Magnetic resonance imaging for assessment of radiofrequency lesions in kidney tissue immediately after ablation: an experimental study.
OBJECTIVE
Radiofrequency ablation (RFA) is an attractive minimally invasive treatment option for small renal masses. The purpose of this study was to investigate the morphologic imaging appearance of RF lesions immediately after the ablation of kidney tissue using standard clinical MR sequences, as well as to investigate the correlation between MR and gross lesion size.


METHODS
Ablations were performed 17 times in a standardized model of ex-vivo perfused porcine kidneys using a resistance-controlled RF device (250 W, 470 kHz) and a nonexpandable bipolar applicator inserted into the center of healthy renal parenchyma. The RF current was applied for 9 minutes at 20 W. Imaging was performed after ablation using standard clinical MR sequences: morphologic T(1)/T(2)- weighted images and an isotropic post-contrast T(1) high-resolution measurement (VIBE). Maximum lesion diameters were measured in three directions and were compared with the measurements of the gross lesions. Histologic (hematoxylin + eosin and nicotinamide adenine dinucleotide staining) and statistical analyses were performed.


RESULTS
The gross pathologic examination showed a firm, white-yellow ablation zone sharply demarcated from the untreated tissue. The histologic examination confirmed cellular viability outside but not in the treatment zone. The RF lesions were hyperintense on T(1)-weighted images and hypointense on T(2)-weighted images. The lesion size measured in the VIBE images correlated best with the macroscopic lesion size (N = 16).


CONCLUSIONS
Morphologic MR T(1) and T(2) sequences of RF lesions immediately after ablation produce reliable and consistent imaging characteristics. The post-contrast, high-resolution sequence (VIBE) enables the extent of the lesion to be determined accurately. The potential uses of this imaging strategy in clinical practise warrant further investigation on human renal-cell carcinoma.
Häcker
Axel
A
Department of Urology, University Hospital Mannheim, Ruprecht-Karls University of Heidelberg, Heidelberg, Germany. axel.haecker@chir.ma.uni-heidelberg.de
Risse
F
F
Peters
Kristina
K
Fink
Christian
C
Weiss
Christel
C
Huber
Peter E
PE
Alken
Peter
P
Michel
Maurice Stephan
MS
Jenne
Jürgen W
JW
D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation; D066298:In Vitro Techniques; D007668:Kidney / Q000473:pathology* / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D013552:Swine