Magnetically programmable shunt valve: MRI at 3-Tesla

The safety profile of Tumor Treating Fields (TTFields) therapy in glioblastoma patients with ventriculoperitoneal shunts

INTRODUCTION

Tumor Treating Fields (TTFields, 200 kHz) therapy is a noninvasive, locoregional cancer treatment approved for use in newly diagnosed glioblastoma (GBM), recurrent GBM, and malignant pleural mesothelioma. GBM patients with hydrocephalus may require implantation of a ventriculoperitoneal (VP) shunt, however, the current TTFields therapy label does not include the use of VP shunts in GBM patients due to insufficient safety data. This analysis evaluates the safety of TTFields therapy use in this population.

METHODS

Unsolicited post-marketing global surveillance data from patients with GBM and a VP shunt (programmable/non-programmable) who received TTFields therapy between November 2012-April 2021 were retrospectively analyzed. Adverse events (AEs) were assessed using the Medical Dictionary for Regulatory Activities version 24.0.

RESULTS

Overall, 156 patients with VP shunts were identified and included in this analysis. In total, 77% reported  ≥ 1 AE; the most common TTFields therapy-related AEs were non-serious and localized, beneath-array skin AEs (43%). The incidence and categories of AEs were comparable between patients with or without VP shunts. Six patients with VP shunts experienced seven serious TTFields therapy-related AEs: skin erosion at the shunt site (n = 3); wound dehiscence at the shunt site (n = 2) and at the resection scar (n = 2). No shunt malfunctions were deemed related to TTFields therapy.

CONCLUSIONS

In the real-world setting, TTFields therapy in GBM patients with VP shunts demonstrated good tolerability and a favorable safety profile. There was no evidence that TTFields therapy disrupted VP shunt effectiveness. These results suggest TTFields therapy may be safely used in patients with VP shunts.

Magnetic resonance imaging in children with implants

As access to MRI in pediatrics increases, the radiologist needs to become acquainted with the basic principles of MRI safety. As part of the image acquisition, the static magnetic field, gradient system, and the radiofrequency transmit-receive coil interact with medical and non-medical implants and can result in serious injury. The main stage of risk triage is based on the determination of whether the implant is MRI-safe, conditional, unsafe or unknown. Guiding principles include the strict adherence to manufacturer specifications for MRI-conditional implants and the assumption that an unknown implant is MR-unsafe. In this article we review considerations for common medical implants encountered in pediatrics including ventriculoperitoneal shunts, orthopedic hardware, orthodontic hardware, pacemakers, vascular stents, vagal nerve stimulators and cochlear implants. Finally, we review a set of high-yield considerations, including the non-communicative patient (sedated or non-verbal), susceptibility artifacts from unclear source, and the approach to an unknown implant.

Smartphones and Programmable Shunts: Are These Indispensable Phones Safe and Smart?

OBJECTIVE

This study aimed to determine whether smartphones affect programmable shunts.

METHODS

iPhone 5S (Apple Inc., Cupertino, CA, USA) and Samsung Galaxy S5 (Samsung Electronics, Gumi, South Korea) smartphones were chosen for this study. For both phones, magnetic field mapping was performed with 3-dimensional magnetic scanning systems constructed with high-precision motorized stages, and a Hall effect sensor was used to measure the flux density on the smartphone surface. The distance (h) between the distal outlet of the reservoir and the rugby ball of the Strata valve (Medtronic Inc., Minneapolis, MN, USA) was measured using highly sensitive microanalysis optical method. During optical microanalysis, while keeping a 3-cm distance between the valve and the magnetic generator, the h value (μm) was recorded for different magnetic flux densities (MFDs). Then, direct x-ray radiography was performed for radiologic assessment after each process under different magnetic fields. For analysis of the Codman Certas valve (Codman Neuro, Raynham, MA, USA), the magnet orientation and the angle between the magnet with the tantalum ball were measured with the same optical analysis.

RESULTS

Maximum MFDs found 62 G for iPhone 5S and 61 G for Samsung Galaxy S5. When the magnetic generator formed a current at 0, 30, 60, and 90 G, the h values of the Strata valve adjusted to 100 mm H₂O opening pressure were 320, 280, 190, and 175 μm, respectively. When the magnetic generator was removed from the environment, the h value returned to 320 μm. In direct graphs taken after each optical analysis at different Gauss values, substitution was not observed at the indicator. The angle in the Codman Certas valve was 123.9°, 112.5°, and 103.6° at the magnetic flux densities of 0, 60, and 90 G, respectively. When the magnetic field was removed (0 G), the angle was still 103.6°, suggesting an irreversible effect in the shunt construct.

