Published online before print December 10, 2004, 10.1148/radiol.2341031951
(Radiology 2005;234:551-557.)
© RSNA, 2004
Transfemoral Catheterization of Carotid Arteries with Real-time MR Imaging Guidance in Pigs1
Lei Feng, MD, PhD,
Charles L. Dumoulin, PhD,
Stephen Dashnaw, BS,
Robert D. Darrow, MS,
Renee Guhde, MS,
Robert L. DeLaPaz, MD,
Paul L. Bishop, BS and
John Pile-Spellman, MD
1 From the Department of Radiology, Columbia University, 177 Fort Washington Ave, MHB 8SK, New York, NY 10032 (L.F., S.D., R.L.D., J.P.S.); and General Electric Global Research Center, Schenectady, NY (C.L.D., R.D.D., R.G., P.L.B.). Received December 3, 2003; revision requested February 12, 2004; revision received March 2; accepted March 29. J.P.S. supported by a grant from GE Medical Systems. Address correspondence to J.P.S. (e-mail: jp59@columbia.edu).
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ABSTRACT
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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.
Supplemental material: radiology.rsnajnls.org/cgi/content/full/2341031951/DC1.
© RSNA, 2004
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INTRODUCTION
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For diagnostic and interventional neurovascular procedures, real-time magnetic resonance (MR) imaging guidance offers many advantages over conventional radiographic guidance (1). For example, the absence of ionizing radiation makes MR imaging–guided endovascular procedures safer for both patients and operators. In addition, gadolinium-based contrast agents have lower nephrotoxicity and allergic potential than do iodinated contrast agents (2). Multiplanar magnetic MR angiograms with online three-dimensional (3D) reconstructions facilitate visualization of the complicated vascular anatomy in the head and neck (3–5). Furthermore, the continuous assessment of tissue viability and brain function with diffusion-weighted, perfusion-weighted (6), and functional MR imaging (7,8) during the procedure adds new dimensions to the treatment of cerebral vascular diseases, particularly ischemic stroke.
Passive and active MR tracking techniques have been developed for interventional MR imaging (9–12). The passive-tracking method involves the use of either a contrast agent–filled catheter (13,14) or the susceptibility artifacts caused by the guidewire or the stent (15–19) to visualize the device on conventional MR images. Although passive methods require little hardware modification to the MR imaging system, they are acquisition dependent and limited by low temporal resolution. Furthermore, the tip of the device must remain within the imaging plane to be visualized, and ensuring this often requires great care.
Compared with passive-tracking devices, active MR tracking devices offer a substantial improvement in temporal resolution and device conspicuity. Small receiver coils that are incorporated into the body of the device enable localization of the catheter in real time and in three dimensions (11). Active MR tracking devices have been successfully used in animal models to perform transfemoral catheterization of first-order vessels, such as the renal, mesenteric, and coronary arteries (20–22).
Smaller vessels, such as the third- to fourth-order vessels in the head and neck, require more precise catheter manipulation at vessel bifurcations and are therefore more difficult to catheterize. We hypothesized that these vessels can be catheterized within a clinically acceptable time frame by using an active-tracking system that offers high temporal resolution and facilitates unambiguous identification of the device (11,23–27). This system includes software that is capable of collecting MR angiographic "road maps." This software enables identification of small receiver coils that are mounted at strategic points on and near the catheter device tip.
The strategic placement of the coils helps to determine the 3D coordinates of the catheter device. The coil coordinates are represented by small color icons on the display screen, and when these icons are superimposed on the MR angiographic maps, the system enables instantaneous localization of the guidewires and catheters within the vasculature (11). Thus, the purpose of our study was to assess the feasibility of performing transfemoral catheterization of the carotid arteries with real-time MR imaging guidance by using active MR tracking techniques.
