Photoacoustic-Based-Close-Loop Temperature Control for Nanoparticle Hyperthermia

Photoacoustic thermal-strain measurement towards noninvasive and accurate temperature mapping in photothermal therapy

Photothermal therapy is a promising tumor treatment approach that selectively eliminates cancer cells while assuring the survival of normal cells. It transforms light energy into thermal energy, making it gentle, targeted, and devoid of radiation. However, the efficacy of treatment is hampered by the absence of accurate and noninvasive temperature measurement method in the therapy. Therefore, there is a pressing demand for a noninvasive temperature measurement method that is real-time and accurate. This article presents one such attempt based on thermal strain photoacoustic (PA) temperature measurement. The method was first modelled, and a circular array-based photoacoustic photothermal system was developed. Experiments with Indian ink as tumor simulants suggest that the temperature monitoring in this work achieves a precision of down to 0.3 °C. Furthermore, it is possible to accomplish real-time temperature imaging, providing accurate two-dimensional temperature mapping for photothermal therapy. Experiments were also conducted on human fingers and nude mice, validating promising potentials of the proposed method for practical implementations.

Multi-Wavelength Photoacoustic Temperature Feedback Based Photothermal Therapy Method and System

Photothermal therapy (PTT) is a new type of tumor treatment technology that is noninvasive, repeatable, and does not involve radiation. Owing to the lack of real-time and accurate noninvasive temperature measurement technology in current PTT surgical procedures, empirical and open-loop treatment laser power control mode inevitably leads to overtreatment. Thermal radiation causes irreversible damage to normal tissue around cancer tissue and seriously affects the therapeutic effect of PTT and other therapies conducted at the same time. Therefore, real-time measurement and control of the temperature and thermal damage of the therapeutic target are critical to the success of PTT. To improve the accuracy and safety of PTT, we propose a multi-wavelength photoacoustic (PA) temperature feedback based PTT method and system. PA thermometry information at different wavelengths is mutually corrected, and the therapeutic light dose is regulated in real time to accurately control the treatment temperature. The experimental results on the swine blood sample confirm that the proposed method can realize real-time temperature measurement and control of the target area with an accuracy of 0.56 °C and 0.68 °C, demonstrating its good prospects for application.

Spatiotemporal Evolution of Temperature During Transient Heating of Nanoparticle Arrays

Nanoparticles (NPs) are promising agents to absorb external energy and generate heat. Clusters of NPs or NP array heating have found an essential role in several biomedical applications, diagnostic techniques, and chemical catalysis. Various studies have shed light on the heat transfer of nanostructures and greatly advanced our understanding of NP array heating. However, there is a lack of analytical tools and dimensionless parameters to describe the transient heating of NP arrays. Here we demonstrate a comprehensive analysis of the transient NP array heating. Firstly, we develop a set of analytical solutions for the NP array heating and provide a useful mathematical description of the spatial-temporal evolution of temperature for 2D, 3D, and spherical NP array heating. Based on this, we introduce the concept of thermal resolution that quantifies the relationship between minimal heating time, NP array size, energy intensity, and target temperature. Lastly, we define a set of dimensionless parameters that characterize the transition from confined heating to delocalized heating. This study advances the understanding of nanomaterials heating and guides the rational design of innovative approaches for NP array heating.

Glutathione-Sensitive Mesoporous Organosilica-Coated Gold Nanorods as Drug Delivery System for Photothermal Therapy-Enhanced Precise Chemotherapy

The combination of photothermal therapy (PTT) and chemotherapy can remarkably improve the permeability of the cell membrane and reduce the concentration of chemotherapy agents that not only kill the tumor cells effectively but also have adverse effects on normal tissues. It is of great meaning to construct nanomaterials that could be simultaneously applied for tumor eradication with PTT and chemotherapy. In this work, we developed a novel gold nanorod coated with mesoporous organosilica nanoparticles (oMSN-GNR), which presented as an optimal photothermal contrast agent. Moreover, after doxorubicin loading (oMSN-GNR–DOX), the organosilica shell exhibited biodegradable properties under high glutathione in the tumor microenvironment, resulting in massively releasing doxorubicin to kill tumor cells. More importantly, the hyperthermia effect of GNR cores under near-infrared light provided promising opportunities for localized photothermal ablation in vivo. Therefore, the combination of precise chemotherapy and highly effective PTT successfully inhibited tumor growth in liver tumor-bearing mice. This versatile synergistic therapy with local heating and chemotherapeutics precise release opens up the potential clinical application of PTT and chemotherapy therapeutics for malignant tumor eradication.

