Why does the structure of an individual cesium-iodide (CsI) crystal allow for better resolution?

The structure of an individual cesium-iodide (CsI) crystal minimizes light spread, which is a crucial factor in achieving better resolution in imaging. CsI crystals are structured in a way that promotes columnar growth, creating elongated, cylindrical shapes. This structure leads to a highly directional emission of light when the crystal is exposed to X-rays, reducing the diffusion of light that can occur within the phosphor layer.

Minimizing light spread ensures that emitted light travels more directly to the photodetector rather than scattering in multiple directions. This direct transfer of light improves image sharpness and contrast, as the potential for blurring is significantly reduced. Consequently, better resolution in imaging directly results from this effective management of light pathways in the CsI crystal structure.

In other contexts, factors like modulation transfer function (MTF) and the thickness of the phosphor layer play important roles, but the specific structural feature of cesium-iodide crystals primarily enhances resolution by controlling and minimizing the light spread.