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Computer-Assisted Imaging
Improving Neurosurgical Efficiency and Safety
Limited 3-D applications of MR/CT imaging have only recently been integrated into clinical practice as applied craniofacial reconstruction or cranioplasty. Three-dimensional imaging to neurosurgery, both preoperatively and intra-operatively, currently available at Rady Children’s includes the use of:
“Since increases in the availability of anatomical information contribute to surgical approach and outcome, we have integrated a virtual imaging system into our operating practice,” said Dr. Michael Levy, director of Rady Children’s Division of Neurosurgery. “We have developed a new head-mounted display (HMD) that allows surgeons to visualize surgical fields with high-resolution stereoscopic vision while allowing free movement of the surgeon.” Dr. Levy said computer-generated images including CT, MRI, and three-dimensional reconstructions can be simultaneously displayed. “By improving the surgeon’s situation awareness, visualization of depth, and access to navigational information, this technology results in improved surgical efficiency and safety in both endoscopic and open microsurgical procedures,” he said. Most endoscopic surgery systems display the camera imagery on a large video monitor positioned away from the surgeon, which results in the surgeon looking up and away from the patient to view the monitor. In addition, the orientation of the surgeon’s body and hands to the patient is often different from the monitor-viewing angle. With an HMD the imagery remains in view regardless of head or body movement and allows for the overlay of radiographic images in a picture-in-picture format. The surgeon either views the deep-field imagery or simply glances downward to directly view the surgical field. The imagery provided by the HMD allows the surgeon to assume any posture that is comfortable while providing improved situation awareness. HMD simulations allow for rehearsals of the procedure before surgery and maximize teaching. Connection to inter- and intrafacility networks will allow the surgeon to review distant images on the HMD allowing for telemedicine applications over a broadening patient base.
Volume-rendering, as a technique, allows for perspective rendering of anatomic detail. That is, anatomic features may be viewed from an internal perspective and hollow cavities, such as the ventricular system of the brain, can be rendered with striking detail. “The most obvious application of virtual imaging is the use of reconstructions in the operating room for comparison with actual anatomic findings during a procedure,” said Dr. Michael Levy, director of Rady Children’s Division of Neurosurgery. “Virtual imaging can also be used for preparation of virtual endoscopic reconstructions to allow for peri-operative visualization.” Currently the neurosurgery division uses two modalities for incorporation of the images into the operating room. The first is via the use of a CD-ROM to transfer a completed image array into the hardware in the operating room. Image-based workstations provide a second method for generating three-dimensional reconstructions directly from CT or MRI data. “Display 3-D is useful for globally viewing the reconstruction and evaluating its completeness and quality as well as performing simulated ‘walk-throughs’ and ‘walk-arounds’ through the anatomy,” said Dr. Levy. The computer can be operated via voice control. Images may be manipulated by varying image plane, fading tissue planes and stacking image slices. Comparison between preoperative and intraoperative views from multiple angles offers the surgeon maximum information. The virtual journey may be used traditionally as either surgical rehearsal or for strictly didactic purposes. However, “fly-throughs” are of particular benefit in the operating room in recognizing structures as the operation progresses. As a final application of the software, handheld anatomic models may be generated from the 3-D image files created on the CD-ROM or Indigo2 Workstation and are produced through a rapid-prototyping process. These stereolithographic techniques recently have been employed to create prosthetic devices for maxillofacial applications. More complex applications in craniofacial, cranial base surgery, and spinal instrumentation can be anticipated. Stereolithography has direct application in a number of facets of neurosurgical practice and education. In presurgical planning, the creation of a physical model eliminates the need to have a workstation available. Though stereoscopic visualization of all reformatted digital images can be performed using the workstation, the construction of stereolithographic models allows for a better understanding of the anatomy. In order to maximize the amount of anatomic information available to the surgeon during the procedure, the images can be displayed via a headmounted display system or via a picture-in-picture modification that Rady Children’s has integrated into the surgeon’s optics of its operating microscope. The modifications allow the surgeon to operate under the microscope with the benefit of an endoscopic view but without real-time use of an endoscope. With increasing technologies available for intraoperative use, the integration of advanced imaging and computerized anatomic environments remains incompletely characterized. Since increases in the availability of anatomical information contribute to surgical approach and outcome, Rady Children’s is currently integrating a virtual imaging system into it’s operative suite. “We have developed and employed a computerized system for neurosurgical intraoperative visualization which integrates real and virtual image modalities,” said Dr. Levy. Input to the system is via computer-based anatomic renderings. Three-dimensional images are generated from anatomic MRI, CT, or spiral CT data acquired preoperatively and are supplied on an interactive optical disk for use in the operating room. Corresponding actual and virtual images are displayed concurrently to the surgeon during the procedure using picture-in-picture technology and are available for manipulation in various planes by voice control. Interface is provided via a liquid crystal display, heads-up display that can be visualized via a headset or through the optics of the operating microscope. Input can be updated and provides an endoscopic view for the primary surgeon while working under the operating microscope without the need for the continuous use of an endoscope during surgery. These modalities supplement each other and are suitable for integration with frameless stereotaxy.
Children's Specialists Division of Neurosurgery © Children's Specialists of San Diego - Physician-to-Physician News - No.5, Spring 2003 |
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The development of minimally invasive surgery requires innovation in surgical technologies to maximize safety. There is no intrinsic reason why surgeons need not benefit from the remarkable capabilities of computer-generated anatomic environments provided today.
Computer-based anatomic renderings are commonly used by radiologists and surgeons, but have not been fully integrated into standard operating practice. Although numerous three-dimensional rendering systems are available, volume-rendered based systems provide a distinct advantage to the neurosurgeon.
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