Federal government websites often end in. Before sharing sensitive information, make sure you're on a federal government site. The site is secure. NCBI Bookshelf. Conventional X-ray production involves the excitation of tungsten metal to release photons. The resultant photons released can be absorbed or transmitted through the body to provide information on the amount of attenuation.
These attenuation gradients are used to reconstruct an image by mapping the amount of primary or returning photons that hit a photosensitive detector plate and produce a planar image.
Alternatively, photons can be completely absorbed into the tissue. In particular, tissue density, thickness, and atomic number alter the trajectory and absorption of X-rays. These properties create contrast among different tissues within the body, allowing for a separation of intensity values and evaluating potential pathology. X-ray image production procedures focus on optimizing settings to produce the appropriate contrast among the anatomy of interest while limiting noise and artifacts that may detract from the evaluation of the image.
Important aspects of determining appropriate protocol in clinical settings include X-ray tube voltage kilovoltage peak [kVp] , current milliamperes [mA] , and exposure time seconds. The kVp is the difference in potential applied to the X-ray tube. Penetrance is characterized by the number of photons reaching the image receptor to discern differences between structures. For example, in underexposed chest X-ray acquisitions in which the diaphragm cannot be visualized to the intersection of the spine, kVp can be increased to mitigate this issue.
An adequate penetrance ensures the ability to separate definable structures of interest; recent advances have allowed altering digital windowing levels to achieve the same effect. Changes in kVp affect radiation dose, exposure, and contrast. Also, the dose increases proportionally with higher kVp. In contrast, this decrease is primarily due to an increased proportion of Compton scatter at higher kVp.
