Anatomical Model Uncertainty for RF Safety Evaluation of Metallic Implants Under MRI Exposure

Abstract

The Virtual Population (ViP) phantoms have been used in many dosimetry studies, yet, to date, anatomical phantom uncertainty in radiofrequency (RF) research has largely been neglected. The objective of this study is to gain insight, for the first time, regarding the uncertainty in RF‐induced fields during magnetic resonance imaging associated with tissue assignment and segmentation quality and consistency in anatomical phantoms by evaluating the differences between two generations of ViP phantoms, ViP1.x and ViP3.0. The RF‐induced 10g‐average electric (E‐) fields, tangential E‐fields distribution along active implantable medical devices (AIMD) routings, and estimated AIMD heating were compared for five phantoms that are part of both ViP1.x and ViP3.0. The results demonstrated that differences exceeded 3 dB (−29%, +41%) for local quantities and 1 dB (±12% for field, ±25% for power) for integrated and volume‐averaged quantities (e.g., estimated AIMD‐heating and 10 g‐average E‐fields), while the variation across different ViP phantoms of the same generation can exceed 10 dB (−68% and +217% for field, −90% and +900% for power). In conclusion, the anatomical phantom uncertainty associated with tissue assignment and segmentation quality/consistency is larger than previously assumed, i.e., 0.6 dB or ±15% (k = 1) for AIMD heating. Further, multiple phantoms based on different volunteers covering the target population are required for quantitative analysis of dosimetric endpoints, e.g., AIMD heating, which depend on patient anatomy. Phantoms with the highest fidelity in tissue assignment and segmentation should be used, as these ensure the lowest uncertainty and possible underestimation of exposure. To verify that the uncertainty decreases monotonically with improved phantom quality, the evaluation of differences between phantom generations should be repeated for any improvement in segmentation. Bioelectromagnetics. 2019;40:458–471. © 2019 Bioelectromagnetics Society

Radiofrequency‐induced heating of broken and abandoned implant leads during magnetic resonance examinations

“…The corresponding tangential E‐fields are statistically summarized (see Supporting Information Figure S1 ). As previously shown, 31 the variation of the RF‐induced SAR across different ViP models of the same generation can exceed 10 dB. Figure 5 shows that the mean and maximum enhancement ratio of the Tier 3 deposited in vivo lead‐tip power between the single‐wire lead with the wire broken at 50 cm ( b = 50 cm) and the intact lead ( b = 0 cm), computed for exposures where the lead‐tip power was ≥5% of the maximum value, varied from more than a 16‐fold enhancement to <0.2‐fold enhancement (reduction) depending on the exposure scenario.…”

Induced radiofrequency fields in patients undergoing MR examinations: insights for risk assessment

“…This is consistent with previous work that showed that local quantities can vary over more than 10 dB as a function of anatomy and scan landmark. (Yao et al, 2019).…”

Development, validation, and pilot MRI safety study of a high-resolution, open source, whole body pediatric numerical simulation model

“…The areas of computational modeling with human body are wide: fluid dynamics [1], electromagnetics [2], optics [3], ultrasound [4], thermodynamics [5], and mechanics [6,7]. Computational modeling with virtual humans is helpful in studying the interaction of complex biological problems in silico [7], for source localization [8,9], radio-frequency (RF) and specific absorption rate (SAR) exposure [10], and neurostimulation [11][12][13]. The accurate anatomical representation of human numerical models has become an integral part of many state-of-the-art safety studies, such as computed tomography (CT) dosimetry [14] and in MRI RF exposure [15][16][17].…”