Mikhail Kozlov, Leonardo Angelone, Wolfgang Kainz

We investigated the dependence of the incident electric field (E) generated in the ASTM phantom on the coil losses. The results showed that magnetic field (H) normalized to √wbSAR, depends on capacitor Q factors. To avoid systematic errors in predicting the induced electric fields inside a human body the coil model should include realistic coil losses. Our results indicate that the use of ratio E to ||H|| at the coil iso-center normalization to predict E inside a human body located in a commercial birdcage coil based on a numerical coil model with arbitrary coil losses can result in high errors.

Thérèse Barbier, Sarra Aissani, Nicolas Weber, Julie Kabile, Cédric Pasquier, Jacques Felblinger

An MR compatible low-frequency voltage probe design will be presented. This tool is used to monitor active implanted medical devices during MRI exam as well as measuring the gradients switching induced voltage or RF rectification thus allowing MRI safety assessment and combined field tests.

Johannes Erhardt, Maria Vomero, Jochen Leupold, Calogero Gueli, Sam Kassegne, Thomas Stieglitz

The combination of implantable neural electrodes and fMRI holds great potential for better understanding the human brain. However, the image acquisition - especially in the vicinity of the implants - is compromised by artifacts caused by metal components. In this work we address this issue by studying different types of devices in terms of designs and materials, and by quantifying their MRI artifacts. Doing so we demonstrate the quasi artifact-free behavior of a hybrid probe combining surface and penetrating carbon electrodes into a single sheet of polyimide, after comparing it with conventional implants in high field MRI and clinical fMRI.

Aurelien Destruel, Kieran O'Brien, Markus Barth, Jin Jin, Feng Liu, Stuart Crozier

The lack of study and guidelines means there is currently no imaging of orthopaedic metal implants at 7T MRI. Local RF heating should preferably be monitored to ensure that no heating occurs close to the implant. SAR_10g is the current preferred method to monitor the patients’ local radiofrequency exposure. This study shows that keeping SAR_10g under recommended values does not ensure that heating remains under safe values close to a hip prosthesis when compared with the more relevant thermal simulations. A new adaptive SAR mass-averaging approach is introduced and gives more reliable prediction of the location and magnitude of heating.

Annie Papadaki, M. Jorge Cardoso, Stephen Wastling, Tarek Yousry, Ludvic Zrinzo, Indran Davagnanam, John Thornton

We modified routine clinical head MRI protocols to be compliant with a new MR conditional product label for deep brain stimulation (DBS) devices limiting B_1+RMS to ≤2.0μT. 12 healthy volunteers were scanned using the routine and modified protocols. Quantitative signal to noise (SNR) and contrast to noise ratio (CNR) analysis was performed, as well as blinded rating of images by a neuroradiologist. Routine and B_1+RMS -limited sequences yielded very similar SNR and grey vs. white matter CNR values, indicating that the B_1+RMS condition had been achieved with minimum impact on image quality, consistent with the neuroradiologist’s qualitative assessment.

Xi Lin Chen, Shiloh Sison, Xin Huang, Shi Feng, Richard Williamson

When a patient with implantable device such as deep brain stimulator undergoes MR scan, the exposure to gradient fields can induce strong voltage across the lead and cause unintended stimulation to the patient or damage the device. In this study, three tiers of voltage determination approach recommended by ISO/TS 10974 ED2 were executed. The analysis results indicate that the tier 3 approach which utilizes realistic gradient coil designs, anatomical models and numerical simulations may arrive at predicted voltage value five times lower than tier 1 approach because of the avoidance of over-conservative assumptions.

Giuseppe Carluccio, Christopher Collins

Among the several parameters that affect temperature computation, blood perfusion is one of the most relevant. According to some studies, perfusion may change significantly with local temperature changes: therefore, it is relevant to characterize both the baseline value of perfusion and its dependence on local temperature for a correct temperature estimation with numerical simulations. In this work, we compare the efficiency and the robustness to noise levels of three different methods to estimate blood perfusion based on the analysis of temperature images which can be acquired, for example, with MR thermometry sequences.

