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prototypes that can be modi
ed for new visualization techniques or evaluationmetrics
with minimal additional development work, such as the Perk Tutor platform [ 11 ].
Skill levels and performance scores of trainees are essential in any training
program. Access to position data in tracked ultrasound and needle systems can be
used to record tool trajectories, which correspond to hand motions of trainees.
Recorded tool trajectories can be used in many ways to compute objective per-
formance metrics. The most common performance metrics are total procedure time
and needle insertion time. The latter corresponds to the total amount of time when
the needle was inside the phantom. An important motion economy parameter is
total needle path inside the phantom. Longer needle paths add up from multiple
reinsertions and probing. These are clinically proven risks for infection and
bleeding complications, therefore they are always good to be treated as primary
measures of skill. Novice operators often do sideways or rotating motions with the
needle, which is not recommended because the needle inside the tissue bends,
which cannot be directly seen, so aiming at the correct target becomes more dif-
ficult. Sideways needle motion can be measured using the potential tissue damage
parameter [ 7 ]. Procedures have speci
c success criteria that can be measured or
observed during practice insertions to compute success rate. In case of lumbar
puncture phantoms, the arti
cial spinal canal is usually
filled with water, so the
back
nes successful completion of the
procedure. In facet joint injections or other nerve blocks the position of the needle
tip may de
fl
ow of that water through the needle de
ne success or failure. These metrics are readily implemented in the Perk
Tutor platform.
Cost of the training system can be reduced by simulated ultrasound. Low cost
training simulators are important because none of the training enhancement tech-
nologies substitute a good amount of hands-on practice. Trainees should ideally be
given opportunity to deliberately practice until leaning objectives are met. Trackers
are typically an order of magnitude less expensive devices compared to ultrasound
machines. And ultrasound compatible training phantoms wear out over hundreds of
needle insertions, which deteriorate ultrasound image quality. Simulated ultrasound
can be generated from the tracked position of a needle and a non-functional
ultrasound transducer. Simulated ultrasound has been shown to be useful in
learning ultrasound skills usable with real ultrasound [ 12 ]. An open-source ultra-
sound simulator is available in the PLUS software library.
10 Extending Needle Navigation Techniques
Position tracking of the ultrasound and the needle extends the possibilities in
ultrasound-guided needle insertion techniques. Direct visual aiming is only possible
with conventional ultrasound when the needle is parallel to the ultrasound imaging
plane. This is called the in-plane insertion technique (Fig. 13 a). The out-of-plane
technique (Fig. 13 b) is more challenging, because the transducer needs to be moved
back and forth, and the needle position needs to be assessed mentally from multiple
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