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  4. Protocol Optimization for Microcalcification Detectability in Breast CT: A Phantom Study Using Model Observers

Protocol Optimization for Microcalcification Detectability in Breast CT: A Phantom Study Using Model Observers

A Hernandez1*, A Becker2, S Lyu2, C Abbey3, J Boone1,4, (1) Department of Radiology, University of California Davis, (2) Biomedical Engineering Graduate Group, University of California Davis, (3) Department of Psychological & Brain Sciences, University of California Santa Barbara, (4) Department of Biomedical Engineering, University of California Davis

Presentations

(Tuesday, 7/14/2020) 11:30 AM - 12:30 PM [Eastern Time (GMT-4)]

Room: Track 1

Purpose: To quantify the effects of detector binning, dose, and number of projections on microcalcification (MC) detectability in breast CT (bCT) under clinically realistic constraints of minimal total scan time and dose.

Methods: Calcium carbonate grains, ranging in size from 140 to 320 µm, were embedded between layers of agar in cylindrical tubes as a surrogate for MCs within a fibroglandular background. The MC phantoms were placed in a realistic-shaped, average-sized breast phantom and imaged on a bCT system under conditions of various detector binning (0.075 mm native dexel pitch), dose levels (3–9 mGy MGD), and number of projections “N” (300-500). Signal templates, generated from high dose bCT images of the MC phantoms in-air, were then used to estimate MC detectability (d´) by means of a non-prewhitening-matched-filter model observer. Detectability was estimated for transverse and longitudinal slices through each MC and compared across the range of scanning parameters.

Results: Detectability was higher in longitudinal slices compared with transverse slices and increased with increasing MC size and MGD. For 1×1 binning mode (0.1 mm voxel size) d´ was up to 30% higher than for 2×2 binning (0.2 mm voxel size) depending on MC grain size. In 1×1 binning mode at a fixed dose of 6 mGy, d´ for 300 projections was within 5% of d´ for 500 projections.

Conclusions: High resolution acquisitions (1×1 binning) provides improved MC detectability, but at the expense of an increase in scan time due to the lower frame rate (23 fps) compared to 2×2 binning (43.5 fps). Results from this work indicate that by using 300 projections, high resolution bCT acquisitions are achievable within a realistic time for a patient to hold their breath (13 s) without compromising detectability. Future work is focused on further optimizing the protocol for improved MC detectability.

Funding Support, Disclosures, and Conflict of Interest: JMB and AMH have patents pending on various breast CT concepts. JMB is a board member for Izotropic Imaging

Keywords

Breast, Microcalcifications, Cone-beam CT

Taxonomy

IM- Breast X-Ray Imaging: Breast CT

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