Safety and function of programmable ventriculo-peritoneal shunt valves: An in vitro 7 Tesla magnetic resonance imaging study

OBJECTIVE

The quantity of ultra-high field MRI neuroimaging studies has rapidly increased. This study tests function, safety, and image artifacts of two frequently implanted programmable ventriculo-peritoneal (VP) shunt valves in a 7T MRI system.

METHODS

All tests were performed using a whole-body 7T MRI system. Three proGAV 2.0 and 3 CODMAN CERTAS® Plus programmable VP-shunt valves were tested in three steps. 1) Deflection angle tests close to the bore opening at the location of a static magnetic field gradient of 3-5 T/m. 2) Valves were fixed on a spherical phantom in 3 positions (a. lateral, b. cranial, c. cranial with 22.5° tilt anteriorly) and assessed for keeping the programmed pressure setting and reprogrammability. 3) Valves were fixed on the phantom and positioned lateral in a radiofrequency head coil. MRI scans were performed for both models, including MPRAGE, GRE and SE sequences.

RESULTS

Deflection angles were moderate (13°, 14°, 13°) for the proGAV valves and close to critical (43°, 43°, 41°) for the CODMAN valves at the test location. Taking a scaling factor of 2-3 for the maximum spatial magnetic field gradient accessible to a patient within the magnet bore into account renders both valves MR unsafe regarding ferromagnetic attraction. The proGAV valves kept the pressure settings in all positions and were reprogrammable in positions a. and b. In position c., reprogrammability was lost. The CODMAN valves changed their pressure setting and reprogrammability was lost in all positions. MR image signal homogeneity was unaltered in the phantom center, artifacts limit the assessability of structures in close vicinity to the valves.

CONCLUSION

Both tested programmable VP-shunt valves are MR unsafe for 7T systems. Novel programming mechanisms using permanent magnets with sufficient magnetic coercivity or magnet-free mechanisms may allow the development of programmable VP-shunt valves that are conditional for 7T MR systems.

Development of shunt valves used for treating hydrocephalus: comparison with endoscopy treatment

The pathophysiology of hydrocephalus is not clearly defined. Thus, treatment will remain empirical until a fuller understanding of the various forms of hydrocephalus is achieved. Valve-controlled shunting has been the mainstay of therapy since the late 1950s. Initially, shunting occurred from the ventricular system to the atrium. In the 1970s, VA shunts were replaced by ventriculoperitoneal shunts as the primary location for the distal end. Multiple types of one-way valve systems have been developed in the pursuit of draining the appropriate amount of CSF that avoids either overdrainage or underdrainage while preserving normal brain development and cognition. These valves are reviewed and compared as to their function. Other locations for the distal end of the shunting system are reviewed to include pleural space and gallbladder. The lumbar subarachnoid space as the proximal location for a shunt is also reviewed. The only other surgical alternative for treating hydrocephalus is endoscopic third ventriculostomy. Since 2000, approximately 50% of children with hydrocephalus have been shown to be candidates for ETV. The benefits are the lack of need for an artificial shunt system and thus lower rates of infection and over time fewer reoperations. Future progress is dependent on improved shunt valve systems that are affordable worldwide and ready availability of ETV in developing countries. Anatomic and molecular causes of hydrocephalus need to be defined so that medications or genetic modifications become available for potential cure of hydrocephalus.

Breast Tissue Expander With Radiofrequency Identification Port: Assessment of MRI Issues

OBJECTIVE. Breast tissue expanders with magnetic ports are MRI unsafe, preventing patients from benefiting from the diagnostic capabilities of MRI. A tissue expander was recently developed with a radiofrequency identification (RFID) port used for needle location and expansion that may be acceptable for a patient undergoing MRI. The purpose of this investigation was to evaluate MRI issues using standardized techniques and well-accepted methods for this tissue expander with RFID port. MATERIALS AND METHODS. The breast tissue expander with RFID port (Motiva Flora Tissue Expander, Establishment Labs) was assessed for magnetic field interactions (translational attraction and torque, 3 T), MRI-related heating (1.5 T/64 MHz and 3 T/128 MHz), artifacts (3 T), and functional changes associated with different MRI conditions (1.5 T/64 MHz and 3 T/128 MHz). RESULTS. Magnetic field interactions were minor (deflection angle of 2° and no torque) and thus will not pose a risk. At 1.5 T/64 MHz and 3 T/128 MHz, the highest temperature elevations (1.7°C and 1.9°C, respectively) were physiologically inconsequential. The tissue expander with RFID port exhibited relatively small artifacts on MRI. Exposures of the tissue expander with RFID port to different MRI conditions did not impact the ability to localize the RFID port or to read the electronic serial number. CONCLUSION. The findings indicated that this tissue expander with RFID port is "MR Conditional" for a patient referred for MRI at 1.5 T or 3 T. Importantly, the relatively small artifact associated with this implant offers potential advantages for patients undergoing MRI compared with tissue expanders that have magnetic ports that create substantial signal losses and distortions on MR images.

