Intensifying Screen Fluorescence – Radiographic Lab

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Objectives:

  1. To observe fluorescence
  2. To study the effect of kV and mAs on intensifying screen fluorescence.

Materials:

  • 3 cassettes; Du Pont Extremity Cassette; Fuji Film EC-BW Cassette; Du Pont Cassette

Suggested Procedure:

  1. To observe the fluorescence; make all exposures with the X-ray room lights and collimator lights off.  The control panel provides enough light to see the equipment and to safely navigate between the X-ray table and control panel.  Note: If anyone is uncomfortable in this environment; please alert a staff member who will assist you with this laboratory activity.
  2. Place the first cassette “open” on the X-ray table.  With the X-ray tube at 100 cm SID to the table top, collimate to ~ half of the intensifying screen.  Turn the room and collimator lights off.
  3. Make the following 4 exposures using the large focal spot size for all exposures; note of the colour of fluorescence and change, if any, in the degree of brightness.

Exposure 1      40 kV   100 mA at 1 sec

Exposure 2      40 kV   200 mA at 1 sec

Exposure 3      80 kV   100 mA at 1 sec

Exposure 4      80 kV   200 mA at 1 sec

 

  1. Repeat steps 1 and 2 for the remaining two cassettes.
  2. Using Exposure 3 or 4 technical factors include a portion of all three intensifying screens in the same collimation light field.  Ensure to turn off the collimator light before making this final exposure!  Note your observation.
  3. Answer the questions on page 2 of this document.

Cassette

Exposure #1

Exposure #2

Exposure #3

Exposure #4

* Rate the RS

of each cassette

Du Pont Extremity Cassette

 

 

1

Light blue

2 3 4

Dark    blue

Slow
Fuji Film EC-BW Cassette

 

 

2

Light green

3 4 5

Dark green

Fast
Du Pont Cassette

 

 

 

2

Light blue

3 4 5

Dark    blue

Medium

 

* Rate the RS of each by assigning each cassette one of the following descriptions; Fast, Medium or Slow.

Intensifying Screen Fluorescence Questions

 

 

  1. Indicate the colour of fluorescence for each cassette evaluated. 

My colour intensity evaluation is number based. Number 1 means lightest (blue or green) and number 5 means darkest. It is shown on the table.

 

  1. How did kV affect fluorescence?    Explain using a textbook reference.  

Higher kV= stronger fluorescence, because kilovoltage  determines the kinetic energy of the electrons accelerated in the X-ray tube. So in intensifying screen, according to Carlton p. 322-323: “AS kVp is increased the efficiency of the intensifying screen will also increase. An increase in kVp will cause an increase in screen speed.” In our experience increasing kVp result to stronger light on intensifying screen, since as kVp increases the energy of the electrons in the x-ray tube that effect intensifying screen will increase.

 

  1. How did mAs affect fluorescence?  Explain using a textbook reference.

We’ve seen an increase in light, when increased mAs, in view of the fact that mAs controls how many electrons are produced at the cathode. The more electrons produced at the cathode the more x-rays that will be produced at the anode. So in intensifying screen, according to Carlton p. 173: “As mA increases, so does the number of electrons which are able to cross the tube to reach the x-ray target. mA is directly proportional to tube current.” In our experience increasing mAs result to stronger light on intensifying screen, that means increasing the number of photons will affect the stronger light of the intensifying screen.

 

  1. Based on your results of Procedure Step 5, classify the speeds of the cassettes.  Indicate how you decided on the classification.

Our calcification was based on quicker viewing of the light.

Du Pont Extremity Cassette was slow. Slow screens because it has a thin layer and relatively small crystals are used, speed is slow necessitating a higher dose of ionizing radiation.

Fuji Film EC-BW Cassette was fast, because it has thick layer, and relatively large crystals used.

Du Pont Cassette was medium. because it has medium thick layer of medium sized crystals.

 

  1. Based on your findings, which factor would produce more predictable changes in OD on a radiograph? 

kVp determines the ability for the beam to penetrate the tissue. kVp has more effect than any other factor on image receptor exposure because it affects beam quality. The number of x-rays are directly proportional to the mA assuming a fixed exposure time. According to Carlton p. 177: “kVp has a tremendous impact on radiographic density… because changes in kilovoltage create changes in beam penetrability, kVp is the primary controller of the difference in radiographic densities…An increase in kVp courses an increase in penetrability, which will result in an image with less contrast… an increase in kVp by 15 percent will cause a doubling in exposure, the same effect as doubling the mA or doubling exposure time”.

 

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