Enhanced precision of real-time control photothermal therapy using cost-effective infrared sensor array and artificial neural network

Photothermal therapy (PTT) requires tight thermal dose control to achieve tumor ablation with minimal thermal injury on surrounding healthy tissues. In this study, we proposed a real-time closed-loop system for monitoring and controlling the temperature of PTT using a non-contact infrared thermal sensor array and an artificial neural network (ANN) to induce a predetermined area of thermal damage on the tissue. A cost-effective infrared thermal sensor array was used to monitor the temperature development for feedback control during the treatment. The measured and predicted temperatures were used as inputs of fuzzy control logic controllers that were implemented on an embedded platform (Jetson Nano) for real-time thermal control. Three treatment groups (continuous wave = CW, conventional fuzzy logic = C-Fuzzy, and ANN-based predictive fuzzy logic = P-Fuzzy) were examined and compared to investigate the laser heating performance and collect temperature data for ANN model training. The ex vivo experiments validated the efficiency of fuzzy control with temperature method on maintaining the constant interstitial tissue temperature (80 ± 1.4 ^°C) at a targeted surface of the tissue. The linear relationship between coagulation areas and the treatment time was indicated in this study, with the averaged coagulation rate of 0.0196 cm²/s. A thermal damage area of 1.32 cm² (diameter ∼1.3 cm) was observed under P-Fuzzy condition for 200 s, which covered the predetermined thermal damage area (diameter ∼1 cm). The integration of real-time feedback temperature control with predictive ANN could be a feasible approach to precisely induce the preset extent of thermal coagulation for treating papillary thyroid microcarcinoma.

Real-Time Control of Nanoparticle-Mediated Thermal Therapy Using Photoacoustic Imaging

OBJECTIVE

This work aims to determine whether photoacoustic (PA) thermometry from a commercially available PA imaging system can be used to control the temperature in nanoparticle-mediated thermal therapies.

METHODS

The PA imaging system was interfaced to obtain PA images while scanning ex-vivo tissue. These images were then used to obtain temperature maps in real-time during heating. Validation and calibration of the PA thermometry were done using a fluoroptic thermometer. This thermometer was also used to develop and tune a software-based proportional integral derivative (PID) controller. Finally, a PA-based PID closed-loop controller was used to control gold nanorod (GNR) mediated laser therapy.

RESULTS

The use of GNRs substantially enhanced laser heating; the temperature rise increased 7-fold by injecting a GNR solution with a concentration of 0.029 mg/mL. The control experiments showed that the desired temperature could be achieved and maintained at a targeted location in the ex-vivo tissue. The steady-state mean absolute deviations (MAD) from the targeted temperature during control were between 0.16 [Formula: see text] and 0.5 [Formula: see text], depending on the experiment.

CONCLUSION

It was possible to control hyperthermia treatments using a software-based PID controller and a commercial PA imaging system.

SIGNIFICANCE

The monitoring and control of the temperature in thermal-based therapies are important for assuring a prescribed temperature to the target tissue while minimizing the temperature of the surrounding healthy tissue. This easily implemented non-invasive control system will facilitate the realization of a broad range of hyperthermia treatments.

Nonlinear mechanisms in photoacoustics-Powerful tools in photoacoustic imaging

Many nonlinear effects have been discovered and developed in photoacoustic imaging. These nonlinear mechanisms have been explored for different utilizations, such as enhancing imaging contrast, measuring tissue temperature, achieving super-resolution imaging, enabling functional imaging, and extracting important physical parameters. This review aims to introduce different nonlinear mechanisms in photoacoustics, underline the fundamental principles, highlight their representative applications, and outline the occurrence conditions and applicable range of each nonlinear mechanism. Furthermore, this review thoroughly discusses the nonlinearity rule concerning how the mathematical structure of the nonlinear dependence is correlated to its practical applications. This summarization is useful for identifying and guiding the potential applications of nonlinearity based on their mathematical expressions, and is helpful for new nonlinear mechanism discovery or implementation in the future, which facilitates further breakthroughs in nonlinear photoacoustics.