Unexpectedly Smaller Artifacts of 3.0-T Magnetic Resonance Imaging than 1.5 T: Recommendation of 3.0-T Scanners for Patients with Magnet-Resistant Adjustable Ventriculoperitoneal Shunt Devices

BACKGROUND

Magnetic resonance imaging (MRI) artifacts of adjustable shunt devices are thought to be similar to metal clip artifacts, in that they are larger with higher field strength scanners. We have published several reports about the artifacts of new MRI-resistant adjustable shunt devices, and we found a case in which a 3.0-T scanner showed smaller artifacts than the 1.5-T scanner. We aimed to clarify whether this claim is true or not.

METHODS

Under permission of our institutional Ethical Committee, 2 volunteers underwent imaging studies using 3.0-T and 1.5-T scanners from GE, Siemens, and Philips. Four MRI-resistant adjustable shunt devices-proGAV2.0 (Miethke), Codman Certas Plus (Johnson & Johnson), Polaris (Sophysa), and Strata MR valve (Medtronic)-were fixed on the left temporal scalp. Routine MRI images, including T1-and T2-weighted imaging, fluid-attenuated inversion recovery, diffusion-weighted imaging (DWI), and magnetic resonance angiography (MRA), were obtained. We also compared artifacts between a 3.0-T scanner and a-1.5 T scanner in 4 patients.

RESULTS

The 3.0 T-scanners showed smaller artifacts than the 1.5-T scanners on DWI and MRA images for all shunt devices and scanners. In the other sequences, the results depended on the MRI scanner manufacturer; however, the GE 3.0-T scanner showed smaller artifacts in every sequence. This was also true in the 4 clinical cases.

CONCLUSIONS

A 3.0-T scanner is recommended over a 1.5-T scanner for patients with MRI-resistant adjustable shunt devices in the diagnosis of acute ischemic condition or when using GE scanners.

Setting pressure can change the size and shape of MRI artifacts caused by adjustable shunt valves: a study of the 4 newest models

OBJECTIVE

Adjustable shunt valves that have been developed for the management of hydrocephalus all rely on intrinsically magnetic components, and artifacts with these valves on MRI are thus inevitable. The authors have previously reported that the shapes of shunt artifacts differ under different valve pressures with the proGAV 2.0 valve. In the present study the authors compared the size and shape of artifacts at different pressure settings with 4 new-model shunt valves.

METHODS

The authors attached 4 new models of MRI-resistant shunt valve to the temporal scalp of a healthy volunteer: the proGAV 2.0; Codman Certas Plus; Polaris; and Strata MR. They set 3 different scales of pressures for each valve, depending on magnet orientation to the body axis. Artifacts were evaluated and compared among all valves on a 3.0-T GE scanner and 2 valves were also evaluated on a Philips scanner and a Siemens scanner. In-plane artifact sizes were evaluated as the maximum distance of the artifact from the expected scalp.

RESULTS

The sizes and shapes of artifacts changed depending on valve pressure for all valves on the 3 different MRI scanners. Artifacts were less prominent on spin echo sequences than on gradient echo sequences. For diffusion-weighted imaging and time-of-flight MR angiography, the authors matched image numbers within the same sequence and compared appearances of artifacts. For all valves, the number of images affected by artifacts and the image number showing the largest artifact differed among valve settings.

CONCLUSIONS

Artifacts of all adjustable shunt valves showed gross changes corresponding to pressure setting. Not only the maximum distance of artifacts but also the shape changed significantly. The authors suggest that changing pressure settings offers one of the easiest ways to minimize artifacts on MRI.

