The aim of this study was to explore the feasibility of magnetic resonance elastography (MRE) for characterizing indeterminate small renal tumors (SRTs) as part of a multiparametric magnetic resonance (MR) imaging protocol.
After institutional review board approval and informed consent were obtained, 21 prospective adults (15 men; median age, 55 years; age range, 25–72 years) with SRT were enrolled. Tumors (2–5 cm Ø) were imaged using 3-directional, gradient echo MRE. Viscoelastic parametric maps (shear wave velocity [c] and attenuation [α]) were analyzed by 2 independent radiologists. Interobserver agreement (Bland-Altman statistics and intraclass correlation coefficients) was assessed. Anatomical T2-weighted, dynamic contrast-enhanced (DCE) and diffusion sequences completed the acquisition protocol. Imaging parameters were compared between groups (Mann-Whitney U test).
Quality of MRE was good in 18 cases (mean nonlinearity <50%), including 1 papillary renal cell carcinoma and 1 metanephric adenoma. A cohort of 5 oncocytomas and 11 clear-cell renal cell carcinomas (ccRCCs) was analyzed for statistical differences. The MRE viscoelastic parameters were the strongest imaging discriminators: oncocytomas displayed significantly lower shear velocity c (median, 0.77 m/s; interquartile range [IQR], 0.76–0.79) (P = 0.007) and higher shear attenuation α (median, 0.087 mm−1; IQR, 0.082–0.087) (P = 0.008) than ccRCC (medians, 0.92 m/s and 0.066 mm−1; IQR, 0.84–0.97 and 0.054–0.074, respectively). T2 signal intensity ratio (tumor/renal cortex) was lower in oncocytomas (P = 0.02). The DCE and diffusion MR parameters overlapped substantially (P ≥ 0.1). Oncocytomas displayed a consistent MRE viscoelastic profile, corresponding to data point clustering in a bidimensional scatter plot. Values for MRE intraclass correlation coefficient were 0.982 for c and 0.984 for α, indicating excellent interobserver agreement.
Magnetic resonance elastography is feasible for SRT characterization; MRE viscoelastic parameters were stronger discriminators between oncocytoma and ccRCC than anatomical, DCE and diffusion MR imaging parameters.
From the *King's College London, School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital; †Guy's and St Thomas' NHS Foundation Trust, Radiology, London; ‡Siemens Healthcare UK, MR Research Collaborations, Frimley, Surrey; and §The Urology Centre and ∥Pathology, Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom.
Received for publication November 1, 2017; and accepted for publication, after revision, December 22, 2017.
Conflicts of interest and sources of funding: This work was financially supported by the Royal College of Radiologists through the Clinical Radiology Pump Priming Grant scheme; by the Department of Health via the National Institute for Health Research (NIHR) Comprehensive Biomedical Research Centre award to Guy's and St Thomas' NHS Foundation Trust, in partnership with King's College London and King's College Hospital NHS Foundation Trust; and by the King's College London/University College London Comprehensive Cancer Imaging Centre funded by Cancer Research UK and Engineering and Physical Sciences Research Council, in association with the Medical Research Council and Department of Health. The views expressed in this publication are those of the authors and not necessarily those of the NHS, the NIHR, or the Department of Health.
The authors report no conflicts of interest.
Correspondence to: Davide Prezzi, FRCR, School of Biomedical Engineering & Imaging Sciences, Level 4, Lambeth Wing, St Thomas' Hospital, Westminster Bridge Road, London SE1 7EH, United Kingdom. E-mail: firstname.lastname@example.org.