Contrast-Enhanced Subharmonic and Harmonic Ultrasound of Renal Masses Undergoing Percutaneous Cryoablation

Imaging modalities for characterising T1 renal tumours: A systematic review and meta-analysis of diagnostic accuracy

Objectives

International guidelines recommend resection of suspected localised renal cell carcinoma (RCC), with surgical series showing benign pathology in 30%. Non-invasive diagnostic tests to differentiate benign from malignant tumours are an unmet need. Our objective was to determine diagnostic accuracy of imaging modalities for detecting cancer in T1 renal tumours.

Methods

A systematic review was performed for reports of diagnostic accuracy of any imaging test compared to a reference standard of histopathology for T1 renal masses, from inception until January 2023. Twenty-seven publications (including 2277 tumours in 2044 participants) were included in the systematic review, and nine in the meta-analysis.

Results

Forest plots of sensitivity and specificity were produced for CT (seven records, 1118 participants), contrast-enhanced ultrasound (seven records, 197 participants), [99mTc]Tc-sestamibi SPECT/CT (five records, 263 participants), MRI (three records, 220 participants), [18F]FDG PET (four records, 43 participants), [68Ga]Ga-PSMA-11 PET (one record, 27 participants) and [111In]In-girentuximab SPECT/CT (one record, eight participants). Meta-analysis returned summary estimates of sensitivity and specificity for [99mTc]Tc-sestamibi SPECT/CT of 88.6% (95% CI 82.7%-92.6%) and 77.0% (95% CI 63.0%-86.9%) and for [18F]FDG PET 53.5% (95% CI 1.6%-98.8%) and 62.5% (95% CI 14.0%-94.5%), respectively. A comparison hierarchical summary receiver operating characteristic (HSROC) model did not converge. Meta-analysis was not performed for other imaging due to different thresholds for test positivity.

Conclusion

The optimal imaging strategy for T1 renal masses is not clear. [99mTc]Tc-sestamibi SPECT/CT is an emerging tool, but further studies are required to inform its role in clinical practice. The field would benefit from standardisation of diagnostic thresholds for CT, MRI and contrast-enhanced ultrasound to facilitate future meta-analyses.

Contrast-enhanced ultrasound (CEUS) as a follow-up method after the focal treatment of renal tumors: systematic review and meta-analysis

CONTEXT

Contrast-enhanced ultrasound (CEUS) is a cost-effective radiation-free diagnostic method that can be used for renal tumor postoperative visualization after ablative treatment.

OBJECTIVE

To assess CEUS diagnostic accuracy comparing with CT and MRI as a follow-up method in short-term and long-term postoperative periods after renal tumor ablation.

MATERIALS AND METHODS

A systematic review and meta-analysis were performed in Scopus and Medline databases using the query "(kidney OR rena* OR RCC) AND (ablation OR RFA OR MWA OR cryo*) AND CEUS". The endpoint of the study was the evaluation of the overall accuracy of CEUS.

RESULTS

Twelve trials were included in the review. With CT or MRI as a reference, for a short-term group (< 6 weeks after ablation) pooled sensitivity was 90.2%, I2 = 0%; pooled specificity was 99.3%, I2 = 0%; pooled NPV was 98.6%, I2 = 0%; pooled PPV was 94.6%, I2 = 0%; the AUC on the SROC curve was 0.971. For the long-term group (> 6 weeks after ablation), pooled sensitivity was 95.3%, I2 = 0%; pooled specificity was 97.6%, I2 = 0%; PPV was 74.2%, I2 = 4%; NPV was 99.4%, I2 = 5%; AUC = 0.93.

CONCLUSION

CEUS has high sensitivity and specificity in ruling out the presence of local recurrence after renal tumor ablation with a higher risk of false-positive results within follow-up > 6 weeks compared with that for CT or MRI. Further studies with a unified protocol and morphological control of local renal tumor recurrence after ablation are needed.

Second-Generation Differential Tissue Harmonic Imaging Improves the Visualization of Renal Lesions

OBJECTIVES

To compare to three nonlinear imaging techniques to conventional, grayscale ultrasound imaging of renal lesions.

