IEEE Robotics & Automation Magazine - September 2018 - 73

involving the actuation and steering of
magnetic instruments describe active
actuation involving solenoid coils and
magnetic resonance (MR) scanners,
and passive actuation involving permanent magnets and electromagnets.
Recently, these actuation methods
have been adapted, and methods for
visualizing, controlling, and tracking
the instruments inside the human
body have been developed. In accordance with previous studies, catheters
are equipped with various magnetic components, e.g., ferromagnetic
spheres, steerable microcoils, and single- or multiple-permanent magnets
attached to the catheter body or tip
(Figure 2). The use of each particular
component has both benefits and limitations, which are highly dependent on
the framework used. Table 1 compares
the different catheter components used
in relevant studies.

Ferromagnetic Sphere

Catheter Body

Coils

Catheter Body

(a)

(b)

Permanent Magnets

Catheter Body

(c)
Permanent Magnet
Tether

Magnetically Actuated
Endovascular Catheter

Catheter
Body

Tether
Fix End
(d)

Figure 2. Four different catheter concepts showing (a) the use of ferromagnetic spheres
at the catheter tip, (b) a custom clinical-grade microcatheter prototype with a solenoid
coil at the distal tip adapted from [17], (c) multiple neodymium permanent magnets in a
flexible catheter, and (d) a permanent magnet connected to the distal end of a catheter
by a string-like tether [18].

Table 1. A comparison between catheter components (grouped according to
active and passive actuation) used in studies for magnetic navigation in endovascular procedures.
Catheter Components

Magnetic System
and Studies

Advantages

Limitations

Active Magnetic Actuation
Ferromagnetic spheres

MR scanner [21], [22]

●

●

●

More ferromagnetic material
allows for larger magnetic forces.
Artifacts caused by spheres can
be used for tracking.
Small spheres can be easily
removed to reduce artifacts.

●

●

●

Microcoils

MR scanner [5], [19],
[20], [23]-[25]

●

●

●

Can be guided under MR imaging navigation; hence, no radiation exposure.
Has the potential, as a radio-frequency transmitter-receiver, to
enhance imaging of soft tissues
near the catheter tip.
Reduced levels of artifacts can
be helpful for tracking of the
catheter tip.

●

●

●

●

Multiple ferromagnetic spheres
introduce undesired dipole-dipole
artifacts.
Heavy spheres cause the catheter
tip to drop and induce large slide
friction against vessel walls.
Only low saturation magnetization
materials can be used.
Resonant heating of coils requires
additional heat reduction
techniques.
DC current causes imaging-related
artifacts.
Fabrication of microcoils using the
laser lathe technique limits size.
Microcoils require high magnetic
fields and are restricted to active
actuation using MR scanners.

Passive Magnetic Actuation
Permanent magnets

Electromagnets [18],
[30], [31], [36], [38]
Permanent magnets
[32], [42], [88]

●

●

●

●

Can generate high deflection
forces.
Exhibits a large field-strength-tovolume ratio.
Can be manufactured in various
shapes and sizes.
Enables catheter tip to reach
difficult positions within the
vasculature.

●

●

●

Multiple magnets along the body
of a catheter are difficult to control
individually.
Multiple curvatures between
magnets cannot be adopted in
two-dimensional and 3-D, without
using support from vasculature
contact.
Most actuation systems use mathematical models related to singlemagnet-tipped catheters only.

september 2018

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IEEE Robotics & Automation Magazine - September 2018

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