Mathias Hoernig

Estimating breast density with dual energy mammography: a simple model based on calibration phantoms

Dual energy digital mammography has been used to suppress specific breast tissue, primarily for the purpose of iodine contrast-enhanced imaging. Another application of dual energy digital mammography is to estimate breast density, as defined by the fraction of glandular tissue, by suppressing adipose tissue. Adipose equivalent phantoms were used to derive the weighting factor for dual energy subtraction at 2, 4, 6, and 8 cm thickness. For each thickness besides 8 cm, measurements were taken over a range of densities (0, 50, and 100%) and used for calibration measurements to model a density map. Once the density map was verified with uniform slabs, the density map was evaluated with 50/50 CIRS 020 phantom at 2, 4, and 6 cm thickness and demonstrated the feasibility of using dual energy subtraction to estimate breast density on complex phantoms.

Lesion assessment and radiation dose in contrast-enhanced digital breast tomosynthesis.

Contrast-Enhanced Digital Breast Tomosynthesis (CEDBT) provides a three-dimensional (3D) contrast-enhancement map with co-registered anatomical information from low-energy DBT. It combines the benefits from Contrast-Enhanced Digital Mammography (CEDM) and Digital Breast Tomosynthesis (DBT), and may improve breast cancer detection and assessment of lesion morphology. We investigate the efficacy of CEDBT in the assessment of lesion contrast enhancement and margin identification, and evaluate the dose efficiency. We generate synthetic CEDM images from CEDBT data, similar to synthesis of 2D mammograms from DBT data, which may facilitate overall lesion assessment without additional radiation dose. Preliminary results from a patient study show that CEDBT depicts lesion margins better compared to CEDM, while the contrast-enhancement level for in-plane slice is not as high as in CEDM. CEDBT delivers less radiation dose compared to CEDM + DBT. Synthetic CEDM is able to provide lesion contrast-enhancement level comparable to CEDM.

Photodiode gain calibration of flat dynamic x-ray detectors using reset light

Due to spatial gain differences of the photo diodes and inhomogeneities in the converter (CsI) a gain calibration is usually applied for flat dynamic X-ray detectors. This calibration is calculated from X-ray images. Using the reset light, integrated in the detector, a calibration of the photo diode gain is possible. Since neither the reset light intensity nor the X-ray field distribution in combination with the converter efficiency are spatially homogeneous the ratio of these two effects has to be measured and stored once in an X-ray reset-light map. In a reset light calibration the photo diode gain will be estimated and the final calibration is then calculated from this gain image and the stored X-ray reset-light map. The reset light gain image contains the same information as the X-ray image except the influence of the scintillator which should be very stable over time. Changes in the photo diode gain can easily and automatically be corrected using the reset light calibration. Defect pixels can be determined from the reset light gain images. This method would allow a continuous calibration during the lifetime of the detector without the need for any user interaction.