Investigation of Multiple Concaved Strip-shaped Ultrasound Transducers for Liver Tumor Thermal Therapy
Date Issued
2010
Date
2010
Author(s)
Chang, Wei-Ran
Abstract
The high temperature treatment for liver tumor, such as radiofrequency(RF) ablation、laser ablation、microwave ablation, are minimally invasive surgery. The advantage of focused ultrasound for liver tumor surgery is noninvasive. However, there are some problems of clinical surgery: the narrow ultrasound window due to ribs, the motion of tumor due to breath, and the long period of surgery time.
This study used multiple concaved strip-shaped ultrasound transducers with a radius of curvature of 15 cm, arc length of 17.7 cm, and width of 1 cm to arrange the foci at the same point. The sound pressure was investigated at the depth of 3, 6, and 9 cm below the skin. In the situation of end-of-exhale and breath hold, the thermal dose accumulated to a volume of about 1cm3 ~5cm3 after five thermal ablations with shifts of the focus location.
For a target region at the depth of 9 cm, five transducers were used. To avoid the ribs from obstructing the ultrasound beam path, the transducers were placed 15o apart from each other. Thus the computer simulation didn’t considered the effect of ribs on sound pressure. The pseudo inverse method was applied to obtain complementary sound pressure patterns. These patterns was switched to ablate the target region with a frequency of 10Hz. The results showed that the thermal dose accumulated along the motion direction caused by the breath (X direction). Multiple heating with the transducers moved in the Y direction, the thermal lesion up to 1cm3 could be formed for both situations of end-of-exhale and breath hold. When the target regions were at the depth of 3 cm or 6 cm, the number of transducers reduced, so that the ribs did not block the beam path. The transducers were placed to form a focus at the desired depth. High intensity sound pressure was obtained. The pseudo inverse method was used to obtain complementary sound pressure and the thermal dose accumulated to a volume of about 5cm3 after five thermal ablations with shifts of the focus location. The simulation results, demonstrated that the thermal lesion can be accumulated at different depths from 3cm to 9cm by using appropriate number of transducers and sonication modes.
Subjects
ultrasound transducer
high temperature hyperthermia
pseudo inverse
Type
thesis
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