Mercuric iodide and lead iodide x-ray detectors for radiographic and fluoroscopic medical imaging

Mercuric iodide (HgI2) and lead iodide (PbI2) have been under development for several years as direct converter layers in digital x-ray imaging. Previous reports have covered the basic electrical and physical characteristics of these and several other materials. We earlier reported on 5cm x 5cm and 10cm x 10cm size imagers, direct digital radiography X-ray detectors, based on photoconductive polycrystalline mercuric iodide deposited on a flat panel thin film transistor (TFT) array, as having great potential for use in medical imaging, NDT, and security applications. This paper, presents results and comparison of both lead iodide and mercuric iodide imagers scaled up to 20cm x 25cm sizes. Both the mercuric iodide and lead iodide direct conversion layers are vacuum deposited onto TFT array by Physical Vapor Deposition (PVD). This process has been successfully scaled up to 20cm x 25cm -- the size required in common medical imaging applications. A TFT array with a pixel pitch of 127 microns was used for this imager. In addition to increasing detector size, more sophisticated, non-TFT based small area detectors were developed in order to improve analysis methods of the mercuric and lead iodide photoconductors. These small area detectors were evaluated in radiographic mode, continuous fluoroscopic mode and pulsed fluoroscopic mode. Mercuric iodide coating thickness ranging between 140 microns and 300 microns and lead iodide coating thickness ranging between 100 microns and 180 microns were tested using beams with energies between 40 kVp and 100 kVp, utilizing exposure ranges typical for both fluoroscopic and radiographic imaging. Diagnostic quality radiographic and fluoroscopic images have been generated at up to 15 frames per second. Mercuric iodide image lag appears adequate for fluoroscopic imaging. The longer image lag characteristics of lead iodide make it only suitable for radiographic imaging. For both material the MTF is determined primarily by the aperture and pitch of the TFT array (Nyquist frequency of ~3.93 mm-1 (127 micron pixel pitch).

[1]  Robert A. Street,et al.  Radiological x-ray response of polycrystalline mercuric-iodide detectors , 2000, Medical Imaging.

[2]  Robert A. Street,et al.  Mercuric iodide thick films for radiological x-ray detectors , 2000, SPIE Optics + Photonics.

[3]  Haim Hermon,et al.  Theoretical and experimental sensitivity to X-rays of single and polycrystalline HgI2 compared with different single-crystal detectors , 2001 .

[4]  Robert A. Street,et al.  Deposition of thick films of polycrystalline mercuric iodide x-ray detectors , 2001 .

[5]  Arnold Burger,et al.  Comparison of cadmium zinc telluride crystals grown by horizontal and vertical Bridgman and from the vapor phase , 2001 .

[6]  Haim Hermon,et al.  Polycrystalline mercuric iodide detectors , 1999, Optics & Photonics.

[7]  Gary Virshup,et al.  Large-area mercuric iodide x-ray imager , 2002, SPIE Medical Imaging.

[8]  Robert A. Street,et al.  Approaching the theoretical x-ray sensitivity with Hgl2 direct detection image sensors , 2002, SPIE Medical Imaging.

[9]  Robert A. Street,et al.  Thick films of X-ray polycrystalline mercuric iodide detectors , 2001 .

[10]  Kanai S. Shah,et al.  Comparison of PbI2 and HgI2 for direct detection active matrix x-ray image sensors , 2002 .

[11]  Kanai S. Shah,et al.  Comparative study of Pbl2 and Hgl2 as direct detector materials for high-resolution x-ray image sensors , 2001, SPIE Medical Imaging.

[12]  Gary Virshup,et al.  Large area mercuric iodide thick film x-ray detectors for fluoroscopic (on-line) imaging , 2002, Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring.

[13]  Haim Hermon,et al.  Characterization of CZT detectors grown from horizontal and vertical Bridgman , 2000, SPIE Optics + Photonics.

[14]  Robert A. Street,et al.  Technology and Applications of Amorphous Silicon , 2000 .

[15]  Robert A. Street,et al.  Nondestructive imaging with mercuric iodide thick film x-ray detectors , 2001, SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring.

[16]  J A Rowlands,et al.  X-ray imaging using amorphous selenium: feasibility of a flat panel self-scanned detector for digital radiology. , 1995, Medical physics.