Program Information
Task-Specific Optimization of Scintillator Thickness for CMOS-Detector Based Cone-Beam Breast CT
S Vedantham*, S Shrestha , L Shi , G Vijayaraghavan , A Karellas , University of Massachusetts Medical School, Worcester, MA
Presentations
SU-D-206-6 (Sunday, July 31, 2016) 2:05 PM - 3:00 PM Room: 206
Purpose: To optimize the cesium iodide (CsI:Tl) scintillator thickness in a complimentary metal-oxide semiconductor (CMOS)-based detector for use in dedicated cone-beam breast CT.
Methods: The imaging task considered was the detection of a microcalcification cluster comprising six 220μm diameter calcium carbonate spheres, arranged in the form of a regular pentagon with 2 mm spacing on its sides and a central calcification, similar to that in ACR-recommended mammography accreditation phantom, at a mean glandular dose of 4.5 mGy. Generalized parallel-cascades based linear systems analysis was used to determine Fourier-domain image quality metrics in reconstructed object space, from which the detectability index inclusive of anatomical noise was determined for a non-prewhitening numerical observer. For 300 projections over 2π, magnification-associated focal-spot blur, Monte Carlo derived x-ray scatter, K-fluorescent emission and reabsorption within CsI:Tl, CsI:Tl quantum efficiency and optical blur, fiberoptic plate transmission efficiency and blur, CMOS quantum efficiency, pixel aperture function and additive noise, and filtered back-projection to isotropic 105μm voxel pitch with bilinear interpolation were modeled. Imaging geometry of a clinical prototype breast CT system, a 60 kV Cu/Al filtered x-ray spectrum from 0.3 mm focal spot incident on a 14 cm diameter semi-ellipsoidal breast were used to determine the detectability index for 300–600 μm thick (75μm increments) CsI:Tl. The CsI:Tl thickness that maximized the detectability index was considered optimal.
Results: The limiting resolution (10% modulation transfer function, MTF) progressively decreased with increasing CsI:Tl thickness. The zero-frequency detective quantum efficiency, DQE(0), in projection space increased with increasing CsI:Tl thickness. The maximum detectability index was achieved with 525μm thick CsI:Tl scintillator. Reduced MTF at mid-to-high frequencies for 600μm thick CsI:Tl lowered the detectability index than 525μm CsI:Tl.
Conclusion: For the x-ray spectrum and imaging conditions considered, a 525μm thick CsI:Tl scintillator integrated with the CMOS detector is optimal for detecting microcalcification cluster.
Funding Support, Disclosures, and Conflict of Interest: Funding support: Supported in part by NIH R01 CA195512. The contents are solely the responsibility of the authors and do not reflect the official views of the NIH or the NCI. Disclosures: SV, GV and AK - Research collaboration, Koning Corp., West Henrietta, NY.
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