Contrast-Enhanced Ultrasound in Renal Imaging and Intervention

Contrast-enhanced ultrasound of renal masses in the pre-transplant setting: literature review with case highlights

With the rising incidence of chronic kidney disease worldwide, an increasing number of patients are expected to require renal transplantation, which remains the definitive treatment of end stage renal disease. Medical imaging, primarily ultrasonography and contrast-enhanced CT and/or MRI, plays a large role in pre-transplantation assessment, especially in the characterization of lesions within the native kidneys. However, patients with CKD/ESRD often have relative contraindications to CT- and MR-contrast agents, limiting their utilization within this patient population. Contrast-enhanced ultrasound (CEUS), which combines the high temporal and spatial resolution of ultrasonography with intravascular microbubble contrast agents, provides a promising alternative. This review aims to familiarize the reader with the literature regarding the use of CEUS in the evaluation of cystic and solid renal lesions and provide case examples of its use at our institution in the pre-transplant setting.

Qualitative and quantitative analysis of solid renal tumors by high-frame-rate contrast-enhanced ultrasound

OBJECTIVE

To analyze the characteristics of high-frame-rate contrast-enhanced ultrasound (H-CEUS) in solid renal tumors using qualitative and quantitative methods.

METHODS

Seventy-five patients who underwent preoperative conventional ultrasound (US), conventional contrast-enhanced ultrasound (C-CEUS), and H-CEUS examination of renal tumors were retrospectively analyzed, with a total of 89 renal masses. The masses were divided into the benign (30 masses) and malignant groups (59 masses) based on the results of enhanced computer tomography and pathology. The location, diameter, shape, border, calcification, and color doppler blood flow imaging (CDFI) of the lesions were observed by US, and the characteristics of the C-CEUS and H-CEUS images were qualitatively and quantitatively analyzed. The χ² test or Fisher's exact probability method was used to compare the US image characteristics between the benign and malignant groups, and the image characteristics of C-CEUS and H-CEUS between the benign and malignant groups. Moreover, the nonparametric Mann-Whitney test was used to compare the differences in C-CEUS and H-CEUS time-intensity curve (TIC) parameters.

RESULTS

Significant differences in gender, surgical approach, echogenicity, and CDFI were observed between the malignant and benign groups (p = 0.003, < 0.001, < 0.001, = 0003). Qualitative analysis also revealed significant differences in the mode of wash-out and fill-in direction between C-CEUS and H-CEUS in the malignant group (p = 0.041, 0.002). In addition, the homogeneity of enhancement showed significant differences between the two contrast models in the benign group (p = 0.009). Quantitative analysis indicated that the TIC parameters peak intensity (PI), deceleration time (DT) /2, area under the curve (AUC), and mean transition time (MTT) were significantly lower in the H-CEUS model compared to the C-CEUS model in both the benign and malignant groups. (all p < 0.001). In contrast, ascending slope of rise curve (AS) was significantly higher in the H-CEUS model compared to the C-CEUS model in the malignant group (p = 0.048).

CONCLUSIONS

In renal tumors, H-CEUS shows clearer internal enhancement of the mass and the changes in the wash-out period. The quantitative TIC parameters PI, DT/2, AUC, and MTT were lower in H-CEUS compared to C-CEUS. Both the quantitative and qualitative analyses indicated that H-CEUS better displays the characteristics of solid renal masses compared with C-CEUS.

High-frame-rate contrast-enhanced ultrasound to differentiate between clear cell renal cell carcinoma and angiomyolipoma

BACKGROUND

To investigate the diagnostic efficacy of high-frame-rate contrast-enhanced ultrasound (H-CEUS) in differentiating between clear cell renal cell carcinoma (CCRCC) and angiomyolipoma (AML).

