Interventional MR Research Articles

Selective MR neurography-guided lumbosacral plexus perineural injections: techniques, targets, and territories.

The T12 to S4 spinal nerves form the lumbosacral plexus in the retroperitoneum, providing sensory and motor innervation to the pelvis and lower extremities. The lumbosacral plexus has a wide range of anatomic variations and interchange of fibers between nerve anastomoses. Neuropathies of the lumbosacral plexus cause a broad spectrum of complex pelvic and lower extremity pain syndromes, which can be challenging to diagnose and treat successfully. In their workup, selective nerve blocks are employed to test the hypothesis that a lumbosacral plexus nerve contributes to a suspected pelvic and extremity pain syndrome, whereas therapeutic perineural injections aim to alleviate pain and paresthesia symptoms. While the sciatic and femoral nerves are large in caliber, the iliohypogastric and ilioinguinal, genitofemoral, lateral femoral cutaneous, anterior femoral cutaneous, posterior femoral cutaneous, obturator, and pudendal nerves are small, measuring a few millimeters in diameter and have a wide range of anatomic variants. Due to their minuteness, direct visualization of the smaller lumbosacral plexus branches can be difficult during selective nerve blocks, particularly in deeper pelvic locations or larger patients. In this setting, the high spatial and contrast resolution of interventional MR neurography guidance benefits nerve visualization and targeting, needle placement, and visualization of perineural injectant distribution, providing a highly accurate alternative to more commonly used ultrasonography, fluoroscopy, and computed tomography guidance for perineural injections. This article offers a practical guide for MR neurography-guided lumbosacral plexus perineural injections, including interventional setup, pulse sequence protocols, lumbosacral plexus MR neurography anatomy, anatomic variations, and injection targets.

Interventional cardiac magnetic resonance imaging: current applications, technology readiness level, and future perspectives.

Background:Cardiac magnetic resonance (CMR) provides excellent temporal and spatial resolution, tissue characterization, and flow measurements. This enables major advantages when guiding cardiac invasive procedures compared with X-ray fluoroscopy or ultrasound guidance. However, clinical implementation is limited due to limited availability of technological advancements in magnetic resonance imaging (MRI) compatible equipment. A systematic review of the available literature on past and present applications of interventional MR and its technology readiness level (TRL) was performed, also suggesting future applications.Methods:A structured literature search was performed using PubMed. Search terms were focused on interventional CMR, cardiac catheterization, and other cardiac invasive procedures. All search results were screened for relevance by language, title, and abstract. TRL was adjusted for use in this article, level 1 being in a hypothetical stage and level 9 being widespread clinical translation. The papers were categorized by the type of procedure and the TRL was estimated.Results:Of 466 papers, 117 papers met the inclusion criteria. TRL was most frequently estimated at level 5 meaning only applicable to in vivo animal studies. Diagnostic right heart catheterization and cavotricuspid isthmus ablation had the highest TRL of 8, meaning proven feasibility and efficacy in a series of humans.Conclusion:This article shows that interventional CMR has a potential widespread application although clinical translation is at a modest level with TRL usually at 5. Future development should be directed toward availability of MR-compatible equipment and further improvement of the CMR techniques. This could lead to increased TRL of interventional CMR providing better treatment.

Safety Profile of Infinity Deep Brain Stimulation Electrode Placement in a 1.5T Interventional MRI Suite: Consecutive Single-Institution Case Series.

"Asleep" deep brain stimulation using general anesthesia and intraoperative MR imaging guidance is considered "off-label" use by current FDA guidelines but is widely used in neurosurgical practice, and excellent safety has been demonstrated using first-generation, omnidirectional electrodes. Safety data for second-generation, directional electrodes in the interventional MR imaging environment have not yet been published. Herein, we report 34 cases of asleep deep brain stimulation using second-generation, directional electrodes in an interventional MR imaging suite at a single institution. Procedural complications and imaging data are described. All patients underwent postoperative MR imaging with fully implanted ("internalized") electrodes after scalp closure; 4 patients also underwent MR imaging with "externalized" electrodes before scalp closure. No MR imaging-related complications were observed, and procedural complication rates were comparable to prior series. This suggests that the use of second-generation, directional electrodes in the interventional MR imaging environment appears to be safe when following manufacturer-published imaging guidelines.

