rad 206 p12 fundamentals of imaging - control of scatter radiation
TRANSCRIPT
![Page 1: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/1.jpg)
FUNDAMENTALS OF IMAGING
RAD 206
Control of Scatter Radiation
![Page 2: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/2.jpg)
![Page 3: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/3.jpg)
Contrast changes with the use of a gridLess scatter radiation & less radiographic noise – shorter scale = “better contrast”
With Grid No Grid
![Page 4: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/4.jpg)
GRIDS
![Page 5: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/5.jpg)
CONTRAST & CONTRAST RESOLUTIONTwo devices are used to reduce Compton effect beam-restricting devices and radiographic gridsBeam-restricting devices effects what reaches the patient. Grids effect the remnant beam
![Page 6: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/6.jpg)
CONTRAST & CONTRAST RESOLUTIONContrast = the comparison of areas of light, dark and shades of gray on the imageContrast Resolution = the ability to image adjacent similar tissues
![Page 7: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/7.jpg)
BEAM-RESTRICTING DEVICESAre helpful to improve contrast resolution however the inherent problem is they are placed between the source and the patient. Even under the most favorable conditions, most if the remnant x-rays are scattered.
![Page 8: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/8.jpg)
EFFECTS OF SCATTER RADIATION ON IMAGE CONTRAST Contrast is the degree of difference in OD between areas of an imageIf you could only capture transmitted, unscattered x-rays, the image would be very sharpThe corresponding bone-soft tissue interface, would be very abrupt, and therefore the image contrast would be high
![Page 9: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/9.jpg)
GRIDSAre very effective device for reducing scatter radiationThe grid is a series of sections of radiopaque material (grid strips) alternating with sections of radiolucent material (interspace material)The grid is designed to transmit only x-rays that are traveling in a straight line from the source to the IR
![Page 10: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/10.jpg)
GRIDS “CLEAN UP” SCATTER RADIATIONA high quality grid can attenuate 80 –90 percent of scatterradiation
![Page 11: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/11.jpg)
GRID STRIPSShould be very thin and have high photon absorption properties
Lead is most common
Tungsten, platinum, gold, and uranium have been tried but Pb is still most desirable
![Page 12: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/12.jpg)
INTERSPACE MATERIALUsed to maintain precise separation between the delicate lead strips
Aluminum or Plastic Fiber
Grid Casing = covered completely by thin aluminum to provide rigidity and to seal out moisture. Yuck!
![Page 13: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/13.jpg)
![Page 14: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/14.jpg)
GRID RATIO3 important dimensions on a grid: The thickness of the grid strips, the width of the interspace material, and the height of the grid
The grid ratio is the HEIGHT of the grid divided by the INTERSPACE WIDTH:
Grid ratio = h D
![Page 15: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/15.jpg)
H = HEIGHT OF THE GRID, T = THICKNESS OF THE GRID STRIP, D = WIDTH OF THE INTERSPACE MATERIAL
![Page 16: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/16.jpg)
GRID RATIOHigh-ratio grids are more effective in cleaning up scatter radiation than low-ratio gridsThe angle of deviation is smaller for high-ratio grids. (the photon must be traveling in a straighter line to make it through the grid)However, the higher the ratio the more radiation exposure necessary to get a sufficient number of x-rays through the grid to the IR
![Page 17: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/17.jpg)
THE HIGHER THE RATIO THE STRAIGHTER THE PHOTON MUST TRAVEL TO REACH THE IR
Grid ratios rangefrom 5:1 to 16:1Most common8:1 to 10:1A 5:1 grid will clean up 85% 16:1 clean up 97%
![Page 18: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/18.jpg)
GRID FREQUENCYThe number of grid strips or grid lines per inch or centimeter The higher the frequency the more strips and less interspace material and the higher the grid ratioAs grid frequency increases, patient does is increase because more scatter will be absorbed
![Page 19: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/19.jpg)
GRID FREQUENCYSome grids reduce the thickness of the strips to reduce the exposure to the patient, this over all reduces the grid clean up
Grids have frequencies in the range of 25 to 45 lines per centimeter (60 to 110 lines per inch)
![Page 20: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/20.jpg)
HIGHER FREQUENCY WITH THE SAME INTERSPACE DISTANCE REDUCES THE GRID EFFECTIVENESS
![Page 21: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/21.jpg)
GRID PERFORMANCEThe principal function of a grid is to improve image contrastContrast Improvement Factor (k) = the ratio of the contrast of a radiograph made with a grid to the contrast of the radiograph made without a grid. A contrast improvement factor of 1 indicates no improvements
The higher the grid ratio & frequency the higher the k
![Page 22: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/22.jpg)
Using grids require more patient dose. Why is this?
