MR Environment Research Articles

Research on Information Fusion Method for Human Computer Interaction Interface of Command and Control System in MR Environment

In response to the challenge of high cognitive pressure and difficulty for commanders in cross-layer operations during the transition from traditional two-dimensional command and control system interfaces to mixed reality human-computer interaction interfaces, this paper conducts research on the information fusion display method for the human-computer interaction interface of the mixed reality command and control system. First, based on the findings of previous research, we developed a five-layer human-computer interaction interface for a mixed reality command and control system in typical combat scenarios. An evaluation experiment was designed and the resulting data analyzed. This analysis revealed that there are problems with low work efficiency and high cognitive load in the information acquisition process in cross-layer interaction operations. Consequently, we conducted research into the methods of integrating and displaying interactive interface information, integrating and displaying interactive and display interface information, and integrating and displaying complex situation interface information. The research findings indicate that: (1) The optimal display ratio for mixed reality 2D interface integration is 3:2. (2) The optimal display scheme for mixed reality 2D interface fusion is a combination of the main and secondary interfaces, with the main interface table displaying global information and the secondary interface displaying accurate information. (3) The optimal display scheme for mixed reality 2D and 3D interface fusion is the display of overall class information in 2D and the accurate identification of class information in 3D. The findings of this research can be applied to the design of human-computer interaction interfaces for mixed reality command and control systems in complex battlefield environments.

MRgFUS ablation of a recurrent tenosynovial giant cell tumor in the foot using ExAblate 2100 system in combination with patient immobilization device

IntroductionMagnetic Resonance–guided Focused Ultrasound (MRgFUS) treatment for certain anatomy locations can be extremely challenging due to patient positioning and potential motion. This present study describes the treatment of a recurrent tenosynovial giant cell tumor of the plantar forefoot using the ExAblate 2100 system in combination with patient immobilization device. MethodsPrior to the treatment, several patient immobilization devices were investigated. Vacuum cushions were selected and tested for safety and compatibility with the treatment task and the MR environment. ResultsDuring the treatment, one vacuum cushion immobilized the patient's right leg in knee flexion and allowed the bottom of the foot to be securely positioned on the treatment window. Another vacuum cushion supported the patient upper body extended outside the scanner bore. 19 sonications were successfully executed. The treatment was judged to be successful. No immediate complications were observed. ConclusionsMRgFUS treatment of a recurrent tenosynovial giant cell tumor of the right plantar forefoot was successful with the use of patient immobilization vacuum cushions. Implications for practiceThe immobilization system could be utilized to aid future MRgFUS treatment of lesions in challenging anatomic locations. Various sizes of the vacuum cushions are available to potentially better accommodate other body parts and treatment configurations.

Design and Analysis of an MRI-Compatible Soft Needle Manipulator

Needle manipulation with the guidance of magnetic resonance imaging (MRI) plays a key role in minimally invasive procedures such as biopsy and ablation. However, the confined bore and strong magnetic field of the MR environment pose great challenges in developing a robotic system that fulfills the needle manipulation function. This paper presents the design and analysis of a soft needle manipulator (SoNIM) that can achieve needle manipulation in the MR environment. This pneumatically actuated manipulator consists of two bending actuators and one elongation actuator that are completely made of non-magnetic materials. These soft pneumatic actuators can generate flexible movements while maintaining a compact design, ensuring that the SoNIM is accommodated within the MRI bore. The kinematic modeling and closed-loop control of the SoNIM are investigated to achieve the position control of the needle tip. Experiments showed that the SoNIM was capable of directing the needle tip to reach the targets with a satisfactory accuracy of 2.9 ± 0.98 mm. Furthermore, the functionality and MRI compatibility of the SoNIM were validated in the clinical setting, demonstrating the capability of the SoNIM to perform needle manipulation in the MRI bore with negligible degradation to the image quality. With excellent MRI compatibility, compact design, and flexible movements, the SoNIM provides a promising solution for manipulating surgical needles in MRI-guided minimally invasive surgeries.

Comparison of triple quantum (TQ) TPPI and inversion recovery TQ TPPI pulse sequences at 9.4 and 21.1 T.

