This weeks topic on digital radiography is spatial resolution. Spatial resolution is the capacity for distinguishing fine detail in an image. The term used to identify this is line pairs per millimeter (lp/mm). The higher the spatial resolution, the greater the capacity for distinguishing fine detail. An average observer is able to view 6 lp/mm with no magnification. Analog film has up to 20 lp/mm under magnification. This high spatial resolution is due to a small silver halide grain size in the film emulsion. Digital radiography (sensors) have a theoretical spatial resolution of 25 lp/mm, but in reality are able to achieve closer to 20 lp/mm due to electronic noise. Computed radiography (phosphor plates) have a range available. The settings are determined largely by the scanning unit. A typical range is 8 lp/mm to 24 lp/mm.
While these are all the numbers available from the companies that sell the products only recently has there been a phantom created to determine the true spatial resolution of a sensor or phosphor plate. In the current issue Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics (November 2011 112;5:632-639) an article by Peter Mah presents a phantom created to determine the actual spatial resolution of the imaging surface (sensor or phosphor plate). It showed that not all sensors and phosphor plates had the same spatial resolution even when made by the same manufacturer. While this is a new area of research, it is encouraging that it may be possible in the future to determine the true quality of a digital sensor or phosphor plate.
I hope this information about spatial resolution is helpful. If you have any questions or comments, please let me know.
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