In this study, temperature distribution inside a tissue - mimicking material induced by a HIFU (High Intensity Focused Ultrasound) transducer was investigated with two different methods. In first method T-type thermocouple (TC) temperature sensors and in second method, infrared (IR) camera system was used for determining the temperature distribution on the tissue-mimicking material (TMM). Temperature increase and distribution in the TMM have been characterized during the ultrasonic power application. Temperature measurements were actualized inside a TMM which has characteristics very similar to human liver tissue. Temperature rise has been characterized for different input ultrasonic powers and durations. Two different temperature measuring tools were compared and consistency between these methods was presented.

Every year, millions of people are subjected to cancer around the world and more than half of the patients die from it. In almost all countries, cancer ranks among the most common cause of death. As elderly people are most susceptible to cancer and population aging continues in many countries, cancer will remain a major health problem around the globe [1]. An important approach in the fight against cancer is the discovery of novel techniques for diagnosis and treatment [2]-[5]. Accurate diagnosis and treatment methods will empower the therapy for patient care. High intensity focused ultrasound (HIFU) is a novel technique in cancer treatment. An HIFU transducer coupled to an electronic supply system generates high frequency sound waves and delivers a strong beam to a specific part of cancer tissue [6], [7]. Some cells die when the high intensity ultrasound beam is focused directly onto them. This type of treatment uses only sound waves to kill the cancer cells and it does not result in significant side effects as observed with other types of cancer treatment techniques such as ionizing radiation. Other heating techniques such as laser or microwave therapy have some disadvantages compared to the HIFU technique. When a laser is directed to tissue, it effectively burns throughout its path, and microwaves are harmful for the human body. The basic principle of focused ultrasound is analogous to using a magnifying glass to focus sunlight. Focusing the ultrasound beam generates enough heat for burning. Focusing can be done geometrically, for example with a lens or with a spherically curved transducer, or electronically, by adjusting the relative phases of elements in an array of transducers. Ultrasound beams pass through tissue with no effect except at the focal point where the beams converge, where they produce high energy as seen in Fig. 1. The energy can have both thermal and mechanical effects. HIFU is currently used in treatment in certain situations for some types of cancers such as prostate, kidney, or liver cancers. The HIFU technique in cancer treatment can be used individually or with other techniques like ionizing radiation. As this treatment results in critical necrosis in the part of tissue, it must be well investigated by using sophisticated systems in light of available metrological tools.

Realization of temperature characterization on focused ultrasound treatment devices by using tissue-mimicking phantom systems (Tissue-Mimicking Material, TMM) is indispensible in pre-clinical studies. In this survey, in order to examine the viscous heating effect of thermocouples, temperature rise due to excitation of a HIFU transducer has been measured by using two different types of T-type thermocouples embedded inside the TMM. In order to obtain the temperature values from the thermocouples more effectively, a PC-based multi-channel data acquisition and monitoring interface were developed by using LabVIEW graphical development platform. Measurements were carried out inside a TMM which has characteristics like human liver tissue. Temperature rise has been characterized for the different input ultrasonic powers (25 W, 38 W and 50 W) and frequencies (1,1 MHz and 3.3 MHz) and the time intervals applied (1 s, 2 s and 3 s). The temperature values obtained from two different types of T-type thermocouple were compared to each other and discrepancies between these two different thermocouple measurements were shown with the study.

The heating effect produced by a focused ultrasound transducer has been investigated by using visual techniques with a positioning system. Ultrasound power, distance, frequency and harmonics of heating effect was investigated. Three experiments were performed on TMM (Tissue Mimicking Material), sheep liver and sheep lung. HIFU (High Intensity Focused Ultrasound) transducer with a resonance frequency of 1.1 MHz and 3.3 MHz was used as source. Effect of ultrasound in liver and lung's pieces were displayed and dimension of cauterization has been measured. Previous temperature measurement results for TMM were compared with liver and lung measurement results so that it is possible to transfer the laboratory measurements to the clinical studies. All measurements were carried out in the system at TÜBİTAK UME (The Scientific and Technological Research Council of Turkey, the National Metrology Institute) Ultrasound laboratory.