| In comparison to single/multi slice spiral CT, the potential of cone beam volume CT (CBVCT) to improve data acquisition efficiency, imaging performance and x-ray utilization efficiency for volumetric tomography imaging is well recognized. Recently, the advent of x-ray flat panel imager (FPI) is making research in CBVCT more competitive. A novel x-ray FPI-based CBVCT prototype is implemented in this work and its performance evaluation is also conducted. To meet the data sufficiency condition, the CBVCT prototype employs a circle-plus-two-arc orbit accomplished by a tiltable circular gantry. By adding two arc sub-orbits, the implemented prototype becomes an accurate CBVCT, which significantly reduces contrast and geometry distortion existing in approximate CBVCT, such as that implemented under the circular orbit associated with the CB filtered backprojection (CB-FBP) reconstruction algorithm proposed by Feldkamp et al. The imaging performances, including reconstruction accuracy, low contrast resolution, spatial resolution and capability of reconstructing a region of interest (ROI) within a longitudinally unbounded object, are experimentally evaluated through phantom studies. The results obtained encourage an expectation of medical applications of the CBVCT prototype, particularly the application in image-guided interventional procedures, such as neurological surgery and radiotherapy, where the movement of a patient table is usually prohibited.; This work has addressed three primary issues that are challenges faced by the CBVCT community. (1) Derivation of a CB-FBP reconstruction algorithm under the circle-plus-two-arc data acquisition orbit, which can accurately reconstruct an ROI within a longitudinally unbounded object, and is computationally efficient due to the adoption of a window function to exclude Radon information redundancy. (2) Correction of CBVCT image artifacts caused by primary x-ray FPI performance drawbacks, particularly those caused by defective cell in an x-ray FPI by proposing a 2D wavelet-analysis-based algorithm that is robust over variable x-ray exposures. (3) Suppression of x-ray scatter interference in CBVCT by proposing a general algorithm based upon the beam stop array technique and imaging sequence processing, as well as employing the anti-scatter approaches inherited from projection imaging, such as the air gap, bow-tie attenuator and anti-scatter grid. |