Mikhail Kozlov, Wolfgang Kainz

In this case study we show the dependence of the lead transfer function and the RF-induced power deposition (P) on the presence of heterogeneous tissues around of the lead tip. Depending on the lead length, our results shows a dramatic non-linear dependence of P on a small volume of a different tissue surrounding the lead tip, i.e., a fatty pocket, when using a TF derived in a homogeneous media. Thus, using TFs derived in a homogeneous media can result in large systematic errors in predicting P, and consequently the lead tip heating, of AIMDs inside a human body.

Tanvir Baig, Bhumi Bhusal, Pallab Bhattacharyya, Stephen Jones, Michael Martens

A SEEG electrode contains a number of contact points and as many number of insulated wires each following a contact. Here, we studied the coupling among the contact wires of SEEG electrode inserted into phantom, by using temperature measurements at different contact points, and varying the lengths of contact wires. From the experiment, we saw that, changing the length of one contact wire will result in change in temperature rise to other contacts also, even if wire lengths corresponding to those contacts are unchanged. This shows significant coupling among the wires at the RF frequency of 3T MRI system.

Peter Shin, Daniel Vigneron

An analytical, closed-form solution for the electric field induced inside an ellipsoidal conductor by time-varying gradients in MRI was developed. We applied the method to calculate the electric field for an ellipsoid centered on the isocenter having the semi-axis lengths 20 cm, 15 cm, and 40 cm in LR, AP, and SI directions. We observed that, due to the geometry, ramping up on the Y-axis resulted in the highest electric field intensity. Furthermore, we found that, when the ellipsoid is shifted in the SI direction, the electric field intensity increases approximately 100%.

Malek MAKKI

We designed high spatio-temporal resolution imaging sequence by reducing the excited 3D volume to the object of interest in the slab. A fast spoiled gradient recalled echo acquisition sequence was modified by incorporating spiral selective 2DRF excitation in 2 perpendicular gradients. Three different combinations of slice-select gradient axis (XY, YZ, and XZ) were tested simultaneously in axial, coronal and sagittal prescription planes and different imaging parameters to define the best scheme that provides extremely high resolution spatial imaging, with low SAR and minimum artefact on clinically available scanner.

Oliver Kraff, Yacine Noureddine, Eileen Frerk, Andreas Bitz, Mark Ladd, Harald Quick

Potential RF-induced heating from an implanted port catheter in direct vicinity of a local transmit head coil at 7T was investigated. The assessment included direct measurements of E-field and temperature in a rectangular head/shoulder phantom filled with tissue simulating liquid as well as numerical SAR and thermal simulations in two human body models. Two different RF coils were used for the evaluation, a custom-made 8-channel head coil and the widely-available Nova Medical head coil. No evidence of RF-induced heating was found. Identical transmit power restrictions apply with or without port for both investigated RF coil types.

Youngseob Seo

Heating of patients or burning of biological tissues by RF power induced by medical implants during MRI scan is a significant patient safety concern. The poor reliability and repeatability of the manufacturer-reported SAR values on clinical MRI systems have been acknowledged. High SAR and temperature change occur on both head and tail of artificial hip joints. It is essential to assess the safety of MRI system for patient with medical implant by measuring not only accurate SAR deposited in the body, but also temperature elevation due to the deposited SAR during clinical MRI.

Scott Kalpin, Norbert Kaula, Ramez Shehada

A formula based methodology for predicting Sacral Nerve Stimulation lead temperatures when undergoing MRI exposures is presented. A generalized lead pathway model having 4 primary factors is used to represent the clinical placement. Twelve experimental configurations are selected based on variation of these generalized factors. Heating data measured in an MRI phantom is used to formulate an analytical model. Predictions from the model are compared against the actual data measured in MRI testing. The mean squared error for the model against the 12 test cases is 0.112 °C.