CONCLUSIONS

Smartphones exert reversible effects on Strata programmable valves without producing remarkable radiologic findings and irreversible effects on Codman Certas valves.

Shunt Overdrainage Caused by Displacement of the Pressure Control Cam after Pressure Adjustment

Although the Codman-Hakim programmable valve is one of most popular shunt systems used in the clinical practice for the treatment of hydrocephalus, malfunctions related with this system have been also reported which lead to underdrainage or overdrainage of the cerebrospinal fluid. While obstruction of the ventricular catheter by tissue materials or hematoma and catheter disconnection are relatively common, the malfunction of the valve itself is rare. Herein, we report on a rare case of shunt overdrainage caused by displacement of the pressure control cam after pressure adjustment. A 57-year-old female, who underwent a ventriculoperitoneal shunt eight years ago, experienced aggravating symptoms of shunt overdrainage after pressure adjustment. Displacement of the pressure control cam was revealed on the X-ray, and a shunt revision was performed. The purpose of this report is to provide a working knowledge of the valve structure and to enhance the ability to interpret the valve setting on an X-ray for diagnosis of valve malfunction.

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.

Evaluation of magnetic resonance imaging issues for implantable microfabricated magnetic actuators

The mechanical robustness of microfabricated torsional magnetic actuators in withstanding the strong static fields (7 T) and time-varying field gradients (17 T/m) produced by an MR system was studied in this investigation. The static and dynamic mechanical characteristics of 30 devices were quantitatively measured before and after exposure to both strong uniform and non-uniform magnetic fields. The results showed no statistically significant change in both the static and dynamic mechanical performance, which mitigate concerns about the mechanical stability of these devices in association with MR systems under the conditions used for this assessment. The MR-induced heating was also measured in a 3-T/128-MHz MR system. The results showed a minimal increase (1.6 °C) in temperature due to the presence of the magnetic microactuator array. Finally, the size of the MR-image artifacts created by the magnetic microdevices were quantified. The signal loss caused by the devices was approximately four times greater than the size of the device.

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.

Maintained functionality of an implantable radiotelemetric blood pressure and heart rate sensor after magnetic resonance imaging in rats

Radiotelemetric sensors for in vivo assessment of blood pressure and heart rate are widely used in animal research. MRI with implanted sensors is regarded as contraindicated as transmitter malfunction and injury of the animal may be caused. Moreover, artefacts are expected to compromise image evaluation. In vitro, the function of a radiotelemetric sensor (TA11PA-C10, Data Sciences International) after exposure to MRI up to 9.4 T was assessed. The magnetic force of the electromagnetic field on the sensor as well as radiofrequency (RF)-induced sensor heating was analysed. Finally, MRI with an implanted sensor was performed in a rat. Imaging artefacts were analysed at 3.0 and 9.4 T ex vivo and in vivo. Transmitted 24 h blood pressure and heart rate were compared before and after MRI to verify the integrity of the telemetric sensor. The function of the sensor was not altered by MRI up to 9.4 T. The maximum force exerted on the sensor was 273 ± 50 mN. RF-induced heating was ruled out. Artefacts impeded the assessment of the abdomen and thorax in a dead rat, but not of the head and neck. MRI with implanted radiotelemetric sensors is feasible in principal. The tested sensor maintains functionality up to 9.4 T. Artefacts hampered abdominal and throacic imaging in rats, while assessment of the head and neck is possible.

More malfunctioning Medos Hakim programmable valves: cause for concern?

Object

In recent years, the authors have noticed a growing number of programmable valve defects at their institution. Therefore, they conducted this study to evaluate the increased incidence of malfunctioning valves.

Methods

They investigated all revisions that had been performed at their institution between 1994 and 2010 for dislodgement of the stator of a standard Medos Hakim programmable valve with a prechamber.

Results

Fifteen valves were removed because of dislodged stators. The valves had been implanted between May 16, 1993, and December 27, 2002, and were explanted between February 19, 2006, and January 22, 2010. Thus, the valves had been in place for a mean period of 11 years (median 11 years, range 7–14 years). The percentage of dislodged stators was almost 3% (15 of 546 valves). Particularly noteworthy is that all malfunctioning valves were found in children who had been younger than 1 year of age at the time of implantation.

Conclusions

Medos Hakim programmable valve malfunctions are rare events but should receive careful attention. When the pressure setting cannot be adjusted, a malfunction should always be suspected and radiographic imaging should be performed to assess the valve. Stator dislodgement is the most serious form of valve adjustment failure.