Assessment of MRI issues at 1.5 T for the Temperature Logger Implant

PURPOSE

The Temperature Logger Implant is a newly developed device that is capable of providing data for animal studies on thermoregulatory function, hibernation, hypothermia, and general health. During research, it may be necessary to conduct a magnetic resonance imaging (MRI) examination on an animal with this device implanted to assess anatomical changes or other conditions. Notably, this new device was specially designed to be unaffected by the electromagnetic fields used for MRI. Therefore, to verify that there would be no problems related to MRI, the purpose of this investigation was to evaluate MRI-related issues for the Temperature Logger Implant.

METHODS

Tests were performed on the Temperature Logger Implant using well-accepted techniques to evaluate magnetic field interactions (translational attraction and torque, 1.5 T), MRI-related heating (whole body averaged specific absorption rate, 2.9 W/kg), artifacts (T1-weighted, spin echo and gradient echo pulse sequences), and functional changes related to exposure to eight different imaging conditions.

RESULTS

Magnetic field interactions were relatively low (deflection angle 4°, no torque) and heating was minor (highest temperature rise, > 1.1 °C) indicating that these factors will not pose a hazard to an animal. The largest artifact (gradient echo pulse sequence) extended 10 mm from the size and shape of the Temperature Logger Implant. Exposure to the eight different conditions at 1.5 T/ 64 MHz did not alter or damage the operational aspects of the device.

CONCLUSIONS

The findings demonstrated that MRI can be performed safely on an animal with this new Temperature Logger Implant and, thus, this device is deemed "MR Conditional" (i.e., using current labeling terminology), according to the conditions used in this investigation.

Assessment of MRI issues for a new cerebral spinal fluid shunt, gravitational valve (GV)

PURPOSE

A gravitational valve (GV) may be used to treat hydrocephalus, offering possible advantages that include avoidance of over drainage and long-term complications. Because a GV is made from metal, there are potential safety and other problems related to the use of MRI. The objective of this investigation was to evaluate MRI-related issues (i.e., magnetic field interactions, heating, and artifacts) for a newly developed, metallic GV.

METHODS

Tests were performed on the GV (GAV 2.0) using well-accepted techniques to assess magnetic field interactions (translational attraction and torque, 3-Tesla), MRI-related heating (1.5-T/64-MH and 3-T/128-MHz, whole body averaged SAR, 2.7-W/kg and 2.9-W/kg, respectively), artifacts (3-Tesla; gradient echo and T1-weighted, spin echo sequences), and possible functional changes related to exposures to different MRI conditions (exposing six samples each to eight different pulse sequences at 1.5-T/64-MHz and 3-T/128-MHz).

RESULTS

Magnetic field interactions were not substantial (deflection angle 2°, no torque) and heating was minor (highest temperature rise, ≥1.9°C, highest background temperature rise, ≥1.7°C). Artifacts on the gradient echo pulse sequence extended approximately 10mm from the size and shape of the GV. The different exposures to 1.5-T/64-MHz and 3-T/128-MHz conditions did not alter or damage the operational aspects of the GV samples.

CONCLUSIONS

The findings demonstrated that MRI can be safely used in patients with this GV and, thus, this metallic implant is deemed acceptable or "MR Conditional" (i.e., using current labeling terminology), according to the conditions used in this study.

Breast Tissue Expanders with Magnetic Ports: Clinical Experience at 1.5 T

BACKGROUND

The purpose of this study was to evaluate breast tissue expanders with magnetic ports for safety in patients undergoing abdominal/pelvic magnetic resonance angiography before autologous breast reconstruction.

METHODS

Magnetic resonance angiography of the abdomen and pelvis at 1.5 T was performed in 71 patients in prone position with tissue expanders with magnetic ports labeled "MR Unsafe" from July of 2012 to May of 2014. Patients were monitored during magnetic resonance angiography for tissue expander-related symptoms, and the chest wall tissue adjacent to the tissue expander was examined for injury at the time of tissue expander removal for breast reconstruction. Retrospective review of these patients' clinical records was performed. T2-weighted fast spin echo, steady-state free precession and gadolinium-enhanced spoiled gradient echo sequences were assessed for image artifacts.

RESULTS

No patient had tissue expander or magnetic port migration during the magnetic resonance examination and none reported pain during scanning. On tissue expander removal (71 patients, 112 implants), the surgeons reported no evidence of tissue damage, and there were no operative complications at those sites of breast reconstruction.