Both sodium T1 triple quantum (TQ) signal and T1 relaxation pathways have a unique sensitivity to the sodium molecular environment. In this study an inversion recovery time proportional phase increment (IRTQTPPI) pulse sequence was investigated for simultaneous and reliable quantification of sodium TQ signal and bi-exponential T1 relaxation times. The IRTQTPPI sequence combines inversion recovery TQ filtering and time proportional phase increment. The reliable and reproducible results were achieved by the pulse sequence optimized in three ways: (1) optimization of the nonlinear fit for the determination of both T1-TQ signal and T1 relaxation times; (2) suppression of unwanted signals by assessment of four different phase cycles; (3) nonlinear sampling during evolution time for optimal scan time without any compromises in fit accuracy. The relaxation times T1 and T2 and the TQ signals from IRTQTPPI and TQTPPI were compared between 9.4 and 21.1 T. The motional environment of the sodium nuclei was evaluated by calculation of correlation times and nuclear quadrupole interaction strengths. Reliable measurements of the T1-TQ signals and T1 bi-exponential relaxation times were demonstrated. The fit parameters for all four phase cycles were in good agreement with one another, with a negligible influence of unwanted signals. The agar samples yielded normalized T1-TQ signals from 3% to 16% relative to single quantum (SQ) signals at magnetic fields of both 9.4 and 21.1 T. In comparison, the normalized T2-TQ signal was in the range 15%-35%. The TQ/SQ signal ratio was decreased at 21.1 T as compared with 9.4 T for both T1 and T2 relaxation pathways. The bi-exponential T1 relaxation time separation ranged from 15 to 18 ms at 9.4 T and 15 to 21 ms at 21.1 T. The T2 relaxation time separation was larger, ranging from 28 to 35 ms at 9.4 T and 37 to 40 ms at 21.1 T. The IRTQTPPI sequence, while providing a less intensive TQ signal than TQTPPI, allows a simultaneous and reliable quantification of both the T1-TQ signal and T1 relaxation times. The unique sensitivities of the T1 and T2 relaxation pathways to different types of molecular motion provide a deeper understanding of the sodium MR environment.

A novel pneumatic drill for bone biopsy under MRI imaging.

Bone biopsies are currently conducted under computed tomography (CT) guidance using a battery-powered drill to obtain tissue samples for diagnosis of suspicious bone lesions. However, this procedure is suboptimal as images produced under CT lack soft tissue discrimination and involve ionizing radiation. Therefore, our team developed an MRI-safe pneumatic drill to translate this clinical workflow into the MR environment, which can improve target visualization and eliminate radiation exposure. We compare drill times and quality of samples between the 2 drills using animal bones. Five porcine spare rib bones were obtained from a butcher shop. Each bone was drilled twice using the Arrow OnControl battery-powered drill and twice using our pneumatically actuated drill. For this study, we used an 11-gauge bone biopsy needle set with an internal core capturing thread. A stopwatch recorded the overall time of drilling for each specimen obtained. All 20 samples collected contained a high-quality inner core and cortex. The total average time for drilling with the pneumatic drill was 8.5s (+ / - 2.5s) and 7.1s (+ / - 1.4s) with the standard battery-powered drill. Both drills worked well and were able to obtain comparable specimens. The pneumatic drill took slightly longer, 1.39s on average, but this extra time would not be significant in clinical practice. We plan to use the pneumatic drill to enable MRI-safe bone biopsy for musculoskeletal lesions. Biopsy under MRI would provide excellent lesion visualization with no ionizing radiation.

Developing a novel quasi-3D movable water phantom for radiation therapy workable in the magnetic resonance environment.

