (mSMI) in renal allograft chronic rejection (CR).

METHODS

From November 2021 to February 2022 in the Lanzhou University Second Hospital, the US features of 54 patients with renal allograft were retrospectively analyzed. Patients were categorized into two groups: stable group(n = 44) and CR group(n = 10), with clinical diagnosis as reference standard. The vascular index (VI) on mSMI and parenchymal stiffness were measured in the middle cortex of all renal allografts and receiver operating characteristic (ROC) curves were drawn to evaluate the feasibility of differentiation. Statistically significant US features and biochemical indicators such as creatinine were scored, and the results of the scores were analyzed by ROC curve.

RESULTS

The VI on mSMI of the stable group (49.5±2.0) was significantly greater than that of the CR group (33.8±5.9) (P = 0.028). There was a statistically significant difference in parenchymal stiffness between stable group (16.2kPa±1.2) and CR group (33.9kPa±6.6) (P = 0.027). The sensitivity was 90% and specificity was 81.8% of the scores in the differentiation of stable group from CR group (cut-off value, 2; P = 0.000).

CONCLUSION

SWE combined with mSMI may help differentiate stable renal allograft from renal allograft CR and have the potential application value in the diagnosis of renal allograft CR.

Value of contrast-enhanced ultrasound for diagnosis and follow-up of renal artery stenosis in patients with chronic kidney disease

OBJECTIVE

To evaluate whether contrast-enhanced ultrasound (CEUS) is an accurate, non-nephrotoxic diagnostic method and follow-up tool for use in patients with chronic kidney disease (CKD) and renal artery stenosis (RAS).

METHODS

In this prospective and monocentric study, we compared the sensitivity and specificity of CEUS for the diagnosis of RAS in CKD patients, using digital subtraction angiography (DSA) or computed tomographic angiography (CTA) as the gold standard methods. Further, the value of CEUS for distinguishing restenosis from other diseases was assessed. The ultrasound physicians conducted the examinations and served as the CEUS report readers who were blinded to the DSA or CTA results.

RESULTS

Patients with RAS (n = 60) were enrolled. Average patient age was 64.4 ± 18.0 years and median estimated glomerular filtration rate was 66.1 mL/min/1.73 m². CEUS was used to image 94 stenotic renal arteries and DSA- or CTA-verified stenosis was present in 96 renal arteries. The kappa value for CEUS was 0.776 (P < 0.001), with an accuracy of 92.5%, a sensitivity of 94.7%, and a specificity of 84.0%. The accuracy of CEUS was the same for the diagnosis of the CKD3b-5 group as for the CKD1-3a group (100% vs. 87.5%, P = 0.148). There was no difference in CEUS accuracy for the diagnosis of Takayasu RAS compared with atherosclerotic RAS (95.8% vs. 91.7%, P = 0.795). Twenty-nine CEUS examinations were performed to follow in-stent restenosis or progression of RAS, with a median follow-up time of 5.0 months (range 1.0-20.0). Two cases of in-stent restenosis in patients suffering from deteriorating kidney function and recurrent hypertension were examined by CEUS.

CONCLUSION

CEUS examination is a credible alternative for diagnosing moderate and severe RAS in patients with CKD, and is a reliable tool for follow-up surveillance after renal artery revascularization treatment. It shouldn't be thought as a color-coded duplex ultrasonography rescue in these patients.

Clinical and Renal Cortical Blood Perfusion Characteristics in Patients with Severe Atherosclerotic Renal Artery Stenosis Who Underwent Stent Implantation: A Single-center Retrospective Cohort Study

Objective This study aimed to observe the clinical imaging features of patients with severe atherosclerotic renal artery stenosis (ARAS) receiving stent implantation, and to evaluate the associations between baseline clinical and imaging factors and renal-function deterioration at a 1-year follow-up.Methods This study was a single-center retrospective cohort study. A total of 159 patients with unilateral severe ARAS who underwent stent implantation at Beijing Hospital between July 2017 and December 2020 were consecutively enrolled. According to the renal glomerular filtration rate (GFR), detected by radionuclide renal imaging at 1-year follow-up, all patients were divided into a poor-prognosis group (with a ≥30% decrease in renal GFR; n=32 cases) and a control group (127 cases). Clinical imaging data, including the renal cortical blood perfusion pre- and post-sent implantation, were analyzed. Univariate and multivariate logistic regression analysis was used to evaluate the associations between clinical and imaging factors and renal-function deterioration.Results Of the 159 patients enrolled, 83 (52.2%) were men, with an average age of (57.2±14.7) years. The patient age, rate of diabetes, and systolic blood and diastolic blood pressure in the poor-prognosis group were significantly higher than those in the control group (all P<0.05). Before stent treatment, patients in the poor-prognosis group, compared with the control group, had a significantly smaller area under the ascending curve (AUC1), area under the descending curve (AUC2), and peak intensity (PI), and a longer time to peak intensity (TTP) and mean transit time (MTT) (all P<0.05). After stent treatment, patients in the poor-prognosis group, compared with the control group, showed significantly smaller AUC1, AUC2, and PI, and longer MTT (all P<0.05). Multivariate logistic regression analysis indicated that age (OR=1.251, 95%CI: 1.113–1.406, P=0.0002), diabetes (OR=1.472, 95%CI: 1.110–1.952, P=0.007), systolic blood pressure (OR=1.339, 95%CI: 1.082–1.657, P=0.007), renal GFR (OR=2.025, 95%CI: 1.217–3.369, P=0.006), and AUC1 post-stent (OR=2.173, 95%CI: 1.148–4.113, P=0.017) were the factors associated with renal deterioration at the 1-year follow-up.Conclusions Patients with severe RAS with renal-function deterioration after stent implantation were older, and often had diabetes, hypertension, and impaired renal cortical perfusion. Age, diabetes, systolic blood pressure, renal GFR, and AUC1 after stent implantation were independent factors associated with short-term renal deterioration.

