1. No category

RF Heating of DBS Lead with T/R Head Coil versus T/R Body Coil
The manufacturer of the deep brain stimulator (DBS) does not recommend body coil transmit when
scanning patients with such a device implanted and connected through an extension to an implanted
pulse generator (IPG) away from the head region [1-2]. This is because the use of a T/R head coil
instead of body coil transmit reduces the RF heating and is necessary for patient safety. However, the
currently-available transmit-receive (T/R) head coils may not be suitable for intra-op MRI when the
patient is positioned in a head fixation device. In additional, a single-channel T/R coil precludes the use
of parallel imaging and typically provides lower SNR than a phased-array design. During intra-op and
immediate post-op DBS MRI, however, only the leads of DBS are implanted in the patient WITHOUT
the extension cable and IPG connected. The leads are typically coiled at the patient’s scalp. Under
such conditions, one might expect the potential heating in the DBS leads to be equivalent regardless of
whether transmission is through a T/R head coil or a T/R body coil, since the same B1 amplitude is
needed to achieve a given flip angle over the head region. Eliminating the need to switch to a T/R head
coil can simplify the workflow of intra-op DBS MRI and improve image quality.
To validate such hypothesis, a phantom study was
performed to compare the temperature changes at the
tip of a DBS lead (Model 3389, Medtronic, Minneapolis,
MN) with and without a 51cm extension cable (Model
7482-51) connecting to an IPG (Soletra Model 7426)
while imaging with either a T/R head coil (Quality
Electrodynamics, OH) or the built-in T/R body coil on a
1.5T IMRIS Intra-op MRI scanner (Winnipeg, Canada)
which is modified from a short-bore Siemens Espree (Malvern, PA). In the lead only configuration, the
lead is coiled outside of head phantom, but not conneced to extension cable and IPG.
B1rms (µT) / Head SAR (W/kg)
/ Absorbed RF Power (W)
With T/R head coil
With T/R body coil
Lead only
3D MPRAGE
3D TSE
0.6 / 0.06 / 0.2
4.4 / 3.2 / 12.5
0.6 / 0.03 / 3.8
3.9 / 2.2 / 174.8
3D MPRAGE
The measured
temperature change
at tip of DBS lead for
lead only and
lead+Ext+IPG using
either head and
body coil transmit.
3D TSE
60
24.5
Lead + Ext. + IPG
3D MPRAGE
3D TSE
0.6 / 0.06 / 0.3
4.4 / 3.2 / 16.7
0.6 / 0.06 / 4.2 3.9 / 2.2 / 186.2
55
Temperature (degree)
Temperature (degree)
24.0
T/R Head Lead Only
T/R Body Lead Only
T/R Head Lead+Ext.+IPG
T/R Body Lead+Ext.+IPG
23.5
23.0
22.5
50
45
40
T/R Head Lead Only
T/R Body Lead Only
T/R Head Lead+Ext.+IPG
T/R Body Lead+Ext.+IPG
35
30
25
22.0
20
0
100
200
Time (sec)
300
400
500
0
50
100
Time (sec)
150
200
Our conclusion is based on preliminary phantom experiments and has not been validated in clinical
settings. In particular, if the excess portion of an unconnected lead is improperly coiled, we expect the
temperature rise at the lead tip to be greater than what we observed.
1. Shellock FG, Magnetic resonance safety update 2002: implants and devices. J Magn Reson
Imaging 2002; 16: 485–496.
2. Gupte AA, et al. MRI-related heating near deep brain stimulation electrodes: more data are needed.
Stereotact Funct Neurosurg. 2011;89(3):131-40