The use of magnetic resonance linear accelerators (MR-LINACs) for clinical treatment has opened up new possibilities and challenges in the field of radiation oncology. However, annual quality assurance (QA) is relatively understudied due to practical considerations. Thus, to overcome the difficulty of measuring the dose with a small water phantom for TRS-398 or TG-51 in all external beam radiation treatment unit environments, such as MR compatibility, we designed a remote phantom with a three-axis changeable capacity for QA. The designed water phantom was tested under an MR environment. The water phantom system comprised of three parts: a phantom box, a dose measurement tool, and a PMD401 drive system. The UNIDOSE universal dosimeter was used to collect beam data. The manufacturer's developer tools were utilized to position the measurement. To ensure magnetic field homogeneity, a distortion phantom was prepared using sixty fish oil capsules aligned radially to distinguish the oil and free air. The phantom was scanned in both the MR simulator and computed tomography (CT), and the acquired images were analyzed to determine the position shift. The dimensions of the device are 30 cm in the X-axis, 20 cm in the Y-axis, and 17 cm in the Z-axis. Total cost of materials was no more than $10,000 US dollars. Our results indicate that the device can function normally in a regular 1.5 T MR environment without interference from the magnetic field. The water phantom's traveling speed was found to be approximately 5 mm/s with a position difference confined within 6 cm intervals during normal use. The distortion test results showed that the prepared MR environment has uniform magnetic field homogeneity. In this study, we constructed a prototype water phantom device that can function in an MR simulator without interference between the magnetic field and electronic components. Compared to other commercially available MR-LINAC water phantoms, our device offers a more cost-effective solution for routine monthly QA. It can shorten the duration of QA tests and relieve the burden on medical physicists.

Managing Patients With Unlabeled Passive Implants on MR Systems Operating Below 1.5 T.

The standard of care for managing a patient with an implant is to identify the item and to assess the relative safety of scanning the patient. Because the 1.5 T MR system is the most prevalent scanner in the world and 3 T is the highest field strength in widespread use, implants typically have "MR Conditional" (i.e., an item with demonstrated safety in the MR environment within defined conditions) labeling at 1.5 and/or 3 T only. This presents challenges for a facility that has a scanner operating at a field strength below 1.5 T when encountering a patient with an implant, because scanning the patient is considered "off-label." In this case, the supervising physician is responsible for deciding whether to scan the patient based on the risks associated with the implant and the benefit of magnetic resonance imaging (MRI). For a passive implant, the MRI safety-related concerns are static magnetic field interactions (i.e., force and torque) and radiofrequency (RF) field-induced heating. The worldwide utilization of scanners operating below 1.5 T combined with the increasing incidence of patients with implants that need MRI creates circumstances that include patients potentially being subjected to unsafe imaging conditions or being denied access to MRI because physicians often lack the knowledge to perform an assessment of risk vs. benefit. Thus, physicians must have a complete understanding of the MRI-related safety issues that impact passive implants when managing patients with these products on scanners operating below 1.5 T. This monograph provides an overview of the various clinical MR systems operating below 1.5 T and discusses the MRI-related factors that influence safety for passive implants. Suggestions are provided for the management of patients with passive implants labeled MR Conditional at 1.5 and/or 3 T, referred to scanners operating below 1.5 T. The purpose of this information is to empower supervising physicians with the essential knowledge to perform MRI exams confidently and safely in patients with passive implants. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 3.

Rapid prediction of MRI-induced RF heating of active implantable medical devices using machine learning.

The interaction between an active implantable medical device and magnetic resonance imaging (MRI) radiofrequency (RF) fields can cause excessive tissue heating. Existing methods for predicting RF heating in the presence of an implant rely on either extensive phantom experiments or electromagnetic (EM) simulations with varying degrees of approximation of the MR environment, the patient, or the implant. On the contrary, fast MR thermometry techniques can provide a reliable real-time map of temperature rise in the tissue in the vicinity of conductive implants. In this proof-of-concept study, we examined whether a machine learning (ML) based model could predict the temperature increase in the tissue near the tip of an implanted lead after several minutes of RF exposure based on only a few seconds of experimentally measured temperature values. We performed phantom experiments with a commercial deep brain stimulation (DBS) system to train a fully connected feedforward neural network (NN) to predict temperature rise after ~3 minutes of scanning at a 3 T scanner using only data from the first 5 seconds. The NN effectively predicted ΔTmax-R2 = 0.99 for predictions in the test dataset. Our model also showed potential in predicting RF heating for other various scenarios, including a DBS system at a different field strength (1.5 T MRI, R2 = 0.87), different field polarization (1.2 T vertical MRI, R2 = 0.79), and an unseen implant (cardiac leads at 1.5 T MRI, R2 = 0.91). Our results indicate great potential for the application of ML in combination with fast MR thermometry techniques for rapid prediction of RF heating for implants in various MR environments.Clinical Relevance- Machine learning-based algorithms can potentially enable rapid prediction of MRI-induced RF heating in the presence of unknown AIMDs in various MR environments.

