1. RAD 354 Chapt. 13 Intensifying Screens
Physical purpose: to convert x-ray photons into light photons (done at the phosphor layer). The RESULT does lower patient dose.

2. Most in use – if not ALL – are “rare earth”
Rare earth crystals include (but are NOT limited to):
Gadolinium
Lanthanum
Yttrium

3. Other Intensifying Crystals Used
Barium lead sulfate (very early phosphor used)
Calcium Tungstate

4. Desired Physical Properties of Crystals
High atomic number = high absorption (DETECTIVE QUANTUM EFFICIENCY {DQE})
Phosphor should emit a LARGE # of light photons for EACH x-ray photon – CONVERSION EFFICIENCY (CE)
Color of light should match the color light the film is sensitive to – SPECTRAL MATCHING
ZERO afterglow (“lag”)

5. Important Screen Terms
Luminescence – process of giving off light when stimulated
Fluorescence – giving off light ONLY when stimulated
Phosphorescence – continuing to give off light after stimualation
Intensification factor – amount of radiation reduction WITH screens vs NO screens

6. Screen Speed Can be judged by intensification factor (IF)
Increasing speed INCREASES noise
Increasing speed REDUCES spatial rresolution
Increasing speed INCREASES quantum mottle (line-pair test pattern device is used to measure this)

7. Tech CONTROLABLE Screen Items
Screen attributes the tech can control:
Radiation quality (kVp, grid/no grid, filters, etc.)
Image processing and temperature
Care of and cleaning of screens

8. Cassette Construction
Rigid, light proof protective housing for the film and screens
Felt/rubber/sponge “compression” layer to assure good film-screen contact
K-edge of crystals determines light spectrum

9. Screen Cleaning
Compare/contrast screen cleaning solutions (home made vs commercially produced)
Cotton balls vs 4 X 4’s

10. Screen – Film Contact Test
Wire mesh test for screen-film contact and proper resolution/visibility of detail

11. RAD 254 Chapt. 14 Control of Scatter
Break down into: Those that reduce patient dose and those that are geometrical in nature and those not

12. 3 (primary) factors affecting scatter
Increased kVp
Increased field size
Increased patient thickness

13. Spatial Resolution & Contrast Resolution
Spatial resolution may be thought of as geometric in nature (F.S. size, emission spectrum, OID, SID – dealing with geometric image formation
Contrast resolution – driven by scatter and other sources of “noise”

14. Scatter
INCREASED filed sizes = MORE scatter – collimation is the MOST readily available and EASIEST thing to lower the amount of scatter
Patient thickness also INCREASES scatter – compression may be used to help avoid this (IVP’s and mammos are examples where compression may be used)

15. Beam restricting devices limit the radiation to the patient
Aperature diaphram (size and resultant field size are a DIRECT proportion – draw the damn picture and figure the problem)
Cones and cylinders – GREAT for absorbing scatter, but are circular shaped = great for improving contrast and removing scatter, BUT required MUCH MORE mAs as a result

16. Variable Aperature Diaphram
Mandated in 1974 by the Food and Drug Administration (mandate later removed)
Positive Beam Limitation Device (PBL’s)
Automatically collimate to the size of the cassette/receptor in the bucky and CANNOT be a BIGGER size than the cassette/receptor

17. Filtration
Filtration also will DECREASE the low energy rays and LIMIT patient dose and some scatter

18. The Grid
Only “FORWARD” scatter is of any benefit to the radiographic image – ALL other scatter degrades the image!

19. Scatter = LOWER Contrast
Using a grid (alternating strips of fine leaded strips with alternating radiolucent interspace material) can effectively reduce the amount of ANGLED scatter from reaching the cassette/receptor

20. Grid Terms
Grid ratio = height of the lead lines divided by the interspace width
Grid frequency/lines per inch = the MORE lines per inch, the more clean up
Grid clean up = scatter w/o a grid vs scatter reaching the film/receptor with a grid AKA “Contrast Improvement Factor”
Grid function = improved image contrast

