An Investigation of Rare Earth Co-doping in Fluorochlorozirconate Glass-Ceramic Imaging Plates to Improve the Storage Phosphor Properties for Computed Radiography

Computed radiography is a standard medical imaging technology that uses photostimulable storage phosphor imaging plates to create an image. X-rays create electron hole pairs within the plate which recombine upon stimulation by a laser, producing light which is read out and stored as a digital image. Modern imaging plates contain an active layer of crystalline storage phosphors embedded in a polymer binder. The resolution of images from these plates is reduced due to light scattering at grain boundaries during readout. Fluorochlorozirconate (FCZ) glass-ceramic imaging plates containing BaCl₂:Eu²⁺ [barium chloride] [europium]nanocrystals in the orthorhombic phase have been developed to decrease light scattering during readout and improve resolution for applications such as mammography where a high level of detail is required. However, these plates lack the conversion efficiency (CE) of current plates and therefore require a higher x-ray dose to provide sufficient light to produce an image. This work investigates the use of co-doping to increase the CE of FCZ glass-ceramic imaging plates.

A series of fluorochlorozirconate (FCZ) glass samples were produced, replacing the EuCl₂ with HoF₃ [holmium] to determine the effects of co-doping on light output. The samples were characterized using differential scanning calorimetry to determine the temperature at which orthorhombic BaCl₂ crystallization occurs. Thermal treatments were performed to precipitate BaCl₂ nanocrystals in the orthorhombic phase, creating a glass ceramic. The heat treated samples were characterized using phosphorimetry and x-ray diffraction to confirm the crystalline phases present. Photostimulated luminescence (PSL) experiments were conducted to evaluate light output. The results indicate that the addition of HoF₃ increases the CE even though HoF₃ singly doped FCZ glass ceramics do not exhibit any PSL.

In an effort to reduce the costs of the FCZ glass-ceramic imaging plates, experiments were conducted to see if less costly EuCl₃ could be reduced to form the more expensive EuCl₂ through heating in an inert atmosphere. Three different heating profiles were tested. The percent conversion was evaluated using Mössbauer [Mossbauer] spectroscopy. The results show that EuCl₂ can be successfully synthesized from EuCl₃.

The project described was supported by the National Science Foundation under Grant Number DMR1001381 and the National Institutes of Health under Grant Number 5R01EB006145- National Institute of Biomedical Imaging and Bioengineering. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Science Foundation,the National Institute of Biomedical Imaging and Bioengineering or the National Institutes of Health.