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10. What three principal geometric factors may affect radiographic quality?

11. What are standard SIDs? 12. List and explain the five factors that affect subject contrast.

13. What is the difference between foreshortening and elongation?

14. Describe the H & H contrast curve.

15. Discuss the factors that influence radiographic optical density and contrast

 

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10. The three principal geometric factors that may affect radiographic quality are:

a) Object-to-Film Distance (OFD): The distance between the object being imaged and the film or image receptor. A longer OFD can reduce magnification and increase image sharpness.

b) Object-to-Source Distance (OSD): The distance between the object being imaged and the X-ray source. A longer OSD can reduce magnification and increase image sharpness.

c) Object-to-Image Receptor Distance (OID): The distance between the object being imaged and the image receptor. A shorter OID can reduce magnification and increase image sharpness.

11. Standard SIDs (Source-to-Image Receptor Distance) refer to the predetermined distances between the X-ray source and the image receptor (usually the film or digital detector). These distances are standardized to ensure consistent image quality and accurate measurements. Common standard SIDs include 40 inches (100 cm) for general radiography and 72 inches (180 cm) for chest radiography.

12. The five factors that affect subject contrast are:

a) Kilovoltage (kVp): Increasing kVp increases the overall penetration of X-rays, resulting in a decrease in subject contrast. Lower kVp values produce higher subject contrast.

b) Scattered Radiation: Scatter radiation reduces subject contrast by introducing unwanted radiation that contributes to the overall image density. Techniques such as using grids or collimators can minimize scatter.

c) Subject Thickness: As subject thickness increases, subject contrast decreases. This is due to the increasing attenuation of X-rays by the thicker anatomical structures within the subject.

d) Tissue Density and Atomic Number: Tissues with higher atomic numbers and densities, such as bones, absorb more X-rays and produce higher subject contrast.

e) Contrast Agents: Certain contrast agents, such as iodine-based dyes, can be introduced into the body to enhance subject contrast in specific areas during certain imaging procedures.

13. Foreshortening and elongation are two terms used to describe distortions in radiographic images:

- Foreshortening occurs when an object is angled or positioned in such a way that it appears shorter on the image compared to its actual size. This can happen when the X-ray beam is not perpendicular to the object being imaged.

- Elongation occurs when an object is angled or positioned in such a way that it appears longer on the image compared to its actual size. This can happen when the X-ray beam is not perpendicular to the object being imaged.

Both foreshortening and elongation can be minimized by ensuring proper alignment and positioning of the X-ray beam and the object being imaged.

14. The H & H contrast curve, also known as the Hurter and Driffield curve, is a graphical representation of the relationship between exposure (X-ray intensity) and radiographic density (image blackness). It shows how different levels of X-ray exposure result in varying degrees of image density.

The H & H contrast curve typically has three regions: the toe region, the straight line region, and the shoulder region. In the toe region, small changes in exposure result in significant changes in density, providing high contrast. In the straight line region, changes in exposure have minimal impact on density, resulting in a medium contrast. In the shoulder region, further increases in exposure have limited influence on density, leading to low contrast.

15. Several factors influence radiographic optical density and contrast:

a) Kilovoltage (kVp): Increasing kVp leads to increased X-ray penetration, resulting in higher optical density but lower contrast. Decreasing kVp has the opposite effect.

b) Milliamperage (mA): Increasing mA increases the quantity of X-rays produced, which can increase optical density. However, it has minimal impact on contrast.

c) Exposure Time: Longer exposure times can increase optical density, but they do not significantly affect contrast.

d) Grids: Using grids can reduce scatter radiation, improving contrast by reducing unwanted density.

e) Processing Techniques: The chemical processing of radiographic films or digital image processing can significantly affect optical density and contrast. Proper processing techniques can optimize these parameters.

 

[Slayinasian]

10. The three principal geometric factors that may affect radiographic quality are:

a) Object-to-Film Distance (OFD): The distance between the object being imaged and the film or image receptor. A longer OFD can reduce magnification and increase image sharpness.

b) Object-to-Source Distance (OSD): The distance between the object being imaged and the X-ray source. A longer OSD can reduce magnification and increase image sharpness.

c) Object-to-Image Receptor Distance (OID): The distance between the object being imaged and the image receptor. A shorter OID can reduce magnification and increase image sharpness.

11. Standard SIDs (Source-to-Image Receptor Distance) refer to the predetermined distances between the X-ray source and the image receptor (usually the film or digital detector). These distances are standardized to ensure consistent image quality and accurate measurements. Common standard SIDs include 40 inches (100 cm) for general radiography and 72 inches (180 cm) for chest radiography.

