title: A method for the assessment of time-varying brain shift during navigated epilepsy surgery.
abstract: OBJECTIVE
  Image guidance is widely used in neurosurgery. Tracking systems (neuronavigators) allow registering the preoperative image space to the surgical space. The localization accuracy is influenced by technical and clinical factors, such as brain shift. This paper aims at providing quantitative measure of the time-varying brain shift during open epilepsy surgery, and at measuring the pattern of brain deformation with respect to three potentially meaningful parameters: craniotomy area, craniotomy orientation and gravity vector direction in the images reference frame.
  
  
  METHODS
  We integrated an image-guided surgery system with 3D Slicer, an open-source package freely available in the Internet. We identified the preoperative position of several cortical features in the image space of 12 patients, inspecting both the multiplanar and the 3D reconstructions. We subsequently repeatedly tracked their position in the surgical space. Therefore, we measured the cortical shift, following its time-related changes and estimating its correlation with gravity and craniotomy normal directions.
  
  
  RESULTS
  The mean of the median brain shift amount is 9.64 mm ([Formula: see text] mm). The brain shift amount resulted not correlated with respect to the gravity direction, the craniotomy normal, the angle between the gravity and the craniotomy normal and the craniotomy area.
  
  
  CONCLUSIONS
  Our method, which relies on cortex surface 3D measurements, gave results, which are consistent with literature. Our measurements are useful for the neurosurgeon, since they provide a continuous monitoring of the intra-operative sinking or bulking of the brain, giving an estimate of the preoperative images validity versus time.
authors.affiliation: Department of Electronics, Information and Bioengineering (DEIB), Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 , Milan, Italy. elena.demomi@polimi.it.
authors.forename: E
authors.initials: E
authors.lastname: De Momi
authors.affiliation: Department of Electronics, Information and Bioengineering (DEIB), Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 , Milan, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Ferrigno
authors.affiliation: Department of Electronics, Information and Bioengineering (DEIB), Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 , Milan, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Bosoni
authors.affiliation: Department of Electronics, Information and Bioengineering (DEIB), Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 , Milan, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Bassanini
authors.affiliation: Department of Electronics, Information and Bioengineering (DEIB), Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 , Milan, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Blasi
authors.affiliation: "Claudio Munari" Centre for Epilepsy and Parkinson Surgery A.O. Ospedale Niguarda Ca' Granda, Milan, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Casaceli
authors.affiliation: "Claudio Munari" Centre for Epilepsy and Parkinson Surgery A.O. Ospedale Niguarda Ca' Granda, Milan, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Fuschillo
authors.affiliation: "Claudio Munari" Centre for Epilepsy and Parkinson Surgery A.O. Ospedale Niguarda Ca' Granda, Milan, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Castana
authors.affiliation: "Claudio Munari" Centre for Epilepsy and Parkinson Surgery A.O. Ospedale Niguarda Ca' Granda, Milan, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Cossu
authors.affiliation: "Claudio Munari" Centre for Epilepsy and Parkinson Surgery A.O. Ospedale Niguarda Ca' Granda, Milan, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Lo Russo
authors.affiliation: "Claudio Munari" Centre for Epilepsy and Parkinson Surgery A.O. Ospedale Niguarda Ca' Granda, Milan, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Cardinale
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000473:pathology* / Q000601:surgery; D002648:Child; D003399:Craniotomy / Q000379:methods; D004569:Electroencephalography; D004827:Epilepsy / Q000601:surgery*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D038361:Neuronavigation / Q000379:methods*; D019635:Neurosurgical Procedures / Q000379:methods; D025321:Surgery, Computer-Assisted / Q000379:methods; D055815:Young Adult
keywords: Brain shift; Epilepsy surgery; Frameless stereotaxy; Image-guided neurosurgery; Neuronavigation