METHODS

A retrospective study was performed on the clinical data of 79 patients diagnosed with CCRCC and 31 patients diagnosed with AML at the First Affiliated Hospital of Nanchang University between October 2022 and December 2023. Conventional ultrasound (US) and H-CEUS examinations were conducted on all patients prior to surgery, dynamic images were recorded from the US, and the qualitative and quantitative parameters of H-CEUS were collected. The t-test, χ² test and non-parametric Mann-Whitney test were employed to assess differences in clinical data, US characteristics, and qualitative and quantitative parameters of H-CEUS between the CCRCC and AML groups. The independent risk factors of CCRCC were identified using binary logistic regression. The receiver operator characteristic (ROC) curve was constructed to evaluate the diagnostic effectiveness of clinical + US and H-CEUS in differentiating between CCRCC and AML.

RESULTS

The CCRCC group and the AML group exhibited significant differences in patient gender, operation mode, nodular echo, and nodule blood flow (χ²=11.698, -, -,=10.582; P<0.001, <0.001, <0.001, and = 0.014, respectively). In addition, the H-CEUS qualitative analysis demonstrated significant differences between the AML group and the CCRCC group with respect to enhancement mode, regression mode, peak intensity, enhancement uniformity, no enhancement, and presence or absence of pseudocapsule (χ²=41.614, -, -, = 2.758, = 42.099, -; P<0.001, <0.001, <0.001, 0.097, <0.001, and <0.001, respectively). The Arrival time (AT) in the CCRCC group was significantly shorter than that in the AML group, as determined by quantitative analysis of H-CEUS (Z=-3.266, P = 0.001). Furthermore, the Peak intensity (PI), Ascent slope (AS), and The area under the curve (AUC) exhibited significantly higher values in the CCRCC group compared to the AML group (Z=-2.043,=-2.545,=-3.565; P = 0.041, = 0.011, and <0.001, respectively). Logistic regression analysis indicated that only gender, nodule echo, the pseudocapsule, AS, and AUC of H-CEUS were independent risk factors of CCRCC. The ROC curve revealed that combining gender and nodule echo yielded a sensitivity of 92.4%, specificity of 64.5%, and an AUC of 0.847 in distinguishing between CCRCC and AML. When combining the H-CEUS parameters of pseudocapsule, AS, and AUC, the sensitivity, specificity, and AUC for distinguishing between CCRCC and AML were 84.8%, 96.8%, and 0.918, respectively. No statistically significant difference was observed in the diagnostic effectiveness of the two methods (Z=-1.286, P = 0.198). However, H-CEUS demonstrated better AUC and specificity.

CONCLUSIONS

H-CEUS enhances the sensitivity and specificity of differentiating between CCRCC and AML by improving the temporal resolution, offering a more precise diagnostic foundation for identifying the most appropriate therapy for patients.

Development and validation of a clinical and ultrasound features-based nomogram for preoperative differentiation of renal urothelial carcinoma and central renal cell carcinoma

PURPOSE

This study aimed to develop and validate an ultrasound (US)-based nomogram for the preoperative differentiation of renal urothelial carcinoma (rUC) from central renal cell carcinoma (c-RCC).

METHODS

Clinical data and US images of 655 patients with 655 histologically confirmed malignant renal tumors (521 c-RCCs and 134 rUCs) were collected and divided into training (n = 455) and validation (n = 200) cohorts according to examination dates. Conventional US and contrast-enhanced US (CEUS) tumor features were analyzed to determine those that could discriminate rUC from c-RCC. Least absolute shrinkage and selection operator regression was applied to screen clinical and US features for the differentiation of rUC from c-RCC. Using multivariate logistic regression analysis, a diagnostic model of rUC was constructed and visualized as a nomogram. The diagnostic model's performance was assessed in the training and validation cohorts by calculating the area under the receiver operating characteristic curve (AUC) and calibration plot. Decision curve analysis (DCA) was used to assess the clinical usefulness of the US-based nomogram.

RESULTS

Seven features of both clinical features and ultrasound imaging were selected to build the diagnostic model. The nomogram achieved favorable discrimination in the training (AUC = 0.996, 95% CI: 0.993-0.999) and validation (AUC = 0.995, 95% CI: 0.974, 1.000) cohorts, and good calibration (Brier scores: 0.019 and 0.016, respectively). DCA demonstrated the clinical usefulness of the US-based nomogram.

