Measurement, simulation and uncertainty assessment of implant heating during MRI

Abstract

The heating of tissues around implants during MRI can pose severe health risks, and careful evaluation is required for leads to be labeled as MR conditionally safe. A recent interlaboratory comparison study has shown that different groups can produce widely varying results (sometimes with more than a factor of 5 difference) when performing measurements according to current guidelines. To determine the related difficulties and to derive optimized procedures, two different generic lead structures have been investigated in this study by using state-of-the-art temperature and dosimetric probes, as well as simulations for which detailed uncertainty budgets have been determined. The agreement between simulations and measurements is well within the combined uncertainty. The study revealed that the uncertainty can be kept below 17% if appropriate instrumentation and procedures are applied. Optimized experimental assessment techniques can be derived from the findings presented herein.

Assessing the Electromagnetic Fields Generated By a Radiofrequency MRI Body Coil at 64 MHz: Defeaturing Versus Accuracy

“…2) Measurements setup-Data of ||E ⃗ || and ||B ⃗ || were collected using a robotic measurement system (DASY 5NEO, SPEAG, Zurich, Switzerland) [22,38,39] with two ||E ⃗ || probes (ER3DV6 and EX3DV4 for measurements in air and saline, respectively) and a ||H ⃗ || probe (H3DV7) (SPEAG, Zurich, Switzerland). For each measurement point the probes returned three RMS values -one for each field component x, y, and z.…”

“…The distributed capacitors present in the physical coil were modeled as two conductive rectangular slabs connected by numerically defined lumped elements, as in [22]. The two baluns present at the physical sources were not modeled in the numerical coils.…”

“…Lastly, a hybrid model [15,[35][36][37] includes both the multiport excitation and presence of lumped elements, the convenience of such an approach, over a specific model, is the independence of the frequency response from the loading conditions [22].…”

Role of the lead structure in MRI‐induced heating: In vitro measurements on 30 commercial pacemaker/defibrillator leads

“…The system is installed at the Department of Technology and Health of the Italian National Institute of Health and has been specially designed to provide a controlled exposure for MRI safety testing with regards to the RF field. Systems with the same features have been widely used in previous published studies (17,(22)(23)(24). It has also been demonstrated that, given the same implant configuration and the same WB-SAR delivered to the phantom, the induced heating inside the isolated birdcage coil is comparable with the one obtained in an actual MRI system using clinical MRI sequences (23).…”

Interaction between the RF Field of MRI Apparatus and Pacemakers

“…11d) (Bassen et al 2006;Neufeld et al, 2009). In particular Neufeld et al, (2009) realized their catheter staring from a 0.6 mm thick wire wound to form a helix and including a 10-mm long straight section. The helical wire is insulated by a thin coating (0.012 mm).…”