Radiographic Grids

[AUDIO LOGO] Hey, everybody, welcome back. In this video, we're discussing radiographic grids. Radiographic grids have a very specific design and purpose. A grid uses a plate of thin lead strips to prevent scatter from striking the image receptor. And that improves image quality by increasing image contrast. Grids are not always necessary, but an X-ray operator must understand how they function and how to use them correctly. Failure to use grids correctly can result in nondiagnostic images and excessive patient dose. Several types of X-ray imaging equipment use grids, including stationary X-ray rooms, fluoroscopy equipment, computed tomography, and mammography. Grids are sometimes necessary because of scatter radiation. When the x-ray beam is passing through the patient, some photons are completely absorbed through the photoelectric effect. Some are transmitted through the patient without interacting at all. And some will be scattered through interactions called coherent scattering and Compton scattering. Absorbed photons and transmitted photons are good for image quality because these processes create the radiographic shadow of the patient's anatomy. Scatter radiation is not good because these photons are no longer in line with the rest of the X-ray beam. As a result, scatter radiation creates a layer of noise in the image that disrupts the visibility of the patient's anatomy and any pathologies. Compare this process to how you can use a flashlight to make a shadow of your hand. Some of the light is absorbed by your hand. And some of the light transmits past your hand. The combination of absorption and transmission is what creates that nice, high-contrast shadow of your hand. Now imagine what would happen if we added other light sources that are out of alignment with the flashlight. These other light photons add light to the image. But this added light actually degrades the visibility of your hand. Scatter radiation is like this. Scatter radiation adds useless information to the image and degrades the image quality. Digital radiography processing is quite effective at maintaining optimal image contrast, even when scatter radiation is high. Still, radiographic image quality can be improved by decreasing the proportion of scatter radiation striking the image receptor. There are several ways to do this, such as using culmination to create a small exposure field and using other beam-limiting devices. But even when these methods are used, there is still scatter created in the patient that can be removed by using a radiographic grid. So how do grids work? A grid is placed between the patient and the image receptor to absorb scatter before it strikes the image receptor. Grids do not decrease the production of scatter within the patient. But they do remove scatter from the beam before it strikes the image receptor and degrades the image quality. Grids are constructed from very thin, vertical lead strips that are spaced apart by a radiolucent material, such as aluminum or plastic. Due to this vertical orientation of the lead strips, transmitted photons from the main beam that carry good information are allowed to pass right through the grid to the image receptor. And that's what we want. However, scatter photons that are out of line with the main beam and carry only meaningless noise strike the vertical strips and are absorbed. Useful photons are allowed to pass through, but scatter photons are obstructed by the grid. The efficiency of a grid in removing scatter is designated by its grid ratio. The grid ratio is defined as the height of the lead strip compared to the distance between them. For example, a grid having lead strips 2 millimeters high and having 1 millimeter of distance between each strip has a grid ratio of 2 divided by 1, which is 2 to 1. If the distance between the strips decreases to 0.5 millimeters, then the new grid ratio is 2 divided by 0.5, which is the same as 4 to 1. There is a direct relationship between grid ratio and grid efficiency. As grid ratio increases, scatter reduction increases and contrast improvement increases. Common grid ratios include 5 to 1, 6 to 1, 8 to 1, 10 to 1, 12 to 1, and 16 to 1. The choice of a grid ratio depends on several factors, including the body part being imaged, the size of the patient, the kVp used, and giving consideration to the patient dose. For example, imaging of small extremities, such as hands or feet, on small patients, usually does not require a grid at all. The kVp is low. And the proportion of scatter radiation striking the image receptor is so minimal that the use of a grid does not have a meaningful effect on image quality. Grids are generally not necessary on body parts less than 10 centimeters thick. Conversely, imaging of large body parts, those 10 centimeters or greater, like the skull, abdomen, or pelvis, on large patients can be significantly improved by using a high-ratio grid, like, 12 to 1 or 16 to 1. The kVp is high. And the proportion of scatter radiation striking the image receptor is so high, that a grid does provide a meaningful increase in image quality. Patient dose is also a consideration because using a grid does require a significant increase in the exposure technique. Here's why. Grids absorb mostly scatter radiation. But a percentage of the useful beam is also absorbed. As a result, using a grid significantly reduces the receptor exposure. When using a grid then, the mAs must be increased to maintain the appropriate receptor exposure. Without adjusting the mAs, the noise from scatter radiation will just be replaced by quantum noise, called model, from inadequate receptor exposure. So how much should the mAs be increased? I'm sure you'll be excited to know there is some math involved. This is called the Grid Conversion Formula. The base formula looks like this, mAs-2 mAs-1 is equal to Grid Conversion Factor 2 over Grid Conversion Factor 1. mAs-2 is just the new mAs. That's the number that we have to calculate. mAs-1 is the original mAs. That's the mAs we would use based on the original grid ratio. Grid Conversion Factor 2 is the Grid Conversion Factor for the new grid. And Grid Conversion Factor 1 is the Grid Conversion Factor for the original grid. A very useful form of this formula looks like this, mAs-2 equals mAs-1 multiplied by Grid Conversion Factor 2 divided by Grid Conversion Factor 1. It's actually the same formula. But in this form, we can solve directly for the new mAs without any extra steps or cross multiplication. Here's the average Grid Conversion Factors that we must to use this formula. No grid is equal to 1. 