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飛利浦超導磁共振成像儀液氦的灌注

發布者:
MRI維修
最后修訂:
2018年06月20日 17:45
核磁共振成像MRI維修 13259

 

 

 

飛利浦超導磁共振成像儀液氦的灌注

超導核磁共振MRI液氦充裝聯系電話+8613805690379


公司名稱:合肥迅即影像科技有限公司

地址:中國·安徽省·合肥市錦繡大道合肥桃花科創中心
網址:www.xunji.net.cn
郵箱:medcmz@163.com
手機/微信:13805690379
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傳真:0551-68993055
郵編:230000


 
磁共振成像儀在安裝以后,磁體正常使用期間,液氦會不斷損耗。為了防止失超現象,保持磁體在超導狀態下正常運行,應維持液氦容器中液面的穩定,因此必須定期灌注液氦,具體操作如下。 降流(discharge) 為了安全起見,液氦的灌注最好在退磁狀態下進行。連接主電源與超導磁體之間的電流引線,合上主電源跳閘開關及瞬息開關,將升流水平置所需電流值,升流方向置“升流”(RAMP)處,當電流升至磁體電流值時,合上主線圈超導開關加熱器電源開關(Main heater),停留1min左右,然后將升流方向改置為降流方式,降流速率為25A/s。置B0加熱器(B0 heater)為閉合狀態,保持主線圈超導開關加熱器連續通電工作10min左右,至供電電流降至零為止,再斷開各加熱器電源,把電流引線從磁體中撤除出來,密封引線入口。 退磁過程應注意:旋開磁體上方電流引線接口時,應迅速將電極引子插入管套內,注意電極極性不能插反,然后再緩慢往深處插并旋緊固定。退磁后,撤離電流引子時,先用電吹風加熱電流引子上方,讓凝結的冰塊熔化,然后再拔出電流引子。降流速度不易過快,防止回路電流過大,產生產熱現象。 液氦的灌注安裝合適長度的輸液管后,調整輸液管至杜瓦罐之間的長度,將其正確固定。用氦氣流吹洗1min左右,清除管內空氣,打開杜瓦罐的球閥頂端,把真空輸液管垂直緩慢插入杜瓦液氦罐內。液氦杜瓦管與液氦容器連接好后,可開啟液氦容器的放液閥,往杜瓦器中注入少量液氦,這樣既起預冷輸液杜瓦管的作用,又再一次清潔輸液杜瓦管。一旦氦蒸汽從輸液管的另一端逸出,則立即將輸液管與磁體液氦層的灌注口連接并固定??刂戚斠汗苤械膲毫?,使液氦緩慢而均勻地注入到磁體的液氦容器中,輸液過程中應隨時監視液氦層中的液面狀態和內部蒸汽壓力的變化。定時用數字萬用表測量差壓開關(differential pressure switch, DPS)兩端的電阻,讓磁體處于正壓狀態。若R=0歐姆,開關閉合,磁體處于正壓。若R≥1千歐姆,磁體壓力不夠,此時可閉合B0加熱器30min再檢查,若仍沒壓力,說明有氦氣泄漏,檢漏正常后再繼續灌注。在灌注液氦的過程中,開啟液氦層的排氣管閥門,有條件的醫院可對蒸發產生的氦蒸汽加以回收,以防灌注時遇熱蒸發產生的氦蒸汽在液氦層中聚集起來而導致磁體內部過壓。灌注液氦時速度應保持200~250l/h,每15min觀察一下液面的檢測情況,做好液面讀數的記錄,及時調整灌注速率。當氦液面檢測指示液氦容器已滿時,停止灌注液氦,撤除輸液管,將磁體的液氦灌注口密封起來。 液氦的灌注應注意:液氦的溫度極低,與裸露的皮膚接觸后會造成類似燒傷那樣的凍傷,灌注液氦操作時須格外小心,配戴保護手套。液氦的灌注速率亦不易過快。灌注完液氦后必須檢漏(測壓)。若使用“O”型墊圈時,應加溫后再使用并密封旋緊。磁體上方的灌注口暴露時間應盡可能短,防止空氣進入氦氣灌中,產生凍結或結冰現象。 升流(ramp) 磁體的液氦灌注完成后,進入超狀態,下一步的工作就是給磁體升流。連接磁體供電電源與超導磁體電流引子,接通主線圈超導開關加熱器電源,使主線圈超導開關轉變為正常態,然后把升流水平設置在所需的電流值,電壓調節控制開關置最大(3.0V的標記線上),升流速率為25A/s,合上主電源瞬息開關,將升流方向從降流位置轉至“升流”處,開始升流。1.0T MRI升流電壓為6.5V,1.5T為10V。升流過程中觀察主電流輸出電壓的變化情況(U<4V)。待輸出電流穩定時,用數字萬用表mv檔測量磁體電流引線電極兩端的電壓,U<20mv,調節電流水平控制旋鈕至所需輸出電流,鎖定此值,當磁體電流上升到預定值后(0.5T 455A,1.0T 413A,1.5T 381A),保持主電源穩流輸出10min左右,然后斷開主線圈超導開關加熱器電源,使超導開關轉變為超導態,10s后把升流方向轉至“保持”方式再轉至降流位置,電流引線上的電流逐漸減小到零,斷開主電源瞬息開關和跳闡開關,把電流引線從磁體中撤除出來,密封引線入口,使超導磁體進入持久電源工作狀態。 升流過程應注意:磁體升流前應先預冷,撤除檢查房內所有磁性金屬物品,防止意外事故。電極的連接極性不能接反。升流速度不易過快。充磁電流達到所需磁體電流時應維持一定時間才能穩定。 體會液氦的灌注工作主要由設備廠家工程師及液氦供應商來完成,放射科維修工程師也參與此工作,因此應具備一些液氦灌注的常識。液氦的溫度極低,打開磁體灌注口時應格外小心,由于內壓大,操作時除配戴防護手套外,臉面部盡量遠離出氣口,以防高壓冷凍氣流凍傷顏面部。往磁體的熱容器中灌注液氦時,液氦會受熱而大量蒸發,如果蒸發產生的氦氣從冷卻導管中大量泄漏出來,就會使空氣中氧氣的含量減少,從而引起窒息,因此在液氦灌注過程要開啟空調的通風設施,打開門窗,保持磁共振工作室的通風。 為了達到高效的輸液效率,輸液速度應控制好,盡量降低輸液環境溫度。輸液完后需靜置24h后液面才能相對穩定,剛灌注完由于液氣關系,測量出的液面值出入較大,此值與穩定后的液面讀數相差十幾ltr。液面≥30%磁體才能動作,為了防止失超,當液面指示≤50%時應補充液氦。液氦灌注完后每天要記錄液氦的蒸發率,蒸發率≥2ltr/d時應更換冷頭。 液氦灌注結束后應做一次定期圖像質量測試掃描(PIQT),檢查一下磁體的穩定性、均勻度以及圖像的信噪比、線性度、空間分辨率等,以確保設備的正常運作。

