Magnetic Resonance Imaging Environment Research Articles

Development of an MRI-powered robotic system for cryoablation.

This study proposes a novel MRI-powered robotic system controlled with the magnetic field generated by a magnetic resonance imaging (MRI) scanner. In the proposed system, we use an MRI-powered actuator unit proposed in the previous study and a spherical positioning mechanism. The actuator unit contains a ferromagnetic sphere, which acts as a power source and is used to control the positioning unit inside the MRI environment. These elements enable the development of a remote needle tip positioning system for use within the MRI scanner. Potential applications of the developed system include the automation of procedures during under MRI inspections, especially the cryoablation of breast cancer. In this paper, we report on the performance evaluation and the MR-safety of the proposed system and describe the newly developed spherical positioning mechanism, which can be activated by the actuator units.

Wrong detection of ventricular fibrillation in an implantable cardioverter defibrillator caused by the movement near the MRI scanner bore.

The static magnetic field generated by MRI systems is highly non-homogenous and rapidly decreases when moving away from the bore of the scanner. Consequently, the movement around the MRI scanner is equivalent to an exposure to a time-varying magnetic field at very low frequency (few Hz). For patients with an implanted cardiac stimulators, such as an implantable cardioverter/defibrillator (ICD), the movements inside the MRI environment may thus induce voltages on the loop formed by the leads of the device, with the potential to affect the behavior of the stimulator. In particular, the ICD's detection algorithms may be affected by the induced voltage and may cause inappropriate sensing, arrhythmia detections, and eventually inappropriate ICD therapy.We performed in-vitro measurements on a saline-filled humanshaped phantom (male, 170 cm height), equipped with an MRconditional ICD able to transmit in real-time the detected cardiac activity (electrograms). A biventricular implant was reproduced and the ICD was programmed in standard operating conditions, but with the shock delivery disabled. The electrograms recorded in the atrial, left and right ventricle channels were monitored during rotational movements along the vertical axis, in close proximity of the bore. The phantom was also equipped with an accelerometer and a magnetic field probe to measure the angular velocity and the magnetic field variation during the experiment. Pacing inhibition, inappropriate detection of tachyarrhythmias and of ventricular fibrillation were observed. Pacing inhibition began at an angular velocity of about 7 rad/s, (dB/dt of about 2 T/s). Inappropriate detection of ventricular fibrillation occurred at about 8 rad/s (dB/dt of about 3 T/s). These findings highlight the need for a specific risk assessment of workers with MR-conditional ICDs, which takes into account also effects that are generally not considered relevant for patients, such as the movement around the scanner bore.

New aspects from legislation, guidelines and safety standards for MRI

Many aspects of magnetic resonance (MR) operation are not directly regulated by law but in standards, guidelines and the operating instructions of the MR scanner. The mandatory contents of the operating instructions are regulated in a central standard of the International Electrotechnical Commission (IEC) 60601-2-33. In this standard, the application of static magnetic fields in MRI up to 8 Tesla (T) in the clinical routine (first level controlled mode) has recently been approved. Furthermore, the equally necessary CE certification of ultra-high field scanners (7-8 T) in Europe is expected for future devices. The existing installations will not be automatically certified but will retain their experimental status. The current extension of IEC 60601-2-33 introduces a new add-on option, the so-called fixed parameter option (FPO). This option might also be switched on in addition to the established operating modes and defines a fixed device constellation and certain parameters of the energy output of MR scanners designed to simplify the testing of patients with implants in the future.The employment of pregnant workers in an MRI environment is still not generally regulated in Europe. In parts of Germany and Austria pregnant and lactating employees were prohibited from working in the MR control zone (0.5 mT) in 2014. This is based on the mostly unresolved question of the applicability of limits for employees (exposure of extremities to static magnetic fields up to 8 T allowed) or the thresholds for the general population (maximum 400 mT). According to the European Society of Urogenital Radiology (ESUR), the discarding of breast milk after i.v. administration of gadolinium-based contrast agents in the case of a breastfeeding woman is only recommended when using contrast agents in the nephrogenic systemic fibrosis (NSF) high-risk category.

