Validation of injection parameters for catheter-directed intraarterial gadolinium-enhanced MR angiography

RATIONALE AND OBJECTIVES: Catheter-directed intraarterial (IA) injections of gadolinium contrast agents may be used during endovascular interventions with magnetic resonance (MR) imaging guidance. Injection protocols require further validation. Using a flow phantom and swine, the authors aimed to (a) measure the optimal arterial gadolinium concentration ([Gd]) required for MR angiography and (b) validate a proposed IA injection protocol for gadolinium-enhanced MR angiography. MATERIALS AND METHODS: For in vitro experiments, the authors placed a catheter in the aorta of an aorto-renal-iliac flow phantom. Injected [Gd], injection rates, and aortic blood flow rates were varied independently for 36 separate IA gadolinium injections. The authors performed 2D and 3D MR angiography with a fast spoiled gradient-recalled echo sequence. For subsequent in vivo experiments, they selectively placed catheters within the aorta, renal artery, or common iliac artery of three pigs. Injection rate and injected [Gd] were varied. The authors performed 32 separate IA gadolinium injections for 2D MR angiography. Signal-to-noise ratios (SNRs) were compared for the various combinations of injection rate and injected [Gd]. RESULTS: In vitro, an arterial [Gd] of 2%-4% produced an optimal SNR for 2D MR angiography, and 3%-5% was best for 3D MR angiography. In swine, an arterial [Gd] of 1%-4% produced an optimal SNR. In the phantom and swine experiments, SNR was maintained at higher injection rates by inversely varying the injected [Gd]. CONCLUSION: Dilute arterial [Gd] is required for optimal IA gadolinium-enhanced MR angiography. To maintain an optimal SNR, injection rates and injected [Gd] should be varied inversely. The postulated injection protocol was validated.     

MR-guided intravascular catheter manipulation: feasibility of both active and passive tracking in experimental study and initial clinical applications

PURPOSE: To evaluate clinically the feasibility and usefulness of MR-guided intravascular procedures with either active or passive tracking. METHODS: With an active MR tacking system and a 0.2 Tesla open MR imager, real-time and biplane displays of positions of a receive-only coil at the tip of catheters were obtained. For passive tracking, 4 Fr catheters with suitable susceptibility for passive tracking were used. Passive tracking with a 1.5 Tesla MR imager could be performed with parameters of TR 15-50 msec, TE 2.2-2.7 msec, and FA 30 degrees. The temperature of each tracking catheter was monitored in vitro. Clinical trials were performed on six patients (three each). The catheter was introduced to the superior mesenteric artery (SMA) under MR guidance by active or passive tracking to perform MR imaging during arterial portography. RESULTS: The temperature increased minimally. In humans, the SMA and celiac artery could be easily introduced on active tracking. MR-guided manipulation of catheters by active or passive tracking in the model and in dogs' vessels was very successful. Introduction of the catheter into the SMA was successful in two cases of active tracking and in all cases of passive tracking. CONCLUSION: The MR-guided intravascular manipulation of catheters by active or passive tracking may be a clinically feasible method.     

Catheter tracking and visualization using 19F nuclear magnetic resonance.

This work presents an investigation into catheter visualization and localization using 19F nuclear magnetic resonance (NMR) in conjunction with proton imaging. For this purpose, the imaging capabilities of a standard system were extended to allow for 19F excitation and signal detection. Two modes of operation were implemented: 1) a real-time tracking mode that provides tip tracking and automatic slice position updates interleaved with real-time, interactive proton imaging; and 2) a non-real-time catheter length visualization mode in which the entire length of a catheter can be assessed. Initial phantom experiments were conducted with the use of an angiographic balloon catheter filled with the blood substitute perfluorooctylbromide (PFOB). Using limited bandwidth excitation centered at the resonances of the CF2 groups of PFOB, we found that sufficient signal could be received to facilitate tip tracking during catheter motion and length visualization for various catheter configurations. The present approach is considered a promising alternative to existing methods, which either are associated with safety concerns (if active markers are employed) or suffer from insufficient, direction-dependent contrast (if passive visualization is used). Furthermore, our approach enables visualization of the entire length of the catheter. The proposed method provides a safe technique that, unlike electrical or optical devices, does not require modification of commercially available catheters.     

