RAD 103- UNIT 6 CLOVER

Which of the following situations will result in grid cut-off? 1. Incorrect SID with a focused grid 2. Upside down focused grid 3. Upside down non-focused grid

1 and 2 only The lead strips in a focused grid are designed to match the divergence of the x-ray beam, but only when used at the correct source-to-image distance (SID). At an incorrect SID, the useful radiation can be traveling directly into the lead strips and will be absorbed. A focused grid, when used upside-down, will absorb almost all of the useful radiation, except for a small amount in the center of the x-ray field. Because the lead strips are parallel to each other in a non-focused grid, using it upside-down will have no effect.

Which of the following statements are true concerning a higher ratio grid compared to a lower ratio grid? 1. high ratio grids demonstrate increased efficiency (contrast improvement) 2. high ratio grids absorb less scatter radiation 3. high ratio grids require increased mAs to maintain receptor exposure

1 and 3 only A higher ratio grid demonstrates increased efficiency, or contrast improvement, but also requires an increase in mAs to maintain the receptor exposure. For example, a 16:1 grid absorbs more scatter than an 8:1 grid and therefore increases contrast improvement. However, the removal of scatter also reduces total receptor exposure. This is corrected by increasing the mAs used for higher ratio grids.

The primary cause of scatter radiation within a radiographic image is: A. Compton interactions B. Photoelectric interactions C. Coherent interactions D. Photon transmission

A. Compton interactions Compton interactions or Compton scatter, is the primary cause of scatter radiation within the radiographic image. During a Compton interaction, the incident photon is partially absorbed in the patient, and the remaining photon energy exits in a different direction not aligned with the primary beam.

What is the advantage of a focused grid as compared to a non-focused grid? A. Decreased grid cut-off B. Increased image contrast C. Increased recorded detail D. Decrease distortion

A. Decreased grid cut-off There is less grid cut-off with the focused grid. There is less absorption of useful radiation by the grid because the lead strips are angled to match the divergence of the beam.

Which of the following statements best describes a focused grid? A. Lead strips are angled to match the divergence of the x-ray beam B. Lead strips are perpendicular to each other C. Two sets of lead strips are present at 90 degrees to each other D. Lead strips are closer together in focused grids

A. Lead strips are angled to match the divergence of the x-ray beam Lead strips are angled to match the divergence of the x-ray beam in a focused grid. The angled lead strips allow more of the useful beam to penetrate through the grid without absorption, which prevents grid cut-off.

What is the main effect of grid cut-off? A. Underexposure of the image receptor B. Overexposure of the image receptor C. Decreased image contrast D. Reduced image spatial resolution

A. Underexposure of the image receptor Grid cut-off results in underexposure of the image receptor. Grid cut-off is the absorption of some of the useful x-ray beam, meaning that less radiation will reach the image receptor.

The height of the lead strips within a radiographic grid compared to the distance between them is described as the: A. grid ratio B. grid conversion C. grid frequency D. grid efficiency

A. grid ratio The grid ratio is the height of the lead strip compared to the width, or distance between them. Calculated by the formula "H" divided by "D," where H equals the height of the lead strips, and D equals the distance between them (H/D). Grid ratio is directly related to the efficiency of a grid.

A patient has been brought to the imaging department for a radiograph of his knee. Previously, the patient had a portable knee exam completed in the emergency department, using 70 kV,2.5 mAs, and a 6:1 grid. In the x-ray room, the exposure will be completed with the image receptor in the Bucky tray with a 12:1 grid. What new mAs will be required for the exposure in the department to compensate for the higher ratio grid? A. 1.5 mAs B. 4.16 mAs C. 7.5 mAs D. 12.6 mAs

B. 4.16 mAs The exam should be completed with 4.0 mAs. According to the grid conversion formula, (2.5 x 5)/3 = 4.0, is the correct calculation for this problem. The original mAs is multiplied by the new grid conversion factor, and then that product is divided by the original grid conversion factor. Since the grid ratio is higher in the x-ray room, mAs must be increased in order to maintain an appropriate receptor exposure. The grid conversion formula is: (mAs1)/(mAs2) = (GF1)/(GF2). When all known variables are added to the formula, this becomes (2.5)/(x) = (3)/(5). Solving for (x), this becomes (x) = (2.5) x (5)/(3) = 4.16 mAs.

The primary effect of scatter radiation on radiographic image quality is: A. Decreased receptor exposure B. Decreased contrast C. Decreased brightness D. Decreased spatial resolution

B. Decreased contrast Scatter radiation decreases image quality by decreasing contrast. Scatter radiation adds a layer of gray fog over the image and contributes no meaningful information to image formation. A grayer image is one with reduced, or lower contrast.