When a grid is used technique must be increased to maintain OD
The amount of increase is given by the Bucky factor (B) or grid factor
BUCKY FACTOR OR GRID FACTOR
![Page 23: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/23.jpg)
BUCKY FACTOR OR GRID FACTOR
The higher the grid ratio or frequency the higher the bucky factor
The Bucky factor increases with increasing kVp
Pg 235: We will use the average values for calculations.
![Page 24: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/24.jpg)
Selectivity or ability to “clean up”the heavier the grid the more Pb it contains
![Page 25: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/25.jpg)
GRID CUTOFFDistance to cutoff SID Grid ratioWith decreasing SID more potential for grid cutoffIR size will alsoInfluence grid cutoff
![Page 26: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/26.jpg)
GRID TYPES
PARALLEL GRID simplest type of gridAll the lead strips are parallelOnly clean up scatter in one direction (along the axis of the grid)
Inexpensive, Easy to make, however can cause noticeable grid cutoff with short SID’s (the greater the SID the lesser artifact seen) .
![Page 27: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/27.jpg)
GRID CUTOFF FROM PARALLEL GRID
THE HIGHER-RATIO THE MORE CUTOFF POTENTIAL
![Page 28: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/28.jpg)
FOCUSED GRIDDesigned to minimize grid cutoffLead strips are aligned with the divergence of the x-ray beam
Each focused grid must be identified with the appropriate SIDWrong SID = Grid cutoff
![Page 29: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/29.jpg)
Focused grid have a little SID latitude or tolerance (e.g. 100cm Focused grid would produce artifacts if used at less than 90cm – or more than 110cm)
![Page 30: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/30.jpg)
CROSSED GRIDAKA crosshatchHave lead strips running along the long and short axes of the gridMade by placing two parallel grid on top of each other
![Page 31: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/31.jpg)
CROSSED GRID
Have twice the grid ratio as Parallel (linear) grids
However, CR vs grid placement is critical. The CR must align with the center of the grid and the grid and CR must be exactly parallel or grid cutoff will occur
e.g.
![Page 32: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/32.jpg)
MOVING GRIDSAll stationary grids will give you grid lines on your radiograph. Thinner Pb strips will give you less noticeable lines. However, thinner strips have less Pb content not “cleaning up” as well
Grid Lines are made when primary x-rays are absorbed in the grid strips.
![Page 33: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/33.jpg)
FOCUSED GRIDS ARE USUALLY USED AS MOVING GRIDSThe grid is placed in a holding mechanism that begins moving just before the x-ray exposure and continues moving after the exposure ends
2 types of movement Reciprocating & Oscillating
Reciprocating: moving back and forth about 2 cm
Oscillating: moving in a circular motion 2-3 cm
![Page 34: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/34.jpg)
GRID MOTIONReciprocating = moves several times about 2cm back and forth during the exposure
Oscillating = moves several times about 2 – 3 cm in a circular pattern
Most grids are moving. Except for portable imaging
![Page 35: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/35.jpg)
GRID PROBLEMSIncreased OID, especially with moving gridsThe biggest problem with grids is misalignment
GRID PROBLEMS RESULT IN:UNDEREXPOSED IMAGEOR UNDEREXPOSEDEDGES OF IMAGE
https://www.youtube.com/watch?v=mZPD_gLs5Dw
![Page 36: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/36.jpg)
GRID PROBLEMS – OFF LEVEL
![Page 37: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/37.jpg)
GRID PROBLEMS – OFF CENTER
A problem with focused & crossed grids
![Page 38: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/38.jpg)
GRID PROBLEMS – OFF FOCUS (WRONG SID)
![Page 39: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/39.jpg)
GRID PROBLEMS – UPSIDE-DOWN
A problem with focused & crossed grids
![Page 40: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/40.jpg)
GRID SELECTIONPatient Dose
• Pg 241 – mAs changesExamDetail requiredPart thicknessDesired technique (kVp)Equipment availability
![Page 41: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/41.jpg)
Contrast Improvement by Using an Air Gap
![Page 42: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/42.jpg)
![Page 43: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/43.jpg)
![Page 44: Rad 206 p12 Fundamentals of Imaging - Control of Scatter Radiation](https://reader036.vdocuments.us/reader036/viewer/2022070601/588014af1a28abbc128b476d/html5/thumbnails/44.jpg)
QUESTIONS….?