Fig 1.
Numerical models of a 1.5 T 16-rung low-pass birdcage coil tuned at 64 MHz, a 3 T 16-rung low-pass birdcage coil tuned at 127 MHz, a 7 T 16-rung hybrid birdcage coil tuned at 297 MHz, and a 10.5 T 8-channel bumped dipole array tuned at 447 MHz all loaded with a homogeneous human head model with no implant.
The geometrical dimensions of the coils were the same as the coils reported in literature [18–21].
Fig 2.
(A) Examples of postoperative CT images (ID1-ID8). (B) Reconstructed models of isolated DBS leads (ID1—ID20). Lead trajectories were constructed based on the postoperative CT images of 13 patients with bilateral DBS implantations (ID1—ID13), and 7 patients with unilateral DBS implantations (ID14—ID20) and were incorporated in a homogeneous head model for EM simulations.
Fig 3.
Example of mesh density in the lead, insulation, and SAR boxes of a representative patient (ID12) at 3 T.
A1: Closeup view of leads withing the high-resolution mesh regions. A2-A3: Schematic of mesh in the cubic area surrounding the lead tips and on the lead electrodes. A3: View of interconnections between electrodes and the central core. The coil’s input power was adjusted to generate a GHSAR of 3 W/kg. The distribution of 1g-SAR on a plane passing through the lead tips, the distribution of B1+ on an axial plane passing through the patient’s forehead, and the lead’s contacts’ geometrical details are also presented.
Fig 4.
1g-SAR distributions in patient 12 (ID12) for the 1.5 T, 3 T, 7 T, and 10.5 T coils over an axial plane passing through the electrode contacts.
The coils’ input powers are adjusted (A) to generate a GHSAR of 3 W/kg and (B) to generate an average of B1+ = 2 μT over an axial plane passing through the patient’s forehead. The B1+ field distributions over the mentioned axial plane, which passes through the patient’s forehead, are also presented. Additionally, 1g-SARmax, the average of B1+ field, and GHSAR are also reported for all four coils.
Fig 5.
1g-SARmax, B1+, and ||E|| when the coils’ input powers were balanced to produce a global head SAR (GHSAR) of 3 W/kg, and (B) 1g-SARmax and GHSAR when the coils’ input powers were adjusted to generate an average of B1+ = 2 μT, over all 33 DBS lead models for the 1.5 T, 3 T, 7 T, and 10.5 T coils. Box and whisker plots display the range, median, and interquartile range (IQR) of the data. Each outlier was specified with a red ’+’ symbol.
Fig 6.
Normalized B1+ maps of the 1.5 T, 3 T, 7 T and 10.5 T coils on an axial plane passing through the iso-center in human head model with no implants (top rows) and with implants (bottom row). All four coils are driven in the CP excitation mode, where their inputs are adjusted to keep the accepted power (Pac) as 1 W. The B1+ maps of the second row were acquired for patient 12 (ID12).