Browsing by Subject "Interventional MRI"

Now showing 1 - 12 of 12

Open Access
Endoluminal coils for interventional MRI procedures
(2010) Viskuşenko, V. Nikolay
In this study we designed endoluminal magnetic resonance imaging (MRI) coils to be used for interventional procedures under the guidance of MRI. The first coil we developed is a two-channel endocervical coil for the treatment of cervical cancer. The coil was embedded into the brachytherapy applicator without interfering with its functions. It provides magnetic resonance (MR) images of the cervix with high signal-to-noise ratio (SNR) that is required for a more accurate radiation dose calculation in the treatment of cervical cancer with high dose rate brachytherapy (HDRB). The performance of this coil was tested with phantom experiments and the results proved that the design worked properly. Second, we developed an MRI guidewire and an MR EP catheter for the treatment of atrial fibrillation (AF). The MRI guidewire had similar mechanical properties with the common cardiovascular guidewires and it was proved successful in obtaining high SNR images of the heart. The MR EP catheter could also provide high SNR images as well as clean intracardiac electrocardiogram (IECG) signal during the MR scan. Due to the loopless antenna embedded inside both of these catheters, they could be navigated in the body under the MRI. They may be used to guide complex interventional procedures such as RF ablation. The performance of these catheters was tested and confirmed with in vitro experiments. To sum up, these two technologies can play a significant role in the treatment of cervical cancer and AF as well as contributing to the development of interventional MRI.
Open Access
Imitation of radiofrequency ablation with fiber delivered laser system for magnetic resonance guided treatment of atrial fibrillation
(2010) Kerse, M. Can
Atrial Fibrillation (AF) is among the most common cardiac arrhythmias with a high risk of mortality and morbidity. As a cure several minimally invasive catheter approaches are performed under imaging guidance. These treatments imitate linear and transmural cuts and sutures along the atrial walls similar to the widely accepted surgical Cox Maze procedure to block undesired currents. Catheter delivery of RF energy to the cardiac chamber is widely used and approved as safe and successful. The operation is commonly performed under X-Ray which is deprived of soft tissue contrast. Besides, combination of the image with ECG (electrocardiogram) data makes the operation technically difficult and time consuming. Due to the long exposure times, X-Ray burns may be seen on the patient. MR images can be taken during RF ablation with proper matching and tuning circuits, however, during the operation RF and ECG catheters may cause artifacts in the image for some orientations. On the other hand, fiber delivery of laser energy has no significant MR compatibility issues and can be used under MR guidance. Nevertheless, MR guided laser ablation is not in clinical practice as a minimally invasive technique for curing AF possibly because of the risk of perforating the myocardial wall. Excess light intensity at the end of the fiber tip causes rapid changes in the temperature gradients which may cause charring. This is an undesired effect and especially in cardiac ablations, light intensity should be diffused. There are several diffusing tip designs to emit light in cylindrical symmetry, but, due to their orientation with respect to the cardiac chamber, common RF delivery methods cannot be applied directly. In this thesis, we propose a novel multiple fiber laser energy delivery with catheter approach and a system that imitates the scars created with RF probes under MR guidance. The system closely imitates the ablation pattern of RF delivery and therefore is expected to have quick adaptation by physicians. As a proof of principle, we used 3 fibers oriented in different directions and obtained real time MR thermometry maps of the ex-vivo and in-vitro ablation zones during laser delivery. In addition, various light diffusion methods are considered for single fiber power delivery. We believe the combination of these methods will be the solution for the MR compatible RF laser ablation system.
Open Access
Interventional MRI: tapering improves the distal sensitivity of the loopless antenna
(Wiley, 2010) Qian, D.; El-Sharkawy, A. M. M.; Atalar, Ergin; Bottomley, P. A.
