Veterinary Radiography Ch. 8

The radiographic contrast refers to the difference in brightness between different areas on a radiograph. It is primarily determined by the kilovoltage peak (kVp) setting used during the imaging process. Higher kVp settings produce a higher energy beam, which results in greater penetration of the X-rays through the body, leading to decreased contrast. Conversely, lower kVp settings produce a lower energy beam, resulting in less penetration and increased contrast. Therefore, kVp is the main factor influencing radiographic contrast.

As kVp increases, the energy of the x-ray beam also increases. This higher energy allows the x-rays to penetrate deeper into the patient's body, resulting in less scatter radiation being produced. However, at very high kVp levels, the probability of Compton scattering also increases, which can lead to an increase in scatter radiation. Therefore, it is correct to say that as kVp increases, scatter radiation can increase.

In a radiograph of a laterally positioned animal, the head should face the viewer's left with the spine at the top. This positioning allows for better visualization and interpretation of the anatomical structures.

The degree of blackness on a radiograph refers to the density of the image. Density is determined by the amount of radiation that reaches the film or digital detector. A higher density indicates a darker image, while a lower density indicates a lighter image. This can be adjusted by changing the exposure factors, such as increasing or decreasing the mAs (milliamperage-seconds) or the kVp (kilovoltage peak). Therefore, the correct answer is density.

If a body part exceeds 10 cm in thickness, it will require the use of a grid to reduce fog-producing scatter radiation. A grid is used in radiography to improve image quality by reducing scatter radiation that can cause fogging on the image. The grid consists of thin lead strips that are placed between the patient and the image receptor. It absorbs the scattered radiation, allowing only the primary radiation to reach the image receptor and produce a clear image. Therefore, any body part exceeding 10 cm will require the use of a grid to ensure a high-quality image.

Density refers to the overall darkness or blackness of an image. It is primarily determined by the mAs (milliampere-seconds) setting, which controls the amount of radiation exposure received by the image receptor. Increasing the mAs increases the amount of radiation, resulting in a darker image with higher density. Therefore, the correct answer is mAs.

An overexposed film appears too dark because it has received too much radiation, resulting in excessive blackening of the film. To correct this, the mAs or kVp needs to be decreased. Decreasing the mAs or kVp will reduce the amount of radiation reaching the film, allowing for a proper exposure and resulting in a lighter image.

If a radiograph is too light after taking a view of the lateral abdomen, increasing the mAs by 30% to 50% may be recommended. This is because increasing the mAs will increase the amount of radiation exposure to the image receptor, which will result in a darker image. This adjustment compensates for the underexposure that caused the radiograph to appear too light. Increasing the kVp or decreasing the mAs by 30% to 50% would not address the issue of underexposure and would not result in a darker image.

Increasing the kVp by 10% to 15% will increase the energy of the x-rays, which will result in shorter wavelength and increased penetrating power. This will help improve the visibility of anatomic silhouettes on the abdominal film.

If a radiograph includes many shades of gray, it indicates that there is a wide range of densities present in the image. This suggests that the image has low contrast, as there is not a significant difference between the lightest and darkest areas. Additionally, the use of high kVp (kilovoltage peak) contributes to the low contrast by increasing the overall penetration of the x-rays, resulting in a more uniform distribution of shades of gray.

Increasing the mAs by 30% to 50% would be the next step to take. This is because the film has an overall appearance of being too light, indicating that it is underexposed. By increasing the mAs, which controls the amount of radiation used, more radiation will be used to expose the film, resulting in a darker image. Increasing the kVp, on the other hand, would primarily affect the contrast of the image, not the overall brightness.

The correct answer is to decrease mAs by 50%. This is because the thoracic film is too dark, indicating that there is an overexposure of the image. By decreasing the mAs (milliampere-seconds), which controls the amount of radiation used to expose the film, the image will become less dark and more appropriately exposed.