Tracked Ultrasound in Navigated Spine Interventions - Spinal Imaging and Image Analysis - page 471

calibration methods, data acquisition, and data processing methods (e.g. 3-D vol-
ume reconstruction) [ 3 ]. PLUS is distributed under a permissive open-source
license that allows both academic and commercial use without restrictions ( www.
plustoolkit.org ) . PLUS provides real-time data streams to end-user applications.
Applications can be rapidly prototyped in the 3D Slicer framework ( www.slicer.org ) .
The advantage of 3D Slicer is that hundreds of medical image processing algorithms
are implemented and deployed in this framework. They are readily available, and can
be used for visualization that best helps intervention navigation.

9 Tracked Ultrasound in Interventions Training

Long learning curve is probably the only disadvantage of ultrasound guidance in
spinal needle placement procedures [ 1 ]. The interpretation of musculoskeletal
ultrasound images is dif cult, and the operator has to do it in real time during

interventions, while manipulating the ultrasound transducer in one hand and insert a
needle with the other hand. This challenge is largely related to visuospatial coor-
dination skills. Ideally, these necessary skills are learned before they are

rst per-
formed on patients. Learning in a simulated environment on phantom models is not
only safer for patients, but is also shown to improve the learning process [ 4 ].
Phantom models are proven tools in teaching spinal needle insertions to prepare
medical residents for patient encounters [ 5 ]. Needle coordination skills in dif cult

procedures can be improved by providing augmented reality visual feedback while
practicing the procedures on phantom models [ 6 , 7 ].
Objective measurement of operator skills is of utmost importance in procedural
skills training. Medical training is currently transforming according to the principles
of competence-based medical education. The goal of this trend is to assure proper
acquisition of skills before physicians perform interventions on patients. This
demand requires simulation-based training and quantitative performance feedback
for the trainees, as well as quantitative evaluation of skills. Teaching of ultrasound-
guided spine interventions can greatly bene

t from tracked ultrasound technology,
both as an augmented reality system for improving visuospatial skills, and using
tracking to objectively analyze hand motion data for skills evaluation. Systems with
position tracking are inherently able to record motion trajectories that can be
analyzed for qualitative and quantitative measures of procedural pro

ciency.

Algorithms borrowed from arti cial intelligence are shown to be able to classify

motion gestures [ 8 ] and skill levels of the operator [ 9 , 10 ].
Sonographic anatomy of the spine is dif cult to master due to poor visibility and

the complex shape of vertebrae. Tracked ultrasound along with tracked needle
offers an excellent augmented reality training system. 3-D anatomical models of the
training phantoms can be registered to the navigation scene to show what structures
are responsible for characteristic features on the ultrasound image. When the needle
is inserted incorrectly, the 3-D scene shows the trainee the exact relation of the
actual needle position and the target point in relation to the spine anatomy. The