Estimation of the information content of medical images produced by scintillators interacting with diagnostic X-ray beams

Abstract

The information content of medical images produced by X-ray beam–scintillator interaction was assessed by a method involving detective quantum efficiency (DQE) and information capacity determination. The method was based on emitted light fluence and modulation transfer function (MTF) measurements and it was employed to evaluate the performance of (Gd 0.5La 0.5) 2O 2S:Tb scintillator, which was used in the form of laboratory prepared scintillator screens with coating weights ranging between 20 and 139 mg/cm 2. Screens were excited to luminescence using 80 and 120 kVp X-ray beams. The 83 mg/cm 2 scintillator layer exhibited the highest DQE at zero spatial frequency. Thick scintillator layers displayed higher DQE values in the low frequency range while at high frequencies the DQE of thin scintillators were higher. Additionally, thin scintillator layers showed slow DQE variation with increasing frequency. The information capacity of scintillator layers decreased with increasing coating weight indicating that the information content of images produced by thin scintillating layers is higher and more evenly distributed with respect to spatial frequencies.