Abstract
BackgroundBreast density is a significant breast cancer risk factor measured from mammograms. The most appropriate method for measuring breast density for risk applications is still under investigation. Calibration standardizes mammograms to account for acquisition technique differences prior to making breast density measurements. We evaluated whether a calibration methodology developed for an indirect x-ray conversion full field digital mammography (FFDM) technology applies to direct x-ray conversion FFDM systems.MethodsBreast tissue equivalent (BTE) phantom images were used to establish calibration datasets for three similar direct x-ray conversion FFDM systems. The calibration dataset for each unit is a function of the target/filter combination, x-ray tube voltage, current × time (mAs), phantom height, and two detector fields of view (FOVs). Methods were investigated to reduce the amount of calibration data by restricting the height, mAs, and FOV sampling. Calibration accuracy was evaluated with mixture phantoms. We also compared both intra- and inter-system calibration characteristics and accuracy.ResultsCalibration methods developed previously apply to direct x-ray conversion systems with modification. Calibration accuracy was largely within the acceptable range of ± 4 standardized units from the ideal value over the entire acquisition parameter space for the direct conversion units. Acceptable calibration accuracy was maintained with a cubic-spline height interpolation, representing a modification to previous work. Calibration data is unit specific, can be acquired with the large FOV, and requires a minimum of one reference mAs sample. The mAs sampling, calibration accuracy, and the necessity for machine specific calibration data are common characteristics and in agreement with our previous work.ConclusionThe generality of our calibration approach was established under ideal conditions. Evaluation with patient data using breast cancer status as the endpoint is required to demonstrate that the approach produces a breast density measure associated with breast cancer.
Highlights
Mammographic breast density is a significant breast cancer risk factor [1,2,3]
The exposure response quantities vary across all systems, the response linearity is a common characteristic across all units (H1, Hologic Selenia unit 2 (H2), Hologic Selenia unit 3 (H3), and General Electric Senographe 2000D (GE))
We showed that the calibration data could be acquired with the large field of view (FOV) only without impacting the calibration accuracy for images acquired with the small FOV
Summary
Mammographic breast density is a significant breast cancer risk factor [1,2,3]. Used extensively in research, breast density is not generally used in the clinical environment for breast cancer risk applications [4] due in large part to the lack of an automated measurement. There are various methods under evaluation for estimating breast density from either raw or calibrated mammograms [5]. Calibration research is still in its early stage of development and there are few published reports evaluating its potential application relative to the volume of published breast density research using raw mammograms. Breast density is a significant breast cancer risk factor measured from mammograms. Calibration standardizes mammograms to account for acquisition technique differences prior to making breast density measurements. We evaluated whether a calibration methodology developed for an indirect x-ray conversion full field digital mammography (FFDM) technology applies to direct x-ray conversion FFDM systems
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