<title>Ultrahigh-resolution CT and DR scanner</title>

Abstract

A new technique called Variable-Resolution X-ray (VRX) detection that dramatically increases the spatial resolution in computed tomography (CT) and digital radiography (DR) is presented. The technique is based on a principle called "projective compression" that allows the resolution element of a CT detector to scale with the subject or field size. For very large (40-50cm) field sizes, resolution exceeding 2 cy/nun is possible and for very small fields, microscopy is attainable with resolution exceeding 100 cy/mm. Several effects that could limit the performance of VRX detectors are considered. Experimental measurements on a 16-channel, CdWO, scintillator + photodiode test array yield a limiting MTF of 64 cy/mm (8.t) in the highest-resolution configuration reported. Preliminary CT images have been made of small anatomical specimens and small animals using a storage phosphor screen in the VRX mode. Measured detector resolution of the CT projection data exceeds 20 cy/mrn (<25 pt); however, the final, reconstructed CT images produced thus far exhibit 10 cy/mm (5O.t) resolution because of non-flatness of the storage phosphor plates, focal spot effects and the use of a rudimentary CT reconstruction algorithm.A 576-channel solid-state detector is being fabricated that is expected to achieve CT image resolution in excess ofthat of the 16-channel test array.

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.…”

“…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.…”

“…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]. …”

“…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].…”

“…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.…”