本文關(guān)鍵詞： 高強(qiáng)度聚焦超聲 層狀組織 熱損傷 頻率選擇　出處：《重慶醫(yī)科大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：高強(qiáng)度聚焦超聲(High Intensity Focused Ultrasound, HIFU)是一種非侵入式的新型治療技術(shù),目前己應(yīng)用于多種腫瘤以及非腫瘤疾病的治療。HIFU治療依賴于組織對(duì)超聲能量的吸收,但更大的組織聲吸收也意味著更快的衰減和有限的組織穿透距離。因此,在臨床治療深部的腫瘤時(shí),選擇合適的超聲頻率以平衡組織熱吸收效率和超聲穿透距離這兩個(gè)因素,從而達(dá)到最大的組織熱損傷是一個(gè)非常重要的問(wèn)題。本文基于KZK方程和分層介質(zhì)模型計(jì)算了超聲在層狀生物組織中的非線性傳播,利用HIFU換能器聲場(chǎng)掃描實(shí)驗(yàn)來(lái)驗(yàn)證計(jì)算結(jié)果。基于Pennes生物熱傳導(dǎo)方程求解了組織中的溫度分布,并考慮組織聲速和衰減系數(shù)隨溫度的變化；利用等效熱劑量模型計(jì)算組織中的熱劑量,并選擇30EM作為產(chǎn)生熱損傷的閾值。利用HIFU輻照離體牛肝組織形成凝固性壞死的實(shí)驗(yàn)來(lái)驗(yàn)證數(shù)值計(jì)算熱損傷范圍的方法。本文計(jì)算模型中使用開(kāi)口外徑22 cm內(nèi)徑8 cm焦距16 cm的球殼式自聚焦換能器,在聲輸出總功率為400 W條件下,聲束透過(guò)皮膚、脂肪、肌肉三層組織后聚焦于靶區(qū)肝組織中。選取了不同的靶區(qū)深度即焦點(diǎn)到皮膚表面深度(5,7,10,15 cm),不同的超聲頻率(0.4,0.6,0.8,1.0,1.2,1.4,1.6MHz),計(jì)算了每個(gè)靶區(qū)深度條件下不同的超聲頻率對(duì)于焦域尺寸、最大聲強(qiáng)、最大熱吸收率和損傷體積的影響,分析了這些量隨頻率變化的原因。同時(shí)還計(jì)算了焦點(diǎn)處諧波滋生系數(shù)和機(jī)械指數(shù)隨頻率的變化,分析了機(jī)械效應(yīng)對(duì)于組織損傷的影響。聲場(chǎng)掃描實(shí)驗(yàn)結(jié)果與仿真計(jì)算結(jié)果吻合較好；離體牛肝實(shí)驗(yàn)中,在靶區(qū)聲強(qiáng)較低的情況下,實(shí)驗(yàn)結(jié)果與仿真計(jì)算吻合較好,在靶區(qū)聲強(qiáng)較高的情況下,實(shí)驗(yàn)結(jié)果大于仿真計(jì)算,這是由于本文仿真計(jì)算模型未考慮空化和微泡對(duì)于組織機(jī)械及熱損傷的貢獻(xiàn)。對(duì)于同一靶區(qū)深度,隨著超聲頻率的增加,焦域-6dB尺寸劇烈減�。粚�(duì)于同一超聲頻率,隨著靶區(qū)深度的增加,焦域-6dB尺寸幾乎不變。隨著超聲頻率的增加,焦域處最大聲強(qiáng)、最大熱吸收率、損傷體積均出現(xiàn)了先增大后減小；對(duì)于不同靶區(qū)深度,達(dá)到各個(gè)量最大值的最優(yōu)頻率均不一樣。在不同靶區(qū)深度(5,7,10,15 cm)達(dá)到最大的熱吸收的最佳頻率分別為1.5 MHz、1.3 MHz.1.1 MHz和0.9MHz,達(dá)到最大損傷體積的最佳頻率分別為0.8 MHz、0.7 MHz.0.7 MHz和0.6 MHz。隨著超聲頻率的增加,諧波滋生系數(shù)先增大后減小,在某一頻率取得最大值；機(jī)械指數(shù)線性下降,發(fā)生空化的幾率減小。綜合考慮靶區(qū)組織的熱吸收效率、組織熱損傷體積和機(jī)械指數(shù)等因素,在治療深部腫瘤時(shí),需要選擇較低的超聲頻率,以獲得較大的熱損傷和機(jī)械作用,且這個(gè)超聲頻率可以使用仿真模型計(jì)算得到。
[Abstract]:High intensity focused ultrasound (HIFU) is a new non-invasive treatment technique. At present, HIFU has been used in the treatment of various tumor and non-tumor diseases. HIFU therapy depends on the absorption of ultrasonic energy by tissues. But greater tissue acoustic absorption also means faster attenuation and limited tissue penetration. Therefore, in clinical treatment of deep tumors. The appropriate ultrasonic frequency was chosen to balance the heat absorption efficiency of tissue and the ultrasonic penetration distance. In this paper, the nonlinear propagation of ultrasound in layered biological tissue is calculated based on KZK equation and layered medium model. The HIFU transducer acoustic field scanning experiment is used to verify the calculation results. The temperature distribution in the tissue is solved based on the Pennes biological heat conduction equation, and the variation of the tissue sound velocity and attenuation coefficient with the temperature is considered. The equivalent heat dose model was used to calculate the heat dose in the tissue. 