【摘要】：磁共振圖像引導(dǎo)高強度聚焦超聲的無創(chuàng)熱療方法是腫瘤治療的一種重要手段。在熱療過程中,磁共振儀的作用是提供目標(biāo)組織斷層圖像和靶區(qū)空間溫度圖像,以引導(dǎo)聚焦超聲焦點移動和監(jiān)控靶區(qū)體素?zé)釀┝�。目前磁共振技術(shù)能夠提供良好的人體組織斷層圖像;但在測溫準(zhǔn)確性與時空分辨率方面,磁共振空間溫度定量測量技術(shù)尚未達到熱療關(guān)于溫度監(jiān)控的臨床要求。在各種磁共振測溫方法中,質(zhì)子共振頻率(PRF)法應(yīng)用最為廣泛;然而,該方法在實際應(yīng)用中易受磁共振儀主磁場漂移、被測體運動及脂類質(zhì)子的影響而導(dǎo)致測溫不準(zhǔn)確。本文提出一種基于水脂分離自參考相位差的PRF測溫模型,以解決上述PRF法的測溫問題。通過分析被測體空間溫度信息的磁共振獲取技術(shù),掌握質(zhì)子共振頻率測溫方法并對該方法作具體的測溫因子分析。針對主磁場漂移以及被測體幀間運動導(dǎo)致的測溫誤差,建立自參考相位差測溫模型予以校正。該模型考慮主磁場即時強度變化和幀間運動的影響,將實時幀圖像中未加熱區(qū)域的體素相位作為參考相位,并以此生成擬合平面作為靶區(qū)PRF相位相減測溫法的計算參考相位,該計算參考相位只與實時幀信息相關(guān)而消除幀間運動和磁場變化等時變干擾因素的影響。針對自參考相位差測溫模型因脂類質(zhì)子溫度不敏感所帶來的測溫誤差,擬對所獲體素信號進行水脂分離以獲取與溫度具有線性關(guān)系的水質(zhì)子相位。模型獲得的水質(zhì)子相位包括參考區(qū)及靶區(qū)水質(zhì)子相位,參考區(qū)水質(zhì)子相位用于擬合靶區(qū)溫度計算的最后參考相位,靶區(qū)水質(zhì)子相位用于和最后參考相位作差得到模型相位差值。為節(jié)約模型的數(shù)據(jù)采集和參數(shù)計算時間,提出根據(jù)參考區(qū)相位變化的閾值判據(jù)作斷續(xù)水脂分離,擬提出理想模型下的矢量運算計算兩次水脂分離間各幀圖像各體素點的水質(zhì)子相位,所得水相位將被用于各幀圖像的自參考相位差模型測溫。針對MR測溫數(shù)據(jù)復(fù)數(shù)三角運算導(dǎo)致相位的2π截斷現(xiàn)象即相位纏繞問題,將測溫過程由檢測相位復(fù)現(xiàn)出真實相位的相位解纏繞,分解為空間域和時域上的相位求真解問題。提出基于馬爾可夫隨機場最大后驗的相位解纏繞算法用于空間域的靜態(tài)相位求解,與基于溫度-相位關(guān)系的先驗?zāi)Ｐ陀糜跁r域相位的解算。為評估新模型的測溫效果,使用Bstar 150T超導(dǎo)磁共振儀對不同水脂比仿體進行測溫實驗,并將測溫結(jié)果與光纖測溫結(jié)果相比對。實驗結(jié)果顯示,新模型對于水脂比為5:5的測試體的測溫結(jié)果與光纖測溫結(jié)果的最大差值為1.12℃,且測溫過程無溫度奇異點,說明相位解纏繞有效。本研究工作為磁共振儀進一步應(yīng)用于臨床熱療作了前期技術(shù)準(zhǔn)備。
[Abstract]:Noninvasive hyperthermia guided by high intensity focused ultrasound (HIFU) is an important method for tumor treatment. In the process of hyperthermia, the purpose of Mr is to provide the target tissue tomograph and target spatial temperature image to guide the focus of focused ultrasound and monitor the thermal dose of voxel in the target area. At present, magnetic resonance technology can provide good image of human tissue, but in terms of temperature measurement accuracy and space-time resolution, magnetic resonance spatial temperature quantitative measurement technology has not met the clinical requirements of hyperthermia temperature monitoring. The proton resonance frequency (PRF) method is the most widely used in all kinds of magnetic resonance temperature measurement methods, however, it is easy to be affected by the drift of the main magnetic field of the magnetic resonance instrument and the influence of the body motion and the lipid proton in the practical application, which leads to the inaccuracy of the temperature measurement. In this paper, a PRF temperature measurement model based on the self-reference phase difference of water-lipid separation is proposed to solve the temperature measurement problem of the PRF method mentioned above. The method of proton resonance frequency temperature measurement is grasped by magnetic resonance (Mr) acquisition technique of the temperature information of the body measured in space, and the temperature factor of the method is analyzed in detail. In view of the temperature measurement error caused by the drift of the main magnetic field and the motion of the measured body between frames, the self-reference phase difference temperature measurement model is established to correct the temperature measurement. The model takes into account the influence of real time intensity change of the main magnetic field and the motion between frames. The voxel phase of the unheated region in the real time frame image is taken as the reference phase, and the fitting plane is used as the target PRF phase subtraction method to calculate the reference phase. The reference phase is only correlated with the real-time frame information and eliminates the influence of time-varying interference factors such as inter-frame motion and magnetic field change. In view of the temperature measurement error caused by the temperature insensitivity of lipid protons in the self-reference phase difference temperature measurement model, the obtained voxel signal is proposed to be separated from water and lipid to obtain the sub-phase of water quality which has a linear relationship with temperature. The water quality sub-phase obtained by the model includes the reference area and the target water quality sub-phase, the reference water quality sub-phase is used to fit the final reference phase of the temperature calculation of the target area, and the model phase difference value is obtained by the difference between the target water quality sub-phase and the final reference phase. In order to save the time of data acquisition and parameter calculation of the model, the threshold criterion of phase change in the reference region is proposed to separate water and lipid intermittently. In this paper, a vector operation based on ideal model is proposed to calculate the water quality sub-phase of each voxel point of each frame image between two water and lipid separations. The resulting water phase will be used to measure the temperature of each frame image using the self-reference phase difference model. Aiming at the phenomenon of 2 蟺 truncation of phase caused by complex triangulation of MR temperature measurement data, namely phase winding problem, the phase unwinding of the real phase is repeated from the detection phase, which is decomposed into the phase truth-seeking problem in spatial domain and time domain. A phase unwinding algorithm based on the maximum a posteriori of Markov random field is proposed to solve the static phase in spatial domain and a prior model based on temperature-phase relation to solve the phase in time domain. In order to evaluate the effect of the new model, the Bstar 150T superconducting magnetic resonance instrument was used to measure the temperature of different water-lipids, and the results were compared with those of optical fiber. The experimental results show that the maximum difference between the temperature measurement results of the new model and the optical fiber temperature measurement results is 1.12 鈩，

本文編號：2393579