Computed tomography utilizes x-rays to generate images. These images, in turn, can be utilized in a wide variety of applications such as medical imaging. Computed tomography detectors are typically used to translate the x-rays passed through an imaging object into electronic data that is used to generate images. CT detectors are commonly based on structured x-ray to light conversion scintillators of phosphor materials. Scintillators are utilized to convert x-rays into light photons. These light photons may then be converted into electrical impulses by elements such as photodiodes.
In some CT applications, high x-ray absorption is required. These applications often require the use of thick dense scintillator structures. Existing scintillator structures commonly are comprised of diced single crystals or transparent ceramic imaging plates. An important consideration, however, is the prevention or minimization of pixel to pixel contamination of the light produced within each luminescent module of the scintillator structures. In order to minimize this contamination, the scintillator plates have been diced and reflectors have been introduced in an effort to maintain as much of the generated light remaining within an individual pixel as possible.
The problems arising from contamination have further grown as CT technology has moved towards the use of smaller and smaller diode arrays. The smaller diode arrays require the use of smaller pixel arrays. Thus the pixel arrays must often be more finely divided and the pixel size must be reduced. Traditional methodologies for scintillator production such as dicing crystals and ceramics can become increasingly expensive as additional cuts and finer definition is required. When pixel size has been over 1 mm in pitch, inner diameter and outer diameter dicing has been successful in separating luminescent ceramics or single crystals into individualized pixels for mating to photodiode arrays. For the reduced size pixel arrays, however, existing attempts have turned to phosphors such as needles of CsI as well as phosphors deposited onto fiber optic face plates. These systems have been used to convey light into finely pitched pixels. These materials, however, are often found to not be adequate or desirable in terms of their luminescent or absorption properties for the more stringent requirements of many CT applications. In computed tomography, the afterglow and gain instability of the CsI will result in artifacts in the resultant CT image set. While the absorption characteristics of phosphors on fiber optics make this technology undesirable as-dose considerations to the patient becomes a concern.
To facilitate image reconstruction, the pixels of single crystals or ceramic scintillators are optically separated with a reflector material. The optimal reflector system is one that is very thin so it does not contribute a significant fraction to the overall surface area of the array exposed to x-rays. Often, very thin reflectors (except those comprised of metal) will leak light from neighboring channels. This often leads to image quality degradation. By increasing the reflector thickness to reduce the light leakage or cross talk, the overall efficiency of the array to converting x-rays to light is reduced due to the decreased surface fraction of scintillator.
Similar problems are exhibited in existing collimator designs. Current methods often require that individual plates of tungsten be placed at the correct angle to the beam to reduce scatter. As the detector pitch gets smaller, and the CT detectors get larger, the task of properly placing the collimators becomes difficult. It can also result in excessive production and assembly costs. Thus a technology that addressed both the limitations of existing scintillator designs as well as the limitations of collimator designs would be highly beneficial to the use of conversion devices in modern computer tomography systems.
It would, therefore, be highly desirable to have a methodology of scintillator construction and production that was suited for small pixel arrays. It would additionally be highly desirable to have a methodology that could further incorporate inexpensive and reliable production techniques. Finally, it would be highly desirable to develop a technology that could advance both collimator and scintillator design and performance.