Jarkko Oikarinen

Apparent diffusion coefficient in thoracolumbar intervertebral discs of healthy young volunteers.

Apparent diffusion coefficient values (ADC) of healthy intervertebral discs of young volunteers in the thoracolumbar spine were determined using a single‐shot EPI sequence. ADCz was in the lumbar spine slightly higher than ADCx or ADCy. In vivo diffusion measurements of intervertebral discs may offer a novel diagnostic tool to evaluate disc diseases in early phases. J. Magn. Reson. Imaging 2000;12:255–260.

A visibility determination algorithm for interactive virtual endoscopy

We present a new visibility determination algorithm for interactive virtual endoscopy. The algorithm uses a modified version of template-based ray casting to extract a view dependent set of potentially visible voxels from volume data. The voxels are triangulated by Marching Cubes and the triangles are rendered onto the display by a graphics accelerator. Early ray termination and space leaping are used to accelerate the ray casting step and a quadtree subdivision algorithm is used to reduce the number of cast rays. Compared to other recently proposed rendering algorithms for virtual endoscopy, our rendering algorithm does not require a long preprocessing step or a high-end graphics workstation, but achieves interactive frame rates on a standard PC equipped with a low-cost graphics accelerator.

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.

MR perfusion, diffusion and BOLD imaging of methotrexate-exposed swine brain

To evaluate the methotrexate (MTX)‐exposed swine brain, functional magnetic resonance imaging (MRI), including perfusion, diffusion, and blood‐oxygen‐level‐dependent (BOLD) contrast imaging, was used.

Functional magnetic resonance imaging of swine brain during change in thiopental anesthesia into EEG burst-suppression level--a preliminary study.

Deepening anesthesia produces well known changes in electroencephalogram (EEG) and evoked potentials, differing in pathological and normal brain. Yet, it is not known how the T2*-weighted signal changes in the healthy brain during deepening anesthesia. We studied the effect of thiopental bolus on functional magnetic resonance imaging (fMRI) in the healthy brain using porcine model. In five pigs (2–3 months, 20–25 kg), the control bolus prior to fMRI resulted in a change into burst-suppression. After the recovery of continuous EEG, fMRI (4 min) was performed with a single bolus of thiopental (11.4-17.1 mg/kg) administered 1 min after the onset of imaging. This was repeated in four of five pigs. Positive (6-8%) or negative (-3 to -8%) signal intensity changes correlated to the thiopental bolus injection were seen in the group average fMRI response. Positive response was 1.6% and negative response 2.3% of the total brain region of interest (ROI) voxels. Responding voxels were distributed more prominently in the thalamic ROI (4.5%) than in the cortical ROI (2.2%). The group average of unthresholded voxel time courses showed that the net effect of thiopental bolus was a small (0.5%) but a clear positive change in the thalamic region, while variance changed in the global level. In conclusion, this study is the first to show that significant signal intensity changes occur in fMRI response during the sudden deepening of thiopental anesthesia. However, these responses are neither anatomically constant nor global in the healthy swine brain.

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.

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.

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.