Scott Kalpin, Norbert Kaula, Ramez Shehada

This work evaluates the suitability of various pathway models to represent the worst-case heating for a Spinal Cord Stimulation lead when subjected to MRI RF-intensive exposure. The ideal model represents relevant pathways that a lead can take between any two points with the fewest variable factors.  One model, used for evaluation of safety for Spinal Cord Stimulation (SCS) devices, describes a path with 4 variable factors – IPG starting position (Z), vertical rise of the proximal end of the lead (H1), lateral span width (W), and rise of the distal end of the lead within the central axis (H2).  The “right angle” model is evaluated direct diagonal, half-way diagonal, and one in which all vertical rise is confined to the central axis of the MRI. 

Laleh Golestanirad, Amir Ali Rahsepar, Jeremy Collins, Rod Passman, Giorgio Bonmassar, Boris Keil, James Carr, Lawrence Wald

Despite the tremendous effort to develop MRI safety protocols to reduce complications in patients with cardiac implantable electronic devices with intact leads, almost nothing is known about the variation and extent of RF heating in patients with fractured or abandoned leads. Here we report the preliminary results of the first systematic simulation study of RF-induced SAR amplification at and around abandoned cardiac leads in patients undergoing MRI at 1.5 T and 3.0 T with different imaging landmarks.

Takashi Hamaguchi, Tosiaki Miyati, Naoki Ohno, Tatsuhiko Matsushita, Masanori Ozaki, Tetsuya Minami, Wataru Kouda, Toshifumi Gabata

The purpose of our study was to evaluate the spatial distribution of a gradient-pulse-to-acoustic-noise transfer function (GPAN-TF) with and without a phantom inside the bore. This study showed that the spatial distribution of GPAN-TFs with a phantom in the bore was significantly larger than that with an empty imager. The GPAN-TF spectrum for high frequency range were increased by the phantom. Therefore, the patient would be exposed to a more unpleasant sound than conventional evaluation in an empty scanner. The multipoint analysis using GPAN-TFs revealed structural differences in respective gradient coils under a situation similar to actual MR examination.

Bastien Guerin, Stephen Cauley, Jorge Villena, Athanasios Polimeridis, Elfar Adalsteinsson, Luca Daniel, Jacob White, Lawrence Wald

We extend our previously reported methodology for computation of the ultimate signal-to-noise ratio in realistic body models to the computation of the ultimate specific absorption rate (SAR) in the head of the Duke body model at 3 Tesla. We optimize 90° magnitude least-squares RF pulses subject to hundreds of thousands of SAR constraint for increasing numbers of electromagnetic fields in the basis set. As the size of the basis set increases, we show that the local SAR decreases toward a value that we call the “ultimate local SAR”.

Gianluigi Tiberi, Mauro Costagli, Laura Biagi, Nunzia Fontana, Riccardo Stara, Mark Symms, Mirco Cosottini, Renzo Guerrini, Michela Tosetti

In this study we compare B1+ simulations performed on generic anatomic models with subject-specific measured B1+ maps, performed on both adults and children. We introduce a cost function, based on the normalized standard deviations (the ratio between standard deviation and average) of B1+ maps (magnitude), to guide the selection of generic human model to be used for subject-specific maximum local SAR evaluation. Maximum local SAR does not show a significant variation with subject weight and with subject cranial circumference. Limits on maximum SAR are always met for the sequence here considered (SILENT), in all adults and children.

Mohit Saxena, Cameron McIntyre, Benjamin Walter

We present a method to conduct fMRI in Parkinson’s disease patients with fully implanted bilateral STN Medtronic Activa DBS. This allows for fMRI evaluation of clinically optimized settings or other settings that may reveal anatomical correlations with benefits and side effects.

Spencer Parent, William Handler, John Drozd, Blaine Chronik

The current procedures and guidelines for testing forces on medical devices require that testing be performed in a MR setting, which is both timely and costly. To reduce test time and cost, a computational model of magnetic force was developed. Using a test case where an analytic solution of magnetic force can be applied, it is shown that for materials with magnetic susceptibility (chi)<10⁵ ppm, a computational model of magnetic force was correct within 10% error and this error decreases to less than 1% for chi<10⁴ ppm. Size of object is shown to have little effect on error. 

