Xiaoming Yang, MD, PhDErgin Atalar, PhD

Index terms:AnimalsInterventional procedures,

experimental studies, 943.1282,943.7229

Magnetic resonance (MR), contrastenhancement, 943.12943,961.12943

Magnetic resonance (MR), guidance,943.1282

Magnetic resonance (MR), vascularstudies, 81.129412, 81.12942,81.12943, 943.129412,943.12942, 943.12943

Radiology 2000; 217:501–506

1 From the Department of Radiology,Johns Hopkins University School ofMedicine, Outpatient Center Rm4243, 601 N Caroline St, BaltimoreMD 21287-0845. Received Septem-ber 21, 1999; revision requested No-vember 1; final revision received Feb-ruary 4, 2000; accepted February 22.Supported in part by National In-stitutes of Health grant numberR29HL57483, the Whitaker Founda-tion, and Surgi-Vision. Address corre-spondence to X.Y. (e-mail: xyang@mri.jhu.edu).

Ergin Atalar, PhD, is a founder andstockholder of Surgi-Vision.© RSNA, 2000

Author contributions:Guarantors of integrity of entire study,X.Y., E.A.; study concepts and design,X.Y., E.A.; definition of intellectualcontent, X.Y., E.A.; literature research,X.Y., E.A.; experimental studies, X.Y.,E.A.; data acquisition and analysis,X.Y., E.A.; manuscript preparation, ed-iting, and review, X.Y., E.A.

Intravascular MRImaging–guided BalloonAngioplasty With anMR Imaging Guide Wire:Feasibility Study in Rabbits1

PURPOSE: To develop a technique for intravascular magnetic resonance (MR)–guided balloon angioplasty with use of an MR imaging guide wire.

MATERIALS AND METHODS: An MR imaging guide wire (0.6-mm loopless an-tenna) that could be placed within a balloon catheter was manufactured. The guidewire was expected to function as either an MR receiver probe in real-time MRimaging or a guide wire for use with interventional devices. Laparotomy wasperformed in eight rabbits, and a dilatable stenosis was created at the upperabdominal aorta. Balloon angioplasty, validated at pre- and postoperative MRaortography with renal contrast enhancement was performed by using a 1.5-T MRunit with a fast spoiled gradient-echo pulse sequence, short repetition and echotimes, and a rate of three frames per second.

RESULTS: During MR tracking, the entire length of the MR imaging guide wire wasalways visible as a band of high signal intensity. In all cases, the MR imaging guidewires were passed through the aortic stenoses dilated by means of balloon inflation.Before balloon angioplasty, flow in the aorta distal to the stenosis was decreased,which caused mild contrast enhancement in each kidney. After balloon angioplasty,distal flow was restored, resulting in substantial renal enhancement.

CONCLUSION: The MR imaging guide wire is a potential tool for use in endovas-cular interventional MR imaging.

Interventional magnetic resonance (MR) imaging is a rapidly expanding field. Severalstudies about MR imaging–guided vascular interventions have been reported (1). Someauthors (2–4) demonstrated passive MR tracking of interventional instruments, which isbased on the depiction of signal void and susceptibility artifacts caused by the instrumentsthemselves. Passive tracking has several advantages: For example, it allows visualization ofthe entire device and has no safety or maneuverability problems with the catheters (4).However, because of the dependence of the passive tracking technique on field strength,device orientation, and particular pulse sequence parameters, the passively depicted sus-ceptibility artifacts are often inconsistent, and the temporal resolution is usually inade-quate.

Other investigators (5–7) developed an active tip-tracking technique in which theposition of an interventional instrument is determined from the MR signal received by aminiature radio-frequency coil attached to its tip. Active tip-tracking provides robustdetermination of the position of the device tip and offers higher tracking speeds. However,since only the tip of the device can be located, possible kinks in the body of the devicecannot be observed during active tip tracking. In addition, the miniature radio-frequencycoils may have several limitations, such as reduced maneuverability of an interventionaldevice and reduced suitability for use in the tracking of microcatheters and guide wires atMR imaging.