Intelligent Avatars, Holographic Tools, Digitized Objects: An Extended Reality Simulation Demonstration

How can we design engaging and effective medical education both online and on site? Extended reality (XR) is a term referring to all real-and-virtual combined environments and human-machine interactions generated by computer technology and wearables. It includes representative forms such as AR, VR, and MR, and the areas interpolated among them. MR is a domain of particular interest today: It takes place not only in the physical world or in the virtual world, but is a mix of the real and the virtual. Metaverses can be enabled by MR wearable augments. Glasses-free MR is another very interesting dimension: e-REALâ, as a MR environment for hybrid simulation and medical education in general, can be a stand-alone solution or even networked between multiple places through a link to a special videoconferencing system. Digital humans and human-sized holograms are part of the e-REAL scenarios, making this solution unique, rich, and diversified.

Abstract P3-04-07: Safety and artifact testing of a nitinol breast biopsy clip in an ultra-high resolution magnetic resonance imaging (MRI) environment

Abstract Background: The lack of safety clearance of several metallic breast implants in 7T(Tesla) poses a significant hurdle to standard clinical breast cancer care and research from reaping the benefits of ultra-high resolution MR imaging. A breast biopsy clip (Ultracor Twirl, Becton, Dickinson and Company, Vernon Hills, IL) composed of nitinol, was tested for safety and artifact susceptibility clearance in a 7T MRI scanner, using standardized procedures. This clearance is significant in henceforth allowing patients with this implant to be scanned in now FDA approved ultra-high-field MRI scanners of 7T or less for clinical and research purposes. Methods: Tests for magnetic susceptibility (torque and translational attraction), MRI-related heating, and artifacts were conducted as per standardized protocols. The torque and translational attraction tests evaluated the effects of magnetic force by the MRI to cause the clip to move and twist respectively. The heating test was conducted with customized MR parameters of short TR (repetition time) and maximum echo-train length, designed to induce temperature change. The artifact test using T1 weighted spin and gradient echo imaging sequences, evaluated potential localized signal loss that may result in misrepresentation of the imaged area. This may occur due to the presence of the metallic clip in the MR environment. Results: The torque and translational attraction tests respectively indicated that the MR environment did not induce any movement in the clip in eight orientations, with a deflection angle of 0 degrees. Results of the heating test indicated no significant temperature change of the clip. A temperature change of less than 0.45C° was observed in the phantom gel in both the absence and presence of the clip, which is well within the safety threshold (< 1°C). Results of the artifact test indicated a very small artifact, with the largest artifact cross-sectional area appearing on gradient echo images. Conclusion: These cumulative results indicate that the Ultracor Twirl breast biopsy clip is safe for imaging patients at 7T. Citation Format: William Dong, Kanchna Ramchandran, Adam Galloy, Marco A. Nino, Marla Kleingartner, Madhavan L. Raghavan, Sneha Phadke, Vincent A. Magnotta. Safety and artifact testing of a nitinol breast biopsy clip in an ultra-high resolution magnetic resonance imaging (MRI) environment [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-04-07.

ACPSEM position paper: the safety of magnetic resonance imaging linear accelerators

Magnetic Resonance Imaging linear-accelerator (MRI-linac) equipment has recently been introduced to multiple centres in Australia and New Zealand. MRI equipment creates hazards for staff, patients and others in the MR environment; these hazards must be well understood, and risks managed by a system of environmental controls, written procedures and a trained workforce. While MRI-linac hazards are similar to the diagnostic paradigm, the equipment, workforce and environment are sufficiently different that additional safety guidance is warranted. In 2019 the Australasian College of Physical Scientists and Engineers in Medicine (ACPSEM) formed the Magnetic Resonance Imaging Linear-Accelerator Working Group (MRILWG) to support the safe clinical introduction and optimal use of MR-guided radiation therapy treatment units. This Position Paper is intended to provide safety guidance and education for Medical Physicists and others planning for and working with MRI-linac technology. This document summarises MRI-linac hazards and describes particular effects which arise from the combination of strong magnetic fields with an external radiation treatment beam. This document also provides guidance on safety governance and training, and recommends a system of hazard management tailored to the MRI-linac environment, ancillary equipment, and workforce.