Feasibility of MR imaging-guided percutaneous drainage of pancreatic fluid collections

PURPOSE: To assess the feasibility and safety of magnetic resonance (MR) imaging-guided percutaneous drainage of pancreatic fluid collections in an open configuration low field MR imaging system. MATERIALS AND METHODS: Ten patients with pancreatic fluid collections were examined prospectively. Five of the fluid collections were symptomatic pseudocysts and five were pancreatic abscesses. All percutaneous drainages were performed solely under MR imaging guidance with a 0.23-T open configuration C-arm shaped MR imaging scanner with interventional optical tracking. Every step of the procedure was monitored using balanced fast field echo sequences. In each case, the drainage of the fluid collection was performed with a MR imaging-compatible drainage kit using the Seldinger technique. The kit included an 18-gauge needle, a 0.035-inch stiff guide wire, 6-F and 8-F dilators, and an 8-F pigtail drainage catheter. RESULTS: All drainage catheters could successfully be placed into the pancreatic fluid collections under MR imaging guidance. Visualization of the needle, dilator, and drainage catheter was excellent. However, visualization of the guide wire was suboptimal. The mean time needed for the MR-guided drainage procedure was 44 minutes. No immediate complications occurred. The clinical success rate of the percutaneous drainage was 70%; three patients were subsequently treated surgically. There were no deaths. The average duration of catheterization was 40 days. CONCLUSION: MR imaging-guided percutaneous drainage of pancreatic fluid collections is feasible and safe. The presented technique has limitations--lack of real-time imaging control and small selection of MR imaging-compatible devices--that necessitate further technical developments before the procedure can be recommended for routine clinical use.     

Interventional MR angiography with a floating table

A floating table was integrated into a setup for performance of interventional magnetic resonance (MR) angiography procedures with actively visualized catheters and biplanar real-time image fusion. The setup was evaluated by performing catheterizations in eight pigs. The floating table enabled the authors to follow actively visualized instruments in the pigs' vasculature during MR imaging-guided interventional angiography procedures while performing real-time biplanar MR imaging. Interventional MR angiography with a floating table enables the field of view to be moved along with the instrument tip to the region of interest and thus enhances the usability and flexibility of the interventional MR imaging setup.     

A polymer-based MR-compatible guidewire: a study to explore new prospects for interventional peripheral magnetic resonance angiography (ipMRA)

PURPOSE: To introduce a newly developed polymer-based and magnetic resonance (MR)-compatible guidewire and to explore its capabilities with respect to interventional peripheral magnetic resonance angiography (ipMRA) in a flow phantom. MATERIALS AND METHODS: The guidewire is based on a polyetheretherketone (PEEK) polymer core, and small iron particles are embedded in its coating. A passive device tracking technique was designed utilizing a susceptibility artifact induced by the wire in images acquired with a balanced steady-state free precession (b-SSFP) sequence using small flip angles. The position of the guidewire tip was determined from image intensity maxima and overlayed onto a roadmap in near real-time. Guidewire tracking and balloon angioplasty of an artificial stenosis were attempted in two configurations of a flow phantom. RESULTS: Successful passive guidewire tracking was performed for all phantom configurations. Robustness and accuracy of the tracking technique were sufficient for phantom studies. A balloon catheter was placed into the stenosis using the guidewire under complete MR guidance, and subsequent balloon angioplasty yielded improved flow conditions. CONCLUSION: The new guidewire is well-suited for clinical application due to an absence of the risk of core fracture and its atraumatic flexible tip. It opens novel prospects for the realization of ipMRA in humans that need to be explored in further studies.     

Navigation with electromagnetic tracking for interventional radiology procedures: a feasibility study

PURPOSE: To assess the feasibility of the use of preprocedural imaging for guide wire, catheter, and needle navigation with electromagnetic tracking in phantom and animal models. MATERIALS AND METHODS: An image-guided intervention software system was developed based on open-source software components. Catheters, needles, and guide wires were constructed with small position and orientation sensors in the tips. A tetrahedral-shaped weak electromagnetic field generator was placed in proximity to an abdominal vascular phantom or three pigs on the angiography table. Preprocedural computed tomographic (CT) images of the phantom or pig were loaded into custom-developed tracking, registration, navigation, and rendering software. Devices were manipulated within the phantom or pig with guidance from the previously acquired CT scan and simultaneous real-time angiography. Navigation within positron emission tomography (PET) and magnetic resonance (MR) volumetric datasets was also performed. External and endovascular fiducials were used for registration in the phantom, and registration error and tracking error were estimated. RESULTS: The CT scan position of the devices within phantoms and pigs was accurately determined during angiography and biopsy procedures, with manageable error for some applications. Preprocedural CT depicted the anatomy in the region of the devices with real-time position updating and minimal registration error and tracking error (<5 mm). PET can also be used with this system to guide percutaneous biopsies to the most metabolically active region of a tumor. CONCLUSIONS: Previously acquired CT, MR, or PET data can be accurately codisplayed during procedures with reconstructed imaging based on the position and orientation of catheters, guide wires, or needles. Multimodality interventions are feasible by allowing the real-time updated display of previously acquired functional or morphologic imaging during angiography, biopsy, and ablation.     