Recently, an alternate approach to intravascular MR imaging that involves the insertion

501

of an MR loopless antenna receiver intothe vessel has been developed (8). Thisdevelopment offers potential applica-tions in intravascular MR imaging of ex-aminations and treatments, for example,(a) MR imaging of vessels, (ie, acquisitionof high-spatial-resolution MR angiograms,observation of the cross-sectional imagesof stenotic arteries, and quantitative andqualitative analyses of atheroscleroticplaques [9]) and (b) real-time MR imaging,which may be an alternative to x-ray fluo-roscopy in the guidance of endovascularinterventions (10).

Findings of one recent study (11) dem-onstrated the usefulness of the looplessantenna in monitoring the balloon dila-tion process in an experimental aorticstenosis. However, in this study, the an-tenna and balloon catheter were placedparallel to each other in the vessel. Thisplacement required the use of two vascu-lar access sites and the passage of twodevices (ie, balloon catheter and an-tenna) through the stenosis, which in-creased the risk of technical failure andcomplications, such as dissection of thevessel wall. Usually, interventional de-vices such as a balloon catheter have acentral channel for use in the placementof a guide wire or in the administrationof contrast material. This observation in-spired us to explore the possibility ofplacing a thin loopless antenna in an in-terventional device; this design would re-quire only one vascular access site.

The objective of the present study wasto develop a technique of intravascularMR imaging–guided balloon angioplastyby using a thin loopless antenna, whichwas expected to function not only as anMR imaging guide wire at real-time MRimaging but also as a guide for the endo-vascular interventional procedures.

MATERIALS AND METHODS

Experimental Design

First, the proposed method involvedthe creation of a rabbit model with anexperimental stenosis in the upper ab-dominal aorta. Second, we performedtwo-dimensional contrast medium–en-hanced MR aortography and contrast-en-hanced renal perfusion MR imaging tocompare the changes in aortic stenosisand renal hemodynamics before and af-ter MR imaging–guided interventions.Third, using the MR tracking technique,we steered the loopless antenna to locatethe stenosis. Fourth, a balloon catheter,guided with the loopless antenna, wasdelivered into the stenosis, and the entire

process of dilation of the stenosis bymeans of balloon inflation was moni-tored with real-time MR imaging. Last,postoperative MR aortography and renalperfusion MR imaging were performed toobtain immediate feedback about thesuccess of the MR imaging–guided inter-vention.

Devices

Loopless antenna MR imaging guidewire.—We produced a 75-cm-long loop-less antenna consisting of a soft conduct-ing wire that was an inner conductorfrom a 50-ohm, 0.6-mm, coaxial cablewith a polyester jacket (Pico-Coax, AxonCable, Norwood, Mass); the wire was ex-tended to fit in a 40-cm-long ballooncatheter. The inner and outer conductorsof the coaxial cable were made of silver-plated copper alloy with a fluoroethylenepolymer as the dielectric. The proximalend of the coaxial cable was connectedthrough a matching tuning-decouplingcircuit to the MR imager. The conductingwire was 9 cm in length and 0.4 mm indiameter; the coaxial cable was 66 cm inlength and 0.6 mm (2.1 F) in diameter.

Since this design had a simple struc-ture, it was relatively easy to construct anantenna with a very small diameter,which allowed it to be passed directlythrough the aortic stenosis or directly in-serted into the central channels of theinterventional catheters (Fig 1). Thus, the0.6-mm antenna was expected to func-tion as both an MR receiver probe and aconventional guide wire; it was called anMR imaging guide wire.

The MR imaging guide wire can beused as a probe for transmitting radio-frequency pulses and receiving MR sig-nals simultaneously, or it can be used as areceive-only probe. In the receive-onlymode, the radio-frequency pulses aretransmitted from an external coil such asa body coil. A total of 14 MR imagingguide wires with the same design and sizewere used in 14 animal experiments.