The Introduction of an MR-Conditional Prototype for Cardiopulmonary Bypass Support: Technical Aspects and System Requirements

Introduction: The use of cardiopulmonary bypass (CBP; also known as a heart-lung machine) in newborns with complex congenital heart defects may result in brain damage. Magnetic resonance imaging (MRI) assessments cannot be performed safely because the metal components used to construct CBP devices may elicit adverse effects on patients when they are placed in a magnetic field. Thus, this project aimed to develop a prototype MR-conditional circulatory support system that could be used to perform cerebral perfusion studies in animal models. Methods: The circulatory support device includes a roller pump with two rollers. The ferromagnetic and most of the metal components of the roller pump were modified or replaced, and the drive was exchanged by an air-pressure motor. All materials used to develop the prototype device were tested in the magnetic field according to the American Society for Testing and Materials (ASTM) Standard F2503-13. The technical performance parameters, including runtime/durability as well as achievable speed and pulsation behavior, were evaluated and compared to standard requirements. The behavior of the prototype device was compared with a commercially available pump. Results: The MRI-conditional pump system produced no image artifacts and could be safely operated in the presence of the magnetic field. The system exhibited minor performance-related differences when compared to a standard CPB pump; feature testing revealed that the prototype meets the requirements (i.e., operability, controllability, and flow range) needed to proceed with the planned animal studies. Conclusion: This MR-conditional prototype is suitable to perform an open-heart surgery in an animal model to assess brain perfusion in an MR environment.

Mixed Reality in Vascular Surgery - a Scoping Review

"Mixed reality" (MR) allows the projection of virtual objects into the user's field of view through a head-mounted display (HMD). In the interventional and surgical treatment of vascular diseases MR applications could be of future benefit. The following scoping review aims to provide orientation on the current application of the aforementioned technologies in the field of vascular surgery and to define research goals for the future. A systematic literature search was performed in PubMed (MEDLINE) using the search terms "aorta", "intervention", "endovascular intervention", "vascular surgery", "aneurysm", "endovascular", "vascular access", each in combination with "mixed reality" or "augmented reality". The search was performed according to PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) guidelines for scoping reviews. From 547 references 8 relevant studies were identified. The search results could be classified into two categories: (1) MR aimed at information management and improving periprocedural ergonomics (n=3) and (2) MR aimed at intraoperative navigation (n=5). The registration of the physical patient with the virtual object and the tracking of instruments in the MR environment for intraoperative navigation is currently the focus of scientific interest and could be demonstrated on phantom and animal models with technical success. However, the methods presented so far are associated with high infrastructural costs and important limitations. The use of MR in the field of vascular surgery is promising. For the future, alternative, pragmatic registration methods with appropriate quantification of the positional error should be aimed at. The developed software and hardware solutions should be adapted to the requirements of vascular surgery. Electromagnetic instrument tracking appears to be a useful complementary technology for the implementation of MR-assisted navigation.

Estimation of discomfort by deep learning focusing on sickness-sensitive in MR environment

Estimation of discomfort by deep learning focusing on sickness-sensitive in MR environment

3D-printed gear system for antenna motion in an MR environment: initial phantom imaging experiments.

We have developed a microwave imaging device for breast cancer imaging that can be used concurrently inside an MR imaging system. The microwave measurement system is comprised of a horizontal array of 16 monopole antennas that can be moved vertically for full 3D coverage of the breast. All compatibility issues have been addressed. The motion is achieved using a novel 3D printed gearing device. Initial results demonstrate that the system is capable of accurately recovering the size, shape, location and properties of a 3D shape varying object. This is a critical step towards clinical microwave breast imaging in the MR.

