A variable resolution x‐ray detector for computed tomography: I. Theoretical basis and experimental verification

Abstract

A computed tomography imaging technique called variable resolution x-ray (VRX) detection provides detector resolution ranging from that of clinical body scanning to that of microscopy (1 cy/mm to 100 cy/mm). The VRX detection technique is based on a new principle denoted as "projective compression" that allows the detector resolution element to scale proportionally to the image field size. Two classes of VRX detector geometry are considered. Theoretical aspects related to x-ray physics and data sampling are presented. Measured resolution parameters (line-spread function and modulation-transfer function) are presented and discussed. A VRX image that resolves a pair of 50 micron tungsten hairs spaced 30 microns apart is shown.

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

“…It has been proven [17,14] that due to the projective compression principle the spatial resolution of VRX scanners will in general increase as the VRX angle decreases. Nevertheless, there has not been very extensive work on the influence of projective compression on other aspects of CT imaging, such as contrast and contrast resolution, the production and severity of artifacts, and the effects of miscalibration.…”

“…For this, VRX scanners take advantage of the projective compression principle which states that from the point of view of the x-ray source, the cells in a detector will appear smaller and closer together in projection than their actual size and spacing [17,14].…”

“…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.…”

“…Variable Resolution X-ray (VRX) CT scanners attempt to address this problem by taking advantage of the projective compression principle [17,14], i.e., by making use of the fact that the projected size of an x-ray detector cell will decrease as the detector is tilted, thereby allowing it to register a higher spatial resolution at the expense of having a smaller FOV. The most basic VRX scanners have a single linear detector array, or arm.…”

“…Nevertheless, it has been shown that the negative effect of the crosstalk due to cell traversal is normally smaller than the gains in spatial resolution due to the VRX effect, because the amount of x-rays photons is reduced exponentially as they traverse the detector cells [41]. Another potential drawback of applying the VRX concept is that at extremely small VRX angles a considerable number of photons may be reflected off the arm surface; fortunately this only occurs at "sub-microscopic" angles and can be overcome with a stair-step cell design that is still under development [14]. A third drawback is that proper calibration of multi-arm systems becomes a delicate issue.…”