Balloon catheter.—A 5-F, 40-cm-longballoon catheter was used (Meditech,Boston Scientific, Watertown, Mass). Theballoon portion was 4 cm in length and 6mm in diameter, with a burst pressure of15 atm (1.5 3 106 Pa). There were twoalloy (tantalum) rings at the proximaland distal ends of the balloon. The bal-loon catheter had been tested at MR im-aging and was proved to be MR compat-ible, as it did not produce substantialartifacts.

Cable tie.—To create the experimentalstenosis, a 12-cm-long and 2.5-mm-wide

plastic (polyethylene) cable tie (Baynes-ville Electronics, Baltimore, Md) wasbound around the exposed upper ab-dominal aorta of the rabbit. This createda 5-mm-long stenosis, with a reductionof approximately 80%–90% of the cross-sectional lumen when the cable tie wascompletely tightened. The percentage, or(area of stenotic lumen 4 area of normallumen) 3 100%, of the experimental ste-nosis was measured and calculated by ob-serving the cross section of a 6-mmhomemade phantom with the same ste-nosis that was created by completelytightening the same cable tie. In thephantom, we also proved the capabilityof 100% release of the cable tightness; wefully inflated the balloon and achieved100% dilatation of the stenosis. Since wealways performed the same procedure bycompletely tightening the same cable tieand by fully inflating the same balloon ineach experiment, the 80%–90% reduc-tion of the target aortic lumens and100% opening of the stenoses were iden-tical in the 14 experiments. The cable tiewas tightened in a direction opposite theusual direction so that we could easilyslide it open as the balloon inflated. Thecable tie was also MR compatible.

Surgical Procedure in Animals

Fourteen male New Zealand White rab-bits (Robinson Services, Clemmons, NC;weight, 3.5–4.5 kg) were used. The firstgroup of six rabbits was used for techni-cal refinement, which included surgery,insertion of the balloon catheter and MRimaging guide wire, and development ofthe MR imaging protocol in which differ-ent pulse sequences for different MRtechniques were tested. The remainingeight rabbits were used for feasibility in-vestigation of intravascular MR imaging–guided balloon angioplasty, which wasvalidated at MR aortography and renal

Figure 1. Photograph shows that the MR im-aging guide wire, a 0.6-mm intravascular loop-less antenna, is placed in a 5-F balloon catheter.

502 z Radiology z November 2000 Yang and Atalar

perfusion MR imaging. The animals weretreated according to the Principles ofLaboratory Animal Care of the NationalSociety for Medical Research and theGuide for the Care and Use of LaboratoryAnimals (12). The animal care and usecommittee at our institution approvedthe experimental protocol.

The details about general anesthesiaand surgery for creation of the aortic ste-nosis in rabbits are described elsewhere(11). An ear vein was cannulated, whichpermitted either administration of pen-tobarbital for maintenance of anesthesiaor injection of contrast agent for MR an-giography and perfusion MR imaging.Then, 0.3 mL of heparin (1,000 U/mL)was intravenously infused through theear vein. Nonferromagnetic electrodeswere attached to the limbs for surfaceelectrocardiography. Both electrocardio-graphic and blood pressure signals wereused to monitor the condition of the an-imal during the experiment. At comple-tion of the experiments, the animalswere euthanized by means of intrave-nous injection of 100 mg of pentobarbi-tal per kilogram of body weight.

