X-ray mammography continues to be the primary tool for breast cancer screening and plays an important role in the diagnosis and management of breast cancer. However, the difficulty in resolving overlapping structures in a 2-D projection image leads to reduced sensitivity. A number of research groups and companies are developing dedicated breast tomographic systems to overcome this problem. Most of the systems are based on the conventional mammographic tube mounted on a rotating gantry. These systems have long acquisition times and are hence prone to motion blur. Here we propose to develop a prototype digital breast tomosynthesis (DBT) system based on our novel digitally addressable x-ray source (DAXS) panels in collaboration with M.D. Anderson Cancer Center (MDACC). The DAXS uses an innovative flat panel architecture in which field emission current from arrays of cold cathode field emitters formed in pixel configurations on the source exit window generates x-ray flux from a target opposite the exit window. The flux then passes through the emitters, out the window and on to the subject. The metal x-ray target is a broad, flat sheet which forms part of the vacuum envelope. Depending on the pitch between emitters, over 10,000 emitters can be patterned per mm2. We have demonstrated in Phase I, currents of over 100 5A from single emitters, so high current densities (e.g. 300 mA per mm2, or about 30 mA from the typical 0.3 mm spot size in mammography) are possible. Pixel flux levels can be modulated over a broad range by varying the emitter cathode-gate voltage. The ability to address x-ray pixels, and vary intensity, will offer new flexibility in delivering precise amounts of x-ray flux to target locations for dose modulation. Pixel address speeds are well under a few milliseconds, so motion blurring will be reduced. The flat panel architecture of the DAXS also allows the x-ray source to shift two dimensionally enabling the out-of-focal plane objects to be more effectively blurred with a 2-D kernel. Here we will build up on our Phase I efforts and construct several DAXS panels to be incorporated into a prototype DBT system along with a commercially available flat panel detector. The proposed DBT system will lead to a new generation of compact, fast, affordable and transportable breast tomographic systems for breast cancer screening, diagnosis and management. The primary impact of the proposed work will be to make breast cancer screening more accessible and convenient, and provide motion- free 3-D breast images to radiologists, surgeons, radiation oncologists, for better detection, diagnosis and staging of breast cancers.
The prototype digital breast tomosynthesis system to be developed here is based on novel digitally addressable x-ray source panels which offer unique capabilities not available with current mammography x-ray sources. Since the x-ray pixels can be addressed electronically in few milliseconds no gantry motion is required and these can help reduce exposure time and dose and eliminate motion blurring problems associated with 3-D imaging. Such a device will make 3-D imaging mobile and affordable making more widely available to practitioners new tools and methodologies for early detection and more accurate diagnosis of breast cancer.