Xiaoyi Min, Shiloh Sison

The objective of this study is to compare transfer functions (TFs) of a Spinal Cord Stimulation (SCS) system in high permittivity media (HPM), low permittivity media (LPM) and in spinal cord by using computer simulations.  For a SC model, we modeled the anatomical and conductive properties of the lower thoracic (T7-T10) spinal cord.  The TF curves in HPM and in SCS follow each other closely.   With a SC model, the compound tissue effect around the lead was seen.   Lowering HPM conductivity would shift the curve slightly up that with the SC model for in-vivo.   

Jörg Felder, Chang-Hoon Choi, N. Shah

While the application of loopole configurations may be beneficial to improve B₁ distribution at high fields it comes with the drawback of reduced voltage withstanding capability during transmission. This either implies use with lower transmit power or the addition of more capacitors which in turn degrades the quality factor of the coil and thus efficiency and sensitivity of the antenna element.

Yasuhiro Fujiwara, Hitoshi Fujioka, Tomoko Watanabe, Maiko Sekiguchi, Ryuji Murakami

The purpose of this study was to develop a web-based searchable MRI safety information system for confirming medical implant compatibility and to evaluate the usefulness of the system.  The system allows MRI compatibility confirmation to be performed over internet.  This system facilitates obtaining MRI safety information for medical implants easily and rapidly, thereby improving the safety of MRI examination.

Eugene Huo, Bing Tian, David Saloner, Michael Hope, Christopher Hess, William Dillon, Thomas Hope

Although gadolinium deposition in nephrogenic systemic fibrosis is limited to patients with abnormal renal function, more recent rat and human studies have demonstrated gadolinium deposition in specific brain structures in subjects without renal failure. We report here one of the largest studies evaluating gadolinium deposition in terms of both number of patients and number of doses, verifying the impact of the structural differences between the two most commonly used classes of agents (linear vs macrocyclic) and demonstrating a previously undescribed plateau in signal intensity ratio increase in patients who have received more than 25 administrations of gadolinium.

Thomas Frenzel, Gregor Jost, Chirag Apte, Hubertus Pietsch

After the repeated dosing of linear or macrocyclic GBCAs in rats, the brain was fractionated 3 and 24d p.i. Cerebrum, cerebellum and pons were separated, homogenized and divided into an insoluble and soluble fraction, which was separated into low and high molecular weight molecules. The gadolinium concentration in the brain was very low. A large portion of the Gd in the linear GBCA groups was found in the insoluble fraction and a smaller portion in large macromolecules. The Gd in the macrocyclic GBCA groups was only found in the soluble fraction and in small molecules. Gd excretion was still ongoing.

Michelle Lord, Fiona McNeill, James Gräfe, Michael Noseworthy, David Chettle

The use of gadolinium (Gd) based contrast agents is being questioned due to its recently discovered retention in healthy individuals following administration. Our newest generation x-ray fluorescence system has been used in a small pilot study for in vivo Gd measurements in bones of healthy individuals, who have previously received these contrast agents. Preliminary results show a significant difference between the Gd-exposed and control groups, suggesting Gd accumulation in healthy individuals. Our system has performed the first human in vivo measurement of Gd in bone and has the potential to be used in further studies of accumulation in the body.

Paul DiCamillo, Michael Shvarts, Ravi Patel, Jhimli Mitra, Pallavi Tiwari, Stuart Cook, Diego Cadavid, Robert Naismith, Samantha Lancia, Leo Wolansky

We characterize the brain parenchymal deposition of Gadolinium (Gd) in the dentate nucleus (DN) and globus pallidus (GP) in a cohort of 16 subjects with multiple sclerosis (MS), each of whom had systematically received one year of serial monthly triple dose Gd (3-dose Gd) and optional additional monthly exposure for a second year.  Progressive increase in T1 signal and decrease in T2 signal is found in both the dentate nucleus and globus pallidus.

