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ch.11
| Question | Answer |
|---|---|
| What are the three factors that control the amount of scatter produced? | Kvp, field size, patient thickness |
| Increasing the kVp will produce ____________scatter (more or less?) | more |
| Increasing the collimation will produce ________scatter (more or less?) | less |
| Increasing the field size will produce _________scatter (more or less) | more |
| Thicker patient will produce ______scatter (more or less?) | more |
| Using a compression during an abdominal radiographic procedure will produce ________scatter. (More or less?) Why? | less |
| Which of the following will have more contrast? a. An abdominal radiograph performed in supine position. b. An abdominal radiograph performed in prone position. | B will have more contrast bc prone compresses the pt and therefore decrease scatter, which increases contrast) |
| Which collimation device will produce an image with better contrast (Cone or cylinder?): | cone |
| What is the function of the first stage entrance shutter? | To control off focus radiation; it has multiple collimator blades that protrude from the top of the collimator into the xray tube housing |
| What is the function of a PBL? | Automatic light localizing collimators for fixed radiographic equipment |
| What is PBL stands for? | Positive Beam Lighting |
| What device can be used to minimize the amount of radiation reaching the image receptor? | Beam restrictor and grids are used to reduce the amount of scatter radiation that reaches the IR |
| What is grid ratio? How do you calculate it? **** | Grid ratio is the ratio of the height of the lead strips to the distance btw them. Grid ratio = H/D |
| What is grid frequency? | The number of lead stripes per unit length in in/cm/both |
| What is the average grid frequency used in Film radiography? | 24-45 lines/cm or 60-110 lines/in |
| What is the average grid frequency used in Digital radiography? | 150+ lines/in |
| Patient dose is ___________(increased or decreased ) with the use high ratio grid. | increased |
| In a particular grid the length of the lead strips are 12 mm and are positioned 1mm apart. What is the grid ratio? | H/D = 12mm/1mm = 12:1 |
| A particular radiographic grid is manufactured using led strips that are 16mm long and are separated by an interspacing material of 2mm wide. What is the grid ratio? | H/D = 16mm/2mm = 8:1 |
| A particular radiographic grid is manufactured using led strips that are 16mm long and 4mm wide. What is the grid ratio? | H/D = 16/4 = 4:1 |
| What is the principal function of a radiographic grid? | Reduces the level of scatter radiation that reaches the IR |
| What are the interspacing materials used in radiographic grids? | Typically made of AL or plastic fiber |
| What are the different types of grids that can be used in radiography? | Parallel/linear, crossed, focused, and moving |
| What is the most common type of grid used radiology departments? | Moving grids |
| Which grid will produce more contrast? a. Linear grid b. Crossed grid | b. Crossed grid |
| Which grid has more positioning latitude? a. Linear grid b. Crossed grid. | a. Linear grid |
| Which grid has more positioning latitude? a. High ratio grid b. Low ratio grid | b. Low ratio grid |
| What are the main disadvantage of parallel and crossed grids? | Grid cutoff |
| What is convergent point? | If imaginary lines were drawn from each of the lead lines in a linear focused grid, these lines would meet to form an imaginary point, this point is called the convergent point. |
| What is Convergent line? | If convergent points were connected along the length of the grid, they would form an imaginary line, this line is the convergent line. |
| What is focal distance? | |
| As the Bucky factor increases, the radiographic technique and the patient dose _________(increase or decrease) proportionally. | increase |
| What is the formula for calculating contrast improvement factor? | K = image contrast with grid/image contrast without grid |
| High ratio grid has __________ (higher or lower) contrast improvement factor. | higher |
| How can you calculate Bucky factor? | B = incident remnant xrays/transmitted image-forming xrays = patient dose with grid/patient dose without grid |
| The higher the grid ratio the ________(higher or lower) is the Bucky factor. | higher |
| Bucky factor increases with _____(increasing or decreasing) kVP | increasing |
| What is the purpose of moving grid? | Get rid of grid lines on an image, so if the grid moves while the xray exposure is being made, the lines disappear at little cost of increased radiographic technique |
| What are the different types of grid motions used? | Reciprocating and oscillating |
| How will the image appears if the grid is off level? | Lower OD or intensity at the digital IR; overall loss of density in entire image |
| How will the image appears if the grid is off center? | Lower OD; overall loss of density in entire image |
| How will the image appears if the grid is off focus? | Loss in density on the SIDES of the image |
| How will the image appears if the grid is place Upside-Down? | Loss in density on the SIDES of the image |
| Learn the math problem to calculate the mAs when changing from a non grid to a grid. | Mas1/mas2 = GCF1/GCF2 |
| Learn the math problem to calculate the mAs when changing from a particular grid ratio to a grid with a different grid ratio. | GCF = mas with grid/mas without grid |
Created by:
daniel.velazco004