CONCLUSION

A noninvasive clinical and US-based nomogram combining conventional US and CEUS features possesses good predictive value for differentiating rUC from c-RCC.

Characteristics of high frame frequency contrast-enhanced ultrasound in renal tumors

OBJECTIVE

This study aims to analyze the characteristics of high frame rate contrast-enhanced ultrasound (H-CEUS) in renal lesions and to improve the ability for differential diagnosis of renal tumors.

METHODS

A total of 140 patients with renal lesions underwent contrast-enhanced ultrasound (CEUS) examination in the First Affiliated Hospital of Nanchang University from July 2022 to July 2023. Based on the tumor pathology and the results of enhanced CT, tumor patients were divided into malignant and benign groups. All subjects were examined using gray-scale ultrasound, conventional contrast-enhanced ultrasound (C-CEUS), and H-CEUS, and their dynamic images were recorded. Two radiologists independently analyzed and recorded the results of ultrasound, C-CEUS, and H-CEUS images and statistically analyzed the features of C-CEUS and H-CEUS images. The independent sample t-test was used to compare the difference in age and maximum diameter of nodules between the benign and malignant groups. The χ2 test was used to compare the sex, mode of operation, gray-scale ultrasound characteristics, and enhancement characteristics of the two CEUS modes (enhancement mode, regression mode, enhancement degree, enhancement uniformity, enhancement or not, enhancement direction, post-enhancement boundary and range, and pseudocapsule) between the benign and malignant groups. The difference in vascular morphology of malignant nodules of varying sizes under two angiographic modes.

RESULTS

There were significant differences in gender (χ2 = 10.408, P = 0.001), mode of operation (χ2 = 47.089, P < 0.001), nodule composition (χ2 = 7.481, P = 0.003), nodule echo (χ2 = 20.926, P < 0.001), necrosis (χ2 = 31.343, P < 0.001) and nodule blood flow (χ2 = 9.006, P = 0.029) between the benign and malignant groups. There were significant differences in the regression model (χ2 = 6.782, P = 0.034) and enhancement direction (χ2 = 13.771, P = 0.001) between the two radiographic techniques in the malignant group. There was a significant difference in the enhancement uniformity between the two CEUS techniques in the benign group (χ2 = 8.264, P = 0.004). There was a significant difference between the two CEUS techniques in displaying the vascular morphology in the malignant group with the maximum diameter of nodules ≤ 4.0 cm (χ2 = 11.421, P < 0.022). However, there was no significant difference between the two techniques in the malignant group with the maximum diameter of nodules > 4.0 cm.

CONCLUSION

Increasing the frame rate of ultrasound images is helpful to accurately display the enhanced features and vascular morphology of renal tumors, especially for malignant tumors with a maximum diameter of ≤ 4.0 cm. Thus, H-CEUS can make up for the limitation of CEUS with regard to the display of vascular morphology.

Diagnostic value of pseudocapsule ring hyperenhancement in contrast-enhanced ultrasound in renal focal lesions

OBJECT

To investigate the diagnostic value of pseudocapsule ring hyperenhancement in contrast-enhanced ultrasound (CEUS) of focal renal lesions.

METHOD

Ninety eligible patients admitted were selected as the study subjects. The incidence rate of annular hyperenhancement in different benign and malignant focal lesions during angiography and the shape of annular enhancement were counted. The correlation between the occurrence of benign and malignant renal tumors and annular hyperenhancement and unenhanced areas was also analyzed.

RESULTS

Capsule enhancement was observed in 56 cases, including 50 cases of malignant tumors (89.3%, 50/56) and 6 cases of benign tumors (10.7%, 6/56). Pearson correlation analysis showed that renal malignancy was positively associated with the occurrence of pseudocapsule ring hyperenhancement (γ = 0.489, P < 0.001). Benign and malignant renal tumors were positively correlated with the occurrence of non-enhancing areas (γ = 0.215, P = 0.042). The thickness and peak intensity of pseudocapsule ring enhancement in renal malignant tumors were significantly higher than those in benign tumors (all P < 0.001), while the time to peak was significantly lower than that in benign tumors (P < 0.001). The results of receiver operating characteristic (ROC) curve showed that the ring enhancement thickness, time to peak, and area under ROC curve of peak intensity of tumor reached more than 0.9.