CONCLUSION

Magnetic resonance angiography of the abdomen and pelvis in patients with certain breast tissue expanders containing magnetic ports can be performed safely at 1.5 T for pre-autologous flap breast reconstruction perforator vessel mapping.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

The Contribution of Common Surgically Implanted Hardware to Functional MR Imaging Artifacts

BACKGROUND AND PURPOSE

Blood oxygenation level-dependent MR imaging is increasingly used clinically to noninvasively assess cerebrovascular reactivity and/or language and motor function. However, many patients have metallic implants, which will induce susceptibility artifacts, rendering the functional information uninformative. Here, we calculate and interpret blood oxygenation level-dependent MR imaging artifact impact arising from surgically implanted hardware.

MATERIALS AND METHODS

A retrospective analysis of all blood oxygenation level-dependent MRIs (n = 343; B0 = 3T; TE = 35 ms; gradient echo EPI) acquired clinically (year range = 2006-2014) at our hospital was performed. Blood oxygenation level-dependent MRIs were most commonly prescribed for patients with cerebrovascular disease (n = 80) or patients undergoing language or motor localization (n = 263). Artifact volume (cubic centimeters) and its impact on clinical interpretation were determined by a board-certified neuroradiologist.

RESULTS

Mean artifact volume associated with intracranial hardware was 4.3 ± 3.2 cm(3) (range = 1.1-9.4 cm(3)). The mean artifact volume from extracranial hardware in patients with cerebrovascular disease was 28.4 ± 14.0 cm(3) (range = 6.1-61.7 cm(3)), and in patients with noncerebrovascular disease undergoing visual or motor functional mapping, it was 39.9 (3)± 27.0 cm(3) (range = 6.9-77.1 cm(3)). The mean artifact volume for ventriculoperitoneal shunts was 95.7 ± 39.3 cm(3) (range = 64.0-139.6 cm(3)). Artifacts had no-to-mild effects on clinical interpretability in all patients with intracranial implants. Extracranial hardware artifacts had no-to-moderate impact on clinical interpretability, with the exception of 1 patient with 12 KLS-Martin maxDrive screws with severe artifacts precluding clinical interpretation. All examined ventriculoperitoneal shunts resulted in moderate-to-severe artifacts, limiting clinical interpretation.

CONCLUSIONS

Blood oxygenation level-dependent MR imaging yields interpretable functional maps in most patients beyond a small (30-40 cm(3)) artifact surrounding the hardware. Exceptions were ventriculoperitoneal shunts, particularly those with programmable valves and siphon gauges, and large numbers of KLS-Martin maxDrive screws.

Prosepective Study to Evaluate Rate and Frequency of Perturbations of Implanted Programmable Hakim Codman Valve After 1.5-Tesla Magnetic Resonance Imaging

BACKGROUND

Exposure to magnetic fields may alter the settings of programmable ventriculoperitoneal shunt valves or even cause permanent damages to these devices. There is little information about this topic, none on live patients.

OBJECTIVE

To investigate the effects of 1.5-tesla magnetic resonance imaging (MRI) on Hakim-Codman (HC) pressure programmable valves implanted in our hospital.

METHODS

A single-center prospective study to assess the rate of perturbations of HC programmable valve implanted. One hundred consecutive patients implanted for different clinical reasons between 2008 and 2012 were examined. A conventional skull x-ray before and after a standard MRI on 1.5 tesla. We evaluated before and after results, analyzed modification rate, and verified eventual damages to the implanted devices.

RESULTS

Implanted HC valves are extremely handy and durable, even if they are likely to change often due to the exposure to magnetic fields. None of the patients complained of heating effects. Oscillations range from 10-30 mm H2O with a patient who reached 50 mm H2O and 1 who reached 60 mm H2O. Global alteration rate was 40%: 10 patients (10%) experienced a 10 mm H2O change; 14 patients (14%) had a 20 mm H2O change; 6 patients (6%) had a 30 mm H2O change; 8 patients (8%) had a 40 mm H2O change; 1 patient had a 50 mm H2O change; and 1 patient had a 60 mm H2O change.

CONCLUSIONS

HC valves presented a variable perturbation rate, with an alteration rate of 40% with 1.5-telsa MRI. We have not observed malfunctioning hardware as a result of magnetic influence. We claim ​ a cranial x-ray immediately after the MRI because of a high risk (40%) of decalibration, especially in patients with low ventricles compliance.

