A variable resolution x‐ray detector for computed tomography: II. Imaging theory and performance

Abstract

A computed tomography (CT) imaging technique called variable resolution x-ray (VRX) detection provides variable image resolution ranging from that of clinical body scanning (1 cy/mm) to that of microscopy (100 cy/mm). In this paper, an experimental VRX CT scanner based on a rotating subject table and an angulated storage phosphor screen detector is described and tested. The measured projection resolution of the scanner is > or = 20 lp/mm. Using this scanner, 4.8-s CT scans are made of specimens of human extremities and of in vivo hamsters. In addition, the system's projected spatial resolution is calculated to exceed 100 cy/mm for a future on-line CT scanner incorporating smaller focal spots (0.1 mm) than those currently used and a 1008-channel VRX detector with 0.6-mm cell spacing.

Monte Carlo-based assessment of the trade-off between spatial resolution, field-of-view and scattered radiation in the variable resolution X-ray CT scanner

“…In the VRX CT scanner, the spatial resolution changes according to the object size [2]. In such scanners, by angulation of the detector with respect to the incident X-ray beam, the apparent cells width in the object plane would decrease which consequently results in improved spatial resolution.…”

“…Thus, the optimum magnification is different at each incident angle and as such, utilizing a fixed system magnification would result in spatial resolution degradation within a range of detector angles [6]. The motivation behind the VRX CT design concept is primarily to provide a high spatial resolution, which varies according to the angle between the detector and incident X-ray beam [2]. The influence of focal spot size along with deviation from optimum magnification are the main limiting factors which confine the spatial resolution in the VRX CT scanners [3,6,7].…”

Novel detector design for reducing intercell x‐ray cross‐talk in the variable resolution x‐ray CT scanner: A Monte Carlo study

“…This design provides the possibility to adjust the spatial resolution according to the object size. 4,5 The concept consists of decreasing the apparent cell's width in the object plane to improve the detector's spatial resolution through angulation of the detector with re-spect to the incident x-ray beam. This technique provides substantial improvement in the detector's spatial resolution and by changing the detector angle with respect to the x-ray beam, variable resolution can be achieved.…”

Development and Application of Computational Tools for the Study and Optimization of Variable Resolution X-ray (VRX) Computed Tomography Scanners

“…This last phenomenon is fortunately an issue only for submicroscopic angles, but the other two problems remain an issue. Several different VRX scanner prototypes have been implemented following the detector angulation method including those employed in this project, and a substantial amount of work has been done to study the viability of such a detector for CT imaging [14,16,17,18,40]. In the next sections we will describe several of these implementations.…”

“…In single-slice, single-arm VRX scanners a single linear x-ray detector is tilted around an axis perpendicular to the imaging plane that passes through the center of the face of the detector. Due to the projective compression principle, (i.e., the projected size of an x-ray detector cell will decrease as the detector is tilted), an image reconstructed from a sinogram acquired with the tilted arm will have a higher spatial resolution and also higher quantum detection efficiency since the pathlength in the detection medium becomes longer, at the expense of having a smaller FOV [17,14,16]. …”