Thermal Sensor Circuit Using Thermography for Temperature-Controlled Laser Hyperthermia

Abstract

Laser hyperthermia is a powerful therapeutic modality that suppresses the growth of proliferative lesions. In hyperthermia, the optimal temperature range is dependent on the disease; thus, a temperature-driven laser output control system is desirable. Such a laser output control system, integrated with a thermal sensor circuit based on thermography, has been established. In this study, the feasibility of the developed system was examined by irradiating mouse skin. The system is composed of a thermograph, a thermal sensor circuit (PC and microcontroller), and an infrared laser. Based on the maximum temperature in the laser-irradiated area acquired every 100 ms during irradiation, the laser power was controlled such that the maximum temperature was maintained at a preset value. Temperature-controlled laser hyperthermia using the thermal sensor circuit was shown to suppress temperature fluctuations during irradiation (SD ∼ 0.14 ∘ C) to less than 1/10 of those seen without the thermal sensor circuit (SD ∼ 1.6 ∘ C). The thermal sensor circuit was able to satisfactorily stabilize the temperature at the preset value. This system can therefore provide noncontact laser hyperthermia with the ability to maintain a constant temperature in the irradiated area.

Closed-Loop Temperature Control Based on Fiber Bragg Grating Sensors for Laser Ablation of Hepatic Tissue

“…The set temperature was contained within the proper range, corresponding to specific thermal states of biological tissues inside the low-temperature damage accumulation process [ 52 , 53 ]. Only a few previous studies presented the real-time control of the laser settings according to the tissue temperature, and most of them employed single-point measurements [ 28 , 31 , 51 ], or contactless thermometric systems [ 25 ]. Conversely, our zone-control logic allows for a multipoint control of the tissue temperature, which can be adapted according to the size of the desired tissue region to be treated.…”

“…It has been observed, and further confirmed by this work, that the ON–OFF strategy leads to oscillations of the maximum temperature values across the set threshold [ 51 ]. The oscillations contribute to the thermal history of the treatment, due to the heat that remains in the tissue after the laser is turned off and to the cooling occurring between consecutive irradiations [ 25 ]. Figure 5 shows that these oscillations are marked in correspondence of the center of the ablation zone, but their amplitudes significantly decrease with the radius of the zone under control, providing smoothly increasing temperature trends at 6 mm from the center of the ablation zone ( Figure 5 , blue and green curves).…”

“…As a result, the ablated area has several regions with different biological effects that depend on the duration of the ablation and the maximum temperature reached. In this context, the temperature range between 42 and 45 °C is considered to be optimal for hyperthermal treatment since it activates immune responses by promoting the migration and maturation of Langerhans cells [ 25 ]. At a temperature between 50 to 55 °C, coagulative necrosis starts in organs [ 3 ], and it has been observed that cellular death can occur instantaneously in cell culture [ 26 ].…”

Highly reliable, targeted photothermal cancer therapy combined with thermal dosimetry using indocyanine green lactosome

“…At any fluence rate, there was no correlation between tumor size on day 21 and irradiation time Figure 3 shows that the two tumors that did not disappear were included in the groups of 750 and 1000 mW/cm 2 , and both cases were irradiated for 111 s. 1 1 The results suggested that tumor cure depends on the tumor temperature during NIR irradiation. We have developed a thermal sensor circuit-based NIR laser irradiation system using a non-contact thermometer in order to keep the temperature of the irradiated target constant during irradiation (Nomura et al , 2017). We carried out a NIR irradiation experiment using the temperature-feedback laser system.…”

“…Since the results obtained by PTT suggested that the peak of temperature of the tumor during NIR irradiation is the most reliable index to predict tumor shrinkage, we conducted animal experiments using a system that can control the temperature of the tumor. In order to keep the temperature constant, we used a NIR laser system for which the irradiation power is modulated by a temperature feedback control circuit that we previously reported (Nomura et al, 2017). The temperature was set 40, 41, 42 or 43°C…”