Phosphor material evaluation for use in medical imaging radiation detectors by the noise-equivalent-quanta (NEQ) method

This study presents a method to evaluate the imaging performance of phospho r materials used in medical imaging systems. The advantage of the method is that phosphor evaluation is performed independently of the optical detecto rs (films, photocathodes, photodiodes) used in radiation detectors to captu re phosphor light. The method is based on the noise-equivalent-quanta (NEQ) concept, which provides an index of the signal-to-noise ratio (SNR) associ ated with the diagnostic value of a medical image. NEQ was expressed as a f unction of the phosphor's emitted light wavelength, light energy flux, and modulation transfer function (MTF). All these parameters are related to int rinsic phosphor properties such as effective atomic number, density, activa tor ion. The method was tested on three yttrium-based phosphors, two of the m activated with europium (Eu3+) and one with terbium (Tb3+). Results showe d that europium-activated phosphors (Y2O2S:Eu, Y2O3:Eu) exhibited improved SNR, whereas the terbium phosphor (Y2O2S:Tb) had better MTF.