Hydrocephalus is the accumulation of cerebrospinal fluid in the brain, resulting from increased production, or more commonly, pathway obstruction or decreased absorption of the fluid. Cerebrospinal fluid (CSF) shunts have been used for decades for the treatment of hydrocephalus. A CSF shunt involves establishing an accessory pathway for the movement of CSF to bypass an obstruction of the natural pathways.
The shunt is positioned to enable the CSF to be drained from the cerebral ventricles or sub-arachnoid spaces into another absorption site (e.g., the right atrium of the heart or the peritoneal cavity) through a system of small catheters. A regulatory device, such as a valve, may be inserted into the pathway of the catheters. In general, the valve keeps the CSF flowing away from the brain and moderates the pressure or flow rate. Some valves are fixed pressure valves (i.e., monopressure valves) and others have adjustable or programmable settings. The drainage system using catheters and valves enables the excess CSF within the brain to be evacuated and, thereby, the pressure within the cranium to be reduced.
There are many different types of CSF shunt valves and associated accessories used for treatment of hydrocephalus. In general, for shunt valves that utilize magnetic components, highly specific safety guidelines must be followed in order to perform MRI procedures safely in patients with these devices.
The following content provides information for several different CSF shunt valve products.
CODMAN CERTAS Programmable Valve, CSF Shunt Valve (Codman, a Johnson & Johnson Company)
Warnings
- The use of Magnetic Resonance (MR) systems operating at 3 Tesla or less will not damage the valve mechanism and testing shows that the valve is resistant to unintended changes in the setting. However, it is recommended that the clinician confirm the valve setting after a magnetic resonance imaging (MRI) procedure.
- The valve setting is adjusted with the application and manipulation of strong magnets. A change to the valve setting is unlikely to occur under normal circumstances. However, magnetic fields should not be placed in close proximity to the valve due to the possibility of an unintentional setting change.
- Read MRI Information before performing an MRI procedure on a patient implanted with the valve.
Magnetic Resonance Imaging (MRI) Information
The CODMAN CERTAS Therapy Management System (TMS) is considered “MR Unsafe” in accordance with the American Society for Testing and Materials (ASTM) Standard F2503-05. Do not use the TMS in the MR suite.
The CODMAN CERTAS Programmable Valve contains small metallic parts that are insulated and isolated from patient tissue by nonmetallic, non-conducting materials. There is no metal in contact with the patient. Non-clinical testing has demonstrated that the CODMAN CERTAS Programmable Valve is considered “MR Conditional” in accordance with ASTM F2503-05 and it can be scanned safely under the following conditions and specific guidelines at any time after implantation:
Conditions
· Static magnetic field of 3 Tesla or less.
· Highest spatial gradient magnetic field of 720 Gauss/cm or less.
· The MR system can be operated in either of the following modes:
-Normal Operating Mode (i.e., mode of operation of the MR EQUIPMENT in which none of the outputs has a value that might cause physiological stress to PATIENTS) only with a maximum whole-body averaged specific absorption rate of 2.0-W/kg.
- First Level Controlled Operating Mode (i.e., mode of operation of the MR EQUIPMENT in which one or more outputs reach a value that might cause physiological stress to PATIENTS that needs to be controlled by MEDICAL SUPERVISION) with a whole-body-averaged specific absorption rate of 4.0 W/kg.
Specific Guidelines. It is recommended that the valve setting be verified after the MRI procedure (see Post Implantation Adjustment Procedure Steps 1 through 3 in the Instructions for Use).
MRI TESTING INFORMATION
Static Magnetic Field. Translational attraction and torque associated with a 3 Tesla or lower field strength MR system are at levels that are less than those related to gravity and will not pose an additional hazard or risk to the patient in an MRI environment at 3 Tesla or less.