MR Imaging Techniques

Intravascular MR imaging–guided bal-loon angioplasty.—All experiments wereperformed with a Signa LX 1.5-T cardiacMR unit (GE Medical Systems, Milwau-kee, Wis) with a maximum gradient of 40mT z m21 and a slew rate of 150 T z m21 zsec21. The animals were placed in a supineposition in the unit and were aligned withthe main magnetic field. The MR imagingguide wire was used in the transmit-re-ceive mode. To record the entire proce-dure of intravascular MR imaging–guidedballoon angioplasty (which includedtracking the MR imaging guide wire tolocate the stenosis, tracking the ballooncatheter to target the stenosis, and mon-itoring balloon dilation of the stenosis),we used a fast spoiled gradient-echo pulsesequence (5.0/1.4 [repetition time msec/echo time msec]), a 62.5-kHz bandwidth,a rectangular 24 3 12-cm field of view, a256 3 128 matrix, and no section selec-tion. We acquired a total of 240 images,with 60 images acquired during each ofthe following 20-second procedures: MRimaging guide wire tracking, ballooncatheter tracking, balloon inflation anddeflation, and balloon and antenna with-drawal. With this MR protocol, we per-formed intravascular real-time MR imag-ing at a rate of three frames per second.

MR aortography and renal MR perfusionimaging.—Two-dimensional contrast-en-

hanced coronal MR aortography with re-nal perfusion MR imaging was performedwith manual injection of 1 mL of gado-pentetate dimeglumine (Magnevist; Ber-lex Laboratories, Wayne, NJ; 469 mg/mL)into the ear vein at rate of approximately0.5 mL/sec. We used a cardiac phased-array coil (GE Medical Systems), a fastspoiled gradient-echo pulse sequence(6.3/1.7), 60° flip angle, 31.2-kHz band-width, 24-cm field of view, 256 3 160matrix, 10-mm section thickness (to de-pict both kidneys and the aorta), oneframe per second, and a total imagingtime of 2 minutes. After injection of thecontrast agent, a 3-mL saline bolus wasinjected to ensure rapid delivery of theentire dose into the vein.

Intravascular MR Imaging–guidedBalloon Angioplasty

By using a coaxial technique (ie, plac-ing the MR imaging guide wire into the5-F balloon catheter), we first tracked theMR imaging guide wire through the in-troducer into the upper abdominal aortauntil the aortic stenosis was located. Theentire tracking process was performedwith intravascular real-time MR imagingby using the same MR imaging guidewire. Then, the balloon catheter and theMR imaging guide wire were deliveredand positioned into the stenosis. Thecentral point of the balloon and the mostsensitive region of the MR imaging guidewire (ie, point between the extended in-ner conductor and coaxial cable body)were adjusted and centered just at thelevel of the target stenosis so that high-spatial-resolution MR images of the tar-get vessel could be obtained.

The balloon was inflated by manuallyinjecting 2 mL of contrast medium with a20-mL plastic syringe. The contrast me-dium used consisted of a 6% solution ofthe prior contrast medium (28 mg/mL)diluted with saline. The 6% concentra-tion was previously found to be optimalfor use with the fast spoiled gradient-echo pulse sequence (11). The pressurefor manual inflation of the balloon wasapproximately 8–9 atm (8.1–9.1 3 105

Pa). Balloon inflation was started 4-6 sec-onds after MR imaging began. Inflationwas maintained by means of manualcontrol for 10 seconds and was termi-nated 4–6 seconds before the completionof MR imaging. Then, postoperative MRaortography and renal perfusion MR im-aging were performed by using 1 mL ofthe contrast medium and the same MRprotocols as those used at preoperativeMR aortography and renal perfusion MR

imaging. The interval between pre- andpostoperative MR angiography and renalperfusion MR imaging was approxi-mately 30–40 minutes, which allowedfor near-complete emptying of the kid-neys.

In this study, we performed balloonangioplasty and recorded the results aftereach acquisition. We evaluated the ap-pearance of the MR imaging guide wire,the course of the guide wire into the aor-tic stenosis, and balloon dilation of thestenosis and than compared changes inaortic flow and renal contrast enhance-ment before and after MR imaging–guidedballoon angioplasty.