Akira YAMAMOTO, Tsutomu OKADA, Yasutaka FUSHIMI, Tomohisa OKADA, Kaori TOGASHI

Skin tissue showed enhancement after GBCA administration. This phenomenon was confirmed by profile curve analysis. Subtraction image between pre-post contrast was calculated after image registration. This subtraction image showed distinct contrast effect of the skin tissue and may be helpful for the clinical diagnosis.

Takaki Maeda, Hitomi Hara, Toshihiro Akisue, Yuki Iwama, Ryosuke Kuroda, Masahiko Fujii, Kazuro Sugimura

The purpose of this study was to determine the gadolinium (Gd) retention in human bone tissue after administration of Gd contrast agent such as macrocyclic (Gd-DOTA) or linear (Gd-DTPA-BMA) chelate at a standard single clinical dose and to evaluate its correlation with renal function.

Gregor Jost, Thomas Frenzel, Jessica Lohrke, Diana Lenhard, Shinji Naganawa, Hubertus Pietsch

 

The infiltration of six marketed and one experimental gadolinium based contrast agents (GBCA) from blood into the cerebrospinal fluid (CSF) was evaluated in rats by repeated fluid attenuated (FLAIR) MRI up to 4h.  Quantitative gadolinium measurements in CSF samples (4.5 and 24h) were performed by ICP-MS. No differences in penetration and distribution into the CSF were observed for the marketed GBCAs. FLAIR imaging demonstrates a kinetic from the inner CSF cavities to the subarachnoid space, suggesting an infiltration via the choroid plexus and a passive distribution with CSF flow. After 24h an almost complete GBCA clearance from CSF was observed.

 

 

Eric Gale, Hsiao-Ying Wey, Ian Ramsay, David Sosnovik, Peter Caravan

We evaluated the efficacy of a new manganese-based contrast agent, Mn-PyC3A, in contrast-enhanced MR angiography by comparison to Gd-DTPA in a baboon model at 3T. Mn-PyC3A clearance was assessed by dynamically scanning the excretory organs and performing serial blood draws out to 60 min. Mn-PyC3A plasma clearance and metabolism were quantified from the drawn blood. Mn-PyC3A generates equivalent vessel-to-muscle contrast-to-noise ratios as Gd-DTPA at 3T, clears via a mixed renal and hepatobiliary pathway, and is excreted unchanged. Mn-PyC3A is a functionally equivalent gadolinium-free alternative for contrast-enhanced MRI angiography.  

Kim-Lien Nguyen, Takegawa Yoshida, Isidro Salusky, Peng Hu, J. Paul Finn

Recent concerns about gadolinium deposition in biologic tissues and discontinuation of gadofosveset trisodium have created increased interest in the off-label use of ferumoxytol as an MRI contrast agent. Limited safety data relating to the diagnostic use of ferumoxytol are available.  We summarize our safety experience with ferumoxytol as an alternative MRI contrast agent in 285 unique patients (314 injections) with all levels of renal function.

Ashkan Heshmatzadeh Behzadi, Yize Zhao, Zerwa Farooq, Martin Prince

 Recently there has been increased attention focused on GBCA safety and data on the numbers of reactions have begun to be reported in large Studies.  Here we combine data from multiple papers in a meta-analysis to determine if certain GBCA or classes of GBCA may have different immediate reaction profiles.

Hubertus Pietsch, Thomas Frenzel, Jessica Lohrke, Gregor Jost

The impact of renal insufficiency on the T1-weighted signal intensity (SI) increase in the cerebellar nuclei (CN) and on the brain gadolinium concentration was evaluated by comparing 5/6-nephrectomized to healthy control rats. Eight weeks after repeated high-dose GBCA administrations a significantly higher CN/pons SI ratio compared to a saline control group was found for linear GBCAs. This was independent of the renal status. No altered SI ratios compared to the saline group were observed after administration of macrocyclic GBCAs. Inductive coupled plasma mass spectrometry revealed higher gadolinium concentrations for all GBCAs in the cerebellum of renally impaired rats.  

