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To evaluate the safety of MRI in patients with fragmented retained leads (FRLs) through numerical simulation and phantom experiments.Electromagnetic and thermal simulations were performed to determine the worst-case RF heating of 10 patient-derived FRL models during MRI at 1.5 T and 3 T and at imaging landmarks corresponding to head, chest, and abdomen. RF heating measurements were performed in phantoms implanted with reconstructed FRL models that produced highest heating in numerical simulations. The potential for unintended tissue stimulation was assessed through a conservative estimation of the electric field induced in the tissue due to gradient-induced voltages developed along the length of FRLs.In simulations under conservative approach, RF exposure at BSimulation and experimental results indicate that patients with FRLs can be scanned safely at both 1.5 T and 3 T with most clinical pulse sequences.

IntroductionRadiofrequency (RF) induced tissue heating around deep brain stimulation (DBS) leads is a well-known safety risk during magnetic resonance imaging (MRI), resulting in strict imaging guidelines and limited allowable protocols. The implanted lead’s trajectory and its orientation with respect to the MRI electric fields contribute to variations in the magnitude of RF heating across patients. Currently, there are no consistent requirements for surgically implanting the extracranial portion of the DBS lead. This produces substantial variations in clinical DBS lead trajectories and hinders RF heating predictions. Recent studies showed that incorporating concentric loops in the extracranial trajectory of the lead can reduce RF heating, but the optimal positioning of the loop remains unknown. In this study, we systematically evaluated the RF heating of 244 unique lead trajectories to elucidate the characteristics of the trajectory that minimize RF heating during MRI at 3 T. We also presented the first surgical implementation of these modified trajectories and compared their RF heating to the RF heating of unmodified trajectories.MethodsWe performed phantom experiments to assess the maximum temperature increase, ΔTmax, of 244 unique lead trajectories. We systematically interrogated the effect of three characteristics related to the extracranial portion of the lead trajectory, namely, the number of concentric loops, the size of the loops, and the position of the loops on the skull. Experiments were performed in an anthropomorphic phantom implanted with a commercial DBS system, and RF exposure was generated by applying a high-SAR sequence (T1-weighted turbo spin echo dark fluid pulse sequence, B1+rms= 2.7 μT). Test-retest experiments were conducted to assess the reliability of measurements. Additionally, we determined the effect of imaging landmark and perturbations to the DBS device configuration on the efficacy of low-heating lead trajectories. Finally, recommended modified trajectories were implanted in patients by two neurosurgeons and their RF heating was characterized in comparison with non-modified trajectories.ResultsOur search protocol elicited lead trajectories with ΔTmaxfrom 0.09 – 7.34 °C. Interestingly, increasing the number of loops and positioning them near the surgical burr hole—especially for the contralateral lead—substantially reduced RF heating. Trajectory specifications based on the results from the phantom experiments were easily adopted during the surgical procedure and generated nearly a 4-fold reduction in RF heating.Discussion/ConclusionSurgically modifying the extracranial portion of the DBS lead trajectory can substantially mitigate RF heating during MRI at 3 T. Simple adjustments to the lead’s configuration can be readily adopted during DBS lead implantation by implementing small concentric loops near the surgical burr hole.

PurposeDirectional deep brain stimulation (DBS) leads have become widely used in the past decade. Understanding the asymmetric stimulation provided by directional leads requires precise knowledge of the exact orientation of the lead in respect to its anatomical target. Recently, the DiODe algorithm was developed to automatically determine the orientation angle of leads from the artifact on postoperative computed tomography (CT) images. However, DiODe results are user-dependent. This study analyzed the significance of lead rotation as well as the user agreement of DiODe calculations across the two most common DBS systems and two independent medical institutions.MethodsData from 104 patients who underwent an anterior-facing unilateral/bilateral directional DBS implantation at either Northwestern Memorial Hospital (NMH) or Albany Medical Center (AMC) were retrospectively analyzed. Actual orientations of the implanted leads were independently calculated by three individual users using the DiODe algorithm in Lead-DBS and patients’ postoperative CT images. Deviation from the intended orientation and user agreement were assessed.ResultsAll leads significantly deviated from the intended 0° orientation (pConclusionOur results show that there is a significant lead rotation from the intended surgical orientation across both DBS systems and both medical institutions, however, a bias towards a single direction was only seen in Boston Scientific leads. Additionally, these results raise questions into the user error that occurs when manually refining the orientation angles calculated with DiODe.

