Production and use of X-rays
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How are X-rays produced?
X-rays are produced by the rapid deceleration of high-energy electrons when they bombard a metal target, typically tungsten. This deceleration causes the electrons to lose energy in the form of X-ray photons.
What is the relationship between accelerating potential difference (p.d.) and the minimum wavelength of produced X-rays?
The minimum wavelength (λ_min) is related to the accelerating p.d. (V) by the equation: λ_min = hc/eV, where h is Planck's constant, c is the speed of light, and e is the elementary charge. A higher p.d. results in a shorter minimum wavelength.
What determines contrast in X-ray imaging?
Contrast in X-ray imaging is determined by the differential absorption of X-rays by different tissues or materials. Tissues with higher atomic numbers or densities absorb more X-rays, appearing brighter in the image.
State the equation for the attenuation of X-rays in matter and define each term.
The equation is I = I₀e^(-μx), where: I is the intensity of the X-rays after passing through the material, I₀ is the initial intensity, μ is the linear attenuation coefficient, and x is the thickness of the material.
Explain the principle behind Computed Tomography (CT) scanning.
CT scanning involves taking multiple X-ray images of a section from different angles. These images are then processed to create a 2D image of that section. This process is repeated along an axis, and the resulting 2D images are combined to form a 3D image.
How does the linear attenuation coefficient (μ) affect the intensity of X-rays passing through a material?
A larger linear attenuation coefficient (μ) signifies that the material absorbs X-rays more readily. Therefore, a larger μ will result in a greater decrease in X-ray intensity (I) as the X-rays pass through the material.
Describe two ways to improve the contrast in X-ray imaging.
Contrast can be improved by using contrast agents, which are substances that absorb X-rays more strongly than the surrounding tissue. Contrast can also be improved by adjusting the energy (kV) of the X-ray beam; lower energy beams are absorbed more readily, enhancing differences.
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