A multi-source inverse-geometry CT system: initial results with an 8 spot x-ray source array

Abstract

We present initial experimental results of a rotating-gantry multi-source inverse-geometry CT (MS-IGCT) system. The MS-IGCT system was built with a single module of 2×4 x-ray sources and a 2D detector array. It produced a 75 mm in-plane field-of-view (FOV) with 160 mm axial coverage in a single gantry rotation. To evaluate system performance, a 2.5 inch diameter uniform PMMA cylinder phantom, a 200 μm diameter tungsten wire, and a euthanized rat were scanned. Each scan acquired 125 views per source and the gantry rotation time was 1 second per revolution. Geometric calibration was performed using a bead phantom. The scanning parameters were 80 kVp, 125 mA, and 5.4 us pulse per source location per view. A data normalization technique was applied to the acquired projection data, and beam hardening and spectral nonlinearities of each detector channel were corrected. For image reconstruction, the projection data of each source row were rebinned into a full cone beam data set, and the FDK algorithm was used. The reconstructed volumes from upper and lower source rows shared an overlap volume which was combined in image space. The images of the uniform PMMA cylinder phantom showed good uniformity and no apparent artefacts. The measured in-plane MTF showed 13 lp/cm at 10% cutoff, in good agreement with expectations. The rat data were also reconstructed reliably. The initial experimental results from this rotating-gantry MS-IGCT system demonstrated its ability to image a complex anatomical object without any significant image artefacts and to achieve high image resolution and large axial coverage in a single gantry rotation.

Raw data normalization for a multi source inverse geometry CT system

“…Each module consists of 64 by 16 cells of about 1.1 mm × 1.0 mm each. 12 modules are tiled in z producing a total sensitive area of about 70 mm in the x direction and 192 mm in the z direction [4,5]. Figure 3 shows a picture of the integrated MS-IGCT gantry.…”

“…We only modeled Poisson-distributed photon noise; this should also be relevant to other random noise in the imaging system. For image reconstruction, corrected projection data were rebinned into a full fan beam geometry [5], and then a direct fan beam reconstruction algorithm was used. As a reference, images were reconstructed from projection data without source intensity fluctuation.…”

“…A second series of sources are aligned at a longitudinal offset relative to the first series, and increase the volumetric coverage and provide additional sampling of the object, which reduces cone-beam artifacts. Using a small 2D detector array can reduce the detector cost and the amount of scatter, and by modulating the x-ray flux of each source independently, a concept called virtual bowtie, the effective dose to the patient can be minimized [1][2][3][4][5]. During a scan, X-ray source intensity fluctuations often occur and these must be accounted for in order to avoid artifacts in the reconstructed image.…”

Stationary computed tomography with source and detector in linear symmetric geometry: Direct filtered backprojection reconstruction

“…To substantially increase the scanning field of view (FOV), multieye IGCT was proposed employing additional detector arrays, in which each detector sees only a portion of the FOV . In addition, a prototype has been developed and evaluated with gantry‐based multisource IGCT . It is reported that the temporal resolution of IGCT is still limited by the gantry rotation speed, which is largely determined by electrical and mechanical designs and implementations.…”

Multisource inverse-geometry CT. Part I. System concept and development

“…We previously presented the development of multisource reconstruction methods [12][13][14][15][16][17][18][19][20] and calibration methods. [21][22][23][24] Several progress updates on the system development and initial results were published in Refs. [25][26][27][28][29][30][31][32].…”