Factors influencing the time-intensity curve analysis of contrast-enhanced ultrasound in kidney transplanted patients: Toward a standardized contrast-enhanced ultrasound examination

Sarah Friedl; Ernst Michael Jung; Tobias Bergler; Hauke C Tews; Miriam C Banas; Bernhard Banas; Franz Josef Putz

doi:10.3389/fmed.2022.928567

Factors influencing the time-intensity curve analysis of contrast-enhanced ultrasound in kidney transplanted patients: Toward a standardized contrast-enhanced ultrasound examination

Front Med (Lausanne). 2022 Aug 25:9:928567. doi: 10.3389/fmed.2022.928567. eCollection 2022.

Authors

Sarah Friedl¹, Ernst Michael Jung², Tobias Bergler¹, Hauke C Tews³, Miriam C Banas¹, Bernhard Banas¹, Franz Josef Putz¹

Affiliations

¹ Department of Nephrology, University of Regensburg, Regensburg, Germany.
² Department of Radiology, Interdisciplinary Ultrasound, University of Regensburg, Regensburg, Germany.
³ Department of Internal Medicine I, Gastroenterology, Hepatology, Endocrinology, Rheumatology and Infectious Diseases, University Hospital, Regensburg, Germany.

Abstract

Background: Time-intensity curve analysis (TIC analysis) based on contrast-enhanced ultrasound (CEUS) provides quantifiable information about the microcirculation of different tissues. TIC analysis of kidney transplantations is still a field of research, and standardized study protocols are missing though being mandatory for the interpretation of TIC parameters in the clinical context. The aim of this study was to evaluate the impact of different sizes and forms of regions of interest (ROIs) on the variance of different TIC parameters and the level of interoperator variance between the different ROI methods in kidney transplantations.

Methods: In 25 renal transplanted patients, 33 CEUS of the transplanted kidney were performed, and TIC analysis with ROIs sized 5 mm² (ROI₅), 10 mm² (ROI₁₀), and ROIs circumscribing the outlines of anatomical regions (ROI _Anat ) were analyzed based on CEUS examination. The TIC analysis was repeated by a second independent operator for ROI₅ and ROI _Anat .

Results: Statistical analysis revealed significant differences between TIC parameters of different ROI methods, and overall, the interoperator variance was low. But a greater ROI surface (ROI₁₀) led to higher values of the intensity parameters A and AUC compared with ROI₅ (p < 0.05). The difference in the ROI form led to high variation of certain TIC parameters between ROI₅ and ROI _Anat in the myelon [intraclass correlation coefficient (A, ICC = 0.578 (0.139-0.793); TIC parameter (TTP); and ICC = 0.679 (0.344-0.842) (p < 0.05)]. A mean variation of 1 cm of the depth of ROI₅ in the cortex did not show significant differences in the TIC parameters, though there was an impact of depth of ROI _Anat on the values of TIC parameters. The interoperator variance in the cortex was low and equal for ROI₅ and ROI _Anat , but increased in the myelon, especially for ROI _Anat . Furthermore, the analysis revealed a strong correlation between the parameter AUC and the time interval applied for the TIC analysis in the cortex and myelon (r = 0.710, 0.674, p < 0.000).

Conclusion: Our findings suggest the application of multiple ROIs of 5 mm² in the cortex and medulla to perform TIC analysis of kidney transplants. For clinical interpretation of AUC, a standardized time interval for TIC analysis should be developed. After the standardization of the TIC analysis, the clinical predictive value could be investigated in further studies.

Keywords: CEUS; ROI; TIC-analysis; contrast-enhanced ultrasound; kidney transplantation; perfusion analysis; region of interest.