the devel. of a-si materials,have the same structure as single crystals over short distances but are less ordered over larger distances, has enabled fabrication of flat-panel TFT arrays large enough to be used as the basis for all flat panel XR detec
spatial resolution
a characteristic of the imaging system. Max spat. res. (Nyquist freq-line pairs per mm)is equal to half the number of pixel/mm. Spa res depends on the sampling freq for cassette-based systems & the detector element size for cassette less
contrast resolution
the smallest exposure change (signal difference) that can be captured by a detector. Ultimately, contrast resolution is limited by the dynamic range and the quantization (number of bits per pixel) of the detector. Increased contrast resolution is consider
Dynamic range
the range of exposure over which a detector can acquire image data. Digital image acquisition systems are capable of capturing an image across a much larger range of exposures than film-screen. The increased dynamic range allows more anatomical structures
exposure latitude
the range of receptor exposures that provides a quality, low-noise imageat an appropriate patient exposure consistent with ALARA. Exposure latitude is not the exposure range which will be rescaled to consistent image brightness.
modulation transfer function (MTF)
a measure of the ability of the imaging system to preserve signal contrast as a function of the spatial resolution. every image can be described in terms of the amount of energy for each of its spatia frequency components.
histogram
a data set, in a graphical form, of the pixel digital values vs. the prevalence number of those values inthe image. The horizontal axis represents pixel exposure, the vertical axis represents incidence of those values. The software has histogram models fo
image noise
all images have unwanted fluctuations in brightness that are unrelated to the object being imaged. These are collectively described as image noise.
look up table (LUT)
the default gradient curve applied to the data set of your image determining the intial display contrast. The LUT can be adjusted after the initial image processing has been applied.
software function maps the gray-scale to the values of interest (VOI) in the histogram. This feature provides image brightness that is at a prescribed level over a large range of exposure. With some digital systems the image brightness will be consistent