作 者 曾瓊新 (廣東省人民醫院MR室) ; 譚紹恒 (廣東省人民醫院MR室) ; 鄭君惠 (廣東省人民醫院MR室) ;

Philips superconducting magnetic resonance imager perfusion liquid helium
MRI superconducting NMR helium filling Tel +8613805690379
Magnetic resonance imaging after installation , the magnet during normal use , liquid helium will continue to wear and tear. In order to prevent quench phenomenon , keeping the magnet in the normal operation of the superconducting state should remain stable liquid helium vessel must therefore be regularly perfusion liquid helium , as follows . Reducing flow (discharge) For security reasons, the best in the perfusion liquid helium demagnetization state. Connect the main power supply and current leads between the superconducting magnets , close the main power switch and momentary switch tripped , will set up the required level of current flow , up-flow direction is set to " up-flow " (RAMP) office, when the current rises magnet current value, close the main coil superconducting switch heater power switch (Main heater), stay 1min or so, and then the up-flow direction was changed to the downflow mode , reducing flow rate of 25A / s. Set B0 heater (B0 heater) is closed , keep the main coil superconducting switch heater is energized continuously work about 10min to supply current drops to zero until then disconnect the heater power , the current lead removed from the magnet out , sealed Lead entrance. Demagnetization process should pay attention to : Unscrew the top of the magnet current leads interface, shall promptly primer electrode insertion tube kit, note counter electrode polarity can not be inserted , and then insert and tighten the fixing slow deep down . Demagnetization after evacuation current primer , the first primer with a hair above the heating current , so that condensation of ice melted , and then pull out the current primer . Downflow velocity easy too fast to prevent the loop current is too large, the production capacity thermal phenomena . Install the appropriate length of the perfusion liquid helium infusion tube , infusion tube to adjust the length between the Dewar , be properly fixed. Purged with helium flow around 1min , clear air in the tube , open the top of the Dewar tank valve , the vacuum infusion tube inserted into the Dewar vertical slow helium tank . Tubes with liquid helium dewar of liquid helium container connected, the container can be opened up liquid helium valve to inject a small amount of liquid helium dewar vessel , both from the pre-cooling effect of the infusion tube Dewar , once again clean infusion Dewar tube . Once the helium vapor from escaping the other end of the infusion tube , the infusion tube immediately magnet helium layer fill port connected and fixed . Control of fluid pressure in the tube , the helium slowly and uniformly injected into the magnet helium vessel , the infusion process should always monitor the liquid level in the state of liquid helium layer and the internal steam pressure changes. Timing with a digital multimeter to measure differential pressure switch (differential pressure switch, DPS) across the resistor , so the magnet positive pressure state . If R = 0 ohms , the switch is closed , the magnet in the pressure . If R ≥ 1 kilohms , magnets pressure is not enough , then you can close B0 heater 30min and then check if still did not pressure , indicating a helium leak , leak detection and then continue normal perfusion. During the infusion of liquid helium , helium layer on the exhaust pipe valves , hospital conditions produced by evaporation can be recycled helium vapor , heated to prevent perfusion helium vapor produced by evaporation in the helium layer gathered internal overpressure caused by the magnet . Infusion rate should be maintained at liquid helium 200 ~ 250l / h, every 15min look at the case level detection , good level of reading records , timely adjustment of infusion rate. When the liquid level detection indicator helium helium container is full, stop the infusion liquid helium , remove the infusion tube , the magnet helium fill port sealed. Helium perfusion should be noted: liquid helium temperature is very low , after contact with bare skin can cause burns similar to frostbite as perfusion liquid helium to be extra careful when operating , wear protective gloves. Liquid helium rapid infusion rates would not be easy . After