5 to 1 Is equal to 2. A 6 to 1 grid is 3. 8 to 1 equals 4. 10 to 1 is 5. 12 to 1 is also 5. And a 16 to 1 grid has a Grid Conversion Factor of 6. We'll use a practice problem to explain how this formula works. A radiograph of the chest was performed in a cart, without a grid, using 100 kVp, and 2 mAs. The resulting image demonstrated adequate receptor exposure, but excessive scatter radiation. How should the exposure technique be modified if the examination is repeated with a 10 to 1 radiographic grid? The mAs should be modified using the Grid Conversion Formula. We can't just guess. This is necessary to ensure the scatter is decreased, while maintaining the same receptor exposure. The kVp should not be changed. So we'll start with the formula and insert all known variables. The formula is mAs-2 is equal to mAs-1 times Grid Conversion Factor 2 over Grid Conversion Factor 1. The original mAs was 2. The new Grid Conversion Factor for a 10 to 1 grid is 5. The original Grid Conversion Factor for no grid is 1. To calculate mAs-2-- that's the new mAs-- we simply follow the math in the formula. The new mAs, that's mAs-2, is equal to 2 times 5 divided by 1, which equals 10 mAs. That's all there is to it. There's no additional steps. Here's another example. A portable radiograph of the pelvis is to be acquired. If the technique chart indicates 12 mAs should be used with an 8 to 1 grid, how should the technique be changed if the procedure is performed with a 16 to 1 grid? It might be tempting to just double the mAs, since the grid ratio doubled. But that's actually not how it works. Start with the formula and we'll insert all known variables. mAs-2 equals mAs-1 times Grid Conversion Factor 2 divided by Grid Conversion Factor 1. The prescribed mAs, according to the technique chart, is 12. The new Grid Conversion Factor for a 16 to 1 grid is 6. The original Grid Conversion Factor for an 8 to 1 grid is 4. So to calculate the new mAs, we just follow the math that's in this formula. The new mAs, that's mAs-2, is equal to 12 times 6 divided by 4, which equals 18 mAs. To summarize the key points, grids prevent scatter from striking the image receptor, grids can improve image quality by increasing image contrast. Digital processing does most of the work, but sometimes grids help. Grids are constructed from very thin vertical lead strips, spaced apart by a radiolucent material. The efficiency of a grid is determined by the grid ratio, which is equal to the lead strip height divided by the space between the strips. Finally, when changing grid ratio, the mAs must also be changed to maintain the correct receptor exposure.1. Why does a grid improve contrast? A grid improves contrast by absorbing scatter radiation before it reaches the image receptor. Scatter radiation reduces image contrast because it adds unwanted exposure that is not related to the anatomy being imaged. 2. As a general rule, when should a grid be used? A grid should be used when the body part being imaged is greater than 10 cm in thickness or when the procedure requires more than 60 kVp. These conditions produce enough scatter to require grid use for quality imaging. 3. How is a grid constructed? A grid consists of thin, radiopaque lead strips separated by radiolucent interspace material such as aluminum or carbon fiber. The entire structure is encased in aluminum or plastic for protection. 4. Define grid ratio. Grid ratio is the ratio of the height of the lead strips to the distance between them. A higher grid ratio increases scatter cleanup but also requires higher exposure. 5. What type of grid pattern has lead strips running in only one direction? A linear grid has lead strips running in only one direction, which allows the x-ray tube to be angled along the direction of the strips. 6. How is a focused grid designed? In a focused grid, the lead strips are angled to match the divergence of the x-ray beam. This design allows more primary radiation to pass through while still absorbing scatter, but it must be used at a specific source-to-image distance (SID). 7. As the ability of a grid to clean up scatter increases, what is the effect on patient dose and image receptor exposure? When grid efficiency increases (higher grid ratio), more scatter is absorbed, but this also reduces the exposure reaching the image receptor. To compensate, patient dose must be increased by raising mAs. 8. Explain how to evaluate the performance of a grid. Grid performance is evaluated by two main criteria: • Selectivity: Measures the grid’s ability to allow primary radiation to reach the receptor while absorbing scatter. • Contrast Improvement Factor (K-factor): Compares the contrast of an image with and without a grid. 9. How is the contrast improvement of a grid measured? Contrast improvement is measured using the K-factor, which is the ratio of image contrast with a grid to contrast without a grid. A higher K-factor indicates better contrast improvement. 10. How does an off-level grid error occur? An off-level grid error occurs when the x-ray beam is angled against the lead strips, which can happen if the grid or x-ray tube is tilted improperly. This results in grid cut-off across the entire image. 11. How does the air-gap technique improve contrast? The air-gap technique improves contrast by increasing the distance between the patient and the image receptor, allowing scatter radiation to diverge and miss the receptor. This technique mimics the scatter cleanup effect of a grid. 12. Explain the effect grid replacement software applications have on the reduction of visible scatter radiation. Grid replacement software digitally removes scatter from the final image, simulating the contrast enhancement of a physical grid without actually using one. This reduces grid-related artifacts and can lower patient dose.

