mri技術(shù)ppt課件(已修改)
2025-05-10 22:07 本頁(yè)面
【正文】 Imaging Techniques of Application 回顧 ? 核磁共振成像方法 人體中三分之二是水。水分子由兩個(gè)氫原子和一個(gè)氧原子組成。氫原子的核子，即質(zhì)子，可以比做一個(gè)磁性陀螺儀。磁共振系統(tǒng)就是利用這種物理特性制成的。在一個(gè)強(qiáng)磁場(chǎng)中 ——通常比地球磁場(chǎng)強(qiáng) 30,000倍，任意旋轉(zhuǎn)的質(zhì)子通常順著磁場(chǎng)方向平行排列或反磁場(chǎng)方面平行排列。根據(jù)磁場(chǎng)的強(qiáng)度，所有的質(zhì)子擺成一行，這就產(chǎn)生了一個(gè)可以測(cè)量的磁矩。 ? 排列的質(zhì)子在電磁頻率的干擾下，隊(duì)列會(huì)發(fā)生變化。磁矩開(kāi)始在磁場(chǎng)的場(chǎng)線附近旋轉(zhuǎn)。當(dāng)電磁干擾結(jié)束的時(shí)候，質(zhì)子釋放從磁場(chǎng)獲得的能量，這些能量被線圈接收。越多核子按同一方面排列，說(shuō)明信號(hào)強(qiáng)度越高，磁場(chǎng)強(qiáng)度也越大。通過(guò)從空間上改變磁場(chǎng)，人們可以確定磁共振信號(hào)的發(fā)源點(diǎn)，從而利用計(jì)算機(jī)程序重建圖像，這種方法類似于 CT成像。磁共振圖像的對(duì)比度依賴于人體器官中水的空間分布。人體在放松休息的時(shí)候，就等同于電磁頻率被切斷而進(jìn)行圖像重建的時(shí)刻。 MRI技術(shù)應(yīng)用 MR Subsystems ? RF Coils – Body Coil – Head Coil – Surface Coils – Phased Array Coils MR Subsystems ? Five Types – RF – Gradient – Shimming – Mag – Computer MR Subsystems ? Body Coil – large cylinder (volume coil) sending RF pulses into the patient that provide ―flip‖ for protons – also can be used as a receiver for large FOV scans (abdominal, full spine, etc) MR Subsystems ? Head Coil – smaller cylinder – usually volume coil ? with quadrature or phased array design – many different designs exist ? high field ? low field Quadrature Head Low field Head Head amp。 Neck Phased Array MR Subsystems ? Surface Coils – specialized coils, varying in size – receive signal from localized regions and have higher SNR – quadrature or linear design Extremity amp。 Breast TMJ amp。 Neck MR Subsystems ? Phased Array Coils – allow large FOV scanning – providing the SNR of a surface coil – . CTL, Pelvis, TMJ, Head/Neck, etc. Head amp。 Neck Body amp。 Spine MR Subsystems ? Gradient Coils – consists of three sets of X, Y, and Z Coils – located within the mag – provides a means to spatially encode the image and locate the slice – produces small changes in the main magic field X Coils Y Coils Z Coils Summary ? Five Types – Radio Frequency – Gradient – Shimming – Mag – Computer There are three general types of MRA： ? TimeofF
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