Numerical investigations of MRI RF field induced heating for external fixation devices

Liu, Yan; Shen, Jiale; Kainz, Wolfgang; Qian, Songsong; Wu, Wenwen; Ji-min, Chen

doi:10.1186/1475-925x-12-12

Cited by 19 publications

(22 citation statements)

References 13 publications

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“…The pattern recognition approach we employed allowed us to quantify the degree of separation between groups and therefore also the degree to which shared familial risk factors present in patients and unaffected siblings are expressed in patterns of brain activity. In line with earlier studies that identified patterns of shared risk between siblings of participants with autism and schizophrenia ( Fan et al, 2008 , Segovia et al, 2014 , Yu et al, 2013 ), we could distinguish unaffected siblings from participants with ADHD and, although to a lesser degree, from healthy controls. The patterns associated with these distinctions showed an overlap, with the pattern associated with the distinction of participants with ADHD from healthy controls, primarily in frontolateral regions.…”

Section: Discussionsupporting

confidence: 89%

“…In studies on unaffected siblings of schizophrenia and autism spectrum disorders, researchers used neural patterns to distinguish siblings from their respective patient group and healthy controls ( Fan et al, 2008 , Segovia et al, 2014 , Yu et al, 2013 ). However, until now no pattern recognition study has investigated unaffected siblings of participants with ADHD.…”

Section: Introductionmentioning

confidence: 99%

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Quantifying patterns of brain activity: Distinguishing unaffected siblings from participants with ADHD and healthy individuals

Wolfers

Rooij

Oosterlaan

et al. 2016

NeuroImage: Clinical

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Attention-deficit/hyperactivity disorder (ADHD) is one of the most prevalent and heritable psychiatric disorders. While previous studies have focussed on mapping focal or connectivity differences at the group level, the present study employed pattern recognition to quantify group separation between unaffected siblings, participants with ADHD, and healthy controls on the basis of spatially distributed brain activations. This was achieved using an fMRI-adapted version of the Stop-Signal Task in a sample of 103 unaffected siblings, 184 participants with ADHD, and 128 healthy controls. We used activation maps derived from three task regressors as features in our analyses employing a Gaussian process classifier. We showed that unaffected siblings could be distinguished from participants with ADHD (area under the receiver operating characteristic curve (AUC) = 0.65, p = 0.002, 95% Modified Wald CI: 0.59–0.71 AUC) and healthy controls (AUC = 0.59, p = 0.030, 95% Modified Wald CI: 0.52–0.66 AUC), although the latter did not survive correction for multiple comparisons. Further, participants with ADHD could be distinguished from healthy controls (AUC = 0.64, p = 0.001, 95% Modified Wald CI: 0.58–0.70 AUC). Altogether the present results characterise a pattern of frontolateral, superior temporal and inferior parietal expansion that is associated with risk for ADHD. Unaffected siblings show differences primarily in frontolateral regions. This provides evidence for a neural profile shared between participants with ADHD and their healthy siblings.

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Section: Discussionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Quantifying patterns of brain activity: Distinguishing unaffected siblings from participants with ADHD and healthy individuals

Wolfers

Rooij

Oosterlaan

et al. 2016

NeuroImage: Clinical

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“…Studies have been conducted to evaluate the RF heating induced by orthopedic implants. Commonly a phantom or homogenous media is used to mimic the environments as the implants locate in human body in experiments and/or numerical simulations [24][25][26][27][28][29][30][31][32].…”

Section: In-vivo and In-vitromentioning

confidence: 99%

MRI RF-Induced Heating in Heterogeneous Human Body with Implantable Medical Device

Guo¹,

Zheng²,

Chen³

2018

High-Resolution Neuroimaging - Basic Physical Principles and Clinical Applications