Interactive MR imaging and tracking of catheters with multiple tuned fiducial markers

PURPOSE: The lack of magnetic resonance (MR) safe catheters and guide wires remains an important obstacle to widespread clinical use of MR-guided endovascular procedures. The authors looked at the feasibility of using multiple tuned fiducial markers (TFM) and novel imaging sequences to track catheters reliably under MR and to evaluate the safety of such markers in terms of heating. MATERIALS AND METHODS: The visualization and tracking of a catheter with six quadrature tuned fiducial coils was carried out in a special designed in-vitro setup within a 1.5-T MR imager simulating an MR-guided endovascular intervention. The fiducial markers were also tested for heating. RESULTS: The excellent signal contrast between the fiducial and the background when using novel interleaved real time and interactive sequences allowed for rapid and reliable identification of the fiducial markers and therefore the catheter. No significant heating of the marker was noted. CONCLUSIONS: The authors have shown that catheters with multiple tuned fiducial markers are superior to passive catheter designs in terms of visualization and do not carry the risk of heating that is commonly associated with active catheters.     

SPIO与Gd-DTPA联合增强检测大鼠肝癌病灶的实验研究

目的 :观察联合使用SPIO和Gd DTPA对大鼠肝癌模型的增强特点。材料和方法 :制作 3 0只大鼠肝癌模型 ,增强前后行MR扫描 ,平扫序列包括SE、TSE、GRE的T1、T2WI序列。增强扫描分为 4组 ,其中Gd +SPIO联合增强组 10只 ,先注射Gd DTPA ,行SE、GRET1WI扫描 ,随后给予SPIO造影剂 ,扫描序列同平扫 ;SPIO +Gd联合增强组 10只 ,先注射SPIO ,行SE、GRET1WI扫描 ,12min后再给予Gd DTPA ,扫描序列同平扫 ;Gd、SPIO增强组各为 5只 ,增强扫描序列同平扫。分析各增强扫描组中病灶的增强特点。结果 :两种联合增强方法中 ,肝脏信号强度在所有扫描序列中均较平扫时下降 ,但与SPIO增强组无差异 ;病灶的SNR、CNR在SE、GRET1WI中明显高于平扫和SPIO、Gd DTPA增强法 ;在T2WI中病灶的SNR、CNR和单独使用SPIO无显著性差异。两种联合增强方法之间的SNR和CNR在每种扫描序列中没有显著性差异。结论 :SPIO和Gd DTPA联合增强方法利用了两种造影剂的优势 ,增加了肿瘤病变的对比 ,可提高发现病变的几率。     

Determination of optimal gadolinium concentration using SSFP for catheter-directed contrast-enhanced coronary MR angiography

RATIONALE AND OBJECTIVES: To determine the optimal gadolinium concentration for catheter-directed coronary magnetic resonance angiography (MRA) using magnetization-prepared steady-state free-precession (SSFP) in swine. MATERIALS AND METHODS: In six pigs, we performed real-time MR imaging-guided coronary artery catheterization using a 1.5 T MR scanner. For catheter-directed coronary MRA, we injected 3-4 mL of dilute Gd at 1 mL/second for each tested concentration (4%, 8%, 10%, and 12% Gd). Eleven images per concentration were acquired using electrocardiographic-triggered, magnetization-prepared two-dimensional (2D) projection SSFP. We compared mean relative signal-to-noise ratio (SNR) values for each concentration using two-way analysis of variance. RESULTS: The targeted coronary artery was catheterized under real-time MR guidance in all pigs. Magnetization-prepared 2D projection SSFP successfully depicted the coronary arteries in all 44 injections. Mean relative SNR (+/- standard error) was 7.2 +/- 0.49 for 4%, 8.8 +/- 0.47 for 8%, 9.5 +/- 0.38 for 10%, and 8.8 +/- 0.41 for 12%. Injections of 4% dilute gadolinium yielded significantly less relative SNR than the other tested concentrations (P < .05). There were no statistically significant differences between the remaining concentrations. CONCLUSION: For catheter-directed contrast-enhanced coronary MRA, the ideal gadolinium concentration should maximize relative SNR and limit the total gadolinium dose. Using these criteria, of those concentrations we tested in the swine model, 8% injected gadolinium was superior for catheter-directed SSFP coronary MRA.     