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Materials and Methods
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Animals and Monitoring
All of the described procedures and protocols were approved by the institutional animal care and use committee of Columbia University. Real-time MR imaging–guided transfemoral catheterization of the carotid arteries was performed in six 18–25-kg female domestic pigs (Animal Biotech Industries, Danboro, Pa). The procedures were performed by using an MR imaging–compatible anesthesia machine (Anestiva/5; Datex Ohmeda, Madison, Wis) to administer isoflurane (Henry Schein Pharmaceutical, Long Island, NY) for general anesthesia in the animals. The animals’ heart rate, blood pressure, and oxygen saturation were monitored throughout the procedure by using the Millennia Vital Signs Monitoring System (In vivo Research, Orlando, Fla). Their body temperature was monitored with an oral mercury thermometer and was recorded every 15–20 minutes.
Our laboratory personnel (including P.L.B.) constructed active MR tracking devices by winding small receiver coils around the tips of 5-F catheters and micro–guidewires (Fig 1a). Steam was used to manipulate the 5-F catheter until it had a headhunter shape. The catheter was constructed with one coil 1 mm from the tip and one or two coils 1–2 cm more proximally. The guidewire, with its tip shaped to a 45° curve, had only one coil 8 mm from the tip. The receiver coils were connected, by microcoaxial cables, to adaptors near the proximal end of the device (Fig 1b). The adaptors were connected to the device interface module, which contained MR system preamplifiers and adaptors to the receiver ports of the MR imaging unit.
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Figure 1a. Active-tracking devices. (a) Arrows point to copper wires of the receiver coils. The receiver coil on the active-tracking guidewire is near the tip of the device; the distal curve maintains the flexibility of the wire tip. (b) Active-tracking catheter and guidewire are seen inside 90-cm 7-F vascular sheath (A), which extends the vascular access outside the magnet bore. The 5-F active-tracking catheter (C) is connected to a heparinized saline flush line (D) via a Y adapter. The 5-F active-tracking catheter also is connected to the sheath. Arrow B points to the nonheparinized saline flush line. The 0.035-inch active-tracking guidewire is labeled E. The microcoaxial cables on the two receiver coils (F and H) on the catheter and the single coil (G) on the guidewire are connected to the preamplifier on the MR imaging table (not shown).
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Figure 1b. Active-tracking devices. (a) Arrows point to copper wires of the receiver coils. The receiver coil on the active-tracking guidewire is near the tip of the device; the distal curve maintains the flexibility of the wire tip. (b) Active-tracking catheter and guidewire are seen inside 90-cm 7-F vascular sheath (A), which extends the vascular access outside the magnet bore. The 5-F active-tracking catheter (C) is connected to a heparinized saline flush line (D) via a Y adapter. The 5-F active-tracking catheter also is connected to the sheath. Arrow B points to the nonheparinized saline flush line. The 0.035-inch active-tracking guidewire is labeled E. The microcoaxial cables on the two receiver coils (F and H) on the catheter and the single coil (G) on the guidewire are connected to the preamplifier on the MR imaging table (not shown).
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All examinations were performed by using a 1.5-T MR imaging system (TwinSpeed; GE Medical Systems, Milwaukee, Wis) and a neurovascular array coil. An in-room display system (model MRI/18H; Aydin Displays, Birdsboro, Pa) was placed adjacent to the magnet bore opening so that images and tracking data could be presented to the operators (L.F., J.P.S.). The anesthesia equipment and the monitors on this equipment were mounted behind and above the in-room display system to allow immediate reading of the vital signs by the operator. To prescribe the MR imaging pulse sequences and change the imaging parameters, the operators communicated with the MR imaging technologist (S.D.) in the imaging control room through a headphone.
The active-tracking software enabled the use of several imaging sequences, including fast spoiled gradient-recalled acquisition (FSPGR); fast imaging employing steady-state acquisition, or FIESTA; and phase-contrast MR imaging for road-map MR angiography. After testing these pulse sequences for imaging various parts of the vascular tree, we chose sagittal time-resolved contrast material–enhanced MR angiography of the aortic arch and coronal phase-contrast MR angiography of the great vessels for guidance in the identification of the brachiocephalic and carotid arteries, respectively.