RESULTS

The MR imaging guide wire enabled us(a) to obtain real-time intravascular MRimages for tracking the devices (includ-ing the MR imaging guide wire itself andthe balloon catheter) and (b) to performballoon angioplasty by using it as a guidewire. During tracking with real-time MRimaging, the entire length of the MR im-aging guide wire in the field of view wasdisplayed as a band of high signal inten-sity that was approximately 5–6 mm indiameter with a cone-shaped tip.

The MR imaging guide wire passedthrough the aortic stenosis in all 14 cases.The aortic stenosis were clearly depictedat MR aortography and were always visi-ble during tracking of the MR imagingguide wire (Fig 2). In two cases, the MRimaging guide wire traveled into the aor-tic branches, such as the renal arteries,during the first attempt. However, theMR imaging guide wire was removed,and after two additional attempts, itreached the stenoses. Motion artifactsfrom either the aorta or MR imagingguide wire were not notable primarily be-cause of the fast imaging acquisitiontechnique that we used and the highheart rate of rabbits, which reduced thepulsatility of the blood flow.

In all 14 cases, the balloon was guidedby the MR imaging guide wire and wassent into the stenosis; the aortic stenoseswere completely dilated by inflating theballoon with MR contrast agent (Fig 2).The contrast medium injected into theballoon produced high signal intensity.The two tantalum rings of the balloonwere depicted as two small image arti-facts, or signal voids, that were 4–5 mmin diameter. These two image artifactswere excellent markers; we used them toprecisely adjust the position of the bal-loon during MR imaging. When the MR

Volume 217 z Number 2 Intravascular MR Imaging–guided Balloon Angioplasty: Feasibility Study in Rabbits z 503

imaging guide wire stayed in the ballooncatheter, its signal intensity appeared tobe relatively low. However, as we trackedthe MR imaging guide wire out of theballoon catheter into the stenosis, its sig-nal intensity increased (Fig 2); the bal-loon catheter caused a slight reduction inthe signal intensity of the MR imagingguide wire.

In the group of eight rabbits used inthe feasibility investigation, two-dimen-sional contrast-enhanced MR aortogra-phy also clearly demonstrated decreasedflow in the aorta distal to the stenosesbefore balloon angioplasty, whereas aor-tic distal flow was restored after balloonangioplasty (Fig 3). The experimentalaortic stenoses resulted in only mild con-trast enhancement in the cortex of bothkidneys at preoperative renal perfusionMR imaging. After balloon angioplasty,contrast enhancement immediately in-creased and quickly expanded in the en-tire kidney (Fig 3). Time to peak contrastenhancement in the kidneys before bal-loon angioplasty was longer than 2 min-utes, whereas time to peak enhancementafter balloon angioplasty was in therange of 30–40 seconds in our eight ex-periments. One milliliter of intrave-nously administered contrast materialwas enough for detection of the aorticstenosis and examination of renal perfu-sion in the same imaging plane.

DISCUSSION

There have been several attempts tomake conventional guide wires visible atMR imaging with the use of either passiveor active tracking techniques. With pas-sive tracking, some investigators (13)demonstrated the use of a fiberglass-based guide wire with a tip impregnatedwith dysprosium oxide rings. With thisdesign, only these paramagnetic rings areclearly depicted; the guide wire showspoor contrast enhancement at MR imag-ing. With active guide wire tracking, oth-ers (14) tested electrically coupled wires,which have the potential to be incorpo-rated into conventional guide wires. Ef-forts have also been made to build min-iature coils in the tips of commerciallyavailable guide wires (6). The miniatureradio-frequency coil delivers a high-con-trast signal over its full length and en-ables depiction of the position and cur-vature of the tip of the guide wire. Theproblem with active guide-wire trackingis that the signal is limited to the minia-ture coil at the guide-wire tip.

