Editorial for “Effect of Device Configuration and Patient's Body Composition on the Nonsusceptibility Artifact and RF Heating of Deep Brain Stimulation Devices During MRI at 1.5T and 3T”

In the past two decades, magnetic resonance imaging (MRI) has become an indispensable and widespread diagnostic modality with an ever-growing number of exams. At the same time, also the availability and use of various types of active medical implants (AMI) has steadily increased and meanwhile there are millions of potential MRI patients living with such devices. In the case of, for example, cardiac pacemakers and implantable cardioverter-defibrillators (ICDs), it is estimated that up to 75% of patients will require MRI after implantation. It is well known that, concerning AMIs, there is always great concern that interactions with the static magnetic field, gradient magnetic field, or radiofrequency field (RF) pose dangers to the patients or lead to permanent device damage. In addition, imaging artifacts could render obtained images useless. Frequently, especially in private practice, there is great insecurity regarding the safe performance of MRI and patients are often denied important examinations. For years, device manufacturers have made great efforts to ensure the safety of patients and regulatory bodies have introduced standards that have to be met in order to obtain appropriate labeling of the given device. With respect to device labeling in recent years, a widely recognized standard has been established, classifying devices as MR safe, MR conditional, or MR unsafe. Many AMIs nowadays are labeled as MR conditional and manufacturers of such devices must describe and list in their instructions of use all parameters necessary to ensure a safe MRI exam with the device at hand. In many cases, however, the conditions to perform MRI are very restrictive and sometimes difficult to comply with in clinical practice. This is especially the case for deep brain stimulation (DBS) devices that have been approved since 1997 for the treatment of essential tremor and Parkison’s disease and by now are well established. DBS devices usually consist of three components—electrodes, extensions, and implantable pulse generators (IPG). During implantation, one or two thin electrodes, typically made of titanium, are stereotactically inserted deep into certain areas of the brain. These electrodes are fixed to the skull and a connection to the IPG, which is located in the chest, is established using subcutaneous leads and extensions. Patients with DBS systems are frequently referred to MRI to check the exact localization of the electrodes or for functional follow-up studies. As most parts of the DBS system are nonferromagnetic, the major concern regarding MR safety of these systems is heating of tissue due to the antenna effect, which is a complex function of a variety of factors such as device configuration, orientation, or tissue properties. Thus, as pointed out by Bhusal et al in this issue, MRI guidelines are rather restrictive, eg, only allowing 1.5T horizontal bore scanners and pulse sequences are limited to reduced power levels, which is often difficult to handle in clinical routine. For older DBS systems, even a special transmit/receive coil had to be available. In their work, Bhusal et al studied RF heating and image artifacts for different lead configurations and patient body composition at 1.5T and 3T. They used two commercially available DBS devices from different manufacturers and tested various extracranial trajectories of the DBS leads. A very interesting aspect of this work is that, in contrast to phantoms recommended by the ASTM standard, an anthropomorphic phantom with realistic body shapes obtained from computer tomography scans of a patient was used that could be filled with saline solution or a combination of saline and oil to simulate subcutaneous fat. Bhusal et al found a notable temperature increase in the case of the oil/saline combination