Image quality, scatter, and dose in compact CBCT systems with flat and curved detectors

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Purpose: A number of cone-beam CT (CBCT) applications demand increasingly compact system designs for smaller footprint and improved portability. Such compact geometries can be achieved via reduction of air gap and integration of novel, curved detectors; however, the increased x-ray scatter in presents a major challenge to soft-tissue image quality in such compact arrangements. This work investigates pre-patient modulation (bowtie filters) and antiscatter grids to mitigate such effects for compact geometries with curved detectors. Methods: The effects of bowtie filters on dose and x-ray scatter were investigated in a compact geometry (180 mm air gap), for three detector curvatures: Flat, Focused at source, and Compact focused at isocenter. Experiments used bowtie filters of varying curvature combined with antiscatter grids (GR: 8:1, 80 lpmm). Scatter was estimated via GPU-accelerated Monte Carlo simulation in an anthropomorphic head phantom. Primary fluence was estimated with a polychromatic Siddon projector. Realistic Poisson noise (total dose: 20 mGy) was added to the total signal. Scatter magnitude and distribution were evaluated in projection data, and CT image quality was assessed in PWLS reconstructions. Results were validated in physical experiments on an x-ray test-bench for CBCT. Results: Moderate bowties combined with grids reduced average scatter magnitude and SPR, reduced cupping from 90 to 5 HU, and yielded net benefit to CNR despite attenuation of primary fluence. Dose to sensitive organs (eye lens) was reduced by 27%. More aggressive bowties showed further potential for dose reduction (35%) but increased peripheral SPR and increased non-uniformity and artifacts at the periphery of the image. Curved detector geometry exhibited slightly improved uniformity but a slight reduction in CNR compared to conventional flat detector geometry. Conclusion: Highly portable, soft-tissue imaging, CBCT systems with very compact geometry and curved detectors appear feasible, despite elevated x-ray scatter, through combination of moderate pre-patient collimation and antiscatter grids.

Original languageEnglish (US)
Title of host publicationMedical Imaging 2018
Subtitle of host publicationPhysics of Medical Imaging
EditorsTaly Gilat Schmidt, Guang-Hong Chen, Joseph Y. Lo
PublisherSPIE
ISBN (Electronic)9781510616356
DOIs
StatePublished - 2018
EventMedical Imaging 2018: Physics of Medical Imaging - Houston, United States
Duration: Feb 12 2018Feb 15 2018

Publication series

NameProgress in Biomedical Optics and Imaging - Proceedings of SPIE
Volume10573
ISSN (Print)1605-7422

Other

OtherMedical Imaging 2018: Physics of Medical Imaging
Country/TerritoryUnited States
CityHouston
Period2/12/182/15/18

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Atomic and Molecular Physics, and Optics
  • Radiology Nuclear Medicine and imaging

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