Fabrication and calibration of three temperature probes for monitoring the effects of thermal cancer ablation

Minimally invasive thermal techniques are gaining acceptance in cancer removal. These approaches aim at destroying the tumour while minimizing the damage of surrounding healthy structures. Several solutions have already proved their effectiveness in improving treatment outcomes and in minimizing adverse events. However, it is still challenging to selectively remove the cancer. To help tackle this challenge, several groups of research are focusing on the use of thermometry for monitoring the effects on biological tissue of hyperthermal treatments, since the irreversible damage of tissue depends on temperature and time of application. Given the rising complexity of treatment settings, a temperature feedback may be useful to improve the clinical outcome by minimizing the thermal damage of surrounding healthy tissue. Fiber Bragg grating (FBG) sensors are used in this scenario thanks to several advantages, such as the small size, Magnetic Resonance (MR) compatibility and the possibility to perform spatially distributed measurements; moreover, with the use of specific coating their thermal sensitivity may be increased. However, they are fragile and their insertion within the organ can be challenging and time consuming. In this paper we describe the fabrication of three thermal probes embedding FBG sensors. Each probe consists of a MR-compatible needle which embeds a FBG sensor glued with epoxy adhesive. The three probes showed a sensitivity of about 24 pm/°C, which his higher than the one showed by non-encapsulated FBG (about 10 pm/°C). Moreover, the output of the three probes showed a negligible output drift and a negligible sensitivity drift after 4 thermal cycles in a wide range of temperature (i.e., from environmental temperature up to about 80 °C). The investigated solution shows some advantages considering the specific field of application: it allows an easy insertion within the organ being embedded within a needle; the probes' sensitivity is better than non-encapsulated FBGs; it can be used also during MR-guided procedures since both the needle and the FBG are MR-compatible. Future testing will assess the feasibility for temperature monitoring during thermal ablation treatment of the probes in ex vivo and in vivo animal model.