Percutaneous MR-guided prostate cancer cryoablation technical updates and literature review.

Prostate cancer (PCa) is the most common malignant tumor in males. The benefits in terms of overall reduction in specific mortality due to the widespread use of Prostate Specific Antigen (PSA) screening and the advancements in the curative treatments (radical prostatectomy or radiotherapy) appear to have reached a plateau. There remains, however, the questions of overdiagnosis and overtreatment of such patients. Currently, the main challenge in the treatment of patients with clinically organ-confined PCa is to offer an oncologically efficient treatment with as little morbidity as possible.Amongst the arising novel curative techniques for PCa, cryoablation (CA) is the most established one, which is also included in the NICE and AUA guidelines. CA is commonly performed under ultrasound guidance with the inherent limitations associated with this technique. The recent advancements in MRI have significantly improved the accuracy of detecting and characterizing a clinically significant PCa. This, alongside the development of wide bore interventional MR scanners, has opened the pathway for in bore PCa treatment. Under MRI guidance, PCa CA can be used either as a standard whole gland treatment or as a tumor targeted one. With MR-fluoroscopy, needle guidance capability, multiplanar and real-time visualization of the iceball, MRI eliminates the inherent limitations of ultrasound guidance and can potentially lead to a lower rate of local complications.The aim of this review article is to provide an overview about PCa CA with a more specific insight on MR guided PCa CA; the limitations, challenges and applications of this novel technique will be discussed.

Functionalization of endovascular devices with superparamagnetic iron oxide nanoparticles for interventional cardiovascular magnetic resonance imaging.

Presently, cardiovascular interventions such as stent deployment and balloon angioplasty are performed under x-ray guidance. However, x-ray fluoroscopy has poor soft tissue contrast and is limited by imaging in a single plane, resulting in imprecise navigation of endovascular instruments. Moreover, x-ray fluoroscopy exposes patients to ionizing radiation and iodinated contrast agents. Magnetic resonance imaging (MRI) is a safe and enabling modality for cardiovascular interventions. Interventional cardiovascular MR (iCMR) is a promising approach that is in stark contrast with x-ray fluoroscopy, offering high-resolution anatomic and physiologic information and imaging in multiple planes for enhanced navigational accuracy of catheter-based devices, all in an environment free of radiation and its deleterious effects. While iCMR has immense potential, its translation into the clinical arena is hindered by the limited availability of MRI-visible catheters, wire guides, angioplasty balloons, and stents. Herein, we aimed to create application-specific, devices suitable for iCMR, and demonstrate the potential of iCMR by performing cardiovascular catheterization procedures using these devices. Tools, including catheters, wire guides, stents, and angioplasty balloons, for endovascular interventions were functionalized with a polymer coating consisting of poly(lactide-co-glycolide) (PLGA) and superparamagnetic iron oxide (SPIO) nanoparticles, followed by endovascular deployment in the pig. Findings from this study highlight the ability to image and properly navigate SPIO-functionalized devices, enabling interventions such as successful stent deployment under MRI guidance. This study demonstrates proof-of-concept for rapid prototyping of iCMR-specific endovascular interventional devices that can take advantage of the capabilities of iCMR.

Real-Time Motor Cortex Mapping for the Safe Resection of Glioma: An Intraoperative Resting-State fMRI Study.

Resting-state functional MR imaging has been used for motor mapping in presurgical planning but never used intraoperatively. This study aimed to investigate the feasibility of applying intraoperative resting-state functional MR imaging for the safe resection of gliomas using real-time motor cortex mapping during an operation. Using interventional MR imaging, we conducted preoperative and intraoperative resting-state intrinsic functional connectivity analyses of the motor cortex in 30 patients with brain tumors. Factors that may influence intraoperative imaging quality, including anesthesia type (general or awake anesthesia) and tumor cavity (filled with normal saline or not), were studied to investigate image quality. Additionally, direct cortical stimulation was used to validate the accuracy of intraoperative resting-state fMRI in mapping the motor cortex. Preoperative and intraoperative resting-state fMRI scans were acquired for all patients. Fourteen patients who successfully completed both sufficient intraoperative resting-state fMRI and direct cortical stimulation were used for further analysis of sensitivity and specificity. Compared with those subjected to direct cortical stimulation, the sensitivity and specificity of intraoperative resting-state fMRI in localizing the motor area were 61.7% and 93.7%, respectively. The image quality of intraoperative resting-state fMRI was better when the tumor cavity was filled with normal saline (P = .049). However, no significant difference between the anesthesia types was observed (P = .102). This study demonstrates the feasibility of using intraoperative resting-state fMRI for real-time localization of functional areas during a neurologic operation. The findings suggest that using intraoperative resting-state fMRI can avoid the risk of intraoperative seizures due to direct cortical stimulation and may provide neurosurgeons with valuable information to facilitate the safe resection of gliomas.

