Radiation Monitoring Devices (`RMD') is developing a digital radiographic imaging technology that is based upon a semiconductor x-ray receptor. The more specific, targeted application is mammographic imaging (including breast tomosynthesis) for which the benefits of this technology will later be described. At the core of this research, RMD is developing the process for creating `direct imaging'x-ray detectors fabricated from polycrystalline layers of the semiconductor mercuric iodide (HgI2). A significant part of this work will involve tailoring the electrical, chemical and physical properties of these layers for the intended purpose. To utilize HgI2 as an x-ray receptor, it must be coupled with an amorphous silicon (a-Si) thin film transistor (TFT) array. The TFT array provides pixelation, charge storage and frame readout necessary to form a complete imager. In order to enable digital mammography to achieve its full potential and thereby, have a major clinical impact, x-ray detection technology needs to be advanced. RMD is investigating a `direct'detection method using mercuric iodide (HgI2) as the x-ray detector. The HgI2 film acts as the sensor, detecting the incoming x-rays with high quantum efficiency due to its high x-ray stopping power. The detected x-ray image is converted directly into an electronic charge image due to the formation of electron-hole pairs in HgI2. Due to efficient collection of these charges with minimal lateral spreading, this approach does not suffer from the light spreading effects observed in phosphors and thereby, provides high detection efficiency as well as high spatial resolution. HgI2 has nearly ideal characteristics for mammography such as high stopping efficiency, large gain, good charge transport, and good stability. Finally, the method by which RMD is proposing to deposit the HgI2 films is highly cost effective and can be used to readily cover large areas, making it very complimentary to the large sized a-Si:H TFT arrays that are increasingly becoming available. RMD plans to deposit and test the key HgI2 layers on two types of substrates: 1) simple conductive plates for testing electrical bulk properties, and 2) a range of a-Si TFT arrays that will provide the key imaging data. RMD will perform all the fabrication tasks associated with the layers and conduct most evaluations on the simpler devices. To aid with the a-Si TFT tasks, RMD has joined with two collaborators Varian Medical Systems and the University of Michigan to provide materials and expertise with testing. Dr. Mitchell Goodsitt of the University of Michigan has joined our team to provide guidance on the specific imaging requirements for high resolution mammography and digital breast tomosynthesis (DBT). Dr. Daniel Kopans and Richard Moore of MGH have also joined our team as clinical consultants. Dr. Kopans and Richard Moore are specialists in mammography and DBT and will provide guidance and input on clinical goals and evaluate our imagers under conditions applicable to digital mammography and DBT.
RMD is proposing to develop a new type of mammography x-ray detector that holds the promise of very high spatial resolution and superior images at low exposure levels. The proposed fabrication technique is both cost effective and readily scaleable, both helping to remove manufacturing barriers that can impede adoption of technology.
| Jiang, Hao; Zhao, Qihua; Antonuk, Larry E et al. (2013) Development of active matrix flat panel imagers incorporating thin layers of polycrystalline HgI(2) for mammographic x-ray imaging. Phys Med Biol 58:703-14 |
