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Investigation of the hydrodynamic properties of a new MRI-resistant programmable hydrocephalus shunt.

Allin DM, Czosnyka M, Richards HK, Pickard JD, Czosnyka ZH - Cerebrospinal Fluid Res (2008)

Bottom Line: External programming proved to be easy and reliable.The Polaris Valve is a reliable, adjustable valve.Unlike other adjustable valves (except the Miethke ProGAV valve), the Polaris cannot be accidentally re-adjusted by an external magnetic field.

View Article: PubMed Central - HTML - PubMed

Affiliation: Shunt Evaluation Laboratory & Academic Neurosurgical Unit, Addenbrooke's Hospital, P,O, Box 167, Hills Road, Cambridge CB2 2QQ, UK. mc141@medschl.cam.ac.uk.

ABSTRACT

Background: The Polaris valve is a newly released hydrocephalus shunt that is designed to drain cerebrospinal fluid (CSF) from the brain ventricles or lumbar CSF space. The aim of this study was to bench test the properties of the Polaris shunt, independently of the manufacturer.

Methods: The Polaris Valve is a ball-on-spring valve, which can be adjusted magnetically in vivo. A special mechanism is incorporated to prevent accidental re-adjustment by an external magnetic field. The performance and hydrodynamic properties of the valve were evaluated in the UK Shunt Evaluation Laboratory, Cambridge, UK.

Results: The three shunts tested showed good mechanical durability over the 3-month period of testing, and a stable hydrodynamic performance over 45 days. The pressure-flow performance curves, operating, opening and closing pressures were stable. The drainage rate of the shunt increased when a negative outlet pressure (siphoning) was applied. The hydrodynamic parameters fell within the limits specified by the manufacturer and changed according to the five programmed performance levels. Hydrodynamic resistance was dependant on operating pressure, changing from low values of 1.6 mmHg/ml/min at the lowest level to 11.2 mmHg/ml/min at the highest performance level. External programming proved to be easy and reliable. Even very strong magnetic fields (3 Tesla) were not able to change the programming of the valve. However, distortion of magnetic resonance images was present.

Conclusion: The Polaris Valve is a reliable, adjustable valve. Unlike other adjustable valves (except the Miethke ProGAV valve), the Polaris cannot be accidentally re-adjusted by an external magnetic field.

No MeSH data available.


Related in: MedlinePlus

Artifact on MR image: The Polaris valve was placed in a water-filled container, with diameter equivalent to adult skull). A) Gradient echo image; B) T1 image.
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Figure 8: Artifact on MR image: The Polaris valve was placed in a water-filled container, with diameter equivalent to adult skull). A) Gradient echo image; B) T1 image.

Mentions: The valve cannot be re-programmed by an external magnetic field of up to 3T (MRI magnet). It does not heat up when placed within the magnetic field. The maximal translational force measured was 81G. These values are still considered as safe after implantation. Distortion of the MRI scan was significant: gradient echo 954 cm3, and T1 100 cm3 (Figure 8).


Investigation of the hydrodynamic properties of a new MRI-resistant programmable hydrocephalus shunt.

Allin DM, Czosnyka M, Richards HK, Pickard JD, Czosnyka ZH - Cerebrospinal Fluid Res (2008)

Artifact on MR image: The Polaris valve was placed in a water-filled container, with diameter equivalent to adult skull). A) Gradient echo image; B) T1 image.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2365935&req=5

Figure 8: Artifact on MR image: The Polaris valve was placed in a water-filled container, with diameter equivalent to adult skull). A) Gradient echo image; B) T1 image.
Mentions: The valve cannot be re-programmed by an external magnetic field of up to 3T (MRI magnet). It does not heat up when placed within the magnetic field. The maximal translational force measured was 81G. These values are still considered as safe after implantation. Distortion of the MRI scan was significant: gradient echo 954 cm3, and T1 100 cm3 (Figure 8).

Bottom Line: External programming proved to be easy and reliable.The Polaris Valve is a reliable, adjustable valve.Unlike other adjustable valves (except the Miethke ProGAV valve), the Polaris cannot be accidentally re-adjusted by an external magnetic field.

View Article: PubMed Central - HTML - PubMed

Affiliation: Shunt Evaluation Laboratory & Academic Neurosurgical Unit, Addenbrooke's Hospital, P,O, Box 167, Hills Road, Cambridge CB2 2QQ, UK. mc141@medschl.cam.ac.uk.

ABSTRACT

Background: The Polaris valve is a newly released hydrocephalus shunt that is designed to drain cerebrospinal fluid (CSF) from the brain ventricles or lumbar CSF space. The aim of this study was to bench test the properties of the Polaris shunt, independently of the manufacturer.

Methods: The Polaris Valve is a ball-on-spring valve, which can be adjusted magnetically in vivo. A special mechanism is incorporated to prevent accidental re-adjustment by an external magnetic field. The performance and hydrodynamic properties of the valve were evaluated in the UK Shunt Evaluation Laboratory, Cambridge, UK.

Results: The three shunts tested showed good mechanical durability over the 3-month period of testing, and a stable hydrodynamic performance over 45 days. The pressure-flow performance curves, operating, opening and closing pressures were stable. The drainage rate of the shunt increased when a negative outlet pressure (siphoning) was applied. The hydrodynamic parameters fell within the limits specified by the manufacturer and changed according to the five programmed performance levels. Hydrodynamic resistance was dependant on operating pressure, changing from low values of 1.6 mmHg/ml/min at the lowest level to 11.2 mmHg/ml/min at the highest performance level. External programming proved to be easy and reliable. Even very strong magnetic fields (3 Tesla) were not able to change the programming of the valve. However, distortion of magnetic resonance images was present.

Conclusion: The Polaris Valve is a reliable, adjustable valve. Unlike other adjustable valves (except the Miethke ProGAV valve), the Polaris cannot be accidentally re-adjusted by an external magnetic field.

No MeSH data available.


Related in: MedlinePlus