The Variable Resolution X-ray (VRX) technique has been successfully used in a Cone-Beam CT (CBCT) system
to increase the spatial resolution of CT images in the transverse plane. This was achieved by tilting the Flat
Panel Detector (FPD) to smaller vrxy angles in a VRX Cone Beam CT (VRX-CBCT) system. In this paper, the
effect on the axial spatial resolution of CT images created by the VRX-CBCT system is examined at different
vrxx angles, where vrxx is the tilting angle of the FPD about its x-axis. An amorphous silicon FPD with a
CsI scintillator is coupled with a micro-focus x-ray tube to form a CBCT. The FPD is installed on a rotating
frame that allows rotation of up to 90° about x and y axes of the FPD. There is no rotation about the z-axis
(i.e. normal to the imaging surface). Tilting the FPD about its x-axis (i.e. decreasing the vrxx angle) reduces
both the width of the line-spread function and the sampling distance by a factor of sin vrxx, thereby increasing
the theoretical detector pre-sampling spatial resolution proportionately. This results in thinner CT slices that
in turn help increase the axial spatial resolution of the CT images. An in-house phantom is used to measure the
MTF of the reconstructed CT images at different vrxx angles.
A new Cone-Beam CT (CBCT) system is introduced that uses the concept of Variable Resolution X-ray (VRX)
detection, which has previously been demonstrated to significantly increase spatial resolution for small objects.
An amorphous silicon Flat Panel Detector (FPD) with a CsI scintillator (PaxScan 2020, Varian, Salt Lake City,
UT) is coupled with a micro-focus x-ray tube (35 - 80 kVp, 10 - 250 μA) to form a CBCT. The FPD is installed
on a rotating arm that can be adjusted to any angle θ, called the VRX angle, between 90° and 0° with respect to
the x-ray direction. A VRX angle of 90° for the detector corresponds to a conventional CBCT whereas a VRX
angle of 30° means that the detector is tilted 90° - 30° = 60° from its perpendicular position. Tilting the FPD in
this manner reduces both the line-spread function width and the sampling distance by a factor of sin(&thgr;), thereby
increasing detector spatial resolution proportionately. An in-house phantom is used to measure the MTF of the
reconstructed CT images using different VRX angles. An increase by a factor of 1.67 ± 0.007 is observed in the
MTF cutoff frequency at 30° compared to 90° in images acquired at 75 kVp. Expected theoretical value for this
case is 2.0. The new Cone-Beam Variable Resolution X-ray (CB-VRX) CT system is expected to significantly
improve the images acquired from small objects - such as small animals - while exploiting the opportunities
offered by a conventional CBCT.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.