title: Limits on the accuracy of 3-D thickness measurement in magnetic resonance images--effects of voxel anisotropy.
abstract: Measuring the thickness of sheet-like thin anatomical structures, such as articular cartilage and brain cortex, in three-dimensional (3-D) magnetic resonance (MR) images is an important diagnostic procedure. This paper investigates the fundamental limits on the accuracy of thickness determination in MR images. We defined thickness here as the distance between the two sides of boundaries measured at the subvoxel resolution, which are the zero-crossings of the second directional derivatives combined with Gaussian blurring along the normal directions of the sheet surface. Based on MR imaging and computer postprocessing parameters, characteristics for the accuracy of thickness determination were derived by a theoretical simulation. We especially focused on the effects of voxel anisotropy in MR imaging with variable orientation of sheet-like structure. Improved and stable accuracy features were observed when the standard deviation of Gaussian blurring combined with thickness determination processes was around square root of 2/2 times as large as the pixel size. The relation between voxel anisotropy in MR imaging and the range of sheet normal orientation within which acceptable accuracy is attainable was also clarified, based on the dependences of voxel anisotropy and the sheet normal orientation obtained by numerical simulations. Finally, in vitro experiments were conducted using an acrylic plate phantom and a resected femoral head to validate the results of theoretical simulation. The simulated thickness was demonstrated to be well-correlated with the actual in vitro thickness.
authors.affiliation: Division of Interdisciplinary Image Analysis, Osaka University Graduate School of Medicine, Suita, Japan. yoshi@image.med.osaka-u.ac.jp
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Sato
authors.forename: Hisashi
authors.initials: H
authors.lastname: Tanaka
authors.forename: Takashi
authors.initials: T
authors.lastname: Nishii
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Nakanishi
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Sugano
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Kubota
authors.forename: Hironobu
authors.initials: H
authors.lastname: Nakamura
authors.forename: Hideki
authors.initials: H
authors.lastname: Yoshikawa
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ochi
authors.forename: Shinichi
authors.initials: S
authors.lastname: Tamura
mesh_terms: D019412:Anatomy, Cross-Sectional / Q000379:methods*; D000818:Animals; D016880:Anisotropy; D016477:Artifacts; D003198:Computer Simulation; D005270:Femur Head / Q000033:anatomy & histology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008954:Models, Biological; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity