Phase One Pilot Study Using Magnetic Resonance Spectroscopy to Predict the Histology of Radiofrequency-Ablated Renal Tissue

Introduction and Objective: Recent advances in magnetic resonance (MR) technology have allowed for high-resolution ex vivo spectroscopy on small, intact tissue samples. We examined the capability of ¹H magnetic resonance magic angle spinning (MR-MAS) to correctly characterize post-radiofrequency ablation (RFA) renal biopsies from human samples, compared with standard histology and cross-sectional imaging. Methods: A minimum of two, 18G, percutaneous renal biopsies were obtained from ten biopsy-confirmed renal tumors at a mean 26.6 mo (range, 15-48) post-RFA. All patients were considered free of disease by computed tomography criteria. A portion of each sample was immediately frozen at -80 °C for spectroscopy and the remainder used for pathological analysis. ¹H MR-MAS was performed blinded with a 14.1-tesla field strength. Prior renal biopsies from nonablated tissue were used as positive controls for the spectral analysis. Concordance between, computed tomography, histology, and MR-MAS was analyzed. All spectroscopy was processed with VNMR software. Results: Histological analysis of all ten post-RFA biopsies demonstrated no cancer or viable tissue. All MR-MAS spectral peaks for each biopsy were consistent with necrosis and, more importantly, indicated an absence of small molecule metabolites characteristic of both normal and malignant renal tissue. Both MR-MAS and histology confirmed, in each case, the conventional computed tomography determination of complete ablation. Conclusions: MR spectroscopy can correctly diagnose the molecular absence of disease in post-RFA tissue biopsies. This proof of principle study warrants in vivo evaluation to confirm the clinical correlates of this modality.