The "loopless antenna" is an interventional MRI detector consisting of a tuned coaxial cable and an extended inner conductor or "whip". A limitation is the poor sensitivity afforded at, and immediately proximal to, its distal end, which is exacerbated by the extended whip length when the whip is uniformly insulated. It is shown here that tapered insulation dramatically improves the distal sensitivity of the loopless antenna by pushing the current sensitivity toward the tip. The absolute signal-to-noise ratio is numerically computed by the electromagnetic method-of-moments for three resonant 3-T antennae with no insulation, uniform insulation, and with linearly tapered insulation. The analysis shows that tapered insulation provides an ∼400% increase in signal-to-noise ratio in trans-axial planes 1 cm from the tip and a 16-fold increase in the sensitive area as compared to an equivalent, uniformly insulated antenna. These findings are directly confirmed by phantom experiments and by MRI of an aorta specimen. The results demonstrate that numerical electromagnetic signal-tonoise ratio analysis can accurately predict the loopless detector's signal-to-noise ratio and play a central role in optimizing its design. The manifold improvement in distal signal-to-noise ratio afforded by redistributing the insulation should improve the loopless antenna's utility for interventional MRI.
Open Access
Magnetic resonance imaging–guided coronary interventions
(John Wiley & Sons, 2004) Tsekos, N. V.; Ergin, A.; Li, D.; Omary, R. A.; Serfaty, J.-M.; Woodard, P. K.
Magnetic resonance imaging (MRI) guidance for coronary interventions offers potential advantages over conventional x‐ray angiography. Advantages include the use of nonionizing radiation, combined assessment of anatomy and function, and three‐dimensional assessment of the coronary arteries leading to the myocardium. These advantages have prompted a series of recent studies in this field. Real‐time coronary MR angiography, with low‐dose catheter‐directed intraarterial (IA) infusion of contrast media, has achieved in‐plane spatial resolution as low as 0.8 × 0.8 mm2 and temporal resolution as short as 130 msec per image. Catheter‐based IA injection of contrast agent has proven useful in the collection of multislice and three‐dimensional images, not only for coronary intervention guidance, but also in the assessment of regional myocardial perfusion fed by the affected vessel. Actively visible guidewires and guiding catheters, based on the loopless antenna concept, have been effectively used to negotiate tortuous coronary vessels during catheterization, permitting placement of coronary angioplasty balloon catheters. Passive tracking approaches have been used to image contrast agent–filled coronary catheters and to place susceptibility‐based endovascular stents. Although the field is in its infancy, these early results demonstrate the feasibility for performing MRI‐guided coronary interventions. Although further methodological and technical developments are required before these methods become clinically applicable, we anticipate that MRI someday will be included in the armamentarium of techniques used to diagnose and treat coronary artery disease.
Open Access
Measuring local RF heating in MRI: Simulating perfusion in a perfusionless phantom
(John Wiley & Sons, Inc., 2007) Akca, I. B.; Ferhanoglu, O.; Yeung, C. J.; Guney, S.; Tasci, T. O.; Atalar, Ergin
Purpose: To overcome conflicting methods of local RF heating measurements by proposing a simple technique for predicting in vivo temperature rise by using a gel phantom experiment. Materials and Methods: In vivo temperature measurements are difficult to conduct reproducibly; fluid phantoms introduce convection, and gel phantom lacks perfusion. In the proposed method the local temperature rise is measured in a gel phantom at a timepoint that the phantom temperature would be equal to the perfused body steady-state temperature value. The idea comes from the fact that the steady-state temperature rise in a perfused body is smaller than the steady-state temperature increase in a perfusionless phantom. Therefore, when measuring the temperature on a phantom there will be the timepoint that corresponds to the perfusion time constant of the body part. Results: The proposed method was tested with several phantom and in vivo experiments. Instead, an overall average of 30.8% error can be given as the amount of underestimation with the proposed method. This error is within the variability of in vivo experiments (45%). Conclusion: With the aid of this reliable temperature rise prediction the amount of power delivered by the scanner can be controlled, enabling safe MRI examinations of patients with implants. © 2007 Wiley-Liss, Inc.
