Magnetic Trackers: Robot Control and Vasculature Imaging - Microsurgery: Advances, Simulations, and Applications - page 252

Tracking System (NDI Corp., CA), with magnetic sensors with 1.8
mm diameter and 8 mm length, were used for motion capture of the
catheter with six degrees of freedom (DOF). The magnetic sensor
was installed on the tip of IVUS catheter to obtain its posture. The
position precision is 0.30 mm, and that for orientation is 0.20 ° . After
connecting the hybrid probe to the VH TM IVUS Imaging System, a
PXC200-AL video capture card was used with sampling rate of 20
frames per second (fps). An additional hybrid probe was built using
a 5DOF micro tracker and a Visions PV.018 IVUS (20 MHz) (Fig.
7.21(b)).

7.5.2 Estimation of Disturbance on Magnetic Tracker

Measurements

The transducer of the IVUS catheter used in the experiment belongs
to the type of multi-element array, which can obtain a 360 ° cross-
sectional image and the ultrasound beam direction and delection
on the display is synchronized [17]. Miniaturized piezoelectric
transducers are positioned at the tip to allow small diameter and
high-resolution image. Piezoelectric transducers may induce changes
on the magnetic ield, which may cause dynamic disturbances
to the magnetic sensor when close to each other. To quantify the
magnitude of this disturbance, measurements with the hybrid probe
were done inside a silicone tube illed with glycerin and ixed to a
PMMA frame. The disturbance was measured at ive locations over
a line separated by 20 mm from each other; the measurement was
repeated with the silicone tube placed at four different directions in
XZ plane. Posture samples from the magnetic tracker were captured
during 10 seconds for each location on every direction to measure
the dispersion of the samples with IVUS probe enabled and disabled.
The disturbance measurements were done with the 5DOF hybrid
probe. The dispersion for a single point is shown in Fig. 7.22, the
average radius of dispersion r for the four measured directions is
shown in Fig. 7.22, r is less than 1.5 mm for all measurements, r
increased 1 mm when the IVUS is enabled. This enables imaging of
aorta because its diameter is above 20 mm.