gms | German Medical Science

Objective: In the last years, the quantity of ultra-high field magnetic resonance imaging (MRI) studies demonstrating diagnostic benefits in neuro imaging has increased rapidly. This in vitro study tests function, safety and image artifacts of the two worldwide most frequently implanted programmable ventriculo-peritoneal (VP) shunt valves in a 7T MRI system.

Methods: All tests were performed using a whole-body MRI system (Magnetom 7T; Siemens Healthcare, Germany). Three proGAV 2.0 programmable VP-shunt valves (Miethke GmbH, Germany) and 3 CODMAN CERTAS® Plus programmable VP-shunt valves (Codman & Shurtleff, Inc., MA), all certified as 3T MR conditional, were tested in a three-step procedure. 1) Deflection angle tests were performed at the location of the highest static magnetic field gradient (5 T/m) close to the scanner opening. 2) The valves were fixed on a standard spherical phantom in 3 positions (a. strictly lateral, b. strictly cranial, c. cranial with 22.5° tilt anteriorly) and tested for keeping the programmed pressure setting and ability to be reprogramed. 3) The valves were fixed on a spherical phantom and positioned strictly right lateral in the head coil. Scans were performed for both VP shunt models separately, including MPRAGE, gradient echo and spin echo sequences.

Results: Deflection angles were moderate (13°, 14°, 13°) for the proGAV 2.0 programmable VP-shunt valves and close to critical (43°, 43°, 41°) for the CODMAN CERTAS® Plus programmable VP-shunt valves. The proGAV 2.0 programmable VP-shunt valves kept the programmed pressure settings and were reprogrammable in position a and b. In position c, the valves kept their pressure setting, but ability to be reprogramed was lost. The CODMAN CERTAS® Plus programmable VP-shunt valves changed their pressure setting and ability to be reprogramed was lost in position a, b and c, respectively. A magnetometer also showed reversed polarity of the permanent magnets that are the crucial part of the programming mechanism within both valves. The image signal homogeneity was unaltered by the shunt valves in the center of the phantom and image artifacts adjacent to the valves were tolerable.

Conclusion: Both tested programmable VP-shunt valves are unsafe for use in 7T systems in their current design. Altered programming mechanisms using permanent magnets with sufficient magnetic coercivity may allow development of programmable VP-shunt valves that are conditional for use in 7T MR systems.