Article
Effect of 3 Tesla MRI on the function of shunt valves : evaluation of Paedi GAV, Dual Switch and proGAV
Einfluss eines 3 Tesla Magnetfeldes auf die Ventilfunktion: Untersuchung an Paedi GAV, Dual Switch und proGAV
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Published: | May 4, 2005 |
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Outline
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Objective
There is no universal protocol for the assessment of MR- compatibility of shunt valves in terms of function and the apparatus to characterize the hydrodynamic performance after exposure to high magnetic fields differs among manufacturers. That’s why we initiated together with Miethke-Aesculap our study to evaluate independently their typical gravitational valves, the Dual switch, the Paedi GAV and as a new programmable one the proGAV in a 3 Tesla magnetism field.
Methods
MR scan evaluation were analysed in a typical producing protocol comparable the standard ASTM F647. A roll-pump delivers a constant flow of water or air through the valve in an adjustable range of 5 –50 ml / hour. A computerized system measured the opening pressure permanently with a tolerance of ±0,5 cm H20 (standard deviation).After completion of the pre- scan tests, the valves underwent MRI- scan. All magnetic resonance imaging (MRI) experiments were performed on a 3-T Magnetom Trio (Siemens, Erlangen, Germany). The MRI protocol is analogous to clinical practice and consists of a scout, T 2-weighted (T2w) two-dimensional (2D) spin-echo (SE) imaging, T 1-weighted (T1w) three-dimensional (3D) gradient-recalled echo (GRE) imaging, and diffusion-weighted (dw) 2D echo planar imaging (EPI). For T2w-imaging, RARE ('rapid acquisition with relaxation enhancement') sequences were acquired. A sagittal 3D slab (thickness 176 mm) was acquired for T1w-imaging with MP-RAGE ('magnetization-prepared rapid gradient echo'). The valves remained in the magnet for 45 min with a total scanning time of 34:57 min.
Results
The results from pre- scan and post- scan measurements were calculated as a mean value from 3 single measurements. The average deviation of the valves without the negative control (no. SN 010048) was 0,6 H20 ±0,2 for the air flow test and 0,7 H20 ±0,2 for the water flow test. Note, that the results for the negative control differ significantly indicating a shift of the pressure adjustment.
Conclusions
The aim of the study was to evaluate the function of different valves after exposure to a 3 T MR field. In sum, our 3T magnetic field had no influence on stability and safety of the tested Miethke valves. The proGAV as a programmable valve can only be exposed to 3 Tesla if the brake mechanism is safely adjusted.