Sagittal time-resolved contrast-enhanced (with gadolinium diethylenetriaminepentaacetic acid; Sigma/Aldrich, Grand Island, NY) MR angiograms of the aortic arch were obtained by using continuous two-dimensional FSPGR and oversampling of center k-space techniques. The image parameters typically used were 9/3 (repetition time msec/echo time msec), a 30° flip angle, a 10-mm section thickness, a 30 x 30-cm field of view, a 62.5-kHz bandwidth, and a 256 x 128 matrix. The images were recorded in a memory buffer, and the best image was selected as the road map. Coronal phase-contrast MR angiograms were obtained by using the following parameters: 30/5.1, a 20° flip angle, a 62.5-kHz bandwidth, a 28-cm field of view, a 15-cm section thickness, a 128 x 256 matrix, and 26 acquired signals. Imaging took 2 minutes to complete.
The active-tracking devices were localized by using a gradient-echo pulse sequence with a 20°–35° flip angle, a 40-cm field of view, and a 30-cm section thickness. Although the 3D coordinates of the receiver coils on the active-tracking devices could be updated much faster, in most cases a frame rate of 9–15 frames per second was used to improve the tracking signal-to-noise ratio.
Catheterization
The operator(s) (L.F., J.P.S.) gained percutaneous access to the right femoral artery by using a micropuncture kit. A 9-F vascular sheath was inserted into the right femoral artery over a 0.035-inch guidewire (Terumo; Boston Scientific, Natick, Mass). After sagittal and coronal road-map images were obtained, the 5-F active-tracking catheter and active-tracking guidewire were inserted into the femoral vascular sheath and advanced to the aortic arch. The catheter and guidewire were manipulated to avoid the left subclavian artery, which is almost directly in line with the descending aorta in pigs. In the aortic arch, the catheter tip was turned toward the orifice of the brachiocephalic artery and the guidewire was used to probe this vessel. The catheter position was adjusted in real time until the guidewire entered the brachiocephalic artery. The catheter was then advanced over the guidewire into the brachiocephalic artery, and the position of the catheter in the coronal plane was confirmed (Movie 1, radiology.rsnajnls.org/cgi/content/full/2341031951/DC1).
One of the operators (L.F. or J.P.S.) catheterized the common carotid arteries bilaterally in a similar fashion by using the coronal road-map image of the great vessels. The catheter was placed in the brachiocephalic artery and turned simultaneously, whereas the guidewire was used to probe the common carotid artery. Once the guidewire was inside the common carotid artery, the catheter was advanced over the wire (Movie 2, radiology.rsnajnls.org/cgi/content/full/2341031951/DC1). The catheter position in the common carotid arteries was confirmed at intraarterial contrast-enhanced MR angiography. Catheterization was performed on the opposite side in a similar fashion. The left common carotid artery was always selected before the right common carotid artery. Both common carotid arteries were catheterized twice in each animal.
Vascular Anatomy
The operators (L.F., J.P.S.) examined the anatomies of the aortic arch, brachiocephalic artery, bicarotid trunk, and bilateral carotid arteries in the pigs by using 3D intravenous contrast-enhanced FSPGR MR angiography (3.6/1, 30° flip angle, 62.5-kHz bandwidth, 32 x 29-cm field of view, 288 x 160 x 116 matrix, 2-mm section thickness, interpolation factor of 4, elliptic centric k-space sampling) with 15 mL of 0.5 mol/L gadopentetate dimeglumine (Magnevist; Berlex Laboratories, Wayne, NJ) intravenously injected at 5 mL/sec. Intraarterial contrast-enhanced 3D FSPGR MR angiograms (5.2/minimal, 50° flip angle, 62.5-kHz bandwidth, 26 x 26-cm field of view, 2.4-mm section thickness, 0 skip, 256 x 128 x 116 matrix, one acquired signal, interpolation factor of 2) were obtained while 3–4 mL of gadopentetate dimeglumine was manually injected into the catheter at approximately 0.2 mL/sec. A mask image was acquired before contrast agent injection and subtracted from the MR angiographic data.