MRI-Related Heating. In non-clinical testing, the valve produced a temperature rise of 1.8 degrees C at a maximum MR system reported whole-body-averaged specific absorption rate (SAR) of 3.0 W/kg as assessed by calorimetry for 15 minutes of MR scanning (per pulse sequence) in a 3 T EXCITE MR Scanner, HDx, Software 14X.M5, General Electric Healthcare, Milwaukee, WI, USA.
MRI Artifacts. Artifacts were assessed using T1-weighted spin echo (SE) and gradient echo (GRE) pulse sequences. The details of these pulse sequences and the corresponding artifact sizes are listed in Table 2 (please refer to Instructions for Use). MR image quality might be compromised if the area of interest is in the exact location or relatively close to the location of the CODMAN CERTAS Programmable Valve. However, MRI artifacts can be minimized by careful selection of pulse sequence parameters. Note: The maximum artifact size, as seen on the gradient echo pulse sequence, extends approximately15-mm relative to the size and shape of the valve.
Codman Hakim Precision Valve, CSF Shunt Valve
Description. The CODMAN HAKIM Precision Fixed Pressure Valve (CSF shunt valve, Codman, a Johnson & Johnson Company, Raynham, MA) offers five distinct and narrow bandwidths to assure the correct pressure setting for each individual case. It also uses the proven ball and cone technology to insure that each pressure range is correct within a + / -10mm H2O variance. The CODMAN HAKIM Precision Fixed Pressure Valve is available in eight basic configurations, and each of these configurations can be purchased with a unitized distal catheter or as a valve only.
The Codman Hakim Precision CSF Shunt Valve (CSF shunt valve, Codman, a Johnson & Johnson Company, Raynham, MA) is "MR Conditional” according to ASTM F2503. The valve demonstrates no known hazards when an MRI is performed under the following conditions:
· MRI can be performed at any time after implantation
· Use an MR system with a static magnetic field of 3-T or less
· Use an MR System with a spatial gradient of 720 gauss/cm or less
· Limit the exposure to RF energy to a whole-body-averaged specific absorption rate (SAR) of 3 W/kg for 15 minutes (per pulse sequence)
MR image quality may be compromised if the area of interest is relatively close to the device. Distortion may be seen at the boundaries of the artifact. Therefore, optimization of the MR imaging parameters may be necessary.
CODMAN HAKIM Programmable Valves
Description. The CODMAN HAKIM Programmable Valve (CSF shunt valve, Codman, a Johnson & Johnson Company, Raynham, MA) includes a valve mechanism that incorporates a flat 316L stainless steel spring in which the calibration is accomplished by a combination between a pillar and a micro-adjustable telescoping fulcrum. The valve chassis is made of titanium. The ball and cone are manufactured from synthetic ruby. Intraventricular pressure is maintained at a constant level by the ball and cone valve seat design.
The pressure setting of the spring in the inlet valve unit is noninvasively adjusted by the use of an external programmer, which activates the stepper motor within the valve housing. The programmer transmits a codified magnetic signal to the motor allowing eighteen pressure settings, ranging from 30 mm to 200 mm H2O (294 to 1960 Pa) in 10 mm (98 Pa) increments. These are operating pressures of the valve unit and have been determined with a flow rate of 15 to 25 ml H2O per hour.
The valve is classified by its working pressure with a specified flow rate and not by the opening and closing pressures. The pressure that a valve sustains with a given flow is the parameter that reflects the working pressure of the valve once it is implanted. Before shipment, each valve is calibrated with special equipment: Duplication of these test procedures cannot be accomplished in the operating room.
Indications. The CODMAN HAKIM Programmable Valves are implantable devices that provide constant intraventricular pressure and drainage of CSF for the management of hydrocephalus.
Programmable Valve Configurations
· In-line with SIPHONGUARD Device
· In-line
· Right Angle with SIPHONGUARD Device
· Right Angle
· Cylindrical with Prechamber
· Cylindrical
· Micro with RICKHAM® Reservoir
· Micro
CODMAN HAKIM In-line and Right Angle Valves include a programmable valve with a low profile and flat bottom, and an in-line or right angle integral reservoir with or without SIPHONGUARD.