Near-infrared laser-triggered drug release in a tellurium nanosystem for simultaneous chemo-photothermal cancer therapy

Tumor cells can be selectively killed by heat application based on the different tolerances of normal cells and tumor cells to temperature. However, the limited clinical application of photothermal therapy (PTT) is mainly due to various practical implementation difficulties, of which the most important is how to fully heat the tumor. The combination of PTT and chemotherapy can synergistically enhance cell membrane permeability and reduce the dose of chemotherapy drugs to not only effectively kill the tumor but also reduce the damage to normal tissues. It is of great significance to develop materials that can be simultaneously used for tumor PTT and chemotherapy. Therefore, in this study, a functionalized tellurium (Te) nanosystem (DOX/PEI@TeNPs) was prepared to achieve chemo-photothermal cancer combination therapy. Our research showed that the DOX/PEI@TeNP morphology was controllable, and it had good photothermal conversion efficiency and light stability. Moreover, DOX/PEI@TeNPs containing doxorubicin (DOX) showed almost no drug release in normal tissues and neutral-pH environments, while in tumor cells and tissues, it massively released DOX to kill cancer cells. The as-synthesized DOX/PEI@TeNP system can produce reactive oxygen species (ROS) under near-infrared (NIR) light irradiation and features a high photothermal conversion efficiency due to its strong NIR absorbance. Therefore, this study provides an effective strategy for the effective design of nano-drugs, which can be used for the accurate chemical-photothermal synergistic therapy of tumors.

Adjustable Handheld Probe Design for Photoacoustic Imaging:Experimental Validation

Photoacoustic (PA) imaging is an emerging imaging technique that combines light illumination and ultrasound detection. Conventional design of PA probe usually combines light and sound in a straightforward way without adjustable capability. In this paper, we propose a new PA imaging system based on light-adjustable handheld probe. The proposed PA imaging system includes a control unit that can adaptively find the light illumination pattern for the PA signal generation with optimized signal-to-noise ratio (SNR). Compared with traditional design of PA probe, our proposed apparatus enables the following advantages: (1) The system can automatically find the specific position parameters of the illumination scheme, and obtain the PA signal with optimized SNR by implementing a scanning process. (2) The proposed apparatus can be fully automatic and adaptive by electronic control. By scanning the sample, it can automatically obtain the optimized light exposure position. (3) Spot size and distance are adjustable. Both simulation and experimental results demonstrate the feasibility of the proposed system to have great potential in biomedical imaging with versatile configurations.

Adjustable Handheld Probe Design for Photoacoustic Imaging: Mathematical Modelling and Simulation Study

Photoacoustic imaging is an emerging imaging technique that combines light illumination and ultrasound detection. Conventional design of photoacoustic probe usually combines light and sound in a straightforward way without any adjustable capability. In this paper, we propose a new photoacoustic imaging system based on light-adjustable handheld probe. Compared with traditional design of photoacoustic probe, our proposed apparatus has the following advantages: (1) Spot size and distance are adjustable. By tuning parameters, it can achieve bright-field, dark-field, and mixed-field light illumination schemes. (2) Different excitation modes can be selected as needed. Monte Carlo simulation results show that distinct light fields have different excitation advantages for optimizing photoacoustic generation. Both simulation and experimental testing results demonstrate the proposed system to have great potential in biomedical imaging with versatile configurations.

Photoacoustic temperature imaging based on multi-wavelength excitation

Building further upon the high spatial resolution offered by ultrasonic imaging and the high optical contrast yielded by laser excitation of photoacoustic imaging, and exploiting the temperature dependence of photoacoustic signal amplitudes, this paper addresses the question whether the rich information given by multispectral optoacoustic tomography (MSOT) allows to obtain 3D temperature images. Numerical simulations and experimental results are reported on agarose phantoms containing gold nanoparticles and the effects of shadowing, reconstruction flaws, etc. on the accuracy are determined.

Pattern-learning-based Noise Elimination Algorithm in Photoacoustic Sensing and Imaging

As one of the fastest-growing imaging modalities in recent years, photoacoustic (PA) imaging has attracted tremendous research interest for various applications including anatomical, functional and molecular imaging. However, the PA signal's amplitude is usually quite weak and can be easily distorted by instrumental noise and interference, which can severely degrade the image quality. To improve the PA signal's signal-to-noise ratio efficiently, this paper introduces a pattern-learning based PA (PLPA) detection method to eliminate the periodically interference noise for PA sensing and imaging. Both simulation and experimental results are demonstrated to prove the validity of the proposed algorithm.

