MRI技術應用部分(醫(yī)學院)

1、Imaging Techniques of Application回顧核磁共振成像方法 人體中三分之二是水。水分子由兩個氫原子和一個氧原子組成。氫原子的核子，即質(zhì)子，可以比做一個磁性陀螺儀。磁共振系統(tǒng)就是利用這種物理特性制成的。在一個強磁場中通常比地球磁場強30,000倍，任意旋轉(zhuǎn)的質(zhì)子通常順著磁場方向平行排列或反磁場方面平行排列。根據(jù)磁場的強度，所有的質(zhì)子擺成一行，這就產(chǎn)生了一個可以測量的磁矩。 排列的質(zhì)子在電磁頻率的干擾下，隊列會發(fā)生變化。磁矩開始在磁場的場線附近旋轉(zhuǎn)。當電磁干擾結(jié)束的時候，質(zhì)子釋放從磁場獲得的能量，這些能量被線圈接收。越多核子按同一方面排列，說明信號強度越高，磁場強度也越

2、大。通過從空間上改變磁場，人們可以確定磁共振信號的發(fā)源點，從而利用計算機程序重建圖像，這種方法類似于CT成像。磁共振圖像的對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候，就等同于電磁頻率被切斷而進行圖像重建的時刻。 大學臨床醫(yī)學院影像專業(yè)MRI技術應用部分MRI技術應用部分頸部軟組織及其血管成像線圈Head & Neck Phased Array定位頭先進,舒適位置為主.統(tǒng)一三個中心.序列傳統(tǒng)序列.(T1W+T2W)水激勵或脂抑制序列.(WET+STIR)增強掃描.(GRE)示例食道.甲狀腺.血管,肌肉及其神經(jīng)組織.鼻咽部鼻竇圖像鼻竇圖像食道甲狀腺頸部軟組織顳合關節(jié)的掃描方法T1+T

3、2橫斷位。PDW矢狀斜位。層厚13mm。顳合關節(jié)的閉口位圖像顳合關節(jié)的張口位圖像神經(jīng)涎腺及其導管Angio Imaging(血管成像）ToF Angio imaging techniques rely primarily on flow-related enhancement to distinguish moving spins from stationary spinsBlood that has flowed into the slice will not have experienced RF pulses and will appear brighter than stationar

4、y tissues依靠流入性增強效應來成像3D ToF Angio Imaging 靜脈像（一）3D-PC法(二)3D CE-Angio DSA Imaging 動靜脈(三）3D CE-Angio DSA Imaging 動靜脈（四)CE-MRA-DSA定位要求上包大腦動脈環(huán)(Willis環(huán))下包主動脈弓部，一般用2D PCA來作參考定位像。 掃描序列3D-CEMRA。一般來講先平掃，打藥后掃兩次。注射部位選擇健側(cè)上臂血管為主，注藥開始后11秒啟動掃描或利用造影劑自動跟蹤序列視主動脈弓進藥時啟動掃描。CE-MRA與CE-MRA-DSACE-MRV與MPR小結(jié)序列選擇技巧.脂抑制成功的關鍵.腹部

5、MR成像技術腹部實質(zhì)臟器。腹部空腔臟器。盆腔臟器。水成像。線圈體線圈或包饒式體部表面線圈、相控陣線圈。檢查前準備和體位舒適體位，頭、足先進皆可。呼吸訓練?？诜煊皠?。掃描序列SE、FSE和GRE。門控或閉氣掃描。實例肝、膽、脾。胰腺。MRC。MRCP。MRU。盆腔。門控(Gating)人體許多部位的器官和組織都會或多或少地受呼吸.液體流動.脈搏和心跳的影響，所以在做相應部位檢查的時候為了采集相對靜止的圖像，人們采取了一些措施，一般的方法為增加預飽和脈沖序列，其中目前主要的方法是利用“門控”。類型主要為：呼吸觸發(fā).周圍脈搏和心電門控。什么是門控？In Magnetic Resonance Im

6、agingIt is a device to synchronize MR data collection with the physiological motions of the patientIt significantly reduces motion-related artifacts due to RespirationFlowCardiac MotionOverviewTypes of GatingRespiratory TriggeringPPG GatingCardiac GatingRespiratory TriggeringTypes of Gating What is