CODMAN HAKIM Cylindrical Valves include a programmable valve, a pumping chamber, and an outlet valve available with or without a prechamber.
CODMAN HAKIM Micro Valves include a programmable valve with or without an integral RICKHAM reservoir.
WARNINGS. Subjecting the valve to strong magnetic fields may change the setting of the valve.
· The use of Magnetic Resonance (MR) systems up to 3-Tesla will not damage the valve mechanism, but may change the setting of the valve. Confirm the valve setting after an MRI procedure.
· Common magnets greater than 80 gauss, such as household magnets, loudspeaker magnets, and language lab headphone magnets may affect the valve setting when placed close to the valve.
· Magnetic fields generated from microwaves, high-tension wires, electric motors, transformers, etc., do not affect the valve setting.
Read the MRI Information before performing an MRI procedure on a patient implanted with the programmable valve.
MRI Information
The CODMAN HAKIM Programmable Valve (CSF shunt valve, Codman, a Johnson & Johnson Company, Raynham, MA) is “MR Conditional” according to ASTM F 2503. The valve demonstrates no known hazards when an MRI is performed under the following conditions:
· MRI can be performed at any time after implantation
· Use an MR system with a static magnetic field of 3 T or less
· Use an MR System with a spatial gradient of 720 gauss/cm or less
· Limit the exposure to RF energy to a whole-body-averaged specific absorption rate (SAR) of 3 W/kg for 15 minutes
· Verify the valve setting after the MRI procedure (see Programming the Valve)
In non-clinical testing, the valve produced a temperature rise of 0.4-degrees C at a maximum whole-body-averaged specific absorption rate (SAR) of 3-W/kg for 15 minutes of MR scanning in a 3-T Excite General Electric MR scanner.
MR image quality may be compromised if the area of interest is relatively close to the device. Distortion may be seen at the boundaries of the artifact. Therefore, optimization of the MR imaging parameters may be necessary.
The following table provides a comparison between the signal void and imaging pulse sequence at 3-Tesla:
Signal Void Pulse Sequence Imaging Plane
1,590-mm2 T1-weighted, spin echo Parallel
1,022-mm2 T1-weighted, spin echo Perpendicular
2,439-mm2 Gradient echo Parallel
2,404-mm2 Gradient echo Perpendicular
Delta Shunt Assembly
The Delta Shunt Assembly (Medtronic Neurosurgery, Goleta, CA) combines the Delta valve with an integral, open-end, radiopaque peritoneal catheter. All Delta shunt assemblies incorporate the same product features as the Delta valves. These include injectable reservoir domes, occluders for selective flushing, and a completely non-metallic design. The valves are fabricated of dissimilar materials - polypropylene and silicone elastomer - reducing the chance of valve sticking and deformation. The normally closed Delta chamber mechanism minimizes over-drainage by utilizing the principles of hydrodynamic leverage. Because of the non-metallic design, the Delta shunt is safe for patients undergoing MRI procedures.
proGAV Programmable Valve
The programmable valve, proGAV (Aesculap, Inc., Center Valley, PA), has magnetic components used for the programming mechanism. This device underwent evaluation relative to the use of a 3-Tesla MR system (i.e., tested for magnetic field interactions, heating, artifacts, and functional alterations). In consideration of the results of these tests, in order to take proper precautions to ensure patient safety, the following guidelines are recommended for scanning a patient with this device:
1) A patient with the programmable valve, proGAV, may undergo MRI at 3-T or less immediately after implantation.
2) Prior to MRI, the programmable valve setting should be determined by appropriate personnel using proper equipment.
3) The exposure to RF energy should be limited to a whole body averaged SAR of 2.1-W/kg for 15-min. (i.e., per pulse sequence).
