A Lundervold — Page 3 | Search PubMed

In this study we focus on the problem of segmentation and visualization of soft tissue structures in three-dimensional (3D) magnetic resonance (MR) imaging. We introduce a classification method which is a combination of a recently proposed contour detection algorithm and Haslett's contextual classification method extended to 3D. This classification method is used in the classification step of a rendering model suggested by Drebin et al. for visualizing normal and pathological tissue structures in the brain. We evaluate the combination of these two methodologies, and identify some problems which have to be solved in order to develop a clinical useful tool.

Algorithms↗

PubMedDate not supplied

Functional magnetic resonance imaging (fMRI) study of sex differences in a mental rotation task.

The main purpose of the present study was to: 1) to investigate differences between males and females in brain activation when performing a mental rotation task, 2) investigate hemisphere differences in brain activation during mental rotation. Brain activation was measured with functional magnetic resonance imaging (fMRI). Image acquisition was performed with a 1.5 Tesla Siemens Vision MR scanner equipped with 25 m T/m gradients. Scanning of anatomy was done with a T1-weighted 3D FLASH pulse sequence. Serial imaging with 70 BOLD sensitive echo planar (EPI) whole brain measurements was done during stimulus presentations, divided into 7 blocks of 10 EPI multi-slice volume measurements each. Eleven subjects were presented with black-and-white drawings of 3-D shapes taken from the set of 3-D perspective drawings developed by Shepard and Metzler [1], alternated with 2-D white bars as control stimuli. In the experimental condition, the subjects were shown 36 pairs of 3-D drawings, presented in three blocks of 12 pairs of drawings. The drawings were always presented pairwise. On half of the trials, the two 3-D shapes were congruent but portrayed with different orientation, in the other half the two shapes were incongruent. MR data were analyzed with the SPM-96 analysis software. After subtraction of activity related to the 2-D control stimuli, clusters of significant activation were found in the superior parietal lobule (BA 7), more intensely over the right hemisphere, and bilaterally in the inferior frontal gyrus (BA 44/45). Males showed predominantly parietal activation, while the females showed inferior frontal activation. It is suggested that males and females may differ in the processing strategy used when approaching a 3-D mental rotation task, males using a 'gestalt' strategy and females using a 'serial' reasoning strategy.

Adult↗