BackgroundSince the advent of magnetic resonance imaging (MRI) nearly four decades ago, there has been a quest for ever-higher magnetic field strengths. Strong incentives exist to do so, as increasing the magnetic field strength increases the signal-to-noise ratio of images. However, ensuring patient safety becomes more challenging at high and ultrahigh field MRI (i.e., ≥3 T) compared to lower fields. The problem is exacerbated for patients with conductive implants, such as those with deep brain stimulation (DBS) devices, as excessive local heating can occur around implanted lead tips. Despite extensive effort to assess radio frequency (RF) heating of implants during MRI at 1.5 T, a comparative study that systematically examines the effects of field strength and various exposure limits on RF heating is missing.PurposeThis study aims to perform numerical simulations that systematically compare RF power deposition near DBS lead models during MRI at common clinical and ultra-high field strengths, namely 1.5, 3, 7, and 10.5 T. Furthermore, we assess the effects of different exposure constraints on RF power deposition by imposing limits on either the B1+or global head specific absorption rate (SAR) as these two exposure limits commonly appear in MRI guidelines.MethodsWe created 33 unique DBS lead models based on postoperative computed tomography (CT) images of patients with implanted DBS devices and performed electromagnetic simulations to evaluate the SAR of RF energy in the tissue surrounding lead tips during RF exposure at frequencies ranging from 64 MHz (1.5 T) to 447 MHz (10.5 T). The RF exposure was implemented via realistic MRI RF coil models created based on physical prototypes built in our institutions. We systematically examined the distribution of local SAR at different frequencies with the input coil power adjusted to either limit the B1+or the global head SAR.ResultsThe MRI RF coils at higher resonant frequencies generated lower SARs around the lead tips when the global head SAR was constrained. The trend was reversed when the constraint was imposed on B1+.ConclusionAt higher static fields, MRI is not necessarily more dangerous than at lower fields for patients with conductive leads. Specifically, when a conservative safety criterion, such as constraints on the global SAR, is imposed, coils at a higher resonant frequency tend to generate a lower local SAR around implanted leads due to the decreased B1+and, by proxy,Efield levels.

BackgroundChildren with congenital heart defects often have life-sustaining indications for a cardiac implantable electronic device (CIED). In children, these devices are typically sewn to the heart epicardium, but the FDA has never licensed an epicardial system as MR-Conditional due to limited data. Children’s hospitals default to either refusing MRI service to a vast majority of pediatric CIED patients or adopting a scan-all strategy based on results from adult studies. We argue that both approaches are flawed, and the risk-benefit decisions should be made on an individual basis.PurposeTo provide evidence-based knowledge on RF-induced heating of CIEDs in children and adults with epicardial and endocardial leads of different lengths.Study TypePhantomField Strength/Sequence1.5 T.Assessment120 clinically relevant epicardial and endocardial device configurations were implemented in adult and pediatric anthropomorphic phantoms. Temperature rise was recorded during RF exposure at 1.5 T.Statistical TestsMeans comparisons were implemented using two-sample t-tests, reliability analysis using interclass correlation coefficient based on a single rating, absolute-agreement, 2-way mixed-effects model.ResultsThere was significantly higher RF heating of epicardial leads compared to endocardial leads in the pediatric phantom (3.4 ± 3.0 vs. 0.6 ± 0.4 °C, pData ConclusionBody size and lead length significantly affected RF heating. For models based on younger children with short epicardial leads (e.g., 25cm), RF heating up to 12 °C was observed, delivering a cumulative thermal dose previously associated with tissue necrosis. In contrast, RF heating in model based on children with endocardial leads was well below the heating expected from physiologic fever (3 °C).

PurposeInfants and children with congenital heart defects, inherited arrhythmia syndromes, and congenital cardiac conduction disorders often receive epicardial implantable electronic devices. Unfortunately, once an epicardial device is implanted, the patient is no longer eligible to receive MRI exams due to an elevated risk of RF heating. Here we show that a simple modification in the trajectory of epicardial leads can substantially and reliably reduce RF heating during MRI at 1.5 T, with benefits extending to abandoned leads.MethodsElectromagnetic simulations were performed to assess RF heating of two common epicardial lead trajectories exhibiting different degrees of coupling with MRI incident electric fields. Experiments in anthropomorphic phantoms implanted with commercial cardiac implantable electronic devices (CIEDs) confirmed the findings.ResultsSimulations of an epicardial lead with a trajectory where the excess length of the lead was looped and placed on the anterior surface of the heart showed a 9-fold reduction in 0.1g-averaged SAR compared to the lead with excess length looped on the inferior surface of the heart. Repeated experiments with a commercial epicardial device confirmed the results, showing a 16-fold reduction in the average temperature rise for fully implanted systems with leads following low-SAR trajectories, and a 20-fold reduction in RF heating on an abandoned lead.ConclusionSurgical modification of epicardial lead trajectory can substantially reduce RF heating at 1.5 T, with benefits extending to abandoned leads.