21. Bucky Factor
Refers to the AMOUNT of radiation to the patient with a grid vs W/O a grid
The HIGHER the grid ratio, the HIGHER the “bucky factor”
The HIGHER the kVp, the HIGHER the “bucky factor”
Grid WEIGHT refers to how HEAVY the grid is – duhhhh- the MORE lead the heavier it is

22. Grid Types
Parallel
Crossed (cross hatch)
Focused
Focused crossed

23. Grid Problems
Grid cut-off = short SID’s result in the vertical, parallel strips absorbing the “diverging” beam at the OUTER margins of the grid/film/receptor; MOST pronounced at SHORT SID’s
Most grid problems are positioning related
Uneven grid/off level grid
Off centered (lateral decentering)
Off focus grid
Upside down, focused grid

24. Focused Grid Misalignment
Off level = grid cutoff across image; underexposed image (light OD)
Off Center = ditto
Off focus = CR centered to one side of the other of a focused grid
Upside down grid = SEVER grid cut-off (NO density/OD) at BOTH sides of the image

25. Grid Ratio Selection 8:1 grid is the MOST widely used
5:1 grid is the most PORTABLE use grid ration
Grid ratio is kVp driven
Higher kVp’s warrant HIGHER grid ratios
Higher grid ratios = HIGHER patient dose (more radiation needed to produce an image)
As kVp increases pat MAXIUM OPTIMUM kVp, patient dose INCREASES

26. mAs – Grid Considerations
AS grid ratio INCREASES, so must mAs
5:1 = 2 X mAs
8:1 = 4 X mAs
12:1 = 5 X mAs
16:1 = 6 X mAs

27. Air Gap Technique
By allowing the scatter radiation to “diffuse” in the atmosphere AFTER the patient but BEFORE the cassette/receptor, the image has HIGHER contrast, as the scatter diffuses and does NOT reach the receptor
C-spine is a good example of this

28. RAD 354 Chap. 15 Radiographic Technique
Four PRIMARY exposure factors:
kVp mA
Time
distance

29. In the next 5 minutes
Write down “bullets” about what happens when on RAISES kVp

30. Memory “jerk” for grids
Write the following:
5 2
8 4
12 5
16 6

31. Now What???
5:1 = 2X mAs
8:1 = 4 X mAs
12:1 = 5 X mAs
16:1 = 6 X mAs

32. kVp Beam Qualtiy Penatration Beam intensity HVL
Primarily responsible for quality, BUT INCREASES in kVp also make x-ray production SLIGHT more productive
Penatration
Beam intensity
HVL
Biggest exposure factor affecting CONTRAST

33. mA
DIRECTLY responsible for AMOUNT of radiation produced (Quantity). As mAs is doubled, so is the number of photons produced and so is PATIENT DOSE
mA stations are responsible for focal spot size selection

34. Time
Exposure times should be practical and short enough to stop patient motion, but the shortest times also result in the most radiation output per unit of time – thus MORE wear and tear on the x-ray tube
mAs = time X mA
mAs is only measured by tube current
Responsible for Optical Density (OD)

35. Distance (SID)
The most “forgotten” exposure factor, but perhaps the most important
Inverse Square Law
Primarily effects Optical Density (OD)
NO effect on quality
Other distance related terms:
FFD, FOD, OFD, FRD, ORD, SSD
Other geometric factors (F.S. size, pt. size, part orientation to CR and receptor

36. Filtration kVp driven Inherent (.5 mm al equiv)
Added (2.0 which may also include some filtration from localizer light apparatus, etc.) in a kVp unit
Total filtration : inherent + added (2.5 mm al equivalent)

37. Generators
Half wave (120 cycles/sec = 60 impulses per second) – 100% ripple
“self rectified” is also half wave where the X-RAY TUBE is the DIODE
Full wave rectification (120 cycles per second = 120 impulses per second) – 1--% ripple
3 phase, 6 pulse = 14% ripple (33% more radiation per exposure over full wave)
3phase, 12 pulse = 4% ripple (40% more per exposure over full wave
Hi frequency = <1% ripple