Open Access
MR safety watchdog for active catheters: wireless impedance control with real‐time feedback
(Wiley, 2020) Özen, A. Ç.; Silemek, Berk; Lottne, T.; Atalar, Ergin; Bock, M.
Purpose: To dynamically minimize radiofrequency (RF)‐induced heating of an active catheter through an automatic change of the termination impedance. Methods: A prototype wireless module was designed that modifies the input impedance of an active catheter to keep the temperature rise during MRI below a threshold, ΔTmax. The wireless module (MR safety watchdog; MRsWD) measures the local temperature at the catheter tip using either a built‐in thermistor or external data from a fiber‐optical thermometer. It automatically changes the catheter input impedance until the temperature rise during MRI is minimized. If ΔTmax is exceeded, RF transmission is blocked by a feedback system. Results: The thermistor and fiber‐optical thermometer provided consistent temperature data in a phantom experiment. During MRI, the MRsWD was able to reduce the maximum temperature rise by 25% when operated in real‐time feedback mode. Conclusion: This study demonstrates the technical feasibility of an MRsWD as an alternative or complementary approach to reduce RF‐induced heating of active interventional devices. The automatic MRsWD can reduce heating using direct temperature measurements at the tip of the catheter. Given that temperature measurements are intrinsically slow, for a clinical implementation, a faster feedback parameter would be required such as the RF currents along the catheter or scattered electric fields at the tip.
Open Access
MR-trackable intramyocardial injection catheter
(John Wiley & Sons, 2004) Karmarkar, P. V.; Kraitchman, D. L.; Izbudak, I.; Hofmann, L. V.; Amado, L. C.; Fritzges, D.; Young, R.; Pittenger, M.; Bulte, J. W. M.; Atalar, Ergin
There is growing interest in delivering cellular agents to infarcted myocardium to prevent postinfarction left ventricular remodeling. MRI can be effectively used to differentiate infarcted from healthy myocardium. MR-guided delivery of cellular agents/therapeutics is appealing because the therapeutics can be precisely targeted to the desired location within the infarct. In this study, a steerable intramyocardial injection catheter that can be actively tracked under MRI was developed and tested. The components of the catheter were arranged to form a loopless RF antenna receiver coil that enabled active tracking. Feasibility studies were performed in canine and porcine myocardial infarction models. Myocardial delayed-enhancement (MDE) imaging identified the infarcted myocardium, and real-time MRI was used to guide left ventricular catheterization from a carotid artery approach. The distal 35 cm of the catheter was seen under MRI with a bright signal at the distal tip of the catheter. The catheter was steered into position, the distal tip was apposed against the infarct, the needle was advanced, and a bolus of MR contrast agent and tissue marker dye was injected intramyocardially, as confirmed by imaging and post-mortem histology. A pilot study involving intramyocardial delivery of magnetically labeled stem cells demonstrated the utility of the active injection catheter system.
Open Access
Reverse polarized inductive coupling to transmit and receive radiofrequency coil arrays
(Wiley, 2011-06-07) Celik, H.; Atalar, Ergin
In this study, the reverse polarization method is implemented using transmit and receive arrays to improve the visibility of the interventional devices. Linearly polarized signal sources-inductively and receptively coupled radiofrequency coils-are used in the experimental setups to demonstrate the ability of the method to separate these sources from a forward polarized anatomy signal. Two different applications of the reverse polarization method are presented here: (a) catheter tracking and (b) fiducial marker visualization, in both of which transmit and receive arrays are used. The performance of the reverse polarization method was further tested with phantom and volunteer studies, and the results proved the feasibility of this method with transmit and receive arrays.
Open Access
RF heating of deep brain stimulation implants in open-bore vertical MRI systems: a simulation study with realistic device configurations
(International Society for Magnetic Resonance in Medicine, 2020) Golestanirad, L.; Kazemivalipour, Ehsan; Lampman, D.; Habara, H.; Atalar, Ergin; Rosenow, J.; Pilitsis, J.; Kirsch, J.