Contrast-enhanced ultrasound of transplant organs - liver and kidney - in children

Ultrasound (US) is the first-line imaging tool for evaluating liver and kidney transplants during and after the surgical procedures. In most patients after organ transplantation, gray-scale US coupled with color/power and spectral Doppler techniques is used to evaluate the transplant organs, assess the patency of vascular structures, and identify potential complications. In technically difficult or inconclusive cases, however, contrast-enhanced ultrasound (CEUS) can provide prompt and accurate diagnostic information that is essential for management decisions. CEUS is indicated to evaluate for vascular complications including vascular stenosis or thrombosis, active bleeding, pseudoaneurysms and arteriovenous fistulas. Parenchymal indications for CEUS include evaluation for perfusion defects and focal inflammatory and non-inflammatory lesions. When transplant rejection is suspected, CEUS can assist with prompt intervention by excluding potential underlying causes for organ dysfunction. Intracavitary CEUS applications can evaluate the biliary tract of a liver transplant (e.g., for biliary strictures, bile leak or intraductal stones) or the urinary tract of a renal transplant (e.g., for urinary obstruction, urine leak or vesicoureteral reflux) as well as the position and patency of hepatic, biliary and renal drains and catheters. The aim of this review is to present current experience regarding the use of CEUS to evaluate liver and renal transplants, focusing on the examination technique and interpretation of the main imaging findings, predominantly those related to vascular complications.

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.

Advances of Contrast-Enhanced Ultrasonography and Elastography in Kidney Transplantation: From Microscopic to Microcosmic

Kidney transplantation is the best choice for patients with end-stage renal disease. To date, allograft biopsy remains the gold standard for revealing pathologic changes and predicting long-term outcomes. However, the invasive nature of transplant biopsy greatly limits its application. Ultrasound has been a first-line examination for evaluating kidney allografts for a long time. Advances in ultrasound in recent years, especially the growing number of studies in elastography and contrast-enhanced ultrasonography (CEUS), have shed new light on its application in kidney transplantation. Elastography, including strain elastography and shear wave elastography, is used mainly to assess allograft stiffness and, thus, predict renal fibrosis. CEUS has been used extensively in evaluating blood microperfusion, assessing acute kidney injury and detecting different complications after transplantation. Requiring the use of microbubbles also makes CEUS a novel method of gene transfer and drug delivery, enabling promising targeted diagnosis and therapy. In this review, we summarize the advances of elastography and CEUS in kidney transplantation and evaluate their potential efficiency in becoming a better complement to or even substitute for transplant biopsy in the future.

Evaluation of Skeletal Muscle Microcirculation and Reserve Function of the Type 2 Diabetes with Contrast-Enhanced Ultrasonography

OBJECTIVE

This study aimed to discuss clinical application value of contrast-enhanced ultrasonography on lesion skeletal muscle microcirculation and arterial perfusion reserve in type 2 diabetes mellitus and complicated microvessels.

METHODS

Patients in the control group, type 2 diabetes mellitus (DM) group, diabetic microangiopathy (DM + MC) group underwent contrast-enhanced ultrasonography before and after temporary arterial occlusion to observe blood perfusion of gastrocnemius muscle; draw the time-intensity curve of arteriole, muscular tissue, and venule, and obtain perfusion parameters such as contrast agent arrival time and contrast agent transit time. Blood glucose, insulin, insulin resistance index, and relevant blood rheology parameters were measured.

