Program Information
An Investigation of Dose Reduction Strategies in Cone-Beam CT Using a Channelized Hotelling Observer
A Ferrero*, K Fetterly , B Schueler , Mayo Clinic, Rochester, MN
Presentations
SU-E-201-2 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: 201
Purpose: Cone-beam CT (CBCT) contributes substantially to patient dose when used during an x-ray guided interventional procedure. The purpose of the work was to compare the influence of three dose-reduction techniques on CBCT image quality.
Methods: A custom phantom insert containing fillable rods of diameter 2, 4 and 8 mm was placed inside an anthropomorphic abdominal phantom of 30 cm in lateral dimension and projection images were acquired over a 200 degree range. Dose reduction strategies included: a) modifying the detector target dose (DTD, range 100-540 nGy/frame); b) increasing the angular distance between projection images from 0.8 to 1.5 °/frame; and c) hardening the x-ray beam with a 0.3 mm Cu spectral filter. The phantom was scanned 5 times for each acquisition protocol and dose level investigated, and the absorbed dose at the center of the phantom was measured with a 0.6 mm ionization chamber. Projection data was reconstructed with isotropic voxels of 0.9 mm in linear dimension. Region of interests around each rod were obtained from 150 independent CBCT slices for each object and for background regions which were used to estimate detectability index (d’) of a channelized Hotelling observer model. d’ was estimated for the 2 and 4 mm rods and CNR was calculated from the 8 mm rod.
Results: For equal absorbed dose, both d’ and CNR for the 0.8 °/frame protocol were 2x greater than for the 1.5°/frame protocol. In addition, both d’ and CNR were 1.9x lower when using an additional 0.3 mm of Cu spectral filter and DTD was adjusted to the same absorbed dose.
Conclusion: For a given absorbed dose, the 0.8 °/frame protocol demonstrated superior low-contrast detectability and CNR. Therefore, reducing the DTD for the 0.8º/frame protocol was the most effective dose reduction strategy.
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