COMPOSITE X-RAY IMAGE ASSEMBLY FOR LARGE-FIELD DIGITAL MAMMOGRAPHY WITH ONE-DIMENSIONAL AND 2-DIMENSIONAL POSITIONING OF A FOCAL-PLANE ARRAY

To demonstrate the feasibility of a novel large-field digital mammogra phy technique, a 1024 x 1024 pixel Loral charge-coupled device (CCD) f ocal plane array (FPA) was positioned in a mammographic field with one -and two-dimensional scan sequences to obtain 950 x 1800 pixel and 360 0 x 3600 pixel composite images, respectively. These experiments verif y that precise positioning of FPAs produced seamless composites and th at the CCD mosaic concept has potential for high-resolution, large-fie ld imaging. The proposed CCD mosaic concept resembles a checkerboard p attern with spacing left between the CCDs for the driver and readout e lectronics. To obtain a complete x-ray image, the mosaic must be repos itioned four times, with an x-ray exposure at each position. To reduce the patient dose, a lead shield with appropriately patterned holes is placed between the x-ray source and the patient. The high-precision m otorized translation stages and the fiber-coupled-scintillating-screen -CCD sensor assembly were placed in the position usually occupied by t he film cassette. Because of the high mechanical precision, seamless c omposites were constructed from the subimages. This paper discusses th e positioning, image alignment procedure, and composite image results. The paper only addresses the formation of a seamless composite image from subimages and will not consider the effects of the lead shield, m ultiple CCDs, or the speed of motion. (C) 1998 American Association of Physicists in Medicine.