METHODS

Twenty adults with a known renal lesion and a body mass index >25 kg/m² were enrolled in this prospective, institutional review board approved study. Each subject was imaged with an Aplio 500 scanner (Canon Medical Systems, Tokyo, Japan) using grayscale ultrasound, tissue harmonic imaging (THI) and two dual-frequency, differential tissue harmonic imaging modes (DTHI and DTHI-II, respectively). In total 184 images were scored by three independent and blinded observers for detail resolution, image quality, margin delineation, and depth penetration. Quantitative contrast-to-noise ratios (CNRs) were also calculated.

RESULTS

Readers and CNR values showed that nonlinear imaging was superior to grayscale ultrasound (P < .0014). DTHI-II outperformed DTHI, THI, and grayscale ultrasound with respect to detail resolution, image quality, and margin delineation (P < .012). The depth penetration of DTHI and DTHI-II was similar (P = .16), but superior to grayscale ultrasound and THI (P < .001). Two observers saw improvements in detail resolution with DTHI-II over DTHI (P < .05), while image quality and margin delineation were considered similar by two readers (P > .07) and improved with DTHI-II by one (P < .017).

CONCLUSIONS

DTHI-II improves the imaging of renal lesions compared to DTHI, THI, and grayscale ultrasound, albeit based on a limited sample size.

Volumetric Quantitative Contrast-enhanced Ultrasonography Evaluation of Complex Renal Cysts: An Adjunctive Metric to the Bosniak Classification System to Predict Malignancy

BACKGROUND

Management of complex renal cysts is guided by the Bosniak classification system, which may be inadequate for risk stratification of patients for intervention. Fractional tumor vascularity (FV) calculated from volumetric contrast-enhanced ultrasound (CEUS) images may provide additional useful information.

OBJECTIVE

To evaluate CEUS and FV calculation for risk stratification of patients with complex renal cysts.

DESIGN, SETTING, AND PARTICIPANTS

This was a pilot prospective study with institutional review board approval involving patients undergoing surgery for Bosniak IIF-IV complex renal cysts. CEUS was performed preoperatively on the day of surgery with two-dimensional (2D) and three-dimensional (3D) imaging and sulfur hexafluoride lipid-type A microspheres as the ultrasound contrast agent.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

A custom MATLAB program was used to select regions of interest on CEUS scans. FV was calculated according to FV = 1 - (total nonenhancing area/total lesion area). We assessed the ability of 2D- and 3D-derived percentage FV (2DFV%, and 3DFV%) and Bosniak classification schemes (pre-2019 [P2019B] and post-2019 [B2019]) to predict malignancy, aggressive histology, and upstaging on surgical pathology. Performance was assessed as area under the receiver operating characteristic curve (AUC).

RESULTS AND LIMITATIONS

Twenty eligible patients were included in final analysis, of whom 85% (n = 17) had Bosniak IV cysts and 85% (n = 17) had malignant disease on final pathology. Four (24%) of the malignant lesions were International Society of Urological Pathology grade 3-4. The AUC for predicting malignancy was 0.980, 0.824, 0.863, and 0.824 with P2019B, B2019, 2DFV%, and 3DFV%, respectively. When the Bosniak classification was combined with FV%, three models had an AUC of 1, while the combined 2DFV% + B2019 model had AUC of 0.980.

CONCLUSIONS

FV is a novel metric for evaluating complex cystic renal masses and enhances the ability of the Bosniak classification system to predict malignancy. This metric may serve as an adjunct in risk stratification for surgical intervention. Further prospective evaluation is warranted.

PATIENT SUMMARY

Cysts in the kidney are currently classified using a scheme called the Bosniak system. We assessed measurement of the percentage of vascular tissue (called fractional vascularity) in cysts on a special type of ultrasound scan. This promising test adds information when combined with the Bosniak system and can help in guiding appropriate treatment.

Effects of Contrast-Enhanced Ultrasound of Indeterminate Renal Masses on Patient Clinical Management: Retrospective Analysis From 2 Institutions

OBJECTIVES

To investigate the long-term impact of contrast-enhanced ultrasound (CEUS) on the treatment of patients with indeterminate renal masses.

