Biomedical Engineering Reference
In-Depth Information
adult neurosurgery,
7-9,22,57
pediatric neurosurgery,
10
and ENT.
6
The method is
rapidly gaining acceptance.
Image-guided surgery is also well established in computer-assisted ortho-
pedic surgery. Systems are available for image-guided reconstructive hip
surgery, knee reconstruction and ligament surgery, trauma surgery, and
spinal surgery. In total hip replacement, image guidance allows accurate
alignment of the femoral head implant and orientation of the acetabular cup
using a computer model of the pelvis derived from CT. This is the basis of
the HipNav™ system.
21
Either bone-implanted markers visible on CT or the
surface of the bones of the pelvis are used for intraoperative registration. In
the latter, a pointer is used to palpate the bone during surgery, and an algo-
rithm similar to the ICP algorithm described in Chapter 3 is used for registra-
tion. The results of total hip replacements in 100 patients show improved
clinical outcomes and reduced soft tissue damage and incision length.
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The
KneeNav™ system for total knee replacement and anterior cruciate ligament
reconstruction has been developed using the same principles as HipNav.
Robotic devices such as the ROBODOC™
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are being introduced to provide
good registration, greater stability during cutting of the bone, and improved
accuracy of cutting. The ROBODOC pinless system uses a thin pointer to
collect bone surface points percutaneously on the distal femur
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and the
exposed proximal surface. The ROBODOC system drills the bone very accu-
rately according to the plan. As of April 1999, 2000 ROBODOC operations
had been undertaken successfully at BGU, Frankfurt, and as of September
2000 over two dozen systems were in operation in Germany.
In spinal surgery, image guidance methods allow accurate pedicle screw
placement. The pedicle is the strongest part of the vertebrae and therefore
ideal for screw type anchoring. Unfortunately, insertion of screws without
guidance has a high risk (10 to 40%) of incorrectly placed screws. One hundred
consecutive patients were randomly assigned to image-guided pedicle screw
insertion or the conventional manual method. For those with image guid-
ance, 0.4% (1 /219) had pedicle perforation, compared with 11.5% (32/277)
using the conventional method.
Interventional radiology attempts to provide surgery that is minimally
invasive by using small approach incisions and accurate guidance by intra-
operative imaging. If the guidance is by fluoroscopy, there may be features
visible in a preoperative CT scan that are not readily visible in the x-ray
image. These data can be overlaid on the fluoro image to aid the interventionist.
This process is shown in Figure 12.2, where an overlay of the aorta can be
used to help guide a catheter.
Radiotherapy does not require interactive display for the therapist, but
accurate alignment to the patient is vital for treatment to be given in accor-
dance with the plan. Immobilization in a molded plastic mask is the most
common technique to ensure that the patient is in the same position as he
was in the simulator room. Accuracy becomes even more important when
planning is performed using 3D scans in conjunction with techniques such as
conformal therapy or radiosurgery. Video registration may provide a means
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