What is the main advantage of the use of a moving grid over a stationary grid? A. Grid lines will be more visible with a moving grid B. Grid lines will be blurred and not visible with a moving grid C. A moving grid is more efficient at absorbing scatter radiation D. A moving grid will produce higher contrast images

B. Grid lines will be blurred and not visible with a moving grid. Gridlines are blurred and not visible with a moving grid. By creating the movement of the grid in the table or upright Bucky, grid lines become blurred and are not visible on the image. A stationary grid may not be moved during the exposure so that grid lines may be visible on the image. The movement of the grid does not change the efficiency of the grid at absorbing scatter radiation.

A radiographic image that has excessive fogging due to scatter radiation would be described as: A. high contrast B. low contrast C. high spatial resolution D. low spatial resolution

B. low contrast A radiographic image with excessive fogging due to scatter is described as low contrast. Contrast is defined as the difference in adjacent shades of gray on an image. Scatter adds a layer of fog, or uniform gray, over an image. All shades become more gray, including the brighter whites, and the overall image has lower contrast.

A radiographer typically uses 80 kVp and 3 mAs on a portable chest exam without a grid. If the radiographer decides to use an 8:1 grid on a portable chest, what new mAs would be required to compensate for the grid? A. 6 mAs B. 9 mAs C. 12 mAs D. 15 mAs

C. 12 mAs In this situation, 12 mAs would be needed to compensate for the addition of an 8:1 grid. The grid conversion factor for an 8:1 grid is 4. Using the formula presented in the video, the calculation would be the following: mAs1/mAs2=Grid Factor1/Grid Factor2. Reminder that no grid equals "1." The formula with "x" being the "new mAs" would then be 3/x=¼, further multiplying 3 times 4 =12. mAs must always be increased when adding a grid to an exposure .

A grid that has lead strips with a height of 4mm that are spaced 0.5 mm apart will have a grid ratio of: A. 2:1 B. 4:1 C. 8:1 D. 16:1

C. 8:1 This grid has a ratio of 8:1. Grid ratio is determined by dividing the height of lead strips by the distance between them. For the described grid, the ratio is calculated as 4/0.5 = 8, making the grid ratio 8:1.

What is the primary advantage of using a grid for a radiographic procedure? A. Reduced scatter production B. Increased recorded detail C. Decreased scatter reaching the image receptor D. Decreased image contrast

C. Decreased scatter reaching the image receptor Grids decrease the amount of scatter radiation reaching the image receptor. The function of the grid is to absorb the scatter radiation coming from the patient before it hits the receptor, therefore increasing image contrast. Because the grid is located behind the patient, it will not affect the amount of scatter produced.

Which of the following errors in grid use will have the same results as an angulation error? A. Upside down focused grid B. Off-focus, or incorrect SID with a focused grid C. Off-level, or tilted grid error D. Upside down non-focused grid

C. Off-level, or tilted grid error Off-level grids, or tilted grid error, have the same effect as angulation grid errors. The beam angled across the lead strips and a tilted grid will both result in useful radiation being directed into the lead strips instead of between the lead strips. The result of either error is an overall decrease in exposure across the entire image.

A radiology department's routine protocol is to complete knee exams with the use of a grid. However, in a portable situation, the technologist does not have a grid and decides to complete the exam without a grid and without making any changes to the technique. How will the image quality change without the use of the grid? A. decreased receptor exposure B. decreased noise C. decreased contrast D. decreased spatial resolution

C. decreased contrast The image created without a grid will demonstrate lower contrast without the absorption of scatter radiation by a grid. A grid has no effect on spatial resolution.

Which grid error results in grid cut-off and loss of exposure on the outside edges of the image receptor? A. Upside down non-focused grid B. Incorrect angulation of the beam across lead strips C. Off-level, or tilted grid error D. Incorrect SID with a focused grid

D. Incorrect SID with a focused grid Using an incorrect SID with a focused grid result in grid cut-off and loss of exposure on the outside edges of the image receptor. This is also called off-focus grid error Focused grids are designed to be used with specific SID ranges as specified by the manufacturers. Grid cut-off will occur more at the outer edges of the grid when the SID is outside of this range, resulting in loss of exposure to the image receptor in those areas.

Which situation is most likely to result in grid errors? A. Stationary radiography at the upright bucky B. Tabletop radiography C. Stationary radiography at the table bucky D. Mobile radiography

D. Mobile radiography Mobile radiography is most likely to result in grid errors. Mobile radiography creates more difficulties in maintaining the correct alignment of the x-ray beam to the grid and image receptor.

A patient presents to the imaging department on a stretcher for a shoulder exam. The technologist decides to complete the exam leaving the patient on the stretcher and no grid will be used. However, the technologist fails to adjust mAs typically used for a shoulder exam with a grid. How will the image quality change without the use of the grid? A. The image will be higher contrast than typical shoulder images B. The image will have decreased recorded detail than typical shoulder images C. The image will be underexposed compared to typical shoulder images D. The image will be overexposed as compared to typical shoulder images.

D. The image will be overexposed as compared to typical shoulder images. The image created without a grid will be overexposed. If the technologist does not use a grid, then less radiation is needed. If no adjustment is made then too much radiation will reach the image receptor and it will be overexposed.