Sub-acute changes in lesion conspicuity and geometry following MR-guided radiofrequency ablation.
OBJECTIVE
To evaluate MR signal and lesion zone volume evolution through the sub-acute phase following image-guided radiofrequency (RF) thermal ablation.


METHODS
For many tissues, including muscle and liver, thermal lesions that result from RF heating have a characteristic two-boundary appearance featuring an inner core (zone I) surrounded by a hyper-intense margin (zone II) and normal tissue (zone III), found in both T(2) and contrast enhanced (CE) T(1)-weighted MR images, both immediately post-ablation and four days later. First, we compared corresponding points between manually segmented zone boundaries apparent in T(2)- and CE T(1)-weighted images. Second, we examined the contrast-to-noise ratio (CNR) between all zone combinations. Third, we quantified the volume of zone I, zone II, and the entire lesion using a three-dimensional lesion geometry model fitted to segmented images.


RESULTS
On a slice-by-slice basis, no statistically significant differences were found between zone boundaries apparent in T(2) and CE T(1)-weighted images. The contrast to noise ratio (CNR) of zone I vs. zone II, zone I vs. background muscle, and zone II vs. background muscle was always equal or greater for T(2)-weighted images than for CE T(1)-weighted images. In addition, by day four, zone II significantly increased in intensity compared to background muscle. The median Zone I volume increase was 44.2% (42.6%) using T(2) weighted images and 55.5% (68.7% interquartile range) using CE T(1)- weighted images. This expansion likely corresponds to an enlargement of the ablated, coagulative necrosis, region. The median Zone II volume increase was 15.0% (42.6%) using T(2)- weighted images 1.5% (38.8%) using CE T(1)-weighted images.


CONCLUSIONS
1) There are no significant differences between the apparent zone boundaries in T(2)- and CE T(1)-weighted images; 2) CNR is equal or greater for T(2)-weighted images as compared to CE T(1)-images; and 3) both the inner and outer lesion zone volumes typically increase several days post-ablation.
Lazebnik
Roee S
RS
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA. dlw@po.cwru.edu
Weinberg
Brent D
BD
Breen
Michael S
MS
Lewin
Jonathan S
JS
Wilson
David L
DL
D000818:Animals; D017115:Catheter Ablation / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging; D009132:Muscles / Q000473:pathology; D011817:Rabbits; D025321:Surgery, Computer-Assisted / Q000379:methods