Fig 1.
The Medtronic 3389 deep brain stimulation electrode studied in this work.
The deepest (most distal) contacts are 0 and 8.
Fig 2.
In vitro model of DBS patient implanted at this centre.
Note that the extension cables are routed along the external surface of the phantom. (A) Phantom dimensions. * = thermometer recording site, IPG = Implantable pulse generator. (B) Recording the voltage output of the IPG. EL = left electrode, ER = right electrode.
Fig 3.
The fibre-optic temperature sensors positioned at the distal electrode contacts.
The fine golden leads are the temperature probe optical fibres, whereas the grey leads with 4 visible metal contacts are the DBS electrode leads. Suture silk was used to ensure that the thermometer probes were in close thermal contact with the distal electrode contact surfaces, previously demonstrated to be the sites of greatest MRI-induced heating.
Fig 4.
Typical temperature time courses observed during a TSE sequence at the 4 thermometer sites using the body-transmit coil.
Green line is our safety threshold (1°C). Pink line indicates the end of the scan. Note the TSE sequence acted as positive control, producing temperature increases greater than the sequences used for subjects with in situ DBS at our centre.
Fig 5.
Temperature increases at the 4 measurement sites during ‘pre-scan’ system calibration periods.
Note the change in scale for the 3T plots.
Fig 6.
Maximum electrode-tip temperature change induced by the TSE sequence at 1.5T and 3T systems, and GE-EPI sequence at 1.5T.
Fig 7.
The effect of phantom position relative to the body-transmit coil on electrode-tip temperature increase.
In contrast to the head-transmit coil, which moved with the patient table, the body-transmit coil is embedded at a fixed position in the scanner bore. By displacing the patient table we were able to systematically alter the position of the DBS circuit with respect to the body-transmit coil, as illustrated beneath the x-axis.
Fig 8.
The implantable pulse generator voltage output during a typical GE-EPI fMRI sequence.
Table 1.
The effect of lead immersion in the phantom gel.