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Science to Practice |
Department of Radiology, National Naval Medical Center, 8901 Wisconsin Ave, Bethesda, MD 20889-5600; Department of Radiology and Radiological Sciences, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD.
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Remote guidance of surgical instruments during minimally invasive surgical procedures can improve navigation and guidance, provide three-dimensional modeling, and enhance operator dexterity (1). Remote guidance technology for manipulation of intravascular catheters and guide wires is less developed, and its advantages are less obvious. In this issue of Radiology, Schiemann et al (2) describe their use of a magnetic guidance system in the performance of subselective vascular catheterizations, and they demonstrate potential reductions in procedure time and fluoroscopy time.
The Science
Remote guidance of intravascular catheters by means of an external magnetic field was described more than 50 years ago, and use of this technique in humans was reported in 1991; however, the technology had been limited by the size and power of the external magnets used for guidance and the inability to manipulate the catheter in more than one plane (3). The recent development of multicoil superconducting electromagnets has permitted three-dimensional guidance and intravascular navigation in the brain and heart with magnet-tipped guide wires (3,4).
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The magnetic guidance system is integrated with a C-arm single-plane digital angiography system. Navigational guidance is performed with two fluoroscopic reference images of the target region, which are obtained at an angle of at least 41° from each other. No stereotactic frame is required.
Schiemann et al (2) compare the magnetic navigation system with conventional catheterization techniques in a generic glass model of a vascular bed and in a model of the hepatic arterial tree by using 0.014-inch magnet-tipped or standard nitinol guide wires and a coaxial microcatheter. Magnetically-guided catheterization had a greater success rate in the liver model, a significantly shorter procedure time in the liver model, and significantly shorter fluoroscopy times in both vascular models.
The Practice
Clinical use.—Fluoroscopically-guided interventional procedures have become increasingly complex and can result in high radiation doses (5). Radiation-induced patient injuries can result from cardiac electrophysiology examinations; coronary angioplasty; interventional neuroradiology procedures in the brain, face, and spine; embolization procedures anywhere in the body; transjugular intrahepatic portosystemic shunt creation; and angioplasty of vessels in the abdomen and pelvis (6,7). New catheter guidance methods that require less fluoroscopy time would be of immediate value for reducing patient radiation doses. Their value would be further enhanced if they also reduced total procedure time and enabled subselective catheterization of otherwise inaccessible vessels.
Future opportunities and challenges.—This guidance system is still in the early stages of development. Animal and human studies are necessary to prove the safety and efficacy of this system. The device needs to be smaller, with less restriction of C-arm rotation. Additional guidance capabilities that use rotational angiography, three-dimensional reconstructions, or biplanar images would be helpful in clinical use. A robotic mechanism for advancing and withdrawing the guide wire and microcatheter, in addition to deflecting the guide wire tip, would permit additional control. This might reduce fluoroscopy time even further. It might also allow truly remote guidance, with the operator positioned at a distance from the x-ray beam. This would reduce the operator’s radiation dose and might also improve ergonomics in the interventional fluoroscopy suite.
Summary
Schiemann et al (2) have shown in vitro that remote guidance of an intravascular guide wire may reduce procedure time and fluoroscopy time for subselective vascular catheterizations. Further development of this technology may permit complex fluoroscopically guided interventions to be performed with reduced radiation doses.
FOOTNOTES
See also the article by Schiemann et al in this issue.
The opinions expressed herein are those of the author and do not necessarily reflect those of the United States Navy, the Department of Defense, or the Department of Health and Human Services.
REFERENCES
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