A characteristic of the intravascular

Figure 2. Coronal fast spoiled gradient-echo MR images (5.0/1.4) of the MR imaging guidewire overlaid on road-map images depict intravascular MR imaging–guided balloon angio-plasty in a rabbit aorta. Intensity of the road-map image is intentionally decreased for betterdepiction of the guide wire. A, Aortic stenosis (arrows) is located by tracking the MR imagingguide wire. During tracking, the guide wire comes out of the balloon and goes into thestenosis, so more signals are depicted in the field of view. B, Balloon is delivered into theaortic stenosis (arrows). Image shows two tantalum rings (arrowheads) of the balloon. C,Image shows balloon dilation of the aortic stenosis (arrows) and two tantalum rings (arrow-heads) of the balloon. D, Image shows withdrawal of the MR imaging guide wire and ballooncatheter from the treated stenotic aorta. Thus, the entire process of intravascular MR imag-ing–guided balloon angioplasty is accomplished.

504 z Radiology z November 2000 Yang and Atalar

MR loopless antenna (MR imaging guidewire) used in our study is that its entirelength in the field of view can be de-picted during MR tracking. This is differ-ent from passively or actively tracked MRimaging guide wires with which only thesignals from the paramagnetic rings orminiature radio-frequency coil can be de-picted (6,13). The MR imaging parame-ters used in this study enabled us to seethe MR imaging guide wire and sur-rounding tissues, such as blood, as a5–6-mm bright band and to clearly out-line the stenosis of the 6-mm vessel. Onegroup (10) reported that the loopless an-tenna with the highest signal intensitystands at the central line of this brightband, and adjustment of the radio-fre-quency power applied to the antenna canchange the thickness of this bright band.

Other characteristics of the looplessantenna include the following: (a) highsensitivity to the MR signal along its en-tire length; (b) sensitivity that is inverselyproportional to the distance it; (c) pro-duction of very high signal around itwhen it is used as a transmitter-receiverprobe; and (d) ability to be used in thecreation of projection image, since theantenna localizes the MR signal arounditself and does not require section selec-tion (10).

The tip of the antenna is loopless andis essentially a dipole. Since the antennahas limited space for the placement of atuning and coupling component at itsdistal (neck) portion (between the tip ofthe inner conductor wire and long coax-ial cable), this MR imaging guide wire istuned and matched at its proximal end

(at the interface between the coaxial ca-ble and surface coil input of the imager);this end remains outside the vessels anddoes not have performance degradation.This design enables us to make the loop-less antenna with a very small diameter.Currently, the thinnest MR imagingguide wire has a diameter of 0.6 mm andcan be easily built in our laboratory.

Cardiovascular MR imaging techniquesprovide high-spatial-resolution images ofthe vessel wall and atheroscleroticplaques (15,16) that are not possible withX-ray fluoroscopic techniques. Intravas-cular MR technology provides us withthe opportunity to combine high-spatial-resolution MR imaging with interven-tional procedures in a single setting. Theintravascular MR loopless antenna wasshown to be useful in the acquisition ofhigh-spatial-resolution MR images of theaortic wall (9) and in the performance ofintravascular MR fluoroscopy (10,11).

In the present study, we produced athin (0.6-mm) loopless antenna that en-abled us not only to generate intravascu-lar real-time MR images but also to locatethe stenosis and guide the balloon cath-eter into the stenosis. These overall re-sults suggest that the loopless antennamay be used as an MR imaging guidewire, functioning either as an intravascu-lar MR receiver probe in the acquisitionof high-spatial-resolution MR images andat MR fluoroscopy or as a conventionalguide wire for endovascular interven-tions performed with MR imaging guid-ance. Indeed, for reasons of safety and foroperational purposes (such as torquecontrol, subselective placement, and ne-

gotiation of hard atherosclerotic lesions),an MR imaging guide wire with both im-aging and guidance functions is required.