METHODS

In this retrospective study, consecutive charts of all patients receiving renal CEUS at 1 of 2 academic medical centers between January 1, 2014, and December 31, 2018, were reviewed. Patients were included in the study if they had documented chronic renal disease (estimated glomerular filtration rate < 60 mL/min/1.73 m² ) or prior nephrectomy and received CEUS for a previously untreated renal mass.

RESULTS

A total of 215 lesions in 157 patients were used for analysis. Contrast-enhanced ultrasound provided a final treatment recommendation in 71.6% of lesions (154 of 215). Of these 154 lesions, 7.8% (12 of 154) were lost to follow-up despite CEUS suggesting malignancy; 15.6% (24 of 154) went directly for surgical intervention, with malignancy confirmed by pathologic results in 87.5% (21 of 24) of these cases; and the remaining 76.6% (118 of 154) were deemed benign and required no additional follow-up. Of the 118 lesions diagnosed by CEUS as benign and requiring no follow-up, none showed evidence of later renal cell carcinoma development and, only 5.1% (6 of 118) of the total population was referred for further cross-sectional imaging of the mass in question. In 28.4% of all lesions (61 of 215), CEUS resulted in a recommendation for surveillance imaging at a 6- to 12-month interval, and less than 10% (6 of 61) of these underwent additional cross-sectional imaging within the recommended 6 months after CEUS.

CONCLUSIONS

These findings highlight the impact of CEUS on clinical treatment of indeterminate renal masses, including reducing the use of the potentially nephrotoxic contrast agents and providing a direct pathway to transplant.

Contrast-Enhanced Subharmonic Aided Pressure Estimation (SHAPE) using Ultrasound Imaging with a Focus on Identifying Portal Hypertension

Noninvasive, accurate measurement of pressures within the human body has long been an important but elusive clinical goal. Contrast agents for ultrasound imaging are gas-filled, encapsulated microbubbles (diameter < 10 μm) that traverse the entire vasculature and enhance signals by up to 30 dB. These microbubbles also produce nonlinear oscillations at frequencies ranging from the subharmonic (half of the transmit frequency) to higher harmonics. The subharmonic amplitude has an inverse linear relationship with the ambient hydrostatic pressure. Here an ultrasound system capable of performing real-time, subharmonic aided pressure estimation (SHAPE) is presented. During ultrasound contrast agent infusion, an algorithm for optimizing acoustic outputs is activated. Following this calibration, subharmonic microbubble signals (i.e., SHAPE) have the highest sensitivity to pressure changes and can be used to noninvasively quantify pressure. The utility of the SHAPE procedure for identifying portal hypertension in the liver is the emphasis here, but the technique has applicability across many clinical scenarios.

Sonoporation for Augmenting Chemotherapy of Pancreatic Ductal Adenocarcinoma

Pancreatic cancer is the third most common cancer diagnosed in the United States, with more than 53,000 new cases in 2017. It is the fourth leading cause of cancer-related death in both men and women. Nonetheless, there has been no significant improvement in survival for pancreatic ductal adenocarcinoma (PDAC) patients over the past 30+ years. For this reason, there is a considerable and urgent clinical need to develop innovative strategies for effective drug delivery and treatment monitoring, resulting in improved outcomes for patients with PDAC.This chapter describes the development of contrast-enhanced ultrasound image-guided drug delivery (CEUS-IGDD or sonoporation) to be that method and to translate it from the lab to the clinic. The initial clinical focus has been on a Phase I clinical trial for enhancing the effectiveness of standard chemotherapeutics for treatment of inoperable PDAC, which demonstrated a median survival increase from 8.9 months to 17.6 months in ten subjects augmented with sonoporation compared to 63 historical controls (p = 0.011). Recent efforts to optimize this platform and move forward to a larger Phase II clinical trial will be described.

Influence of Data Parsing on Contrast Enhanced Ultrasound Exams

RATIONALE AND OBJECTIVES

To explore the influence of data parsing (either selection of frames at set time intervals or by an experienced sonographer) of contrast-enhanced ultrasound (CEUS) exams on physician diagnoses and confidence levels.