[AUDIO LOGO] Hey, everybody, welcome back. In this video, we're discussing radiographic grids. Radiographic grids have a very specific design and purpose. A grid uses a plate of thin lead strips to prevent scatter from striking the image receptor. And that improves image quality by increasing image contrast. Grids are not always necessary, but an X-ray operator must understand how they function and how to use them correctly. Failure to use grids correctly can result in nondiagnostic images and excessive patient dose. Several types of X-ray imaging equipment use grids, including stationary X-ray rooms, fluoroscopy equipment, computed tomography, and mammography. Grids are sometimes necessary because of scatter radiation. When the x-ray beam is passing through the patient, some photons are completely absorbed through the photoelectric effect. Some are transmitted through the patient without interacting at all. And some will be scattered through interactions called coherent scattering and Compton scattering. Absorbed photons and transmitted photons are good for image quality because these processes create the radiographic shadow of the patient's anatomy. Scatter radiation is not good because these photons are no longer in line with the rest of the X-ray beam. As a result, scatter radiation creates a layer of noise in the image that disrupts the visibility of the patient's anatomy and any pathologies. Compare this process to how you can use a flashlight to make a shadow of your hand. Some of the light is absorbed by your hand. And some of the light transmits past your hand. The combination of absorption and transmission is what creates that nice, high-contrast shadow of your hand. Now imagine what would happen if we added other light sources that are out of alignment with the flashlight. These other light photons add light to the image. But this added light actually degrades the visibility of your hand. Scatter radiation is like this. Scatter radiation adds useless information to the image and degrades the image quality. Digital radiography processing is quite effective at maintaining optimal image contrast, even when scatter radiation is high. Still, radiographic image quality can be improved by decreasing the proportion of scatter radiation striking the image receptor. There are several ways to do this, such as using culmination to create a small exposure field and using other beam-limiting devices. But even when these methods are used, there is still scatter created in the patient that can be removed by using a radiographic grid. So how do grids work? A grid is placed between the patient and the image receptor to absorb scatter before it strikes the image receptor. Grids do not decrease the production of scatter within the patient. But they do remove scatter from the beam before it strikes the image receptor and degrades the image quality. Grids are constructed from very thin, vertical lead strips that are spaced apart by a radiolucent material, such as aluminum or plastic. Due to this vertical orientation of the lead strips, transmitted photons from the main beam that carry good information are allowed to pass right through the grid to the image receptor. And that's what we want. However, scatter photons that are out of line with the main beam and carry only meaningless noise strike the vertical strips and are absorbed. Useful photons are allowed to pass through, but scatter photons are obstructed by the grid. The efficiency of a grid in removing scatter is designated by its grid ratio. The grid ratio is defined as the height of the lead strip compared to the distance between them. For example, a grid having lead strips 2 millimeters high and having 1 millimeter of distance between each strip has a grid ratio of 2 divided by 1, which is 2 to 1. If the distance between the strips decreases to 0.5 millimeters, then the new grid ratio is 2 divided by 0.5, which is the same as 4 to 1. There is a direct relationship between grid ratio and grid efficiency. As grid ratio increases, scatter reduction increases and contrast improvement increases. Common grid ratios include 5 to 1, 6 to 1, 8 to 1, 10 to 1, 12 to 1, and 16 to 1. The choice of a grid ratio depends on several factors, including the body part being imaged, the size of the patient, the kVp used, and giving consideration to the patient dose. For example, imaging of small extremities, such as hands or feet, on small patients, usually does not require a grid at all. The kVp is low. And the proportion of scatter radiation striking the image receptor is so minimal that the use of a grid does not have a meaningful effect on image quality. Grids are generally not necessary on body parts less than 10 centimeters thick. Conversely, imaging