Necropsy
After all of the MR angiographic and endovascular procedures were completed, the animals were euthanized by means of pentobarbital (Henry Schein Pharmaceutical) overdose. Either of the operators performed necropsy on all animals. The bilateral common carotid arteries and the brachiocephalic artery were exposed through a midline incision in the neck. Gross pathologic examination was performed to look for perforation and dissection.
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Results
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Intravenous contrast-enhanced 3D MR angiography depicted the vascular anatomy of domestic pigs (Fig 2), which differs from that of humans (28). In pigs, there are two great vessels stemming from the aortic arch: the brachiocephalic artery and the left subclavian artery. The brachiocephalic artery branches into the right subclavian artery and an approximately 2-mm bicarotid trunk at an almost right angle. The bicarotid trunk divides into the left and right common carotid arteries. Therefore, the common carotid arteries are third-order vessels that require navigation at three branching points, which makes their catheterization more difficult than that of the coronary, renal, or mesenteric arteries, which are first-order vessels. Domestic pigs do not have cervical internal carotid arteries. The ascending pharyngeal arteries provide the major cerebral blood supply. These vessels form an arteriolar network at the skull base, the rete mirabile, which converges to form the ipsilateral intracranial internal carotid arteries and communicates with the contralateral side.
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Figure 2a. Intravenous contrast-enhanced 3D FSPGR MR angiograms (3.6/1, 30° flip angle, 62.5-kHz bandwidth, 32 x 29-cm field of view, 288 x 160 x 116 matrix, 2-mm section thickness, interpolation factor of 4, elliptic centric k-space sampling) show vascular anatomy in a pig. AP = ascending pharyngeal artery, BC = brachiocephalic artery, IM = internal maxillary artery, LA = lingual artery, LCC = left common carotid artery, LSC = left subclavian artery, RCC = right common carotid artery, RM = rete mirabile, RSC = right subclavian artery. (a) Anteroposterior MR angiogram of great vessels shows very short bicarotid trunk stemming from brachiocephalic artery at sharp angle (approximately 60°) and bifurcating into left and right common carotid arteries. Note absence of cervical internal carotid arteries. Cerebral blood supply is derived mainly from the ascending pharyngeal arteries, which form the rete mirabile more distally. The intracranial internal carotid arteries that arise from the rete mirabile are not shown. L = left, R = right. (b) On lateral MR angiogram, origin of bicarotid trunk is posterior to right subclavian artery. A = anterior, Ao = aorta, P = posterior.
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Figure 2b. Intravenous contrast-enhanced 3D FSPGR MR angiograms (3.6/1, 30° flip angle, 62.5-kHz bandwidth, 32 x 29-cm field of view, 288 x 160 x 116 matrix, 2-mm section thickness, interpolation factor of 4, elliptic centric k-space sampling) show vascular anatomy in a pig. AP = ascending pharyngeal artery, BC = brachiocephalic artery, IM = internal maxillary artery, LA = lingual artery, LCC = left common carotid artery, LSC = left subclavian artery, RCC = right common carotid artery, RM = rete mirabile, RSC = right subclavian artery. (a) Anteroposterior MR angiogram of great vessels shows very short bicarotid trunk stemming from brachiocephalic artery at sharp angle (approximately 60°) and bifurcating into left and right common carotid arteries. Note absence of cervical internal carotid arteries. Cerebral blood supply is derived mainly from the ascending pharyngeal arteries, which form the rete mirabile more distally. The intracranial internal carotid arteries that arise from the rete mirabile are not shown. L = left, R = right. (b) On lateral MR angiogram, origin of bicarotid trunk is posterior to right subclavian artery. A = anterior, Ao = aorta, P = posterior.
