Cone beam micro-CT system for small animal imaging and performance evaluation

Abstract

A prototype cone-beam micro-CT system for small animal imaging has been developed by our group recently, which consists of a microfocus X-ray source, a three-dimensional programmable stage with object holder, and a flat-panel X-ray detector. It has a large field of view (FOV), which can acquire the whole body imaging of a normal-size mouse in a single scan which usually takes about several minutes or tens of minutes. FDK method is adopted for 3D reconstruction with Graphics Processing Unit (GPU) acceleration. In order to reconstruct images with high spatial resolution and low artifacts, raw data preprocessing and geometry calibration are implemented before reconstruction. A method which utilizes a wire phantom to estimate the residual horizontal offset of the detector is proposed, and 1D point spread function is used to assess the performance of geometric calibration quantitatively. System spatial resolution, image uniformity and noise, and low contrast resolution have been studied. Mouse images with and without contrast agent are illuminated in this paper. Experimental results show that the system is suitable for small animal imaging and is adequate to provide high-resolution anatomic information for bioluminescence tomography to build a dual modality system.

Figure 1

Schematic diagram of the micro-CT system. It consists of a microfocus X-ray source, a flat panel X-ray detector and a three-degree programmable stage. All of them are mounted on an optical bench and controlled by a host computer.

Figure 2

Projection and backprojection of a point with a small detector horizontal offset.

Figure 3

Illumination the production of the ring caused by the horizontal offset.

Figure 4

Dimensions of the micro-CT wire phantom.

Figure 5

Dimensions of the micro-CT water phantom.

Figure 6

Wire reconstruction results with different horizontal offset calibration: (a) reconstruction image with a horizontal offset, (b) calibration implemented in incorrect direction, (c) excellent geometric calibration results.

Figure 7

1D point spread function with and without a horizontal offset.

Figure 8

Modulation transfer function (MTF) of the system.

Figure 9

Radial profile of the reconstructed water phantom.

Figure 10

Relationship between voxel noise standard deviation and exposure intensity.

Figure 11

3D reconstruction results of a mouse: (a) transaxial view, (b) sagittal view, (c) coronal view, and (d) bone structure.

Figure 12

Mouse image enhanced by Fenestra LC.