A comparison of high resolution ex vivo and interventional in vivo MR images and cellular response for thermal ablation treatment evaluation

We are treating patient tumors using radiofrequency (RF) ablation under interventional MRI (iMRI) guidance. We investigated the ability of high resolution ex vivo and interventional in vivo MR images to predict cellular response by comparing MR thermal lesion images to cellular damage as seen histologically. Our new methodology allows three dimensional (3D) registration that enables more accurate correlation than previous two dimensional (2D) methods. Using a low-field (0.2 T) open magnet iMRI system for electrode guidance, we applied RF current to the thigh muscles of 16 New Zealand White rabbits. After tissue dissection, a 1.5 T MRI system was used to obtain high resolution ex vivo images. To relate MR and histology images, we obtained intermediate pictures of thick tissue slices using a specially designed apparatus. Registration was done with a computer algorithm that matches tracks of needle fiducials placed near the site of interest. After registration, we determined the region inside the circular, hyper-intense rim in MR closely corresponds to the region of necrosis. This is good evidence that high resolution ex vivo and interventional in vivo MR images can be used to predict the cellular response for RF ablation treatments.