Purpose Patients with deep brain stimulation (DBS) implants benefit highly from MRI, however, access to MRI is restricted for these patients because of safety hazards associated with RF heating of the implant. To date, all MRI studies on RF heating of medical implants have been performed in horizontal closed‐bore systems. Vertical MRI scanners have a fundamentally different distribution of electric and magnetic fields and are now available at 1.2T, capable of high‐resolution structural and functional MRI. This work presents the first simulation study of RF heating of DBS implants in high‐field vertical scanners. Methods We performed finite element electromagnetic simulations to calculate specific absorption rate (SAR) at tips of DBS leads during MRI in a commercially available 1.2T vertical coil compared to a 1.5T horizontal scanner. Both isolated leads and fully implanted systems were included. Results We found 10‐ to 30‐fold reduction in SAR implication at tips of isolated DBS leads, and up to 19‐fold SAR reduction at tips of leads in fully implanted systems in vertical coils compared to horizontal birdcage coils. Conclusions If confirmed in larger patient cohorts and verified experimentally, this result can open the door to plethora of structural and functional MRI applications to guide, interpret, and advance DBS therapy.
Open Access
Safety of metallic implants in magnetic resonance imaging
(2005) Ferhanoğlu, Onur
Magnetic Resonance Imaging (MRI) is safe only if we take safety precautions. In the presence of a metallic implant inside the body, three types of magnetic fields encountered in MRI (Static magnetic field, radiofrequency field, gradient field) may become the sources of safety problems. In this thesis, temperature increase created by a pacemaker under MRI is investigated. Electromagnetic simulations are performed, in-vivo, phantom experiments are conducted and finally bioheat equation is solved to find the corresponding temperature increase. Using this temperature increase the input power can be limited to ensure safe scans. MRI compatible lead design is the essential innovation of this thesis which is directly applicable to any kind of metallic, wire shaped interventional MRI device.
Open Access
System for prostate brachytherapy and biopsy in a standard 1.5 T MRI scanner
(John Wiley & Sons, 2004) Susil, R.C.; Camphausen, K.; Choyke, P.; McVeigh, E. R.; Gustafson, G. S.; Ning, H.; Miller, R. W.; Atalar, Ergin; Coleman, C. N.; Ménard, C.
A technique for transperineal high-dose-rate (HDR) prostate brachytherapy and needle biopsy in a standard 1.5 T MRI scanner is demonstrated. In each of eight procedures (in four patients with intermediate to high risk localized prostate cancer), four MRI-guided transperineal prostate biopsies were obtained followed by placement of 14-15 hollow transperineal catheters for HDR brachytherapy. Mean needle-placement accuracy was 2.1 mm, 95% of needle-placement errors were less than 4.0 mm, and the maximum needle-placement error was 4.4 mm. In addition to guiding the placement of biopsy needles and brachytherapy catheters, MR images were also used for brachytherapy treatment planning and optimization. Because 1.5 T MR images are directly acquired during the interventional procedure, dependence on deformable registration is reduced and online image quality is maximized.
Open Access
Tracking planar orientations of active MRI needles
(John Wiley & Sons, Inc., 2007) Sathyanarayana, S.; Aksit P.; Arepally, A.; Karmarkar, P. V.; Solaiyappan, M.; Atalar, Ergin
Purpose: To determine and track the planar orientation of active interventional devices without using localizing RF microcoils. Materials and Methods: An image-based tracking method that determines a device's orientation using projection images was developed. An automated and a manual detection scheme were implemented. The method was demonstrated in an in vivo mesocaval puncture procedure in swine, which required accurate orientation of an active transvascular needle catheter. Results: The plane of the catheter was determined using two projection images. The scan plane was adjusted automatically to follow the catheter plane, and its orientation with respect to a previously acquired target plane was displayed. The algorithm facilitated navigation for a fast and accurate puncture. Conclusion: Using image-based techniques, with no mechanical design changes, the orientation of an active intravascular probe could be tracked.