Design of catheter radio frequency coils using coaxial transmission line resonators for interventional neurovascular MR imaging.

It is technically challenging to design compact yet sensitive miniature catheter radio frequency (RF) coils for endovascular interventional MR imaging. In this work, a new design method for catheter RF coils is proposed based on the coaxial transmission line resonator (TLR) technique. Due to its distributed circuit, the TLR catheter coil does not need any lumped capacitors to support its resonance, which simplifies the practical design and construction and provides a straightforward technique for designing miniature catheter-mounted imaging coils that are appropriate for interventional neurovascular procedures. The outer conductor of the TLR serves as an RF shield, which prevents electromagnetic energy loss, and improves coil Q factors. It also minimizes interaction with surrounding tissues and signal losses along the catheter coil. To investigate the technique, a prototype catheter coil was built using the proposed coaxial TLR technique and evaluated with standard RF testing and measurement methods and MR imaging experiments. Numerical simulation was carried out to assess the RF electromagnetic field behavior of the proposed TLR catheter coil and the conventional lumped-element catheter coil. The proposed TLR catheter coil was successfully tuned to 64 MHz for proton imaging at 1.5 T. B1 fields were numerically calculated, showing improved magnetic field intensity of the TLR catheter coil over the conventional lumped-element catheter coil. MR images were acquired from a dedicated vascular phantom using the TLR catheter coil and also the system body coil. The TLR catheter coil is able to provide a significant signal-to-noise ratio (SNR) increase (a factor of 200 to 300) over its imaging volume relative to the body coil. Catheter imaging RF coil design using the proposed coaxial TLR technique is feasible and advantageous in endovascular interventional MR imaging applications.

Hybrid Approach for Biliary Interventions Employing MRI-Guided Bile Duct Puncture with Near-Real-Time Imaging.

To assess the feasibility of a hybrid approach employing MRI-guided bile duct (BD) puncture for subsequent fluoroscopy-guided biliary interventions in patients with non-dilated (≤3mm) or dilated BD (≥3mm) but unfavorable conditions for ultrasonography (US)-guided BD puncture. A total of 23 hybrid interventions were performed in 21 patients. Visualization of BD and puncture needles (PN) in the interventional MR images was rated on a 5-point Likert scale by two radiologists. Technical success, planning time, BD puncture time and positioning adjustments of the PN as well as technical success of the biliary intervention and complication rate were recorded. Visualization even of third-order non-dilated BD and PN was rated excellent by both radiologists with good to excellent interrater agreement. MRI-guided BD puncture was successful in all cases. Planning and BD puncture times were 1:36±2.13 (0:16-11:07) min. and 3:58±2:35 (1:11-9:32) min. Positioning adjustments of the PN was necessary in two patients. Repeated capsular puncture was not necessary in any case. All biliary interventions were completed successfully without major complications. A hybrid approach which employs MRI-guided BD puncture for subsequent fluoroscopy-guided biliary intervention is feasible in clinical routine and yields high technical success in patients with non-dilated BD and/or unfavorable conditions for US-guided puncture. Excellent visualization of BD and PN in near-real-time interventional MRI allows successful cannulation of the BD.

P5. Variation in head and trunk staff exposure to magnetic fields in 1.5T interventional MRI

