title: Investigation of spatial resolution characteristics of an in vivo micro computed tomography system.
abstract: The spatial resolution characteristics of an in vivo micro computed tomography (CT) system was investigated in the in-plane (x-y), cross plane (z) and projection imaging modes. The micro CT system utilized in this study employs a flat panel detector with a 127 μm pixel pitch, a micro focus x-ray tube with a focal spot size ranging from 5-30 μm, and accommodates three geometric magnifications (M) of 1.72, 2.54 and 5.10. The in-plane modulation transfer function (MTF) curves were measured as a function of the number of projections, geometric magnification (M), detector binning and reconstruction magnification (MRecon). The in plane cutoff frequency (10% MTF) ranged from 2.31 lp/mm (M=1.72, 2×2 binning) to 12.56 lp/mm (M=5.10, 1×1 binning) and a bar pattern phantom validated those measurements. A slight degradation in the spatial resolution was observed when comparing the image reconstruction with 511 and 918 projections, whose effect was visible at the lower frequencies. Small value of MReconhas little or no impact on the in-plane spatial resolution owning to a stable system. Large value of MReconhas implications on the spatial resolution and it was evident when comparing the bar pattern images reconstructed with MRecon=1.25 and 2.5. The cross plane MTF curves showed that the spatial resolution increased as the slice thickness decreased. The cutoff frequencies in the projection imaging mode yielded slightly higher values as compared to the in-plane and cross plane modes at all the geometric magnifications (M). At M=5.10, the cutoff resolution of the projection and cross plane on an ultra-high contrast resolution bar chip phantom were 14.9 lp/mm and 13-13.5 lp/mm. Due to the finite focal spot size of the x-ray tube, the detector blur and the reconstruction kernel functions, the system's spatial resolution does not reach the limiting spatial resolution as defined by the Nyquist's detector criteria with an ideal point source. The geometric magnification employed in the micro CTs provide a tradeoff between field of view and spatial resolution for a wide range of applications.
authors.affiliation: Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman OK 73019, USA.
authors.forename: Muhammad U
authors.initials: MU
authors.lastname: Ghani
authors.affiliation: Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman OK 73019, USA ; School of Precision and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China.
authors.forename: Zhongxing
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman OK 73019, USA.
authors.forename: Liqiang
authors.initials: L
authors.lastname: Ren
authors.affiliation: Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman OK 73019, USA.
authors.forename: Yuhua
authors.initials: Y
authors.lastname: Li
authors.affiliation: Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman OK 73019, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Zheng
authors.affiliation: Department of Radiology, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA.
authors.forename: Kai
authors.initials: K
authors.lastname: Yang
authors.affiliation: Center for Bioengineering and School of Electrical and Computer Engineering, University of Oklahoma, Norman OK 73019, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Liu
keywords: MTF; Spatial resolution; geometric magnification; interpolation; micro CT; x-ray