Programmable shunt valves: in vitro assessment of safety of the magnetic field generated by a portable game machine

Cerebrospinal fluid (CSF) shunts are frequently used to treat hydrocephalus. The use of a programmable shunt valve allows physicians to easily change the opening pressure. Since patients with adjustable CSF shunt valves may use portable game machines, the permanent magnets in these machines may alter the shunt valve programmed settings or permanently damage the device. This study investigated the risk of unintentional valve adjustment associated with the use of game machines in patients with programmable CSF shunt valves. Four adjustable valves from 4 different manufacturers, Sophysa Polaris model SPV (Polaris valve), Miethke proGAV (proGAV), Codman Hakim programmable valve (CHPV), and Strata II small valve (Strata valve), were evaluated. Magnetic field interactions were determined using the portable game machine, Nintendo DS Lite (DS). The maximum distance between the valve and the DS that affected the valve pressure setting was measured by x-ray cinematography. The Polaris valve and proGAV were immune to unintentional reprogramming by the DS. However, the settings of the CHPV and Strata valves were randomly altered by the DS. Patients with an implanted shunt valve should be made aware of the risks posed by the magnetic fields associated with portable game machines and commonly used home electronics.

Adjustable shunt valve-induced magnetic resonance imaging artifact: a comparative study

OBJECT

In this paper, the authors' goal was to compare the artifact induced by implanted (in vivo) adjustable shunt valves in spin echo, diffusion weighted (DW), and gradient echo MR imaging pulse sequences.

METHODS

The MR images obtained in 8 patients with proGAV and 6 patients with Strata II adjustable shunt valves were assessed for artifact areas in different planes as well as the total volume for different pulse sequences.

RESULTS

Artifacts induced by the Strata II valve were significantly larger than those induced by proGAV valve in spin echo MR imaging pulse sequence (29,761 vs 2450 mm(3) on T2-weighted fast spin echo, p = 0.003) and DW images (100,138 vs 38,955 mm(3), p = 0.025). Artifacts were more marked on DW MR images than on spin echo pulse sequence for both valve types.

CONCLUSIONS

Adjustable valve-induced artifacts can conceal brain pathology on MR images. This should influence the choice of valve implantation site and the type of valve used. The effect of artifacts on DW images should be highlighted pending the development of less MR imaging artifact-inducing adjustable shunt valves.

Evaluation of RF heating on hip joint implant in phantom during MRI examinations

PURPOSE

We evaluate radiofrequency (RF) heating of two kinds of hip joint implants of different sizes, shapes and materials. Temperature rises at various positions of each implant are measured and compared with a computer simulation based on electromagnetic-field analysis.

METHODS

Two kinds of implants made of cobalt-chromium alloy and titanium alloy were embedded at a 2-cm depth of tissue-equivalent gel-phantom. The phantom was placed parallel to the static magnetic field of a 1.5 T MRI device. Scans were conducted at the specific absorption rate of 2.5 W/kg for 15 min, and temperatures were recorded with RF-transparent fiberoptic sensors. Temperatures of the implant surface were measured at 6 positions, from the tip to the head. Measured temperature rises were compared with the results of electromagnetic-field analysis.

RESULTS

The maximum temperature rise was observed at the tip of each implant, and it was 9.0 degrees C for the cobalt- chromium implant and 5.3 degrees C for the titanium implant. The simulated heating positions with electromagnetic-field analysis accorded with experimental results. However, a difference in temperature rise was seen with the titanium implant.

CONCLUSION

RF heating was confirmed to take place at both ends of the implants in spite of their different shapes. The maximum temperature rise was observed at the tip where there is large curvature. The value was found to depend on physical properties of the implant materials. The discrepancy between experimental and simulated temperature rises was presumed to be the result of an incomplete model for the titanium implant.

MRI safety: nephrogenic systemic fibrosis and other risks

Magnetic resonance imaging (MRI) is now a commonly used imaging modality in many neurosurgical and neurological conditions. Although generally regarded as safe, there are a number of important safety considerations. These include a recently recognised, rare condition termed nephrogenic systemic fibrosis (NSF) that occurs in patients with significant renal impairment who receive gadolinium based contrast. Currently, NSF remains poorly understood and there is no universally effective treatment beyond the avoidance of contrast in patients with significant renal impairment. Other safety considerations include MRI contraindicated devices and the role of MRI in pregnancy.

