飞利浦超导磁共振成像仪液氦的灌注

发布者:
合肥迅即
最后修订:
2017年06月15日 02:58
核磁共振成像MRI维修 375

飞利浦超导磁共振成像仪液氦的灌注

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磁共振成像仪在安装以后,磁体正常使用期间,液氦会不断损耗。为了防止失超现象,保持磁体在超导状态下正常运行,应维持液氦容器中液面的稳定,因此必须定期灌注液氦,具体操作如下。 降流(discharge) 为了安全起见,液氦的灌注最好在退磁状态下进行。连接主电源与超导磁体之间的电流引线,合上主电源跳闸开关及瞬息开关,将升流水平置所需电流值,升流方向置“升流”(RAMP)处,当电流升至磁体电流值时,合上主线圈超导开关加热器电源开关(Main heater),停留1min左右,然后将升流方向改置为降流方式,降流速率为25A/s。置B0加热器(B0 heater)为闭合状态,保持主线圈超导开关加热器连续通电工作10min左右,至供电电流降至零为止,再断开各加热器电源,把电流引线从磁体中撤除出来,密封引线入口。 退磁过程应注意:旋开磁体上方电流引线接口时,应迅速将电极引子插入管套内,注意电极极性不能插反,然后再缓慢往深处插并旋紧固定。退磁后,撤离电流引子时,先用电吹风加热电流引子上方,让凝结的冰块熔化,然后再拔出电流引子。降流速度不易过快,防止回路电流过大,产生产热现象。 液氦的灌注安装合适长度的输液管后,调整输液管至杜瓦罐之间的长度,将其正确固定。用氦气流吹洗1min左右,清除管内空气,打开杜瓦罐的球阀顶端,把真空输液管垂直缓慢插入杜瓦液氦罐内。液氦杜瓦管与液氦容器连接好后,可开启液氦容器的放液阀,往杜瓦器中注入少量液氦,这样既起预冷输液杜瓦管的作用,又再一次清洁输液杜瓦管。一旦氦蒸汽从输液管的另一端逸出,则立即将输液管与磁体液氦层的灌注口连接并固定。控制输液管中的压力,使液氦缓慢而均匀地注入到磁体的液氦容器中,输液过程中应随时监视液氦层中的液面状态和内部蒸汽压力的变化。定时用数字万用表测量差压开关(differential pressure switch, DPS)两端的电阻,让磁体处于正压状态。若R=0欧姆,开关闭合,磁体处于正压。若R≥1千欧姆,磁体压力不够,此时可闭合B0加热器30min再检查,若仍没压力,说明有氦气泄漏,检漏正常后再继续灌注。在灌注液氦的过程中,开启液氦层的排气管阀门,有条件的医院可对蒸发产生的氦蒸汽加以回收,以防灌注时遇热蒸发产生的氦蒸汽在液氦层中聚集起来而导致磁体内部过压。灌注液氦时速度应保持200~250l/h,每15min观察一下液面的检测情况,做好液面读数的记录,及时调整灌注速率。当氦液面检测指示液氦容器已满时,停止灌注液氦,撤除输液管,将磁体的液氦灌注口密封起来。 液氦的灌注应注意:液氦的温度极低,与裸露的皮肤接触后会造成类似烧伤那样的冻伤,灌注液氦操作时须格外小心,配戴保护手套。液氦的灌注速率亦不易过快。灌注完液氦后必须检漏(测压)。若使用“O”型垫圈时,应加温后再使用并密封旋紧。磁体上方的灌注口暴露时间应尽可能短,防止空气进入氦气灌中,产生冻结或结冰现象。 升流(ramp) 磁体的液氦灌注完成后,进入超状态,下一步的工作就是给磁体升流。连接磁体供电电源与超导磁体电流引子,接通主线圈超导开关加热器电源,使主线圈超导开关转变为正常态,然后把升流水平设置在所需的电流值,电压调节控制开关置最大(3.0V的标记线上),升流速率为25A/s,合上主电源瞬息开关,将升流方向从降流位置转至“升流”处,开始升流。1.0T MRI升流电压为6.5V,1.5T为10V。升流过程中观察主电流输出电压的变化情况(U<4V)。待输出电流稳定时,用数字万用表mv档测量磁体电流引线电极两端的电压,U<20mv,调节电流水平控制旋钮至所需输出电流,锁定此值,当磁体电流上升到预定值后(0.5T 455A,1.0T 413A,1.5T 381A),保持主电源稳流输出10min左右,然后断开主线圈超导开关加热器电源,使超导开关转变为超导态,10s后把升流方向转至“保持”方式再转至降流位置,电流引线上的电流逐渐减小到零,断开主电源瞬息开关和跳阐开关,把电流引线从磁体中撤除出来,密封引线入口,使超导磁体进入持久电源工作状态。 升流过程应注意:磁体升流前应先预冷,撤除检查房内所有磁性金属物品,防止意外事故。电极的连接极性不能接反。升流速度不易过快。充磁电流达到所需磁体电流时应维持一定时间才能稳定。 体会液氦的灌注工作主要由设备厂家工程师及液氦供应商来完成,放射科维修工程师也参与此工作,因此应具备一些液氦灌注的常识。液氦的温度极低,打开磁体灌注口时应格外小心,由于内压大,操作时除配戴防护手套外,脸面部尽量远离出气口,以防高压冷冻气流冻伤颜面部。往磁体的热容器中灌注液氦时,液氦会受热而大量蒸发,如果蒸发产生的氦气从冷却导管中大量泄漏出来,就会使空气中氧气的含量减少,从而引起窒息,因此在液氦灌注过程要开启空调的通风设施,打开门窗,保持磁共振工作室的通风。 为了达到高效的输液效率,输液速度应控制好,尽量降低输液环境温度。输液完后需静置24h后液面才能相对稳定,刚灌注完由于液气关系,测量出的液面值出入较大,此值与稳定后的液面读数相差十几ltr。液面≥30%磁体才能动作,为了防止失超,当液面指示≤50%时应补充液氦。液氦灌注完后每天要记录液氦的蒸发率,蒸发率≥2ltr/d时应更换冷头。 液氦灌注结束后应做一次定期图像质量测试扫描(PIQT),检查一下磁体的稳定性、均匀度以及图像的信噪比、线性度、空间分辨率等,以确保设备的正常运作。

作 者 曾琼新 (广东省人民医院MR室) ; 谭绍恒 (广东省人民医院MR室) ; 郑君惠 (广东省人民医院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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