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Either of the two operators performed transfemoral catheterization of the carotid arteries a total of 24 times in the six animals. It took approximately 10–15 minutes to obtain a sagittal road map image of the aortic arch and a coronal vascular road map image of the bifurcation of the carotid arteries. Catheterization of the common carotid artery from the femoral artery access point was typically accomplished within 5 minutes (closer to 1–2 minutes toward the end of the study, as experience was gained). A typical sequence of the steps involved in bilateral carotid artery catheterization is shown in Figures 3 and 4. Confident real-time visualization of the catheter and the guidewire tip allowed simultaneous turning and pushing of the catheter and the guidewire, greatly facilitating the identification and selection of various target vessels (Movies 1 and 2, radiology.rsnajnls.org/cgi/content/full/2341031951/DC1). There was no evidence of vascular injury at gross pathologic examination of the necropsy specimens.
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Figure 3a. Sagittal contrast-enhanced MR angiograms (9/3, 30° flip angle, 10-mm section thickness, 30 x 30-cm field of view, 62.5-kHz bandwidth, 256 x 128 matrix) of aortic arch show catheterization of brachiocephalic artery (BCA) with active-tracking devices. Active-tracking catheter is marked by green square, yellow circle, and cyan triangle; guidewire is marked by magenta cross. (a) Active-tracking catheter and guidewire are placed in descending thoracic aorta (Ao). CCA = common carotid artery, L = left, LSCA = left subclavian artery, R = right. (b) Catheter tip is turned toward orifice of brachiocephalic artery. (c) Active-tracking guidewire is used to probe brachiocephalic artery. (d) After guidewire is inserted into brachiocephalic artery, catheter is advanced over wire into this vessel.
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Figure 3b. Sagittal contrast-enhanced MR angiograms (9/3, 30° flip angle, 10-mm section thickness, 30 x 30-cm field of view, 62.5-kHz bandwidth, 256 x 128 matrix) of aortic arch show catheterization of brachiocephalic artery (BCA) with active-tracking devices. Active-tracking catheter is marked by green square, yellow circle, and cyan triangle; guidewire is marked by magenta cross. (a) Active-tracking catheter and guidewire are placed in descending thoracic aorta (Ao). CCA = common carotid artery, L = left, LSCA = left subclavian artery, R = right. (b) Catheter tip is turned toward orifice of brachiocephalic artery. (c) Active-tracking guidewire is used to probe brachiocephalic artery. (d) After guidewire is inserted into brachiocephalic artery, catheter is advanced over wire into this vessel.
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Figure 3c. Sagittal contrast-enhanced MR angiograms (9/3, 30° flip angle, 10-mm section thickness, 30 x 30-cm field of view, 62.5-kHz bandwidth, 256 x 128 matrix) of aortic arch show catheterization of brachiocephalic artery (BCA) with active-tracking devices. Active-tracking catheter is marked by green square, yellow circle, and cyan triangle; guidewire is marked by magenta cross. (a) Active-tracking catheter and guidewire are placed in descending thoracic aorta (Ao). CCA = common carotid artery, L = left, LSCA = left subclavian artery, R = right. (b) Catheter tip is turned toward orifice of brachiocephalic artery. (c) Active-tracking guidewire is used to probe brachiocephalic artery. (d) After guidewire is inserted into brachiocephalic artery, catheter is advanced over wire into this vessel.
