Establishing an efficient, department-wide digital mammography QC program
Based on the fact that each digital mammography system has its own QC program and many facilities utilize several systems made by different vendors, keeping up with quality control in mammography is a complicated task. Those were the observations of Martin Yaffe, PhD, of the Imaging Research Program as the Sunnybrook and Women’s College in Toronto as a part of the digital mammography seminar this week at the Society for Imaging Informatics in Medicine (SIIM, formerly SCAR) annual meeting in Austin, Texas.
“It is clear that any performance advantages of digital mammography [as demonstrated by the DMIST study] will only accrue if the imaging is performed in an optimal manner,” Yaffe opined. “This implies the equipment is performing properly, the technologist is skilled at positioning the breast and selecting the exposure factors and the radiologist is expert at interpreting the mammogram. To satisfy the first of these conditions, it is critical that an effective quality control program be in place.”
Based on experience gained during the DMIST study, the American College of Radiology has established a subcommittee to develop a harmonized QC program. The program is still under development, but its goals are: to provide as much as possible, a uniform set of tests that can be used across the range of commercial digital mammography systems that will be used clinically; to effectively test those aspects of imaging performance that are relevant to diagnostic quality and safety; streamline the program to make it as efficient as possible, thereby eliminating unnecessary costs and labor; and, as much as possible to keep these tests similar or familiar to those currently performed by technologists and medical physicists who carry QC in screen-film mammography.
The tests involve x-ray equipment and detector performance, image quality and dose parameters, evaluation of image artifacts, characterization of noise, modulation transfer functions, linear and reproducibility and image display systems, including monitor and printer calibration. They are grouped by whether they are performed by a technologist or medical physicist and by recommended frequency.
It is being recommended that some tests necessary for film-screen are unnecessary for digital mammography while other tests should be added to answer the needs of FFDM – such as the relationship between digital signal and noise and the radiation dose as well as the performance of the soft-copy workstation and image printer. Specialized test tools also are necessary such as a uniform phantom, modulation transfer function (MTF) tool, TG-18 test pattern and MISTY-2 phantom. He also recommended several tests that would be unnecessary with digital – such as evaluation of image plate fogging on CR systems; collimation and alignment tests, kV accuracy and reproducibility, x-ray linearity, output rate and reproducibility and detector linearity and reproducibility, among others.
Yaffe concluded that digital imaging systems lend themselves to quantitative, automated, self-logging testing procedures that would result in high compliance but at the same time save time and staff resources, and thus costs.