perfusion liquid helium leak and must ( manometry ) . If you use the "O" -rings , should be warmed before use and sealed tight. Above the magnet perfusion oral exposure time should be as short as possible to prevent air from entering the helium filling , resulting in freezing or icing . L flow (ramp) magnet helium perfusion is complete, enter the super state , the next step is to give the magnet up-flow . Bonded magnet current power supply and a superconducting magnet primer , on the superconducting main coil heater power switch , the main switch is converted to the superconducting coil normal state , then the up-flow set at the desired current level , voltage regulation control switch set maximum (3.0V tag line ) , l flow rate of 25A / s, closing the main power momentary switch, the up-flow direction of the flow from the lower position to the " up-flow " at start up stream. 1.0T MRI upflow voltage of 6.5V, 1.5T is 10V. L flow observed during the main current of the output voltage variation (U <4V). With the output current is stable , measured with a digital multimeter mv file magnets current leads the voltage across the electrodes , U <20mv, adjust the control knob to the desired current level output current , lock this value, when the magnet current rises to a predetermined value (0.5T 455A, 1.0T 413A, 1.5T 381A), to keep the main power output steady flow about 10min , then switch off the main superconducting coil heater power , the superconducting switch into the superconducting state , 10s go after the up-flow direction "Hold" mode and then go down stream position , current leads the current is gradually reduced to zero , disconnect the main power switch and jump illustrates momentary switch, the current lead removed from the magnet out of sealed Lead entrance, the superconducting magnet into lasting work of state power . Up-flow process should pay attention to : magnet up-flow should be preceded by pre-cooling , remove all check room magnetic metal items, to prevent accidents . Electrode connection polarity can not be reversed . Up-flow speed is not easy too fast. Magnetizing current reaches the desired magnet current should maintain a certain time to stabilize . Experience working mainly by liquid helium perfusion equipment manufacturers engineers and helium suppliers to complete radiology maintenance engineers are also involved in this work , it should have some knowledge of perfusion liquid helium . Liquid helium temperature is very low , open mouth magnet perfusion should be careful , because a large internal pressure , in addition to wear protective gloves when operating outside , far away from the outlet face portion , to prevent high pressure freezing airflow facial frostbite . Heat to the magnet helium vessel perfusion when substantial evaporation of liquid helium will heat and , if the evaporation of helium from leaking out of a large number of cooling ducts , and it will reduce the content of oxygen in the air , causing suffocation , so the liquid helium infusion process to the open air ventilation , open windows and doors to keep magnetic resonance studio ventilation. In order to achieve high efficiency of the infusion , the infusion rate should be controlled to minimize transfusion ambient temperature. After allowed to stand for 24h after the infusion liquid to be relatively stable to just finished the perfusion liquid and gas between the measured fluid access to a larger nominal value , this value readings are stable level after ten ltr. Level ≥ 30% magnets to action, in order to prevent loss of ultrasound, when the liquid level indication ≤ 50% should be added helium . After perfusion liquid helium to record daily rate of evaporation of liquid helium evaporation rate ≥ 2ltr / d should be replaced with the cold head . After perfusion liquid helium should be done once a periodic image quality test scan (PIQT), check the stability of the magnet , the signal to noise ratio and image uniformity , linearity, spatial resolution , so as to ensure the normal operation of the device .

Author Joan has a new ( Guangdong Provincial People's Hospital, MR room ) ; Tan Shaoheng ( Guangdong Provincial People's Hospital, MR room ) ; Zheng Junhui ( Guangdong Provincial People's Hospital, MR room ) ;






 

 

 

 

 

 

 

 

 

 


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