This experiment was performed byusing an animal model with a short ste-nosis in a straight vessel. To negotiatecomplex, tortuous, and eccentric athero-sclerotic stenoses, the MR imaging guidewire must be modified before clinical use.Various properties of the MR imagingguide wire—including its ability to betorqued, resistance to kinking, lubricity,floppiness, preset or shapeable curvature,stiffness, bluntness, and taper—need tobe made similar to those of standard con-ventional guide wires.

An important concern about active MRtracking is the heating caused by the ra-dio-frequency conductive parts of the de-vices from either the miniature coils at-tached to the conventional guide-wiretips or from the entire coaxial cable bodyof the loopless antenna. To our knowl-edge, there are few data available on thesafety of the intravascular MR technique.Some investigators (6) have found thatwhen the active tracking guide wires areused in the transmit/receive mode, notemperature rise can be detected. Others(17) tested a field-inhomogeneity cathe-ter that was equipped with a current in-duction wire. There was no proof of elec-trically induced damage in the vesselwall. Recently, we also evaluated the lo-cal thermal effect of the 0.6-mm MR im-aging guide wire and found no evidenceof radio-frequency–induced thermal in-jury during intravascular MR imaging ofa normal rabbit aorta (18). However, thebiologic and operative safety of this in-travascular MR technology needs to beextensively evaluated and confirmed.

Functional MR pre- and posttherapeu-tic interventions are a current reality, andthe online monitoring of the effective-ness of such interventions for guidanceof the next therapeutic step promisesmore effective patient care. The combi-nation of MR angiography, perfusion MRimaging, and MR imaging–guided inter-ventions will refine the method of com-prehensive management of organ isch-emia with the use of a single modality ina single sitting. MR angiography can beused to assess the angioplastic site itself,while perfusion MR imaging can be usedto validate the physiologic response toangioplasty.

In conclusion, we demonstrated an al-ternative approach to balloon angioplastywith the use of an MR imaging guidewire. The MR imaging guide wire offersthe potential to function as either an MRreceiver probe for real-time MR imaging

Figure 3. Two-dimensional contrast-enhanced, coronal fast spoiled gradient-echo MR aorto-grams and renal perfusion MR images in a rabbit (6.3/1.7). A, Before balloon angioplasty, onlymild enhancement of both kidneys is depicted because of aortic stenosis (arrow). There is a smallamount of distal flow into the downstream aorta and right renal artery. B, After balloon angio-plasty, contrast medium immediately flows through the stenosis (arrow), and both kidneys(K) quickly show enhancement. Images in both A and B were selected 2 seconds after the bolusof contrast material arrived at the aortic stenosis. Time to peak contrast enhancement in thekidneys before balloon angioplasty was longer than 2 minutes; after balloon angioplasty, 30seconds.

Volume 217 z Number 2 Intravascular MR Imaging–guided Balloon Angioplasty: Feasibility Study in Rabbits z 505

or as a conventional guide wire for use inendovascular interventional procedures.

Practical application: CardiovascularMR technology provides high-spatial-res-olution images of the vessel (includingthe vessel wall), multiple diagnostic eval-uations of organ function and morphol-ogy, and imaging in multiple planeswithout risk of ionizing radiation. Com-bined with MR angiography and func-tional MR imaging, the development ofintravascular MR imaging–guided inter-ventions is an important step toward fu-ture online comprehensive managementof cardiovascular atherosclerotic diseaseswith MR technology. This potential shouldfacilitate clinical acceptance and, there-fore, more extensive clinical use of MRmethods to improve the diagnosis andtreatment of cardiovascular disorders.

Acknowledgment: The authors thank MaryA. McAllister, MA, for her editorial assistance.

References1. Yang X, Atalar E, Zerhouni EA. Intravas-

cular MR imaging and intravascular MR-guided interventions. Int J Cardiovasc In-tervent 1999; 2:85–96.

