title: Spatial heterogeneity analysis of brain activation in fMRI.
abstract: In many brain diseases it can be qualitatively observed that spatial patterns in blood oxygenation level dependent (BOLD) activation maps appear more (diffusively) distributed than in healthy controls. However, measures that can quantitatively characterize this spatial distributiveness in individual subjects are lacking. In this study, we propose a number of spatial heterogeneity measures to characterize brain activation maps. The proposed methods focus on different aspects of heterogeneity, including the shape (compactness), complexity in the distribution of activated regions (fractal dimension and co-occurrence matrix), and gappiness between activated regions (lacunarity). To this end, functional MRI derived activation maps of a language and a motor task were obtained in language impaired children with (Rolandic) epilepsy and compared to age-matched healthy controls. Group analysis of the activation maps revealed no significant differences between patients and controls for both tasks. However, for the language task the activation maps in patients appeared more heterogeneous than in controls. Lacunarity was the best measure to discriminate activation patterns of patients from controls (sensitivity 74%, specificity 70%) and illustrates the increased irregularity of gaps between activated regions in patients. The combination of heterogeneity measures and a support vector machine approach yielded further increase in sensitivity and specificity to 78% and 80%, respectively. This illustrates that activation distributions in impaired brains can be complex and more heterogeneous than in normal brains and cannot be captured fully by a single quantity. In conclusion, heterogeneity analysis has potential to robustly characterize the increased distributiveness of brain activation in individual patients.
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Lalit
authors.initials: L
authors.lastname: Gupta
authors.affiliation: Epilepsy Center Kempenhaeghe, Heeze, The Netherlands ; Research School for Mental Health & Neuroscience, Maastricht University, Maastricht, The Netherlands.
authors.forename: René M H
authors.initials: RM
authors.lastname: Besseling
authors.affiliation: Epilepsy Center Kempenhaeghe, Heeze, The Netherlands ; Research School for Mental Health & Neuroscience, Maastricht University, Maastricht, The Netherlands ; Department of Neurology, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Geke M
authors.initials: GM
authors.lastname: Overvliet
authors.affiliation: Epilepsy Center Kempenhaeghe, Heeze, The Netherlands ; Research School for Mental Health & Neuroscience, Maastricht University, Maastricht, The Netherlands ; Department of Neurology, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Paul A M
authors.initials: PA
authors.lastname: Hofman
authors.affiliation: Epilepsy Center Kempenhaeghe, Heeze, The Netherlands.
authors.forename: Anton
authors.initials: A
authors.lastname: de Louw
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands ; Epilepsy Center Kempenhaeghe, Heeze, The Netherlands ; Research School for Mental Health & Neuroscience, Maastricht University, Maastricht, The Netherlands.
authors.forename: Maarten J
authors.initials: MJ
authors.lastname: Vaessen
authors.affiliation: Epilepsy Center Kempenhaeghe, Heeze, The Netherlands ; Department of Neurology, Maastricht University Medical Center, Maastricht, The Netherlands.
authors.forename: Albert P
authors.initials: AP
authors.lastname: Aldenkamp
authors.affiliation: Philips Research, Philips Electronics India Ltd., Manyata Tech. Park, Bangalore, India.
authors.forename: Shrutin
authors.initials: S
authors.lastname: Ulman
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands ; Research School for Mental Health & Neuroscience, Maastricht University, Maastricht, The Netherlands.
authors.forename: Jacobus F A
authors.initials: JF
authors.lastname: Jansen
authors.affiliation: Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands ; Research School for Mental Health & Neuroscience, Maastricht University, Maastricht, The Netherlands.
authors.forename: Walter H
authors.initials: WH
authors.lastname: Backes
mesh_terms: D000293:Adolescent; D000465:Algorithms; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D002648:Child; D019305:Epilepsy, Rolandic / Q000503:physiopathology; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D062206:Spatial Analysis
keywords: Activation patterns; BOLD activation maps; Co-occurrence Matrix; Fractal dimensions; Functional magnetic resonance imaging; Lacunarity; Spatial heterogeneity