Classification Scheme of Heating Risk during MRI Scans on Patients with Orthopaedic Prostheses

Abstract

Due to the large variety of possible clinical scenarios, a reliable heating-risk assessment is not straightforward when patients with arthroplasty undergo MRI scans. This paper proposes a simple procedure to estimate the thermal effects induced in patients with hip, knee, or shoulder arthroplasty during MRI exams. The most representative clinical scenarios were identified by a preliminary frequency analysis, based on clinical service databases, collecting MRI exams of 11,658 implant carrier patients. The thermal effects produced by radiofrequency and switching gradient fields were investigated through 588 numerical simulations performed on an ASTM-like phantom, considering four prostheses, two static field values, seven MR sequences, and seven regions of imaging. The risk assessment was inspired by standards for radiofrequency fields and by scientific studies for gradient fields. Three risk tiers were defined for the radiofrequency, in terms of whole-body and local SAR averages, and for GC fields, in terms of temperature elevation. Only 50 out of 588 scenarios require some caution to be managed. Results showed that the whole-body SAR is not a self-reliant safety parameter for patients with metallic implants. The proposed numerical procedure can be easily extended to any other scenario, including the use of detailed anatomical models.

An In-Silico Testbed for Fast and Accurate MR Labeling of Orthopaedic Implants

“…The results do not take into account the impact of low-frequency induction heating of metallic implants naturally caused by switched gradient fields. Important work on this subject matter has recently been reported in [21], [22], [23], [24], [25], [26], [27]. Unless an orthopaedic implant has a loop path, heating due to gradient fields is typically less than heating due to RF energy deposition.…”

“…One major safety concern, relevant to both passive and active implants, is implant heating within MR radiofrequency and gradient coils [5], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28].…”

“…One major safety concern, relevant to both passive and active implants, is implant heating within MR radiofrequency and gradient coils [5],[19],[20],[21],[22],[23],[24],[25],[26],[27],[28]. Along with the required yet not entirely anatomical ASTM phantom test and other similar phantom tests [5],[19],[21],[22],[25],[26], numerical simulations with virtual human models generate accurate predictions of temperature rise [20],[21],[22],[24],[27],[28] accepted by the FDA [28]. The electromagnetic and thermal simulation algorithms based on finite element, finite difference, and boundary element methods are reasonably well developed [29],[30],[33],[34].…”

Orthopedic implants affect the electric field induced by switching gradients in MRI

“…[7][8][9] The interaction between a metallic object implanted in a patient's body and MRI gradient fields has been analyzed in several papers, specifically dealing with the risk of heating. [10][11][12][13][14][15][16][17] Conversely, the possibility that such an interaction might alter the E-field distribution in native tissues surrounding the object, and its possible effects on PNS, has received little attention. Some authors published on investigations involving spinal fusion devices, 18,19 generic active implant electrodes, 20 and infusion pumps.…”

Efficient prediction of MRI gradient‐induced heating for guiding safety testing of conductive implants

“…Radiofrequency (RF) tissue heating has gained a wide attention both from the literature and relevant standards due to its potential to cause significant temperature increases when the incident RF field, implant characteristics, and exposure scenario meet specific criteria 11‐17 . While RF remains the most important source of heating in MRI, recent studies showed that heating induced by gradient fields could also represent a risk in the presence of bulky conductive objects 5,18,19 …”