IEEE Robotics & Automation Magazine - September 2018 - 76

direction, and gradient. The direction of a magnetized electrophysiology ablation catheter was automatically controlled
and allowed for accurate navigation. Today, the system exists
as one of the commercially available electromagnetic systems
[39] called the catheter guidance control and imaging (CGCI)
system, developed by Magnetecs Corporation. A noncommercial system, the Institute of Electrical Engineering (IEE)
Magnetic Navigation System (MNS) [40] provides real-time
navigation of a catheter in a beating heart and is under
development by the IEE, Chinese Academy of Sciences. As
opposed to the CGCI, the magnetic field of this system is
fairly homogeneous in the navigation region, such that only
sufficient torque is exerted on a catheter tip. The Aeon Phocus [41] is another noncommercial electromagnetic catheter
steering system for treating cardiac arrhythmias, and it
operates in a similar fashion to the CGCI with submillimeter accuracy.
In contrast, a commercially available catheter control system, the Niobe MNS, uses two permanent magnets to guide
magnetic catheters. Guidance is accomplished by mechanically rotating the magnets, which navigates catheters with magnetic tips. With regard to (1), deflection is achieved through
torque exerted by a magnetic field interacting with a permanent magnet in the catheter tip. The Niobe successfully dem-

onstrated the control of soft catheters having three magnets on
the distal tip in a study conducted by Choi et al. [42]. Results
from this study showed decreased radiation exposure and safe
and effective procedures [43]. Furthermore, Kratchman et al.
[32] demonstrated the guidance of a magnet-tipped rod along
arbitrary 3-D trajectories using a single, robot-manipulated
permanent magnet. The magnet was attached to a 6-DoF serial robot, which demonstrated trajectory following and obstacle
avoidance using resolved-rate motion control. Table 2 summarizes specifications of existing and representative technologies
concerning passive magnetic systems.
When considering actuation techniques, electromagnets
have often been preferred due to their ability to control the
field strength by changing the coil current [44]. However, substantial field generation results in a significant temperature
rise within the coils. The main advantage of permanent
magnets is that they exhibit a nondecaying magnetization
and do not require currents to generate a magnetic field as
with electromagnets [36]. This makes it difficult to use during studies that require instruments to track or visualize
catheters, which may be damaged by constant exposure to
magnetic fields [45].
Field adjustment is another factor that distinguishes permanent and electromagnetic actuation methods. Permanent

Table 2. A summary of four main passive magnetic systems for endovascular procedures.
Magnets
Actuation
System (Company)
IEE MNS1

Type

Number
(Maximum
Field)

Electromagnets

8 (0.22T)

(non-commercial)

CGCI2 (Magnetecs
Corporation)

8 (0.16T)

Aeon Phocus
(Aeon Scientific)

8 (0.10T)

Applications
and Studies

Reported
Accuracy

Aligned
spherically
surrounding the
subject's torso

Cardiac arrhythmias

11 mm

Placed around
the subject's
torso

Cardiac arrhythmia
mapping and ablation

Fixed position

Atrial fibrillation (AF)
ablation [38], [58], [91]

Placed around
the subject's
torso

Mapping and ablation
of arrhythmias, such
as AF [18], [34]

0.42 mm 3

Aligned
externally to
each side of
the subject

Radiofrequency
catheter ablation

11 mm

Mechanically
positioned using
computer-aided
motors

Ablation of AF [3],
[13], [27], [28], [42],
[77], [88], [89], [94]

Actuation

Arrangement

Electrophysiology [40]
1.9 ! 0.4 mm

Fixed position
with rotation
around subject
Niobe (Stereotaxis)

1IEE

Permanent
magnets

2 (0.08T)

MNS

2CGCI

3Based

on extrapolated data from the results of [33]. Limited information has been published on the Aeon Phocus. According to [18], the accuracy
depends greatly on the measurement conditions (operation inside a moving heart or in a static model).

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IEEE Robotics & Automation Magazine - September 2018

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