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Magnetic resonance imaging (MRI) radio frequency (RF)-induced heating is one of the most important concerns of MRI safety for patients, especially with orthopaedic healthcare products. In this chapter, numerical modelling and simulations were conducted to study the RF-induced heating within a 1.5T and 3T magnetic resonance (MR) environment. Numerical simulations were firstly conducted to study the difference between the cases of implantable medical devices inside the phantom and the human body. Then, numerical modelling were conducted to describe the difference of electromagnetic behaviours between the homogeneous phantom and heterogeneous human tissues. The MRI RF-induced heating due to an implantable medical device behaves significantly different in homogeneous media and in heterogeneous human body. For typical orthopaedic medical devices, such as healthcare products applied to shoulder, humerus, hip, femur and tibia, the properties of the RF-induced heating are different in general phantom and in human body. The hot spot location, as well as worst case configuration were evaluated and it was found that they were determined by the incident field and electromagnetic properties of medium. With further scaling, the RF-induced heating in human body for the orthopedic devices can be assessed by phantom studies.

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“…Many papers show that a significant heating can be associated with the exposure of such bodies to RF fields, especially with wire‐like structures, which may act as antennas . In this case, RF typically deposits a relatively low power inside the metallic parts, but their presence may cause the enhancement of the specific absorption rate directly developed in the tissues anyway.…”

Section: Total Joule Losses P (In Watt) Developed Within the Spherementioning

confidence: 99%

The underestimated role of gradient coils in MRI safety

Zilberti

Arduino

Bottauscio

et al. 2016

Magnetic Resonance in Med

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MRI scanning of patients carrying implants is becoming a reality in many hospitals, because of the wide increase of population with implants, particularly in the orthopedic ones (1). The responsibility for this practice falls on the subscribing physicians or radiologists, who rely on guidance establishing safety and compatibility of implants in the MR environment (eg, (2)), which basically address issues related to magnetically induced mechanical actions and radiofrequency (RF) induced heating of tissues. Even if large-scale MR safety studies on orthopedic implants have been published that show no evidence of specific risks for patients' health (eg, (3)), additional analyses of the interaction between MR fields and metallic implants can contribute to support the scan decision on a firm scientific rationale.In a recent paper (4), we showed that the tissues surrounding a metallic hip prosthesis exposed to a gradient field (GF) may undergo a nonnegligible heating (up to some degree), as a result of the electromagnetic energy deposited in the implant. Since then, we have realized that in the MR community these results are generally received with some skepticism, probably because of the fact that most of the scientific papers dealing with thermal problems in MRI focus on RF fields (5-16). Similarly, the attention of relevant standardization and regulatory bodies is focused solely on RF-induced heating (2,17). This tendency is absolutely well-grounded when studying native tissues, where GFs are not able to develop significant thermal effects. However, in the presence of metallic foreign bodies the situation is different.Many papers show that a significant heating can be associated with the exposure of such bodies to RF fields, especially with wire-like structures, which may act as antennas (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). In this case, RF typically deposits a relatively low power inside the metallic parts, but their presence may cause the enhancement of the specific absorption rate directly developed in the tissues anyway. What we would like to highlight here is that, in presence of bulky metallic prostheses, GFs can produce a nonnegligible heating too, because of the thermal power generated inside the metal (Joule effect), which involves the tissues indirectly, by diffusion ("indirect effect" (31)). The GF thermal effect, which becomes sizable only for prostheses far from the coils' isocenter, has been considered up until now by a few articles (4,32-34). To sustain these findings, we exploit an analytical solution (35) that is not affected by possible artifacts of numerical results. The solution provides the current density J (in complex notation) induced within a nonmagnetic metallic sphere, with radius R, conductivity s and permeability m 0 , immersed in a nonconductive background. When the sphere is radiated by a homogeneous, timeharmonic, magnetic flux density B (peak value) at frequency f, the current density in an internal point iswhere r is the distance from the sphere center, u is the cola...

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Numerical investigations of MRI RF field induced heating for external fixation devices

Cited by 19 publications

References 13 publications

Quantifying patterns of brain activity: Distinguishing unaffected siblings from participants with ADHD and healthy individuals

Quantifying patterns of brain activity: Distinguishing unaffected siblings from participants with ADHD and healthy individuals

MRI RF-Induced Heating in Heterogeneous Human Body with Implantable Medical Device

The underestimated role of gradient coils in MRI safety

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