Guenther Schneider, Paul Raczeck, Arno Buecker, Jonas Stroeder

The possibility of Gd deposition in the pediatric brain following exposure to GBCAs is a potentially serious issue. Our study of 34 pediatric patients that received between 5 and 15 administrations of low dose (0.05 mmol/kg bodyweight) gadobenate dimeglumine (MultiHance; Bracco) revealed no differences in T1-signal in the DN, GP, pons and thalamus relative to measurements made in 24 age- and weight-matched control subjects that had never been exposed to any GBCA. Likewise no meaningful differences were seen in DN–pons and GP–thalamus SI ratios. We consider low dose gadobenate to be safe and effective for diagnosis and routine follow-up of pediatric oncologic patients.

Ken Masuyama, Masayuki Taguchi, Toru Yamamoto

High T1-weighted signal appears in brain of patients who have experienced MRI examinations using gadolinium contrast agent several times. The relaxation effect of gadolinium contrast agent strongly depends on the viscosity of the solution, and the average viscosity in the cell is higher than that of the free water. However, the relaxation effect of the gadolinium contrast agent in the cell has been unknown. In this study, we investigated the longitudinal relaxivity of it – concentration dependence of longitudinal relaxation rate in solution with intracellular viscosity. The intracellular viscosity strongly enhances the longitudinal relaxivity of the gadolinium contrast agent.

Scott Reeder, Elizabeth Simcock, Bryan Ramirez, Joseph Rowley, Howard Rowley

In this work, we describe the design, implementation, and utilization of an online and smartphone gadolinium calculator used to calculate gadolinium-based contrast agent (GBCA) dose. By providing a readily available, reliable, and rapid means of calculating the volume of a GBCA, we aim to ensure accurate dosing so as to avoid accidental over- or under-dosing. Utilization tracking demonstrated progressively increasing use of the online gadolinium calculator with a total of 22,074 page visits from 68 countries, logged during a 9-month tracking period.

Saravanabavaan Suntharalingam, Emil Mladenov, Georg Iliakis, Michael Forsting, Oliver Kraff, Harald Quick, Kai Nassenstein

Magnetic resonance imaging is considered to be a safe alternative to other imaging techniques that use ionizing radiation, such as computed tomography. Initially driven by X-ray and CT imaging studies, within the recent years different in vitro and in vivo studies analyzed the impact of MR imaging on DNA integrity in human lymphocytes but reported contradictory results. In this study on patients referred to clinical abdominal MRI, γ-H2AX immunofluorescence microscopy was used to determine DNA integrity. No evidence of DNA damage induced by abdominal MRI in a clinical setting was found.

Yigitcan Eryaman, Russell Lagore, Arcan Erturk, Lynn Utecht, Patrick Zhang, Angel Torrado-Carvajal, Esra Abaci Turk, Lance DelaBarre, Gregory Metzger, Gregor Adriany, Kamil Ugurbil, J. Thomas Vaughan

We measured temperature increase (ΔT) in anesthetized swine using fluoroscopic probes and compared our results to the simulated solutions obtained from digital models of the same swine. For our studies, we used a 4 channel fractionated dipole array that is placed on the neck/upper back region. Electromagnetic and thermal simulations were performed along with in vivo experiments with different RF excitation patterns at 10.5 T. 

Thomas Fiedler, Stephan Orzada, Martina Flöser, Harald Quick, Mark Ladd, Andreas Bitz

RF safety assessment for a 32-ch body coil for 7T was performed based on SAR, tissue temperature, and a thermal dose model (CEM43°C). Temperature simulations considered a temperature-dependent thermoregulation. The tissue temperature limit is exceeded when SAR limits are adhered to. However, based on the thermal dose limit, the maximum input power determined from SAR limits can be exceeded by up to a factor of 5 without noticeable limitations in permissible exposure time in MR examinations. This increased input power allows for improved B₁⁺homogeneity with 50% reduced flip angle error compared to the input power determined from SAR limits.