Purpose Percutaneous procedures, such as thermal ablations or biopsies, are increasingly performed under real-time MRI-guidance. During the interventional MRI procedure, physicians are continuously exposed to electromagnetic fields (EMF) generated by the MRI scanner, during the active MRI-guided insertion as well as during ”passive” times such as higher resolution 3D acquisitions or therapy. The European union has suggested electromagnetic field (EMF) threshold values to not be overtaken. These values require EMF assessment methods, thus, in a previous study, EMF exposition variation between head and trunk have been observed in a 3T clinical MRI. We now want to focus on these variations for interventional MRI staff. Material and method An in house developed MR exposimeter has been designed allowing 3D monitoring of magnetic field, and storage of the information at a 60 Hz sampling rate for a complete working day. Two MR exposimeters were placed simultaneously on the headband of ear defender and the “thoracic pocket” of two interventional MR radiologists at 1.5T. Physicians were monitored during two tumor cryo-ablations that lasted about 3 h each. Magnetic field normalized vector is used to compare MR exposure. Exposure curves and comparative measurements were performed: mean, peak and cumulative (time integration) assessment of magnetic field (B) and time derivative magnetic field (dB/dt). Results Comparison of head and trunk exposures are shown in Table 1. Higher peak exposure is seen for the head (red curves) than for the trunk during active needle insertion, while during wait times higher trunk exposure is measured. Overall, a higher mean of exposure is found for trunk than for head. Conclusion and discussion In this study, as expected and shown in 3T, the head is exposed to greater magnetic field during staff motion in the vicinity of the bore. Indeed during needle introduction, the radiologist bends inside the bore leading to higher head exposure peaks. While during wait times when physician stand next to the bore, their trunk is directly inside magnetic field lines explaining its higher exposition compared to the head. These wait times are specific to the interventional MRI staff compared to clinical MRI staff that directly leaves the room after patient setup. Therefore, global exposure (mean and cumulative values) measured for the trunk is higher in interventional MRI when the opposite tendency was found in 3T clinical staff. These tendencies are expected to vary with physician height and posture. This is why monitoring both head and trunk magnetic field exposures seems better than a unique trunk assessment. Indeed ear defenders wore by staff during interventional MRI appears as an optimal support for head MR exposimeter devices.

Interventional MR elastography for MRI-guided percutaneous procedures.

MRI-guided thermal ablations require reliable monitoring methods to ensure complete destruction of the diseased tissue while avoiding damage to the surrounding healthy tissue. Based on the fact that thermal ablations result in substantial changes in biomechanical properties, interventional MR elastography (MRE) dedicated to the monitoring of MR-guided thermal therapies is proposed here. Interventional MRE consists of a needle MRE driver, a fast and interactive gradient echo pulse sequence with motion encoding, and an inverse problem solver in real-time. This complete protocol was tested in vivo on swine and the ability to monitor elasticity changes in real-time was assessed in phantom. Thanks to a short repetition time, a reduction of the number of phase-offsets and the use of a sliding window, one refreshed elastogram was provided every 2.56 s for an excitation frequency of 100 Hz. In vivo elastograms of swine liver were successfully provided in real-time during one breath-hold. Changes of elasticity were successfully monitored in a phantom during its gelation with the same elastogram frame rate. This study demonstrates the ability of detecting elasticity changes in real-time and providing elastograms in vivo with interventional MRE that could be used for the monitoring of thermal ablations.

10:00 AM, Abstract No. 1 - Endovascular embolization of aneurysms by interventional MR coagulation

10:00 AM, Abstract No. 1 - Endovascular embolization of aneurysms by interventional MR coagulation

Feasibility of intermittent pneumatic compression for venous thromboembolism prophylaxis during magnetic resonance imaging-guided interventions

PurposeVenous thromboembolism (VTE) is a common cause of morbidity and mortality in hospitalized and surgical patients. To reduce risk, perioperative VTE prophylaxis is recommended for cancer patients undergoing surgical or interventional procedures.Magnetic resonance imaging (MRI) is increasingly used in interventional oncology when alternative imaging modalities do not adequately delineate malignancies. Extended periods of immobilization during MRI-guided interventions necessitate an MR compatible sequential compression device (SCD) for intra-procedural mechanical VTE prophylaxis. Such devices are not commercially available. Materials and methodsA standard SCD routinely used at our institution for VTE prophylaxis during interventional procedures was used. To satisfy MR safety requirements, the SCD controller was placed in the MR control room and connected to the compression sleeves in the magnet room through the wave guide using tubing extensions. The controller pressure sensor was used to monitor adequate pressure delivery and detect ineffective low or abnormal high pressure delivery.VTE prophylaxis was provided using the above mentioned device for 38 patients undergoing MR-guided ablations. ResultsThere was no evidence of device failure due to loss of pressure in the extension tubing assembly. No interference with the anesthesia or interventional procedures was documented. ConclusionAlthough the controller of a standard SCD is labeled as “MR-unsafe”, the SCD can be used in interventional MR settings by placing the device outside the MR scanner room. Using serial tubing extensions did not cause device failure. The described method can be used to provide perioperative mechanical VTE prophylaxis for high risk patients undergoing MR-guided procedures.