Targeting Accuracy, Procedure Times and User Experience of 240 Experimental MRI Biopsies Guided by a Clinical Add-On Navigation System.

ObjectivesMRI is of great clinical utility for the guidance of special diagnostic and therapeutic interventions. The majority of such procedures are performed iteratively ("in-and-out") in standard, closed-bore MRI systems with control imaging inside the bore and needle adjustments outside the bore. The fundamental limitations of such an approach have led to the development of various assistance techniques, from simple guidance tools to advanced navigation systems. The purpose of this work was to thoroughly assess the targeting accuracy, workflow and usability of a clinical add-on navigation solution on 240 simulated biopsies by different medical operators.MethodsNavigation relied on a virtual 3D MRI scene with real-time overlay of the optically tracked biopsy needle. Smart reference markers on a freely adjustable arm ensured proper registration. Twenty-four operators – attending (AR) and resident radiologists (RR) as well as medical students (MS) – performed well-controlled biopsies of 10 embedded model targets (mean diameter: 8.5 mm, insertion depths: 17-76 mm). Targeting accuracy, procedure times and 13 Likert scores on system performance were determined (strong agreement: 5.0).ResultsDifferences in diagnostic success rates (AR: 93%, RR: 88%, MS: 81%) were not significant. In contrast, between-group differences in biopsy times (AR: 4:15, RR: 4:40, MS: 5:06 min:sec) differed significantly (p<0.01). Mean overall rating was 4.2. The average operator would use the system again (4.8) and stated that the outcome justifies the extra effort (4.4). Lowest agreement was reported for the robustness against external perturbations (2.8).ConclusionsThe described combination of optical tracking technology with an automatic MRI registration appears to be sufficiently accurate for instrument guidance in a standard (closed-bore) MRI environment. High targeting accuracy and usability was demonstrated on a relatively large number of procedures and operators. Between groups with different expertise there were significant differences in experimental procedure times but not in the number of successful biopsies.

Magnetic Field-Induced Vertigo in the MRI Environment

This review discusses the theory behind, and the experimental evidence for, the perception of vertigo in a high magnetic field found in a magnetic resonance imaging (MRI) environment. Recent experiments have shown that there is an eye nystagmus response that is proportional to magnetic field exposure and not purely one of rate of change of magnetic field. The mechanism of transduction can be attributed to the Lorentz forces on the endolymph in the ear canals, producing a static pressure due to the vector product of the magnetic field and current density. The adaption and response of the measurable effect reveals time constants which support such a mechanism and explain why the balance system responds in the way we observe and feel. The position and movement of the head relative to the direction of field is of fundamental importance to the sensation of vertigo, as are ambient conditions such as lighting levels. Recent surveys of subjects undergoing seven tesla or higher MRI scans report that although there is a high perception of vertigo-like effects, these are not intolerable and are not generally the cause of subject withdrawal. This review argues that the International Commission on Non-Ionizing Radiation guidelines on low-frequency fields still need to acknowledge the role of a high magnetic field in producing vertigo sensations rather than rate of change of field alone.

Safety of Implanted Cardiac Devices in an MRI Environment

Magnetic resonance imaging (MRI) has evolved into an essential diagnostic modality for the evaluation of various conditions. In line with the increase in MRI applications, the use of cardiac implantable electronic devices (CIED) is growing and many of the CEID recipients of today may require MRI examinations in the future. Traditionally, MRI examination of CIED recipients has been considered a contraindication. However, recent studies have provided strong evidence that MRI can safely be performed in selected patients with specific precautions. This review highlights the interactions of MRI with CIEDs, summarizes the literature, and outlines the Johns Hopkins Safety Protocol.

