Regular articleAutomated detection of gray matter malformations using optimized voxel-based morphometry: a systematic approach
Introduction
Malformation of cortical development (MCD) are a recognized cause of chronic epilepsy. Their special significance lies in the fact that they are amenable to treatment by surgical resection and that they are increasingly diagnosed due to the more common use of high-resolution magnetic resonance imaging (MRI) Andermann, 2000, Barkovich et al., 2001, Sisodiya, 2000. However, diagnosis is time-consuming and difficult, and standard MRI can be unrevealing in a high percentage of patients (Tassi et al., 2002). Especially in subtle cases, diagnosis relies heavily on the experience of the radiologist reading the images (Hong et al., 2000). In order to address this problem, a number of attempts have been made to employ modern postprocessing image strategies to aid in the diagnosis of these disorders Bastos et al., 1999, Woermann et al., 1999.
We have recently suggested a simple, voxel-based technique to detect cortical dysplasias by comparison with a healthy control group (Kassubek et al., 2002). We aimed at systematically optimizing this approach in a large patient and control population by (1) applying a newly suggested, optimized processing stream for structural imaging data (Good et al., 2001) and testing its suitability and (2) finding the combination of processing parameters that offers the highest rate of detection of MCD and the best distinction between MCD patients and healthy controls. In order to avoid possible user errors and to minimize the amount of time necessary, all procedures and evaluations should be automated as far as possible.
Section snippets
Subjects
Patients with MCD were recruited from the patient population of the Freiburg Epilepsy Center. Diagnosis was made by visual assessment of all images by two experienced neuroradiologists. We could include 20 patients with MCD, 10 female and 10 male, with a mean age of 29.1 ± 10.9 years (range, 14 to 51 years). All but 4 patients had a focal cortical dysplasia, 3 had polymicrogyria, and 1 presented with a complex cortical gyration abnormality. Malformations were located in the frontal (11),
Global difference
The number of remaining voxels calculated on the final difference images was not able to unambiguously distinguish (i.e., without overlap between the groups) patients from controls. However, a number of approaches were able to discriminate the two populations to a high degree of significance (see Table 2a). The best results were obtained with an affine-only approach and 6-mm smoothing (P = 0.0102). Averaging all approaches, the discriminatory power of the number of remaining voxels was not
Approach
Our rationale for systematically modifying the spatial normalization parameters was to find the combination with the best possible discriminatory power between a normal control population and patients with a cortical malformation. Among the parameters determined to assess the success of the respective processing streams, the successful detection of malformed cortex should be given most emphasis since our procedure was meant to detect potentially abnormal regions of gray matter with a high
Acknowledgements
We thank all the participants for their time and willingness to contribute to this study.
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