2. Kochli VD, McKinnon GC, Hofmann E,von-Schulthess GK. Vascular interven-tions guided by ultrafast MR imaging:evaluation of different materials. MagnReson Med 1994; 31:309–314.

3. Glowinski A, Adam G, Bucher A, Neuer-burg J, van-Vaals JJ, Gunther RW. Cathe-

ter visualization using locally induced,actively controlled field inhomogeneities.Magn Reson Med 1997; 38:253–258.

4. Bakker CJ, Hoogeveen RM, Hurtak WF,van-Vaals JJ, Viergever MA, Mali WPTM.MR-guided endovascular interventions:susceptibility-based catheter and near-re-al-time imaging technique. Radiology1997; 202:273–276.

5. Leung DA, Debatin JF, Wildermuth S, etal. Intravascular MR tracking catheter:preliminary experimental evaluation. AJRAm J Roentgenol 1995; 164:1265–1270.

6. Ladd ME, Zimmermann GG, Quick HH,et al. Active MR visualization of a vascularguidewire in vivo. J Magn Reson Imaging1998; 8:220–225.

7. Wendt M, Busch M, Wetzler R, et al.Shifted rotated keyhole imaging and ac-tive tip-tracking for interventional proce-dure guidance. J Magn Reson Imaging1998; 8:258–261.

8. Ocali O, Atalar E. Intravascular magneticresonance imaging using a loopless cath-eter antenna. Magn Reson Med 1997; 37:112–118.

9. Correia LCL, Atalar E, Kelemen MD, et al.Intravascular magnetic resonance imag-ing of aortic atherosclerotic plaque com-position. Arterioscler Thromb Vasc Biol1997; 17:3626–2632.

10. Atalar E, Kraitchman DL, Carkhuff B,et al. Catheter-tracking FOV MR fluoros-copy. Magn Reson Med 1998; 40:865–872.

11. Yang X, Bradley D, Bolster J, KraitchmanDL, Atalar E. Intravascular MR-monitoredballoon angioplasty: an in vivo feasibilitystudy. J Vasc Interv Radiol 1998; 9:953–959.

12. Guide for the care and use of laboratory

animals. Bethesda, Md: National Acad-emy of Sciences. 1996.

13. Bakker CJ, Smits HF, Bos C, et al. MR-guided balloon angioplasty: in vitro dem-onstration of the potential of MRI forguiding, monitoring, and evaluating en-dovascular interventions. J Magn ResonImaging 1998; 8:245–250.

14. McKinnon GC, Debatin JF, Leung DA,Wildermuth S, Holtz DJ, von-SchulthessGK. Towards active guidewire visualiza-tion in interventional magnetic reso-nance imaging. MAGMA 1996; 4:13–18.

15. Toussaint J, LaMuraglia G, Southern J,Fuster V, Kantor H. Magnetic resonanceimages lipid, fibrous, calcified, hemor-rhagic, and thrombotic components ofhuman atherosclerosis in vivo. Circula-tion 1996; 94:932–938.

16. Zimmermann GG, Erhart P, Schneider J,von-Schulthess GK, Schmidt M, Deba-tin JF. Intravascular MR imaging of ath-erosclerotic plaque: ex vivo analysis ofhuman femoral arteries with histologiccorrelation. Radiology 1997; 204:769–774.

17. Adam G, Glowinski A, Neuerburg J,Bucker A, van-Vaals JJ, Gunther RW. Vi-sualization of MR-compatible cathetersby electrically induced local field inho-mogeneities: evaluation in vivo. J MagnReson Imaging 1998; 8:209–213.

18. Yang X, Ji H, Atalar E. Local thermalsafety in intravascular MR imaging: an invivo evaluation (abstr). Proceedings fromthe Seventh Meeting of the InternationalSociety for Magnetic Resonance in Medi-cine. Berkeley, Calif: International Soci-ety for Magnetic Resonance in Medicine,1999; 579.

506 z Radiology z November 2000 Yang and Atalar