Purpose: To investigate the potential RF heating risk when the high-pressure gas supply line (HPGSL) is placed close to the patient during MRI-guided cryoablation.
Methods: Three ex-vivo experiments were performed on a 1.5T MRI scanner using a VISUAL ICE cryoablation system. The metallic cryoneedle used in this system is attached to HPGSL, which connects to a mobile connection panel (MCP). The inner component of HPGSL is metallic. A 30 cm porcine tissue sample was placed ~10 cm off the patient table center and covered by a layer of operating room (OR) towel. An IceSeed cryoneedle was inserted at an approximately 30° angle relative to the patient table. A temperature monitoring system with four thermal sensors (three attached to HPGSL and one placed on tissue surface) were used to record the temperature changes during executions of a T2-weighted (T2W) MRI sequence (~2.3 minutes; SAR: 2.3 W/kg). With a segment (~3 cm) of HPGSL placed on the towel directly above the thermal sensor placed on the tissue surface, two experiments were performed with HPGSL disconnected and connected to MCP, respectively. With HPGSL connected, a third experiment was performed after inserting a large, 2.5 cm thick pad between HPGSL and the towel.
Results: With just the towel separating the tissue and HPGSL, the maximum tissue temperature rises were about 5-6℃ and 40℃ with the HPGSL disconnected and connected to MCP, respectively, at the end of the T2W sequence. Temperature rises on HPGSL were much lower and localized to the segment close proximity to the tissue. With HPGSL connected to MCP and the thick pad inserted between tissue and HPGSL, no temperature rise was observed.
Conclusion: HPGSL could potentially introduce significant RF heating and cause skin burns during MR-guided cryoablation. Sufficient padding/separation between HPGSL and patient skin should be applied to mitigate this risk.
MRI, Image-guided Surgery, Thermal Ablation