Dynamic coronary MR angiography and first-pass perfusion with intracoronary administration of contrast agent

PURPOSE: To evaluate whether dynamic imaging of the coronary arteries can be performed with intracoronary infusion of low-dose gadolinium (Gd)-based contrast agent and assess the effect of long duration and multiple infusions on the image signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). MATERIALS AND METHODS: Dynamic coronary magnetic resonance (MR) imaging (130 msec/image) and contrast agent first pass myocardial perfusion studies were performed with intracoronary infusions of low-dose Gd-based MR contrast agent on dogs (N = 4) using a fast multislice gradient recalled echo (GRE) sequence. RESULTS: Contrast-enhanced coronary arteries were clearly imaged during infusion periods as long as 2.3 minutes. The SNR and CNR of the contrast-enhanced coronary arteries remained essentially unchanged over multiple consecutive angiographic sessions. In addition, we demonstrated that first pass studies performed with intracoronary injection of MR contrast agent can be used as a means of assessing regional myocardial perfusion. CONCLUSION: These studies demonstrated that, using intracoronary infusion of Gd, coronary magnetic resonance angiography (MRA) can be performed with high temporal resolution, and multiple low-dose slow infusions of Gd-based MR contrast agent can be performed without compromise of the vessel SNR and CNR.     

Transfemoral catheterization of carotid arteries with real-time MR imaging guidance in pigs

All procedures and protocols were approved by the institutional animal care and use committee of Columbia University. To determine whether transfemoral catheterization of the carotid arteries can be performed entirely with real-time magnetic resonance (MR) imaging guidance, the authors catheterized the carotid arteries in six domestic pigs by using active-tracking catheters and guidewires and MR tracking software created for neurovascular procedures. The carotid arteries were successfully catheterized 24 times, on average within 5 minutes after insertion of the catheter into the femoral artery. Results demonstrated the feasibility of performing transfemoral catheterization of the carotid arteries with active MR tracking devices in a conventional MR imaging unit.     

Intraarterial gadolinium-enhanced 2D and 3D MR angiography: a preliminary study

PURPOSE: To evaluate, in phantom and canine models, intraarterial gadolinium-enhanced two-dimensional (2D) and three-dimensional (3D) magnetic resonance angiography (MRA). MATERIALS AND METHODS: The in vitro experiments examined gadodiamide solutions ranging in gadolinium (Gd) concentration from 0.1% to 100%. A spoiled gradient-recalled echo (SPGR) sequence was used with various repetition time/echo time (TR/TE) parameters. Signal was measured to determine which concentration yielded the highest signal. For in vivo experiments, pigtail catheters were placed in the abdominal aortae of two dogs. Intraarterial injections of 20-30 mL of 0.5%-25% Gd solutions were performed. We acquired images with use of 2D and 3D SPGR techniques. Depiction of the abdominal aortae and renal vessels was assessed qualitatively and quantitatively. RESULTS: Phantom experiments demonstrated that a 2%-6% solution of Gd produced the highest MR signal, depending on the imaging parameters. In the canine model, a 2% Gd solution was best for 2D techniques, whereas 7%-14% Gd solutions were optimal for 3D techniques. CONCLUSIONS: Intraarterial contrast material-enhanced 2D and 3D MRA can be successfully implemented with use of dilute Gd. Dilution permits the administration of more intraarterial injections per day, without exceeding the dose limit, compared with intravenous Gd-enhanced MRA. Intraarterial injections also limit scan synchronization and contrast material dispersion issues. This technique may have application in MR-guided endovascular procedures.     

