Dark noise digital xray4/29/2023 In radiography, the two important determinants of x-ray beam quality are tube voltage and beam filtration. Notice dramatic reduction in material thickness as atomic number increases. 1 -Material thickness (atomic number, Z) needed to attenuate x-ray beam (80 kV + 3 mm aluminum filtration) by 50%. Table 1 shows representative values of kerma-area product for complete examinations in radiologic imaging. For most patients, the stochastic risk can be taken as the carcinogenic risk. Kerma-area product quantifies the total amount of radiation incident on the patient and is most closely related to the total stochastic patient risk. Air kerma is used to estimate the entrance skin dose and thereby the likelihood of a deterministic (skin) radiation risk. The kerma-area product is the total amount of radiation incident on the patient and will affect the energy deposited into the patient. When air kerma is multiplied by the corresponding beam area, one obtains the kerma-area product in grays times square centimeters (Gy = cm 2), which is often referred to as the dose-area product. The higher the air kerma, the higher the x-ray beam's intensity, and the more photons will be incident on the patient. Because air kerma is well defined and universally understood, it is the metric of choice for specifying x-ray beam intensity. The air kerma in any x-ray beam is directly proportional to both the tube current and the corresponding exposure time. Air kerma can be thought of as the number of x-rays per unit area, with the photon energies of minimal concern. Air kerma is the energy transferred to electrons when normalized by the mass of air (energy/mass) and is measured using grays or milligrays. The intensity of an x-ray beam is quantified by an air kerma, which relates to the kinetic energy released per unit mass when x-rays interact with air. For this reason, it is generally not very helpful or informative to describe any radio-graphic examination as being performed at a given milliampere-second value. The milliampere-second value indicates the relative radiation output for a given x-ray tube when operated at a specified tube voltage, but does not account for differences between xray systems using a variety of tubes and filtration. The product of the tube current and exposure time, known as the milliampere-second value, is the primary indicator of the x-ray beam intensity. Important determinants of x-ray beam quantity are the choice of tube current (milliamperes) and the corresponding x-ray beam exposure times (seconds). Although artifacts in radiographic imaging are of obvious importance for image quality, these are beyond the scope of this article. Key x-ray choices include the voltage across the x-ray tube (kilovoltage), the size of the x-ray tube current (milliamperes), and the imaging exposure time (seconds). It is therefore essential for radiologists to understand how choices for each protocol parameter will affect the resultant image being generated. The most important aspect of the choice of protocol parameters is to ensure that the image quality will be sufficient for a given diagnostic imaging task. The choice of protocol parameter also affects the amount of radiation received by the patient, and radiologists need to ensure that patients are not being subjected to unnecessary radiation exposure. Radiographic protocol parameters should be selected to ensure adequate diagnostic performance, and radiologists therefore need to understand the image creation process, in addition to interpreting radiologic examinations. Radiologists are responsible for the manner in which radiologic examinations, including radiographs, mammograms, and CT images, are obtained.
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