Taking surgery into an MRI
Ashley L. Brenon
Surgeons can acquire magnetic resonance images during an operation to resolve spatial relationships and to evaluate whether their objectives have been achieved — but only if they pause the operation. Dr. Garnette R. Sutherland and his colleagues at the University of Calgary in Alberta, Canada, are working to change that. They have developed an MRI-compatible robot that allows microscale brain surgery within a near real-time magnetic resonance image. The development offers more than the convenience of interruption-free surgery. The scientists expect advances in accuracy, patient recovery and education.
They partnered with engineers at MacDonald, Dettwiler and Associates Ltd. of Richmond, British Columbia, Canada, the designers of the US space shuttle’s mechanical arm. Chosen for their experience in remote operation, sensory information and manipulation technologies, the engineers encountered challenges no previous project had presented. Most notably, the group had to create a system that could operate safely in a sterile surgical suite within a strong magnetic field. The requirement eliminates many materials and any sensors that employ magnetic fields. The team chose titanium and a plasticlike compound called PEEK for most of the construction.
The neuroArm’s tool holder interfaces with many specially designed tools, including those for soft-tissue manipulation, needle insertion and blunt dissection.
Dubbed the neuroArm, the device is mounted on a mobile base inside the MRI system. Surgeons view the surgical site, control the arms and collect data at a workstation.
Two arms, deployed into the imaging field, are manipulated with handlike controllers. With 7° of freedom, the arms’ ends are equipped with three-dimensional force sensors that quantify tissue deformation and provide surgeons with a sense of touch.
As with the focus knobs on a microscope, the device moves in coarse and fine modes: coarse motion for broad extracranial displacement, such as moving to the work site or changing tools, and fine mode, for the small, precise motion within the brain. The device allows spatial accuracy of 50 μm, as compared with the human hand, which can maintain accuracy only within 1 to 2 mm.
The surgical microscope, equipped with two high-definition Ikegami cameras, provides three-dimensional stereoscopic video. Images of the operation site, the virtual image of the robot in space and a view of the entire operation site are projected to the workstation and operating room on high-definition displays.
Surgical simulation software allows the user to determine the optimal incision site and to plan a path that avoids critical structures. Particularly useful for students, the software permits risk-free rehearsals on patient-specific virtual brains and playback of past procedures.
In addition to viewing the actual surgical site, the surgeon can conceptualize how the operation affects other areas of the brain.
The researchers anticipate that the device will decrease risk, minimize complication rates and shorten recovery times. They are developing training programs and exploring how the technology may be used in other types of surgeries.
They plan to operate on their first patient this summer.
- An instrument consisting essentially of a tube 160 mm long, with an objective lens at the distant end and an eyepiece at the near end. The objective forms a real aerial image of the object in the focal plane of the eyepiece where it is observed by the eye. The overall magnifying power is equal to the linear magnification of the objective multiplied by the magnifying power of the eyepiece. The eyepiece can be replaced by a film to photograph the primary image, or a positive or negative relay...
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