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Figure 3d. Sagittal contrast-enhanced MR angiograms (9/3, 30° flip angle, 10-mm section thickness, 30 x 30-cm field of view, 62.5-kHz bandwidth, 256 x 128 matrix) of aortic arch show catheterization of brachiocephalic artery (BCA) with active-tracking devices. Active-tracking catheter is marked by green square, yellow circle, and cyan triangle; guidewire is marked by magenta cross. (a) Active-tracking catheter and guidewire are placed in descending thoracic aorta (Ao). CCA = common carotid artery, L = left, LSCA = left subclavian artery, R = right. (b) Catheter tip is turned toward orifice of brachiocephalic artery. (c) Active-tracking guidewire is used to probe brachiocephalic artery. (d) After guidewire is inserted into brachiocephalic artery, catheter is advanced over wire into this vessel.
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Figure 4a. Two-dimensional phase-contrast MR angiographic vascular road maps (9/3, 30° flip angle, 10-mm section thickness, 30 x 30-cm field of view, 62.5-kHz bandwidth, 256 x 128 matrix) show catheterization of bilateral common carotid arteries with active-tracking devices. Active-tracking catheter is marked by green square, yellow circle, and cyan triangle; guidewire is marked by magenta cross. (a) Active-tracking catheter is placed in brachiocephalic artery. Active-tracking guidewire is in right subclavian artery, which is direct continuation of brachiocephalic artery. BCT = bicarotid trunk, L = left, LCCA = left common carotid artery, LEJV = left external jugular vein, R = right, RCCA = right common carotid artery, REJV = right external jugular vein. (b) Catheter and guidewire are pulled back and twisted to point to left common carotid artery. (c) Guidewire is inserted into left common carotid artery. (d) Catheter is advanced over guidewire into left common carotid artery.
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Figure 4b. Two-dimensional phase-contrast MR angiographic vascular road maps (9/3, 30° flip angle, 10-mm section thickness, 30 x 30-cm field of view, 62.5-kHz bandwidth, 256 x 128 matrix) show catheterization of bilateral common carotid arteries with active-tracking devices. Active-tracking catheter is marked by green square, yellow circle, and cyan triangle; guidewire is marked by magenta cross. (a) Active-tracking catheter is placed in brachiocephalic artery. Active-tracking guidewire is in right subclavian artery, which is direct continuation of brachiocephalic artery. BCT = bicarotid trunk, L = left, LCCA = left common carotid artery, LEJV = left external jugular vein, R = right, RCCA = right common carotid artery, REJV = right external jugular vein. (b) Catheter and guidewire are pulled back and twisted to point to left common carotid artery. (c) Guidewire is inserted into left common carotid artery. (d) Catheter is advanced over guidewire into left common carotid artery.
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Figure 4c. Two-dimensional phase-contrast MR angiographic vascular road maps (9/3, 30° flip angle, 10-mm section thickness, 30 x 30-cm field of view, 62.5-kHz bandwidth, 256 x 128 matrix) show catheterization of bilateral common carotid arteries with active-tracking devices. Active-tracking catheter is marked by green square, yellow circle, and cyan triangle; guidewire is marked by magenta cross. (a) Active-tracking catheter is placed in brachiocephalic artery. Active-tracking guidewire is in right subclavian artery, which is direct continuation of brachiocephalic artery. BCT = bicarotid trunk, L = left, LCCA = left common carotid artery, LEJV = left external jugular vein, R = right, RCCA = right common carotid artery, REJV = right external jugular vein. (b) Catheter and guidewire are pulled back and twisted to point to left common carotid artery. (c) Guidewire is inserted into left common carotid artery. (d) Catheter is advanced over guidewire into left common carotid artery.
