|[Frontiers in Bioscience 1, b5-7, August 1, 1996]|
COMPARISON OF CONTRAST DETAIL CURVES OF FULL FIELD DIGITAL
WITH SCREEN FILM BREAST PHANTOM IMAGES
Aparna Visweswaran, M.D., Hong Liu, Ph.D., Laurie L. Fajardo, M.D., Gia A. DeAngelis, M.D.
Department of Radiology, University of Virginia Health Sciences Center, Charlottesville, VA 22908, USA
Received 05/15/96; Accepted 07/08/96; On-line 08/01/96
Breast cancer is the most common cancer of American women and is the leading cause of cancer related death among women aged 35-50 years old in the United States (1). It is estimated that in 1996, 185,700 women will be diagnosed with breast cancer and that 44,560 women will die from this disease (2). Early detection of breast cancer results in a high probability of cure (3-5). Currently, virtually all mammographies are performed using screen-film systems and dedicated mammographic x-ray units. However, because of several inherent limitations of film as a recording device for the mammographic image, conventional screen-film mam-mography is limited in its ability to detect cancers in patients with radiodense breast tissue (6-8). These women, including premenopausal women or those undergoing hormone replacement therapy, comprise approximately 40% of the general population (9). Through increased sensitivity, wider dynamic range, lower noise, and improved contrast resolution, x-ray sensors that acquire the mammographic image in direct digital format provide a means of overcoming many of the drawbacks of screen-film mammography.
We have recently begun to evaluate a prototype full breast digital mammography unit (LORAD/ Thermotrex, San Diego, CA). The x-ray source is equipped with a tungsten target and a 50 µm silver filter. The digital detector utilizes two 1k x 1k charge-coupled devices (CCDs) which are optically coupled with cesium iodide (CsI) scintillators by two large aperture and finite conjugate Schmidt lenses (Figure 1). Twelve sub-images are acquired by shifting the CCD cameras to six positions. Each sub-image covers a field of 6cm x 6cm (64 µm pixel size). A computer stitching algorithm combines the sub-images into a single 24cm x 18cm mammographic image. The final image is a 4K x 3K x 12 bit digital array. The objective of this technical evaluation was to compare the contrast detail curves of mam-mographic phantom images obtained using the full breast digital mammographic system with a conventional screen film mammographic system at equivalent, clinically relevant radiation doses.
Fig. 1. Schematic of a CsI-Lens-CCD imaging module. The LORAD full breast digital mammography system utilizes two such modules.