An integrated navigation system based on a dedicated breast support device for MRI-guided breast biopsy.

Breast cancer is currently the cancer type with the highest incidence in the world, and it is extremely harmful to women's health. MRI-guided breast biopsy is a common method in clinical examination of breast cancer. However, traditional breast biopsy is less accurate and takes a long time. In this study, an integrated navigation system (INS) based on a dedicated breast support device (DBSD) was proposed to assist doctors in biopsy. The grid-shaped DBSD can reduce the displacement and deformation of the breast during the biopsy operation and is convenient for puncture. The robot system based on the DBSD is designed to assist doctors in performing puncture action. The software system has functions such as registration, path planning, and real-time tracking of biopsy needles based on the DBSD, which can assist doctors in completing the entire biopsy procedure. A series of experiments are designed to verify the feasibility and accuracy of the system. Experiments prove that the robot system has reasonable structure and meets the requirements of MR compatibility. The latency of the INS during intraoperative navigation is 0.30 ± 0.03s. In the phantom puncture experiment, the puncture error under the navigation of the INS is 1.04 ± 0.15mm. The INS proposed in this paper can be applied to assist doctors in breast biopsy in MR environment, improve the accuracy of biopsy and shorten the time of biopsy. The experimental results show that the system is feasible and accurate.

Respirators and Surgical Masks Artefacts on Phantom using Magnetic Resonance Imaging during COVID-19: A Cross-sectional Study

Introduction: It is suitable for a patient to wear a respirator or face mask during any radiological investigation during Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) pandemic. Some face masks may have nanoparticles, or antimicrobial coating, which may comprise metal to help shape the mask according to user face shape. This kind of ferromagnetic substances can cause artefacts in the image. Aim: To detect and compare the artefacts while using different types of respirators and surgical masks in the Magnetic Resonance Imaging (MRI) phantom images. Materials and Methods: This was a prospective cross-sectional study which was conducted from July 2021-September 2021. Two Not resistant to oil-based aerosols with 95% efficiency to airborne particles (N95) respirators and two types of three-ply surgical disposable masks with a metal and plastic nose holder were used. The N95 respirators were of Halo N95 Filtering Facepiece 2 Particulate Matter (FFP2) PM 2.5 and Suchi N95 S-7400, while the surgical masks were from Venus 3 ply V-1010 with a metal nose holder and the Thea Tex Filtra 3 ply with plastic nose holder. A polymethyl methacrylate plastic phantom was used with 1.5 Tesla (Siemens Magnetom Avanto) MRI scanner for imaging. Results: When exposed to the metal detector both N95 respirators and one of the surgical masks with a metal nose clip showed strong ferromagnetic attraction. Both respirators and a surgical mask with a metal nasal holder showed magnetic susceptibility artefacts. The signal loss is caused by dephasing of spins from metal strip on the image. Conclusion: All the patients must have a recognised MR safe masks prior to an MRI investigation. When this is not possible to follow, metallic components from the face mask should be removed before the patient's arrival at the MR room. After removing the metal strip from the mask, the paper tape may be applied across the nasal bridge region for adequate transmission control and to maintain the intended function of the mask. The mask with a plastic nasal holder was ideal to use in an MR environment since it doesn’t have any distortion in the image.

Experimental Validation of the MRcollar: An MR Compatible Applicator for Deep Heating in the Head and Neck Region.