CONCLUSION

In CEUS, the pseudocapsule of focal renal lesions is a characteristic feature of renal malignant tumors, which can be used as a differential basis for benign and malignant tumors to improve the accuracy of benign and malignant renal tumors.

Artificial intelligence for renal cancer: From imaging to histology and beyond

Artificial intelligence (AI) has made considerable progress within the last decade and is the subject of contemporary literature. This trend is driven by improved computational abilities and increasing amounts of complex data that allow for new approaches in analysis and interpretation. Renal cell carcinoma (RCC) has a rising incidence since most tumors are now detected at an earlier stage due to improved imaging. This creates considerable challenges as approximately 10%–17% of kidney tumors are designated as benign in histopathological evaluation; however, certain co-morbid populations (the obese and elderly) have an increased peri-interventional risk. AI offers an alternative solution by helping to optimize precision and guidance for diagnostic and therapeutic decisions. The narrative review introduced basic principles and provide a comprehensive overview of current AI techniques for RCC. Currently, AI applications can be found in any aspect of RCC management including diagnostics, perioperative care, pathology, and follow-up. Most commonly applied models include neural networks, random forest, support vector machines, and regression. However, for implementation in daily practice, health care providers need to develop a basic understanding and establish interdisciplinary collaborations in order to standardize datasets, define meaningful endpoints, and unify interpretation.

Contrast-enhanced ultrasonography for assessing histopathology in pediatric immunoglobulin A nephropathy and Henoch-Schönlein purpura nephritis

BACKGROUND

Glomerular disease, including immunoglobulin A nephropathy (IgAN) and Henoch-Schönlein purpura nephritis, is one of the most common kidney diseases in children. The diagnosis of these diseases depends on pathological biopsy, although this procedure is seriously limited by its invasive and high-risk nature.

OBJECTIVE

To investigate the potential of contrast-enhanced ultrasonography (CEUS) for evaluating the histopathological severity of IgAN and Henoch-Schönlein purpura nephritis (HSPN).

MATERIALS AND METHODS

We investigated a total of 13 children with IgAN and 12 children with HSPN confirmed by renal histopathology. We reevaluated the pathological lesions of the children according to the Oxford classification and the Lee grading system and then all the children underwent CEUS. Using SonoLiver software, we constructed time-intensity curves of CEUS for regions of interest in the renal cortex. We analyzed CEUS quantitative parameters for IgAN and HSPN and used Spearman correlation analysis to examine the correlation between CEUS parameters and clinicopathological indexes in the study cohort.

RESULTS

The CEUS parameters rise time (RT) and time to peak (TTP) were significantly higher in children with Lee grade IV than in those with Lee grades II or III. Spearman correlation analysis revealed a positive correlation between rise time and time to peak with Lee grade in the overall cohort of children, and a positive correlation between rise time and time to peak and severity of crescents in the Oxford classification scoring system.

CONCLUSION

Contrast-enhanced US may be used as a noninvasive imaging technique to evaluate the severity of renal pathology and formation of crescents in children with IgAN and HSPN.

