Comparative Evaluations on Real-Time Monitoring of Temperature Sensors during Endoscopic Laser Application

Abstract

Temperature sensors, such as Fiber Bragg Grating (FBG) and thermocouple (TC), have been widely used for monitoring the interstitial tissue temperature during laser irradiation. The aim of the current study was to compare the performance of both FBG and TC in real-time temperature monitoring during endoscopic and circumferential laser treatment on tubular tissue structure. A 600-µm core-diameter diffusing applicator was employed to deliver 980-nm laser light (30 W for 90 s) circumferentially for quantitative evaluation. The tip of the TC was covered with a white tube (W-TC) in order to prevent direct light absorption and to minimize temperature overestimation. The temperature measurements in air demonstrated that the measurement difference in the temperature elevations was around 3.5 °C between FBG and W-TC. Ex vivo porcine liver tests confirmed that the measurement difference became lower (less than 1 °C). Ex vivo porcine esophageal tissue using a balloon-integrated catheter exhibited that both FBG and W-TC consistently showed a comparable trend of temperature measurements during laser irradiation (~2 °C). The current study demonstrated that the white tube-covered TC could be a feasible sensor to monitor interstitial tissue temperature with minimal overestimation during endoscopic laser irradiation. Further in vivo studies on gastroesophageal reflux disease will investigate the performance of the W-TC to monitor the temperature of the esophageal mucosa surface in real-time mode to warrant the safety of endoscopic laser treatment.

Keywords: Fiber Bragg Grating; diffusing fiber; thermal coagulation; thermocouple.

Figure 1

Characterization of diffusing optical fiber: (a) He-Ne light distribution along fiber, (b) longitudinal emissions from proximal (P) to distal (D) ends, and (c) polar emissions. Note that the sensor positions at 0, 2, 4, and 6 mm are indicated as M₀, M₂, M₄, and M₆, respectively.

Figure 2

Schematic illustrations of experimental set-ups to evaluate temperature changes measured by Fiber Bragg Grating (FBG) and thermocouple (TC): (a) evaluations of white plastic tube covering TC tip, (b) ex vivo porcine liver tissue tests with 18- and 22-mm glass tubes (top) and balloon catheter-integrated diffusing applicator (bottom), and (c) ex vivo esophagus tissue tests. A 980 nm laser light was irradiated at 30 W for 90 s for all testing.

Figure 3

Comparison of temperature elevations on 18-mm glass tube measured at various positions (0, 2, 4, and 6 mm from the middle of the diffusing tip) by FBG and TC with white tubing cover (W-TC) during laser irradiation of 30 W for 90 s: (a) temperature elevations (ΔT) at various positions and (b) measurement differences between FBG and W-TC (ΔT_W-TC − ΔT_FBG; N = 6). The sensor positions at 0, 2, 4, and 6 mm are denoted as M₀, M₂, M₄, and M₆, respectively.

Figure 4

Comparison of temperature elevations at the tissue–glass tube interface using two different glass tubes (18 and 22 mm in outer diameter) on ex vivo porcine liver tissue during laser irradiation 30 W for 90 s: (a) temperature elevations measured by FBG and W-TC and (b) measurement differences between FBG and W-TC (ΔT_W-TC − ΔT_FBG; N = 6). The sensor was positioned at the center of the diffusing tip (0 mm).

Figure 5

Evaluations of temperature elevations during laser irradiation of 30 W for 90 s on ex vivo porcine liver tissue using balloon catheter-integrated diffusing applicator: (a) comparison of temperature elevations at tissue-balloon interface measured by FBG and W-TC and (b) measurement differences between FBG and W-TC (ΔT_W-TC − ΔT_FBG; N = 6).

Figure 6

Thermal responses of ex vivo esophageal tissue to 980-nm laser irradiation (30 W for 90 s) using balloon catheter-integrated diffusing applicator: (a) infrared (IR) images captured before (top) and after (bottom) irradiation (N = 3), (b) comparison of temperatures in tissue lumen measured by FBG, W-TC, and IR camera (MP = measured point on outer surface), and (c) measurement differences between FBG and W-TC (ΔT_W-TC − ΔT_FBG; N = 3).