Validity and reliability of computerized measurement of lumbar intervertebral disc height and volume from magnetic resonance images

Background contextMagnetic resonance (MR) examinations of morphologic characteristics of intervertebral discs (IVDs) have been used extensively for biomechanical studies and clinical investigations of the lumbar spine. Traditionally, the morphologic measurements have been performed using time- and expertise-intensive manual segmentation techniques not well suited for analyses of large-scale studies.. PurposeThe purpose of this study is to introduce and validate a semiautomated method for measuring IVD height and mean sagittal area (and volume) from MR images to determine if it can replace the manual assessment and enable analyses of large MR cohorts. Study design/settingThis study compares semiautomated and manual measurements and assesses their reliability and agreement using data from repeated MR examinations. MethodsSeven healthy asymptomatic males underwent 1.5-T MR examinations of the lumbar spine involving sagittal T2-weighted fast spin-echo images obtained at baseline, pre-exercise, and postexercise conditions. Measures of the mean height and the mean sagittal area of lumbar IVDs (L1–L2 to L4–L5) were compared for two segmentation approaches: a conventional manual method (10–15 minutes to process one IVD) and a specifically developed semiautomated method (requiring only a few mouse clicks to process each subject). ResultsBoth methods showed strong test-retest reproducibility evaluated on baseline and pre-exercise examinations with strong intraclass correlations for the semiautomated and manual methods for mean IVD height (intraclass correlation coefficient [ICC]=0.99, 0.98) and mean IVD area (ICC=0.98, 0.99), respectively. A bias (average deviation) of 0.38 mm (4.1%, 95% confidence interval 0.18–0.59 mm) was observed between the manual and semiautomated methods for the IVD height, whereas there was no statistically significant difference for the mean IVD area (0.1%±3.5%). The semiautomated and manual methods both detected significant exercise-induced changes in IVD height (0.20 and 0.28 mm) and mean IVD area (5.7 and 8.3 mm2), respectively. ConclusionsThe presented semiautomated method provides an alternative to time- and expertise-intensive manual procedures for analysis of larger, cross-sectional, interventional, and longitudinal MR studies for morphometric analyses of lumbar IVDs.

A controllable susceptibility marker for passive device tracking

To design and demonstrate a new susceptibility-based tracking device with an artifact that can be mechanically turned on and off, thus permitting tracking and imaging at the device tip with limited artifact. The magnetic susceptibilities of readily obtainable grades of titanium and graphite were measured. Using numerical optimization, layer thicknesses for three concentric cylinders were found where the field from the graphite layer maximally cancelled the fields from titanium layers. The tracking elements were fabricated for an outer diameter of 3 mm and attached to a catheter to show feasibility of detection in phantoms and in vivo. The device was successfully integrated into a 9F catheter, and its use with conventional guidewires under fluoroscopy was demonstrated by guiding the catheter through the bifurcation into the carotid artery. MR images including the catheter tip were acquired with the device in both the "on" and "off" positions. A new passive tracking device with a susceptibility effect that can be enabled and disabled by sliding one of the components was designed, fabricated, and demonstrated in phantoms and in vivo. The device may also be integrated into many different interventional MR devices such as needles, ultrasound transducers for prostate biopsy, or any catheter-based devices.

Temporomandibular joint injections: interventional MR imaging demonstrates anatomical landmark approach to be inaccurate when compared to direct visualization of the injectant

