【正文】 moglobin. It has emerged as the method of choice for functional brain imaging because the scans can be made rapidly (50 sec), have good spatial resolution (3 mm3), and are pletely noninvasive. 。 CT的特點在于它能區(qū)別差異極小的 X光吸收值。 Wilhelm Roentgen 倫琴 (18451923) was the first to use Xray in medicine in 1895 to see inside the body. The ray was called Xray because no one knew what they were. This extremely short wave electromagic radiation moves through the body exposing a photographic plate to form a radiograph. Bones and radiopaque(輻射透不過的） dyes absorb the rays and create underexposed areas that appear white on the photographic film. ? Xrays have been in mon use for many years and have numerous applications. Almost everyone has had a radiograph taken, either to visualize a broken bone or to check for a cavity in a tooth. ? A major limitation of radiographs, is that they give only a flat, two dimensional(2D) image of the body, which is a threedimensional(3D) structure. 正常胸部 X光片 Ultrasound Ultrasound is the second oldest imaging technique. It was first developed in the early 1950s as an extension of World War II sonar technology and uses high frequency sound waves. The sound waves are emitted from a transmitterreceiver placed on the skin over the area to be scanned. The sound waves strike internal ans and bounce back to the receiver on the skin. Even though the basic technology is fairly old, the most important advance in the field occurred only after it became possible to analyze the reflect sound wave by puter. ? One of the more recent advances in ultrasound technology is the ability of more powerful puters to analyze change in positions through time and to display those changes as “real time ” movements. ? Ultrasound is monly used to evaluate the condition of the fetus during the pregnancy. Computed tomography(CT) Computed tomography, or CT, was developed by Godfrey Hounsfield and Allan Cormack, who shared the Nobel Prize in 1979. The goal of CT is to generate an image of a slice of brain. (the word tomography is derived from the Greek word for “cut”) To acplish this, an Xray source is rotated around the head within the plane of the desired cross section. On the other side of the head, in the trajectory (軌道 ) of the Xray beam, are sensitive electronic sensors of Xirradiation. The information about the relative radiopacity obtained with different viewing angles is fed to a puter that executes a mathematical algorithm (運算 ) on the data. The end result is a digital reconstruction of the position and amount of radiopaque material within the plane of the slice. ? CT的特點是操作簡便，對病人來說無痛苦，其密度分辯率高，可直接顯示 X線平片無法顯示的器官和病變，它在發(fā)現(xiàn)病變、確定病變的位置、大小、數(shù)目方面非常敏感而可靠，而在病理性質(zhì)的診斷上存在一定的限制。影像技術(shù)可以使醫(yī)生不需要打開病人的身體就能以高清晰度觀察到人體內(nèi)部。 第三節(jié) 醫(yī)學(xué)影像技術(shù)簡介 ? 醫(yī)學(xué)（解剖）影像技術(shù)極大地促進了醫(yī)學(xué)的發(fā)展。 髓鞘是由神經(jīng)膜細胞的細胞膜反復(fù)包卷軸突形成的。軸突的側(cè)支均從郎飛氏節(jié)發(fā)出。根據(jù)有無髓鞘可分為有纖維和無髓纖維兩種 有髓神經(jīng)纖維 無髓神經(jīng)纖維 有髓神經(jīng)纖維 有神經(jīng)纖維是由神經(jīng)元的軸突和包裹其周圍的髓鞘和神經(jīng)膜構(gòu)成。手術(shù)治療的原則是在保存神經(jīng)功能的前提下盡可能切除腫瘤。膠質(zhì)瘤的部位與年齡也有一定關(guān)系，如大腦星形細胞瘤和膠質(zhì)母細胞瘤多見于成人，小腦膠質(zhì)瘤（星形細胞瘤、髓母細胞瘤、室管膜瘤）多見于兒童。 相關(guān)鏈接－－神經(jīng)膠質(zhì)細胞瘤 膠質(zhì)瘤以男性較多見，特別在多形性膠質(zhì)母細胞瘤、髓母細胞瘤，男性明顯多于女性。神經(jīng)外胚層發(fā)生的腫瘤有兩類，一類由間質(zhì)細胞形成，稱為膠質(zhì)瘤；另一類由實質(zhì)細胞形成，稱神經(jīng)元腫瘤。 根據(jù)神經(jīng)膠質(zhì)細胞的形態(tài)和功能可分為：星形細胞、少突膠質(zhì)細胞、小膠質(zhì)細胞、施旺氏細胞。分布于神經(jīng)元周圍和血管周圍，交織成網(wǎng)，構(gòu)成神經(jīng)組織的網(wǎng)狀支架。 軸突長短不一，短者僅數(shù)微米，長者可達 1米以上。 2. 突起 樹突 分支多，呈樹枝狀愈向外周分枝愈細。核大而圓，多位于細胞中央。樹突和胞體接受其它神經(jīng)元，通過軸突將信號傳至另一與之相聯(lián)系的神經(jīng)元。 ? 神經(jīng)膠質(zhì)細胞不參與神經(jīng)沖動的傳導(dǎo)，但對神經(jīng)元起營養(yǎng)和支持的作用，并參與髓鞘的形成。 （四）神經(jīng)組織（ nerve tissue) ? 神經(jīng)組織是神經(jīng)系統(tǒng)的主要組成成分，由神經(jīng)細胞和神經(jīng)膠質(zhì)細胞組成。 ? 平滑肌纖維呈梭形，無橫紋，長約 20 ~ 200?m，直徑 2 ~ 20 ?m。 （三）平滑肌 ? 平滑肌主要由平滑肌纖維組成，分布于胃腸道、子宮、輸尿管和血管壁等處。它有利于化學(xué)物質(zhì)的傳遞和電沖動的快速傳導(dǎo)，使心肌成為一個功能性的整體。細胞核位于細胞中央。 ? 根據(jù)結(jié)構(gòu)和功能肌肉組織可分為骨骼肌、心肌和平滑肌三種 （一）骨骼肌 屬于橫紋肌，骨骼肌纖維是細長圓柱狀多核細胞，長度變化范圍很大，如鐙骨肌纖維長度為 1mm，縫匠肌纖維為 125mm，而臀大肌為400mm。肌細胞之間有少量的結(jié)締組織、血管和神經(jīng)纖維等。 細胞有 骨原細胞、成骨細胞、