IntroductionDeep brain stimulation (DBS) is a common treatment for a variety of neurological and psychiatric disorders. Recent studies have highlighted the role of neuroimaging in localizing the position of electrode contacts relative to target brain areas in order to optimize DBS programming. Among different imaging methods, postoperative magnetic resonance imaging (MRI) has been widely used for DBS electrode localization; however, the geometrical distortion induced by the lead limits its accuracy. In this work, we investigated to what degree the difference between the actual location of the lead’s tip and the location of the tip estimated from the MRI artifact varies depending on the MRI sequence parameters such as acquisition plane and phase encoding direction, as well as the lead’s extracranial configuration. Accordingly, an imaging technique to increase the accuracy of lead localization was devised and discussed.MethodsWe designed and constructed an anthropomorphic phantom with an implanted DBS system following 18 clinically relevant configurations. The phantom was scanned at a Siemens 1.5 Tesla Aera scanner using a T1MPRAGE sequence optimized for clinical use and a T1TSE sequence optimized for research purposes. We varied slice acquisition plane and phase encoding direction and calculated the distance between the caudal tip of the DBS lead MRI artifact and the actual tip of the lead, as estimated from MRI reference markers.ResultsImaging parameters and lead configuration substantially altered the difference in the depth of the lead within its MRI artifact on the scale of several millimeters − with a difference as large as 4.99 millimeters. The actual tip of the DBS lead was found to be consistently more rostral than the tip estimated from the MR image artifact. The smallest difference between the tip of the DBS lead and the tip of the MRI artifact using the clinically relevant sequence (i.e., T1MPRAGE) was found with the sagittal acquisition plane and anterior-posterior phase encoding direction.Discussion/ConclusionThe actual tip of an implanted DBS lead is located up to several millimeters rostral to the tip of the lead’s artifact on postoperative MR images. This distance depends on the MRI sequence parameters and the DBS system’s extracranial trajectory. MRI parameters may be altered to improve this localization.

BACKGROUND Patients with deep brain stimulation (DBS) implants have limited access to MRI due to safety concerns associated with RF-induced heating. Currently, MRI in these patients is allowed in 1.5T horizontal bore scanners utilizing pulse sequences with reduced power. However, the use of 3T MRI in such patients is increasingly reported based on limited safety assessments. Here we present the results of comprehensive RF heating measurements for two commercially available DBS systems during MRI at 1.5T and 3T. PURPOSE To assess the effect of imaging landmark, DBS lead configuration, and patient's body composition on RF heating of DBS leads during MRI at 1.5T and 3T. STUDY TYPE Phantom and ex vivo study. POPULATION/SUBJECTS/PHANTOM/SPECIMEN/ANIMAL MODEL Gel phantoms and cadaver brain. FIELD STRENGTH/SEQUENCE 1.5T and 3T, T1 -weighted turbo spin echo. ASSESSMENT RF heating was measured at the tips of DBS leads implanted in brain-mimicking gel. Image artifact was assessed in a cadaver brain implanted with an isolated DBS lead. STATISTICAL TESTS Descriptive. RESULTS We observed substantial fluctuation in RF heating, mainly affected by phantom composition and DBS lead configuration, ranging from 0.14°C to 23.73°C at 1.5T, and from 0.10°C to 7.39°C at 3T. The presence of subcutaneous fat substantially altered RF heating at the electrode tips (3.06°C

Interaction of an active electronic implant such as a deep brain stimulation (DBS) system and magnetic resonance imaging (MRI) radiofrequency (RF) fields can induce excessive tissue heating, limiting MRI accessibility. Efforts to quantify RF heating mostly rely on electromagnetic (EM) simulations to assess individualized specific absorption rate (SAR), but such simulations require extensive computational resources. Here, we investigate if a predictive model using machine learning (ML) can predict the local SAR in the tissue around tips of implanted leads from the distribution of the tangential component of the MRI incident electric field, E tan. A dataset of 260 unique patient-derived and artificial DBS lead trajectories was constructed, and the 1 g-averaged SAR, 1 g SARmax, at the lead-tip during 1.5 T MRI was determined by EM simulations. E tan values along each lead's trajectory and the simulated SAR values were used to train and test the ML algorithm. The resulting predictions of the ML algorithm indicated that the distribution of E tan could effectively predict 1 g SARmax at the DBS lead-tip ( R = 0.82). Our results indicate that ML has the potential to provide a fast method for predicting MR-induced power absorption in the tissue around tips of implanted leads such as those in active electronic medical devices.

Patients with cardiovascular implantable electronic devices (CIEDs) are often prevented from receiving magnetic resonance imaging (MRI) due to risks associated with radiofrequency (RF) heating of tissue around the implanted leads. Although MR-conditional CIEDs are available, the safety labeling of such devices does not extend to patients with fragmented retained leads (FRLs), where segments of the leads are left in the tissue after the original device is extracted. Unlike intact and isolated leads of CIEDs, FRLs are often bare conductive lead fragments in direct contact with the tissue. No experimental work has been reported that assess RF heating of FRL during MRI thus far. In this work, we performed phantom experiments to measure RF heating of 4 patient-derived FRL models in a gel-based ASTM-like phantom during RF exposure at 64 MHz (proton imaging at 1.5 T) and 123 MHz (proton imaging at 3 T). We found FRL models to generate negligible temperature rise in the gel (∆T1.84 °C) during a 10-minute scan at both 1.5 T and 3 T. These results are in agreement with previous simulation studies and suggest MRI may be performed safely in patients with fragmented retained leads.