Simple SummaryHyperthermia treatments where tumor tissue is heated to 40–44 °C for 60–90 min can be hampered by a lack of accurate temperature monitoring. To solve this need, we have designed an MR compatible head and neck hyperthermia applicator: the MRcollar. In this work, we experimentally validated the design, heating capabilities and the MR compatibility of the MRcollar. The MRcollar antennas efficiently transfer the power and have low interaction between the antenna elements. The heating and focusing capabilities satisfy the requirements. The MRcollar can operate in an MR scanner and it can acquire higher quality MR images due to the built in receiver elements. The MRcollar has great potential to improve hyperthermia treatment in the head and neck region and it is now ready for in vivo studies.Clinical effectiveness of hyperthermia treatments, in which tumor tissue is artificially heated to 40–44 °C for 60–90 min, can be hampered by a lack of accurate temperature monitoring. The need for noninvasive temperature monitoring in the head and neck region (H&N) and the potential of MR thermometry prompt us to design an MR compatible hyperthermia applicator: the MRcollar. In this work, we validate the design, numerical model, and MR performance of the MRcollar. The MRcollar antennas have low reflection coefficients (<−15 dB) and the intended low interaction between the individual antenna modules (<−32 dB). A 10 °C increase in 3 min was reached in a muscle-equivalent phantom, such that the specifications from the European Society for Hyperthermic Oncology were easily reached. The MRcollar had a minimal effect on MR image quality and a five-fold improvement in SNR was achieved using the integrated coils of the MRcollar, compared to the body coil. The feasibility of using the MRcollar in an MR environment was shown by a synchronous heating experiment. The match between the predicted SAR and measured SAR using MR thermometry satisfied the gamma criteria [distance-to-agreement = 5 mm, dose-difference = 7%]. All experiments combined show that the MRcollar delivers on the needs for MR—hyperthermia in the H&N and is ready for in vivo investigation.

Development and evaluation of a numerical simulation approach to predict metal artifacts from passive implants in MRI

ObjectiveThis study presents the development and evaluation of a numerical approach to simulate artifacts of metallic implants in an MR environment that can be applied to improve the testing procedure for MR image artifacts in medical implants according to ASTM F2119.MethodsThe numerical approach is validated by comparing simulations and measurements of two metallic test objects made of titanium and stainless steel at three different field strengths (1.5T, 3T and 7T). The difference in artifact size and shape between the simulated and measured artifacts were evaluated. A trend analysis of the artifact sizes in relation to the field strength was performed.ResultsThe numerical simulation approach shows high similarity (between 75% and 84%) of simulated and measured artifact sizes of metallic implants. Simulated and measured artifact sizes in relation to the field strength resulted in a calculation guideline to determine and predict the artifact size at one field strength (e.g., 3T or 7T) based on a measurement that was obtained at another field strength only (e.g. 1.5T).ConclusionThis work presents a novel tool to improve the MR image artifact testing procedure of passive medical implants. With the help of this tool detailed artifact investigations can be performed, which would otherwise only be possible with substantial measurement effort on different MRI systems and field strengths.

B-PO04-108 FIRST IN CLINICAL ROUTINE ISTHMUS-DEPENDENT ATRIAL FLUTTER ABLATION ENTIRELY PERFORMED IN THE INTERVENTIONAL MRI SUITE USING ACTIVE CATHETER IMAGING

Recently, magnetic resonance imaging (MRI) has been established as a radiation-free alternative to fluoroscopy to image anatomy and structural alterations causative for arrhythmogenesis during cavotricuspid isthmus (CTI) dependent atrial flutter (AFl) ablation procedures. Describe the first real-world experience of CTI ablations performed completely in the interventional cardiac magnetic resonance (iCMR) suite using active catheter imaging. Fifteen patients (73% male, median age 70 yrs (IQR 67-82) underwent ablations in the iCMR suite. Procedures were performed in a 1.5T MRI with MR-conditional ablation catheters. Catheter guidance was performed using active catheter imaging leveraging MR receive coils within the catheter tip [Figure]. Ablation success, complications, and time for procedure were collected. All 15 patients achieved acute procedure success without complication. Median procedure time was 43min (IQR 33-58) with an RF delivery time of 18 min (interquartile range (IQR) 12-26). Post-procedure lesion visualization scanning was 32 min (IQR 10-42). In 5 patients left ventricular ejection fraction improved from 28±7 % to 47±6% after ablation. Of the13 patients that made it to 6 month follow up (1 lost to follow up, 1 death at 6 months), none of the patients had AFl recurrence. CTI-dependent AFl ablation using active catheter imaging can successfully be performed entirely in the iCMR suite. The MR environment allows anatomic visualization of the CTI, intra-procedural lesion visualization, and exclusion of a pericardial effusion.