Affiliations: Engineering Research Center of Industrial Computed
Tomography Nondestructive Testing, Key Lab of Optoelectronic Technology and
System, Ministry of Education, Chongqing University, Chongqing, China | School of Biomedical Engineering and Sciences,
Virginia Tech, Blacksburg, VA, USA | Departments of Radiology and Electrical Engineering,
Stanford University, Stanford, CA, USA | Departments of Bioengineering and Radiology, Stanford
University, Stanford, CA, USA
Note: [] Corresponding authors: Ge Wang, Biomedical Imaging Cluster,
CBIS/BME, Rensselaer Polytechnic Institute, Troy, NY 12180, USA. E-mail:
wangg6@rpi.edu. Norbert J. Pelc, Departments of Bioengineering and Radiology,
Stanford University, Stanford, CA 94305, USA. E-mail: pelc@stanford.edu
Abstract: A bowtie is a filter used to shape an x-ray beam and equalize its
flux reaching different detector channels. For development of spectral CT with
energy discriminating photon-counting (EDPC) detectors, here we propose and
evaluate a dynamic bowtie for performance optimization based on a patient model
or a scout scan. With a mechanical rotation of a dynamic bowtie and an adaptive
adjustment of an x-ray source flux, an x-ray beam intensity profile can be
modulated. First, a mathematical model for dynamic bowtie filtering is
established for an elliptical section in fan-beam geometry, and the contour of
the optimal bowtie is derived. Then, numerical simulation is performed to
compare the performance of the dynamic bowtie in the cases of an ideal phantom
and a realistic cross-section relative to the counterparts without any bowtie
and with a fixed bowtie respectively. Our dynamic bowtie can equalize the
expected numbers of photons in the case of an ideal phantom. In practical
cases, our dynamic bowtie can effectively reduce the dynamic range of detected
signals inside the field of view. Although our design is optimized for an
elliptical phantom, the resultant dynamic bowtie can be applied to a real
fan-beam scan if the underlying cross-section can be approximated as an
ellipse. Furthermore, our design methodology can be applied to specify an
optimized dynamic bowtie for any cross-section of a patient, preferably using
rapid prototyping technology.
