MRI Safety Evaluation of Dual Leads and Fractured Leads Active Implantable Medical Devices in MRI
Magnetic resonance imaging (MRI) radiofrequency (RF)-induced heating is of great concern for patients with active implantable medical devices (AIMDs) undergo MR scanning. RF safety evaluation of AIMDs consists of two steps: (1) the development of the AIMD model (i.e., transfer function (TF) method), and (2) the extraction of the incident E-field along clinically relevant pathways inside human body models. In this dissertation, we first evaluate RF-induced heating of AIMD systems with dual leads using simulations and experiments. Coupling effects, which lead to lower RF-induced SAR or heating, between dual leads are observed in both simulations and experiments. Results show that separation distance of two leads can affect strength of coupling effects. By introducing global TF, in-vivo heating estimations are performed. The findings reveal that dual leads configurations will have lower RF-induced heating compared to that of single lead configuration. Secondly, RF-induced heating of AIMDs with fractured leads and abandoned lead fragments are discussed. Experiments in combination with in-vivo simulations show that AIMDs with fractured lead will induce excessive RF heating and abandoned lead fragments are MRI safe. Third part of the dissertation discusses MR conditionality of abandoned fractured leads. Two proximal treatments (bare-end, capped-end) are compared. Two important observations are summarized: (1) abandoned fractured leads will have unpredictable RF-induced heating (either higher or lower than that of abandoned intact lead), (2) bare-end treatment will lead to lower heating than that of capped-end treatment. Finally, a novel technique to reduce RF-induced of heating from AIMD is proposed. By adding magnetic ferrite beads with high permeability to AIMD systems, Transfer Function (TF) magnitude can be suppressed significantly for both 1.5 T and 3 T. In-vivo results of AIMDs with different magnetic ferrite beads configurations (1 or 2 ferrite beads or 1 bead with two different locations) are studied and indicate that magnetic ferrite beads can reduce RF-induced heating.
MRI, RF-induced heating, Dual leads, Fractured leads, Abandoned leads, Magnetic ferrite material, In vivo
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