Evaluation of a power injection system in the 7‐Tesla MRI environment

ABSTRACTThe injection of contrast media enables the visualization of various pathologies through X‐ray, computed tomography, magnetic resonance imaging (MRI), or other medical imaging modalities. Safety and functionality of power injector systems must be evaluated at high magnetic fields (7‐Tesla). The purpose of this study was to evaluate MRI issues for a power injection system (OptiStar Elite MR Contrast Delivery System, Mallinckrodt Pharmaceuticals, Hazelwood, MO) at 7‐Tesla including magnetic field interaction and 31 injector performance tests. Additionally, effects of operation of the power injection system on MR images were evaluated through observation of image artifacts and signal to noise analysis. The components of the power injection system (powerhead, syringes) exhibited no translational attraction when close to 7‐Tesla MR system. Translational attraction was detected for the power supply, power control, and cables, therefore there is a requirement to maintain these components fixed outside of the 0.1000 Tesla line. 7‐Tesla MR scanning did not impact power injection performance. The power injection system produced no discernible image artifacts or degradation when the power controls and powerhead were positioned in the worst‐case position. The power injection system tested for MRI issues passed evaluation for safety and operation at 7‐Tesla and is labeled MR Conditional for use at 7‐T. © 2015 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 25, 50–55, 2015

Interventional cardiac magnetic resonance imaging in electrophysiology: advances toward clinical translation.

Technical advances in cardiovascular electrophysiology have resulted in an increasing number of catheter ablation procedures reaching 200 000 in Europe for the year 2013.1 These advanced interventions are often complex and time-consuming and may cause significant radiation exposure.2 Furthermore, a substantial number of ablation procedures remain associated with poor (initial) outcomes and frequently require ≥1 redo procedures.3 Innovations in cardiac imaging and image guidance could help improve the results of ablation procedures.4 Among the available imaging modalities, Cardiac MRI (CMR) can be considered the most comprehensive and suitable modality for the complete electrophysiology and catheter ablation process (including patient selection, procedural guidance, and [procedural] follow-up).5 The unique ability of CMR including tissue characterization (eg, T2-weighted imaging for edema visualization, late gadolinium enhancement [for necrosis quantification]) may be of advantage for the evaluation of lesion formation and therapeutic efficacy.6–9 These benefits and the lack of radiation exposure inspired the development of hybrid x-ray/MR (XMR) suites10 and dedicated interventional CMR (iCMR) units.11 This review examines the requirements and clinical feasibility of a dedicated iCMR suite for electrophysiology procedures. First, the limitations of current electrophysiology procedures and ablation strategies are analyzed and the advantages of an iCMR suite for this purpose are discussed. Second, the clinical feasibility is examined by presenting the current challenges of working in an MRI environment. Safety, imaging, and device-related aspects are also reviewed. Finally, the requirements for implementing an iCMR suite and the current state of their developments are addressed. There are different phases during the workup and follow-up of a diagnostic or ablative electrophysiology procedure. The limitation of the current strategy, including the role of fluoroscopy, in diagnosis and treatment of arrhythmias is discussed in the following paragraphs. ### Patient Identification and Procedure Planning Imaging is considered a cornerstone of patient selection for ablation …

Imaging the PM/AICD patient; is it evolving into a routine procedure? An evolutionary report of our first 100 patients

Background Pacemaker/AICD use may no longer be prohibitive in the MRI environment. Seminal work by us and others has pointed towards increasing safety and specifically, the marked additive clinical value. Historically, on only extraordinarily high-risk patients with acute diagnoses were imaged. However, over time, we began to note an interesting trend as our understanding, science and comfort level admixed with zero-event rate almost imperceptibly causes us to ‘relax’ the mandate for acuity. We wondered, “Has imaging a patient with a pacemaker that was once considered a last resort procedure started to evolve into a routine study? What have we learned from performing these procedures?

Considerations on imaging the PM/AICD patient; are we entering a new era? An evolutionary report of our first 100 Patients

Background Pacemaker/AICD use may no longer be prohibitive in the MRI environment. Seminal work by us and others has pointed towards increasing safety and specifically, the marked additive clinical value. Historically, only extraordinarily high-risk patients with acute life-threatening diagnoses were imaged. However, over time, we began to note an interesting trend as our understanding, science and comfort level admixed with zero-event rate almost imperceptibly causes us to ‘relax’ the mandate for ‘acuity’. We wondered, “Has imaging a patient with a pacemaker that was once considered a last resort procedure started to evolve into a ‘routine’ study?

