A New Method for Dosimetry and Image Quality Assurance

Introduction and purpose: The latest developments in breast imaging technology have underlined the need for appropriate dosimetry and image evaluation methods for routine quality assurance. We are presenting QUART evaluation method (phantom and dosimeter) to address this need for digital x-ray mammography and breast tomosynthesis systems. We compare our dose measurements to the dose readings from the console, and the image quality evaluation to the known CDMAM phantom test. Materials and Methods: The evaluation method is based on the visual detection of Landolt C’s, which are constructed to be equivalent to microcalcifications inside the breast. The image quality assessment measures detectability within a wide range of background attenuation and produces a score as a function of the average glandular dose (AGD). Additionally, the phantom contains objects for a software-based evaluation of resolution and contrast-to-noise ratio, and specific features to be used for quality control of digital breast tomosynthesis. To compare the method with the CDMAM test, images were obtained with FFDM flat panel systems in a series of gradually reduced doses and evaluated following the specific protocol of each methodology. Entrance dose was measured by insertion of a small dosimeter in a specifically designed slot of the phantom. Results: A threshold score equal or above 20 (visual test) or 2.7 (contrast-to-noise ratio) has been identified with a passed CDMAM test on acceptable values, showing the equivalence of the methods. An acceptable uncertainty is achieved with the acquisition and evaluation of 3 to5 images. The dose measurements constantly differed from the console readings by 5.0 ± 0.3 %. Conclusion: The presented QUART phantom and dosimeter provide results and reliability equivalent to the CDMAM test. The QUART method covers a wide range of attenuation background in one shot, and is more efficient in terms of manufacture costs, operator time and evaluation effort.