RESULTS

Contrast agent transit time of the DM + MC group before arterial occlusion was significantly longer than that of the DM group and control group (P < 0.05). Contrast agent transit time of the DM + MC group after temporary arterial occlusion was significantly longer than that of the DM group and control group (P < 0.05). Contrast agent transit time of △artery-muscle, △artery-vein, and △muscle-vein of the DM group and control group and △artery-muscle of the DM + MC group after arterial occlusion was significantly shortened, when compared with that before arterial occlusion (P < 0.05). For △muscle-vein and △artery-vein contrast agent transit time in the DM + MC group, the difference was not statistically significant. By comparing blood glucose, insulin, insulin resistance index, and relevant blood rheology parameters among the DM + MC group, DM group, and control group, the difference was statistically significant, and there was a good correlation.

CONCLUSION

Contrast-enhanced ultrasonography can be used to evaluate skeletal muscle microcirculation disturbance and arterial reserve function of patients who had type 2 diabetic microangiopathy.

Role for contrast-enhanced ultrasound in assessing complications after kidney transplant

Kidney transplantation (KT) is an effective treatment for end-stage renal disease. Despite their rate has reduced over time, post-transplant complications still represent a major clinical problem because of the associated risk of graft failure and loss. Thus, post-KT complications should be diagnosed and treated promptly. Imaging plays a pivotal role in this setting. Grayscale ultrasound (US) with color Doppler analysis is the first-line imaging modality for assessing complications, although many findings lack specificity. When performed by experienced operators, contrast-enhanced US (CEUS) has been advocated as a safe and fast tool to improve the accuracy of US. Also, when performing CEUS there is potentially no need for further imaging, such as contrast-enhanced computed tomography or magnetic resonance imaging, which are often contraindicated in recipients with impaired renal function. This technique is also portable to patients' bedside, thus having the potential of maximizing the cost-effectiveness of the whole diagnostic process. Finally, the use of blood-pool contrast agents allows translating information on graft microvasculature into time-intensity curves, and in turn quantitative perfusion indexes. Quantitative analysis is under evaluation as a tool to diagnose rejection or other causes of graft dysfunction. In this paper, we review and illustrate the indications to CEUS in the post-KT setting, as well as the main CEUS findings that can help establishing the diagnosis and planning the most adequate treatment.

Single-center study: the diagnostic performance of contrast-enhanced ultrasound (CEUS) for assessing renal oncocytoma

Purpose: The aim of the present retrospective single-center study is to evaluate the diagnostic performance of contrast-enhanced ultrasound (CEUS) in the evaluation of renal oncocytoma.Method: Thirteen patients with histopathologically confirmed renal oncocytoma and 26 patients with histopathologically confirmed renal cell carcinoma were included in this retrospective single-center study on whom CEUS was performed between 2005 and 2015. The applied contrast agent was a second-generation blood pool agent. CEUS examinations were performed and interpreted by a single radiologist with more than 15 years of experience (EFSUMB Level 3).Results: CEUS examinations were successfully performed in all included patients without any adverse effects. Renal oncocytomas showed varying echogenicity (46% hypoechoic, 23% hyperechoic, 8% iso-/hyperechoic, 8% isoechoic). In two cases renal oncocytoma only demarcated upon i.v. application of contrast medium. In bilateral oncocytosis, lesions presented as hyperechoic. Only 23% of renal oncocytomas showed slight vascularization using Color Doppler. No oncocytoma-specific pattern of microperfusion could be elucidated: 85% of the oncocytomas presented hyperenhancing, of whom 50% also showed delayed venous wash-out; 8% of renal oncocytomas showed venous wash-out without early arterial hyperenhancement.Conclusions: Within the frame of the present study and in line with the recent state of knowledge, no specific sonomorphological feature - including CEUS - could be detected allowing for adequate discrimination between oncocytoma and renal cell carcinoma.

Contrast enhanced ultrasound: A review of radiology applications

Ultrasound contrast agents have been used for decades in Europe and Asia for cardiac and abdominal imaging and are now being more commonly utilized in the United States for radiology applications. Our article reviews the basics of contrast-enhanced ultrasound including how the contrast agent works, advantages and disadvantages, as well as pearls and pitfalls to help the radiologist efficiently integrate this technology into day-to-day clinical practice. We also discuss the diagnosis of focal hepatic lesions as well as off-label applications such as evaluation of renal masses.

Surgical margin follow-up after nephron-sparing surgery: the possible role of CEUS

PURPOSE

To evaluate the possible role of CEUS in the management of patients who underwent nephron-sparing surgery (NSS) and presented questionable findings on the surgical margins at the CECT follow-up exam.

METHODS

In our retro-prospective study, we included 952 patients with small renal masses (SRMs) treated with NSS between 2012 and 2015 and followed with CECT for at least 3 years at Careggi University Hospital. Twenty-two of them presented solid masses on the site of surgery with questionable enhancement at CECT and were further studied with CEUS. This examination was followed by a quantitative analysis of the enhancement pattern.