Overdrainage of cerebrospinal fluid caused by detachment of the pressure control cam in a programmable valve after 3-tesla magnetic resonance imaging

The authors report a rare case of overdrainage of the CSF caused by the malfunction of a Codman-Hakim programmable valve (CHPV) following a 3-T MR imaging procedure. Nine years ago this 72-year-old woman underwent ventriculoperitoneal shunt placement with a CHPV system for hydrocephalus due to subarachnoid hemorrhage. The postoperative course was uneventful and the system functioned well. A radiograph obtained immediately after 3-T MR imaging revealed that the pressure control cam in the valve system was detached from the base plate. Intracranial hypotension syndrome occurred several hours after the MR imaging study, and a CT scan revealed a decrease in ventricle size. A revision of the system promptly resolved the symptoms, and a postoperative CT scan revealed that the ventricle size was restored to normal. Examination of the extracted valve showed a Y-shaped crack in the plastic housing as well as detachment of the white marker and cam from the base plate. A reduction in the power of the flat spring to press the valve ball led to CSF overdrainage because of a loss of support by the cam. Because the patient had incurred no head injury during the day and radiographic studies of the system 5 years previously had shown detachment of the white marker, damage to the system might have been caused by a past impact. These facts may indicate that the antimagnetic performance of the system could have decreased due to a previous impact and that the strong magnetic force in a 3-T MR imaging environment might have caused detachment of the cam.

In vitro evaluation of MR imaging issues at 3T for aneurysm clips made from MP35N: Findings and information applied to 155 additional aneurysm clips

BACKGROUND AND PURPOSE

Aneurysm clips need to be tested at 3T to characterize MR imaging concerns, including magnetic field interactions, MR imaging-related heating, and artifacts. Therefore, we evaluated these risks for aneurysm clips.

MATERIALS AND METHODS

Three different MP35N aneurysm clips (Codman Slim-Line Aneurysm Clip, straight, blade length 25-mm; Codman Slim-Line Aneurysm Clip Graft, 5-mm diameter x 5-mm width; Codman Slim-Line Aneurysm Clip, reinforcing 30 degrees angle, 6-mm x 18-mm) that represented the largest mass for 155 additional clips made from MP35N were tested. The clips were evaluated at 3T for magnetic field interactions, heating, and artifacts. We studied MR imaging-related heating, placing the clip in a gelled-saline-filled phantom with MR imaging performed by using a transmit/receive radio-frequency body coil at a whole-body average SAR of 3 W/kg for 15 minutes. Artifacts were characterized by using T1-SE and GRE pulse sequences.

RESULTS

Each aneurysm clip showed relatively minor magnetic field interactions, which would not cause movement in situ. Heating was not excessive (highest temperature change, <1.8 degrees C). Artifacts may create problems if the area of interest is in the same area or close to the aneurysm clip.

CONCLUSIONS

The results of this investigation demonstrated that it would be acceptable (ie, "MR conditional" using current terminology) for patients with these aneurysm clips to undergo MR imaging at < or =3T. Notably, on the basis of the sizes of the clips that underwent testing, these findings pertain to 155 additional aneurysm clips made from the same material.

Magnetic toys: forbidden for pediatric patients with certain programmable shunt valves?

BACKGROUND

Inadvertent adjustments and malfunctions of programmable valves have been reported in cases in which patients have encountered powerful electromagnetic fields such as those involved in magnetic resonance imaging, but the potential effects of magnetic toys on programmable valves are not well known.

MATERIALS AND METHODS

The magnetic properties of nine toy magnets were examined. To calculate the effect of a single magnet over a distance, the magnetic flux density was directly measured using a calibrated Hall probe at seven different positions between 0 and 120 mm from the magnet. Strata II small (Medtronic Inc.), Codman Hakim (Codman & Shurtleff), and Polaris (Sophysa) programmable valves were then tested to determine the effects of the toy magnets on each valve type.

RESULTS

The maximal flux density of different magnetic toys differed between 17 and 540 mT, inversely proportional to the distance between toy and measurement instrument. Alterations to Strata and Codman valve settings could be effected with all the magnetic toys. The distances that still led to an alteration of the valve settings differed from 10 to 50 mm (Strata), compared with 5 to 30 mm (Codman). Valve settings of Polaris could not be altered by any toy at any distance due to its architecture with two magnets adjusted in opposite directions.

CONCLUSION

This is the first report describing changes in the pressure setting of some adjustable valves caused by magnetic toys in close contact. Parents, surgeons, neurologists, pediatric oncologists, and paramedics should be informed about the potential dangers of magnetic toys to prevent unwanted changes to pressure settings.