Ultrasonographic study of hemodynamics and CEUS in the rhesus monkey kidney

Nonhuman primates share many developmental similarities with humans. As the world has recognized the rhesus monkey as a standard experimental monkey, studies of rhesus monkey are very important and essential. The purpose of this study was to use gray-scale ultrasound, color Doppler flow imaging (CDFI), and contrast-enhanced ultrasound (CEUS) to study the ultrasound appearance of adult healthy rhesus monkey kidneys and to investigate the relationship between renal ultrasound manifestations and body weight, gender, and the left and right kidneys. Thirty adult healthy rhesus monkeys were studied in the experiments. The size of the kidney and the length and diameter of the renal artery were measured. The peak systolic velocity (PSV), end diastolic velocity (EDV), and resistance index (RI) of the renal artery and intrarenal arteries were measured by CDFI. In CEUS, the time-intensity curve (TIC) was used to obtain microvascular perfusion parameters. There were significant differences in renal size, diameter and length of the renal artery, and hemodynamics of the renal arteries between the different weight groups. In CEUS, there were significant differences in area under curve (AUC), time from peak to one half (THP), intensity peak (PI), time to peak (TTP), mean transit time (MTT), and wash-in-slope (WIS) between the different weight groups. There were no statistical differences between genders or the left and right kidneys. Our study provides valuable reference data for the studies of the kidney and indicates that CEUS can be used to evaluate renal perfusion in rhesus monkeys.

Contrast-enhanced Ultrasound for Diagnosis of Renal Cystic Mass

BACKGROUND

Cystic Renal Cell Carcinoma (CRCC) is often challenging to differentiate from complex cysts with sonographic manifestations of renal carcinoma. Contrast-Enhanced Ultrasound (CEUS) is a new technology, and its clinical utility in the diagnosis of renal cystic mass has not been established.

OBJECTIVE

To analyze the characteristics of CEUS of renal cystic masses and to explore the clinical significance and value of CEUS in the diagnosis of CRCC.

METHODS

This study was a retrospective study. A total of 32 cystic masses from January 2018 to December 2019 were selected. The images of conventional ultrasound (US) and CEUS were confirmed via surgical pathology. The routine US was used to observe the location, shape, size, boundary, cyst wall, internal echo, and blood supply of each cystic mass. CEUS observed contrast enhancement of the cyst wall, cystic septa, and solid nodules of cystic masses.

RESULTS

There were 26 cases of CRCC, 5 cases of renal cysts, and 1 case of renal tuberculosis. The enhancement pattern, degree of enhancement, and pseudocapsular sign by CEUS in benign and malignant masses had statistically significant differences (P<.05). In the diagnosis of CRCC, the sensitivity, specificity, accuracy, positive predictive value, and negative predictive value were 92.3%, 83.3%, 90.6%, 96.0%, and 71.4% for CEUS; 57.6%, 66.7%, 59.3%, 88.2%, and 26.7% for conventional US, respectively. CEUS had a higher sensitivity and accuracy than the conventional US (P<.05). However, the diagnostic specificity, positive predictive value, and negative predictive value of the two methods were not significantly different (P>.05).

CONCLUSION

CEUS is more accurate in the diagnosis of renal cystic masses, and it can be used as an effective imaging method.

Controversies in the diagnosis of renal cell carcinoma with tumor thrombus

Diagnosis and treatment of renal cell carcinoma with venous tumor thrombosis remains a challenge today, requiring multidisciplinary teams, mainly in tumor thrombus levels III-IV. Our objective is to present the various diagnostic techniques used and its controversies. A review of the most relevant related articles between January 2000 and August 2020 has been carried out in PubMed, EMBASE and Scielo. Continuous technological development has allowed progress in its detection, in the approximation of the histological subtype, and in the determination of tumor thrombus level. Regardless of the imaging technique used for its diagnosis (CT, MRI, TEE, ultrasound with contrast), the time elapsed until treatment is vitally important to reduce the risk of complications, some of them fatal, such as pulmonary thromboembolism.

Multiparametric ultrasound findings in acute kidney failure due to rare renal cortical necrosis