Toward true 3D visualization of active catheters using compressed sensing

A crucial requirement in MR‐guided interventions is the visualization of catheter devices in real time. However, true 3D visualization of the full length of catheters has hitherto been impossible given scan time constraints. Compressed sensing (CS) has recently been proposed as a method to accelerate MR imaging of sparse objects. Images acquired with active interventional devices exhibit a high CNR and are inherently sparse, therefore rendering CS ideally suited for accelerating data acquisition. A framework for true visualization of active catheters in 3D is proposed employing CS to gain high undersampling factors making real‐time applications feasible. Constraints are introduced taking into account prior knowledge of catheter geometry and catheter motion over time to improve and accelerate image reconstruction. The potential of the method is demonstrated using computer simulations and phantom experiments and in vivo feasibility is demonstrated in a pig experiment. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Magnetic Catheter Manipulation in the Interventional MR Imaging Environment

PurposeTo evaluate deflection capability of a prototype endovascular catheter, which is remotely magnetically steerable, for use in the interventional magnetic resonance (MR) imaging environment.Materials and MethodsCopper coils were mounted on the tips of commercially available 2.3–3.0-F microcatheters. The coils were fabricated in a novel manner by plasma vapor deposition of a copper layer followed by laser lithography of the layer into coils. Orthogonal helical (ie, solenoid) and saddle-shaped (ie, Helmholtz) coils were mounted on a single catheter tip. Microcatheters were tested in water bath phantoms in a 1.5-T clinical MR scanner, with variable simultaneous currents applied to the coils. Catheter tip deflection was imaged in the axial plane by using a “real-time” steady-state free precession MR imaging sequence. Degree of deflection and catheter tip orientation were measured for each current application.ResultsThe catheter tip was clearly visible in the longitudinal and axial planes. Magnetic field artifacts were visible when the orthogonal coils at the catheter tip were energized. Variable amounts of current applied to a single coil demonstrated consistent catheter deflection in all water bath experiments. Changing current polarity reversed the observed direction of deflection, whereas current applied to two different coils resulted in deflection represented by the composite vector of individual coil activations. Microcatheter navigation through the vascular phantom was successful through control of applied current to one or more coils.ConclusionsControlled catheter deflection is possible with laser lithographed multiaxis coil-tipped catheters in the MR imaging environment.     

MR imaging-guided stent placement in iliac arterial stenoses: a feasibility study

PURPOSE: To assess the feasibility of magnetic resonance (MR) imaging-guided stent placement in iliac arterial stenoses. MATERIALS AND METHODS: Thirteen patients with 14 iliac arterial stenoses were examined prospectively. Angioplasty was performed through a femoral sheath by using a conventional 1.5-T MR imaging system. Stents and catheters were visualized on the basis of their artifacts. Nitinol stents were placed with gradient-echo MR imaging guidance. Angioplasty balloons were inflated with gadolinium-based contrast material. Results were evaluated clinically and with both digital subtraction angiography (DSA) and contrast material-enhanced MR angiography. RESULTS: Ten of 13 patients were treated with technical success by using MR imaging-guided intervention alone. Three patients were treated with additional fluoroscopic guidance, because complications (ie, panic attack, subintimal recanalization, and stent misplacement) occurred with MR guidance. The quality of the postinterventional contrast-enhanced MR angiograms of three of 12 lesions with stents was limited owing to stent-induced signal loss of the lumen. The mean stenosis degree after stent placement was significantly higher at contrast-enhanced MR angiography than at DSA (24.6% vs 6.2%). The mean MR imaging-guided procedure time was 74 minutes. CONCLUSION: MR imaging-guided stent placement in iliac arteries is feasible in select patients. The presented technique has limitations-that is, long procedure times, lack of real-time monitoring, and stent artifacts-that necessitate further modifications before it can be recommended for clinical use.     

A novel active MR probe using a miniaturized optical link for a 1.5‐T MRI scanner

Applying an active intravascular MR catheter device that allows signal transmission from the catheter tip requires special means to avoid radiofrequency‐induced heating. This article presents a novel, miniaturized all‐optical active MR probe to use with real‐time MRI in minimally invasive interventions for catheter guidance and intravascular imaging. An optical link transmits the received MR signals from the catheter tip to the MR receiver with inherently radiofrequency‐safe optical fibers. Furthermore, power is supplied optically to the transmitter as well. The complete integration into a small tube of 6‐Fr (2‐mm diameter) size with a 7‐Fr (2.33‐mm diameter) rigid tubing was realized using chip components for the optical modulator and a novel miniaturized optical bench fabricated from silicon substrates with 3D self‐aligning structures for fiber integration. In MRI phantom measurements, projection‐based tip tracking and high‐resolution imaging were successfully performed with the optical link inside a 1.5‐T MRI scanner. Images were obtained in a homogeneous phantom liquid, and first pictures were acquired from inside a kiwi that demonstrates the potential of the MR‐safe optical link. The signal‐to‐noise ratio has significantly improved compared with former systems, and it is demonstrated that the novel optical link exhibits a signal‐to‐noise ratio comparable to a direct electrical link. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