4) After MRI, the proGAV programmable valve setting should be determined and re-set, as needed.
Pulsar Valve
The Pulsar Valve (Sophysa USA, Inc.) for CSF drainage is a monopressure valve. Its principal is based on the play of a silicone membrane, calibrated in low, medium, or high pressure, ensuring a proximal regulation of CSF flow through the shunt system. The Pulsar Valve is safe for patients undergoing MRI procedures.
Sophy Mini Monopressure Valve
The Sophy Mini Monopressure Valve (Sophysa USA, Inc., Costa Mesa, CA) for CSF drainage has a ball-in-cone mechanism. This device is safe for patients undergoing MRI procedures.
Strata, Strata II, and Strata NSC Programmable CSF Shunt Valves
MRI Information
The Strata, Strata NSC, and Strata II Programmable CSF shunt valves (Medtronic Neurosurgery, Goleta, CA) are Magnetic Resonance Conditional (MR Conditional) in accordance with ASTM F2503. MRI systems of up to 3.0-Tesla may be used any time after implantation and will not damage the Strata, Strata NSC, or Strata II valve mechanisms, but can change the performance level setting. The performance level setting should always be checked before and after MRI exposure. The results of the tests performed to assess magnetic ?eld interactions, artifacts, and heating, indicated the presence of the valves evaluated should present no substantial risk to a patient undergoing an MRI procedure using the following conditions:
· Static magnetic ?eld of 3.0 Tesla or less
· Spatial gradient magnetic field of 720 Gauss/cm or less
· Radio Frequency (RF) Fields with an average Speci?c Absorption Rate (SAR) of 3 W/kg for 15 minutes. Using the GE 3T Excite HD MRI System, the valve experienced a maximum temperature change of 0.4°C over a 15 minute exposure period. The table below provides maximum signal voids (artifact sizes) for standard imaging pulse sequences at 3 Tesla per ASTM F2119.
Signal Void Pulse Sequence Imaging Plane
35.16-cm2 T1-weighted, spin echo Parallel
33.03-cm2 T1-weighted, spin echo Perpendicular
75.91-cm2 Gradient echo Parallel
66.55-cm2 Gradient echo Perpendicular
Adjustment Kits
Do NOT take the Adjustment Tool into an MRI facility as these magnets could potentially be a safety hazard to the patient and/or user. Proximity to MRI suite may impede the mechanism in the Indicator Tool due to the ?eld strength of an MRI magnet. Move out of the vicinity prior to attempting to verify a valve setting.
SOPHY Adjustable Pressure Valve
The principle of the SOPHY Adjustable Pressure Valve (Sophysa USA, Inc., Costa Mesa, CA) resides in the variation in pressure exerted on a ball by a semi-circular spring at various points along its circumference. The spring is attached to a magnetic rotor whose position can be noninvasively altered using an adjustment magnet. A series of indentations allows a variety of positions to be selected, each position representing a different pressure setting. The valve’s ball-in-cone mechanism maintains the selected pressure constant without significant drift.
Because a magnetic component is associated with this device, special MR safety precautions exist for scanning patients with the SOPHY Adjustable Pressure Valve, as follows:
· The pressure settings should always be checked in case of shock on the implantation site.
· Changing pressure settings must only be performed by a neurosurgeon.
· The patient must be advised that carrying his Patient Identification Card is important and necessary for the follow-up of the clinical conditions.
· Patients undergoing MRI exposure should be advised that they might feel a small yet harmless effect due to MRI.
· The pressure settings should always be checked before and after MRI exposure, or after strong magnetic field exposure.
· The patient must be advised that in the case of implantation on the skull vibrations due to CSF flow may be perceived.
· Patients with implanted valve systems must be kept under close observation for symptoms of shunt failure.
MR healthcare professionals are advised to contact the respective manufacturer in order to obtain the latest safety information to ensure patient safety relative to the use of an MR procedure.
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