Shaihan Malik, Jeffrey Hand, Joseph Hajnal

Effects on B₁⁺ and local specific absorption rate of varying the conductivity of fetal tissues and amniotic fluid ($$$\sigma_{AF}$$$) in a model of a 7 month pregnant woman within a 3T birdcage coil are investigated numerically. Results indicate that a realistic value of  $$$\sigma_{AF}$$$ is required to estimate power to produce a chosen B₁⁺ in the fetus and fetal SAR_10g. Fetal properties adjusted for gestational age impact on B₁⁺ and result in increased fetal SAR_10g compared to adult value based simulations.  Smaller changes in SAR_10g are predicted between detailed fetal models and homogeneous ones with volume weighted average dielectric properties. 

Amir Ali Rahsepar, Laleh Golestanirad, Hassan Haji-Valizadeh, Haris Saybasili , Julie Blaisdell , Michael Markl, John Kirsch, James Carr, Jeremy Collins

Although SAR value is an important factor in device heating, but this study also provides information about the other factors like the total amount of delivered RF energy, time period of RF delivery and most importantly the pause between pulse sequences should be considered 

Giuseppe Carluccio, Christopher Collins

We demonstrate that the maximum SAR-induced temperature in an examination can be lowered with strategic ordering of the sequences in the exam. Using numerical simulations, here we optimize the order of and time between sequences in a spine exam to minimize the maximum temperature reached in a human body model without increasing the duration of the exam. The optimized sequence has a maximum temperature 0.63 C lower than the original.

Antonino Cassara', Esra Neufeld, Gisela Hagberg, Manuel Guidon, Klaus Scheffler, Niels Kuster

The mechanisms of peripheral nerve stimulation (PNS) induced by the fast switching of MRI gradient coils are only partially understood, stimulation sites and E-field (or dB/dt) thresholds show large inter-subject variability and neurostimulation models based on the amphibian SENN axon model are not ideal. We propose a 3 level computational investigation that combines analysis of E-field exposure, of activation functions, and of multi-parametric EM-electrophysiological simulations in neuro-functionalized human models for different axon models and gradient waveforms. Results concerning E-field/dB/dt thresholds values and sites of neurostimulation are compared with published experimental data. A functional uncertainty analysis is also provided.

Yuliang Du, Xi Lin Chen, Will Lui, Shi Feng, Shiloh Sison

Impacts of SMS imaging technique on the AIMD design, transfer function measurement, model calculation and system validation were thoroughly analyzed. The RF frequency broadening from the SMS imaging sequence has minimal impacts to the existing device design and test methodology.

Gianluigi Tiberi, Guo Liu, Raj Mittra, Michela Tosetti

SAR management is critical at ultra-high field (UHF) strength where RF field energy deposition in the subject increases and its distribution becomes very inhomogeneous. Here we illustrate simulation results for a test example in order to show how a graphene sheet can be used to obtain a SAR reduction without sacrificing the coil efficiency significantly. Specifically, the presence of the graphene sheet leads a maximum local SAR reduction up to 47%. Thus, from the simulation here shown, it follows that graphene sheets can be successfully used in MRI applications at 7T for enhancing the safety with respect to SAR issue

Karsten Wrede, Bixia Chen, Ulrich Sure, Harald Quick, Oliver Kraff

This in vitro study tests function, safety and image artifacts of the two worldwide most frequently implanted programmable VP-shunt valves in a 7 Tesla whole body MRI system. Both tested programmable VP-shunt valves lost their ability to be reprogramed after exposure to the static magnetic field and are therefore unsafe for use in 7 Tesla whole body scanners in their current design. Magnetic coercivity of the permanent magnets in the programming mechanisms was insufficient. Image artifacts adjacent to the valves, however, were tolerable.