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 reported¹, 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).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 gel². 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.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 12.6⁰, 4.3⁰, 3.2⁰ and 2.1⁰C 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.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.