Author :
Ms. Shao Wei
Last Updated : 1 October 2004
Sinus Surgery
Introduction
Sinuses are air filled chambers located inside the skull - under and between
the eyes, just behind the nose, and in the forehead. They are attached to the
nasal passages via small tubes, which allow drainage to take place to clean the
nose. When bacteria infects the sinus cavities, sinusitis may occur due to
blockage of the small tubes attached to the nasal passages. In America, nearly
50 million persons suffered from it annually.
Sinus surgery is required to remove diseased tissues and recover the proper
drainage. The common surgery now is functional endoscopic sinus surgery, which
made the operation minimum invasive compared to the old open surgeries. But it
also bring a big concern when the endoscope and the surgical tools are inserted
and navigated inside the sinus region beyond the surgeon's view. Because the
sinuses are physically close to brain tissue and eyeball, the surgeons often do
not dare probe certain areas for fear of touching something they should not.
Therefore, diseased tissues are sometimes still left behind. To overcome this
problem, the image-guided surgery (IGS) systems were introduced, as provided by
GE MEDICAL, MEDTRONIC XOMED, and BRAINLAB. The most advantage of these systems
is that it shows the location of the surgical tool on the pre-operative medical
images, with which the surgeon can be aware what was going on inside the sinus
and thus avoid those subtle regions. However, it is effort-taking for the
surgeon to relate the tool movement from the three orthogonal views with the
actual movement in physical space. And it is still confined to 2D display. To
overcome these problems, Augmented Reality (AR) assisted sinus surgery is
proposed. This system will enhance the sinus surgery with
"see-through" effort, providing pre-operative CT images superimposed
on the real patient. This could better help the surgeon to plan, rehearse and
perform the surgery more interactively and confidently.
Hardware of the system includes four modules: (1) a Tracking/Detection/
Imaging (TDI) unit, (2) a stereo display device, (3) a graphic workstation, and
(4) a movable cart with one or two passive arms. A stereo camera is installed in
the TDI unit for 3D tracking purpose. A structure light projector is integrated
with the stereo camera to precisely capture object surface. The movable cart is
used to carry the TDI unit, the display device, and the surgical tools.
Software will be made up from three modules, i.e., registration, tracking,
and display modules. Registration is the determination of a one-to-one mapping
or transformation between the coordinates in two spaces, so that the
corresponding anatomic structures can be matched. To avoid invasive marker
implantation on patient, a surface-based registration method is utilized, which
is totally based on the inherent geometric similarity between surfaces. The
rigid forehead is chosen as the surface to be register between the pre-operative
CT images and the physical space in the operative room due to its availability
during operation and its rigidity. The pre-operative surface of the forehead
could be easily extracted from CT images. The other intra-operative forehead
surface was obtained through the real-time capture via structure light. Once the
two surfaces were registered, the virtual reality would be merged with the real
scene, hence the virtual display of the occluded surgical tool tip. Approaches
for tracking usually include optical tracking, magnetic tracking and mechanic
tracking. The first one is realized by identifying objects or markers attached
onto objects by intensity contrast in video; the second kind locates the object
via magnetic sensors in a purposely-introduced magnetic field; the third one is
usually used in medical robots, dependent on the encoder to resolve the
component movement. Currently both optical and mechanical tracking systems are
employed routinely image guided surgery procedure, and these devices can
generally relatively a tracking accuracy of submillimeter.
Relationship of the central components is shown in Figure 1. Registration and
tracking are connected through the spatial transformations between different
components in the AR assisted sinus surgery system.
Figure 1. Spatial transformations in the AR
assisted sinus surgery system. HTL is the transformation between the coordinate
system of the optical tracking device, and the LED infra-red emitters on the
surgical tool. HLP is relates the infra-red emitters to the tip of the tracked
surgical tool. HWT represents the transformation between the tracking device and
the "world" coordinate system (the physical patient). HPW is the
transformation that maps the medical images to the patient coordinate, which is
worked out through registration.
This system is equally valuable for rehearse and surgical navigation. And it
will be especially helpful for patients who lose anatomical landmark due to
infection or revised surgery as navigation based on educated guess becomes more
difficult.
Publications related to Sinus
Surgery.
We would be glad if you could sign our guest
book.
For more information, please contact the principal investigator:
A/P Ng Wan Sing
School of Mechanical &
Aerospace Engineering
Nanyang Technological University
Nanyang Avenue, Singapore 639798
Fax:(65) 6791 1859
Hospital Partner
Dr. Peter Lu
Head of Div. of Otolaryngology
Changi General Hospital
Singapore
Fax: (65) 6781 6435
