Posted in Biomedical Instrumentation and Electrotherapies, Projects (This page is no longer updated. See NEWS page for the latest updates)

Maged Elwassif

There is a growing interest in the use of Deep Brain Stimulation for the treatment of medically refractory movement disorders and other neurological and psychiatric conditions. The extent of temperature increases around DBS electrodes during normal operation (joule heating and increased metabolic activity) or coupling with an external source (e.g. MRI) remains poorly understood and methods to mitigate temperature increases are being actively investigated. We developed a heat transfer technology and validated it using bath phantom measurements and computational simulations of DBS incorporating the realistic architecture of Medtronic 3389 leads. The temperature changes were analyzed considering different electrode configurations, stimulation protocols, and tissue properties. The heat-transfer model results were then validated using micro-thermocouple measurements during DBS lead stimulation in a saline bath. FEM results indicate that lead design (materials and geometry) may have a central role in controlling temperature rise by conducting heat. We show how modifying lead design can effectively control temperature increases.

The robustness of this heat-sink approach over complimentary heat-mitigation technologies follows from several features: 1) it is insensitive to the mechanisms of heating (e.g. nature of magnetic coupling); 2) does not interfere with device efficacy; and 3) can be practically implemented in a broad range of implanted devices without modifying the normal device operations or the implant procedure.

Publications

1. Elwassif MM, Datta A, Rahman A, Bikson M. Temperature control at DBS electrodes using a heat sink: experimentally validated FEM model of DBS lead architecture. Journal of Neural Engineering . 2012; 8(4) PDF

2. Elwassif MM, Kong Q, Vazquez M, Bikson M. Bio-heat transfer model of deep brain stimulation-induced temperature changes. Journal of Neural Engineering. 2006; 3:306-15 PDF

Our heat sink technology can be also practically implemented in a broad range of implanted devices (cardiac / neuro-prosthetics, pumps,…) without modifying device operation or implant procedure (Patent Pending).

 

More Background

 

Over several decades, Deep Brain Stimulation (DBS) has become increasingly adopted for the FDA-approved and investigational treatment of movement and neuropsychiatric disorders [1-5]. Given risks associated with the surgical implantation procedure, DBS is considered well tolerated [6-7]. Some of the most severe injuries have resulted from presumed internal burns generated from coupling with diathermy devices [8-9]. Concerns about coupling in MRI have led to changes in counter-indicated exposure guidelines [10-11].  A range of methods to mitigate temperature increases around leads during external coupling have been proposed [12], often aimed with counter-indication guidelines, of minimizing initial coupling.
For both existing and new brain stimulation implants, safety concerns include: 1) electrochemical interactions at the electrode-tissue interface (which are not automatically mitigated by charge-balanced-waveforms) [13]; 2) undesired behavioral/cognitive outcomes including due to current spread [14-16]; 3) gross cell damage associated with surgery (including axons of passage) [17]; 4) tissue response to the implant; 5) local electro-permeation of blood -brain barrier (BBB) [18]; and 6) heating.  Heating is of special concern because it can also result from unexpected external coupling, as evidenced by past DBS injuries [8-9].  In addition, we previously suggested that even under normal operation small temperature changes may result [12] and discussed how such moderate changes may become incrementally significant when combined with other concurrent contributors to brain heating (e.g. exercise, environmental).
The source of joule heat is current flow generated, due to normal function or external coupling, in metal device components and tissue [19-20].  Changes in metabolic or vascular functions resulting from the current flow would influence temperature changes, along with the relevant physical properties of the tissue and device components [8-12, 21-25].  Rather than control the source of joule heat (e.g. exposure guidelines), our group has considered how changing device design can robustly mitigate peak temperature increase, for example by device components acting as heat sinks that disperse potentially hazardous temperature rises [12].  In this study, we extend this analysis with the first FEM models simulating detailed Medtronic DBS lead architecture and with consideration of electrodes-tissue interface conditions.  In addition, we validate model precision with experimental saline-bath recordings.

 

Over several decades, Deep Brain Stimulation (DBS) has become increasingly adopted for the FDA-approved and investigational treatment of movement and neuropsychiatric disorders [1-5]. Given risks associated with the surgical implantation procedure, DBS is considered well tolerated [6-7]. Some of the most severe injuries have resulted from presumed internal burns generated from coupling with diathermy devices [8-9]. Concerns about coupling in MRI have led to changes in counter-indicated exposure guidelines [10-11].  A range of methods to mitigate temperature increases around leads during external coupling have been proposed [12], often aimed with counter-indication guidelines, of minimizing initial coupling.For both existing and new brain stimulation implants, safety concerns include: 1) electrochemical interactions at the electrode-tissue interface (which are not automatically mitigated by charge-balanced-waveforms) [13]; 2) undesired behavioral/cognitive outcomes including due to current spread [14-16]; 3) gross cell damage associated with surgery (including axons of passage) [17]; 4) tissue response to the implant; 5) local electro-permeation of blood -brain barrier (BBB) [18]; and 6) heating.

Heating is of special concern because it can also result from unexpected external coupling, as evidenced by past DBS injuries [8-9].  In addition, we previously suggested that even under normal operation small temperature changes may result [12] and discussed how such moderate changes may become incrementally significant when combined with other concurrent contributors to brain heating (e.g. exercise, environmental).The source of joule heat is current flow generated, due to normal function or external coupling, in metal device components and tissue [19-20].  Changes in metabolic or vascular functions resulting from the current flow would influence temperature changes, along with the relevant physical properties of the tissue and device components [8-12, 21-25].  Rather than control the source of joule heat (e.g. exposure guidelines), our group has considered how changing device design can robustly mitigate peak temperature increase, for example by device components acting as heat sinks that disperse potentially hazardous temperature rises [12].  We validate our new heat-sink approach with the first FEM models simulating detailed Medtronic DBS lead architecture and with consideration of electrodes-tissue interface conditions.  In addition, we validate model precision with experimental saline-bath recordings.

 

 

 

Some References of Interest

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