Introduction: MR guided laser interstitial thermal therapy (LITT) is an increasingly popular cytoreductive method in neuro-oncologic conditions such as gliomas, metastases and radiation necrosis. Studies have hypothesized that temporary breakdown of the blood-brain barrier (BBB) may occur which may allow for passage of drugs which would otherwise be impermeable to the BBB. These studies have focused on non-invasive measurements of BBB breakdown using DCE-MRI to calculate Ktrans, the vascular transfer constant. This study seeks to establish an in vitro method of laser ablation which can be tracked in real time with MR thermometry.
Methods: Soft tofu was packed without trapping air in 50 mL plastic test tubes and capped. A bare, i.e. without the surrounding cooling catheter, Visualase laser fiber (Medtronic, Minneapolis, MN) was inserted into the tofu. The test tube was then placed into a 7T MRI scanner (Bruker, Billerica, MA). While performing concurrent MR phase imaging, laser ablation was then performed at powers ranging from 2 to 9 W for up to 90 seconds. The phase images were then analyzed to calculate the change in temperatures over time.
Results: Successful tracking of changing temperatures over time was possible from the phase images. Ablation at 2-3 watts resulted in a rise of 30° over the 90 second ablation period, similar to the temperature rise needed to achieve tissue death in brain. At higher wattages, laser ablation caused the temperature to exceed 100°, resulting in gas formation, signal dropout and phase wrap. Post-ablation examination of the tofu demonstrated a clear ablation zone around the tip of the laser fiber.
Conclusions: These preliminary studies demonstrate the viability of this technique to perform laser ablation in vitro. Future studies will translate this technique for use in animal glioma models.
Patient Care: This study demonstrates a method to perform a simulation of laser ablation. It will lead to future studies in animal models to improve the utility of LITT
Learning Objectives: This study demonstrates an in vitro analog of laser ablation