of large body parts, those 10 centimeters or greater, like the skull, abdomen, or pelvis, on large patients can be significantly improved by using a high-ratio grid, like, 12 to 1 or 16 to 1. The kVp is high. And the proportion of scatter radiation striking the image receptor is so high, that a grid does provide a meaningful increase in image quality. Patient dose is also a consideration because using a grid does require a significant increase in the exposure technique. Here's why. Grids absorb mostly scatter radiation. But a percentage of the useful beam is also absorbed. As a result, using a grid significantly reduces the receptor exposure. When using a grid then, the mAs must be increased to maintain the appropriate receptor exposure. Without adjusting the mAs, the noise from scatter radiation will just be replaced by quantum noise, called model, from inadequate receptor exposure. So how much should the mAs be increased? I'm sure you'll be excited to know there is some math involved. This is called the Grid Conversion Formula. The base formula looks like this, mAs-2 mAs-1 is equal to Grid Conversion Factor 2 over Grid Conversion Factor 1. mAs-2 is just the new mAs. That's the number that we have to calculate. mAs-1 is the original mAs. That's the mAs we would use based on the original grid ratio. Grid Conversion Factor 2 is the Grid Conversion Factor for the new grid. And Grid Conversion Factor 1 is the Grid Conversion Factor for the original grid. A very useful form of this formula looks like this, mAs-2 equals mAs-1 multiplied by Grid Conversion Factor 2 divided by Grid Conversion Factor 1. It's actually the same formula. But in this form, we can solve directly for the new mAs without any extra steps or cross multiplication. Here's the average Grid Conversion Factors that we must to use this formula. No grid is equal to 1. 5 to 1 Is equal to 2. A 6 to 1 grid is 3. 8 to 1 equals 4. 10 to 1 is 5. 12 to 1 is also 5. And a 16 to 1 grid has a Grid Conversion Factor of 6. We'll use a practice problem to explain how this formula works. A radiograph of the chest was performed in a cart, without a grid, using 100 kVp, and 2 mAs. The resulting image demonstrated adequate receptor exposure, but excessive scatter radiation. How should the exposure technique be modified if the examination is repeated with a 10 to 1 radiographic grid? The mAs should be modified using the Grid Conversion Formula. We can't just guess. This is necessary to ensure the scatter is decreased, while maintaining the same receptor exposure. The kVp should not be changed. So we'll start with the formula and insert all known variables. The formula is mAs-2 is equal to mAs-1 times Grid Conversion Factor 2 over Grid Conversion Factor 1. The original mAs was 2. The new Grid Conversion Factor for a 10 to 1 grid is 5. The original Grid Conversion Factor for no grid is 1. To calculate mAs-2-- that's the new mAs-- we simply follow the math in the formula. The new mAs, that's mAs-2, is equal to 2 times 5 divided by 1, which equals 10 mAs. That's all there is to it. There's no additional steps. Here's another example. A portable radiograph of the pelvis is to be acquired. If the technique chart indicates 12 mAs should be used with an 8 to 1 grid, how should the technique be changed if the procedure is performed with a 16 to 1 grid? It might be tempting to just double the mAs, since the grid ratio doubled. But that's actually not how it works. Start with the formula and we'll insert all known variables. mAs-2 equals mAs-1 times Grid Conversion Factor 2 divided by Grid Conversion Factor 1. The prescribed mAs, according to the technique chart, is 12. The new Grid Conversion Factor for a 16 to 1 grid is 6. The original Grid Conversion Factor for an 8 to 1 grid is 4. So to calculate the new mAs, we just follow the math that's in this formula. The new mAs, that's mAs-2, is equal to 12 times 6 divided by 4, which equals 18 mAs. To summarize the key points, grids prevent scatter from striking the image receptor, grids can improve image quality by increasing image contrast. Digital processing does most of the work, but sometimes grids help. Grids are constructed from very thin vertical lead strips, spaced apart by a radiolucent material. The efficiency of a grid is determined by the grid ratio, which is equal to the lead strip height divided by the space between the strips. Finally, when changing grid ratio, the mAs must also be changed to maintain the correct receptor exposure.1. Why does a grid improve contrast?
A grid improves contrast by absorbing scatter radiation before it reaches the image receptor. Scatter radiation reduces image contrast because it adds unwanted exposure that is not related to the anatomy being imaged.