12. The five factors that affect subject contrast are:

a) Kilovoltage (kVp): Increasing kVp increases the overall penetration of X-rays, resulting in a decrease in subject contrast. Lower kVp values produce higher subject contrast.

b) Scattered Radiation: Scatter radiation reduces subject contrast by introducing unwanted radiation that contributes to the overall image density. Techniques such as using grids or collimators can minimize scatter.

c) Subject Thickness: As subject thickness increases, subject contrast decreases. This is due to the increasing attenuation of X-rays by the thicker anatomical structures within the subject.

d) Tissue Density and Atomic Number: Tissues with higher atomic numbers and densities, such as bones, absorb more X-rays and produce higher subject contrast.

e) Contrast Agents: Certain contrast agents, such as iodine-based dyes, can be introduced into the body to enhance subject contrast in specific areas during certain imaging procedures.

13. Foreshortening and elongation are two terms used to describe distortions in radiographic images:

- Foreshortening occurs when an object is angled or positioned in such a way that it appears shorter on the image compared to its actual size. This can happen when the X-ray beam is not perpendicular to the object being imaged.

- Elongation occurs when an object is angled or positioned in such a way that it appears longer on the image compared to its actual size. This can happen when the X-ray beam is not perpendicular to the object being imaged.

Both foreshortening and elongation can be minimized by ensuring proper alignment and positioning of the X-ray beam and the object being imaged.

14. The H & H contrast curve, also known as the Hurter and Driffield curve, is a graphical representation of the relationship between exposure (X-ray intensity) and radiographic density (image blackness). It shows how different levels of X-ray exposure result in varying degrees of image density.

The H & H contrast curve typically has three regions: the toe region, the straight line region, and the shoulder region. In the toe region, small changes in exposure result in significant changes in density, providing high contrast. In the straight line region, changes in exposure have minimal impact on density, resulting in a medium contrast. In the shoulder region, further increases in exposure have limited influence on density, leading to low contrast.

15. Several factors influence radiographic optical density and contrast:

a) Kilovoltage (kVp): Increasing kVp leads to increased X-ray penetration, resulting in higher optical density but lower contrast. Decreasing kVp has the opposite effect.

b) Milliamperage (mA): Increasing mA increases the quantity of X-rays produced, which can increase optical density. However, it has minimal impact on contrast.

c) Exposure Time: Longer exposure times can increase optical density, but they do not significantly affect contrast.

d) Grids: Using grids can reduce scatter radiation, improving contrast by reducing unwanted density.

e) Processing Techniques: The chemical processing of radiographic films or digital image processing can significantly affect optical density and contrast. Proper processing techniques can optimize these parameters.

16. Construct a characteristic curve for a typical screen-film combination and carefully label the axes.

17. An x-ray examination of the heart taken at 100 cm SID shows a cardiac silhouette measuring 13 cm in width. If the OID distance is estimated at 15 cm, what is the actual width of the heart?

18. The subject contrast of a thorax is 5.3. Image recep- tor contrast is 3.2. What is the radiographic contrast?

 

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16. Construct a characteristic curve for a typical screen-film combination and carefully label the axes.

17. An x-ray examination of the heart taken at 100 cm SID shows a cardiac silhouette measuring 13 cm in width. If the OID distance is estimated at 15 cm, what is the actual width of the heart?

18. The subject contrast of a thorax is 5.3. Image recep- tor contrast is 3.2. What is the radiographic contrast?

16. A characteristic curve, also known as an H & D curve (Hurter and Driffield curve), is a graphical representation of the relationship between the exposure (intensity or dose of radiation) and the resulting optical density on a film. Here's an example of how a characteristic curve for a typical screen-film combination might look:

On the y-axis, we have the optical density (OD), which represents the degree of blackness or darkness on the film. It usually ranges from 0 (completely transparent) to 4 (completely opaque).

On the x-axis, we have the logarithm of the exposure (logE), which represents the amount of radiation exposure to the film. The logarithmic scale is used because it allows for a wider range of exposure values to be plotted on a manageable scale.

The curve starts at the lower left corner of the graph, indicating low exposure and low optical density. As the exposure increases, the optical density increases, resulting in a steeper slope of the curve. At a certain point, the curve starts to level off, indicating a saturation point where further increases in exposure do not significantly increase the optical density.

The position and shape of the characteristic curve can vary depending on the screen-film combination used.

