Radiographic Grid Lecture 13 (PDF)

RADIOGRAPHIC GRID Elsevier items and derived items © 2005 Elsevier Inc.  DISCUSS CONSULTATION PRESENT COLLI 1- 4 EXPOSURE ROOM 108 1-4 Elsevier items and derived items © 2005 Elsevier Inc.  The grid is designed to transmit only those x-rays whos...

RADIOGRAPHIC GRID Elsevier items and derived items © 2005 Elsevier Inc.  DISCUSS CONSULTATION PRESENT COLLI 1- 4 EXPOSURE ROOM 108 1-4 Elsevier items and derived items © 2005 Elsevier Inc.  The grid is designed to transmit only those x-rays whose direction is on straight line from the source to the image receptor. The grid is positioned between the patient and the image receptor. Elsevier items and derived items © 2005 Elsevier Inc.  Grid is placed between patient (behind table or upright bucky) & cassette If placed BACWARDS CAN CAUSE GRID ERRORS Elsevier items and derived items © 2005 Elsevier Inc. Elsevier items and derived items © 2005 Elsevier Inc.  Construction of Grid The grid is made up of a fabricated of series of section radiopaque material (interspace material). This technique for reducing the amount of scatter radiation that reaches the IR was first demonstrated in 1913 by Gustave Bucky. Elsevier items and derived items © 2005 Elsevier Inc.  The term fundamental to understanding grid technology is GRID RATIO. Elsevier items and derived items © 2005 Elsevier Inc.  Grid Ratio is the height of the grid divided by the interspace width. For example, a 12:1 grid means that the height of the lead strip is 12 inches and the width interspace material is 1 inch. Elsevier items and derived items © 2005 Elsevier Inc.  High ratio grids are more effective in cleaning up scatter radiation than low- ratio grids. This is because the angle of scatter radiation is less compared to low-ratio grids. Elsevier items and derived items © 2005 Elsevier Inc.  High-ratio grids increases patient dose. Elsevier items and derived items © 2005 Elsevier Inc.  Contrast Improvement Factor is the ratio of radiographic contrast with a grid to that without a grid. Measures the improvement of image quality when grids are used. Elsevier items and derived items © 2005 Elsevier Inc.  Bucky Factor ratio of patient dose with and without a grid Measures how much of an increased will be required compared with non-grid exposure. MATH RELATION = MAS & GRID (DIRECT) Elsevier items and derived items © 2005 Elsevier Inc.  WHEN TO USE GRID Elsevier items and derived items © 2005 Elsevier Inc.  kVp is above 60 If body part exceeds 10cm and tissue density is primarily soft tissue and bone. Elsevier items and derived items © 2005 Elsevier Inc.  Classifications of Grid Stationary Moving Elsevier items and derived items © 2005 Elsevier Inc.  Types of Grid Linear Parallel Focused Crossed Elsevier items and derived items © 2005 Elsevier Inc.  Parallel used in portable and OR radiography cleans up scatter radiation in only one direction Grid-cut off Elsevier items and derived items © 2005 Elsevier Inc.  Focused Grid is designed to minimize grid cut-off used in moving grids more superior than parallel Elsevier items and derived items © 2005 Elsevier Inc.  Crossed consists of two linear grids superimposed one above the other. Used in special procedures More efficient in cleaning up scatter radiation. More grid cut-off Is not commonly used. Elsevier items and derived items © 2005 Elsevier Inc.  Moving Grid An obvious and annoying shortcoming of the grids is that they can produce grid lines on the image. Elsevier items and derived items © 2005 Elsevier Inc.  1920- Hollis E. Potter hit on a very simple idea: Move the grid while the x-ray exposure is being made. Elsevier items and derived items © 2005 Elsevier Inc.  GRIDS CAN LEAVE LINES ON THE IMAGE Elsevier items and derived items © 2005 Elsevier Inc.  Two types of moving grid: Reciprocating- back and forth movement Most common Oscillating- operates in circular fashion. Elsevier items and derived items © 2005 Elsevier Inc.  Grid Problems Off-level grid Off-center grid Off-focused grid Upside-down grid Combined off-center, off- focused Elsevier items and derived items © 2005 Elsevier Inc.  Air Gap Technique –The I.R is moved 10 to 15 cm from the patient. –A portion of the scatter x- rays generated in the patient would be scattered away from the I.R and not recorded/detected. Elsevier items and derived items © 2005 Elsevier Inc.