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We investigated the accuracy of CEUS for characterizing cystic and solid kidney lesions in patients with chronic kidney disease (CKD). Cystic lesions are assessed using Bosniak criteria for computed tomography (CT) and magnetic resonance imaging (MRI); however, in patients with moderate to severe kidney disease, CT and MRI contrast agents may be contraindicated. Contrast-enhanced ultrasound (CEUS) is a safe alternative for characterizing these lesions, but data on its performance among CKD patients are limited. We performed flash replenishment CEUS in 60 CKD patients (73 lesions). Final analysis included 53 patients (63 lesions). Four readers, blinded to true diagnosis, interpreted each lesion. Reader evaluations were compared to true lesion classifications. Performance metrics were calculated to assess malignant and benign diagnoses. Reader agreement was evaluated using Bowker's symmetry test. Combined reader sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for diagnosing malignant lesions were 71%, 75%, 45%, and 90%, respectively. Sensitivity (81%) and specificity (83%) were highest in CKD IV/V patients when grouped by CKD stage. Combined reader sensitivity, specificity, PPV, and NPV for diagnosing benign lesions were 70%, 86%, 91%, and 61%, respectively. Again, in CKD IV/V patients, sensitivity (81%), specificity (95%), and PPV (98%) were highest. Inter-reader diagnostic agreement varied from 72% to 90%. In CKD patients, CEUS is a potential low-risk option for screening kidney lesions. CEUS may be particularly beneficial for CKD IV/V patients, where kidney preservation techniques are highly relevant.

Early stages of diabetic kidney disease (DKD) are difficult to diagnose in patients with type 2 diabetes. This work was aimed at identifying contrast-enhanced ultrasound (CEUS) perfusion parameters, a microcirculatory biomarker indicative of early DKD progression. CEUS kidney flash-replenishment data were acquired in control, insulin resistant and diabetic vervet monkeys (N = 16). By use of a mono-exponential model, time-intensity curve parameters related to blood volume (A), velocity (β) and flow rate (perfusion index [PI]) were extracted from 10 concentric kidney layers to study spatial perfusion patterns that could serve as strong indicators of disease. Mean squared error (MSE) was used to assess model performance. Features calculated from the perfusion parameters were inputs for the linear regression models to determine which features could distinguish between cohorts. The mono-exponential model performed well, with average MSEs (±standard deviation) of 0.0254 (±0.0210), 0.0321 (±0.0242) and 0.0287 (±0.0130) for the control, insulin resistant and diabetic cohorts, respectively. Perfusion index features, with blood pressure, were the best classifiers between cohorts (p < 0.05). CEUS has the potential to detect early microvascular changes, providing insight into disease-related structural changes in the kidney. The sensitivity of this technique should be explored further by assessing various stages of DKD., Competing Interests: Conflict of interest disclosure E.H.C. currently receives funding from Lantheus Medical Imaging for projects involving imaging and surveillance of kidney lesions. R.W.W. consulted for SonoVol, Inc., on unrelated imaging projects between November 2021 and April 2022. All other authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

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 m 2 ), 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 m 2 ) 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., Competing Interests: E.H. Chang reports research funding from Lantheus Medical Imaging and is on the medical advisory board for the North Carolina chapter of the National Kidney Foundation. P. Dayton reports consultancy for SonoVascular, Inc., SonoVol, Inc., and Triangle Biotechnology, Inc.; ownership interest in SonoVascular, Inc., SonoVol, Inc., and Triangle Biotechnology, Inc.; research funding from Kitware, LLC, SonoVol, Inc., and Triangle Biotechnology, Inc.; patents or royalties from SonoVascular, Inc., SonoVol, Inc., and Triangle Biotechnology, Inc.; an advisory or leadership role for SonoVascular, Inc., SonoVol, LLC, and Triangle Biotechnology, Inc.; and other interests or relationships with Pfizer, Inc. R. Walmer reports consultancy agreements with SonoVol, Inc. (entered into on November 2, 2021). A. Srivastava reports consultancy agreements with CVS Caremark and Tate & Latham (medicolegal consulting); honoraria from AstraZeneca, Bayer, and Horizon Therapeutics plc.; and participation in a speakers’ bureau for AstraZeneca. All remaining authors have nothing to disclose., (Copyright © 2022 by the American Society of Nephrology.)

Ultrasound molecular imaging (USMI) is a technique used to noninvasively estimate the distribution of molecular markers in vivo by imaging microbubble contrast agents (MCAs) that have been modified to target receptors of interest on the vascular endothelium. USMI is especially relevant for preclinical and clinical cancer research and has been used to predict tumor malignancy and response to treatment. In the last decade, methods that improve the resolution of contrast-enhanced ultrasound by an order of magnitude and allow researchers to noninvasively image individual capillaries have emerged. However, these approaches do not translate directly to molecular imaging. In this work, we demonstrate super-resolution visualization of biomarker expression in vivo using superharmonic ultrasound imaging (SpHI) with dual-frequency transducers, targeted contrast agents, and localization microscopy processing. We validate and optimize the proposed method in vitro using concurrent optical and ultrasound microscopy and a microvessel phantom. With the same technique, we perform a proof-of-concept experiment in vivo in a rat fibrosarcoma model and create maps of biomarker expression co-registered with images of microvasculature. From these images, we measure a resolution of 23 μm, a nearly fivefold improvement in resolution compared to previous diffraction-limited molecular imaging studies., Competing Interests: CONFLICTS OF INTEREST F. Stuart Foster and Paul A. Dayton are inventors on a patent describing dual-frequency imaging, which is now licensed to Perkin Elmer. Thomas M. Kierski, Isabel G. Newsome, Gianmarco F. Pinton, and Paul A. Dayton are inventors on a patent describing dual-frequency ultrasound localization microscopy.