title: Behaviors of cost functions in image registration between 201Tl brain tumor single-photon emission computed tomography and magnetic resonance images.
abstract: OBJECTIVE
  We studied the behaviors of cost functions in the registration of thallium-201 (201Tl) brain tumor single-photon emission computed tomography (SPECT) and magnetic resonance (MR) images, as the similarity index of image positioning.
  
  
  METHODS
  A marker for image registration [technetium-99m (99mTc) point source] was attached at three sites on the heads of 13 patients with brain tumor, from whom 42 sets of 99mTc-201Tl SPECT (the dual-isotope acquisition) and MR images were obtained. The 201Tl SPECT and MR images were manually registered according to the markers. From the positions where the two images were registered, the position of the 201Tl SPECT was moved to examine the behaviors of the three cost functions, i.e., ratio image uniformity (RIU), mutual information (MI), and normalized MI (NMI).
  
  
  RESULTS
  The cost functions MI and NMI reached the maximum at positions adjacent to those where the SPECT and MR images were manually registered. As for the accuracy of image registration in terms of the cost functions MI and NMI, on average, the images were accurately registered within 3 degrees of rotation around the X-, Y-, and Z-axes, and within 1.5 mm (within 2 pixels), 3 mm (within 3 pixels), and 4 mm (within 1 slice) of translation to the X-, Y-, and Z-axes, respectively. In terms of rotation around the Z-axis, the cost function RIU reached the minimum at positions where the manual registration of the two images was substantially inadequate.
  
  
  CONCLUSIONS
  The MI and NMI were suitable cost functions in the registration of 201Tl SPECT and MR images. The behavior of the RIU, in contrast, was unstable, being unsuitable as an index of image registration.
authors.affiliation: Clinical Application Technology Department, FUJIFILM RI Pharma Co., Ltd., 17-10, Kyobashi 1-Chome, Tokyo, 104-0031, Japan. stsutomu@ffri.co.jp
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Soma
authors.forename: Akihiro
authors.initials: A
authors.lastname: Takaki
authors.forename: Satomi
authors.initials: S
authors.lastname: Teraoka
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Ishikawa
authors.forename: Kenya
authors.initials: K
authors.lastname: Murase
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Koizumi
mesh_terms: D000465:Algorithms; D001932:Brain Neoplasms / Q000175:diagnosis*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D013793:Thallium; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; C027549:thallium chloride; D013793:Thallium