Ortler M, Kostron H, Felber S
Universitätsklinik für Neurochirurgie, Innsbruck, Austria.
Neurosurgery. 1997 May;40(5):1050-7; discussion 1057-8. doi: 10.1097/00006123-199705000-00032.
We investigated the compatibility of magnetically adjustable cerebrospinal fluid valves with clinical magnetic resonance imaging. Torque acting on the valves, subjective sensations of valve-carrying volunteers, extension of artifacts on acquired images, changes in valve pressure setting, and accurate valve function after repeated exposure to the magnetic field were tested.
Two externally adjustable differential pressure valves, i.e., the Codman-Medos programmable valve (Medos S.A., Le Locle, Switzerland) (n = 5) and the Sophy programmable pressure valve (Sophysa, Orsay, France) (Model SP3, n = 4; Model SU8, n = 3; and Model SM8, n = 2) were exposed to the magnetic fields of 1.5-T clinical scanners. Ferromagnetic properties were investigated according to an established protocol. Subjective sensations during positioning and scanning and image artifacts were investigated using standard clinical imaging protocols. Changes in opening pressure setting during repeated magnetic field exposure were examined using valves affixed to a dummy.
Deflection forces measured 117 dynes in the Medos valve, and 2439 (Model SP3), 2172 (Model SU8) and 1914 (Model SM8) dynes in the Sophy valves. Torque during positioning and during imaging was reported for the Sophy valves. Distortion of the magnetic field with artifacts on acquired images ranged 6 x 6 x 12 cm around the Sophy valve and 4 x 4 x 4 cm around the Medos valves. Artifact extension increased with longer TE times on T2-weighted images and when using gradient-echo sequences. The pressure setting of the Medos valves did not change in 31 of 88 tests. Below 170 mm H2O, the maximal disadjustment was 60 mm H2O in each direction. Minor changes of the pressure setting were observed at 50 and 30 mm H2O. In 11 of 15 tests at 200 mm H2O, the setting after magnetic field exposure was below 30 mm H2O. One Medos valve could no longer be programmed after being exposed four times to the static magnetic field. Sophy valves remained at or changed to "high" in 68 of 81 tests and to "low" in 9. All Sophy valves exhibited paramagnetic behavior after the tests. All remained programmable. Observed changes always occurred within the safety area of the magnet.
Subjective disturbances resulting from paramagnetic valve behavior are absent in Medos valves and are minor in Sophy valves. Image artifacts require careful planning of valve position. Artifacts observed in magnetic resonance imaging are less disturbing than those observed in computed tomography. Medos valves are more stable regarding disadjustment than are Sophy valves. Radiological control of valve setting after exposure to the magnetic field is mandatory in both. The 0.5-mT safety line encircling the area that patients with pacemakers should not enter is a useful safety borderline for patients with pressure-adjustable valves. Failure of the programming mechanism of one Medos valve after several exposures to the magnetic field requires clarification.
我们研究了磁可调脑脊液阀门与临床磁共振成像的兼容性。测试了作用在阀门上的扭矩、佩戴阀门志愿者的主观感受、采集图像上伪影的范围、阀门压力设置的变化以及反复暴露于磁场后阀门的准确功能。
将两个外部可调压差阀，即Codman - Medos可编程阀（Medos S.A.，瑞士勒洛克勒）（n = 5）和Sophy可编程压力阀（Sophysa，法国奥赛）（SP3型号，n = 4；SU8型号，n = 3；SM8型号，n = 2）暴露于1.5T临床扫描仪的磁场中。根据既定方案研究铁磁特性。使用标准临床成像方案研究定位和扫描过程中的主观感受以及图像伪影。使用固定在假人上的阀门检查反复磁场暴露期间开启压力设置的变化。
Medos阀测得的偏转力为117达因，Sophy阀（SP3型号）为2439达因，（SU8型号）为2172达因，（SM8型号）为1914达因。报告了Sophy阀在定位和成像期间的扭矩。采集图像上带有伪影的磁场畸变范围在Sophy阀周围为6×6×12厘米，在Medos阀周围为4×4×4厘米。在T2加权图像上以及使用梯度回波序列时，随着回波时间延长，伪影范围增大。在88次测试中的31次，Medos阀的压力设置未改变。在170毫米水柱以下，每个方向的最大失调为60毫米水柱。在50和30毫米水柱时观察到压力设置有微小变化。在200毫米水柱的15次测试中的11次，磁场暴露后的设置低于30毫米水柱。一个Medos阀在四次暴露于静磁场后无法再编程。Sophy阀在81次测试中的68次保持或变为“高”，9次变为“低”。所有Sophy阀在测试后均表现出顺磁行为。所有阀门仍可编程。观察到的变化始终发生在磁体的安全区域内。
Medos阀不存在顺磁阀行为导致的主观干扰，Sophy阀的干扰较小。图像伪影需要仔细规划阀门位置。磁共振成像中观察到的伪影比计算机断层扫描中观察到的伪影干扰性小。Medos阀在失调方面比Sophy阀更稳定。两种阀门在暴露于磁场后都必须进行阀门设置的放射学控制。环绕起搏器患者不应进入区域的0.5毫特斯拉安全线对于压力可调阀门患者是一条有用的安全边界。一个Medos阀在多次暴露于磁场后编程机制失效需要进一步明确。