Initial experience with the Codman Certas adjustable valve in the management of patients with hydrocephalus

Background

A new adjustable valve, the Codman Certas^TM valve for treatment of hydrocephalus was introduced into clinical practice in January 2011. It has 8 different settings with an opening pressure varying from 36 to over 400 mm H₂O at a flow rate of 20 mL/h. The 8th setting is designed to provide a "virtual off" function. The objective of this report is to describe the initial clinical experience with the Certas^TM valve and evaluate clinical usage with the main focus on the portable adjustment device - Therapeutic Management System (TMS), the “virtual off” setting and compatibility with magnetic resonance imaging (MRI).

Findings

Forty-two patients with hydrocephalus from different etiologies were treated with the Certas^TM adjustable shunt system. Data regarding implantation procedures, the use of the TMS system, x-ray imaging, and MRI procedures were recorded prospectively. All patients had clinical follow-up at four weeks after implantation and every three months until a stable clinical condition was obtained.

The mean time for follow-up was 8.6 months (1–16.6). Seventy-one adjustments were performed with the TMS, 12 were problematic. Twenty-nine MRI procedures were performed and did not cause accidental resetting. Five patients were treated with the "virtual off" function for a period.

Conclusions

We found the Certas^TM valve valuable in the treatment of hydrocephalus, usability of the TMS was high because it is small and portable, but in some cases we experienced adjustment problems with the first procedures performed by a surgeon, indicating that there is a learning curve. The "virtual off" function provided a possibility of treating over-drainage without the need for shunt ligation or other invasive procedures.

3T magnetic resonance imaging testing of externally programmable shunt valves

Background:

Exposure of externally programmable shunt-valves (EPS-valves) to magnetic resonance imaging (MRI) may lead to unexpected changes in shunt settings, or affect the ability to reprogram the valve. We undertook this study to examine the effect of exposure to a 3T MRI on a group of widely used EPS-valves.

Methods:

Evaluations were performed on first generation EPS-valves (those without a locking mechanism to prevent changes in shunt settings by external magnets other than the programmer) and second generation EPS-valves (those with a locking mechanisms). Fifteen new shunt-valves were divided into five groups of three identical valves each, and then exposed to a series of six simulated MRI scans. After each of the exposures, the valves were evaluated to determine if the valve settings had changed, and whether the valves could be reprogrammed. The study produced 18 evaluations for each line of shunt-valves.

Results:

Exposure of the first generation EPS-valves to a 3T magnetic field resulted in frequent changes in the valve settings; however, all valves retained their ability to be reprogrammed. Repeated exposure of the second generation EPS-valves has no effect on shunt valve settings, and all valves retained their ability to be interrogated and reprogrammed.

Conclusions:

Second generation EPS-valves with locking mechanisms can be safely exposed to repeated 3T MRI systems, without evidence that shunt settings will change. The exposure of the first generation EPS-valves to 3T MRI results in frequent changes in shunt settings that necessitate re-evaluation soon after MRI to avoid complications.

Hydrodynamics of the Certas™ programmable valve for the treatment of hydrocephalus

Background

The new Certas™ shunt for the treatment of hydrocephalus has seven standard pressure settings that according to the manufacturer range from 36 to 238 mmH₂O, and an additional “Virtual Off” setting with an opening pressure >400 mmH₂O. Information on actual pressure response and reliability of shunt performance is important in clinical application, especially the “Virtual Off” setting as a non-surgical replacement for shunt ligation. The objective of this study was to evaluate the in-vitro hydrodynamic performance of the Certas™ shunt.

Methods

Six new Certas™ shunts with proximal and distal catheters were tested with an automated, computerized test system that raised the pressure from zero to a maximum pressure and back to zero at each valve setting. Opening pressure and flow resistance were determined.

Results

For settings 1–7 the measured opening pressure range was 26 to 247 mmH₂O, and the mean change in opening pressure for a one-step adjustment was between 33 and 38 mmH₂O. For setting 8 (“Virtual Off”) the measured mean opening pressure was 494 ± 34 mmH₂O (range 451 to 556 mmH₂O). The mean outflow resistance was 7.0 mmHg/ml/min (outflow conductance 17.9 μl/s/kPa).

Conclusions

The six shunts had similar characteristics and closely matched the manufacturer’s specifications for opening pressure at settings 1–7. The opening pressure for the “Virtual Off” setting was nearly 500 mmH₂O, which is 100 mmH₂O higher than the manufacturer’s specification of “>400” and should be functionally off for most patients with communicating hydrocephalus. Clinical studies are needed to evaluate if the CSF dynamic profile persists after implantation in patients.