Radiography and Fluoroscopy (R&F) modalities are used typically for diagnostic procedures such as GI studies using a contrast agent like barium or Gastografin and vascular studies using iodine. In older analog systems using an image intensifier for fluoro, spot image acquisition at higher doses is accomplished using a light sensor to measure the brightness of the light produced by the image intensifier. Modern R&F systems employing a flat-panel detector use an Automatic Exposure Control (AEC) or ion chamber designed for radiographic use to terminate the exposure. Typically, the AECs are set to their highest sensitivity producing spot images with about 30x the dose of a frame of fluoro imaging. Given the limitations of dynamic flat-panel detector technology, a much lower spot dose of only about 10x higher than fluoroscopic dose is more appropriate. These limitations include exposure time windows and dynamic range. The sensitivity of ion chambers used for AEC is determined fundamentally by their active volume and the gain of the preamplifier. Most radiographic AECs use three to five fields whose outputs are usually averaged. An AEC with a single, much larger ion chamber field provides a 3x improvement in sensitivity without changing the gain of the preamplifier compared to existing AECs used for RAD. Such an AEC has proven to lower the Spot image dose by a factor of three with improved contrast detail in R&F applications without the associated losses in signal to noise ratio associated with raising the gain of the preamplifier.
A large-area electronic x-ray imaging cassette is proposed that has the potential to replace screened film and real-time imaging modalities in diagnostic radiology applications.
A commercial prototype electronic intraoral dental x-ray imaging system employing a direct sensing CCD array has been developed. Image quality parameters were measured using x-ray sources at the National Institute of Standard and Technology radiation physical department in Gaithersburg, MD. Detector response to x-rays in the 10 to 70 keV energy range was measured. The beam hardening effects of human anatomy on a typical 70 kVp spectra was measured using a tissue-equivalent dental phantom.
A commercial prototype intraoral radiography system has been developed that can provide digital x-ray images for diagnosis. The system consists of an intraoral detector head, an intermediate drive electronics package, a main drive electronics package, and a PC-based digital image management system. The system has the potential to replace the use of dental film in intraoral radiographic examinations. High-resolution images are acquired, then displayed on a CRT within seconds of image acquisition.
General Imaging Corp. has developed an Electronic X-ray Imaging Technology (EXIT) which includes a design employed to fabricate large area solid-state x-ray imaging arrays. These arrays are vertically integrated multi-chip modules which have the potential to replace both film and real-time imaging modalities in industrial and medical radiography. The EXIT large- area sensing array is configured to resemble a screened film cassette in size and shape so that adaptation to existing radiographic imaging equipment is facilitated.
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