17. To calculate the actual width of the heart, we need to take into account the object-to-image receptor distance (OID). The actual width (AW) can be calculated using the formula:

AW = (IS - OID) / SID

Where IS is the measured width on the image, OID is the object-to-image receptor distance, and SID is the source-to-image receptor distance.

In this case, the measured width of the cardiac silhouette is 13 cm, the OID distance is estimated at 15 cm, and the SID is 100 cm. Plugging these values into the formula:

AW = (13 cm - 15 cm) / 100 cm = -0.02 cm

The result is negative because the actual width is smaller than the measured width on the image. Therefore, the actual width of the heart is approximately 0.02 cm smaller than the measured width.

18. Radiographic contrast is calculated by subtracting the image receptor contrast from the subject contrast. In this case:

Radiographic Contrast = Subject Contrast - Image Receptor Contrast
= 5.3 - 3.2
= 2.1

Therefore, the radiographic contrast is 2.1.

 

[Slayinasian]

16. A characteristic curve, also known as an H & D curve (Hurter and Driffield curve), is a graphical representation of the relationship between the exposure (intensity or dose of radiation) and the resulting optical density on a film. Here's an example of how a characteristic curve for a typical screen-film combination might look:

On the y-axis, we have the optical density (OD), which represents the degree of blackness or darkness on the film. It usually ranges from 0 (completely transparent) to 4 (completely opaque).

On the x-axis, we have the logarithm of the exposure (logE), which represents the amount of radiation exposure to the film. The logarithmic scale is used because it allows for a wider range of exposure values to be plotted on a manageable scale.

The curve starts at the lower left corner of the graph, indicating low exposure and low optical density. As the exposure increases, the optical density increases, resulting in a steeper slope of the curve. At a certain point, the curve starts to level off, indicating a saturation point where further increases in exposure do not significantly increase the optical density.

The position and shape of the characteristic curve can vary depending on the screen-film combination used.

17. To calculate the actual width of the heart, we need to take into account the object-to-image receptor distance (OID). The actual width (AW) can be calculated using the formula:

AW = (IS - OID) / SID

Where IS is the measured width on the image, OID is the object-to-image receptor distance, and SID is the source-to-image receptor distance.

In this case, the measured width of the cardiac silhouette is 13 cm, the OID distance is estimated at 15 cm, and the SID is 100 cm. Plugging these values into the formula:

AW = (13 cm - 15 cm) / 100 cm = -0.02 cm

The result is negative because the actual width is smaller than the measured width on the image. Therefore, the actual width of the heart is approximately 0.02 cm smaller than the measured width.

18. Radiographic contrast is calculated by subtracting the image receptor contrast from the subject contrast. In this case:

Radiographic Contrast = Subject Contrast - Image Receptor Contrast
= 5.3 - 3.2
= 2.1

Therefore, the radiographic contrast is 2.1.

19.State the reciprocity law and explain its influence on radiography.

20. How does image contrast attained with the use of a radiographic intensifying screen compare with direct film exposure?

 

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19.State the reciprocity law and explain its influence on radiography.

20. How does image contrast attained with the use of a radiographic intensifying screen compare with direct film exposure?

19. The reciprocity law states that for a given level of radiographic exposure, the film density will be the same regardless of the combination of exposure time and intensity of the radiation used to achieve that exposure. In simpler terms, it means that the same film density can be obtained by using different combinations of exposure time and intensity of radiation, as long as the total exposure remains constant.

The influence of the reciprocity law on radiography is important because it allows flexibility in adjusting exposure parameters to achieve the desired image quality while ensuring patient safety. It means that radiographers have the option to vary exposure time and intensity to optimize image quality based on factors such as patient size, anatomy, and radiographic technique. For example, if a shorter exposure time is required to minimize motion blur, a higher radiation intensity (higher mA) can be used to compensate for the reduced exposure time while maintaining the same film density.

20. When using a radiographic intensifying screen, the image contrast attained is typically higher compared to direct film exposure. This is because radiographic intensifying screens are designed to convert X-ray photons into visible light, which in turn exposes the film. The visible light emitted by the intensifying screen amplifies the exposure on the film, resulting in a higher signal-to-noise ratio and enhanced image contrast.

In direct film exposure, the X-ray photons directly interact with the film, without the use of intensifying screens. This results in less amplification of the exposure, leading to lower image contrast compared to using intensifying screens.

The use of radiographic intensifying screens offers advantages such as shorter exposure times, reduced patient exposure to radiation, and improved image quality. However, it's important to note that the use of intensifying screens can also introduce some loss of image resolution due to light diffusion and scattering effects.