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Figure 4d. Two-dimensional phase-contrast MR angiographic vascular road maps (9/3, 30° flip angle, 10-mm section thickness, 30 x 30-cm field of view, 62.5-kHz bandwidth, 256 x 128 matrix) show catheterization of bilateral common carotid arteries with active-tracking devices. Active-tracking catheter is marked by green square, yellow circle, and cyan triangle; guidewire is marked by magenta cross. (a) Active-tracking catheter is placed in brachiocephalic artery. Active-tracking guidewire is in right subclavian artery, which is direct continuation of brachiocephalic artery. BCT = bicarotid trunk, L = left, LCCA = left common carotid artery, LEJV = left external jugular vein, R = right, RCCA = right common carotid artery, REJV = right external jugular vein. (b) Catheter and guidewire are pulled back and twisted to point to left common carotid artery. (c) Guidewire is inserted into left common carotid artery. (d) Catheter is advanced over guidewire into left common carotid artery.
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Intraarterial contrast-enhanced MR angiographic findings confirmed the catheter position. As shown in Figure 5, the distal common carotid artery and its major branches were visualized better at intraarterial contrast-enhanced MR angiography than at intravenous contrast-enhanced MR angiography. The ascending pharyngeal artery, a 1–2-mm vessel, was clearly identified. Even the intracranial internal carotid arteries could be seen emanating from the rete mirabile.
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Figure 5a. Intraarterial contrast-enhanced 3D FSPGR MR angiograms (5.2/minimal, 50° flip angle, 62.5-kHz bandwidth, 26 x 26-cm field of view, 2.4-mm section thickness, skip of 0, 256 x 128 x 116 matrix, one acquired signal, interpolation factor of 2) of distal carotid artery branches. AP = ascending pharyngeal artery, CC = common carotid artery, IC = intracranial internal carotid artery, IM = internal maxillary artery, LA = lingual artery, RM = rete mirabile. (a) Anteroposterior MR angiogram. Catheter is placed in midcervical right common carotid artery. Distal branches of common carotid artery are clearly depicted. The intracranial internal carotid artery, a 1-mm vessel, also can be seen. L = left, R = right. (b) Lateral MR angiogram. A = anterior, P = posterior.
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Figure 5b. Intraarterial contrast-enhanced 3D FSPGR MR angiograms (5.2/minimal, 50° flip angle, 62.5-kHz bandwidth, 26 x 26-cm field of view, 2.4-mm section thickness, skip of 0, 256 x 128 x 116 matrix, one acquired signal, interpolation factor of 2) of distal carotid artery branches. AP = ascending pharyngeal artery, CC = common carotid artery, IC = intracranial internal carotid artery, IM = internal maxillary artery, LA = lingual artery, RM = rete mirabile. (a) Anteroposterior MR angiogram. Catheter is placed in midcervical right common carotid artery. Distal branches of common carotid artery are clearly depicted. The intracranial internal carotid artery, a 1-mm vessel, also can be seen. L = left, R = right. (b) Lateral MR angiogram. A = anterior, P = posterior.
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Discussion
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With use of active MR tracking devices, transfemoral catheterization is feasible within a time frame that is acceptable for clinical applications. In the present study, because a large imaging volume was used to determine the 3D coordinates of the receiver coils, the active MR tracking devices were always in the field of view and were equally well visualized in all orientations. The rapid frame rate and easy identification of the catheter and guidewire tip allowed manipulation of the catheters and guidewires in a manner similar to the manipulation possible with radiographic guidance. Because more than one coil was placed on the tracking device, the orientation of the device tip could be deduced by means of foreshortening between the two icons.
The active MR tracking method described in this study is truly acquisition independent; subject motion is not detected unless the road map is updated periodically. Although the immobility of the cervical and cerebral arteries in anesthetized animals alleviated the need to update the vascular road map, on several occasions we added a 1-second FSPGR pulse sequence to the active MR tracking pulse sequence at various intervals. We found that the addition of this pulse sequence every 10 seconds did not interfere with active tracking.
The active MR tracking software also includes a feature that enables one to select an imaging plane that is defined according to the location of the two receiver coils on the catheter, facilitating an update of the vascular road maps. To catheterize a mobile artery such as the coronary artery, more frequent image acquisition will be required and will slow down the active tracking. However, this difficulty may be resolved by using cine-loop coronary MR angiographic acquisition synchronized to electrocardiography.