2. As a general rule, when should a grid be used?
A grid should be used when the body part being imaged is greater than 10 cm in thickness or when the procedure requires more than 60 kVp. These conditions produce enough scatter to require grid use for quality imaging.

3. How is a grid constructed?
A grid consists of thin, radiopaque lead strips separated by radiolucent interspace material such as aluminum or carbon fiber. The entire structure is encased in aluminum or plastic for protection.

4. Define grid ratio.
Grid ratio is the ratio of the height of the lead strips to the distance between them. A higher grid ratio increases scatter cleanup but also requires higher exposure.

5. What type of grid pattern has lead strips running in only one direction?
A linear grid has lead strips running in only one direction, which allows the x-ray tube to be angled along the direction of the strips.

6. How is a focused grid designed?
In a focused grid, the lead strips are angled to match the divergence of the x-ray beam. This design allows more primary radiation to pass through while still absorbing scatter, but it must be used at a specific source-to-image distance (SID).

7. As the ability of a grid to clean up scatter increases, what is the effect on patient dose and image receptor exposure?
When grid efficiency increases (higher grid ratio), more scatter is absorbed, but this also reduces the exposure reaching the image receptor. To compensate, patient dose must be increased by raising mAs.

8. Explain how to evaluate the performance of a grid.
Grid performance is evaluated by two main criteria:
	•	Selectivity: Measures the grid’s ability to allow primary radiation to reach the receptor while absorbing scatter.
	•	Contrast Improvement Factor (K-factor): Compares the contrast of an image with and without a grid.

9. How is the contrast improvement of a grid measured?
Contrast improvement is measured using the K-factor, which is the ratio of image contrast with a grid to contrast without a grid. A higher K-factor indicates better contrast improvement.

10. How does an off-level grid error occur?
An off-level grid error occurs when the x-ray beam is angled against the lead strips, which can happen if the grid or x-ray tube is tilted improperly. This results in grid cut-off across the entire image.

11. How does the air-gap technique improve contrast?
The air-gap technique improves contrast by increasing the distance between the patient and the image receptor, allowing scatter radiation to diverge and miss the receptor. This technique mimics the scatter cleanup effect of a grid.

12. Explain the effect grid replacement software applications have on the reduction of visible scatter radiation.
Grid replacement software digitally removes scatter from the final image, simulating the contrast enhancement of a physical grid without actually using one. This reduces grid-related artifacts and can lower patient dose.

Transcript for:Radiographic Grids

Transcript for:
Radiographic Grids