Sir, We read with interest the article from Dr. Parra and colleagues [1] published online 2010 March 4. The authors are to be congratulated on their efforts in the development of an imaging guidance technique with the intention to reduce the use of ionizing radiation in children [2]. However, the authors’ routine use of CT of the temporomandibular joints following needle placement exposes children to ionizing radiation and makes their technique less desirable than US alone or interventional MRI. Not least for this fact, the authors discuss interventional MRI as a co-existing technique for temporomandibular joint injections in children. We were, however, surprised about the omission of the citation reporting the technique of real-time MRI guidance for intra-articular injections of the temporomandibular joints resulting in an overall technical accuracy of 100%. We, therefore, wish to provide this necessary reference to the readers of Pediatric Radiology [3]. Dr. Parra and colleagues claim to have assessed the accuracy of US-guided injections “into the intra-articular compartment of the TMJ” [1]. This, however, requires visualization of the injectant for documentation of location and distribution of the delivered drug, which was not performed. Instead, successful or failed intra-articular injection was estimated by visualization of the needle tip on CT images obtained following US-guided needle placement by using an anatomical landmark approach. Injections were performed afterward, which leaves the rate of successful intra-articular drug delivery undetermined. This is of importance, because in our experience the landmark approach is inaccurate and results in a paraarticular location of the needle tip in up to 18% of targeted synovial compartments [3]. These published data were obtained by direct visualization of injections, which were performed after imaging verification of the needle tip in seemingly adequate location when using anatomical landmarks. Figure 1 illustrates a typical case. The authors’ data on US-guided injections of the temporomandibular joints provide evidence of the feasibility of needle guidance; however, no data providing conclusive evidence of the accuracy of US-guided injections into the intra-articular compartment of the TMJ were obtained. The authors wish to provide “reassurance of the accuracy” of their US method; however, we respectfully submit that the conclusion that this technique represents an accurate method is speculative and not firmly supported by their data. Electronic supplementary material The online version of this article (doi:10.1007/s00247-010-1836-y) contains supplementary material, which is available to authorized users. J. Fritz (*) : J. S. Lewin Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, 600 N. Wolfe St., Baltimore, MD 21287, USA e-mail: jfritz9@jhmi.edu

Subthalamic nucleus deep brain stimulator placement using high-field interventional magnetic resonance imaging and a skull-mounted aiming device: technique and application accuracy

The authors discuss their method for placement of deep brain stimulation (DBS) electrodes using interventional MR (iMR) imaging and report on the accuracy of the technique, its initial clinical efficacy, and associated complications in a consecutive series of subthalamic nucleus (STN) DBS implants to treat Parkinson disease (PD). A skull-mounted aiming device (Medtronic NexFrame) was used in conjunction with real-time MR imaging (Philips Intera 1.5T). Preoperative imaging, DBS implantation, and postimplantation MR imaging were integrated into a single procedure performed with the patient in a state of general anesthesia. Accuracy of implantation was assessed using 2 types of measurements: the "radial error," defined as the scalar distance between the location of the intended target and the actual location of the guidance sheath in the axial plane 4 mm inferior to the commissures, and the "tip error," defined as the vector distance between the expected anterior commissure-posterior commissure (AC-PC) coordinates of the permanent DBS lead tip and the actual AC-PC coordinates of the lead tip. Clinical outcome was assessed using the Unified Parkinson's Disease Rating Scale part III (UPDRS III), in the off-medication state. Twenty-nine patients with PD underwent iMR imaging-guided placement of 53 DBS electrodes into the STN. The mean (+/- SD) radial error was 1.2 +/- 0.65 mm, and the mean absolute tip error was 2.2 +/- 0.92 mm. The tip error was significantly smaller than for STN DBS electrodes implanted using traditional frame-based stereotaxy (3.1 +/- 1.41 mm). Eighty-seven percent of leads were placed with a single brain penetration. No hematomas were visible on MR images. Two device infections occurred early in the series. In bilaterally implanted patients, the mean improvement on the UPDRS III at 9 months postimplantation was 60%. The authors' technical approach to placement of DBS electrodes adapts the procedure to a standard configuration 1.5-T diagnostic MR imaging scanner in a radiology suite. This method simplifies DBS implantation by eliminating the use of the traditional stereotactic frame and the subsequent requirement for registration of the brain in stereotactic space and the need for physiological recording and patient cooperation. This method has improved accuracy compared with that of anatomical guidance using standard frame-based stereotaxy in conjunction with preoperative MR imaging.

Interventional cardiovascular MR—The next stage in pediatric cardiology

Real-time magnetic resonance imaging is attractive to guide minimally invasive treatment of structural heart disease not only because it can spare radiation but also because soft tissue imaging may add value. Interventional cardiovascular magnetic resonance imaging will allow simple as well as novel non-surgical treatments of structural heart disease in children. Real-time MRI tools already are available. Catheter tools are emerging. A handful of pediatrics hospitals are installing investigational systems now to explore this promising technology.

