MINOP II - Combined endo- and microscope manipulator system for image guided operations

Direct Development Partner

  • Aesculap AG & Co. KG, Tuttlingen
  • Neurosurgical Department of the Johannes Gutenberg-University of Mainz
  • Schölly Fiberoptic GmbH, Denzlingen


Completed project part at the Helmholtz-Institute of the RWTH Aachen University in the framework of the MINOP II joined project, funded by the German Ministry for Education and Research (BMBF).
(Project term: 10/2001-9/2004)
Funding contract number: 16SV1442/0


In the framework of the development of an electronical operation microscope for endoscopically assisted neurosurgical operations, a compact semirobotical platform for spatial manipulation of a stereoscopic camera ("Exoskop"€œ) was developed. It comprises of an innovative, multifunctional arch for the fixation of the platform on the operation table, a manual pre-positioning construction as well as a mechatronical unit for freehand intraoperative fine-positioning of the exoscope. The platform is controlled by the surgeon using a combination of voice control and head tracking. Modes are thereby activated by spoken commands, while head rotation is used to intuitively adjust the exoscope view. The system was implemented and evaluated with respect to its technical characteristics as well as man-machine interaction.


To fulfill the specific requirements of endoscopic and endoscopically assisted neurosurgical operations [1], a partial aspect in the framework of the MINOP II project was the completely electronic image acquisition, processing and display. Video images are acquired by an extracorporeal stereoscopic camera („exoscope“) and an application specific stereo-endoscope for the direct view on the intraoperative situs. Head-Mounted Displays (HMDs) are used for individualized image output. The achieved independence from conventional microscope oculars offers the surgeon and the assistants the option of a comfortable and ergonomical posture, as opposed so far to the usually irksome, enforced position adapted to the adjustment capabilities of the microscope [3].

For freehand control of the exoscope position and orientation, a telemanipulation platform as well as an application specific user interface were developed in the framework of the MINOP II project. As opposed to the relatively large, heavy and badly transportable current microscopes, the developed system was designed as a flexible, compact unit that can be mounted on any operation table by an innovative, multifunctional arch.


Fig. 1: CAD simulation of the platform

Based on a detailed analysis of the technical boundary conditions and user requirements with regard to working space, characteristics of exoscope movements, safety requirements and OR integration, a semi-robotic platform concept was developed [4]. It comprises a multifunctional anesthesia arch for platform provision in the previously hardly used sterile space above the patient, a manually operated, parallel-guided and weight-balanced prepositioning unit, and a fine-positioning robot for hands-free, preparation-accompanying exoscope handling in 5 degrees of freedom (Fig. 1). For safety reasons in connection with the simultaneous use of a field-of-view restricting HMD and long-handled endoscopic instruments, the sixth degree of freedom, the approach to the surgical site, was realized with the aid of the camera zoom.

The exoscope is controlled by the surgeon hands-free with a head-mounted unit. This consists of a stereoscopic display for reproducing the images recorded by the exoscope and/or endoscope, an orientation sensor for registering head movements, and an acoustic headset (microphone and headphones) for voice input and output of acoustic feedback.
The voice control can be used to select the action modes shown in Tab. 1. While pressing a miniaturized, finger-fixed confirmation button, the corresponding actions are then enabled. The exoscope movements are executed in the coordinate system of the presented image, according to the extent of head rotation, to ensure intuitive coordination between vision and movement.

Tab. 1: Modes and exoscope actions

Rotation around the exoscope center
Rotation around a viewpoint in the situs
Rotation around the optical axis
Translation parallel to the situs
Zoom factor selection
Selection of the focus setting
Return to the workspace center
Initialization and centering

Implementation and Discussion

The conceptualized exoscope platform and its components were implemented in a demonstrator within the framework of the project (Fig. 2). In cooperation with the clinical partners, individual parts were evaluated and a future clinical application was simulated in a neurosurgical OR, combined with the endoscope manipulation platform also implemented within the project.

The evaluation of the usability and the OR integration of the multifunctional arch took place with experienced personnel. In corresponding tests, the duration and comfort of the arch installation as well as the emergency capability were examined through video analysis and user interviews. Both assembly and emergency removal were possible within a very short time (ca. 2-3 minutes for arch installation and only a few seconds for emergency removal). They were assessed as very easy and intuitive. The evaluation of head tracking and positioning modes included for example the determination of effectiveness, efficiency, learnability, reliability and user acceptance. To achieve that, a virtual test environment was implemented and the time needed to fulfil different positioning and orientating tasks was measured. Furthermore, the test persons assessed the system in different aspects using specific questionnaires. The study yielded important conclusions to optimize control and action modes, like the clear advantage of position to velocity control [5].

The semirobotic telemanipulation platform was developed at the Helmholtz Institute in the framework of the MINOP II project, especially to fulfil the particular requirements of endoscopically assisted neurosurgical operations. The specific advantages of a robotic system (e.g. freehand camera manipulation) and human strengths (e.g. high flexibility) were thereby combined to reduce size, weight and costs of the platform. Application specific interfaces and optimized interaction modes were implemented to assist the surgeon by the multidimensional intraoperative camera manipulation as extensively as possible.

Fig 2: Implemented platform in a simulated OR setup


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