Volume comparison after radiofrequency ablation at two different target volumes by means of four different RF generators - MR volumetry in a 1.0 Tesla open MRI vs. macroscopic measurement

No. 303 Volume comparison after radiofrequency ablation at two different target volumes by means of four different RF generators—MR volumetry in a 1.0 Tesla open MRI vs. macroscopic measurement H. Rathke, F.V. Guettler, B. Schnackenburg, J. Rump, B. Hamm, U. Teichgraeber, M. de Bucourt; Department of Radiology, Charite University Medicine Berlin, Berlin, Germany; Department of Radiology, Jena University, Jena, Germany; Healthcare, Philips, Hamburg, Germany Purpose: In several studies radiofrequency ablation (RFA) was found to be safe and reliable for intervention of primary and secondary malignancies. The aim of this study was to evaluate MR volumetry directly after RFA in an open MRI and to validate the visualization of the produced necrosis volume. As the RF necrosis can be subdivided in three zones it was evaluated if the outer zone of the necrosis is detectable with the MR sequences used and whether or not there are differences with respect to lesion size and generator type. Materials and Methods: 64 liver specimens were ablated under constant simulated physiological conditions with four commercially available RF systems (A, B, C, D; n1⁄416 for each system; n1⁄48 for 3cm, and n1⁄48 for 5cm). Target volumes were set to 14.14cm (3cm lesion) and 65.45cm(5cm lesion). T1 and PD weighted TSE sequences were acquired in a 1.0 Tesla open MRI and MR-volumetry was performed by semi-automatic software. After manual dissection actual macroscopic ablation diameters were recorded and volumes calculated. Results: For system A with the 3cm lesion, the manual measured macroscopic volume was 28.2cm in comparison to 15.2cm/ 13.5cm (T1/PDW) using MR volumetry—with the 5cm lesion: 48.3cm vs. 19.3cm/15.6cm. System B: 3cm: 17.1cm vs. 6.5cm/ 6.0cm-5cm: 39.3cm vs. 16.7cm/15.2cm. System C: 3cm 29.7 cm vs. 12.9cm/11.5cm-5cm 71.8cm vs. 29.6cm/27.4cm. System D: 3cm 28.7cm vs. 11.3cm/12.8cm-5cm 93.9cm vs. 42.6cm/37.5cm. Conclusion: MR volumetry yielded smaller appearing volumes than manual measurement after dissection—irrespective of RF system used, target lesion size and MR sequence. Histopathological assessment showed an incomplete cellular damage in the transitional zone of the necrosis. As expected cellular apoptotic processes could not be detected immediately after RFA, probably also because of the ex vivo setting and missing blood perfusion.The exact transition from ablated to vital tissue could not be assessed directly after Intervention with the MR sequences investigated.