Renal cortical necrosis (RCN) is a rare cause of acute kidney failure and is usually diagnosed on the basis of characteristic enhancement patterns on cross-sectional imaging. Contrast-enhanced ultrasound (CEUS) offers benefits in patients with kidney failure in the clinical setting including the use of a nonnephrotoxic intravascular contrast agent and the fact that it can be performed at the bedside in critical cases. Therefore, the aim of this study is to investigate whether CEUS can reliably identify typical imaging features of RCN. We retrospectively analyzed 12 patients with RCN examined in our department and confirmation of the diagnosis by either histopathology, other contrast-enhanced cross-sectional imaging tests, and/or CEUS follow-up. Assessed parameters in conventional US were reduced echogenicity, loss of corticomedullary differentiation, length and width of kidney, hypoechoic rim, resistance index and in CEUS delayed wash-in of contrast agent (> 20 s), reverse rim sign, maximum nonenhancing rim and additional renal infarction. Furthermore, imaging features in RCN were compared with the findings in renal vein thrombosis (RVT), among them echogenicity, corticomedullar differentiation, hypoechoic rim, RI value, delayed cortical enhancement, total loss of cortical perfusion and enhancement of renal medulla. All 12 patients showed the reverse rim sign, while a hypoechogenic subcapsular rim was only visible in four patients on B-mode ultrasound. A resistance index (RI) was available in 10 cases and was always less than 1. RI was a strong differentiator in separating RVT from RCN (RI > 1 or not measurable due to hypoperfusion as differentiator, p = 0.001). CEUS showed total loss of medullary enhancement in all cases of RVT. With its higher temporal resolution, CEUS allows dynamic assessment of renal macro- and microcirculation and identification of the typical imaging findings of RCN with use of a nonnephrotoxic contrast agent.

Quality Assessment of CEUS in Individuals with Small Renal Masses-Which Individual Factors Are Associated with High Image Quality?

Obesity and bowel gas are known to impair image quality in abdominal ultrasound (US). The present study aims at identifying individual factors in B-mode US that influence contrast-enhanced US (CEUS) image quality to optimize further imaging workup of incidentally detected focal renal masses. We retrospectively analyzed renal CEUS of focal renal masses ≤ 4 cm performed at our center in 143 patients between 2016 and 2020. Patient and lesion characteristics were tested for their influence on focal and overall image quality assessed by two experienced radiologists using Likert scales. Effects of significant variables were quantified by receiver operating characteristics (ROC) curve analysis with area under the curve (AUC), and combined effects were assessed by binary logistic regression. Shrunken kidney, kidney depth, lesion depth, lesion size, and exophytic lesion growth were found to influence focal renal lesion image quality, and all factors except lesion size also influenced overall image quality. Combination of all parameters except kidney depth best predicted good CEUS image quality showing an AUC of 0.91 (p < 0.001, 95%-CI 0.863–0.958). The B-mode US parameters investigated can identify patients expected to have good CEUS image quality and thus help select the most suitable contrast-enhanced imaging strategy for workup of renal lesions.

Contrast-enhanced ultrasound (CEUS) of cystic renal lesions in comparison to CT and MRI in a multicenter setting

PURPOSE

Contrast-enhanced-ultrasound (CEUS) has been frequently used in assessment of cystic renal lesions.

OBJECTIVE

The aim of this study was to investigate the Bosniak classification in CEUS compared to CT and MRI in a multi-center setting.

METHODS

Bosniak classification in CEUS examinations of cystic renal lesions were compared to imaging findings in computed-tomography (ceCT) and magnetic-resonance-imaging (ceMRI). Imaging results were correlated to histopathological reports. All examinations were performed by experts (EFSUMB level 3) using up-to-date CEUS examination-protocols.

RESULTS

Overall, 173 cystic renal lesions were compared to subgroups CT (n = 87) and MRI (n = 86). Using Bosniak-classification 64/87 renal cysts (73.6%) were rated equal compared to CT with upgrade of four lesions (4.6%) and downgrade of 19 lesions (21.8%) by CT (Intra-class-correlation [ICC] coefficient of 0.824 [p < 0.001]). CEUS compared to MRI, presenting different scoring especially in classes Bosniak IIF (n = 16/31) and Bosniak III (n = 16/28) with an ICC coefficient of 0.651 (p < 0.001).

CONCLUSION

CEUS can visualize even finest septal and small nodular wall enhancement, which may result in an upgrade of cystic lesions into a higher Bosniak class compared to CT or MRI. Thus, a modification of the Bosniak classification on CEUS may reduce unnecessary biopsies and surgery.