MR-guided angioplasty of renal artery stenosis in a pig model: a feasibility study

PURPOSE: To test the hypothesis that magnetic resonance (MR) imaging can guide the percutaneous treatment of renal artery stenosis in a pig model. MATERIALS AND METHODS: Ameroid constrictors were surgically placed around six renal arteries in four pigs. After 30-36 days, all stenoses were documented by conventional x-ray aortograms. MR-guided renal angioplasty was attempted for three stenoses. For these pigs, MR angiography was performed with use of contrast-enhanced three-dimensional (3D) techniques. The authors visualized catheters by filling them with dilute 4% gadolinium and imaging with two-dimensional (2D) and 3D MR fast spoiled gradient recalled echo techniques. Under MR guidance, the authors advanced a selective catheter into the affected renal artery and crossed the stenosis with a nitinol guide wire. Angioplasty was performed with a balloon catheter filled with dilute gadolinium. Stenosis and luminal diameter measurements were compared before and after angioplasty. RESULTS: After ameroid constrictor placement, four significant stenoses, one mild stenosis, and one occlusion developed. Under MR guidance, the authors achieved technical success in performing three of three (100%) attempted dilations. After MR-guided angioplasty, the mean reduction in stenosis was 35% and the mean increase in luminal diameter was 1.6 mm. CONCLUSION: Use of MR guidance for the angioplasty of renal artery stenosis in pigs is feasible.     

Simultaneous real-time visualization of the catheter tip and vascular anatomy for MR-guided PTA of iliac arteries in an animal model

PURPOSE: To examine the feasibility of simultaneous MR real-time active tip tracking and near real-time depiction of the vascular anatomy for percutaneous angioplasty of iliac arteries under MR guidance. MATERIALS AND METHODS: Nine surgically created stenoses of external iliac arteries in pigs were dilated with MR-compatible balloon catheters (Cordis, Roden, The Netherlands). These catheters were equipped with a microcoil for active tracking of the catheter tip with an in-plane update rate of 10 positions per second. The procedures were performed on an interventional 1.5 T Gyroscan ACS-NT scanner (Philips, Best, The Netherlands). Real-time calculation of images acquired by radial k-space filling was performed on a specially designed backprojector exploiting the sliding window reconstruction technique (Philips Research Laboratories, Hamburg, Germany). The image update rate was 20 frames per second using a radial gradient-echo technique (TR = 12 msec, TE = 3.3 msec, 300 radials). MR angiography and X-ray digital subtraction angiography on the X-ray system positioned in-line next to the interventional MR system served as control for the angioplasty results. RESULTS: Real-time guidance and positioning of the balloon catheters was possible. The actual position of the catheter tip was indicated in the MR images without any time delay for the reconstruction of the anatomical MR images, which were updated with a rate of 20 frames per second. This yielded a combination of a roadmap and fluoroscopy image, in which the catheter position and the anatomical background image both were continuously updated in real time. Six out of nine stenoses were successfully dilated. The effects of the angioplasty could be visualized by the real-time MR technique, as was proven by X-ray digital subtraction angiography. CONCLUSION: Active tip tracking simultaneous with MRI of the vascular anatomy-both in real time-is possible with the applied technique, enabling MR-guided percutaneous dilatation (PTA) of iliac arteries.     

Feasibility of stent placement in carotid arteries with real-time MR imaging guidance in pigs

All examinations were performed with approval from the institutional animal care and use committee of Columbia University. To assess the feasibility of real-time magnetic resonance (MR) imaging-guided neurovascular intervention in a swine model, the authors placed stents in the carotid arteries of five domestic pigs. Seven-French vascular sheaths were placed in the target carotid arteries via femoral access by using active MR tracking. Ten nitinol stents (8-10 x 20-40 mm) were successfully deployed in the target segments of carotid arteries bilaterally. MR imaging and necropsy findings confirmed stent position. Necropsy revealed no gross vascular injury. Study results demonstrated the feasibility of performing real-time MR imaging-guided neurovascular intervention by using an active-tracking technique in an animal model.