30EM was chosen as the threshold to produce thermal damage. The method of numerical calculation of thermal damage range was verified by using HIFU irradiation in vitro bovine liver tissue to form coagulant necrosis. In this paper, the open end was used in the calculation model. Diameter 22. A spherical shell type self-focusing transducer with an internal diameter of 8 cm and a focal length of 16 cm. When the total power of sound output is 400 W, the sound beam passes through the skin, fat and muscle and then focuses on the liver tissue of the target area. The different target depth, that is, the focal point to the skin surface depth, is selected. 10 ~ 15 cm ~ (-1), with different ultrasonic frequencies of 0.4 ~ (0.6) ~ 0.81.0 ~ 1.2m ~ (1. 4) ~ (1.6) MHz). The effects of different ultrasonic frequencies on focal area size, maximum sound intensity, maximum heat absorption rate and damage volume of each target were calculated. The reasons for the variation of these quantities with frequency are analyzed, and the variation of harmonic breeding coefficient and mechanical index with frequency are also calculated. The effect of mechanical effect on tissue damage is analyzed. In the isolated bovine liver experiment, the experimental results are in good agreement with the simulation under the condition of low sound intensity in the target area, and the experimental results are larger than the simulation calculation in the case of higher sound intensity in the target area. This is due to the fact that the contribution of cavitation and microbubbles to the mechanical and thermal damage is not taken into account in this simulation model. For the same target depth, the focal region -6dB size decreases dramatically with the increase of ultrasonic frequency. For the same ultrasonic frequency, with the increase of the depth of the target area, the focal region -6dB size is almost unchanged. With the increase of the ultrasonic frequency, the maximum sound intensity and the maximum heat absorption rate are obtained at the focal region. The damage volume increased first and then decreased. For different target depth, the optimal frequency of reaching the maximum value of each quantity is different. The optimum frequency of thermal absorption is 1. 5 MHz and 1. 3 MHz.1.1 MHz, respectively. The optimum frequencies to reach the maximum damage volume were 0. 8 MHz 0. 7 MHz.0.7 MHz and 0. 6 MHz, respectively, with the increase of ultrasonic frequency. The harmonic breeding coefficient first increases and then decreases, and reaches the maximum value at a certain frequency. The mechanical index decreases linearly, and the probability of cavitation decreases. Considering the heat absorption efficiency of target tissue, tissue thermal damage volume and mechanical index, etc., in the treatment of deep tumor. It is necessary to select a lower ultrasonic frequency to obtain larger thermal damage and mechanical action, and this ultrasonic frequency can be calculated by using the simulation model.
【學(xué)位授予單位】：重慶醫(yī)科大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：R454.3

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1 李興;頻率對(duì)高強(qiáng)度聚焦超聲在層狀生物組織中形成損傷的影響研究[D];重慶醫(yī)科大學(xué);2015年

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