本文關(guān)鍵詞： 射束硬化校正 拉東變換 校正模體 熵　出處：《沈陽工業(yè)大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：在標(biāo)準(zhǔn)的CT圖像重建過程中,被忽視的X射線多能譜特性及其對(duì)圖像重建算法的影響導(dǎo)致了重建后圖像中出現(xiàn)射束硬化偽影,其中包括杯狀偽影、條狀偽影以及退化的骨邊界偽影。這些偽影很大程度上降低了病灶的清晰度,給疾病診斷帶來了困擾。同時(shí),在CT機(jī)性能評(píng)價(jià)過程中,圖像中的射束硬化偽影會(huì)致使測(cè)量值偏離實(shí)際值,進(jìn)而影響檢測(cè)結(jié)果。本課題針對(duì)射束硬化偽影展開研究,其工作內(nèi)容包括以下三個(gè)方面:首先,針對(duì)已有水硬化預(yù)校正方法在實(shí)際工程應(yīng)用中的不靈活性,實(shí)現(xiàn)了一種以拉東變換為基礎(chǔ)的杯狀偽影后處理校正方法。使用閾值方法對(duì)水模體橫斷面CT圖像進(jìn)行分割,將分離出的水部分進(jìn)行拉東變換以獲取不同角度下的觀測(cè)信息;利用該信息進(jìn)行數(shù)學(xué)建模并與預(yù)先構(gòu)建好的無杯狀偽影模板比較,當(dāng)兩者對(duì)比結(jié)果的均方誤差達(dá)到最小時(shí),可計(jì)算出所建模型的關(guān)鍵參數(shù)。在實(shí)際應(yīng)用中,將臨床CT圖像軟組織的拉東變換結(jié)果輸入到已求解的校正模型,該模型的輸出即為杯狀偽影校正后圖像。計(jì)算機(jī)仿真結(jié)果表明,所提方法對(duì)射束硬化杯狀偽影具有較好的抑制效果且對(duì)被校正物體的大小及外形無硬性需求。其次,鑒于已有骨硬化偽影校正方法存在校正速度慢或校正過程繁瑣的缺點(diǎn),提出了一種基于校正模體的快速骨偽影校正方法。以人體頭部解剖結(jié)構(gòu)為依據(jù)構(gòu)造校正模體,將模體圖像中的高衰減物質(zhì)分割出來并通過單能正投影方法獲取相應(yīng)的投影信息;利用圖像的熵與骨硬化偽影存在程度的關(guān)系構(gòu)建數(shù)學(xué)模型并通過一系列算法確定校正系數(shù);然后平均由5臺(tái)CT機(jī)求解得到的校正系數(shù)作為一組通用的校正系數(shù)。在實(shí)際臨床應(yīng)用中,利用通用校正系數(shù)重建偽影圖像,將偽影圖像疊加在原始圖像上得到校正后的CT圖像。通過模體和臨床數(shù)據(jù)驗(yàn)證,所提骨硬化偽影校正方法具有校正效果好、校正速度快的優(yōu)點(diǎn)。所提方法對(duì)于被校正圖像的卷積核和層厚無要求,具有一定的臨床和工程實(shí)現(xiàn)價(jià)值。最后,將射束硬化校正應(yīng)用于CT性能指標(biāo)測(cè)量,研究了射束硬化效應(yīng)對(duì)醫(yī)用全身16排CT機(jī)性能測(cè)量準(zhǔn)確度的影響。實(shí)驗(yàn)結(jié)果表明,射束硬化對(duì)測(cè)量平面內(nèi)空間分辨率的影響與建像參數(shù)有關(guān),不同建像參數(shù)下的影響趨勢(shì)基本不同;在層厚測(cè)量中,射束硬化會(huì)致使測(cè)量值大于實(shí)際值;而在低對(duì)比度分辨率測(cè)量方面,射束硬化對(duì)其影響甚微。
[Abstract]:In the standard CT image reconstruction process, the neglected X-ray multispectral characteristics and its influence on the image reconstruction algorithm lead to the emergence of beam hardening artifacts, including goblet artifacts, in the reconstructed images. Strip artifacts and degenerated bone boundary artifacts. These artifacts greatly reduce the focus's clarity and cause trouble for disease diagnosis. At the same time, during the evaluation of CT performance, The beam hardening artifacts in the image will cause the measured values to deviate from the actual values, and then affect the detection results. In this paper, the beam hardening artifacts are studied. The work includes the following three aspects: first, In view of the inflexibility of existing water hardening precorrection methods in practical engineering applications, a new method of post-processing of cup pseudo-image based on Radon transform is implemented. The threshold method is used to segment the cross-sectional CT images of water motifs. The separated water part is transformed to obtain the observation information at different angles. The information is used for mathematical modeling and compared with the pre-constructed non-goblet artifact template, when the mean square error of the two comparison results reaches the minimum. The key parameters of the model can be calculated. In practical application, the results of Rato transform of soft tissue of clinical CT images are input to the corrected model, and the output of the model is the image corrected by goblet artifacts. The computer simulation results show that, The proposed method has good suppression effect on beam hardening goblet artifacts and has no rigid requirements for the size and shape of the corrected objects. Secondly, because of the shortcomings of the existing methods for correction of bone hardening artifacts, the correction speed is slow or the correction process is cumbersome. A fast bone artifact correction method based on correction motif is proposed. Based on the anatomical structure of human head, the high attenuation material in the motif image is segmented and the corresponding projection information is obtained by single energy orthographic projection. Based on the relationship between image entropy and the degree of existence of bone sclerosis artifact, a mathematical model is constructed and the correction coefficient is determined by a series of algorithms. Then the average correction coefficients obtained by 5 CT machines are taken as a set of general correction coefficients. In practical clinical applications, the artifacts are reconstructed by using the general correction coefficients. The corrected CT image was obtained by superposing the artifact image on the original image. Through the verification of the motif and clinical data, the correction method of bone sclerosis artifact was proved to be effective. The proposed method has no requirement for convolution kernel and slice thickness of corrected image, and has certain clinical and engineering value. Finally, beam hardening correction is applied to the measurement of CT performance index. The effect of beam hardening on the measurement accuracy of medical 16-slice CT machine is studied. The experimental results show that the effect of beam hardening on the spatial resolution in the measurement plane is related to the imaging parameters. In thickness measurement, beam hardening will cause the measured value to be larger than the actual value, but in low contrast resolution measurement, beam hardening has little effect on it.
【學(xué)位授予單位】：沈陽工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TP391.41

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