Is there value beyond safety in CMR imaging of PM/AICD patients?

Background Pacemaker/ AICD imaging is currently clincally performed in the MRI environment. A vigilant team consisting of Cardiologist, EP staff, and technologists with close patient monitoring and supervision has evolved this heretofore risky endeavor into a procedure with established safety if done properly. However, once safety is established, does such add valuable irrefutable information to merit that risk?

Fiber-optic sensors for monitoring patient physiological parameters: a review of applicable technologies and relevance to use during magnetic resonance imaging procedures.

The issues involved with recording vital functions in the magnetic resonance imaging (MRI) environment using fiber-optic sensors are considered in this paper. Basic physiological parameters, such as respiration and heart rate, are fundamental for predicting the risk of anxiety, panic, and claustrophobic episodes in patients undergoing MRI examinations. Electronic transducers are generally hazardous to the patient and are prone to erroneous operation in heavily electromagnetically penetrated MRI environments; however, nonmetallic fiber-optic sensors are inherently immune to electromagnetic effects and will be crucial for acquiring the above-mentioned physiological parameters. Forty-seven MRI-tested or potentially MRI-compatible sensors have appeared in the literature over the last 20 years. The author classifies these sensors into several categories and subcategories, depending on the sensing element placement, method of application, and measure and type. The author includes five in-house-designed fiber Bragg grating based sensors and shares experience in acquiring physiological measurements during MRI scans. This paper aims to systematize the knowledge of fiber-optic techniques for recording life functions and to indicate the current directions of development in this area.

Implementation of a ferromagnetic detection system in a clinical MRI setting

PurposeTo evaluate the implementation of a ferromagnetic detection system (FMDS) into a clinical MRI setting. Materials and methodsOne thousand patients were considered for MRI safety screening using an FMDS. Equipment used was a Ferroguard® Screener (Metrasens Ltd, Malvern, Worcestershire, UK). Fully gowned patients rotated 360° in front of the FMDS in a standardized manner following traditional MRI screening methods (the use of a written questionnaire (Fig. B.1) and verbal interview. ResultsFinal results included 1032 individual screening events performed in 977 patients. There were 922 (94%) initial passes using the FMDS; 34 (4%) failed initial screens but passed a subsequent screen; 21 (2%) failed the initial and subsequent screens. Thus, including all screening events (n = 1032), there were 956 (93%) true negatives (TN); 21 (2%) false positives (FP) and 55 (5%) true positives (TP). No false negatives (FN) were recorded. Therefore, sensitivity was 100% and specificity was 98%. ConclusionImplementation and correct usage of an FMDS proved to increase safety within a clinical MRI environment by alerting staff to ferromagnetic items or implants not identified using traditional MRI screening methods. An FMDS should be used as an adjunct to these methods. The information in this study pertains to the specific equipment used in this investigation.

MRI適合性を有する下肢動作提示システムLoMS

This paper describes a motion simulator for the lower extremities of human in a magnetic resonance imaging (MRI) environment. The motion simulator provides physical support for a wearer to move his/her lower extremities like gait. The simulator also provides his/her sole contact sensation like floor reactive force during gait. An MRI is one of the most powerful tools to measure brain activity, and requires that a device driven in MRI environment is MRI compatible. This paper shows the MRI compatibility of the simulator which consists of nonmagnetic materials and actuators. We confirm that the simulator does not affect quality of image of MRI adversely when a distance between the simulator and a head coil of the MRI is more than 300[mm]. When MRI measures brain activity of human wearing LoMS, the distance is more than 400[mm]. We also confirm that LoMS can measure own joint angles with potentiometers through simple low-pass filters avoiding noise due to MRI. Then we measure brain activity of a man wearing LoMS during gait-like motion and the brain region related to gait is activated by the motion.

