Parallel transmit pulse design for patients with deep brain stimulation implants.

Area of Science:

• Biomedical Engineering
• Medical Imaging Physics
• Neuroscience

Background:

• Diagnostic MRI poses safety risks due to specific absorption rate (SAR) amplification around active implantable medical devices.
• Deep brain stimulation (DBS) implants are particularly vulnerable to SAR amplification, necessitating safety protocols during MRI procedures.

Purpose of the Study:

• To present a parallel transmit (pTx) strategy for safe MRI scanning of patients with DBS implants.
• To mitigate SAR amplification risks at the DBS lead tip during MRI.

Main Methods:

• Electromagnetic simulations were conducted at 3T using a uniform phantom and a realistic head model with a DBS implant.
• An implant-friendly mode strategy was employed, defining array modes that reduce local SAR around the DBS lead tip.
• A spokes pulse design algorithm utilized these modes to achieve uniform flip angle excitations.

Main Results:

• Local SAR at the DBS lead tip was reduced to below 0.1 W/kg, a significant decrease from 31.2 W/kg without mitigation.
• For a realistic head model, peak 10g local SAR and global SAR were 4.52 W/kg and 0.48 W/kg, respectively.
• A uniform axial flip angle was achieved with normalized root mean square error (NRMSE) below 3%.

Conclusions:

• Parallel transmit arrays can effectively generate implant-friendly modes to reduce SAR around DBS implants.
• The proposed strategy successfully constrains peak local and global SAR while maximizing flip angle homogeneity.
• This pTx approach offers a viable solution for enhancing the safety of MRI procedures for patients with DBS implants.