Ultrasound Hyperthermia for Bone Tumor Therapy

• Main Authors: Bing-Yuh Lu, 盧並裕
• Other Authors: Win-Li Lin
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/87395540575205404703

博士 === 國立臺灣大學 === 電機工程學研究所 === 88 === This study focuses on the bone tumor therapy using ultrasound hyperthermia. First, we use the simplified model to study the treatable domain of bone tumor therapy using ultrasound hyperthermia theoretically. The power deposition pattern is modeled as geometric gain with exponential attenuation. The specific absorption rate ratio (SARR) criteria in this work have been used to determine the proper heating domain of ultrasound driving frequency and therapeutic tumor diameter. It provides the information about the proper parameters of treating the bone tumor, choosing the optimal operating frequency of ultrasound transducer and the acoustic window on the skin surface if the tumor size, tumor depth, diameter of bone are known, and designing ultrasound applicator for clinical implementation. Based on the theoretical study, we employ the 2.5 MHz driving frequency ultrasound model to treat the spherical tumor of 1.5 cm diameter using the scanned focused ultrasound system (SFUS) and studies the simulation of the temperature distributions to verify the simulations by the simplified model. The diameter of bone is 3 cm, the thickness of muscle is 5 cm, and the thickness of bone cortex is 4 mm. The diameters of spherical transducers in the applicator of SFUS are all 5 cm with 10 cm radial curvature. Thereafter, we studied the feasibility of treating the tumors inside the bones using the low frequency cylindrical ultrasonic transducer. This study presents the therapeutic ultrasound power pattern simulations for the tumors inside long bone, i.e. intraosseous tumors without cortical breakthrough. We have shown that the 3-D wave equation for damped wave is a kind of Helmholtz''s equation that can be solved by the commercially available software. Therefore, such a wave equation method can be utilized to solve the reflection and refraction issues in the tissue interfaces. Compared with the traditional Rayleigh-Sommerfield diffraction integral method, the wave equation is feasible to calculate the ultrasound intensity distributions. This work sets the cylindrical transducer with 10 cm radius and 10 cm height. Considering the different parameters of bone thickness, driving frequency, muscle depth, radius, and length of tumor through scanning the low-frequency cylindrical transducer, the selected 100 kHz driving frequency transducer is applicable to treat most cases of intraosseous tumors. Finally, this work presents a sixteen-channel driving system for ultrasonic phased arrays of multiple resonant frequencies for ultrasound hyperthermia. The characteristics of the channel include 0.5-3.0 MHz bandwidth, 256 power levels, 16 phase steps, 18 watts of maximal output power, 10% power stability within 100 minutes, and 10% maximal relative phase error. The counters with the function of frequency divider and phase shifter are constructed with programming logic devices (PLDs) which can individually update the phase resolution and frequency division without any change of the system circuits. Therefore, the driving system is able to: (1) drive multi-element applicators or phased arrays of the single resonant frequency through the multi-channel linear power amplifiers, (2) concurrently drive transducers with different resonant frequencies, (3) adjust the relative phase and output power of each channel for the scanning ultrasonic focus, and (4) operate with a good output stability in each channel. Through the proper design of ultrasound applicators, this driving system can be employed in multi-element transducers for ultrasound hyperthermia as an adjuvant treatment. The phantom experiments show that the ability of the on-line control of this driving system. The heating of the bone tumor phantom using 2.11 MHz of driving frequency can avoid the overheating on the bone cortex. The experimental results agree with the theoretical study and computer simulations in Chapter 2, and 3.