RESULTS

Out of the 22 masses, 18 were considered possible granulomas, presenting slow wash-in and low enhancement peaks compared to the surrounding parenchyma and persistent delayed wash-out at CEUS. Four lesions presented a suspicious malignant enhancement pattern, with rapid wash-in, high peak and rapid wash-out. In accordance with instructions from the urologist, the first group of 18 patients was strictly monitored, revealing that the mass dimensions and enhancement pattern were stable for at least 3 years of follow-up, while the other 4 patients underwent a second intervention and their masses were confirmed as tumor recurrence at the histopathological evaluation.

CONCLUSIONS

CEUS can play a key role in the surgical margin follow-up after NSS when a suspicious enhancing mass is detected by CECT, giving an accurate depiction of the enhancement pattern and thus helping the clinician in the management of the patient.

[Reliable diagnosis of cystic renal lesions]

CLINICAL/METHODICAL ISSUE

Cystic renal lesions are commonly seen during routine ultrasound examinations of the abdomen.

STANDARD RADIOLOGICAL METHODS

Some cystic renal lesions cannot be sufficiently characterized using native ultrasound. In these cases additional imaging might be necessary.

METHODICAL INNOVATIONS

Contrast-enhanced ultrasound (CEUS) is a reliable imaging modality to characterize cystic renal lesions. Contrast enhancement of septations and the cystic wall are visualized in high resolution. This information helps to categorize the cystic renal lesions applying the CEUS Bosniak classification. This classification helps to estimate the probability of a malignant etiology of cystic renal lesions.

PERFORMANCE

Using CEUS, cystic renal lesions can be characterized with a high sensitivity and specificity.

ACHIEVEMENTS

The advantages of CEUS include that there is no effect on the function of the kidneys or the thyroid gland and no radiation exposure. In some cases, additional cross-sectional imaging is necessary to optimize diagnostic accuracy.

PRACTICAL RECOMMENDATIONS

CEUS is a helpful imaging modality to characterize cystic renal lesions, to avoid unnecessary follow-ups and to detect malignant cystic renal lesions.

[CEUS-diagnosis of benign liver lesions]

CLINICAL/METHODICAL ISSUE

Focal liver lesions are commonly seen during routine ultrasound examinations.

STANDARD RADIOLOGICAL METHODS

With native ultrasound there are lesions that cannot be sufficiently characterized. In these cases additional imaging might be necessary.

METHODICAL INNOVATIONS

With contrast-enhanced ultrasound (CEUS), focal liver lesions can be characterized with high diagnostic accuracy. After the ultrasound contrast agent has been injected into a peripheral vein, the examiner saves video loops of the arterial, portal venous and late contrast phases. Combing the findings of native and contrast-enhanced ultrasound allows not only assessment of the etiology as benign or malignant but also detailed characterization of the focal liver lesion in most cases.

PERFORMANCE

Using CEUS, focal liver lesions can be characterized with a sensitivity of over 95% and a specificity of about 83%.

ACHIEVEMENTS

The advantages of CEUS include that there is no radiation exposure and that the ultrasound contrast agent has no effects on the function of the liver, kidneys or the thyroid gland. The main limiting factors for CEUS are bowel gas and obesity of the patient.

PRACTICAL RECOMMENDATIONS

CEUS can visualize micro- and macrovascularization of benign focal liver lesions in real time. It is a useful imaging modality in unclear cases.

[A high level of high-density lipoprotein cholesterol is a protective factor against transplant renal artery stenosis]

OBJECTIVE

To investigate the factors associated with the occurrence of transplant renal artery stenosis (TRAS).

METHODS

A retrospective analysis was conducted in 26 recipients who developed TRAS and 40 concurrent renal recipients without TRAS. We also conducted a nested case-control study in 14 patients with TRAS (TRAS-SD group) and another 14 non-TRAS recipients who received the allograft from the same donor (non-TRAS-SD group).

RESULTS

Compared with those in the concurrent recipients without TRAS, acute rejection (AR) occurred at a significantly higher incidence (P=0.004) and the warm ischemia time (WIT) was significantly longer (P=0.015) and the level of high?density lipoprotein cholesterol (HDL--C) significantly lower (P=0.009) in the recipients with TRAS. Logistic regression analysis suggested that AR (P=0.007) and prolonged WIT (P=0.046) were risk factors of TRAS while HDL-C (P=0.022) was the protective factor against TRAS. In recent years early diagnosis of TRAS had been made in increasing cases, the interval from transplantation to TRAS diagnosis became shortened steadily, and the recipients tended to have higher estimated glomerular filtration rate at the time of TRAS diagnosis.

CONCLUSION

Apart from the surgical technique, AR and prolonged WIT are also risk factors of TRAS while a high HDL-C level is the protective factor against TRAS. The improvement of the diagnostic accuracy by ultrasound is the primary factor contributing to the increased rate of early TRAS diagnosis in recent years.