J. Alakuijala

Neuronavigator-Guided Cerebral Biopsy

Neuronavigators are new dynamic interactive instruments that use on-line computers to orient imaging data to the surgical field and guide the neurosurgeon to his target. We have been working since 1987 on a neuronavigator that serves not only as a precise pointer, but also as a dynamic arm that can be used to hold instruments, such as biopsy guides. The neuronavigator arm consists of six joints with optical encoders and is attached to the Mayfield headholder. The arm is connected to a workstation running customized 3D image graphics software. Special instruments and surgical technique have been developed. Here, we report on early clinical experience with ten biopsy procedures: 4 low-grade and 3 high-grade astrocytomas, one craniopharyngioma and one chronic intracerebral haematoma and intracerebral cyst, both of the latter with surrounding tumour suspect tissue. In all glioma cases serial biopsies were taken from optimal sites under ultrasound imaging control. Eight cases showed representative tumour tissue, while in two cases neoplasia was ruled out. The neuronavigator proved to be versatile, allowing comprehensive imaging data to be adapted to the surgical field.

Neurosurgical Navigation System

A mechatronic system for neurosurgical simulation before operation as well as for orientation during surgery is presented. The system consists of a six-jointed robotic arm, workstation and customized 3D visualization software. The robotic arm is used to rigidly transfer multiple image data to the surgical volume. The system has been used in several biopsy and other intracranial operations with good results.

New efficient image segmentation algorithm: competitive region growing of initial regions

Presents a new simple and efficient region growing algorithm and its superior results against the current medical region growing practice. The algorithm uses initial regions and expands them to their natural borders. If all the required regions can be initially enumerated and roughly located the algorithm does not need any control parameters and gives optimal result. The algorithm was designed for both interactive and knowledge-based segmentation of volumetric medical images.

Design of visualization system for neurosurgical workstation

A visualization system for simulating nellrosurgical operations and helping in the orientation during neurosurgical procedures is presented. The system generates 3D and 2D reconstructions from preopertive M R and CT images. These reconstrllctions help in conjunction with intraoperative ultrasound the neurosurgeon in localizing the target in the brain tissue before craniotomy and during the opertion. The system is controlled by a mouse or speech in preoperative planning, while during the operation the neurosurgeon needs to use only voice control tlws leaving hands free. The flexible, expandable and portable design allows the visualization system to grow with the neurosurgical workstation.

Constant Z line texture mapping in interactive visualization of medical images

Presents a simple and efficient method for 3D visualization of perspective-mapped 2D images. In medical image visualization, understanding the spatial relationships of the image elements is of paramount importance. Perspective helps in this respect, but for complex scenes it may be necessary to rotate the scene in real time to perceive all details. The algorithm presented here is fast enough for interactive use.

Rendering system for tomographic images

A rendering system. for fom.ograph.ic inla.ges like M R and CT w a s developed. T h c sgs tem produces 1 h reed i m e ii..sio Ira 1 s h a d ed p rojec f io t i s f roin m e d ical im age duta . The projectioiis cun be modified by cul1iii,g us iny cub i c t ~ o l ~ i i n r s ~ and 1h.e m o u s e can be used i o draw sintulaied crairiototnies t o ih.e i inoyes. T h e fiii.al image i s produced b y ndvaiaced shading algorithms. T h e system creates projections quickly and f u r l h e r developm.rnd ioroards virtual reol i ty app1icafioii.s is possible.

Development of a localization arm for neurosurgery

Basic requrements of a useful localization system for neurosurgery have been formed and presented. A localization arm has been realized fulfilling the requirements. The first version of the arm was undergone laboratory tests and the second version is now under clinical testing.

Image transformation from polar to Cartesian coordinates simplifies the segmentation of brain images

A new image transformation has been designed to simplify the segmentation of the MR and CT brain images. This transformation supposes that the head is a cylindrical object and can be modeled more efficiently in polar coordinates, which gives a new set of geometrically constant image features. For example, the air-skin surface can be modeled with a one-dimensional function. An imagt transformation from the polar coordinate system to the Cartesian coordinate system has been used, because the algorithm rea ization and the actual image processing are easier and faster in Cartesian coordinates and the results equal to polar coordinate processing.

Design of High Robust Voice Interface for Speech Activated Neurosurgical Workstation

Several methods were developed in order to improve reliability and robustness of a voice interface designed for a speech activated neurosurgical workstation that is a command-number-limited system but directly involved in nurosurgical operations. We chose a commercial voice recognizer and synthesizer as basic voice environment of the voice interface. A parallel connection grammar structure in the command recognition and a practical operation procedure oriented logical structure in the command understanding were designed to remove misrecognition and misunderstanding. In the voice recognizing process, by means of setting noise pits and dynamically adjusting tolerance level, the substitution errors caused by uncorrected voice commands and noises in operating room could be greatly reduced. To guarantee the high robust voice control, we employed real-time voice feedback to confirm the accepted commands. Our testing results showed that employing these methods greatly improved voice interface robustness.

3D visualization of radiographs in brachytherapy

Presents a new visualization technique for radiographs and other projection images used in radiotherapy treatment planning. Radiograph, patient anatomy, and treatment applicators are visualized in 3D in the same display. This enables verification of the reconstruction of the treatment geometry and the registration of images. The method provides the treatment planner a greater understanding of the spatial relationships of the treatment geometry. The possibility of overlaying 3D dose distributions on the radiographs has been found to be very useful.