title: Simultaneous surface registration of ictal and interictal SPECT and magnetic resonance images for epilepsy studies.
abstract: BACKGROUND
  Subtraction of ictal and interictal single photon emission computed tomography (SPECT) images is known to be successful in localizing the seizure focus in the pre-surgical evaluation of patients with partial epilepsy. A computer-aided methods for producing subtraction ictal SPECT co-registered to the magnetic resonance image (MRI) (the SISCOM method) is commonly used. The two registrations involved in SISCOM are (1) between the ictal-interictal SPECT images, which was shown to be the more critical, and (2) between the ictal image and MRI.
  
  
  OBJECTIVE
  To improve the accuracy of ictal-interictal registration in SISCOM by registering all three images (ictal, interictal SPECT, MRI) simultaneously.
  
  
  METHODS
  The registration problem is formulated as the minimization of a cost function between three surfaces. Then, to achieve a global minimum of this cost function, the Powell algorithm with randomly distributed initial configurations is used. This technique is tested by a realistic simulation study, a phantom study and a patient study.
  
  
  RESULTS
  The results of the simulation study demonstrate that, in surface-based registration, the triple-registration method results in a smaller ictal-interictal SPECT registration error than the pair-wise registration method (P<0.05) for a range of values of the cost-function parameter. However, the improved registration error is still larger than that obtained by the normalized mutual information method (P<0.001), which is a voxel-based registration algorithm. The phantom and patient studies reveal no observable difference between registration results.
  
  
  CONCLUSIONS
  Although the improved accuracy of triple registration is slightly worse than voxel-based registration, it will soon be possible to apply the results of this study in research utilizing the triple-registration principle to improving voxel-based results of ictal-interictal registration.
authors.affiliation: Informatics Institute, Middle East Technical University, Ankara, Turkey. merkan@metu.edu.tr
authors.forename: Erkan U
authors.initials: EU
authors.lastname: Mumcuoğlu
authors.forename: Fatih
authors.initials: F
authors.lastname: Nar
authors.forename: Yasemin
authors.initials: Y
authors.lastname: Yardimci
authors.forename: Umut
authors.initials: U
authors.lastname: Koçak
authors.forename: Eser Lay
authors.initials: EL
authors.lastname: Ergün
authors.forename: Bilge Volkan
authors.initials: BV
authors.lastname: Salanci
authors.forename: Omer
authors.initials: O
authors.lastname: Uğur
authors.forename: Belkis
authors.initials: B
authors.lastname: Erbaş
mesh_terms: D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging / Q000473:pathology; D003198:Computer Simulation; D004827:Epilepsy / Q000175:diagnosis*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008954:Models, Biological; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*