# Numerical Study on the Application of Near-Infrared Temperature Distribution Measurement of HIFU
## 1 Introduction  
High-intensity focused ultrasound (HIFU) is an emerging tumor treatment method with the potential for a wide range of medical applications due to its non-invasive nature. In clinical practice, HIFU technology can be used in various treatment areas, including the thermal ablation of uterine fibroids [1], thrombolysis [2], drug delivery [3], and gene activation [4]. This technique utilizes the propagation of ultrasound waves within the human body to convert the mechanical energy of ultrasound into thermal energy. It rapidly elevates the temperature of targeted cells by 40-60 \({}^{\circ}\)C within a few seconds, inducing irreversible necrosis. Measuring the temperature distribution during HIFU treatment is pivotal to ensure treatment efficacy, safeguard surrounding normal tissues, and mitigate potential side effects and complications. Scholars, both domestically and internationally, have extensively researched this topic. Among these methods, thermocouples have gained widespread use due to their simplicity, cost-effectiveness, and effectiveness in measuring the transient temperature rise induced by HIFU. [PERSON] et al. studied the temperature distributiongenerated by HIFU using a T-type thermocouple. In this study, the HIFU beam was focused on an array comprising five thermocouples to mitigate errors resulting from direct exposure to the thermocouples [5]. [PERSON] et al. used a thin-film thermocouple array to measure the temperature distribution produced by high-intensity focused ultrasound and estimated the heating errors caused by thermocouples [6]. These studies offer critical insights into temperature monitoring in HIFU therapy while highlighting the limitations of the thermocouple temperature measurement method. Some of the limitations are as follows: Firstly, the insertion of thermocouples into the tissue for temperature measurement does not qualify as a non-invasive use of HIFU. Secondly, measurement errors may arise due to the inaccuracy of the positioning method; that is, the positioning of the thermocouple deviating from the location of the region of interest. Additionally, density differences between the thermocouples and surrounding tissues can lead to issues such as viscous heating artifacts (VHA) [7]. In clinical practice, in addition to thermocouples, several non-destructive temperature measurement methods are extensively utilized for HIFU temperature monitoring [8]. These methods prevent harm to the human body and offer precise and dependable temperature data. For example, [PERSON] et al. used MRI to monitor the temperature field during the ultrasound treatment of central nervous system diseases [9]. [PERSON] et al. used thermochromic films to monitor the temperature distribution on the skin surface during the HIFU treatment of skin diseases [10]. [PERSON] et al. fabricated a temperature film sensor based on flexible thin film materials with two-dimensional measurement characteristics and fast response advantages. This sensor fulfills the real-time monitoring requirements for the surface temperature of non-planar objects [11]. [PERSON] proposed a hybrid method for spatial mapping temperature estimation based on diagnostic ultrasound [12]. Near-infrared temperature measurement technology has emerged as a non-invasive, efficient, and accurate method for thermal effect research in recent years. It can monitor tissue surface temperature in real time with high temporal and spatial resolution. [PERSON] investigated the effect of HIFU on skin surface temperature using infrared thermal imaging technology with the objective of risk identification and the prevention of skin burns [13]. Using the easy visualization of thermal imaging, [PERSON] and [PERSON] utilized infrared thermal imaging to gather qualitative information on the ultrasound field, mapping the strength distribution by measuring the temperature generated by thin sheet materials [14].