Effects of scintillator on the modulation transfer function (MTF) of a digital imaging system.

Objective: To investigate the effects of 2 components (scintillator and x-ray generator) in the imaging chain on the modulation transfer function (MTF) of a charge-coupled device (CCD) digital intraoral radiographic system.

Study Design: Three screens composed of 3 different scintillator materials, namely europium-doped lutetium oxide transparent optical ceramic (TOC), thallium-doped cesium iodide (CsI), and terbium-doped gadolinium oxysulfide (GOS), were compared. Each was used, in turn, in conjunction with a CCD detector having a pixel dimension of 19.5 mum. Two different x-ray generators were also used to evaluate this variable. MTF was investigated using the slanted slit method.

Results: The TOC provided a good modulation response for low and middle frequencies, reducing to 0 only at a high cutoff frequency. With CsI and GOS, the system MTF dropped to 0 at a lower cutoff frequency than was the case with TOC. Hence, TOC provided higher spatial resolution than the other 2 scintillators tested under the experimental conditions applied. The differences in MTF attributed to the scintillator type were proportional and consistent.

Conclusions: Despite constant pixel dimensions, MTF was affected to a considerable degree by the scintillator applied and the x-ray generator used in conjunction with the same CCD imaging device. TOC shows potential as a possible replacement for CsI and GOS as a scintillator screen material for intraoral digital x-ray imaging using a solid-state detector, providing higher spatial resolution under the given experimental conditions.