Voxel‐based magnetic resonance image postprocessing in epilepsy

Abstract

SummaryObjectiveAlthough the general utility of voxel‐based processing of structural magnetic resonance imaging (MRI) data for detecting occult lesions in focal epilepsy is established, many differences exist among studies, and it is unclear which processing method is preferable. The aim of this study was to compare the ability of commonly used methods to detect epileptogenic lesions in magnetic resonance MRI‐positive and MRI‐negative patients, and to estimate their diagnostic yield.MethodsWe identified 144 presurgical focal epilepsy patients, 15 of whom had a histopathologically proven and MRI‐visible focal cortical dysplasia; 129 patients were MRI negative with a clinical hypothesis of seizure origin, 27 of whom had resections. We applied four types of voxel‐based morphometry (VBM), three based on T1 images (gray matter volume, gray matter concentration, junction map [JM]) and one based on normalized fluid‐attenuated inversion recovery (nFSI). Specificity was derived from analysis of 50 healthy controls.ResultsThe four maps had different sensitivity and specificity profiles. All maps showed detection rates for focal cortical dysplasia patients (MRI positive and negative) of >30% at a strict threshold of p < 0.05 (family‐wise error) and >60% with a liberal threshold of p < 0.0001 (uncorrected), except for gray matter volume (14% and 27% detection rate). All maps except nFSI showed poor specificity, with high rates of false‐positive findings in controls. In the MRI‐negative patients, absolute detection rates were lower. A concordant nFSI finding had a significant positive odds ratio of 7.33 for a favorable postsurgical outcome in the MRI‐negative group. Spatial colocalization of JM and nFSI was rare, yet showed good specificity throughout the thresholds.SignificanceAll VBM variants had specific diagnostic properties that need to be considered for an adequate interpretation of the results. Overall, structural postprocessing can be a useful tool in presurgical diagnostics, but the low specificity of some maps has to be taken into consideration.

MP2RAGE multispectral voxel‐based morphometry in focal epilepsy

“…It can be expected that visual interpretation improves the specificity by eliminating false positive findings through expert knowledge. As predicted, specificity across models was higher after visual inspection, but also resulting in a decreased concordant rate, which is in line with previous studies (Kotikalapudi et al, ; Martin et al, ; Wang et al, ). The automated VBM process also had a relevant high number of discordant findings, which reduced after the visual analysis.…”

“…As predicted, specificity across models was higher after visual inspection, but also resulting in a decreased concordant rate, which is in line with previous studies Martin et al, 2017;Wang et al, 2015). The automated VBM process also had a relevant high number of discordant findings, which reduced after the visual analysis.…”

“…Technical advances of the static magnetic fields from 1.5 to 3 T and higher field strengths of 7 T can aid in detecting epileptogenic lesions that are otherwise difficult to perceive (De Ciantis et al, ; Knake et al, ; Veersema et al, ; Zijlmans et al, ). Also, computational methods have been shown helpful in detecting subtle lesions, previously missed in the visual analysis (Kotikalapudi et al, ; Martin, Bender, & Focke, ; Martin et al, ). Voxel‐based morphometry (VBM) is a well‐established method for computer‐aided, volumetric MRI processing (Ashburner & Friston, ).…”

“…However, MP2RAGE and the multispectral MP2RAGE variants have not been systematically analyzed for detecting subtle epileptogenic lesions in a VBM approach. Moreover, it was previously shown that the performance of lesion detection is strongly influenced by the choice of smoothing and statistical thresholds or t ‐scores (Kotikalapudi et al, ; Martin et al, ). The ideal parameters for an MP2RAGE VBM are yet unclear in focal epilepsy.…”

Systematic Assessment of Multispectral Voxel-Based Morphometry in Previously MRI-Negative Focal Epilepsy

“…Also, past studies used variable smoothing (between 5 and 14 mm) [7][8][9] and statistical cutoffs to elucidate VBM findings. 10,11 Studies have shown that changing smoothing kernel size 9 and statistical thresholds have a direct impact on the VBM findings, 10 also affecting the specificity of the results. 10 Recently, multispectral VBM (ie, the combination of multiple MR imaging contrast sequences) was proposed and made available in SPM8/SPM12 (http://www.fil.ion.ucl.ac.uk/spm/software/ spm12) within its unified segmentation framework (New Segment).…”