Differentiation between normal renal tissue and renal tumours using functional optical coherence tomography: a phase I in vivo human study

Abstract

Objective: To determine the ability of optical coherence tomography (OCT) in differentiating human renal tumours in an in-vivo setting by assessing differences in attenuation coefficient (µ(OCT); mm(-1)) as a quantitative measurement.

Methods: Consecutive patients undergoing nephrectomy (partial/radical) or cryoablation for an enhancing solid renal tumour were included in our centre between October 2010 and May 2011. In vivo OCT images were obtained from renal tumour and normal parenchyma during surgery. Ex vivo OCT images of internal (subcapsular) tissue were obtained after longitudinal dissection of the extirpated specimen. Attenuation coefficients of the OCT images were determined off-line and compared between normal renal parenchyma and renal tumours (grouped per tissue type and per individual patient); and between OCT images recorded from tissue surface vs internal (subcapsular) tissue.

Results: In vivo OCT was performed in 16 cases (11 renal cell carcinoma, three benign tumours, one non-diagnostic biopsy and one not-accessible tumour). Median attenuation coefficient of normal renal parenchyma was 5.0 mm(-1) vs 8.2 mm(-1) for tumour tissue (P < 0.001) with normal parenchyma differing significantly from malignant tumour (9.2 mm(-1), P < 0.001) and non-significantly from benign tumour (7.0 mm(-1), P = 0.050). The attenuation coefficient of benign tumours did not differ significantly from that of malignant tumours (7.0 vs 9.2 mm(-1), P = 0.139). Using patients as their own control, attenuation coefficients of normal renal parenchyma differed significantly from malignant tumour (P < 0.001) and non-significantly from benign tumour (P = 0.109). Assessed in 10 patients, there was no significant difference between attenuation coefficients of tumour surface and internal tumour (8.5 vs 9.7 mm(-1) respectively, P = 0.260).

Conclusions: In this first in vivo study on OCT for differentiation of renal tumours in humans the attenuation coefficients (as a quantitative assessment) differed significantly between normal renal parenchyma and malignant tumour. Tumour surface and internal tumour did not differ significantly, suggesting that a superficial OCT attenuation coefficient reliably assesses tissue composition inside the tumour. These results justify further research on OCT for various clinical applications in the diagnosis of renal tumours.