Spacer-Supported Thermal Ablation to Prevent Carbonisation and Improve Ablation Size: A Proof of Concept Study

Abstract

Thermal ablation offers a minimally invasive alternative in the treatment of hepatic tumours. Several types of ablation are utilised with different methods and indications. However, to this day, ablation size remains limited due to the formation of a central non-conductive boundary layer. In thermal ablation, this boundary layer is formed by carbonisation. Our goal was to prevent or delay carbonisation, and subsequently increase ablation size. We used bovine liver to compare ablation diameter and volume, created by a stand-alone laser applicator, with those created when utilising a spacer between laser applicator and hepatic tissue. Two spacer variants were developed: one with a closed circulation of cooling fluid and one with an open circulation into hepatic tissue. We found that the presence of a spacer significantly increased ablation volume up to 75.3 cm3, an increase of a factor of 3.19 (closed spacer) and 3.02 (open spacer) when compared to the stand-alone applicator. Statistical significance between spacer variants was also present, with the closed spacer producing a significantly larger ablation volume (p < 0.001, MDiff = 3.053, 95% CI[1.612, 4.493]) and diameter (p < 0.001, MDiff = 4.467, 95% CI[2.648, 6.285]) than the open spacer. We conclude that the presence of a spacer has the potential to increase ablation size.

The Effect of Cooling Fluid Composition on Ablation Size in Hepatic Laser Ablation: A Comparative Study in an Ex Vivo Bovine Setting

“…The relation between carbonisation and ablation size has been extensively discussed in an author's previous study [29]. It can be concluded that minimising the chance of carbonisation leads to an increase in ablation rate, which is beneficial in a clinical setting.…”

“…Postprocedural MR-based monitoring with its clear imaging, thermometric capabilities and sequence-based motion correction [34,35], along with CT and ultrasound, is one of the most effective tools for assessing ablation success within the first 24 h after ablation procedures [36]. As discussed in a preceding study, the comparison of manual volumetry through displacement of water and MR-based volumetry shows no statistically significant difference [29]. As such, MRbased volumetry is well suited as a non-invasive measuring method.…”

“…As shown in a recent proof-of-concept study, a further method of increasing ablation volume in laser ablation through the prevention or delay of carbonisation is the use of a spacer, which has been linked to significantly delayed carbonisation and thus significantly increased ablation size [29]. Composition of the cooling fluid and its effect on ablation volume could thus be used to further optimize hyperthermic ablation.…”