Whole shaft visibility and mechanical performance for active MR catheters using copper-nitinol braided polymer tubes.

BackgroundCatheter visualization and tracking remains a challenge in interventional MR.Active guidewires can be made conspicuous in "profile" along their whole shaft exploiting metallic core wire and hypotube components that are intrinsic to their mechanical performance. Polymer-based catheters, on the other hand, offer no conductive medium to carry radio frequency waves. We developed a new "active" catheter design for interventional MR with mechanical performance resembling braided X-ray devices. Our 75 cm long hybrid catheter shaft incorporates a wire lattice in a polymer matrix, and contains three distal loop coils in a flexible and torquable 7Fr device. We explored the impact of braid material designs on radiofrequency and mechanical performance.ResultsThe incorporation of copper wire into in a superelastic nitinol braided loopless antenna allowed good visualization of the whole shaft (70 cm) in vitro and in vivo in swine during real-time MR with 1.5 T scanner. Additional distal tip coils enhanced tip visibility. Increasing the copper:nitinol ratio in braiding configurations improved flexibility at the expense of torquability. We found a 16-wire braid of 1:1 copper:nitinol to have the optimum balance of mechanical (trackability, flexibility, torquability) and antenna (signal attenuation) properties. With this configuration, the temperature increase remained less than 2°C during real-time MR within 10 cm horizontal from the isocenter. The design was conspicuous in vitro and in vivo.ConclusionWe have engineered a new loopless antenna configuration that imparts interventional MR catheters with satisfactory mechanical and imaging characteristics. This compact loopless antenna design can be generalized to visualize the whole shaft of any general-purpose polymer catheter to perform safe interventional procedures.

Further Insight into the Technique and Outcomes of “Curative” Catheter Ablation of Atrial Fibrillation

During the past decade, catheter ablation of atrial fibrillation (AF) has emerged as an important treatment option for patients with symptomatic AF refractory to ≥1 antiarrhythmic agents. Electric isolation of the pulmonary vein musculature (PVI) has been identified as the primary end point for both catheter- and surgical-based AF ablation procedures.1 What is less clear is whether the addition of “linear lesions” or ablation of atrial sites demonstrating complex atrial electrograms improves outcome for patients with paroxysmal, persistent, or long-standing persistent AF.2,3 This issue remains an area of active discussion, debate, and investigation. Article see p 269 In this issue of Circulation: Arrhythmia and Electrophysiology , Gaita et al2 report the results of a prospective single-center randomized study of 204 patients who underwent catheter ablation for treatment of paroxysmal or persistent/permanent AF. Patients were stratified according to whether they had paroxysmal (n=125) or persistent/permanent (n=79) AF and were then randomized in a 2:1 fashion to undergo PVI alone or PVI combined with a “roof line” and a “left mitral line.” Follow-up visits that included an ECG, 24-hour Holter, and an echocardiogram were set up at 1, 3, 6, 12, 18, 24, and 30 months and then every year thereafter. If a patient experienced symptoms between follow-up visits, an event monitor was prescribed. A recurrence was defined as a symptomatic or asymptomatic episode of AF or atrial flutter lasting ≥30 seconds after a 2-month blanking period. Patients who developed a recurrence after the blanking period were offered a repeat ablation procedure. The outcome of ablation was evaluated at 12 months of follow-up and at completion of the study. Each patient was followed for a minimum of 3 years. Among the 125 patients with paroxysmal AF, the single-procedure success rate at 12 months was 46% with PVI alone versus …

2097 Automated tracking of a passive intramyocardial needle with off-resonance mri: a feasibility study

Direct intramyocardial therapies aimed at treating myocardial regions affected by severe ischemia may benefit from CMR-guided interventional procedures. Although interventional MR approaches using active devices are considered to be the method of choice, potential tissue heating and altered mechanical properties are some of their limitations. Methods that have the capacity to visualize MR-compatible passive devices may overcome many of these obstacles. Recently, an off-resonance-based real-time positive contrast method (FLAPS) was used to visualize the passage of an intramyocardial needle (PIN) through the aorta and into the heart of swine [1,2]. We envision this procedure may benefit from computer assisted strategies that track the needle's location throughout the MR procedure. However, the feasibility of real-time automated tracking of a PIN has not been established.