MATERIALS AND METHODS

Forty consecutive CEUS exams consisting of 10 cases each of indeterminate liver lesions, indeterminate renal lesions, renal cell carcinoma postablation follow-up, and hepatocellular carcinoma postchemoembolization follow-up were selected for analysis. Exams were parsed into sets consisting of five images selected by the performing sonographer and sets containing systematically stored frames every 10, 30, and 60 seconds. Three blinded physicians then reviewed the cine loop and each set of images in randomized order and provided a diagnosis and confidence level.

RESULTS

For all clinical applications investigated, no statistically significant differences in diagnostic performance measures or reader confidence were observed between review of the entire cine loop and images selected by the performing sonographer (p > 0.42). Diagnostic performance at 10-second intervals did not show statically significant changes compared to the full cine loop review for all applications (p > 0.18), although reader confidence decreased. At 30-60-second intervals, both diagnostic performance and reader confidence showed statistically significant reduction compared to review of the full cine loop (p < 0.045).

CONCLUSIONS

Transfer and review of large cine loops from CEUS exams represent a potential barrier to adoption within the United States workflows. This study demonstrates that images selected by a performing trained sonographer may provide the same value without the review time and data storage costs needed for full cine loop review. Parsing by time points reduced reader confidence and diagnostic performance.

Three-Dimensional Subharmonic Aided Pressure Estimation for Assessing Arterial Plaques in a Rabbit Model

OBJECTIVES

To investigate 3-dimensional subharmonic aided pressure estimation (SHAPE) for measuring intraplaque pressure and the pressure gradient across the plaque cap as novel biomarkers for potentially predicting plaque vulnerability.

METHODS

Twenty-seven rabbits received a high-cholesterol diet for 2 weeks before a balloon catheter injury to denude the endothelium of the aorta, followed by 8 to 10 weeks of the high-cholesterol diet to create arteriosclerotic plaques. SHAPE imagings of the resulting plaques were performed 12, 16, and 20 weeks after injury using a LOGIQ 9 scanner with a 4D10L probe (GE Healthcare, Milwaukee, WI) before and during an infusion of Definity (Lantheus Medical Imaging, North Billerica, MA) and Sonazoid (GE Healthcare, Oslo, Norway). The ratios of the maximum subharmonic magnitudes at baseline and during the infusion were correlated with the intraplaque pressure and pressure gradient across the plaque cap obtained from direct measurements.

RESULTS

Ten rabbits died prematurely after the balloon injury procedure or due to toxicity from the high-cholesterol diet, whereas 2 rabbits were excluded for other conditions. Five rabbits were scanned in the 12-, 16-, and 20-week groups, respectively. Even after 20 weeks, the plaques that developed were very small (mean ± SD, 0.9 ± 0.4 × 0.14 ± 0.05 cm). Definity performed better than Sonazoid in this application but still only achieved a moderate correlation with pressure across the plaque cap (Definity, r = -0.40; Sonazoid, r = 0.22) and intraplaque pressure (Definity, r = -0.19; Sonazoid, r = -0.11).

CONCLUSIONS

Initial findings from plaque pressure estimation using 3-dimensional SHAPE technique showed only moderate correlations with reference standards, but that may be have been due to weaknesses in the animal model studied.

Contrast-enhanced ultrasonography in interventional oncology

Contrast-enhanced ultrasound (CEUS) has evolved from the use of agitated saline to second generation bioengineered microbubbles designed to withstand insonation with limited destruction. While only one of these newer agents is approved by the Food and Drug Administration for use outside echocardiography, interventional radiologists are increasingly finding off-label uses for ultrasound contrast agents. Notably, these agents have an extremely benign safety profile with no hepatic or renal toxicities and no radiation exposure. Alongside diagnostic applications, CEUS has begun to develop its own niche within the realm of interventional oncology. Certainly, the characterization of focal solid organ lesions (such as hepatic and renal lesions) by CEUS has been an important development. However, interventional oncologists are finding that the dynamic and real-time information afforded by CEUS can improve biopsy guidance, ablation therapy, and provide early evidence of tumor viability after locoregional therapy. Even more novel uses of CEUS include lymph node mapping and sentinel lymph node localization. Critical areas of research still exist. The purpose of this article is to provide a narrative review of the emerging roles of CEUS in interventional oncology.