Resonant marker design and fabrication techniques for device visualization during interventional magnetic resonance imaging.

Magnetic resonance imaging (MRI) has great potential as an imaging modality for guiding minimally invasive interventions because of its superior soft tissue contrast and the possibility of arbitrary slice positioning while avoiding ionizing radiation and nephrotoxic iodine contrast agents. The major constraints are: limited patient access, the insufficient assortment of compatible instruments and the difficult device visualization compared to X-ray based techniques. For the latter, resonant MRI markers, fabricated by using the wire-winding technique, have been developed. This fabrication technique serves as a functional model but has no clinical use. Thus, the aim of this study is to illustrate a four-phase design process of resonant markers involving microsystems technologies. The planning phase comprises the definition of requirements and the simulation of electromagnetic performance of the MRI markers. The following technologies were considered for the realization phase: aerosol-deposition process, hot embossing technology and thin film technology. The subsequent evaluation phase involves several test methods regarding electrical and mechanical characterization as well as MRI visibility aspects. The degree of fulfillment of the predefined requirements is determined within the analysis phase. Furthermore, an exemplary evaluation of four realized MRI markers was conducted, focusing on the performance within the MRI environment.

Abstract 12412: Imaging the PM/AICD Patient; Does the Diagnostic Value Justify the Risk?

Background: MR imaging is infrequently performed on patients with implanted pacemakers/AICDs. When the risk justifies the end, however, consideration to perform 'high-risk’ scanning can be made on a case-by-case basis but typically with trepidation. This raises a critically important question: "Is the MRI scan adding valuable and irrefutable information to warrant such risk? Methods: 84 patients with implanted devices (13AICD,10 AICD/PM,5 retained leads, 6 REVO and 50 dual chamber PM.) were imaged via MRI/CMR (1.5T GE, Milwaukee, WI) over 3 years in a single institution. Specific criteria were followed for all patients to objectively define whether final diagnosis by MRI imaging enhanced patient care. A checklist of 3 questions was answered following scan interpretation by both the technologist and performing MRI physician(s): 1) Did the diagnosis change? 2) Did the MRI provide additional information to the existing diagnosis? 3) Did patient management change? If ‘Yes’ was answered to any of the above questions, it was considered that the MRI scan was of value to patient diagnosis and/or therapy. Results: All patients completed the procedure with no death, VT/VF, power-on-reset or adverse events. Average MRI study time: 20±55min. The device was interrogated pre and post MRI by EP/cardiologist to determine changes in impedance, amplitude or threshold. No clinically meaningful changes occurred, no post-procedure revisions to generator/lead or parameters were required. Conclusion: The use of PM/AICD imaging in MRI remains controversial. Our study shows that MR imaging in carefully selected patients under the supervision of experienced physicians is not only safe but extremely beneficial, substantially adding value and often irrefutable information to patient diagnosis and management. PM/AICDs when imaged properly are safe and no longer 'forbidden’ in the MRI environment. Moreover there is frequently marked life-altering and life-saving information obtained.

Simultaneous acquisition of functional magnetic resonance images and impedance cardiography.

While simultaneous acquisition of electrocardiography (ECG) data during MRI is a widely used clinical technique, the effects of the MRI environment on impedance cardiography (ICG) data have not been characterized. We collected echo planar MRI scans while simultaneously recording ECG and thoracic impedance using carbon fiber electrodes and customized amplifiers. Here, we show that the key changes in impedance (dZ/dt) and features of the ECG waveforms are not obstructed during MRI. We present a method for ensemble averaging ICG/ECG signals collected during MRI and show that it performs comparably with signals collected outside the MRI environment. These results indicate that ICG can be used during MRI to measure stroke volume, cardiac output, preejection period, and left ventricular ejection time.

