Investigation of spatial resolution characteristics of an in vivo microcomputed tomography system

Muhammad U. Ghani, Zhongxing Zhou, Liqiang Ren, Molly Wong, Yuhua Li, Bin Zheng, Kai Yang, Hong Liu

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

The spatial resolution characteristics of an in vivo microcomputed tomography (CT) system was investigated in the in-plane (x-y), cross plane (z) and projection imaging modes. The microCT system utilized in this study employs a flat panel detector with a 127 μm pixel pitch, a microfocus 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 MRecon has little or no impact on the in-plane spatial resolution owning to a stable system. Large value of MRecon has 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 microCTs provide a tradeoff between field of view and spatial resolution for a wide range of applications.

Original languageEnglish (US)
Pages (from-to)129-136
Number of pages8
JournalNuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Volume807
DOIs
StatePublished - Jan 21 2016
Externally publishedYes

Keywords

  • Geometric magnification
  • Interpolation
  • MicroCT
  • MTF
  • Spatial resolution
  • X-ray

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Instrumentation

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