Biomedical Engineering Reference
In-Depth Information
information about only one point is provided, and the surgeon needs to look
away from the surgical field to a computer screen.
A better method is to provide overlays directly on the surgical view (Figure
12.4b). For neurosurgery, the use of the operating microscope for this purpose
was originally proposed by Kelly
63
and continued by Roberts.
11
Simple out-
lines or trajectories in one eyepiece have now become standard. The use of
separate overlays in the left and right eyepieces can further enhance the sur-
geon's ability to relate preoperative image data to the intraoperative scene.
We have demonstrated such a stereo system in which segmented structures
from a preoperative scan can be perceived by most people to be sitting
beneath the viewed surface as though the tissue is transparent.
56
An alternative approach is to place a reflecting screen over the patient. A
system proposed in 1938 used x-rays to place a small light source opposite a
bullet or fragment of shrapnel so that the reflection in a half-silvered mirror
could guide the surgeon to the target.
64
Peuchot has developed this method
to incorporate two reflecting surfaces at slightly different angles to enable
projection of stereo graphics onto the patient for spinal surgery.
65
Stereo-
scopic graphics can also be produced using a polarized light, switched by an
active filter screen over the monitor or glasses, to direct a different view to
each eye. Such screens have been proposed for use in preoperative planning
66
and surgical guidance.
67
With any image guidance application it is important to consider how the
therapist will view and interact with the data. Treatment room ergonomics is
an important factor, especially in the already crowded operating room. With
interactive image guidance it is vital not only that the information is pre-
sented in a simple and easy to interpret manner, but also that the clinician is
made aware of possible inaccuracies in the system.
12.7
Conclusions
The applications of therapy guidance using data from images taken before an
intervention have been examined. Simple tracking of pointers or tools has
been presented, along with the enhancement of registration using readily
available intraoperative imaging modalities—video, fluoroscopy, ultrasound,
and iMRI.
As the abundance and quality of data available from intraoperative imag-
ing increases, one may wonder whether alignment of preoperative images to
the patient has a future. However, images from diagnostic scanners are also
developing apace, with higher resolution, better contrast, and more func-
tional data becoming feasible. Applications such as functional MRI, where
considerable scanning and processing time is required, provide information
that cannot currently be acquired in real time during treatment, and which
may more appropriately be obtained prior to treatment when the patient is
alert and there is sufficient time for a comprehensive set of functional tests.
