Pallab K Bhattacharyya1, Howard Goldman2, Mark J Lowe1, Adrienne Quirouet2, and Stephen E Jones1
1Imaging Institute, Cleveland Clnic, Cleveland, OH, United States, 2Glickman Urological Institute, Cleveland Clnic, Cleveland, OH, United States
Synopsis
RF heating testing during
lumbar scans of Medtronic Interstim II (Model 3058) implantable pulse generator
(IPG) connected to Medtronic Quadipolar Nerve Stimulator Lead (Model 3889) at
3T whole body Siemens TIM Trio scanner with receive-only cervical-lumbar-thoracic
coil was performed. Temperatures of the electrodes were measured by using fiber
optic sensors with fluoroptic monitoring with the IPG and lead placed inside an
ASTM gel phantom. No electrode heating was observed when the lead was connected
with the IPG in any of the scans, while considerable heating was observed when
the IPG was disconnected and taken out of the phantom.Purpose
Sacral nerve
stimulation is a type of electrical stimulation therapy to treat voiding
dysfunction, in which a subcutaneously placed programmable stimulator sends low
amplitude electrical stimulation to the sacral nerve via a lead. If subjected
to an MRI procedure, the electrode contacts of the lead and the IPG case can be
subjected to RF induced heating. MRI scans of the head under certain conditions
is allowed to be safely performed for patients implanted with Medtronic
InterStim II model 3058 stimulator, while all other scans are contraindicated. Safety
of running pelvic and lumbar scans at 1.5T with InterStim II implanted has
recently been reported
1, but with the
increasing clinical use of 3T magnets, such investigation at 3T is necessary. We
performed RF heating testing during lumbar scans of Medtronic InterStim II
(Model 3058) implantable pulse generator (IPG) connected to Medtronic
Quadipolar Nerve Stimulator Lead (Model 3889) at 3T. In addition, to understand real-world
situations such as scenarios where (i) the lead was broken or (ii) the
stimulator is left disconnected from the lead, we repeated the study with the
lead only (no stimulator).
Methods
MR scans were performed using a 3 Tesla Siemens
whole body Tim-Trio scanner (Erlangen, Germany) with a receive-only
cervical-lumbar-thoracic (CLT) coil. The IPG connected to the lead with 4
electrode contacts was inserted in the lumbar area of a head and torso phantom
filled with polyacrylic gel
2. The lead and the
IPG were set up in the phantom similar to where it would be in a human (Fig. 1) . Four fluoroptic temperature sensors (model m3300,
LumaSense Technologies, Santa Clara, CA, USA) were used for temperature
measurement. The points of contact of the probes were (i) the proximal contact,
(ii) the distal contact, (iii) on the IPG case, and (iv) the gel as a control.
The probe from case was connected to a contact in the open end in the IPG
disconnected configuration. Prior to immersion into the gel the IPG was programmed
at 4 V amplitude, 210 ms
pulse width, 14 Hz frequency and 32 sec ON/OFF cycle. A lumbar spine MRI
protocol was performed that consisted of the following scans: (i) localizer,
(ii) sagittal and coronal Half-Fourier Acquisition Single-shot Turbo spin-Echo
(HASTE) localizer (TR/TE/FA = 1080ms/97ms/1800, turbo factor = 256),
(v) sagittal Short Tau Inversion Recovery (STIR) (TR/TE/TI/FA =
6390ms/83ms/180ms/1200, turbo factor = 11), (vi) axial T2 weighted
Turbo Spin Echo (TSE) (TR/TE/FA = 4000ms/106ms/1600, turbo factor =
21), (vii) axial T1 weighted TSE (TR/TE/FA = 700ms/11ms/1400, turbo
factor = 3). Specific absorption rate (SAR) values recorded for each scan from
the console are shown in the Table.
Results and Discussion
No electrode heating was observed
when the lead was connected with the IPG, while considerable heating was
observed when the IPG was disconnected and taken out of the phantom (Fig. 2).
Larger heating of electrodes were observed with lead-only configuration for
sequences with higher SAR values, as might be expected. The maximum heating
observed during the HASTE, T1W TSE, T2W TSE and STIR scans were 12.6
0,
4.3
0, 3.2
0 and 2.1
0C respectively, which were
all above the acceptable limit. The results provide evidence that the risk of
heating is low for lumbar MRI in the setting of an intact Medtronic InterStim
II (Model 3058) and lead (Model 3889) system at 3T. However, lumbar MRI in the
presence of a lead disconnected from the IPG can result in electrode heating. These
findings are similar to that reported at 1.5T. It should be noted that these
results do not necessarily generalize and individual centers should validate
safety of performing MR scans in presence of such implants before scanning
patients with implants.
Conclusion
Patients with Medtronic lead (Model 3889) not connected to
InterStim II stimulator (Model 3058) should not be scanned with a lumbar
protocol at 3T using a receive-only CLT coil. In the event of surgeons deciding
to leave the lead only for subsequent implantion of an IPG, the patient should
not be scanned during that time. We also recommend routine checks for broken
leads (by impedance testing with the programmer) prior to scans to avoid
excessive tissue heating.
Acknowledgements
Medtronic, Inc.References
1. Bhattacharyya PK, Goldman H, Lowe MJ,
Quirouet A, Jones SE. Heating of lead electrodes disconnected from sacral
stimulator during routine lumbar and pelvic MRI at 1.5T with receiveonlycoil Proc. Intl. Soc. Mag. Reson. Med. . 2015;23:1857.
2. Baker KB, Tkach
JA, Phillips MD, Rezai AR. Variability in RF-induced heating of a deep brain
stimulation implant across MR systems. J
Magn Reson Imaging. 2006;24(6):1236-1242.