7、it used for?To reduce artifacts caused by respiratory motion or when a patient is unable to perform a breath-holdWhere is it used?Most used in the abdomen to help produce clear, artifact-free images of the anatomical structures in the abdomenWhat is needed?Respiratory bellow and respiratory gating h

8、ardwareHow does it do it?By synchronizing data collection of the sequence to the patients respiratory motion.Respiratory TriggeringTypes of Gating How does it do it?By synchronizing data collection of the sequence to the patients respiratory motion.Changes in the patients chest circumference are con

9、verted to electronic signal and related to the MR Imaging systemProper placement of the bellows is requiredacross the trunk of the patient where the breathing is most evident. They should be place taut across the patient. Avoid stretching of the bellowsInstruct patient to breath normalthis insures a

10、 most accurate waveformRespiratory interval typically ranges from 400 ms - 15000 ms for one respiratory cycle.Respiratory TriggeringRespiratory TriggeringNextTypes of GatingRespiratory TriggeringPPG GatingCardiac GatingPPGWhat is is used for?To reduce artifacts caused by CSF motion or when CINE imag

11、ing with better coverage of diastole is desiredWhere is it used?Cervical & Thoracic SpineWhat is needed?Photoplethysmography (PPG) peripheral pulse monitory and hardwareHow does it work?The patients pulse will trigger data acquisition and synchronize image collection to the patients pulsePeripheral

12、Pulse GatingPeripheral Pulse GatingDichrotic NotchOccurs at the end of systole, and the beginning of diastole when the aortic valve closes. The aorta contracts, causing flow into the coronaries and a slight increase in peripheral flowNextTypes of GatingRespiratory TriggeringPPG GatingCardiac GatingC

13、ardiac GatingECGWhat is is used for?To reduce artifacts from cardiac motion, imaging of the heart or any other areas affected by the cardiac cycleWhere is it used?In the thoraxWhat is needed?ECG Electrodes, Lead Wires & hardwareHow does it work?By synchronizing MR Data collection of the sequence wit

14、h the cardiac cycle of the patientCardiac Gating波形Cardiac GatingDiastoleThe period of ventricular filling beginning near the end of the T wave and ends near the peak of the R waveSystoleThe period of ventricular contraction starting after the R wave and ends near the end of the T waveProblem Solving

15、What to do if gating doesnt work?Check connections of the the gating hardwareCheck proper placement on the patientRespiratoryAre the bellows stretched to far or not far enoughPPGDoes the patient have finger nail polish or long finger nailsECGAre the lead wires braided Did you select the proper gatin

16、g softwareConclusionTypes of GatingRespiratory TriggeringPPG GatingCardiac Gating腹部（上中下）平掃：T1W+T2W，強化：T1W（壓脂）。另外根據(jù)臨床要求，增加水成像，動態(tài)掃描和延遲掃描序列。胰腺和腎臟(腎上腺）的檢查需要作平掃壓脂。水成像要根據(jù)患者情況來決定用2D還是3D掃描。層厚18mm或自定義。方位：在橫斷位的基礎上增加冠 矢以及斜位。肝、膽、脾胰腺、腎臟胃腸道水成像盆腔脊柱、四肢、關節(jié)頸椎、胸椎、腰骶尾椎。上肢、下肢。肩、肘、腕、髖、膝、踝關節(jié)。線圈體位舒適體位，頭、足先進皆可。三個中心。脊髓及脊柱序列與

17、方法矢狀位：SE-T1W+TSE-T2W，橫斷位：FE-T2*+SE -T1W。層厚與間距，3mm/0.6mm。必要時加掃 T2和T1脂肪抑制序列。FOV運用大小要恰當。運用“壓脂”技術時，要盡量減少干擾掃描范圍勻場的因素。注意掃描層線之間在空間上最好不要相交叉。橫斷位的層厚與間距可以根據(jù)病變的范圍大小來調(diào)整。定位線頸椎（一）頸椎（二）頸椎（三）環(huán)樞椎大的FOV圖像（頸胸椎）脊髓及椎體的分辨率明顯不如前頁的好胸椎T1W平掃與強化壓脂腰骶椎（一）同樣的掃描時間。左邊的矩陣大小為：256x256。右邊的矩陣大小為：256x512。仔細觀察兩者信噪比與分辨率有何異同？Increasing the number ofphase steps increases thetime. This is why you maysee images that have fewerphase encodings thanfrequency encodings, e.g.,128 X 256 or 192 X 256,