Indirect conversion flat panel detectors (FPDs) based on amorphous silicon (a-Si) technology are widely used in digital X-ray imaging. In such FPDs a scintillator layer is used for converting X-rays into visible light photons. However, the lateral spread of these photons inside the scintillator layer reduces spatial resolution of the FPD. In this study, FPDs incorporating pixelated scintillators with a barrier rib structure were developed to limit lateral spread of light photons thereby improving spatial resolution. For the pixelated scintillator, a two-dimensional barrier rib structure was first manufactured on a substrate layer, coated with reflective materials, and filled to the rim with the scintillating material of gadolinium oxysulfide (GOS). Several scintillator samples were fabricated, with pitch size varying from 160 to 280 μm and rib height from 200 to 280 μm. The samples were directly coupled to an a-Si flat panel photodiode array with a pitch of 200 μm to convert optical photons to electronic signals. With the pixelated scintillator, the detector modulation transfer function was shown to improve significantly (by 94% at 2 cycle/mm) compared to a detector using an unstructured GOS layer. However, the prototype does show lower sensitivity due to the decrease in scintillator fill factor. The preliminary results demonstrated the feasibility of using the barrier-rib structure to improve the spatial resolution of FPDs. Such an improvement would greatly benefit nondestructive testing applications where the spatial resolution is the most important parameter. Further investigation will focus on improving the detector sensitivity and exploring its medical applications.
Over the last ~15 years, the central goal in external beam radiotherapy of maximizing dose to the tumor while
minimizing dose to surrounding normal tissues has been greatly facilitated by the development and clinical
implementation of many innovations. These include megavoltage active matrix flat-panel imagers (MV
AMFPIs) designed to image the treatment beam, and separate kilovoltage (kV) AMFPIs and x-ray sources
designed to provide high-contrast projection and cone-beam CT images in the treatment room. While these
systems provide clinically valuable information, a variety of advantages would accrue through introduction of
the capability to produce clinically useful, high quality imaging information at multiple energies (e.g., kV and
MV) from a single detector along the treatment beam direction. One possible approach for achieving this
goal involves substitution of the x-ray converters used in conventional MV AMFPIs with thick, segmented
crystalline scintillators designed for dual-energy operation, coupled with the addition of x-ray imaging beams
that contain a significant diagnostic component. A second approach involves introduction of a large area,
monolithic array of photon counting pixels with multiple energy thresholds and event counters, which could
provide multi-spectral views of the treatment beam with improved contrast. In this paper, the motivations
behind, and the merits of each approach are described. In addition, prospects for such dual-energy imagers
and photon counting array designs are discussed in the context of the radiotherapy environment.