Review of Low-Cost Photoacoustic Sensing and Imaging Based on Laser Diode and Light-Emitting Diode

Photoacoustic tomography (PAT), a promising medical imaging method that combines optical and ultrasound techniques, has been developing for decades mostly in preclinical application. A recent trend is to utilize the economical laser source to develop a low-cost sensing and imaging system, which aims at an affordable solution in clinical application. These low-cost laser sources have different modulation modes such as pulsed modulation, continuous modulation and coded modulation to generate different profiles of PA signals in photoacoustic (PA) imaging. In this paper, we review the recent development of the photoacoustic sensing and imaging based on the economical laser sources such as laser diode (LD) and light-emitting diode (LED) in different kinds of modulation types, and discuss several representative methods to improve the performance of such imaging systems based on low-cost laser sources. Finally, some perspectives regarding the future development of portable PAT systems are discussed, followed by the conclusion.

Phase-domain photoacoustics eliminating acoustic detection variations

As one of the fastest-growing imaging modalities in recent years, photoacoustic imaging has attracted tremendous research interest for various applications including anatomical, functional and molecular imaging. Majority of the photoacoustic imaging systems are based on time-domain pulsed photoacoustic method, which utilizes pulsed laser source to induce wideband photoacoustic signal revealing optical absorption contrast. An alternative way is frequency-domain photoacoustic method utilizing chirping modulation of laser intensity to achieve lower system cost. In this paper, we report another way of photoacoustic method, called phase-domain photoacoustic sensing, which explores the phase difference between two consequent intensity-modulated laser pulses induced photoacoustic measurements to reveal the optical property. The basic principle is introduced, modelled and experimentally validated in this paper, which opens another potential pathway to perform photoacoustic sensing and imaging eliminating acoustic detection variations beyond the conventional time-domain and frequency-domain photoacoustic methods.

Photoacoustic-imaging-based temperature monitoring for high-intensity focused ultrasound therapy

Temperature monitoring during high-intensity focused ultrasound (HIFU) application is necessary to ensure effective therapy while minimizing thermal damage to adjacent tissue. In this study, we demonstrate a noninvasive approach for temperature measurement during HIFU therapy based on photoacoustic imaging (PAI). Because of the dependence of photoacoustic (PA) signal amplitude on temperature of the source tissue and the linearity of the PAI system, changes in temperature will cause changes in PA image intensity. Experiments have been conducted in ex-vivo bovine tissue to characterize the linear dependence of PA image pixel values on temperature and subsequently to convert the PA image to a real-time temperature map.

Single laser pulse generates dual photoacoustic signals for differential contrast photoacoustic imaging

Photoacoustic sensing and imaging techniques have been studied widely to explore optical absorption contrast based on nanosecond laser illumination. In this paper, we report a long laser pulse induced dual photoacoustic (LDPA) nonlinear effect, which originates from unsatisfied stress and thermal confinements. Being different from conventional short laser pulse illumination, the proposed method utilizes a long square-profile laser pulse to induce dual photoacoustic signals. Without satisfying the stress confinement, the dual photoacoustic signals are generated following the positive and negative edges of the long laser pulse. More interestingly, the first expansion-induced photoacoustic signal exhibits positive waveform due to the initial sharp rising of temperature. On the contrary, the second contraction-induced photoacoustic signal exhibits exactly negative waveform due to the falling of temperature, as well as pulse-width-dependent signal amplitude. An analytical model is derived to describe the generation of the dual photoacoustic pulses, incorporating Gruneisen saturation and thermal diffusion effect, which is experimentally proved. Lastly, an alternate of LDPA technique using quasi-CW laser excitation is also introduced and demonstrated for both super-contrast in vitro and in vivo imaging. Compared with existing nonlinear PA techniques, the proposed LDPA nonlinear effect could enable a much broader range of potential applications.

Self temperature regulation of photothermal therapy by laser-shared photoacoustic feedback

This article describes a laser-shared photothermal system that achieves tight temperature regulation by frequency-domain photoacoustic (FD-PA) feedback. To this end, a continuous-wave laser system was designed with arbitrarily modulatable laser intensity. And, by fast alternating in the time domain between a constant laser intensity for photothermal heating and a modulated laser intensity for FD-PA temperature measurement, photothermal temperature variations are captured by FD-PA in real time. A proportional-integral-derivative (PID) controller monitors the feedback from FD-PA measurements and controls photothermal heating dose accordingly, thus stabilizing the temperature at preset values. The proposed system is demonstrated to achieve ultrafast temperature measurement at a 4 kHz rate, and with proper averaging, the measurement and regulation accuracy are 0.75 deg and 0.9 deg respectively.