One limitation of the study was the lack of direct temperature measurement of the active MR tracking device. Radiofrequency heating of the active-tracking guidewire has been reported in previous studies (29,30); however, we neither detected an increase in temperature of the active-tracking devices nor observed evidence of thermocoagulation when the devices were removed from the animal. Better grounding with use of the isolation module and the use of microcoaxial cables for connection may have reduced the effects of increased temperatures that have been observed in other studies (29,30). In the future, the use of inductively coupled receiver coils may eliminate the need for a long conductive cable, further improving the safety of active-tracking devices (31). The recent U.S. Food and Drug Administration approval of an endoluminal imaging guidewire (21) is very encouraging for the future development of active-tracking devices. Nevertheless, direct temperature measurement is required to address this safety issue.
In the current study, we did not take full advantage of multiplanar MR angiography road maps because the animal vasculature can be easily visualized by using projectional road maps and anatomic landmarks. To catheterize abnormal and tortuous vessels in patients, multiplanar MR imaging road maps will be required. Subsecond updating of vascular road maps will also be necessary to compensate for patient movement, as well as respiratory and cardiac motion.
Catheter-directed contrast-enhanced MR angiography of carotid arteries may help in identifying trickle flow with severe carotid artery stenosis and thus help in selecting the appropriate treatment candidates. Selective Wada tests may also be improved with MR imaging guidance because the distribution of anesthetic agents mixed with contrast material can be directly visualized. In addition, after anesthetic injection, functional MR imaging may be combined with neurologic examination to characterize functional areas in the brain. Much more important than these potential diagnostic applications are the opportunities to perform interventions that would benefit from an MR imaging tissue-monitoring system that carotid artery catheterization with real-time MR imaging guidance could generate. These interventions include intraarterial thrombolysis for acute stroke (32), carotid angioplasty and stent placement (33–35), intraarterial infusion of drugs for vasospasm treatment (36), and tumor embolization. The availability of concomitant procedures for blood flow measurement, tissue physiologic feature characterization, and functional assessment may improve the clinical outcomes of selected groups of patients who are now being treated without direct monitoring methods and/or with delayed assessment.
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ACKNOWLEDGMENTS
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We are indebted to Michael Baytion, MD, and Gaurav Gupta, MD, for their editorial help and to Joy Hirsch, PhD, Van Corbin, David Liss, and Donna See for their guidance.
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FOOTNOTES
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Abbreviations: FSPGR = fast spoiled gradient-recalled acquisition,
3D = three-dimensional
See also the other article by Feng et al
in this issue.
C.L.D. is the inventor of the MR tracking method described in this article, which is owned by General Electric Global Research Center. R.D.D. is one of the patent holders of this MR tracking method.
Author contributions: Guarantors of integrity of entire study, J.P.S., C.L.D.; study concepts, L.F., J.P.S., C.L.D.; study design, L.F., J.P.S., C.L.D., R.D.D., R.G.; literature research, L.F., R.L.D.; experimental studies, L.F., J.P.S., S.D., P.L.B.; data acquisition, L.F., S.D., P.L.B.; data analysis/interpretation, L.F., J.P.S., R.L.D., S.D.; manuscript preparation, editing, and revision/review, L.F., C.L.D., R.L.D., J.P.S.; manuscript definition of intellectual content, L.F., C.L.D., J.P.S.; manuscript final version approval, L.F., J.P.S.
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L. Feng, C. L. Dumoulin, S. Dashnaw, R. D. Darrow, R. L. DeLaPaz, P. L. Bishop, and J. Pile-Spellman
Feasibility of Stent Placement in Carotid Arteries with Real-time MR Imaging Guidance in Pigs
Radiology,
February 1, 2005;
234(2):
558 - 562.
[Abstract]
[Full Text]
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ABSTRACT
INTRODUCTION
