Abstract
Laser ablation (LA) of cancer is a minimally invasive technique based on targeted heat release. Controlling tissue temperature during LA is crucial to achieve the desired therapeutic effect in the organs while preserving the healthy tissue around. Here, we report the design and implementation of a real-time monitoring system performing closed-loop temperature control, based on fiber Bragg grating (FBG) spatial measurements. Highly dense FBG arrays (1.19 mm length, 0.01 mm edge-to-edge distance) were inscribed in polyimide-coated fibers using the femtosecond point-by-point writing technology to obtain the spatial resolution needed for accurate reconstruction of high-gradient temperature profiles during LA. The zone control strategy was implemented such that the temperature in the laser-irradiated area was maintained at specific set values (43 and 55 °C), in correspondence to specific radii (2 and 6 mm) of the targeted zone. The developed control system was assessed in terms of measured temperature maps during an ex vivo liver LA. Results suggest that the temperature-feedback system provides several advantages, including controlling the margins of the ablated zone and keeping the maximum temperature below the critical values. Our strategy and resulting analysis go beyond the state-of-the-art LA regulation techniques, encouraging further investigation in the identification of the optimal control-loop.
Highlights
Many thermal ablation (TA) therapies are being proposed as alternatives to the traditional cancer treatment methods, e.g., resectional surgery, chemotherapy, and radiation therapy, for the treatment of non-surgical patients [1]
Depending on the frequency of electromagnetic waves that induce tissue’s temperature change, TA techniques are divided into high-intensity focused ultrasound [6], microwave [7], radiofrequency [8], and laser ablation (LA) [9]
fiber Bragg grating (FBG) arrays with high spatial resolution properties (1.2 mm distance between centers of consecutive gratings) and high-temperature resistance coating were fabricated with the femtosecond point-by-point writing technology [46]
Summary
Many thermal ablation (TA) therapies are being proposed as alternatives to the traditional cancer treatment methods, e.g., resectional surgery, chemotherapy, and radiation therapy, for the treatment of non-surgical patients [1]. Depending on the frequency of electromagnetic waves that induce tissue’s temperature change, TA techniques are divided into high-intensity focused ultrasound [6], microwave [7], radiofrequency [8], and laser ablation (LA) [9]. Among all these techniques, LA holds good promises for clinical application, taking advantage of the small and flexible fiber optic applicators guiding laser energy into deep-lying tumors [10], Sensors 2020, 20, 6496; doi:10.3390/s20226496 www.mdpi.com/journal/sensors. The laser can be used for the treatment of superficial tumors, inside of hollow organs, such as the and gastrointestinal mucosa [11,12], and biliary tree [13], and in combination with selectively absorbing nanomaterials for photothermal therapy [14,15]
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