Canadian Heart Rhythm Society and Canadian Association of Radiologists Consensus Statement on Magnetic Resonance Imaging With Cardiac Implantable Electronic Devices

Magnetic resonance imaging (MRI) has historically been considered contraindicated for individuals with cardiac implantable electronic devices (CIEDs) such as pacemakers and implantable defibrillators. Magnetic resonance scanners produce magnetic fields that can interact negatively with the metallic components of CIEDs. However, as CIED technology has advanced, newer MRI conditional devices have been developed that are now in clinical use and these systems have had demonstrated safety in the MRI environment. Despite the supportive data of such CIED systems, physicians remain reluctant to perform MRI scanning of conditional devices. This joint statement by the Canadian Heart Rhythm Society and the Canadian Association of Radiologists describes a collaborative process by which CIED specialists and clinics can work with radiology departments and specialists to safely perform MRI in patients with MRI conditional CIED systems. The steps required for patient and scanning preparation and the roles and responsibilities of the CIED and radiology departments are outlined. We also briefly outline the risks and a process by which patients with nonconditional CIEDs might also receive MRI in highly specialized centres. This document supports MRI in patients with MRI conditional CIEDs and offers recommendations on how this can be implemented safely and effectively.

Closed-chest small animal model to study myocardial infarction in an MRI environment in real time.

Current models for real time study of the effects of myocardial ischemia/reperfusion have major limitations and confounders. Confounders include the surgical stresses of a thoracotomy and abnormal physiology of an open chest. The need to reposition the animal interferes with the study of the early changes associated with ischemia. Direct comparison of pre-ischemia and post-ischemia images is then difficult. We developed a novel "closed chest" model of ischemia/reperfusion to overcome these issues. Following thoracotomy, we sutured a balloon occluder to the left coronary artery of male Sprague-Dawley rats. We used both visual inspection and ECG to assess for successful occlusion and reperfusion of the coronary artery at the time of operation by brief inflation and deflation of the balloon. The tubing was then placed under the skin and the incision closed. Following a recovery period (5-10days), the animals underwent MRI. We performed baseline assessment of left ventricle function, and repeated LV measurement during a 15-min coronary occlusion and again during a 60-min reperfusion period following reopening of the coronary artery. The occluder was successfully placed in 40 of 44 animals. Four developed intraoperative complications; two large myocardial infarction, two terminal bleeding. Six died in the week following surgery, [four sudden deaths (presumed arrhythmic), one anterior infarction, one sepsis]. Cine-MRI demonstrated localised hypokinesia in 31 of the remaining 34 animals. LV ejection fraction (EF) was reduced from 63±7% at baseline, to 49±9% during coronary occlusion. LV EF recovered to 61±2%. The area at risk on staining of the heart was 41.9±15.8%. This method allows the effects of ischemia/reperfusion to be studied before, during, and after coronary occlusion. Ischemia can be caused while the animal is in the MRI. This new and clinically relevant small animal model is a valuable tool to study the effects of single or repeated coronary occlusion/reperfusion in real-time.

Use of a radio frequency shield during 1.5 and 3.0 Tesla magnetic resonance imaging: experimental evaluation.

Radiofrequency (RF) shields have been recently developed for the purpose of shielding portions of the patient’s body during magnetic resonance imaging (MRI) examinations. We present an experimental evaluation of a commercially available RF shield in the MRI environment. All tests were performed on 1.5 T and 3.0 T clinical MRI scanners. The tests were repeated with and without the RF shield present in the bore, for comparison. Effects of the shield, placed within the scanner bore, on the RF fields generated by the scanner were measured directly using tuned pick-up coils. Attenuation, by as much as 35 dB, of RF field power was found inside the RF shield. These results were supported by temperature measurements of metallic leads placed inside the shield, in which no measurable RF heating was found. In addition, there was a small, simultaneous detectable increase (∼1 dB) of RF power just outside the edges of the shield. For these particular scanners, the autocalibrated RF power levels were reduced for scan locations prescribed just outside the edges of the shield, which corresponded with estimations based on the pick-up coil measurements. Additionally, no significant heating during MRI scanning was observed on the shield surface. The impact of the RF shield on the RF fields inside the magnet bore is likely to be dependent on the particular model of the RF shield or the MRI scanner. These results suggest that the RF shield could be a valuable tool for clinical MRI practices.