Evaluation of Acoustic Radiation Force Impulse (ARFI) imaging and contrast-enhanced ultrasound in renal tumors of unknown etiology in comparison to histological findings

Abstract

Purpose: It was the aim of our study to combine the findings of contrast-enhanced ultrasound and ARFI-imaging in the evaluation of renal masses in comparison to the histological findings.

Materials and methods: Fifteen patients with unclear kidney lesions were analyzed. We used a high-end ultrasound machine (Siemens ACUSON S2000™, Siemens Healthcare, Erlangen, Germany) with a multifrequency curved array 4 MHz or linear 9 MHz transducer. Contrast-enhanced ultrasound (bolus injection 1.6–2.4 ml SonoVue^®) was carried out. We obtained fifteen ARFI measurements from each patient with at least five values for quantification. The ARFI-ROI (region of interest) was placed in the ventral margin of the kidney tumor and the whole ROI was covered by the tumor. The “reference-ROI” was placed in the ventral kidney parenchyma of the patient at a distance of at least two centimeters from the tumor. All renal tumors were surgically resected. In cases of complex renal cysts or anatomic variations mimicking renal tumors (“pseudo-tumors”), constant results of ultrasound examinations and additional MRI or multiphase CT over 6 months were required.

Results: Fifteen patients were included in the study and were examined using the diagnostic ultrasound tools of our study The kidney tumors of our patients had diameters ranging from 1.5 to 8 cm and were located at depths ranging from 2 to 5.5 cm. ARFI imaging was also performed in all patients. A field up to a depth of 10 cm could be visualized for diagnostic use. Performing ARFI quantification using Siemens Virtual Touch™ Tissue Quantification we obtained minimum and maximum tissue shear velocities ranging from 1.6 to 3.42 m/s. The reference tissue ROIs showed values from 1.31 to 4.4 m/s. 12 cases were accepted for surgical resection. The visualization of lesions with Virtual Touch™ Tissue Imaging confirmed the measurements of ARFI quantification and were able to depict the different areas of stiffness in the kidney tissue. No infiltration of kidney veins or vena cava was detected by contrast-enhanced ultrasound. Of the 12 cases two “complicated” renal cysts were examined, and both showed Bosniak-III findings.

Conclusion: ARFI imaging improves visualization of unclear renal masses in comparison to fundamental B-scan and adds new information about the tissue stiffness in a less time-consuming and more reproducible way. CEUS with SonoVue^® allows an early evaluation of renal masses or complex cysts.